External Root Resorption Due to Impacted Third Molars: is There a Relationship with Masticatory Muscle Fatigue?

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Samara Caroline Fernandes Galvani, Elisa Bizetti Pelai, Larissa Moreira Souza, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9179312/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective This research aimed to evaluate muscle fatigue in the masseter and anterior temporal masticatory muscles at rest and during maximum dental intercuspation in individuals with external root resorption (ERR) in the second lower molar adjacent to the impacted third molar, compared to a control group. The median frequency (Hz) values ​​obtained between the group with ERR and the control group were compared, based on the results obtained, in order to identify significant differences and their clinical implications. The values ​​obtained at rest in the studied individuals were also analyzed to understand their variations. Methods A observational study with a cross-sectional design was conducted, involving 60 patients (30 with ERR and 30 controls). Cone-beam computed tomography (CBCT), previously collected, images were used for diagnosis, and surface electromyography (EMG) was performed to record muscle activity during rest and maximum molar intercuspation. Median frequency (MF (Hz)) analysis was used to assess muscle fatigue patterns. G-Power was used for sample size calculation. Statistical analysis included Shapiro-Wilk tests, mixed-model ANOVA, GraphPad Prism, and simple linear regression, with a significance level of α = 0.05. Results The group with ERR showed significantly higher muscle activity at rest in the left anterior temporalis (p = 0.001), right anterior temporalis (p = 0.001), left masseter (p = 0.038), and right masseter (p = 0.003) compared to the control group. The ERR group demonstrated significantly lower median frequency (MF (Hz)) values, indicating greater muscle fatigue, particularly in the left masseter (97.63 ± 28.00 Hz vs. 128.05 ± 37.10 Hz in the control group). In simple linear regression analyses in MF (Hz), the RRE group showed lower values ​​(Hz), mainly in the left temporalis muscle. The left masseter muscle showed lower values ​​in the group. Conclusion Individuals with ERR in lower second molars adjacent to impacted third molars exhibit greater muscle activity of the masticatory muscles at rest and greater muscle fatigue during function. Root Resorption Cone Beam Computed Tomography Tooth Wear Electromyography Temporal Muscle Masseter Muscle Figures Figure 1 Introduction External root resorption (ERR) affecting lower second molars represents a significant clinical alteration in dental practice, generally associated with impacted third molars. Characterized by progressive cementum loss, it has been studied from both diagnostic and etiological perspectives, using cone-beam computed tomography (CBCT), considered the gold standard for detection and monitoring (Oenning et al., 2015 ). However, although the structural implications of ERR are well documented, its functional consequences on the masticatory system remain comparatively unexplored, creating a substantial gap in understanding the comprehensive clinical impact of this pathology. The biomechanical alterations resulting from ERR can initiate a cascade of neuromuscular adaptations in the stomatognathic system. Recent investigations have begun to elucidate the relationship between dental structural integrity and the function of the masticatory muscles (Moreira-Souza et al., 2024 ). The presence of impacted third molars in close contact with adjacent roots creates conditions for repetitive microtrauma and inflammatory processes that can transcend local effects, potentially influencing neuromuscular control mechanisms (Sarrafpour et al., 2013 ). This interaction between peripheral structural alterations and central neuromuscular regulation represents a critical area for scientific investigation. Previous research by Moreira-Souza et al. ( 2024 ) provided preliminary evidence of altered electromyographic activity in patients with RRE, demonstrating increased muscle activation during functional tasks. This finding suggests the existence of compensatory neuromuscular mechanisms in response to dental structural changes. The study focused primarily on amplitude-based parameters, leaving unexplored the specific relationship between RRE and muscle fatigue indices, particularly median frequency. This represents a significant limitation in current knowledge, since frequency domain analyses offer potentially more sensitive indicators of muscle metabolic changes than traditional amplitude-based measures. For this purpose, surface electromyography (EMG) was used, which is a fundamental methodology for the objective assessment of masticatory muscle function, providing non-invasive quantification of muscle activity patterns (Pelai et al., 2023 ). Within the analytical framework of EMG, median frequency (FM) analysis has gained prominence as a reliable indicator of muscle fatigue (Konrad, 2005 ). The physiological basis of this relationship lies in the reduction of muscle fiber conduction velocity and the synchronization of motor unit firing patterns that occur during fatiguing contractions (Sharma et al., 2024 ). The clinical relevance of muscle fatigue parameters goes beyond theoretical interest, directly impacting functional capacity. In populations with temporomandibular dysfunction, alterations in median frequency patterns have been correlated with subjective reports of masticatory fatigue and decreased masticatory efficiency (Flores-Orozco et al., 2023 ). Furthermore, evidence suggests that even subtle occlusal disturbances can induce significant changes in muscle activation patterns, potentially leading to compensatory mechanisms that alter normal neuromuscular function (Al Sayegh et al., 2020 ). These adaptations may manifest as increased muscle activity at rest or reduced resistance to fatigue during functional tasks. Based on the results of the research by Moreira-Souza et al. ( 2024 ), this study verifies the hypothesis that individuals with ERR present greater fatigue of the masticatory muscles. This research is justified by the high prevalence of myogenic pain related to temporomandibular dysfunction and the need to establish pathophysiological bases for the prevention of temporomandibular disorders. Materials and methods This is an observational study with a cross-sectional design, according to Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) for cross-sectional studies. involving cone-beam computed tomography (CBCT) scans of sixty patients with CBCT requests approved by CONEP, and which includes CBCT imaging data and surface electromyography examination. It is important to emphasize that this is a secondary analysis of a previous study (Moreira-Souza et al. 2024 ). Sample Data The data used in this study were obtained from a large project investigating cervical spine involvement in patients with TMD. Details about this study are described elsewhere (Moreira-Souza et al. 2024 ). Ethical and legal aspects This cross-sectional observational study was approved by the local Ethical Review Board (protocol: #41652015.7.0000.5418) and was conducted following the Declaration of Helsinki Ethical Principles. All procedures were developed in an oral radiology clinic and a laboratory of a dental school. The project included electromyography and CBCT scans; each patient who agreed to participate in the research signed a previously prepared Informed Consent Form. The Informed Consent Form (ICF) informed and clarified the research subject's decision, allowing them to make a fair and unconstrained decision regarding their participation in the research project. The document was given to the participant in duplicate, signed by both the participant and the researcher, thus establishing responsibilities between both parties, with each party retaining one copy. The sample size calculation was performed using data from 8 patients with the studied condition and 8 without the condition. With a power of 95% and an alpha of 5%, a total of 58 patients was determined, 29 per group. The analysis was performed using GPower software, version 3.1.9.2. Sample selection The sample for this study was a convenience, where patients included in this selection presented a request for cone-beam computed tomography (CBCT) for preoperative planning of impacted third molar extraction; they are of both sexes and are between 21 and 59 years of age. For the group with ERR: presence of second lower molars adjacent to the impacted third molars; computed tomography scans demonstrating ERR of at least one second lower molar, located in the region of impaction with the third molar; third molars with fully formed crowns and roots. For the control group: presence of second lower molars adjacent to the impacted third molars; computed tomography scans showing the integrity of the second lower molars in the region of impaction with the third molar; computed tomography scans showing the integrity of one second lower molar when the contralateral second molar is absent; third molars with fully formed crowns and roots. Patients with complaints of pain of odontogenic origin were excluded (as it may mask temporomandibular dysfunction (TMD) or other orofacial pain); Patients with a BMI equal to or greater than 30 kg/m² (OMS, 2022); patients with a history of trauma or surgery to the maxillofacial structures (since these patients are more likely to receive some type of treatment and their inclusion may introduce bias into the results); patients with cognitive or intellectual disabilities, with facial deformities and/or significant dental anomalies; CBCT images showing third molars associated with cystic or tumoral lesions and/or the presence of extensive caries lesions in the second lower molar; and CBCT images that present positioning errors in the technique and/or the presence of artifacts that hinder diagnosis in the region of interest. Image acquisition and evaluation The Images were previously acquired with the OP300 Maxio unit (Instrumentarium Dental, Tuusula, Finland) set to 90 kVp, 6 mA, exposure time of 6.1 s, voxel size of 0.2 mm and field of view of 6 × 8 cm. After acquisition, CBCT volumes were exported with the metal artifact reduction algorithm and stored in the Digital Imaging and Communications in Medicine (DICOM) format. The CBCT volumes were evaluated as described in Moreira-Souza et al. 2024 to determine the participants in each group, that is, with and without RRE. Electromyographic Evaluation Patients were classified according to findings of impacted lower third molars on CBCT (Cone Beam Computed Tomography) images and then distributed into the two groups (test and control) mentioned previously. In the search for signs of occlusal overload, muscle hyperactivity, and parafunctional habits, the following step was performed, in a blinded manner and executed by a single researcher with extensive experience in performing surface electromyography examination. Electromyography (EMG) data were collected in the oral and maxillofacial surgery laboratory at Faculdade de Odontologia de Piracicaba, which has an environment and conditions suitable for adequate EMG signal collection. For the surface electromyographic examination, equipment was used that followed the recommendations of the International Society of Electrophysiology and Kinesiology (ISEK) with an acquisition module of at least 8 channels, with 16-bit resolution, and an acquisition frequency of 2000 Hz (Trigno System – Delsys). EMG signal normalization was performed to avoid data interference. This was done using a sheet of Parafilm M® folded three times lengthwise and then in half widthwise. It was positioned on the occlusal surfaces of the first and second upper and lower molars, bilaterally, and maximum voluntary contraction was requested. The collected electromyographic signals were sampled synchronously and stored for later visualization and processing. The equipment's software was used to acquire and store the digitized signals in data files. The signals were analyzed offline using Matlab® 8.3 (R2014a) software, in which a 4th-order two-pole Butterworth digital filter with a 10 Hz high-pass filter and a 400 Hz low-pass filter was applied using a specific routine. The analysis was performed in the frequency domain to obtain the EMG power spectral density values using the Fast Fourier Transform (FFT) algorithm to obtain the median frequency (Hz) values and, in the amplitude domain, to obtain the RMS (uV) values. The muscles evaluated were: masseter and anterior temporal, bilaterally, right masseter (RM), left masseter (LM), anterior portion of the right temporal muscle (RT) and left temporal muscle (LT). For bilateral muscle action potential recording, wireless differential electrodes (Trigno System – Delsys) were used. Data collection was performed in an air-conditioned room with a controlled temperature maintained at 23º±2ºC and illuminated with incandescent lamps. The wireless electrodes were positioned on the bellies of the aforementioned muscles, parallel to the muscle fibers, with the silver bars perpendicular to them. They were fixed, using adhesive, to skin that had been previously cleaned with cotton soaked in a 70% alcohol solution, rubbed with sandpaper, and shaved, when necessary, to remove surface fat and dead cells, reduce skin impedance, and thus avoid interference, ensuring signal quality. For electrode placement, a functional test was performed for each muscle. This test consisted of muscle palpation during simultaneous bilateral isotonic contraction, according to the positioning criteria described below: superficial belly of the masseter muscle - between the level of the zygomatic arch and the gonial angle, two cm above the angle of the mandible; anterior belly of the anterior temporal muscle - near the upper lateral corner of the eyebrow, in the longitudinal direction of the fibers of the anterior bundle defined by palpation during teeth clenching (CRAM et al., 1998 ). The research participant was asked to remain seated, in an upright position with their feet flat on the floor, their upper and lower limbs relaxed and uncrossed, and their hands on their thighs. Regarding the head position, the Frankfurt plane should be parallel to the ground, eyes open and fixed on the horizon. The head was not supported, favoring a more spontaneous posture. The electromyographic recordings began with a bilateral assessment of the patient at rest, where each volunteer remained with their facial and masticatory muscles relaxed and their lips in their usual position for 10 seconds. EMG in maximum intercuspation of molar teeth. The volunteers were familiarized with the task of maximum intercuspation of molar teeth prior to the test. A sheet of Parafilm M® folded three times lengthwise and then in half widthwise was used. The volunteers positioned the Parafilm M® on the occlusal surfaces of the first and second upper and lower molars, bilaterally, during data collection, in order to protect the teeth (AP et al., 2010; Berni et al., 2015; Pitta et al., 2015). Two repetitions of clenching were requested, each lasting 10 seconds, with a one-minute interval between them. Then, the recordings were performed bilaterally during habitual chewing. The volunteer was instructed to chew, for 10 seconds, a sheet of Parafim M® paraffin (American National can TM Chicago, IL, 60641), folded into five parts and placed in the molar region, as it is a material that offers less variability in electromyographic recordings (Biasotto et al., 2000). Six cycles were selected. The number of cycles in each ten-second data collection period for all volunteers was counted, and the lowest number of cycles found in a collection was selected as the number of cycles for all volunteers. For the maximum voluntary isometric contraction situation, the volunteer maintained the Parafilm M® interposed between the occlusal surfaces of the molar teeth for 5 seconds. The signal acquisition was repeated three times for each situation, with a 2-minute interval between repetitions for muscle rest (Farina et al., 2005), and the analysis was performed using the average of the three dynamic contractions performed. To normalize the RMS data, the volunteer was asked to hold a cotton ball between their teeth (Pelai et al., 2023 ). After signal acquisition, the data were subjected to a 20Hz high-pass filter and a 500Hz low-pass filter in order to eliminate possible interference, since energy above 500 Hz is negligible, according to Winter ( 1990 ). After signal processing, it was analyzed, and the MF (Hz) value was calculated, an algorithm capable of reflecting the average signal power throughout the study cycle (Konrad, 2005 ). Statistical analysis The normality of the data was verified using the Shapiro-Wilk test. Since the data were considered normal, the analyses were as follows: A mixed-model ANOVA was used for comparisons of factors, with within-subject: muscle (masseter x anterior temporal) and side (right x left) and between-subject: group (With ERR x Without ERR). To representatively describe the change in median frequency over the duration of a fatigable contraction, a simple linear regression analysis was performed using GraphPad Prism for each volunteer in each group, considering the MF (Hz) parameters of the EMG of each muscle evaluated as the dependent variable and the time period (initial, 25%, 50%, 75% and 100%) as the independent variable, with the values ​​of the coefficient of determination (r²) expressed together. Statistical processing was performed using SPSS software, version 17.0 (SPSS Inc, Chicago, IL). RESULTS Table 1 demonstrates the characterization of the sample. Table 1 Sample characterization (n = 30). ERR CONTROL p value Age (years) 25 ± 4.2 23.7 ± 3.1 0.181 IMC (kg/m 2 ) 23.46 ± 3.85 23.54 ± 3.62 0.823 SEX Female Male 21 (70) 17 (56.66) 0.146 9 (30) 13 (43.34) EER = Radicular Reabsorption; Table 2 presents the values of muscle activity (anterior temporal and masseter, bilaterally) at rest, where the group with ERR showed significantly higher values than the control group in the evaluated muscles, left anterior temporal (p = 0.001), right anterior temporal (p = 0.001), left masseter (p = 0.038) and right masseter (p = 0.003). Indicating basal muscle hyperactivity. Table 2 Descriptive data of normalized RMS values expressed as mean and standard deviation (SD), of the masticatory muscles (anterior temporal and masseter, bilaterally) at rest for EER (n = 30) and Control Groups (n = 30). PHASES MUSCLE GROUP MEAN ± SD MINIMUM-MAXIMUN p value Left Anterior Temporal ERR 7.45 ± 4.47 2.13–18.07 0.001** Control 2.66 ± 1.18 1.47–5.75 Left Masseter ERR 2.84 ± 1.61 1.15–6.41 0.038* Control 2.01 ± 1.10 0.71–4.83 Rest Right Anterio Temporal ERR 7.30 ± 5.65 1.45–27.48 0.001** Control 2.72 ± 1.62 1.50–8.98 Right Masseter ERR 3.73 ± 2.86 1.42–16.17 0.003** Control 1.96 ± 0.77 0.92–8.98 RMS= Root Mean Square; EER = Radicular Reabsorption; * Statistically significant; ** Extremely significant. The graphs below represent the MF (Hz) sloop. In blue are the MF (Hz) values over the 10 seconds of maximum molar intercuspation for the control group, and in red for the RRE group. Analysis of the FM (Hz) demonstrated that the group ERR presented significantly lower MF values ​​compared to the control group during maximum intercuspation, indicating greater muscle fatigue. The difference was evident in the right anterior temporal muscle, left anterior temporal muscle, right masseter muscle, and particularly marked in the left masseter muscle, where the average values ​​were 97.63 ± 28.00 Hz in the ERR group versus 128.05 ± 37.10 Hz in the control group, evidencing a pronounced reduction in fatigue resistance in the ERR group. DISCUSSION This study aimed to evaluate muscle fatigue in the masticatory muscles (masseter and anterior temporal) in individuals with external root resorption (ERR) of the lower second molars adjacent to impacted third molars. The results point to a relationship between ERR and changes in the muscle pattern of the anterior temporal and masseter. Confirmation of the initial hypothesis is evidenced by the reduction in median frequency (FM) (Hz) values ​​during maximum intercuspation, mainly evidenced in the left masseter, denoting greater susceptibility of the muscle to fatigue. Another finding was hyperactivity of this musculature at rest. These results suggest that patients with impacted lower third molars, causing root resorption of the adjacent second molars, are susceptible to muscle changes. In the search conducted by the authors, to date, no studies have been found that evaluate the pattern of muscle fatigue using FM (Hz) (EMG as an instrument) of the masticatory muscles (masseter and anterior temporal) in individuals diagnosed with RRE compared to a control group. Moreira-Souza et al. ( 2024 ) observed in their study that there is greater electromyographic activity in patients with RRE during functional activities, suggesting that dental morphological alterations may modulate muscle resistance to fatigue. According to Flores-Orozco et al. ( 2023 ), muscle fatigue is a common finding in individuals with temporomandibular disorders (TMD), and this pattern resembles the reduction in masticatory efficiency observed in the RRE group in this study. The masseter muscle is often the first to show signs of fatigue, due to its greater participation in sustained contractions (Bracci et al., 2018 ), which corroborates the findings of this study.Studies suggest that inflammatory and proprioceptive mechanisms may explain these alterations. Impacted third molars with intimate contact between them and the roots of second molars can lead to repetitive microtrauma, stimulating neurogenic responses that modify the pattern of muscle activation (Sarrafpour et al., 2013 ). This process is further enhanced by the release of chemical mediators of inflammation, which can reduce the muscle fatigue threshold through direct effects on motor units (Conti, 2021 ). EMG studies demonstrate that even subtle occlusal interferences can induce increases of 20–30% in resting muscle activity (Al Sayegh et al., 2020 ), values that corroborate those observed in our sample. Lobbezoo et al. ( 2013 ) reported that 68% of patients with parafunctional activities in the masticatory muscles exhibit increased muscle activity at rest, suggesting common pathophysiological mechanisms. The results of this study showed that individuals with ERR presented significantly elevated muscle activation at rest in the masseter and anterior temporal muscles (RMS values higher than the control with p < 0.05), indicating a state of muscle hyperactivity during resting activity. This finding is aligned with the scientific literature that associates conditions of periradicular and occlusal alterations with increased muscle activity at rest (Castroflorio et al. 2008) The results of this study suggest that patients with impacted mandibular third molars, causing root resorption of adjacent second molars, are susceptible to muscle alterations that can lead to reduced masticatory efficiency due to fatigue and consequent myogenic pain related to temporomandibular dysfunction. Therefore, a diagnosis of ERR should be considered an indication to investigate symptoms of myogenic pain and temporomandibular dysfunction, aiming to institute early treatment and restore mandibular function. Strengths and limitations This study presents a solid scientific basis, with robust theoretical foundations on muscle fatigue, protective co-contraction, and RRE (Repetitive Stress Reduction). The methodological design is characterized as a observational study with a control group and a defined sample (30 patients per group, matched by age and clinical criteria). Methodologies such as CBCT (gold standard for diagnosing RRE), Surface Electromyography (gold standard for assessing muscle activity), and rigorous statistical analyses were used. The study also implements bias controls, such as the participation of experienced examiners, well-defined exclusion criteria, and a standardized environment for EMG data collection. The study's limitations include the inclusion of both female and male participants in the electromyographic evaluation. This limitation suggests caution in interpreting the results and highlights the need for further studies with separate samples for both sexes. Implications for Research This research establishes a methodological approach by combining CBCT images with EMG assessment, offering a replicable model for future investigations. The findings encourage studies exploring the relationship between RRE and the development of temporomandibular disorders, as well as interventional research testing whether early removal of impacted third molars could prevent alterations in muscle fatigue patterns. The discovery of greater EMG activity in the RRE group also raises hypotheses about shared pathophysiological mechanisms between RRE and muscle disorders. Implications for clinical practice The data from this study suggest that the evaluation of patients with impacted third molars and RRE should include, in addition to CBCT examination, a functional analysis of the masticatory musculature. The identification of greater muscle fatigue in these patients reinforces the importance of early diagnosis and interventions such as timely removal of the impacted third molar associated with myofunctional therapies, potentially preventing future complications such as orofacial, headaches, pain and joint dysfunction. The results of this study elucidate that RRE may not only be a local structural alteration, but also associated with alterations in the muscle pattern. These muscles showed alterations in EMG regarding the reduction of the median frequency, mainly in the masseter, suggesting less resistance to prolonged contraction. Suggestions for future studies Based on the results found in this study, it is suggested that further studies be conducted to also evaluate the suprahyoid musculature, in order to verify the agonist and antagonist muscles of mastication. It is also important to relate the positioning of the third molar and the degree of resorption of the second molar with muscle changes. Another important point is the evaluation of the muscle strength of the masticatory muscles using a bite dynamometer. We also suggest correlating muscle electrical activity with fatigue. This was not done in this study because the muscle electrical activity data have already been published (Moreira-Souza et al. 2024 ). CONCLUSION EMG analysis demonstrates that individuals with ERR exhibit muscle activity during rest and greater fatigue of the masticatory muscles, evidenced by a significant reduction in the median frequency (Hz) of the masseter and anterior temporal muscles. Therefore, a diagnosis of ERR should be considered an indication to investigate symptoms of myogenic pain and temporomandibular dysfunction, aiming to institute early treatment and restore mandibular function. Declarations Ethics Approval This cross-sectional observational study was approved by the local Ethical Review Board (protocol: #41652015.7.0000.5418) and was conducted following the Declaration of Helsinki Ethical Principles. All procedures were developed in an oral radiology clinic and a laboratory of a dental school. Contribution from the corresponding author S.C.F.G: Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing – Original Draft, Writing – Revision and Editing, Visualization, Statistical Analysis, Project Management. Author Contribution S.C.F.G : Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing – Original Draft, Writing – Revision and Editing, Visualization, Statistical Analysis, Project Management.E.B.P: Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing – Original Draft, Writing – Revision and Editing, Visualization, Statistical Analysis, Project Management, Final approval.L.M.S e A.C.C.O e D.Q.F: Conceptualization, Methodology, Data Curation.L.A: Conceptualization, Methodology, Formal Analysis, Investigation, Revision and Editing, Visualization, Project Management, Final approval. Acknowledgments This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. Data Availability All data relevant to this research are included in the article itself and in its supplementary information files. 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J Dent ; Res, 83(special issue A). OHSHIMA H, NAKASONE N, HASHIMOTO E, SAKAI H, NAKAKURA-OHSHIMA K, HARADA H (2005) The eternal tooth germ is formed at the apical end of continuously growing teeth. Arch Oral Biol 50:153–157 OKESON JP (1992) Fundamentos de oclusão e desordens temporomandibulares. Artes Médicas, Porto Alegre ONCINS MC, FREIRE RMAC MARCHESAN (2006) Mastigação: análise pela eletromiografia e eletrognatografia. Seu uso na clínica fonoaudiológica. Distúrbios da Comunicação 18(2):155–165 SARRAFPOUR B, RUNGSIYAKULL C, SWAIN M, LI Q (2012) Finite element analysis suggests functional bone strain accounts for continuous post-eruptive emergence of teeth. Arch Oral Biol 57:1070–1078 SARRAFPOUR B, SWAIN M, LI Q (2013) Tooth eruption results from bone remodelling driven by bite forces sensed by soft tissue dental follicles: a finite element analysis. PLoS ONE 8:e58803 SCHIFFMAN E, OHRBACH R, LOOK TRUELOVEE, ANDERSON J, GOULET G (2014) Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) for Clinical and Research Applications: recommendations of the International RDC/TMD Consortium Network and Orofacial Pain Special Interest Group. J Oral Facial Pain Headache 28(1):6–27 Sharma NK, Yadav BS, Hirani MS, Dhiman NK, Singh AK, Tripathi R (2024) Electromyographic Assessment of Masticatory Muscles & their Asymmetries in Adult Indian Population. J Maxillofac Oral Surg 23(1):197–203. 10.1007/s12663-022-01770-x Epub 2022 Aug 9. PMID: 38312955; PMCID: PMC10830968 SILVA NRS, CASTISANO MH (2009) Bruxismo etiologia e tratamento. Revista Brasileira de odontologia 66(2):223–226 STEEDLE WR JR (1985) The pattern and control of eruptive tooth movements. Am J Orthod 87:56–66 de Souza ILB, Nahes CR, de Pierri J (2020) Desordens dos músculos mastigatórios / Masticatory muscle disorders. Brazilian J Dev 6(7):48233–48238. https://doi.org/10.34117/bjdv6n7-460 VAN DER LINDEN W, CLEATON-JONES P LOWNIEM (1995) Diseases and lesions associated with third molars. Review of 1001 cases. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 79:142–145 WHITE SC, PHAROAH MJ (2007) Radiologia Oral: fundamentos e interpretação. 5ª edição, Rio de Janeiro: Elsevier, WINTER DA (1990) The biomechanics and motor control of human movement, 23 edn. Wiley YAMALIK K, BOZKAYA S (2008) The predictivity of mandibular third molar position as a risk indicator for pericoronitis. Clin Oral Investig 12:9–14 YAMAOKA M, FURUSAWA K, IKEDA M, HASEGAWA T (1999) Root resorption of mandibular second molar teeth associated with the presence of the third molars. Aust Dent J 44:112–116 WORLD HEALTH ORGANIZATION, NCD_IMC_30 (2022) Obesity among adults, BMI ≥ 30, prevalence. WHO, Geneva. https://doi.org/10.1016/S0140-6736(23)02750-2 Additional Declarations No competing interests reported. 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Characterized by progressive cementum loss, it has been studied from both diagnostic and etiological perspectives, using cone-beam computed tomography (CBCT), considered the gold standard for detection and monitoring (Oenning et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). However, although the structural implications of ERR are well documented, its functional consequences on the masticatory system remain comparatively unexplored, creating a substantial gap in understanding the comprehensive clinical impact of this pathology.\u003c/p\u003e \u003cp\u003eThe biomechanical alterations resulting from ERR can initiate a cascade of neuromuscular adaptations in the stomatognathic system. Recent investigations have begun to elucidate the relationship between dental structural integrity and the function of the masticatory muscles (Moreira-Souza et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The presence of impacted third molars in close contact with adjacent roots creates conditions for repetitive microtrauma and inflammatory processes that can transcend local effects, potentially influencing neuromuscular control mechanisms (Sarrafpour et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). This interaction between peripheral structural alterations and central neuromuscular regulation represents a critical area for scientific investigation.\u003c/p\u003e \u003cp\u003ePrevious research by Moreira-Souza et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) provided preliminary evidence of altered electromyographic activity in patients with RRE, demonstrating increased muscle activation during functional tasks. This finding suggests the existence of compensatory neuromuscular mechanisms in response to dental structural changes. The study focused primarily on amplitude-based parameters, leaving unexplored the specific relationship between RRE and muscle fatigue indices, particularly median frequency. This represents a significant limitation in current knowledge, since frequency domain analyses offer potentially more sensitive indicators of muscle metabolic changes than traditional amplitude-based measures.\u003c/p\u003e \u003cp\u003eFor this purpose, surface electromyography (EMG) was used, which is a fundamental methodology for the objective assessment of masticatory muscle function, providing non-invasive quantification of muscle activity patterns (Pelai et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Within the analytical framework of EMG, median frequency (FM) analysis has gained prominence as a reliable indicator of muscle fatigue (Konrad, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe physiological basis of this relationship lies in the reduction of muscle fiber conduction velocity and the synchronization of motor unit firing patterns that occur during fatiguing contractions (Sharma et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe clinical relevance of muscle fatigue parameters goes beyond theoretical interest, directly impacting functional capacity. In populations with temporomandibular dysfunction, alterations in median frequency patterns have been correlated with subjective reports of masticatory fatigue and decreased masticatory efficiency (Flores-Orozco et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Furthermore, evidence suggests that even subtle occlusal disturbances can induce significant changes in muscle activation patterns, potentially leading to compensatory mechanisms that alter normal neuromuscular function (Al Sayegh et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These adaptations may manifest as increased muscle activity at rest or reduced resistance to fatigue during functional tasks.\u003c/p\u003e \u003cp\u003eBased on the results of the research by Moreira-Souza et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), this study verifies the hypothesis that individuals with ERR present greater fatigue of the masticatory muscles. This research is justified by the high prevalence of myogenic pain related to temporomandibular dysfunction and the need to establish pathophysiological bases for the prevention of temporomandibular disorders.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e This is an observational study with a cross-sectional design, according to Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) for cross-sectional studies. involving cone-beam computed tomography (CBCT) scans of sixty patients with CBCT requests approved by CONEP, and which includes CBCT imaging data and surface electromyography examination. It is important to emphasize that this is a secondary analysis of a previous study (Moreira-Souza et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSample Data\u003c/h2\u003e \u003cp\u003eThe data used in this study were obtained from a large project investigating cervical spine involvement in patients with TMD. Details about this study are described elsewhere (Moreira-Souza et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEthical and legal aspects\u003c/h3\u003e\n\u003cp\u003e This cross-sectional observational study was approved by the local Ethical Review Board (protocol: #41652015.7.0000.5418) and was conducted following the Declaration of Helsinki Ethical Principles. All procedures were developed in an oral radiology clinic and a laboratory of a dental school.\u003c/p\u003e \u003cp\u003e The project included electromyography and CBCT scans; each patient who agreed to participate in the research signed a previously prepared Informed Consent Form.\u003c/p\u003e \u003cp\u003eThe Informed Consent Form (ICF) informed and clarified the research subject's decision, allowing them to make a fair and unconstrained decision regarding their participation in the research project. The document was given to the participant in duplicate, signed by both the participant and the researcher, thus establishing responsibilities between both parties, with each party retaining one copy.\u003c/p\u003e \u003cp\u003eThe sample size calculation was performed using data from 8 patients with the studied condition and 8 without the condition. With a power of 95% and an alpha of 5%, a total of 58 patients was determined, 29 per group. The analysis was performed using GPower software, version 3.1.9.2.\u003c/p\u003e\n\u003ch3\u003eSample selection\u003c/h3\u003e\n\u003cp\u003eThe sample for this study was a convenience, where patients included in this selection presented a request for cone-beam computed tomography (CBCT) for preoperative planning of impacted third molar extraction; they are of both sexes and are between 21 and 59 years of age. For the group with ERR: presence of second lower molars adjacent to the impacted third molars; computed tomography scans demonstrating ERR of at least one second lower molar, located in the region of impaction with the third molar; third molars with fully formed crowns and roots. For the control group: presence of second lower molars adjacent to the impacted third molars; computed tomography scans showing the integrity of the second lower molars in the region of impaction with the third molar; computed tomography scans showing the integrity of one second lower molar when the contralateral second molar is absent; third molars with fully formed crowns and roots.\u003c/p\u003e \u003cp\u003ePatients with complaints of pain of odontogenic origin were excluded (as it may mask temporomandibular dysfunction (TMD) or other orofacial pain); Patients with a BMI equal to or greater than 30 kg/m\u0026sup2; (OMS, 2022); patients with a history of trauma or surgery to the maxillofacial structures (since these patients are more likely to receive some type of treatment and their inclusion may introduce bias into the results); patients with cognitive or intellectual disabilities, with facial deformities and/or significant dental anomalies; CBCT images showing third molars associated with cystic or tumoral lesions and/or the presence of extensive caries lesions in the second lower molar; and CBCT images that present positioning errors in the technique and/or the presence of artifacts that hinder diagnosis in the region of interest.\u003c/p\u003e\n\u003ch3\u003eImage acquisition and evaluation\u003c/h3\u003e\n\u003cp\u003eThe Images were previously acquired with the OP300 Maxio unit (Instrumentarium Dental, Tuusula, Finland) set to 90 kVp, 6 mA, exposure time of 6.1 s, voxel size of 0.2 mm and field of view of 6 \u0026times; 8 cm. After acquisition, CBCT volumes were exported with the metal artifact reduction algorithm and stored in the Digital Imaging and Communications in Medicine (DICOM) format.\u003c/p\u003e \u003cp\u003eThe CBCT volumes were evaluated as described in Moreira-Souza et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e to determine the participants in each group, that is, with and without RRE.\u003c/p\u003e\n\u003ch3\u003eElectromyographic Evaluation\u003c/h3\u003e\n\u003cp\u003ePatients were classified according to findings of impacted lower third molars on CBCT (Cone Beam Computed Tomography) images and then distributed into the two groups (test and control) mentioned previously. In the search for signs of occlusal overload, muscle hyperactivity, and parafunctional habits, the following step was performed, in a blinded manner and executed by a single researcher with extensive experience in performing surface electromyography examination.\u003c/p\u003e \u003cp\u003eElectromyography (EMG) data were collected in the oral and maxillofacial surgery laboratory at Faculdade de Odontologia de Piracicaba, which has an environment and conditions suitable for adequate EMG signal collection. For the surface electromyographic examination, equipment was used that followed the recommendations of the International Society of Electrophysiology and Kinesiology (ISEK) with an acquisition module of at least 8 channels, with 16-bit resolution, and an acquisition frequency of 2000 Hz (Trigno System \u0026ndash; Delsys).\u003c/p\u003e \u003cp\u003eEMG signal normalization was performed to avoid data interference. This was done using a sheet of Parafilm M\u0026reg; folded three times lengthwise and then in half widthwise. It was positioned on the occlusal surfaces of the first and second upper and lower molars, bilaterally, and maximum voluntary contraction was requested. The collected electromyographic signals were sampled synchronously and stored for later visualization and processing. The equipment's software was used to acquire and store the digitized signals in data files. The signals were analyzed offline using Matlab\u0026reg; 8.3 (R2014a) software, in which a 4th-order two-pole Butterworth digital filter with a 10 Hz high-pass filter and a 400 Hz low-pass filter was applied using a specific routine. The analysis was performed in the frequency domain to obtain the EMG power spectral density values using the Fast Fourier Transform (FFT) algorithm to obtain the median frequency (Hz) values and, in the amplitude domain, to obtain the RMS (uV) values.\u003c/p\u003e \u003cp\u003eThe muscles evaluated were: masseter and anterior temporal, bilaterally, right masseter (RM), left masseter (LM), anterior portion of the right temporal muscle (RT) and left temporal muscle (LT). For bilateral muscle action potential recording, wireless differential electrodes (Trigno System \u0026ndash; Delsys) were used. Data collection was performed in an air-conditioned room with a controlled temperature maintained at 23\u0026ordm;\u0026plusmn;2\u0026ordm;C and illuminated with incandescent lamps. The wireless electrodes were positioned on the bellies of the aforementioned muscles, parallel to the muscle fibers, with the silver bars perpendicular to them. They were fixed, using adhesive, to skin that had been previously cleaned with cotton soaked in a 70% alcohol solution, rubbed with sandpaper, and shaved, when necessary, to remove surface fat and dead cells, reduce skin impedance, and thus avoid interference, ensuring signal quality.\u003c/p\u003e \u003cp\u003eFor electrode placement, a functional test was performed for each muscle. This test consisted of muscle palpation during simultaneous bilateral isotonic contraction, according to the positioning criteria described below: superficial belly of the masseter muscle - between the level of the zygomatic arch and the gonial angle, two cm above the angle of the mandible; anterior belly of the anterior temporal muscle - near the upper lateral corner of the eyebrow, in the longitudinal direction of the fibers of the anterior bundle defined by palpation during teeth clenching (CRAM et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1998\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe research participant was asked to remain seated, in an upright position with their feet flat on the floor, their upper and lower limbs relaxed and uncrossed, and their hands on their thighs. Regarding the head position, the Frankfurt plane should be parallel to the ground, eyes open and fixed on the horizon. The head was not supported, favoring a more spontaneous posture.\u003c/p\u003e \u003cp\u003eThe electromyographic recordings began with a bilateral assessment of the patient at rest, where each volunteer remained with their facial and masticatory muscles relaxed and their lips in their usual position for 10 seconds.\u003c/p\u003e \u003cp\u003eEMG in maximum intercuspation of molar teeth. The volunteers were familiarized with the task of maximum intercuspation of molar teeth prior to the test. A sheet of Parafilm M\u0026reg; folded three times lengthwise and then in half widthwise was used. The volunteers positioned the Parafilm M\u0026reg; on the occlusal surfaces of the first and second upper and lower molars, bilaterally, during data collection, in order to protect the teeth (AP et al., 2010; Berni et al., 2015; Pitta et al., 2015). Two repetitions of clenching were requested, each lasting 10 seconds, with a one-minute interval between them.\u003c/p\u003e \u003cp\u003eThen, the recordings were performed bilaterally during habitual chewing. The volunteer was instructed to chew, for 10 seconds, a sheet of Parafim M\u0026reg; paraffin (American National can TM Chicago, IL, 60641), folded into five parts and placed in the molar region, as it is a material that offers less variability in electromyographic recordings (Biasotto et al., 2000). Six cycles were selected. The number of cycles in each ten-second data collection period for all volunteers was counted, and the lowest number of cycles found in a collection was selected as the number of cycles for all volunteers.\u003c/p\u003e \u003cp\u003eFor the maximum voluntary isometric contraction situation, the volunteer maintained the Parafilm M\u0026reg; interposed between the occlusal surfaces of the molar teeth for 5 seconds.\u003c/p\u003e \u003cp\u003eThe signal acquisition was repeated three times for each situation, with a 2-minute interval between repetitions for muscle rest (Farina et al., 2005), and the analysis was performed using the average of the three dynamic contractions performed.\u003c/p\u003e \u003cp\u003eTo normalize the RMS data, the volunteer was asked to hold a cotton ball between their teeth (Pelai et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAfter signal acquisition, the data were subjected to a 20Hz high-pass filter and a 500Hz low-pass filter in order to eliminate possible interference, since energy above 500 Hz is negligible, according to Winter (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). After signal processing, it was analyzed, and the MF (Hz) value was calculated, an algorithm capable of reflecting the average signal power throughout the study cycle (Konrad, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe normality of the data was verified using the Shapiro-Wilk test. Since the data were considered normal, the analyses were as follows:\u003c/p\u003e \u003cp\u003eA mixed-model ANOVA was used for comparisons of factors, with within-subject: muscle (masseter x anterior temporal) and side (right x left) and between-subject: group (With ERR x Without ERR).\u003c/p\u003e \u003cp\u003eTo representatively describe the change in median frequency over the duration of a fatigable contraction, a simple linear regression analysis was performed using GraphPad Prism for each volunteer in each group, considering the MF (Hz) parameters of the EMG of each muscle evaluated as the dependent variable and the time period (initial, 25%, 50%, 75% and 100%) as the independent variable, with the values ​​of the coefficient of determination (r\u0026sup2;) expressed together.\u003c/p\u003e \u003cp\u003eStatistical processing was performed using SPSS software, version 17.0 (SPSS Inc, Chicago, IL).\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e demonstrates the characterization of the sample.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSample characterization (n\u0026thinsp;=\u0026thinsp;30).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e\u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eERR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCONTROL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep value\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.181\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIMC (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23.46\u0026thinsp;\u0026plusmn;\u0026thinsp;3.85\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.54\u0026thinsp;\u0026plusmn;\u0026thinsp;3.62\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.823\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eSEX Female\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eMale\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21 (70)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17 (56.66)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.146\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9 (30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13 (43.34)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eEER\u0026thinsp;=\u0026thinsp;Radicular Reabsorption;\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the values of muscle activity (anterior temporal and masseter, bilaterally) at rest, where the group with ERR showed significantly higher values than the control group in the evaluated muscles, left anterior temporal (p\u0026thinsp;=\u0026thinsp;0.001), right anterior temporal (p\u0026thinsp;=\u0026thinsp;0.001), left masseter (p\u0026thinsp;=\u0026thinsp;0.038) and right masseter (p\u0026thinsp;=\u0026thinsp;0.003). Indicating basal muscle hyperactivity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDescriptive data of normalized RMS values expressed as mean and standard deviation (SD), of the masticatory muscles (anterior temporal and masseter, bilaterally) at rest for EER (n\u0026thinsp;=\u0026thinsp;30) and Control Groups (n\u0026thinsp;=\u0026thinsp;30).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePHASES\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMUSCLE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGROUP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMEAN\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMINIMUM-MAXIMUN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep value\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eLeft Anterior Temporal\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eERR\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.45\u0026thinsp;\u0026plusmn;\u0026thinsp;4.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.13\u0026ndash;18.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.001**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eControl\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.66\u0026thinsp;\u0026plusmn;\u0026thinsp;1.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.47\u0026ndash;5.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eLeft Masseter\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eERR\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.84\u0026thinsp;\u0026plusmn;\u0026thinsp;1.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.15\u0026ndash;6.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.038*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eControl\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.01\u0026thinsp;\u0026plusmn;\u0026thinsp;1.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.71\u0026ndash;4.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eRest\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eRight Anterio Temporal\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eERR\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.30\u0026thinsp;\u0026plusmn;\u0026thinsp;5.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.45\u0026ndash;27.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.001**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eControl\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.72\u0026thinsp;\u0026plusmn;\u0026thinsp;1.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.50\u0026ndash;8.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eRight Masseter\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eERR\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.73\u0026thinsp;\u0026plusmn;\u0026thinsp;2.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.42\u0026ndash;16.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.003**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eControl\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.92\u0026ndash;8.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003eRMS= Root Mean Square; EER\u0026thinsp;=\u0026thinsp;Radicular Reabsorption; * Statistically significant;\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e** Extremely significant.\u003c/p\u003e \u003cp\u003eThe graphs below represent the MF (Hz) sloop. In blue are the MF (Hz) values over the 10 seconds of maximum molar intercuspation for the control group, and in red for the RRE group.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAnalysis of the FM (Hz) demonstrated that the group ERR presented significantly lower MF values ​​compared to the control group during maximum intercuspation, indicating greater muscle fatigue. The difference was evident in the right anterior temporal muscle, left anterior temporal muscle, right masseter muscle, and particularly marked in the left masseter muscle, where the average values ​​were 97.63\u0026thinsp;\u0026plusmn;\u0026thinsp;28.00 Hz in the ERR group versus 128.05\u0026thinsp;\u0026plusmn;\u0026thinsp;37.10 Hz in the control group, evidencing a pronounced reduction in fatigue resistance in the ERR group.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThis study aimed to evaluate muscle fatigue in the masticatory muscles (masseter and anterior temporal) in individuals with external root resorption (ERR) of the lower second molars adjacent to impacted third molars. The results point to a relationship between ERR and changes in the muscle pattern of the anterior temporal and masseter. Confirmation of the initial hypothesis is evidenced by the reduction in median frequency (FM) (Hz) values ​​during maximum intercuspation, mainly evidenced in the left masseter, denoting greater susceptibility of the muscle to fatigue. Another finding was hyperactivity of this musculature at rest. These results suggest that patients with impacted lower third molars, causing root resorption of the adjacent second molars, are susceptible to muscle changes.\u003c/p\u003e \u003cp\u003eIn the search conducted by the authors, to date, no studies have been found that evaluate the pattern of muscle fatigue using FM (Hz) (EMG as an instrument) of the masticatory muscles (masseter and anterior temporal) in individuals diagnosed with RRE compared to a control group.\u003c/p\u003e \u003cp\u003eMoreira-Souza et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) observed in their study that there is greater electromyographic activity in patients with RRE during functional activities, suggesting that dental morphological alterations may modulate muscle resistance to fatigue. According to Flores-Orozco et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), muscle fatigue is a common finding in individuals with temporomandibular disorders (TMD), and this pattern resembles the reduction in masticatory efficiency observed in the RRE group in this study. The masseter muscle is often the first to show signs of fatigue, due to its greater participation in sustained contractions (Bracci et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), which corroborates the findings of this study.Studies suggest that inflammatory and proprioceptive mechanisms may explain these alterations. Impacted third molars with intimate contact between them and the roots of second molars can lead to repetitive microtrauma, stimulating neurogenic responses that modify the pattern of muscle activation (Sarrafpour et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). This process is further enhanced by the release of chemical mediators of inflammation, which can reduce the muscle fatigue threshold through direct effects on motor units (Conti, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEMG studies demonstrate that even subtle occlusal interferences can induce increases of 20\u0026ndash;30% in resting muscle activity (Al Sayegh et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), values that corroborate those observed in our sample. Lobbezoo et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) reported that 68% of patients with parafunctional activities in the masticatory muscles exhibit increased muscle activity at rest, suggesting common pathophysiological mechanisms. The results of this study showed that individuals with ERR presented significantly elevated muscle activation at rest in the masseter and anterior temporal muscles (RMS values higher than the control with p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), indicating a state of muscle hyperactivity during resting activity. This finding is aligned with the scientific literature that associates conditions of periradicular and occlusal alterations with increased muscle activity at rest (Castroflorio et al. 2008)\u003c/p\u003e \u003cp\u003eThe results of this study suggest that patients with impacted mandibular third molars, causing root resorption of adjacent second molars, are susceptible to muscle alterations that can lead to reduced masticatory efficiency due to fatigue and consequent myogenic pain related to temporomandibular dysfunction. Therefore, a diagnosis of ERR should be considered an indication to investigate symptoms of myogenic pain and temporomandibular dysfunction, aiming to institute early treatment and restore mandibular function.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStrengths and limitations\u003c/h2\u003e \u003cp\u003eThis study presents a solid scientific basis, with robust theoretical foundations on muscle fatigue, protective co-contraction, and RRE (Repetitive Stress Reduction). The methodological design is characterized as a observational study with a control group and a defined sample (30 patients per group, matched by age and clinical criteria). Methodologies such as CBCT (gold standard for diagnosing RRE), Surface Electromyography (gold standard for assessing muscle activity), and rigorous statistical analyses were used. The study also implements bias controls, such as the participation of experienced examiners, well-defined exclusion criteria, and a standardized environment for EMG data collection.\u003c/p\u003e \u003cp\u003eThe study's limitations include the inclusion of both female and male participants in the electromyographic evaluation. This limitation suggests caution in interpreting the results and highlights the need for further studies with separate samples for both sexes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eImplications for Research\u003c/h2\u003e \u003cp\u003eThis research establishes a methodological approach by combining CBCT images with EMG assessment, offering a replicable model for future investigations. The findings encourage studies exploring the relationship between RRE and the development of temporomandibular disorders, as well as interventional research testing whether early removal of impacted third molars could prevent alterations in muscle fatigue patterns. The discovery of greater EMG activity in the RRE group also raises hypotheses about shared pathophysiological mechanisms between RRE and muscle disorders.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eImplications for clinical practice\u003c/h2\u003e \u003cp\u003eThe data from this study suggest that the evaluation of patients with impacted third molars and RRE should include, in addition to CBCT examination, a functional analysis of the masticatory musculature. The identification of greater muscle fatigue in these patients reinforces the importance of early diagnosis and interventions such as timely removal of the impacted third molar associated with myofunctional therapies, potentially preventing future complications such as orofacial, headaches, pain and joint dysfunction.\u003c/p\u003e \u003cp\u003eThe results of this study elucidate that RRE may not only be a local structural alteration, but also associated with alterations in the muscle pattern. These muscles showed alterations in EMG regarding the reduction of the median frequency, mainly in the masseter, suggesting less resistance to prolonged contraction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSuggestions for future studies\u003c/h2\u003e \u003cp\u003eBased on the results found in this study, it is suggested that further studies be conducted to also evaluate the suprahyoid musculature, in order to verify the agonist and antagonist muscles of mastication. It is also important to relate the positioning of the third molar and the degree of resorption of the second molar with muscle changes. Another important point is the evaluation of the muscle strength of the masticatory muscles using a bite dynamometer. We also suggest correlating muscle electrical activity with fatigue. This was not done in this study because the muscle electrical activity data have already been published (Moreira-Souza et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eEMG analysis demonstrates that individuals with ERR exhibit muscle activity during rest and greater fatigue of the masticatory muscles, evidenced by a significant reduction in the median frequency (Hz) of the masseter and anterior temporal muscles. Therefore, a diagnosis of ERR should be considered an indication to investigate symptoms of myogenic pain and temporomandibular dysfunction, aiming to institute early treatment and restore mandibular function.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eEthics Approval\u003c/h2\u003e \u003cp\u003eThis cross-sectional observational study was approved by the local Ethical Review Board (protocol: #41652015.7.0000.5418) and was conducted following the Declaration of Helsinki Ethical Principles. All procedures were developed in an oral radiology clinic and a laboratory of a dental school.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eContribution from the corresponding author\u003c/h2\u003e \u003cp\u003eS.C.F.G: Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing \u0026ndash; Original Draft, Writing \u0026ndash; Revision and Editing, Visualization, Statistical Analysis, Project Management.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eS.C.F.G : Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing \u0026ndash; Original Draft, Writing \u0026ndash; Revision and Editing, Visualization, Statistical Analysis, Project Management.E.B.P: Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing \u0026ndash; Original Draft, Writing \u0026ndash; Revision and Editing, Visualization, Statistical Analysis, Project Management, Final approval.L.M.S e A.C.C.O e D.Q.F: Conceptualization, Methodology, Data Curation.L.A: Conceptualization, Methodology, Formal Analysis, Investigation, Revision and Editing, Visualization, Project Management, Final approval.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis study was financed in part by the Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior \u0026ndash; Brasil (CAPES) \u0026ndash; Finance Code 001.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data relevant to this research are included in the article itself and in its supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAl Sayegh S et al (2020) Pain and fatigue induced by excessive chewing. 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Aust Dent J 44:112\u0026ndash;116\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWORLD HEALTH ORGANIZATION, NCD_IMC_30 (2022) Obesity among adults, BMI\u0026thinsp;\u0026ge;\u0026thinsp;30, prevalence. WHO, Geneva. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S0140-6736(23)02750-2\u003c/span\u003e\u003cspan address=\"10.1016/S0140-6736(23)02750-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","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":"Root Resorption, Cone Beam Computed Tomography, Tooth Wear, Electromyography, Temporal Muscle, Masseter Muscle","lastPublishedDoi":"10.21203/rs.3.rs-9179312/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9179312/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eThis research aimed to evaluate muscle fatigue in the masseter and anterior temporal masticatory muscles at rest and during maximum dental intercuspation in individuals with external root resorption (ERR) in the second lower molar adjacent to the impacted third molar, compared to a control group. The median frequency (Hz) values ​​obtained between the group with ERR and the control group were compared, based on the results obtained, in order to identify significant differences and their clinical implications. The values ​​obtained at rest in the studied individuals were also analyzed to understand their variations.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA observational study with a cross-sectional design was conducted, involving 60 patients (30 with ERR and 30 controls). Cone-beam computed tomography (CBCT), previously collected, images were used for diagnosis, and surface electromyography (EMG) was performed to record muscle activity during rest and maximum molar intercuspation. Median frequency (MF (Hz)) analysis was used to assess muscle fatigue patterns. G-Power was used for sample size calculation. Statistical analysis included Shapiro-Wilk tests, mixed-model ANOVA, GraphPad Prism, and simple linear regression, with a significance level of α\u0026thinsp;=\u0026thinsp;0.05.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe group with ERR showed significantly higher muscle activity at rest in the left anterior temporalis (p\u0026thinsp;=\u0026thinsp;0.001), right anterior temporalis (p\u0026thinsp;=\u0026thinsp;0.001), left masseter (p\u0026thinsp;=\u0026thinsp;0.038), and right masseter (p\u0026thinsp;=\u0026thinsp;0.003) compared to the control group. The ERR group demonstrated significantly lower median frequency (MF (Hz)) values, indicating greater muscle fatigue, particularly in the left masseter (97.63\u0026thinsp;\u0026plusmn;\u0026thinsp;28.00 Hz vs. 128.05\u0026thinsp;\u0026plusmn;\u0026thinsp;37.10 Hz in the control group). In simple linear regression analyses in MF (Hz), the RRE group showed lower values ​​(Hz), mainly in the left temporalis muscle. The left masseter muscle showed lower values ​​in the group.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eIndividuals with ERR in lower second molars adjacent to impacted third molars exhibit greater muscle activity of the masticatory muscles at rest and greater muscle fatigue during function.\u003c/p\u003e","manuscriptTitle":"External Root Resorption Due to Impacted Third Molars: is There a Relationship with Masticatory Muscle Fatigue?","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-26 15:43:57","doi":"10.21203/rs.3.rs-9179312/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":"8de12f9a-4e03-4120-b878-a56d32f61e31","owner":[],"postedDate":"April 26th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Rejected","date":"2026-05-06T15:22:18+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-04T13:34:41+00:00","index":13,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-04T11:13:05+00:00","index":12,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-06T15:41:34+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-26 15:43:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9179312","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9179312","identity":"rs-9179312","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}