Evaluation of the width of attached gingiva: A systematic review and meta-analysis

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Methods An electronic search was performed in PubMed, Embase, Web of Science, and CNKI with no language restrictions. Eligible study selection, data extraction, and evaluation of risk of bias were conducted by two authors independently and in duplicate. Any disagreement was solved by discussion or judged by a third reviewer. Results Six studies were finally included. Upper incisors and upper canines had pooled Means of 4.48 mm and 3.80 mm, while lower incisors and lower canines had pooled Means of 3.23 mm and 2.40 mm, respectively. Upper premolar and lower premolars had pooled Means of 3.13 mm and 2.16 mm, respectively. Upper molars had a pooled Mean of 3.38 mm, while lower molars had a pooled Mean of 2.40 mm. Conclusion The maxillary attached gingiva is always wider than the corresponding mandibular attached gingiva in the same region. In the four quadrants, the attached gingiva from wide to narrow are incisors, canines, molars, and premolars, respectively. Future studies are necessary to evaluate the width of attached gingiva among different gingival phenotypes and age groups. Dentistry Width of attached gingiva Mini-implant Systematic review Meta-analysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Attached gingiva is an anatomic structure of the periodontium continuous with the free gingiva and lies between the free gingival groove and the mucogingival junction. 1 Histologically, the attached gingival epithelium is comprised of keratin as well as thin, prominent epithelial ridges and a thick lamina propria and the connective tissue contains no elastic fibers. 2 All these features highlight the importance and contribution of the attached gingiva to the health and stability of the periodontium, including the provision of increased resistance to external injury, stabilization of the gingival margin, and dissipating physiological forces exerted by the muscular fibers of the alveolar mucosa on the gingival tissue. 3 Especially in the field of orthodontics, the insertion of mini-implants at the mucogingival junction is a common practice. If the mini-implants are positioned too close to the alveolar ridge, they may become unstable and prone to loosening, ultimately resulting in treatment failure. Meanwhile, insertion into the alveolar mucosa could cause inflammation and subsequent failure. 4 Cheng et al., in a prospective clinical study involving 140 mini-implants, found that the absence of keratinized mucosa around mini-implants significantly increased the risk of infection and failure. 5 These scenarios highlight the clinical importance of a healthy attached gingiva with an appropriate width in orthodontic treatments. To date, numerous studies have investigated the width of attached gingiva; however, comprehensive measurements are limited. Padmini et al. measured the width of attached gingiva and vestibular depth of 165 young Malaysian adults, but only included six anterior teeth, from cuspid to cuspid. 6 Sreeja et al. investigated the association between the width of attached gingiva and its impact on dental hygiene care. It is regrettable that they only provided the mean width of the attached gingiva of the gross maxillary and mandibular(3.00mm and 2.01mm,respectively), failing to provide the widths of all sites including incisors, cuspid, premolars and molars. 7 Surprisingly, no scholar has conducted a systematic review of the existing literature on this topic. In line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, we conducted a systematic review to bridge this gap. Our objective was to determine the average widths of attached gingiva in various oral sites, compare and offer valuable insights for future studies. This study aimed to systematically review and meta-analyze the attached gingival width in different oral sites respectively. By providing the mean attached gingival width and comparing them between regions, our results could assist the clinicians in periodontal and orthodontic treatment. Materials And Methods Protocol and Registration The protocol for this systematic review was registered in the International Prospective Register of Systematic Reviews (PROSPERO; http://www.crd.york.ac.uk/prospero; registration number CRD42024568391). Information Sources, Search Strategy, and Study Selection The databases searched included those of PubMed, Embase, Web of Science, and CNKI. Specifically, the online search parameters were articles from time of database inception to August 28, 2023, without language restrictions. A search for published, peer reviewed articles was conducted using keywords “attached gingiva”, “width” and their synonyms. Titles and abstracts were assessed according to the eligibility criteria. The selected articles were evaluated after reading full texts, and a final selection was determined. Searching and assessment of studies was performed independently by two reviewers (Z.H. and Y.L.) separately. The final decisions on inclusion were made after consulting with a third reviewer (H.L.) (Figure 1). Eligibility criteria Owing to the research question of interest, patients with good general health, healthy gingival tissues (no loss of attachment) were included. Both randomized controlled trials (RCTs) and non-randomized studies of the effects of interventions (NRSIs) were eligible. The following exclusion criteria were adopted: patients with systemic illnesses, pregnant or lactating women, patients on medications that could influence the width of the gingiva such as calcium channel blockers, moderate to severe gingival inflammation, presence of gingival recession, and presence of clinical attachment loss were excluded. Data Extraction After conducting full-text reviews of the articles, we organized the data into a standardized table, which included study design, demographic data (age, sample size, grouping, and width of attached gingiva), detailed description (interventions, treatment duration, and comparator), and outcomes. Any discrepancies in the extracted data were resolved through discussion among all three reviewers. Risk of Bias and Quality Assessment The evaluation of risk of bias for the included studies was performed independently and separately by two reviewers (Z.H. and Y.L.) according to the Cochrane tool for assessing risk of bias in nonrandomized trials (ROBINS-I tool). 8 For each bias domain, a judgment score was given following the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions 5.1.0. Any disagreement was solved by discussion or judged by a third reviewer (H.L.). Meta-analysis Original data were subject to statistical pooling through random effect models. Significance analysis was conducted using GraphPad Prism 9 software to evaluate the significance of outcomes between different groups (Figure 2). Heterogeneity across studies was assessed through the I 2 statistic, and an I 2 statistic greater than 50% was considered as substantial heterogeneity. If substantial heterogeneity existed, a subgroup analysis on different study designs and periodontal health condition would be executed to explore the potential heterogeneity. In addition, sensitivity analysis for studies with small sample sizes was conducted to evaluate the robustness of the pooled results in the meta-analysis. The Egger test and Begg test were used to assess publication bias. All the meta-analyses were performed in Comprehensive Meta-Analysis (version 2.2.064, Biostat, Englewood, NJ). Results Description of Studies Initially, 736 articles from the database were identified and 723 were excluded as irrelevant. The remaining thirteen articles were further assessed for eligibility, and six studies were finally included in this systematic review. 3,9-13 The procedures of online searching and selection are shown in Figure 1. Sample size ranges from 45 to 356 in different groups (Table 1). Table 1 . Characteristics of the I ncluded S tudies Study Design No. of patients Age Range Attached Gingival Width of Incisors Attached Gingival Width of Canines Attached Gingival Width of Premolars Attached Gingival Width of Molars Adesola et al. 2018 Cross-sectional Study n = 73 (19males, 54females) 18~34 Upper: 4.59 ± 1.79 Lower: 3.27 ± 1.17 Upper: 3.73 ± 1.51 Lower: 2.51 ± 1.17 Upper: 3.28 ± 1.51 Lower: 2.43 ± 1.07 Upper: 3.44 ± 1.69 Lower: 3.16 ± 1.03 Tenenbaum et al. 1982 Cross-sectional Study n = 100 (68males, 32females) 19~26 Upper: 3.50 ± 1.02 Lower: 2.38 ± 0.96 Upper: 2.40 ± 1.15 Lower: 1.40 ± 0.80 Upper: 2.65 ± 1.08 Lower: 1.63 ± 0.85 Upper: 3.20 ± 1.15 Lower: 2.00 ± 0.89 Bhatia et al. 2015 Before-after Study n = 45 15~60 Upper: 3.71 ± 0.81 Lower: 3.21 ± 0.83 Upper: 3.13 ± 1.05 Lower: 2.10 ± 0.87 Upper: 2.19 ± 0.68 Lower: 1.60 ± 0.47 Upper: 2.45 ± 0.63 Lower: 1.86 ± 0.53 Yang et al. 2017 Cross-sectional Study n = 144 (72males, 72females) 20~30 Upper: 4.98 ± 1.20 Lower: 4.05 ± 1.00 Upper: 4.35 ± 1.20 Lower: 2.90 ± 0.90 Upper: 3.37 ± 1.01 Lower: 2.25 ± 0 .97 Upper: 3.93 ± 1.30 Lower: 2.60 ± 1.05 Wang et al. 1990 Cross-sectional Study n = 356 (173males, 183females) 15~20 Upper: 5.05 ± 2.09 Lower: 3.00 ± 1.00 Upper: 4.70 ± 1.90 Lower: 2.80 ± 1.20 Upper: 3.85 ± 1.50 Lower: 2.74 ± 1.37 Upper: 4.00 ± 1.36 Lower: 2.65 ± 1.22 Liu et al. 2021 Case-control Study n = 66 (18males, 48females) 20~51 Upper: 5.10 ± 1.61 Lower: 3.45 ± 1.05 Upper: 4.50 ± 1.50 Lower: 2.70 ± 1.20 Upper: 3.45 ± 1.24 Lower: 2.30 ± 0.90 Upper: 3.25 ± 1.21 Lower: 2.15 ± 0.92 Description of Outcomes Among the proposed study outcomes, all outcomes were investigated in the included studies. Outcomes from patients with good general health, healthy gingival tissues were studied in this meta-analysis. The average width of attached gingiva for different types of teeth ranges from 4.48 mm (upper incisors) to 2.16 mm (lower premolars). Generally, maxillary teeth exhibit wider attached gingiva than mandibular teeth. The incisors possess the widest attached gingiva while the premolars show the narrowest. Widths of attached gingiva for canines and molars lie between incisors and premolars. Every analysis has a two-sided p <0.0001 except for the analysis between lower canines and lower molars. Risk of Bias and Quality Assessment Quality assessment for the included studies was calculated using ROBINS-I tool. Out of the six articles, four 3,10-12 were rated low in overall risk of bias and two 9,13 were rated medium. Quality assessment is presented in Table 2. Table 3. Risk of bias R ef erence Confounding Selection bias Bias in the classification of interventions Bias due to deviations from intended interventions Bias due to missing data Bias in measurements of outcomes Bias in selection of the reported result Overall Adesola et al. 2018 Low Low Low Low Low Low Low Low Tenenbaum et al. 1982 Mod Mod Low Low Low Low Mod Mod Bhatia et al. 2015 Low Low Low Low Low Low Low Low Yang et al. 2017 Low Low Low Low Low Low Low Low Wang et al. 1990 Low Low Low Low Low Low Low Low Liu et al. 2021 Mod Low Low Low Low Low Low Mod Meta-analysis Six studies 3,9-13 investigated the width of attached gingiva for upper incisors and upper canines, which had pooled Means of 4.48 mm (95% confidence interval [CI]: 3.86, 5.12), 3.80 mm (95% CI: 3.01, 4.59), while lower incisors and lower canines had pooled Means of 3.23 mm (95% CI: 2.76, 3.70) and 2.40 mm (95% CI: 1.87, 2.93), respectively (Figure 3). For posterior teeth, six studies 3,9-13 investigated the width of attached gingiva for upper and lower premolars, which had pooled Means of 3.13 mm (95% CI: 2.59, 3.67) and 2.16 mm (95% CI: 1.75, 2.56), respectively (Figure 3). Six studies 3,9-13 investigated the width of attached gingiva for upper molars, which had a pooled Mean of 3.38 mm (95% CI: 2.82, 3.93), while lower molars had a pooled Mean of 2.40 mm (95% CI: 2.04, 2.76) (Figure 3). Sensitivity Analysis To conduct a sensitivity analysis, one study was excluded from the meta-analysis. However, the results of the meta-analysis remained unchanged, indicating the robustness of the findings in this study (Figure 4). Assessment of Publication Bias The assessment of publication bias is not performed due to insufficient numbers of included studies. Discussion To date, no scholar has conducted a systematic review of the existing literature on the attached gingival width in different oral sites. In this systematic review, the average attached gingival widths of each type of teeth were examined. We aimed to conduct a comprehensive analysis of these studies and identify any enlightenment that may be addressed in future research. The mean attached gingival widths of each type of teeth range d from 2.16 mm (lower premolars) to 4.48 mm (upper incisors). Patients with attached gingiva wider than the average are more suitable to choose mini-implants during orthodontic treatment. Also, the width of the maxillary attached gingiva is always greater than that of the corresponding mandibular teeth, and there is greater overall width of attached gingiva in the maxilla than in the mandible. This is because the maxillary alveolar process is higher than that of the mandibular alveolar process, while the width of which is roughly the same. 14 Whether in the maxilla or mandible, the width of the anterior attached gingiva is generally greater than that of the posterior region. This is probably because the height of the alveolar process i n the anterior teeth is obviously higher than that of the posterior teeth. 15 This is consistent with their physiological function——posterior teeth bear more masticatory force, requiring lower and tougher alveolar process. 16 According to our research, premolars possess the narrowest attached gingiva in both arches, probably due to the buccal frena attachment. Specifically, maxillary buccal frena are generally more prominent than mandibular buccal frena, rendering the mean difference in the widths of attached gingiva between maxillary premolars and other maxillary teeth greater than that of the mandibular ones (Figure 5). Bowers et al. investigated the width of attached gingiva in both healthy volunteers and patients with high frenum attachments, finding that higher frenum attachments are usually associated with narrower attached gingiva. 17 Later he demonstrated that labio- or buccoversion teeth have a narrower zone of attached gingiva, and on the contrary teeth in linguoversion have a broader zone of attached gingiva. 17 Normally, only the mandibular posterior teeth show lingual inclination, while all other teeth exhibit labial or buccal inclination. As a result, the width of the attached gingiva in the mandibular posterior teeth is higher than that of the maxillary posterior teeth (Figure 5). During the past decade, mini-implants have been widely used in the orthodontic treatment. However, mini-implants are also associated with various complications, one of which is the insufficient space between the dental roots and mini-implants. 18 Hu et al. analyzed twenty human mandibles and maxillae, finding that the inter-root distance increased from anterior to posterior teeth and from the cervical line to the root apex in both the maxilla and the mandible. 19 Therefore, the farther mini-screws are from the gingival margin, the less likely they are to cause complications such as root damage, and the distance between the mini-implants and the gingival margin is determined by the width of attached gingiva. Antonio Manni et al. studied 300 mini-screws inserted in the attached gingiva (103 mini-screws), free gingiva (121 mini-screws), and mucogingival line (76 mini-screws). They found that success rates of mini-screws inserted in the attached gingiva and the mucogingival junction did not show statistically significant differences (85.4% and 84.2%，respectively), but the success rate of mini-screws located in the free gingiva was significantly lower (75.2%), which indicates that a healthy attached gingiva with an appropriate width is of great importance in orthodontic treatments. 20 According to our outcomes, there is more sufficient space to insert a mini-screw in maxillary and anterior regions, which might lead to higher success rate and lower incidence of orthodontic complications in these regions. This is consistent with the research by D. Wiechmann et al., which revealed that the cumulative survival rate of mini-implants was significantly higher in the maxilla than those in the mandible. 21 This may be attributed to the wider attached gingiva in the upper arch. When inserting mini-implants in narrowed attached gingiva region, one of the approaches is to augment the insertion angle or the insertion height to gain more inter-radicular space. In premolar regions, extra vigilance should be maintained and oblique insertion is often preferred, since these regions have the narrowest attached gingiva. 22 However, when the insertion height is increased, the head of the mini-implant should still be placed in the safe zone of the width of the attached gingiva so as to avoid mucositis and improve its stability. 5,23 In addition to providing guidance on the insertion of mini-implants, the width of the attached gingiva itself also indicates periodontal status and gingival health. 24 Sreeja et al. assessed the width of attached gingiva in six front teeth and clinical metrics comprising Oral hygiene index and modified gingival index, finding that the association between the attached gingival width and its impact on dental hygiene care was statistically significant. 7 Our results can serve as a reference for normal attached gingival width values, assisting in judgement of gingival recession and whether or not stronger dental hygiene care is indicated. Limitations Despite the strengths of this investigation, our meta-analysis presented some limitations of the current literature. Bhatia et al. found that the width of attached gingiva increases with age. 12 In this meta-analysis, the age of patients varies in each study, which might lead to unreliable results. Unfortunately, we failed to obtain the average attached gingival width for people of different age groups due to the insufficient data available. Therefore, our outcomes might not be referable for all age groups. Nowadays, we can roughly distinguish between three types of gingival phenotype: thin scalloped, thick flat, and moderate. 25 The systematic review conducted by Vlachodimou et al. suggested that patients with different types of gingival phenotype ought to process different widths of attached gingiva. 26 All six studies 3,9-13 included in our review did not distinguish the gingival phenotype of patients, which means our results are applicable for the general public, but failed to describe the attached gingival width of different gingival phenotypes. Alkan et al. found that orthodontic treatment can affect the width of the attached gingiva. 27 Whereas, there is no information on whether the patient has received orthodontic treatment in the articles included in this review, which might have a marginal influence on the results of the outcomes. Besides, different methods were adopted to assess attached gingival width in these studies, such as visual and histochemical methods. But according to the research by Bhatia et al., there was no substantial, consistent variance in the methods of assessing the attached gingival width, which indicates that methods may not significantly influence the final outcomes. 12 Therefore, results of this meta-analysis are still significant. Conclusions This systematic review evaluates the average width of attached gingiva in different oral sites. According to our study, the maxillary attached gingiva is always wider than the corresponding mandibular attached gingiva in the same region. In the four quadrants, the attached gingiva from wide to narrow are incisors, canines, molars, and premolars, respectively. Our study may assist the clinicians in periodontal and orthodontic treatment, such as assisting in judgement of gingival recession and determining mini-implants insertion sites. Implications for clinical practice The success rate of the mini-implant insertion might be higher in maxilla and anterior regions, because the attached gingiva is relatively wider in these sites. When inserting mini-implants, extra vigilance should be maintained and oblique insertion is often preferred in premolar regions, since these regions have the narrowest attached gingiva. Differences between patient’s attached gingival width and the average indicates periodontal status and gingival health. Implications for research Width of attached gingiva should be considered in future researches concerning mini-implants. The success rate and complications of mini-implants insertion is probably related to the width of the attached gingiva Declarations DECLARATION OF COMPETING INTEREST The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ACKNOWLEDGEMENTS This study was supported by National Natural Science Foundation of China (No. 82071147), Sichuan Science and Technology Program (Nos. 2018JY0558, 2018SZ0232 and 2021YJ0428), Research Grant of Health Commission of Sichuan Province (Nos. 19PJ233 and 20PJ090), CSA Clinical Research Fund (CSA-02020-02), and Research and Develop Program, West China Hospital of Stomatology, Sichuan University (No. LCYJ2020-TD-2 and WCHS-201704). References 1 Lozdan, J. & Squier, C. A. The histology of the muco-gingival junction. J Periodontal Res 4 , 83-93, doi:10.1111/j.1600-0765.1969.tb01950.x (1969). 2 Oh, S. L. Attached gingiva: histology and surgical augmentation. Gen Dent 57 , 381-385; quiz 386-387 (2009). 3 Adesola, U. K., Okhiabigie, A. P., Adeola, A., Omowunmi, A. P. & Ayodeji, T. O. Evaluation of the Attached Gingival Width and Sulcus Depth in an Adult Nigerian Population - A Pilot Study. J Int Acad Periodontol 20 , 78-85 (2018). 4 Maldonado Molina, O. Insertion of orthodontic temporary anchorage devices with free gingival grafting for phenotype modification of the peri-implant mucosa. J Oral Biol Craniofac Res 13 , 727-730, doi:10.1016/j.jobcr.2023.09.005 (2023). 5 Cheng, S. J., Tseng, I. Y., Lee, J. J. & Kok, S. H. A prospective study of the risk factors associated with failure of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Implants 19 , 100-106 (2004). 6 Padmini, H., Raja, K. K., Hoe, Z. Y., Teh, Y. J. & Ting, C. J. Correlation of Width of Attached Gingiva, Depth of the Vestibule on Gingival Health and Oral Hygiene Maintenance in Malaysian Young Adults. Journal of Clinical & Diagnostic Research 12 (2018). 7 Sreeja, S. S., Bhandary, R., Bhat, A. R., Venugopalan, G. & Ivaturi, M. S. S. An Interrelation between the Width of Attached Gingiva, Vestibular Depth and its Impact on Dental Hygiene Care. Journal of Health and Allied Sciences NU (2022). 8 Sterne, J. A. et al. ROBINS-I: a tool for assessing risk of bias in non-randomised studies of interventions. Bmj 355 , i4919, doi:10.1136/bmj.i4919 (2016). 9 Liu, R. & Liu, S. Analysis of the attached gingival width and gingival biotype of people with and without history of periodontitis. Journal of Clinical Stomatology 37 , 598-601 (2021). 10 Wang, Z., Yang, R., He, P. & Guo, M. Analysis of attached gingival width in 356 healthy young adults. Chinese Journal of Stomatology 25 , 111-113 (1990). 11 Yang, J. et al. Analysis of attached gingiva width on the facial/buccal side of maxilary and mandibular arches in 144 periodontally healthy young adults. Oral Biomedicine 8 , 163-167 (2017). 12 Bhatia, G., Kumar, A., Khatri, M., Bansal, M. & Saxena, S. Assessment of the width of attached gingiva using different methods in various age groups: A clinical study. J Indian Soc Periodontol 19 , 199-202, doi:10.4103/0972-124x.152106 (2015). 13 Tenenbaum, H. A clinical study comparing the width of attached gingiva and the prevalence of gingival recessions. J Clin Periodontol 9 , 86-92, doi:10.1111/j.1600-051x.1982.tb02536.x (1982). 14 Mazeland, G. R. The mucogingival complex in relation to alveolar process height and lower anterior face height. J Periodontal Res 15 , 345-352, doi:10.1111/j.1600-0765.1980.tb00291.x (1980). 15 Ibrahim, N., Khuder, T., Abd Samad, F. N. B. & Tuan, S. B. Assessment of Anatomical Position of Posterior Teeth and Alveolar Bone Height in Malaysian Population Based on Panoramic Radiographs. Journal of Research in Medical and Dental Science 7 , 110-117 (2019). 16 Peck, C. C. Biomechanics of occlusion--implications for oral rehabilitation. J Oral Rehabil 43 , 205-214, doi:10.1111/joor.12345 (2016). 17 Bowers, G. M. A study of the width of attached gingiva. The Journal of Periodontology 34 , 201-209 (1963). 18 Sreenivasagan, S., Subramanian, A. K. & Rengalakshmi, S. Prevalence and Cause of Mini-Implant Failure Encountered by Orthodontic Residents. J Long Term Eff Med Implants 31 , 1-4, doi:10.1615/JLongTermEffMedImplants.2021035979 (2021). 19 Hu, K. S., Kang, M. K., Kim, T. W., Kim, K. H. & Kim, H. J. Relationships between dental roots and surrounding tissues for orthodontic miniscrew installation. Angle Orthod 79 , 37-45, doi:10.2319/083107-405.1 (2009). 20 Manni, A., Cozzani, M., Tamborrino, F., De Rinaldis, S. & Menini, A. Factors influencing the stability of miniscrews. A retrospective study on 300 miniscrews. Eur J Orthod 33 , 388-395, doi:10.1093/ejo/cjq090 (2011). 21 Wiechmann, D., Meyer, U. & Büchter, A. Success rate of mini- and micro-implants used for orthodontic anchorage: a prospective clinical study. Clin Oral Implants Res 18 , 263-267, doi:10.1111/j.1600-0501.2006.01325.x (2007). 22 Poggio, P. M., Incorvati, C., Velo, S. & Carano, A. "Safe zones": a guide for miniscrew positioning in the maxillary and mandibular arch. Angle Orthod 76 , 191-197, doi:10.1043/0003-3219(2006)076[0191:Szagfm]2.0.Co;2 (2006). 23 L., H., H., X., L., W., L., X. & Pu, L. Orthodontics mini-implants innovative clinical applications . (1st ed. Shanghai scientific and technical publishers, 2022). 24 Marquez, I. C. The role of keratinized tissue and attached gingiva in maintaining periodontal/peri-implant health. Gen Dent 52 , 74-78; quiz 79 (2004). 25 Fischer, K. R., Künzlberger, A., Donos, N., Fickl, S. & Friedmann, A. Gingival biotype revisited-novel classification and assessment tool. Clin Oral Investig 22 , 443-448, doi:10.1007/s00784-017-2131-1 (2018). 26 Vlachodimou, E., Fragkioudakis, I. & Vouros, I. Is There an Association between the Gingival Phenotype and the Width of Keratinized Gingiva? A Systematic Review. Dent J (Basel) 9 , doi:10.3390/dj9030034 (2021). 27 Alkan, Ö., Kaya, Y., Tunca, M. & Keskin, S. Changes in the gingival thickness and keratinized gingival width of maxillary and mandibular anterior teeth after orthodontic treatment. Angle Orthod 91 , 459-467, doi:10.2319/092620-820.1 (2021). Additional Declarations The authors declare no competing interests. Table 2 is not available with this version. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4944197","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Systematic Review","associatedPublications":[],"authors":[{"id":342627243,"identity":"1ff99ef9-f9c0-4e05-ac51-90c75d15c673","order_by":0,"name":"Ziheng Huang","email":"","orcid":"","institution":"State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China School of Stomatology, Sichuan University, Chengdu 610041, 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Long","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsUlEQVRIiWNgGAWjYBACA3YQWQHhSBCnhRlEniFZC2MbKVrMmZmPPfw6r07e4ADzwds8DHZ5BLVYNrOlG8tuO2y44QBbsjUPQ3IxYYcd5jGTltx2IMHgAJDBw3AgsYE4LXPqgFr4vxGvRfJjAzPIFjZitbClSTMcO2w48zCbseUcg2QitBxvPib5o6ZOnu9488MbbyrsCGsBAWYeMAk2gRj1QMD4g0iFo2AUjIJRMEIBAA42NTVUwEwtAAAAAElFTkSuQmCC","orcid":"","institution":"State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China School of Stomatology, Sichuan University, Chengdu 610041, China","correspondingAuthor":true,"prefix":"","firstName":"Hu","middleName":"","lastName":"Long","suffix":""},{"id":342629183,"identity":"99a7ed56-a9a8-400e-a81d-2c496fdde5d9","order_by":5,"name":"Wenli Lai","email":"","orcid":"","institution":"State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China School of Stomatology, Sichuan University, Chengdu 610041, China","correspondingAuthor":false,"prefix":"","firstName":"Wenli","middleName":"","lastName":"Lai","suffix":""}],"badges":[],"createdAt":"2024-08-20 10:19:18","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-4944197/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4944197/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":62985566,"identity":"23e9a039-75f3-44f7-84d0-abf6b3586a5a","added_by":"auto","created_at":"2024-08-21 19:25:30","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":47668,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePRISMA flow diagram for studies retrieved through the search and selection processes.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4944197/v1/87246638bdf4b744e1b73321.png"},{"id":62985162,"identity":"b893a5b9-a88f-467f-8793-b126f26f464e","added_by":"auto","created_at":"2024-08-21 19:17:30","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":53886,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSignificance analysis between different oral sites.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4944197/v1/72448a38850b11d430a27d86.png"},{"id":62985163,"identity":"144a5e67-9d06-484f-9682-7e659a7dad92","added_by":"auto","created_at":"2024-08-21 19:17:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":500462,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eForest plot of the mean attached gingival width in different oral sites (upper incisors, upper canines, upper premolars, upper molars, lower incisors, lower canines, lower premolars and lower molars).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4944197/v1/062c607013483b38a464e180.png"},{"id":62985167,"identity":"c52f9691-05c8-43ef-ad42-557668de768a","added_by":"auto","created_at":"2024-08-21 19:17:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":263336,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSensitivity analysis of outcomes in different oral sites.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4944197/v1/c2d304479154e3c2a2797be8.png"},{"id":62985166,"identity":"9135b5e2-0a84-4f55-9a4c-9a28720725cc","added_by":"auto","created_at":"2024-08-21 19:17:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":159648,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLine chart of mean attached gingival width in different oral sites and mean difference in the width of attached gingiva between incisors and molars (upper \u0026amp;lower).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4944197/v1/8f6d8aedeed63ceb48afb4d0.png"},{"id":62985909,"identity":"7ca1347b-05c9-4220-afe6-af709e092124","added_by":"auto","created_at":"2024-08-21 19:33:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1690239,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4944197/v1/6faa6f92-34ec-4e39-a19c-94484c67ba58.pdf"}],"financialInterests":"\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003eTable 2 is not available with this version.\u003c/p\u003e","formattedTitle":"\u003cp\u003e\u003cstrong\u003eEvaluation of the width of attached gingiva: A systematic review and meta-analysis\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAttached gingiva is an anatomic structure of the periodontium continuous with the free gingiva and lies between the free gingival groove and the mucogingival junction.\u003csup\u003e1\u003c/sup\u003e Histologically, the attached gingival epithelium is comprised of keratin as well as thin, prominent epithelial ridges and a thick lamina propria and the connective tissue contains no elastic fibers.\u003csup\u003e2\u003c/sup\u003e All these features highlight the importance and contribution of the attached gingiva to the health and stability of the periodontium, including the provision of increased resistance to external injury, stabilization of the gingival margin, and dissipating physiological forces exerted by the muscular fibers of the alveolar mucosa on the gingival tissue.\u003csup\u003e3\u003c/sup\u003e Especially in the field of orthodontics, the insertion of mini-implants at the mucogingival junction is a common practice. If the mini-implants are positioned too close to the alveolar ridge, they may become unstable and prone to loosening, ultimately resulting in treatment failure. Meanwhile, insertion into the alveolar mucosa could cause inflammation and subsequent failure.\u003csup\u003e4\u003c/sup\u003e Cheng et al., in a prospective clinical study involving 140 mini-implants, found that the absence of keratinized mucosa around mini-implants significantly increased the risk of infection and failure.\u003csup\u003e5\u003c/sup\u003e These scenarios highlight the clinical importance of a healthy attached gingiva with an appropriate width in orthodontic treatments.\u003c/p\u003e\n\u003cp\u003eTo date, numerous studies have investigated the width of attached gingiva; however, comprehensive measurements are limited. Padmini et al. measured the width of attached gingiva and vestibular depth of 165 young Malaysian adults, but only included six anterior teeth, from cuspid to cuspid.\u003csup\u003e6\u003c/sup\u003e Sreeja et al. investigated the association between the width of attached gingiva and its impact on dental hygiene care. It is regrettable that they only provided the mean width of the attached gingiva of the gross maxillary and mandibular(3.00mm and 2.01mm,respectively), failing to provide the widths of all sites including incisors, cuspid, premolars and molars.\u003csup\u003e7\u003c/sup\u003e Surprisingly, no scholar has conducted a systematic review of the existing literature on this topic. In line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, we conducted a systematic review to bridge this gap. Our objective was to determine the average widths of attached gingiva in various oral sites, compare and offer valuable insights for future studies.\u003c/p\u003e\n\u003cp\u003eThis study aimed to systematically review and meta-analyze the attached gingival width in different oral sites respectively. By providing the mean attached gingival width and comparing them between regions, our results could assist the clinicians in periodontal and orthodontic treatment.\u0026nbsp;\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cp\u003e\u003cstrong\u003eProtocol and Registration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe protocol for this systematic review was registered in the International Prospective Register of Systematic Reviews (PROSPERO; http://www.crd.york.ac.uk/prospero; registration number CRD42024568391).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformation Sources, Search Strategy, and Study Selection\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe databases searched included those of PubMed, Embase, Web of Science, and CNKI. Specifically, the online search parameters were articles from time of database inception to August 28, 2023, without language restrictions. A search for published, peer reviewed articles was conducted using keywords \u0026ldquo;attached gingiva\u0026rdquo;, \u0026ldquo;width\u0026rdquo; and their synonyms. Titles and abstracts were assessed according to the eligibility criteria. The selected articles were evaluated after reading full texts, and a final selection was determined. Searching and assessment of studies was performed independently by two reviewers (Z.H. and Y.L.) separately. The final decisions on inclusion were made after consulting with a third reviewer (H.L.) (Figure 1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEligibility criteria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOwing to the research question of interest, patients with good general health, healthy gingival tissues (no loss of attachment) were included. Both randomized controlled trials (RCTs) and non-randomized studies of the effects of interventions (NRSIs) were eligible.\u003c/p\u003e\n\u003cp\u003eThe following exclusion criteria were adopted: patients with systemic illnesses, pregnant or lactating women, patients on medications that could influence the width of the gingiva such as calcium channel blockers, moderate to severe gingival inflammation, presence of gingival recession, and presence of clinical attachment loss were excluded.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Extraction\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter conducting full-text reviews of the articles, we organized the data into a standardized table, which included study design, demographic data (age, sample size, grouping, and width of attached gingiva), detailed description (interventions, treatment duration, and comparator), and outcomes. Any discrepancies in the extracted data were resolved through discussion among all three reviewers.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRisk of Bias and Quality Assessment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe evaluation of risk of bias for the included studies was performed independently and separately by two reviewers (Z.H. and Y.L.) according to the Cochrane tool for assessing risk of bias in nonrandomized trials (ROBINS-I tool).\u003csup\u003e8\u003c/sup\u003e For each bias domain, a judgment score was given following the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions 5.1.0. Any disagreement was solved by discussion or judged by a third reviewer (H.L.).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMeta-analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOriginal data were subject to statistical pooling through random effect models. Significance analysis was conducted using GraphPad Prism 9 software\u0026nbsp;to evaluate the significance of outcomes between different groups (Figure 2).\u0026nbsp;Heterogeneity across studies was assessed through the I\u003csup\u003e2\u003c/sup\u003e statistic, and an I\u003csup\u003e2\u003c/sup\u003e statistic greater than 50% was considered as substantial heterogeneity. If substantial heterogeneity existed, a subgroup analysis on different study designs and periodontal health condition would be executed to explore the potential heterogeneity. In addition, sensitivity analysis for studies with small sample sizes was conducted to evaluate the robustness of the pooled results in the meta-analysis. The Egger test and Begg test were used to assess publication bias. All the meta-analyses were performed in Comprehensive Meta-Analysis (version 2.2.064, Biostat, Englewood, NJ).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eDescription of Studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInitially, 736 articles from the database were identified and 723 were excluded as irrelevant. The remaining thirteen articles were further assessed for eligibility, and six studies were finally included in this systematic review.\u003csup\u003e3,9-13\u003c/sup\u003e The procedures of online searching and selection are shown in Figure 1. Sample size ranges from 45 to 356 in different groups (Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp style=\"margin:0in;text-align:justify;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eTable\u0026nbsp;\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e1\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e.\u003c/span\u003e \u003cspan style='font-family:\"Times New Roman\",serif;'\u003eCharacteristics of\u0026nbsp;\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003ethe I\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003encluded\u0026nbsp;\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eS\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003etudies\u003c/span\u003e\u003c/p\u003e\n\u003ctable style=\"border: none;width:694.6pt;border-collapse:collapse;\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eStudy\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eDesign\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eNo. of patients\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAge Range\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAttached Gingival Width of Incisors\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAttached Gingival Width of Canines\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAttached Gingival Width of Premolars\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAttached Gingival Width of Molars\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAdesola et al. 2018\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eCross-sectional Study\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003en = 73\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003e(19males, 54females)\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003e18~34\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003e\u0026nbsp;\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 4.59 \u0026plusmn; 1.79\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 3.27 \u0026plusmn; 1.17\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 3.73 \u0026plusmn; 1.51\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 2.51 \u0026plusmn; 1.17\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 3.28 \u0026plusmn; 1.51\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 2.43 \u0026plusmn; 1.07\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 3.44 \u0026plusmn; 1.69\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 3.16 \u0026plusmn; 1.03\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eTenenbaum et al. 1982\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eCross-sectional Study\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003en = 100\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e(68males, 32females)\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e19~26\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 3.50 \u0026plusmn; 1.02\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.38 \u0026plusmn; 0.96\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 2.40 \u0026plusmn; 1.15\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 1.40 \u0026plusmn; 0.80\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 2.65 \u0026plusmn; 1.08\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 1.63 \u0026plusmn; 0.85\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 3.20 \u0026plusmn; 1.15\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.00 \u0026plusmn; 0.89\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBhatia et al. 2015\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBefore-after Study\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003en = 45\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003e15~60\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 3.71 \u0026plusmn; 0.81\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 3.21 \u0026plusmn; 0.83\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 3.13 \u0026plusmn; 1.05\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 2.10 \u0026plusmn; 0.87\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 2.19 \u0026plusmn; 0.68\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 1.60 \u0026plusmn; 0.47\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 2.45 \u0026plusmn; 0.63\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 1.86 \u0026plusmn; 0.53\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eYang et al. 2017\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eCross-sectional Study\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003en = 144\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style=\"font-size:16px;\"\u003e\u0026nbsp;\u003c/span\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e(72males, 72females)\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e20~30\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 4.98 \u0026plusmn; 1.20\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 4.05 \u0026plusmn; 1.00\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 4.35 \u0026plusmn; 1.20\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.90 \u0026plusmn; 0.90\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 3.37 \u0026plusmn; 1.01\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.25 \u0026plusmn; 0 .97\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 3.93 \u0026plusmn; 1.30\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.60 \u0026plusmn; 1.05\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eWang et al. 1990\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eCross-sectional Study\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003en = 356\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003e(173males, 183females)\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003e15~20\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 5.05 \u0026plusmn; 2.09\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 3.00 \u0026plusmn; 1.00\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 4.70 \u0026plusmn; 1.90\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 2.80 \u0026plusmn; 1.20\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 3.85 \u0026plusmn; 1.50\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 2.74 \u0026plusmn; 1.37\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eUpper: 4.00 \u0026plusmn; 1.36\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLower: 2.65 \u0026plusmn; 1.22\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLiu et al. 2021\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.65pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eCase-control Study\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62.7pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003en = 66\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e(18males, 48females)\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82.95pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e20~51\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.15pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 5.10 \u0026plusmn; 1.61\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 3.45 \u0026plusmn; 1.05\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 4.50 \u0026plusmn; 1.50\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.70 \u0026plusmn; 1.20\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 3.45 \u0026plusmn; 1.24\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.30 \u0026plusmn; 0.90\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eUpper: 3.25 \u0026plusmn; 1.21\u003c/span\u003e\u003c/p\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLower: 2.15 \u0026plusmn; 0.92\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp style=\"margin:0in;text-align:justify;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDescription of Outcomes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAmong the proposed study outcomes, all outcomes were investigated in the included studies. Outcomes from patients with good general health, healthy gingival tissues were studied in this meta-analysis. The average width of attached gingiva for different types of teeth ranges from 4.48 mm (upper incisors) to 2.16 mm (lower premolars). Generally, maxillary teeth exhibit wider attached gingiva than mandibular teeth. The incisors possess the widest attached gingiva while the premolars show the narrowest. Widths of attached gingiva for canines and molars lie between incisors and premolars. Every analysis has a two-sided \u003cem\u003ep\u0026nbsp;\u003c/em\u003e\u0026lt;0.0001 except for the analysis between lower canines and lower molars.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRisk of Bias and Quality Assessment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQuality assessment for the included studies was calculated using ROBINS-I tool. Out of the six articles, four\u003csup\u003e3,10-12\u003c/sup\u003e were rated low in overall risk of bias and two\u003csup\u003e9,13\u003c/sup\u003e were rated medium. Quality assessment is presented in Table 2.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp style=\"margin:0in;text-align:justify;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eTable 3. Risk of bias\u003c/span\u003e\u003c/p\u003e\n\u003ctable style=\"border: none;width:694.6pt;border-collapse:collapse;\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eR\u003c/span\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eef\u003c/span\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eerence\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eConfounding\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eSelection bias\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBias in the classification of interventions\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBias due to deviations from intended interventions\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBias due to missing data\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBias in measurements of outcomes\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBias in selection of the reported result\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;background: rgb(174, 170, 170);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eOverall\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eAdesola et al. 2018\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eTenenbaum et al. 1982\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eMod\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eMod\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eMod\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eMod\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eBhatia et al. 2015\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eYang et al. 2017\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eWang et al. 1990\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;background: rgb(242, 242, 242);padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;color:black;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 63.55pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cstrong\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLiu et al. 2021\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69.75pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eMod\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51.05pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85.2pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113.35pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56.7pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99.15pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eLow\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70.85pt;padding: 0in 5.4pt;vertical-align: top;\"\u003e\n \u003cp style=\"margin:0in;text-align:center;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003eMod\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp style=\"margin:0in;text-align:justify;font-size:14px;font-family:DengXian;\"\u003e\u003cspan style='font-family:\"Times New Roman\",serif;'\u003e\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMeta-analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSix studies\u003csup\u003e3,9-13\u003c/sup\u003e investigated the width of attached gingiva for upper incisors and upper canines, which had pooled Means of 4.48 mm (95% confidence interval [CI]: 3.86, 5.12), 3.80 mm (95% CI: 3.01, 4.59), while lower incisors and lower canines had pooled Means of 3.23 mm (95% CI: 2.76, 3.70) and 2.40 mm (95% CI: 1.87, 2.93), respectively (Figure 3).\u003c/p\u003e\n\u003cp\u003eFor posterior teeth, six studies\u003csup\u003e3,9-13\u003c/sup\u003e investigated the width of attached gingiva for upper and lower premolars, which had pooled Means of 3.13 mm (95% CI: 2.59, 3.67) and 2.16 mm (95% CI: 1.75, 2.56), respectively (Figure 3). Six studies\u003csup\u003e3,9-13\u003c/sup\u003e investigated the width of attached gingiva for upper molars, which had a pooled Mean of 3.38 mm (95% CI: 2.82, 3.93), while lower molars had a pooled Mean of 2.40 mm (95% CI: 2.04, 2.76) (Figure 3).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSensitivity Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo conduct a sensitivity analysis, one study was excluded from the meta-analysis. However, the results of the meta-analysis remained unchanged, indicating the robustness of the findings in this study (Figure 4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAssessment of Publication Bias\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe assessment of publication bias is not performed due to insufficient numbers of included studies.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eTo date, no scholar has conducted a systematic review of the existing literature on\u0026nbsp;the attached gingival width in different\u0026nbsp;oral sites. In this systematic review, the average attached gingival widths of each type of teeth were examined. We aimed to conduct a comprehensive analysis of these studies and identify any enlightenment that may be addressed in future research.\u003c/p\u003e\n\u003cp\u003eThe mean attached gingival widths of each type of teeth range\u003cu\u003ed\u003c/u\u003e from 2.16 mm (lower premolars) to 4.48 mm (upper incisors). Patients with attached gingiva wider than the average are more suitable to choose mini-implants during orthodontic treatment. Also, the width of the maxillary attached gingiva is always greater than that of the corresponding mandibular teeth, and there is greater overall width of attached gingiva in the maxilla than in the mandible. This is because the maxillary alveolar process is higher than that of the mandibular alveolar process, while the width of which is roughly the same.\u003csup\u003e14\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eWhether in the maxilla or mandible, the width of the anterior attached gingiva is generally greater than that of the posterior region. This is probably because the height of the alveolar process i\u003cu\u003en the\u003c/u\u003e anterior teeth is obviously higher than that of the posterior teeth.\u003csup\u003e15\u003c/sup\u003e This is consistent with their physiological function\u0026mdash;\u0026mdash;posterior teeth bear more masticatory force, requiring lower and tougher alveolar process.\u003csup\u003e16\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAccording to our research, premolars possess the narrowest attached gingiva in both arches, probably due to the buccal frena attachment. Specifically, maxillary buccal frena are generally more prominent than mandibular buccal frena, rendering the mean difference in the widths of attached gingiva between maxillary premolars and other maxillary teeth greater than that of the mandibular ones (Figure 5). Bowers et al. investigated the width of attached gingiva in both healthy volunteers and patients with high frenum attachments, finding that higher frenum attachments are usually associated with narrower attached gingiva.\u003csup\u003e17\u003c/sup\u003e Later he demonstrated that labio- or buccoversion teeth have a narrower zone of attached gingiva, and on the contrary teeth in linguoversion have a broader zone of attached gingiva.\u003csup\u003e17\u003c/sup\u003e Normally, only the mandibular posterior teeth show lingual inclination, while all other teeth exhibit labial or buccal inclination. As a result, the width of the attached gingiva in the mandibular posterior teeth is higher than that of the maxillary posterior teeth (Figure 5).\u003c/p\u003e\n\u003cp\u003eDuring the past decade, mini-implants have been widely used in the orthodontic treatment. However, mini-implants are also associated with various complications, one of which is the insufficient space between the dental roots and mini-implants.\u003csup\u003e18\u003c/sup\u003e Hu et al. analyzed twenty human mandibles and maxillae,\u0026nbsp;finding that the inter-root distance increased from anterior to posterior teeth and from the cervical line to the root apex in both the maxilla and the mandible.\u003csup\u003e19\u003c/sup\u003e Therefore, the farther mini-screws are from the gingival margin, the less likely they are to cause complications such as root damage, and the distance between the mini-implants and the gingival margin is determined by the width of attached gingiva. Antonio Manni et al. studied 300 mini-screws inserted in the attached gingiva (103 mini-screws), free gingiva (121 mini-screws), and mucogingival line (76 mini-screws). They found that success rates of mini-screws inserted in the attached gingiva and the mucogingival junction did not show statistically significant differences (85.4% and 84.2%，respectively), but the success rate of mini-screws located in the free gingiva was significantly lower (75.2%), which indicates that a healthy attached gingiva with an appropriate width is of great importance in orthodontic treatments.\u003csup\u003e20\u003c/sup\u003e According to our outcomes, there is more sufficient space to insert a mini-screw in maxillary and anterior regions, which might lead to higher success rate and lower incidence of orthodontic complications in these regions. This is consistent with the research by D. Wiechmann et al., which revealed that the cumulative survival rate of mini-implants was significantly higher in the maxilla than those in the mandible.\u003csup\u003e21\u003c/sup\u003e This may be attributed to the wider attached gingiva in the upper arch.\u003c/p\u003e\n\u003cp\u003eWhen inserting mini-implants in narrowed attached gingiva region, one of the approaches is to augment the insertion angle or the insertion height to gain more inter-radicular space. In premolar regions, extra vigilance should be maintained and oblique insertion is often preferred, since these regions have the narrowest attached gingiva.\u003csup\u003e22\u003c/sup\u003e However, when the insertion height is increased, the head of the mini-implant should still be placed in the safe zone of the width of the attached gingiva so as to avoid mucositis and improve its stability.\u003csup\u003e5,23\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eIn addition to providing guidance on the insertion of mini-implants, the width of the attached gingiva itself also indicates periodontal status and gingival health.\u003csup\u003e24\u003c/sup\u003e Sreeja et al. assessed the width of attached gingiva in six front teeth and clinical metrics comprising Oral hygiene index and modified gingival index, finding that the association between the attached gingival width and its impact on dental hygiene care was statistically significant.\u003csup\u003e7\u003c/sup\u003e Our results can serve as a reference for normal attached gingival width values, assisting in judgement of gingival recession and whether or not stronger dental hygiene care is indicated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLimitations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDespite the strengths of this investigation, our meta-analysis presented some limitations of the current literature. Bhatia et al. found that the width of attached gingiva increases with age.\u003csup\u003e12\u003c/sup\u003e In this meta-analysis, the age of patients varies in each study, which might lead to unreliable results. Unfortunately, we failed to obtain the average attached gingival width for people of different age groups due to the insufficient data available. Therefore, our outcomes might not be referable for all age groups.\u003c/p\u003e\n\u003cp\u003eNowadays, we can roughly distinguish between three types of gingival phenotype: thin scalloped, thick flat, and moderate.\u003csup\u003e25\u003c/sup\u003e The systematic review conducted by Vlachodimou et al. suggested that patients with different types of gingival phenotype ought to process different widths of attached gingiva.\u003csup\u003e26\u003c/sup\u003e All six studies\u003csup\u003e3,9-13\u003c/sup\u003e included in our review did not distinguish the gingival phenotype of patients, which means our results are applicable for the general public, but failed to describe the attached gingival width of different gingival phenotypes.\u003c/p\u003e\n\u003cp\u003eAlkan et al. found that orthodontic treatment can affect the width of the attached gingiva.\u003csup\u003e27\u003c/sup\u003e Whereas, there is no information on whether the patient has received orthodontic treatment in the articles included in this review, which might have a marginal influence on the results of the outcomes.\u003c/p\u003e\n\u003cp\u003eBesides, different methods were adopted to assess attached gingival width in these studies, such as visual and histochemical methods. But according to the research by Bhatia et al., there was no substantial, consistent variance in the methods of assessing the attached gingival width, which indicates that methods may not significantly influence the final outcomes.\u003csup\u003e12\u003c/sup\u003e Therefore, results of this meta-analysis are still significant.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis systematic review evaluates the average width of attached gingiva in different\u0026nbsp;oral sites. According to our study, the maxillary attached gingiva is always wider than the corresponding mandibular attached gingiva in the same region. In the four quadrants, the attached gingiva from wide to narrow are incisors, canines, molars, and premolars, respectively. Our study may assist the clinicians in periodontal and orthodontic treatment, such as assisting in judgement of gingival recession and determining mini-implants insertion sites.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImplications for clinical practice\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe success rate of the mini-implant insertion might be higher in maxilla and anterior regions, because the attached gingiva is relatively wider in these sites.\u003c/p\u003e\n\u003cp\u003eWhen inserting mini-implants, extra vigilance should be maintained and oblique insertion is often preferred in premolar regions, since these regions have the narrowest attached gingiva.\u003c/p\u003e\n\u003cp\u003eDifferences between patient\u0026rsquo;s attached gingival width and the average indicates periodontal status and gingival health.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImplications for research\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWidth of attached gingiva should be considered in future researches concerning mini-implants.\u003c/p\u003e\n\u003cp\u003eThe success rate and complications of mini-implants insertion is probably related to the width of the attached gingiva\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDECLARATION OF COMPETING INTEREST\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eACKNOWLEDGEMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by National Natural Science Foundation of China (No. 82071147), Sichuan Science and Technology Program (Nos. 2018JY0558, 2018SZ0232 and 2021YJ0428), Research Grant of Health Commission of Sichuan Province (Nos. 19PJ233 and 20PJ090), CSA Clinical Research Fund (CSA-02020-02), and Research and Develop Program, West China Hospital of Stomatology, Sichuan University (No. LCYJ2020-TD-2 and WCHS-201704).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003cp\u003e1\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Lozdan, J. \u0026amp; Squier, C. 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Changes in the gingival thickness and keratinized gingival width of maxillary and mandibular anterior teeth after orthodontic treatment. \u003cem\u003eAngle Orthod\u003c/em\u003e \u003cstrong\u003e91\u003c/strong\u003e, 459-467, doi:10.2319/092620-820.1 (2021).\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"0084df84-c9d4-4891-a88d-cb65e7c7847c","identifier":"10.13039/501100001809","name":"National Natural Science Foundation of China","awardNumber":"82071147","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China School of Stomatology, Sichuan University, Chengdu 610041, China","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Width of attached gingiva, Mini-implant, Systematic review, Meta-analysis","lastPublishedDoi":"10.21203/rs.3.rs-4944197/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4944197/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eAims\u003c/h2\u003e \u003cp\u003eTo conduct a systematic review and meta-analysis of studies that evaluated the width of attached gingiva.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eAn electronic search was performed in PubMed, Embase, Web of Science, and CNKI with no language restrictions. Eligible study selection, data extraction, and evaluation of risk of bias were conducted by two authors independently and in duplicate. Any disagreement was solved by discussion or judged by a third reviewer.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eSix studies were finally included. Upper incisors and upper canines had pooled Means of 4.48 mm and 3.80 mm, while lower incisors and lower canines had pooled Means of 3.23 mm and 2.40 mm, respectively. Upper premolar and lower premolars had pooled Means of 3.13 mm and 2.16 mm, respectively. Upper molars had a pooled Mean of 3.38 mm, while lower molars had a pooled Mean of 2.40 mm.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe maxillary attached gingiva is always wider than the corresponding mandibular attached gingiva in the same region. In the four quadrants, the attached gingiva from wide to narrow are incisors, canines, molars, and premolars, respectively. Future studies are necessary to evaluate the width of attached gingiva among different gingival phenotypes and age groups.\u003c/p\u003e","manuscriptTitle":"Evaluation of the width of attached gingiva: A systematic review and meta-analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-21 19:17:26","doi":"10.21203/rs.3.rs-4944197/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"991e99ec-d608-4410-b83b-14de47066ccf","owner":[],"postedDate":"August 21st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":36297934,"name":"Dentistry"}],"tags":[],"updatedAt":"2024-08-21T19:17:26+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-21 19:17:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4944197","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4944197","identity":"rs-4944197","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}