Endodontic Microsurgery in Private Practice: Indications and Time-Period Trends Before and After Adoption of Laser-Activated Irrigation - A Retrospective Cohort Study

Endodontic Microsurgery in Private Practice: Indications and Time-Period Trends Before and After Adoption of Laser-Activated Irrigation - A Retrospective Cohort Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Endodontic Microsurgery in Private Practice: Indications and Time-Period Trends Before and After Adoption of Laser-Activated Irrigation - A Retrospective Cohort Study David Han, Christopher Chun, Catherine Kim, Laurel Martinez, Jooyoung Song This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8761178/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Objectives To characterize indications for endodontic microsurgery (EMS) in a large private practice cohort and compare indication distributions before and after adoption of laser-activated irrigation (LAI) in non-surgical treatment. Materials and Methods A retrospective cohort of consecutive EMS cases ( n = 1,672) treated by six endodontists (April 2019–August 2025) was analyzed. Two periods were prespecified: Before-Laser Treatment (BLT) and After-Laser Treatment (ALT) following implementation of an Er,Cr:YSGG intracanal LAI protocol (August 2022). Each surgical tooth was assigned one or two predefined reasons. Proportions were compared between periods with Pearson’s χ² test and 95% Wald confidence intervals. Results The most frequent indications overall were uncleaned accessory canal (22.7%), large post (22.3%) and excessive calcification (14.4%). Surgeries for uncleaned accessory canals decreased from 28.6% (219/767) in BLT to 17.7% (160/905) in ALT (difference − 10.9 percentage points; 95% CI − 14.9 to − 6.8; P < .001). Surgeries for excessive calcification increased from 10.8% (83/767) to 17.3% (157/905) (difference + 6.5 percentage points; 95% CI + 3.2 to + 9.8; P < .001). Conclusions In this practice-based cohort, LAI adoption was associated with fewer EMS for uncleaned accessory canals. By contrast, calcification-related EMS increased, a pattern compatible with delayed pulp-canal obliteration rather than a direct LAI effect. Causal inference is limited by the time-period design. Clinical Relevance The adoption of laser-activated irrigation (LAI) in non-surgical endodontics may reduce the necessity for subsequent microsurgery related to uncleaned accessory anatomy. Conversely, clinicians should anticipate a continued or increasing burden of calcification-related cases, potentially influenced by broader factors like pandemic-associated stress. Endodontic microsurgery (EMS) Laser-activated irrigation (LAI) Er Cr:YSGG laser Before-Laser Treatment (BLT) After-Laser Treatment (ALT) Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Endodontic microsurgery (EMS) encompasses a spectrum of surgical procedures—including root-end apicoectomy, root amputation, intentional replantation, and external root resorption repair—each with distinct clinical applications. The literature indicates that all four types of EMS can yield favorable outcomes, provided that case selection is appropriate and clinical circumstances are carefully considered [ 1 – 4 ]. Although conventional non-surgical endodontic therapy remains the primary modality for treating pulpal and periradicular disease, certain cases necessitate surgical intervention. Modern EMS has demonstrated higher success rates than traditional approaches, largely owing to advances in ultrasonic root-end preparation, biocompatible filling materials, refined microsurgical instrumentation, and enhanced magnification and illumination [ 5 , 6 ]. Reported indications for surgery include persistent extraradicular infection, procedural mishaps such as instrument separation or perforation, untreated anatomy, and root fractures [ 7 – 10 ]. Existing literature has largely focused on isolated indications; however, no known studies to date have comprehensively analyzed the full spectrum of reasons for EMS in a single cohort. This detailed understanding of the common and uncommon indications is important for determining the necessity for surgery, refining treatment protocols, and improving patient care. Concurrently, a growing body of evidence supports the use of adjunctive technologies to enhance the effectiveness of conventional non-surgical endodontic procedures. Among these, laser-activated irrigation (LAI) has emerged as a promising method to enhance disinfection within the complex root canal system and to reduce postoperative pain [ 11 – 15 ]. However, the potential long-term impact of LAI on the subsequent need for EMS has not been clearly established in a clinical setting. To date, no studies have evaluated whether the routine use of LAI during non-surgical treatment is associated with a change in the incidence of EMS. The purpose of this retrospective cohort study was twofold. First, to characterize the specific indications for EMS by quantifying the frequency of 15 reasons in a large private practice cohort. Second, to test whether the distribution of EMS indications differed across pre- and post-LAI periods for two indications (uncleaned accessory canal and excessive calcification), acknowledging that this time-period comparison cannot establish causality. Materials and methods This retrospective observational study is reported in accordance with the STROBE guideline; the completed checklist is provided as a supplementary file and the study flow is detailed in Fig. 1 . Study Cohort and Setting This study analyzed de-identified clinical data from a multi-site private endodontic practice located in a major metropolitan area. The cohort consisted of 1,474 patients who underwent endodontic microsurgery (EMS) on 1,672 teeth between April 1, 2019, and August 31, 2025. Data were divided into two groups based on the implementation of a specific disinfection protocol: -Before-Laser Treatment (BLT): April 1, 2019, to July 31, 2022, using conventional chemomechanical irrigation. -After-Laser Treatment (ALT): August 1, 2022, to August 31, 2025, following the routine adoption of laser-activated irrigation (LAI). The three-month difference in the study period lengths between the two groups is attributed to the COVID-19 pandemic with a one-month office closure and a subsequent two-month period where no endodontic surgeries were performed due to an overabundance of caution taken to minimize the transfer of COVID-19. Clinical Protocols All procedures were performed by six endodontists who received standardized specialist training. The non-surgical endodontic protocol was uniform across all clinicians. After anesthesia and dental-dam isolation, an access cavity was prepared and working length established with an electronic apex locator and confirmed radiographically. Initial glidepath preparation was performed with 0.02-taper stainless-steel hand files, followed by preparation to a 0.20 mm tip size at the working length. Mechanical instrumentation then proceeded using a crown-down approach with 0.04- or 0.06-taper nickel–titanium rotary files under copious irrigation with 4% sodium hypochlorite. In the standard chemomechanical protocol—which defined the BLT period—4% sodium hypochlorite served as the primary irrigant throughout instrumentation. Typically, smear-layer removal was performed at the end of preparation using 17% EDTA followed by a final 4% sodium hypochlorite rinse. However, in selected situations—such as the presence of pulp stones, heavy smear layer, or the need to enhance visualization of canal orifices on the chamber floor—17% EDTA was used earlier in the treatment. After complete preparation, obturation was performed with gutta-percha cones and bioceramic sealer using a downpack-and-backfill technique. The protocol in the ALT period utilized the standard mechanical and shaping procedures described above, with LAI serving as the final disinfection step. At the completion of full canal instrumentation, LAI was performed using the EdgePRO™ (Brasseler USA) Er,Cr:YSGG laser (2780 nm). The system was set to manufacturer-recommended intracanal settings: 0.1–0.15 W output power, 20 Hz pulse frequency, and micro-pulse activation delivered through a radial-firing fiber tip. The tip was positioned in the middle third of the canal without binding, and activation consisted of slow withdrawal with circumferential sweeping motions for approximately five seconds per canal. A Hybrid Technique Protocol was employed where irrigation cycles were performed with the air/water spray disabled, starting with Saline, then 17% EDTA followed by 4% sodium hypochlorite. Notably, the LAI system was occasionally utilized earlier in the protocol, such as in situations where canals were severely calcified and patency could not be achieved; in these instances, LAI with 17% EDTA was employed before final canal preparation to facilitate the negotiation of micro-canals. The sampling frame comprised all EMS cases; non-surgical endodontic treatments were outside the analytic scope because outcomes were defined exclusively as indications for EMS, and our period contrasts are within-EMS proportions. Surgical Indications and Decision Making EMS in this study were performed under operating microscope magnification and illumination using modern microsurgical instrumentation, bioceramic root-end filling material, guided tissue regeneration when indicated, and Cone Beam Computed Tomography (CBCT) imaging. The clinicians share common diagnoses and treatment philosophies, as all were trained at the same specialty/residency program. The endodontists followed a uniform, stepwise approach: Once endodontic disease is diagnosed, non-surgical endodontic therapy or retreatment is first considered. EMS is considered only when non-surgical treatment is infeasible or unlikely to succeed—for example, when root integrity would be compromised (e.g., a large cast post extending > two-thirds of canal length), when canal patency cannot be achieved despite appropriate attempts and the patient has persistent symptoms and/or a periapical radiolucency, or when external root resorption (apical or along lateral external root surface) cannot be excavated and predictably restored non-surgically. When non-surgical retreatment has been unsuccessful or is not possible and EMS is judged less predictable or unsafe due to anatomic risk —(e.g., palatal root of maxillary second molars close to the greater palatine vessels; mandibular second molars with proximity to the inferior alveolar nerve and thick buccal cortical bone), intentional replantation is considered provided key criteria are met—non-divergent root morphology amenable to atraumatic extraction and replantation and a stable periodontal status. Data Collection The study protocol involved a retrospective review where patient charts were de-identified and anonymized prior to data extraction to ensure no identifiable private information was used in the analysis. Data collected included the patient's age and gender, the tooth number, the specific reason for endodontic microsurgery, the type of surgery, and the date of the procedure. Most surgical cases had CBCT analysis done prior to treatment. Per the American Association of Endodontists' Guide to Clinical Endodontics, when an adequate amount of tissue or foreign material could be removed from the periradicular surgical site, a biopsy was taken for histopathologic examination. The types of endodontic microsurgery included root-end apicoectomy, root amputation, intentional replantation, and external root resorption repair. The specific reasons for endodontic microsurgery included: 1) Apical cementicle, 2) Apical cyst, 3) Endodontic-periodontic infection, 4) Excessive calcification, 5) External root resorption, 6) Extrusion, 7) Extraradicular pathosis/Actinomycosis, 8) Failed apical surgery, 9) Large post, 10) Palatal gingival groove, 11) Root fracture, 12) Separated instrument, 13) Transportation/perforation, 14) Uncleaned accessory canal, and 15) Unknown etiology. The "Unknown etiology" category was used for cases where endodontic microsurgery was performed despite all root canal obturations reaching the apex (apices) and no known accessory canals (including delta canals, lateral canals, and isthmi) being visualized during non-surgical nor surgical treatments. In these instances, surgery was necessitated by either persistent symptoms and/or a persistent growth in the periapical radiolucency. In addition, biopsy results for these cases were negative for apical cyst and extraradicular pathosis/Actinomycosis. Each EMS case was assigned one or two indications from the 15-item list. When two applicable indications were present, both were recorded; 116 teeth (6.9% of the cohort) had dual indications. For example, for tooth #19, the mesiobuccal canal exhibited a non-negotiable excessive calcification while the distal canal contained a separated instrument in the apical third around a distal curvature; therefore, the indications assigned were “excessive calcification” and “separated instrument.” For all analyses, each indication was treated as a separate binary variable (“present” or “absent” for that tooth). Frequencies thus represent the number of EMS teeth exhibiting each indication, regardless of whether the indication was primary or secondary. As a result, totals across indications exceed the number of unique teeth. BLT–ALT comparisons were based on the proportion of EMS teeth meeting each indication, ensuring that the presence of dual-reason teeth did not bias period-level differences. Two endodontists independently reviewed each surgical record and assigned up to two indications per tooth from the predefined list. Prior to review, they completed a calibration session using a pilot set with consensus definitions. Disagreements were resolved by consensus, and the final dataset was tabulated for analysis. Surgeon- and site-adjusted logistic models among EMS (outcome = indication yes/no) were fitted including ALT (vs BLT), site, surgeon code, tooth class, age, and sex; robust standard errors were used to account for clustering by surgeon/site. Statistical analysis Proportions were compared using Pearson’s χ² test with two-sided α = .05; 95% confidence intervals were calculated by the Wald method. When expected counts were < 5, Fisher’s exact test was used as a sensitivity check. Analyses were performed in R, version 4.4.1 (R Foundation for Statistical Computing, Vienna, Austria). Descriptive statistics summarized patient demographics, the distribution of reasons for surgery, and procedure types. Because a tooth could contribute up to two indications, percentages for each reason were computed as occurrences divided by the total number of surgeries and may therefore exceed 100%. At most two indications were assigned per tooth. The number of teeth having two reasons for surgery was 116 out of 1,672 (6.9%). As a specificity check, “negative-control” indications that are unlikely to be influenced by LAI (Large post; Root fracture) were analyzed. BLT vs ALT differences for these outcomes using Pearson’s χ² with two-sided α = .05 and 95% confidence intervals (CIs) were tested. Ethics statement This retrospective study analyzed fully de-identified and anonymized clinical records that did not involve patient contact. The project received an Institutional Review Board (IRB) waiver of authorization and exemption status under 45 CFR 164.512, IRB Study No.: 1401656; IRB Pr. No.: 20254353. The study adhered to the Declaration of Helsinki. Results Analysis of patient demographics revealed a slight female predominance in the surgical cohort, with 57.7% of patients being female and 42.3% male. The overall mean age of patients undergoing endodontic microsurgery was 56.4 years, with a median age of 58 years. In the BLT period, the mean age was 56.5 years (median: 58), while in the ALT period, the mean age was 56.2 years (median: 58). Among the 1,672 teeth treated surgically, the most common procedure was root-end apicoectomy, followed by external root resorption repair, root amputation, and intentional replantation (Table 1 ). Table 1 Distribution of Types of EMS and Patient Sex within the Study Cohort (N = 1,672 teeth; 1,474 patients)* Variable n (%) Type of Surgery Root-end apicoectomy 1,573 (94.1%) External root resorption repair 64 (3.8%) Root amputation 21 (1.3%) Intentional replantation 14 (0.8%) Patient Sex Female 851 (57.7%) Male 623 (42.3%) *The denominator differs between surgery type (1,672 teeth) and sex distribution (1,474 patients) because some patients underwent microsurgery on more than one tooth. The reasons for endodontic microsurgery were analyzed in three sections. First, for the entire six-year study period, and then separately for the BLT and ALT groups. Representative cases of each reason for endodontic microsurgery are shown radiographically and/or with photos and/or with CBCT scan images (Fig. 2 ). The arch and tooth-class distribution of EMS-treated teeth is summarized in Fig. 3 (percentages calculated from the total cohort, n = 1,672). Maxillary molars comprised the largest share (558/1,672, 33.4%), followed by mandibular molars, maxillary premolars, maxillary anteriors, mandibular anteriors and lastly, mandibular premolars. The top three indications within each tooth category are summarized in Table 2 (percentages calculated within category). Detailed values are not repeated here; briefly, large posts predominated in anterior and premolar teeth, whereas in molars uncleaned accessory canal and excessive calcification were most common. Table 2 Top three indications for endodontic microsurgery by tooth category (percentages calculated within each category; some totals exceed 100% because up to two reasons could be assigned per tooth). Tooth category 1st reason (n, %) 2nd reason (n, %) 3rd reason (n, %) Maxillary Anteriors Large Post; 140 (46.1%) Apical Cyst; 50 (16.4%) External Root Resorption; 30 (9.9%) Mandibular Anteriors Large Post; 34 (35.8%) External Root Resorption; 20 (21.1%) Unknown etiology; 9 (9.5%) Maxillary Premolars Large Post; 120 (39.0%) Uncleaned accessory canal; 37 (12.0%) Apical Cyst; 30 (9.7%) Mandibular Premolars Large Post; 18 (32.7%) External Root Resorption; 15 (27.3%) Unknown etiology; 9 (16.4%) Maxillary Molars Excessive Calcification; 150 (26.9%) Uncleaned accessory canal; 150 (26.9%) Transportation/perforation; 71 (12.7%) Mandibular Molars Uncleaned accessory canal; 152 (43.2%) Large Post; 53 (15.0%) Excessive Calcification; 50 (14.2%) The analysis for the BLT and ALT groups was conducted across all 15 reasons. For the purpose of the second study aim, the focus was on uncleaned accessory canal and excessive calcification, as these are the indications where the use of LAI during non-surgical treatment could potentially impact the outcome. The number of occurrences for each reason for endodontic microsurgery (n = 1672), ranked from most to least frequent, were as follows: uncleaned accessory canal (n = 379, 22.7%), large post (n = 372, 22.3%), excessive calcification (n = 240, 14.4%), apical cyst (n = 207, 12.4%), transportation/perforation (n = 143, 8.6%), unknown etiology (n = 123, 7.4%), external root resorption (n = 105, 6.3%), extrusion (n = 62, 3.7%), extraradicular pathosis/actinomycosis (n = 46, 2.8%), separated instrument (n = 42, 2.5%), root fracture (n = 37, 2.2%), failed apical surgery (n = 32, 1.9%), endodontic-periodontic infection (n = 5, 0.3%), apical cementicle (n = 4, 0.2%), and palatal gingival groove (n = 1, < 0.1%). For the BLT group (n = 767), the number of occurrences per reason, ranked from most to least frequent, was as follows: uncleaned accessory canal (n = 219), large post (n = 170), apical cyst (n = 115), excessive calcification (n = 83), transportation/perforation (n = 55), external root resorption (n = 51), unknown etiology (n = 36), extrusion (n = 29), extraradicular pathosis/actinomycosis (n = 23), root fracture (n = 22), separated instrument (n = 17), failed apical surgery (n = 12), endodontic-periodontic infection (n = 4), apical cementicle (n = 1), and palatal gingival groove (n = 0). For the ALT group (n = 905), the number of occurrences per reason, ranked from most to least frequent, was as follows: large post (n = 202), uncleaned accessory canal (n = 160), excessive calcification (n = 157), transportation/perforation (n = 88), unknown etiology (n = 87), apical cyst (n = 82), external root resorption (n = 54), extrusion (n = 33), separated instrument (n = 25), extraradicular pathosis/actinomycosis (n = 23), failed apical surgery (n = 20), root fracture (n = 15), apical cementicle (n = 3), endodontic-periodontic infection (n = 1), and palatal gingival groove (n = 1) (Fig. 4 ). Compared with BLT, the ALT period showed a 10.9-percentage-point reduction in surgeries for uncleaned accessory canals (28.6% to 17.7%; 95% CI − 14.9 to − 6.8; P < .001) and a 6.5-percentage-point increase in surgeries for excessive calcification (10.8% to 17.3%; 95% CI + 3.2 to + 9.8; P .10), supporting the specificity of the uncleaned accessory canal association. ALT remained associated with lower uncleaned accessory canal (adjusted odds ratio ≈ 0.54, P< .001) and higher calcification (adjusted odds ratio ≈ 1.73, P< .01), indicating findings were not explained by surgeon nor site mix. Discussion EMS is a reliable treatment option with favorable reported success and survival rates [ 1 , 5 ]. Indications for EMS have been described in the literature, often focusing on isolated reasons for surgery. However, there is a notable lack of large-scale studies from private practice cohorts that comprehensively rank all indications. We did not enumerate or classify all non-surgical endodontic treatments (~ 22,000 cases) because doing so would not alter the within-EMS distributions or BLT–ALT contrasts; to mitigate secular-trend concerns, we included negative-control indications and surgeon/site-adjusted analyses, which yielded consistent results. In this study of 1,672 teeth treated with EMS, the most common reasons were uncleaned accessory canals (22.7%), post-related challenges (22.3%), and excessive calcification (14.4%). Large posts present a particular challenge because attempts at removal during retreatment may compromise root integrity and increase the risk of fracture, rendering the tooth non-restorable or prone to reinfection [ 16 ]. Nevertheless, the decision to forgo retreatment and proceed with EMS in these situations remains partly subjective, as the precise risk of fracture during post removal cannot be fully determined as there are other factors such as post size, length, and type (threaded, non-threated, cast, flexi, para, fibre, etc.). Accessory canals—including delta canals, lateral canals, and isthmi—are another frequent indication, as they are often difficult to completely debride during non-surgical treatment [ 17 , 18 ]. Similarly, excessive calcification, particularly pulp canal obliteration (PCO), poses a significant anatomic barrier that increases the risk of procedural errors such as perforation or instrument separation, making EMS the more predictable treatment option where patency cannot be achieved [ 19 , 20 ]. Therefore, there are reasonable explanations why these three indications ranked highest in our cohort. Less common indications included failed apical surgery (1.9%), endodontic-periodontic infections (0.2%), apical cementicles (0.2%), and palatal gingival groove (< 0.1%). Reported causes of failure after initial apical surgery include beveled root resections that expose infected dentinal tubules, leakage or dislodgement of retrofilling materials, and untreated isthmi or accessory canals not addressed during the first procedure. Modern microsurgery techniques and imaging have substantially improved outcomes in these resurgery scenarios, with success rates approaching those of primary microsurgery [ 21 , 22 ]. The relatively low proportion of failed apical surgeries observed in this study is encouraging. The concept of “modern endodontic microsurgery” emerged in the late 1990s and early 2000s [ 23 ] and gained broader acceptance in the following decade. Because many of the initial surgeries in this cohort were already performed using modern protocols, this likely contributed to the reduced frequency of failures requiring resurgery. Our study showed a high frequency of post-related indications in the maxillary arch, particularly maxillary anterior teeth (140/304, 46.1%) and maxillary premolars (120/308, 39.0%). This distribution is consistent with radiographic surveys reporting that posts are placed more often in the maxilla—especially in maxillary anterior and premolar teeth [ 24 ]. In addition, uncleaned accessory canals were common indications in both maxillary molars (150/559, 26.8%) and mandibular molars (152/353, 43.1%), likely reflecting the high prevalence of isthmus anatomy—between mesiobuccal-1 and mesiobuccal-2 canals in maxillary molars and between the mesiobuccal and mesiolingual canals in mandibular molars—which complicates complete debridement during nonsurgical treatment [ 17 , 18 ]. To our knowledge, no prior clinical investigations have directly evaluated whether routine use of LAI influences the subsequent incidence of EMS. Existing research has focused primarily on antimicrobial efficacy, smear-layer and debris removal, or short-term clinical outcomes such as postoperative pain, rather than on long-term surgical incidence [ 11 , 15 ]. The present study design represents a time-period comparison of surgical incidence rather than a cause-and-effect analysis at the level of individual teeth. Moreover, separated instrument and root fracture—indications unlikely to be influenced by LAI—showed no period-related change, supporting the specificity of the uncleaned accessory canal association. The rise in calcification is addressed separately below through a biologic-lag interpretation. Together, these analyses strengthen the overall robustness of our findings. Nevertheless, the results remain associational and warrant confirmation in prospective, tooth-level studies. The EdgePRO™ system is an Er,Cr:YSGG laser device (2780 nm) designed for intracanal disinfection during root canal treatment with LAI. Its mechanism of action involves rapid heating and vaporization of the irrigant, which generates expanding and collapsing vapor bubbles. The collapse of these bubbles produces acoustic and shock waves that propagate through the canal system, thereby enhancing the removal of microbes and debris from complex root canal anatomy. Among the 15 indications for EMS, the two most likely to be influenced by LAI are primarily, uncleaned accessory canal and secondarily, excessive calcification. The impact of LAI on cleaning accessory anatomy (lateral canals, isthmi, apical ramifications) is supported by multiple studies [ 11 – 14 ]. While LAI does not directly remove calcified dentin, the enhanced irrigant penetration and hydrodynamic agitation—together with improved smear-layer/debris removal in constricted canal portions—may secondarily assist canal negotiation in some cases by revealing micro-anatomic pathways that instruments can subsequently follow. In our study, the proportion of EMS cases performed for uncleaned accessory canals significantly decreased from 28.6% in the BLT group to 17.7% in the ALT group. This reduction suggests that improved intracanal disinfection with LAI may have reduced the need for surgery related to untreated accessory anatomy. In contrast, the proportion of EMS performed for excessive calcification increased from 10.8% in the BLT period to 17.3% in the ALT period. This pattern is biologically plausible as LAI does not mechanically remove calcified dentin and has limited direct effect on hard calcific obstructions. The increase, however, is noteworthy. Because pulp-canal calcifications are known to increase with patient age [ 25 ], we compared mean and median ages between the BLT and ALT groups to exclude age as a potential confounder for the observed rise in calcification-related EMS. The mean ages (56.5 vs 56.2 years) and median ages (58 years in both groups) were nearly identical, indicating that the age distribution between periods was well-matched and unlikely to explain the differential increase in calcification-related surgical indications. One theory of a likely driver is a lagged rise in pulp canal obliteration (PCO) associated with parafunctional loading during the COVID-19 pandemic. Chronic functional stress has been linked to pulpal calcification [ 26 , 27 ], and pandemic-era reports document increased cracked teeth consistent with elevated bruxism/clenching and deferred care [ 28 ]. Notably, PCO is typically recognized ≥ 1 year after the inciting insult and can progress over multiple years [ 29 , 30 ]. Taken together, a biologic lag from the 2020–2021 pandemic stressor to radiographically evident calcification aligns with the higher ALT frequency. Thus, while LAI may or may not improve nonsurgical debridement in some calcified cases, any potential benefit was likely outweighed by a time-shifted increase in the underlying calcification burden, yielding a greater relative proportion of calcification-related EMS in the ALT period. In our study, apical cysts accounted for 12.4% (n = 207) of EMS cases. A landmark histopathologic study by Nair et al. examined 256 extracted teeth with persistent apical periodontitis and reported that 15% were periapical cysts, of which 9% were true cysts and 6% were pocket cysts [ 31 ]. True cysts are self-sustaining lesions that may persist despite adequate nonsurgical treatment, whereas pocket cysts are usually dependent on intraradicular infection and may resolve following conventional root canal therapy. A key limitation of surgical biopsy specimens is that histopathology cannot reliably distinguish between true and pocket cysts, because once the lesion is removed, its anatomic relationship to the root canal system is lost and the pathologist can only evaluate the cystic sac in isolation. Nair’s study overcame this limitation by examining extracted teeth with the periapical tissues intact, preserving the continuity between the root canal system and the lesion and allowing for more definitive classification. This diagnostic limitation highlights the complexity of assigning a single definitive etiology to apical cysts and underscores the need to interpret biopsy findings in the broader clinical and radiographic context. Accordingly, the 12.4% incidence of apical cysts in our cohort is likely more comparable to the overall 15% reported by Nair et al. than to the 9% incidence of true cysts alone. The proportion of true apical cysts within our cohort cannot be determined, as histopathologic analysis alone does not allow this distinction. In this study, “unknown etiology” denotes cases in which recognized indications (e.g., extraradicular infection, cystic pathosis, fractures, procedural mishaps, or identifiable untreated anatomy) were not evident, yet symptoms and/or the periapical radiolucency persisted. The literature describes non-infectious mechanisms that can sustain periapical inflammation despite adequate orthograde treatment, notably cholesterol crystal aggregates that elicit a foreign-body giant-cell response and, more rarely, true foreign-body reactions to endogenous or exogenous material (e.g., sealer components). These processes are seldom distinguishable without surgical access and histopathologic examination, which explains why some clinically “unknown” cases proceed to EMS after conservative options are exhausted [ 7 , 32 – 34 ]. Conclusion In this large private practice cohort of 1,672 EMS cases, among 15 different possible indications, the most frequent were uncleaned accessory canal, post-related challenges, and excessive calcification. The incidence of uncleaned accessory canal–related surgeries significantly decreased after the introduction of LAI suggesting improved nonsurgical debridement. In contrast, calcification-related surgeries increased, which may reflect broader etiologic factors such as stress-associated pulpal changes during the COVID-19 pandemic rather than a direct effect of LAI. Failed apical surgery was a rare indication, a finding consistent with improved outcomes associated with modern EMS. Other uncommon indications, such as apical cementicles, palatal gingival groove, and endodontic-periodontic infections, remain infrequent and are unlikely to be influenced by advances in EMS. LAI may indirectly aid nonsurgical debridement of accessory anatomy, and in this study was associated with a lower proportion of EMS for uncleaned accessory canals after adoption. By contrast, calcification-related EMS increased across periods—likely reflecting a time-lagged rise in COVID-19-related PCO rather than a direct LAI effect. Future tooth-level, prospective studies are needed to establish causality and to clarify whether LAI influences the downstream need for EMS. Declarations Ethical Approval: This study received an Institutional Review Board (IRB) waiver of authorization (IRB Study No.: 1401656). All procedures were in accordance with the ethical standards of the 1964 Helsinki Declaration and its later amendments. Informed Consent: Informed consent was waived by the IRB due to the retrospective, de-identified nature of the data. Conflict of Interest: The authors declare they have no financial or non-financial interests to disclose. Funding: No funds, grants, or other support were received. Author Contribution: [Omitted for blind review]. Data Availability: De-identified data is available from the corresponding author upon reasonable request References Setzer FC (2022) Present status and future directions: surgical endodontics. Int Endod J 55:16–34 Setzer FC, Walter C, Sharma P, Petkovic-Curcin A, Kim S (2019) Outcome of crown and root resection: a systematic review. 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J Endod 41:265–273 von Arx T, Hänni S (2015) Clinical and radiographic assessment of predictors for healing one year after periapical surgery. J Endod 41:589–598 Tawil PZ, Trope M (2020) The endodontic–restorative connection: a 15-year systematic review of longitudinal clinical studies. J Endod 46(5S):S2–S13 Venskutonis T, Plotino G, Tocci L, Gambarini G (2014) Periapical and endodontic status scale using cone-beam computed tomography. J Endod 40:652–658 DiVito E, Peters OA, Peters CI (2014) Effect of laser-activated irrigation on smear layer and debris removal: a scanning electron microscope study. J Endod 40:151–154 Fahim YZ, Ghali RM, Hashem AA, El-Khodary HM, El-Ashry SH, El-Boghdadi RM (2024) The efficacy of 2780-nm Er,Cr:YSGG and 940-nm diode lasers in root canal disinfection: a randomized clinical trial. Clin Oral Investig 28:3589–3597 Suter B, Suter V, Lussi A (2019) The effectiveness of laser-activated irrigation compared with conventional irrigation in root canal disinfection: a systematic review. Int Endod J 52:1663–1675 Meire MA, Van Acker J, Coenye T, De Moor RJ (2024) Principle and antimicrobial efficacy of laser-activated irrigation. Int Endod J 57:1021–1034 Sabeti M, Kazemipoor M, Karimi A, Asgary S (2025) Comparison of ultrasonically activated irrigation and laser-activated irrigation on postoperative endodontic pain: a randomized clinical trial. J Endod 51:123–129 Abramovitz I, Better H, Shacham A, Shlomi B, Metzger Z (2002) Case selection for apical surgery: a retrospective evaluation of associated factors and rationale. J Endod 28:527–530 Ricucci D, Siqueira JF Jr (2010) Fate of the tissue in lateral canals and apical ramifications in response to pathologic conditions and treatment procedures. J Endod 36:1–15 Vertucci FJ (2005) Root canal morphology and its relationship to endodontic procedures. Endod Top 10:3–29 Zuolo ML, Ferreira MO, Gutmann JL (2005) Prognosis in periradicular surgery: a meta-analysis. Int Endod J 38:521–526 Tavares PM, Cândido MS, Souza E et al (2020) Surgical management of endodontic failures due to calcifications and technical difficulties. Dent Press Endod 10:52–61 Kim D, Ku H, Nam T, Shin SJ, Kim E (2018) Outcome of endodontic micro-resurgery: a retrospective study with propensity-matched comparison to primary microsurgery. J Endod 44:183–189 Taschieri S, Del Fabbro M, Testori T, Francetti L, Weinstein RL (2007) Endodontic reoperation using an endoscope and microsurgical instruments: a prospective clinical study. Int Endod J 40:186–193 Kim S, Rethnam S (1997) Modern endodontic surgery concepts and practice: a review. Dent Clin North Am 41:481–497 Almaghrabi J, Alesawi A, Attar E, Alshali S (2022) Radiographic analysis of posts performed by undergraduate dental students: a cross-sectional study. Clin Cosmet Investig Dent 14:37–43 Kiefner P, Connert T (2017) Treatment of calcified root canals in older people. Gerodontology 34:285–292 Malhotra N, Mala K (2013) Calcific metamorphosis: literature review and clinical strategies. Dent Update 40:48–60 Farias Z, Sousa J, Faria C, Vieira J, Sobral A, Silveira M (2023) Pulpal calcifications in orthodontically moved teeth: a scoping review. J Clin Exp Dent 15:e773–e780 Nosrat A, Yu P, Verma P, Dianat O, Wu D, Fouad AF (2022) Was the COVID-19 pandemic associated with an increased rate of cracked teeth? J Endod 48:1241–1247 McCabe PS, Dummer PMH (2012) Pulp canal obliteration: an endodontic diagnosis and treatment challenge. Int Endod J 45:177–197 Andreasen FM, Zhijie Y, Thomsen BL, Andersen PK (1987) Occurrence of pulp canal obliteration after luxation injuries in the permanent dentition. Endod Dent Traumatol 3:103–115 Nair PN, Pajarola G, Luder HU (1996) Types and incidence of human periapical lesions obtained with extracted teeth. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 81:93–102 Duncan HF et al (2023) Treatment of pulpal and apical disease: The European Society of Endodontology (ESE) S3-level clinical practice guideline. Int Endod J 56:239–314 Abramovitz I, Better H, Shacham A, Shlomi B, Metzger Z (2002) Case selection for apical surgery: a retrospective evaluation of associated factors and rationale. J Endod 28:527–530 Torabinejad M, Corr R, Handysides R, Shabahang S (2009) Outcomes of nonsurgical retreatment and endodontic surgery: a systematic review. J Endod 35:930–937 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 17 Feb, 2026 Editor assigned by journal 03 Feb, 2026 Submission checks completed at journal 03 Feb, 2026 First submitted to journal 02 Feb, 2026 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-8761178","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":592783803,"identity":"bdc1a134-50b6-4e28-b2aa-94309b16fe58","order_by":0,"name":"David Han","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYBACAzDJxsDYAKQOMDDYACnGxgNEamEGaUkDaWkgXgsQHAbz8WoxZz978HFBmY1sv3T/wQM//py3W9t+GGhLjU00Li2WPXnJxjPOpRnPnHOY4WBv2+3kbWcSgVqOpeU24HLYgRwzad62w4kbbiQzHGZsuJ1sdgCohbHhMG4t59+Y/4ZrYfhzLtns/EMCWm7kmDEjtLAdsDO7QciWG2+MpXlAfpmRbAD0S3KC2Q2gLQn4/HI+x/AzDyjEJBIff/jxx87e7Hz6wwcfamxwasEAiWCVCcQqBwF7UhSPglEwCkbByAAA1gBpmr/UNcIAAAAASUVORK5CYII=","orcid":"","institution":"Apical Endodontics","correspondingAuthor":true,"prefix":"","firstName":"David","middleName":"","lastName":"Han","suffix":""},{"id":592783804,"identity":"5426a0e0-3981-47e5-b1b7-a236d812428b","order_by":1,"name":"Christopher Chun","email":"","orcid":"","institution":"Apical Endodontics","correspondingAuthor":false,"prefix":"","firstName":"Christopher","middleName":"","lastName":"Chun","suffix":""},{"id":592783805,"identity":"51c3ab0c-3f41-486d-8874-5ebdf2de8fb7","order_by":2,"name":"Catherine Kim","email":"","orcid":"","institution":"Apical Endodontics","correspondingAuthor":false,"prefix":"","firstName":"Catherine","middleName":"","lastName":"Kim","suffix":""},{"id":592783806,"identity":"0b8a05b3-3877-49d7-915c-e27a25034396","order_by":3,"name":"Laurel Martinez","email":"","orcid":"","institution":"Apical Endodontics","correspondingAuthor":false,"prefix":"","firstName":"Laurel","middleName":"","lastName":"Martinez","suffix":""},{"id":592783808,"identity":"5d6deff1-79e6-45bb-8123-8b01b84fc476","order_by":4,"name":"Jooyoung Song","email":"","orcid":"","institution":"Apical Endodontics","correspondingAuthor":false,"prefix":"","firstName":"Jooyoung","middleName":"","lastName":"Song","suffix":""}],"badges":[],"createdAt":"2026-02-02 06:24:49","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8761178/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8761178/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104779228,"identity":"e0467e69-5e88-4ada-addc-27103b30232c","added_by":"auto","created_at":"2026-03-17 07:36:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":302520,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStudy flow diagram (STROBE).\u003c/strong\u003eTwo-site private practice (April 2019–August 2025). All EMS procedures were identified; n = 1,672 teeth (1,474 patients) were included with no tooth-level exclusions. Period classification derived from procedure date (Before–LAI, 1 Apr 2019–31 Jul 2022; After–LAI, 1 Aug 2022–31 Aug 2025).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8761178/v1/13a0ca4f262f3a78e088c43b.png"},{"id":105032552,"identity":"14e43299-bb0d-44fd-8923-35c67d6fbc83","added_by":"auto","created_at":"2026-03-20 07:00:43","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":236927,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative examples for each of the 15 reasons for endodontic microsurgery. For each case, the radiograph prior to the surgical procedure is shown, along with a radiograph after the microsurgery and, when appropriate, postoperative non-surgical endodontic therapy radiographs, CBCT images and/or clinical photos and/or follow up radiographs. (A) Apical Cementicle, arrow pointing to distal apical cementicle on root surface of tooth #25. (B) Apical cyst. (C) Endodontic-Periodontic infection. (D) Excessive calcification. (E) External root resorption (F) Extrusion (G) Extraradicular pathosis/Actinomycosis. (H) Failed apical surgery, Arrow pointing to missed, calcified MB2. (I) Large post. (J) Palatal gingival groove, Tooth #10, intentional replantation performed to repair deep lingual groove. (K) Root fracture, (L) Separated instrument. (M) Transportation/perforation. (N) Uncleaned accessory canal. (O) Unknown etiology, Tooth #8, despite non-surgical endodontic treatment and retreatment, symptomatic with persistent periapical radiolucency.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8761178/v1/bc09a0fce17601da77236974.png"},{"id":102993547,"identity":"d0f7b279-d2a1-4328-95d0-5a6aef430c6f","added_by":"auto","created_at":"2026-02-19 11:48:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":275753,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of EMS-treated teeth by arch and tooth class, with quadrant-level detail for premolars and molars. Values are counts; percentages (where shown) are of the total cohort (\u003cem\u003en\u003c/em\u003e = 1,672). Total (\u003cem\u003en\u003c/em\u003e) per tooth type include: Maxillary anteriors (304), maxillary premolars (308), maxillary molars (558), mandibular anteriors (95), Mandibular premolars (55), and mandibular molars (352); Teeth (\u003cem\u003en\u003c/em\u003e) per quadrant sections: Upper right premolars (152), upper right molars (264), upper left premolars (156), upper left molars (294), lower left premolars (28), lower left molars (180), lower right premolars (27) and lower right molars (172).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8761178/v1/8ec456ee025b0bc7c2d023c0.png"},{"id":103050046,"identity":"ffec5a44-c740-45e7-8676-07ac1162e776","added_by":"auto","created_at":"2026-02-20 07:47:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":358799,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(A)\u003c/strong\u003e Reasons for endodontic microsurgery (EMS) ranked by total occurrences (n = 1,672 teeth), with BLT and ALT distributions shown as stacked segments. Indications are ordered top-to-bottom by overall frequency. Highlighted in green are the two indications potentially influenced by laser-activated irrigation (LAI) during nonsurgical treatment: \u003cstrong\u003euncleaned accessory canal\u003c/strong\u003e (n = 379) and \u003cstrong\u003eexcessive calcification\u003c/strong\u003e (n = 240). Surgeries for uncleaned accessory canals decreased from \u003cstrong\u003e28.6% to 17.7%\u003c/strong\u003e, whereas surgeries for excessive calcification increased from \u003cstrong\u003e10.8% to 17.3%\u003c/strong\u003e. \u003cstrong\u003e(B) \u003c/strong\u003ePercentage-point differences (ALT − BLT) with 95% \u003cstrong\u003econfidence intervals (95% CI)\u003c/strong\u003e: uncleaned accessory canals \u003cstrong\u003e−10.9\u003c/strong\u003e(−14.9 to −6.8); excessive calcification \u003cstrong\u003e+6.5\u003c/strong\u003e (+3.2 to +9.8).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8761178/v1/15d8f8734b688ade7da071b5.png"},{"id":105036871,"identity":"1ff919d3-6f29-4db5-be6f-5f7b12796b74","added_by":"auto","created_at":"2026-03-20 07:36:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1780583,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8761178/v1/f84e3035-147c-494a-8066-cc95ac6360c1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Endodontic Microsurgery in Private Practice: Indications and Time-Period Trends Before and After Adoption of Laser-Activated Irrigation - A Retrospective Cohort Study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eEndodontic microsurgery (EMS) encompasses a spectrum of surgical procedures\u0026mdash;including root-end apicoectomy, root amputation, intentional replantation, and external root resorption repair\u0026mdash;each with distinct clinical applications. The literature indicates that all four types of EMS can yield favorable outcomes, provided that case selection is appropriate and clinical circumstances are carefully considered [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Although conventional non-surgical endodontic therapy remains the primary modality for treating pulpal and periradicular disease, certain cases necessitate surgical intervention. Modern EMS has demonstrated higher success rates than traditional approaches, largely owing to advances in ultrasonic root-end preparation, biocompatible filling materials, refined microsurgical instrumentation, and enhanced magnification and illumination [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Reported indications for surgery include persistent extraradicular infection, procedural mishaps such as instrument separation or perforation, untreated anatomy, and root fractures [\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Existing literature has largely focused on isolated indications; however, no known studies to date have comprehensively analyzed the full spectrum of reasons for EMS in a single cohort. This detailed understanding of the common and uncommon indications is important for determining the necessity for surgery, refining treatment protocols, and improving patient care.\u003c/p\u003e \u003cp\u003eConcurrently, a growing body of evidence supports the use of adjunctive technologies to enhance the effectiveness of conventional non-surgical endodontic procedures. Among these, laser-activated irrigation (LAI) has emerged as a promising method to enhance disinfection within the complex root canal system and to reduce postoperative pain [\u003cspan additionalcitationids=\"CR12 CR13 CR14\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, the potential long-term impact of LAI on the subsequent need for EMS has not been clearly established in a clinical setting. To date, no studies have evaluated whether the routine use of LAI during non-surgical treatment is associated with a change in the incidence of EMS.\u003c/p\u003e \u003cp\u003eThe purpose of this retrospective cohort study was twofold. First, to characterize the specific indications for EMS by quantifying the frequency of 15 reasons in a large private practice cohort. Second, to test whether the distribution of EMS indications differed across pre- and post-LAI periods for two indications (uncleaned accessory canal and excessive calcification), acknowledging that this time-period comparison cannot establish causality.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e This retrospective observational study is reported in accordance with the STROBE guideline; the completed checklist is provided as a supplementary file and the study flow is detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStudy Cohort and Setting\u003c/p\u003e \u003cp\u003eThis study analyzed de-identified clinical data from a multi-site private endodontic practice located in a major metropolitan area. The cohort consisted of 1,474 patients who underwent endodontic microsurgery (EMS) on 1,672 teeth between April 1, 2019, and August 31, 2025. Data were divided into two groups based on the implementation of a specific disinfection protocol: -Before-Laser Treatment (BLT): April 1, 2019, to July 31, 2022, using conventional chemomechanical irrigation. -After-Laser Treatment (ALT): August 1, 2022, to August 31, 2025, following the routine adoption of laser-activated irrigation (LAI). The three-month difference in the study period lengths between the two groups is attributed to the COVID-19 pandemic with a one-month office closure and a subsequent two-month period where no endodontic surgeries were performed due to an overabundance of caution taken to minimize the transfer of COVID-19.\u003c/p\u003e \u003cp\u003eClinical Protocols\u003c/p\u003e \u003cp\u003eAll procedures were performed by six endodontists who received standardized specialist training. The non-surgical endodontic protocol was uniform across all clinicians. After anesthesia and dental-dam isolation, an access cavity was prepared and working length established with an electronic apex locator and confirmed radiographically. Initial glidepath preparation was performed with 0.02-taper stainless-steel hand files, followed by preparation to a 0.20 mm tip size at the working length. Mechanical instrumentation then proceeded using a crown-down approach with 0.04- or 0.06-taper nickel\u0026ndash;titanium rotary files under copious irrigation with 4% sodium hypochlorite. In the standard chemomechanical protocol\u0026mdash;which defined the BLT period\u0026mdash;4% sodium hypochlorite served as the primary irrigant throughout instrumentation. Typically, smear-layer removal was performed at the end of preparation using 17% EDTA followed by a final 4% sodium hypochlorite rinse. However, in selected situations\u0026mdash;such as the presence of pulp stones, heavy smear layer, or the need to enhance visualization of canal orifices on the chamber floor\u0026mdash;17% EDTA was used earlier in the treatment. After complete preparation, obturation was performed with gutta-percha cones and bioceramic sealer using a downpack-and-backfill technique.\u003c/p\u003e \u003cp\u003eThe protocol in the ALT period utilized the standard mechanical and shaping procedures described above, with LAI serving as the final disinfection step. At the completion of full canal instrumentation, LAI was performed using the EdgePRO\u0026trade; (Brasseler USA) Er,Cr:YSGG laser (2780 nm). The system was set to manufacturer-recommended intracanal settings: 0.1\u0026ndash;0.15 W output power, 20 Hz pulse frequency, and micro-pulse activation delivered through a radial-firing fiber tip. The tip was positioned in the middle third of the canal without binding, and activation consisted of slow withdrawal with circumferential sweeping motions for approximately five seconds per canal. A Hybrid Technique Protocol was employed where irrigation cycles were performed with the air/water spray disabled, starting with Saline, then 17% EDTA followed by 4% sodium hypochlorite. Notably, the LAI system was occasionally utilized earlier in the protocol, such as in situations where canals were severely calcified and patency could not be achieved; in these instances, LAI with 17% EDTA was employed before final canal preparation to facilitate the negotiation of micro-canals.\u003c/p\u003e \u003cp\u003eThe sampling frame comprised all EMS cases; non-surgical endodontic treatments were outside the analytic scope because outcomes were defined exclusively as indications for EMS, and our period contrasts are within-EMS proportions.\u003c/p\u003e \u003cp\u003eSurgical Indications and Decision Making\u003c/p\u003e \u003cp\u003eEMS in this study were performed under operating microscope magnification and illumination using modern microsurgical instrumentation, bioceramic root-end filling material, guided tissue regeneration when indicated, and Cone Beam Computed Tomography (CBCT) imaging. The clinicians share common diagnoses and treatment philosophies, as all were trained at the same specialty/residency program. The endodontists followed a uniform, stepwise approach: Once endodontic disease is diagnosed, non-surgical endodontic therapy or retreatment is first considered. EMS is considered only when non-surgical treatment is infeasible or unlikely to succeed\u0026mdash;for example, when root integrity would be compromised (e.g., a large cast post extending\u0026thinsp;\u0026gt;\u0026thinsp;two-thirds of canal length), when canal patency cannot be achieved despite appropriate attempts and the patient has persistent symptoms and/or a periapical radiolucency, or when external root resorption (apical or along lateral external root surface) cannot be excavated and predictably restored non-surgically. When non-surgical retreatment has been unsuccessful or is not possible and EMS is judged less predictable or unsafe due to anatomic risk \u0026mdash;(e.g., palatal root of maxillary second molars close to the greater palatine vessels; mandibular second molars with proximity to the inferior alveolar nerve and thick buccal cortical bone), intentional replantation is considered provided key criteria are met\u0026mdash;non-divergent root morphology amenable to atraumatic extraction and replantation and a stable periodontal status.\u003c/p\u003e \u003cp\u003eData Collection\u003c/p\u003e \u003cp\u003eThe study protocol involved a retrospective review where patient charts were de-identified and anonymized prior to data extraction to ensure no identifiable private information was used in the analysis. Data collected included the patient's age and gender, the tooth number, the specific reason for endodontic microsurgery, the type of surgery, and the date of the procedure. Most surgical cases had CBCT analysis done prior to treatment. Per the American Association of Endodontists' Guide to Clinical Endodontics, when an adequate amount of tissue or foreign material could be removed from the periradicular surgical site, a biopsy was taken for histopathologic examination. The types of endodontic microsurgery included root-end apicoectomy, root amputation, intentional replantation, and external root resorption repair. The specific reasons for endodontic microsurgery included: 1) Apical cementicle, 2) Apical cyst, 3) Endodontic-periodontic infection, 4) Excessive calcification, 5) External root resorption, 6) Extrusion, 7) Extraradicular pathosis/Actinomycosis, 8) Failed apical surgery, 9) Large post, 10) Palatal gingival groove, 11) Root fracture, 12) Separated instrument, 13) Transportation/perforation, 14) Uncleaned accessory canal, and 15) Unknown etiology. The \"Unknown etiology\" category was used for cases where endodontic microsurgery was performed despite all root canal obturations reaching the apex (apices) and no known accessory canals (including delta canals, lateral canals, and isthmi) being visualized during non-surgical nor surgical treatments. In these instances, surgery was necessitated by either persistent symptoms and/or a persistent growth in the periapical radiolucency. In addition, biopsy results for these cases were negative for apical cyst and extraradicular pathosis/Actinomycosis.\u003c/p\u003e \u003cp\u003eEach EMS case was assigned one or two indications from the 15-item list. When two applicable indications were present, both were recorded; 116 teeth (6.9% of the cohort) had dual indications. For example, for tooth #19, the mesiobuccal canal exhibited a non-negotiable excessive calcification while the distal canal contained a separated instrument in the apical third around a distal curvature; therefore, the indications assigned were \u0026ldquo;excessive calcification\u0026rdquo; and \u0026ldquo;separated instrument.\u0026rdquo; For all analyses, each indication was treated as a separate binary variable (\u0026ldquo;present\u0026rdquo; or \u0026ldquo;absent\u0026rdquo; for that tooth). Frequencies thus represent the number of EMS teeth exhibiting each indication, regardless of whether the indication was primary or secondary. As a result, totals across indications exceed the number of unique teeth. BLT\u0026ndash;ALT comparisons were based on the proportion of EMS teeth meeting each indication, ensuring that the presence of dual-reason teeth did not bias period-level differences.\u003c/p\u003e \u003cp\u003eTwo endodontists independently reviewed each surgical record and assigned up to two indications per tooth from the predefined list. Prior to review, they completed a calibration session using a pilot set with consensus definitions. Disagreements were resolved by consensus, and the final dataset was tabulated for analysis. Surgeon- and site-adjusted logistic models among EMS (outcome\u0026thinsp;=\u0026thinsp;indication yes/no) were fitted including ALT (vs BLT), site, surgeon code, tooth class, age, and sex; robust standard errors were used to account for clustering by surgeon/site.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eProportions were compared using Pearson\u0026rsquo;s χ\u0026sup2; test with two-sided α\u0026thinsp;=\u0026thinsp;.05; 95% confidence intervals were calculated by the Wald method. When expected counts were \u0026lt;\u0026thinsp;5, Fisher\u0026rsquo;s exact test was used as a sensitivity check. Analyses were performed in R, version 4.4.1 (R Foundation for Statistical Computing, Vienna, Austria). Descriptive statistics summarized patient demographics, the distribution of reasons for surgery, and procedure types. Because a tooth could contribute up to two indications, percentages for each reason were computed as occurrences divided by the total number of surgeries and may therefore exceed 100%. At most two indications were assigned per tooth. The number of teeth having two reasons for surgery was 116 out of 1,672 (6.9%). As a specificity check, \u0026ldquo;negative-control\u0026rdquo; indications that are unlikely to be influenced by LAI (Large post; Root fracture) were analyzed. BLT vs ALT differences for these outcomes using Pearson\u0026rsquo;s χ\u0026sup2; with two-sided α\u0026thinsp;=\u0026thinsp;.05 and 95% confidence intervals (CIs) were tested.\u003c/p\u003e \u003cp\u003eEthics statement\u003c/p\u003e \u003cp\u003eThis retrospective study analyzed fully de-identified and anonymized clinical records that did not involve patient contact. The project received an Institutional Review Board (IRB) waiver of authorization and exemption status under 45 CFR 164.512, IRB Study No.: 1401656; IRB Pr. No.: 20254353. The study adhered to the Declaration of Helsinki.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eAnalysis of patient demographics revealed a slight female predominance in the surgical cohort, with 57.7% of patients being female and 42.3% male. The overall mean age of patients undergoing endodontic microsurgery was 56.4 years, with a median age of 58 years. In the BLT period, the mean age was 56.5 years (median: 58), while in the ALT period, the mean age was 56.2 years (median: 58). Among the 1,672 teeth treated surgically, the most common procedure was root-end apicoectomy, followed by external root resorption repair, root amputation, and intentional replantation (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\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\u003eDistribution of Types of EMS and Patient Sex within the Study Cohort (N\u0026thinsp;=\u0026thinsp;1,672 teeth; 1,474 patients)*\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eType of Surgery\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot-end apicoectomy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1,573 (94.1%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExternal root resorption repair\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e64 (3.8%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot amputation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e21 (1.3%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntentional replantation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14 (0.8%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePatient Sex\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e851 (57.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e623 (42.3%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e*The denominator differs between surgery type (1,672 teeth) and sex distribution (1,474 patients) because some patients underwent microsurgery on more than one tooth.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe reasons for endodontic microsurgery were analyzed in three sections. First, for the entire six-year study period, and then separately for the BLT and ALT groups. Representative cases of each reason for endodontic microsurgery are shown radiographically and/or with photos and/or with CBCT scan images (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe arch and tooth-class distribution of EMS-treated teeth is summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (percentages calculated from the total cohort, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1,672). Maxillary molars comprised the largest share (558/1,672, 33.4%), followed by mandibular molars, maxillary premolars, maxillary anteriors, mandibular anteriors and lastly, mandibular premolars.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe top three indications within each tooth category are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (percentages calculated within category). Detailed values are not repeated here; briefly, large posts predominated in anterior and premolar teeth, whereas in molars uncleaned accessory canal and excessive calcification were most common.\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\u003eTop three indications for endodontic microsurgery by tooth category (percentages calculated within each category; some totals exceed 100% because up to two reasons could be assigned per tooth).\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 \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTooth category\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1st reason (n, %)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2nd reason (n, %)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3rd reason (n, %)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaxillary Anteriors\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLarge Post; 140 (46.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eApical Cyst; 50 (16.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eExternal Root Resorption; 30 (9.9%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMandibular Anteriors\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLarge Post; 34 (35.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExternal Root Resorption; 20 (21.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUnknown etiology; 9 (9.5%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaxillary Premolars\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLarge Post; 120 (39.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUncleaned accessory canal; 37 (12.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eApical Cyst; 30 (9.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMandibular Premolars\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLarge Post; 18 (32.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExternal Root Resorption; 15 (27.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUnknown etiology; 9 (16.4%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaxillary Molars\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eExcessive Calcification; 150 (26.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUncleaned accessory canal; 150 (26.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTransportation/perforation; 71 (12.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMandibular Molars\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUncleaned accessory canal; 152 (43.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLarge Post; 53 (15.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eExcessive Calcification; 50 (14.2%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe analysis for the BLT and ALT groups was conducted across all 15 reasons. For the purpose of the second study aim, the focus was on uncleaned accessory canal and excessive calcification, as these are the indications where the use of LAI during non-surgical treatment could potentially impact the outcome.\u003c/p\u003e \u003cp\u003eThe number of occurrences for each reason for endodontic microsurgery (n\u0026thinsp;=\u0026thinsp;1672), ranked from most to least frequent, were as follows: uncleaned accessory canal (n\u0026thinsp;=\u0026thinsp;379, 22.7%), large post (n\u0026thinsp;=\u0026thinsp;372, 22.3%), excessive calcification (n\u0026thinsp;=\u0026thinsp;240, 14.4%), apical cyst (n\u0026thinsp;=\u0026thinsp;207, 12.4%), transportation/perforation (n\u0026thinsp;=\u0026thinsp;143, 8.6%), unknown etiology (n\u0026thinsp;=\u0026thinsp;123, 7.4%), external root resorption (n\u0026thinsp;=\u0026thinsp;105, 6.3%), extrusion (n\u0026thinsp;=\u0026thinsp;62, 3.7%), extraradicular pathosis/actinomycosis (n\u0026thinsp;=\u0026thinsp;46, 2.8%), separated instrument (n\u0026thinsp;=\u0026thinsp;42, 2.5%), root fracture (n\u0026thinsp;=\u0026thinsp;37, 2.2%), failed apical surgery (n\u0026thinsp;=\u0026thinsp;32, 1.9%), endodontic-periodontic infection (n\u0026thinsp;=\u0026thinsp;5, 0.3%), apical cementicle (n\u0026thinsp;=\u0026thinsp;4, 0.2%), and palatal gingival groove (n\u0026thinsp;=\u0026thinsp;1, \u0026lt;\u0026thinsp;0.1%).\u003c/p\u003e \u003cp\u003eFor the BLT group (n\u0026thinsp;=\u0026thinsp;767), the number of occurrences per reason, ranked from most to least frequent, was as follows: uncleaned accessory canal (n\u0026thinsp;=\u0026thinsp;219), large post (n\u0026thinsp;=\u0026thinsp;170), apical cyst (n\u0026thinsp;=\u0026thinsp;115), excessive calcification (n\u0026thinsp;=\u0026thinsp;83), transportation/perforation (n\u0026thinsp;=\u0026thinsp;55), external root resorption (n\u0026thinsp;=\u0026thinsp;51), unknown etiology (n\u0026thinsp;=\u0026thinsp;36), extrusion (n\u0026thinsp;=\u0026thinsp;29), extraradicular pathosis/actinomycosis (n\u0026thinsp;=\u0026thinsp;23), root fracture (n\u0026thinsp;=\u0026thinsp;22), separated instrument (n\u0026thinsp;=\u0026thinsp;17), failed apical surgery (n\u0026thinsp;=\u0026thinsp;12), endodontic-periodontic infection (n\u0026thinsp;=\u0026thinsp;4), apical cementicle (n\u0026thinsp;=\u0026thinsp;1), and palatal gingival groove (n\u0026thinsp;=\u0026thinsp;0). For the ALT group (n\u0026thinsp;=\u0026thinsp;905), the number of occurrences per reason, ranked from most to least frequent, was as follows: large post (n\u0026thinsp;=\u0026thinsp;202), uncleaned accessory canal (n\u0026thinsp;=\u0026thinsp;160), excessive calcification (n\u0026thinsp;=\u0026thinsp;157), transportation/perforation (n\u0026thinsp;=\u0026thinsp;88), unknown etiology (n\u0026thinsp;=\u0026thinsp;87), apical cyst (n\u0026thinsp;=\u0026thinsp;82), external root resorption (n\u0026thinsp;=\u0026thinsp;54), extrusion (n\u0026thinsp;=\u0026thinsp;33), separated instrument (n\u0026thinsp;=\u0026thinsp;25), extraradicular pathosis/actinomycosis (n\u0026thinsp;=\u0026thinsp;23), failed apical surgery (n\u0026thinsp;=\u0026thinsp;20), root fracture (n\u0026thinsp;=\u0026thinsp;15), apical cementicle (n\u0026thinsp;=\u0026thinsp;3), endodontic-periodontic infection (n\u0026thinsp;=\u0026thinsp;1), and palatal gingival groove (n\u0026thinsp;=\u0026thinsp;1) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCompared with BLT, the ALT period showed a 10.9-percentage-point reduction in surgeries for uncleaned accessory canals (28.6% to 17.7%; 95% CI\u0026thinsp;\u0026minus;\u0026thinsp;14.9 to \u0026minus;\u0026thinsp;6.8; P \u0026lt; .001) and a 6.5-percentage-point increase in surgeries for excessive calcification (10.8% to 17.3%; 95% CI\u0026thinsp;+\u0026thinsp;3.2 to +\u0026thinsp;9.8; P \u0026lt; .001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNegative-control indications showed no material period change (Large posts: 22.3%\u0026rarr;22.3%; Root fracture: 2.2%\u0026rarr;1.7%; both P \u0026gt; .10), supporting the specificity of the uncleaned accessory canal association. ALT remained associated with lower uncleaned accessory canal (adjusted odds ratio\u0026thinsp;\u0026asymp;\u0026thinsp;0.54, P\u0026lt; .001) and higher calcification (adjusted odds ratio\u0026thinsp;\u0026asymp;\u0026thinsp;1.73, P\u0026lt; .01), indicating findings were not explained by surgeon nor site mix.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eEMS is a reliable treatment option with favorable reported success and survival rates [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Indications for EMS have been described in the literature, often focusing on isolated reasons for surgery. However, there is a notable lack of large-scale studies from private practice cohorts that comprehensively rank all indications. We did not enumerate or classify all non-surgical endodontic treatments (~\u0026thinsp;22,000 cases) because doing so would not alter the within-EMS distributions or BLT\u0026ndash;ALT contrasts; to mitigate secular-trend concerns, we included negative-control indications and surgeon/site-adjusted analyses, which yielded consistent results.\u003c/p\u003e \u003cp\u003eIn this study of 1,672 teeth treated with EMS, the most common reasons were uncleaned accessory canals (22.7%), post-related challenges (22.3%), and excessive calcification (14.4%). Large posts present a particular challenge because attempts at removal during retreatment may compromise root integrity and increase the risk of fracture, rendering the tooth non-restorable or prone to reinfection [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Nevertheless, the decision to forgo retreatment and proceed with EMS in these situations remains partly subjective, as the precise risk of fracture during post removal cannot be fully determined as there are other factors such as post size, length, and type (threaded, non-threated, cast, flexi, para, fibre, etc.). Accessory canals\u0026mdash;including delta canals, lateral canals, and isthmi\u0026mdash;are another frequent indication, as they are often difficult to completely debride during non-surgical treatment [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Similarly, excessive calcification, particularly pulp canal obliteration (PCO), poses a significant anatomic barrier that increases the risk of procedural errors such as perforation or instrument separation, making EMS the more predictable treatment option where patency cannot be achieved [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Therefore, there are reasonable explanations why these three indications ranked highest in our cohort.\u003c/p\u003e \u003cp\u003eLess common indications included failed apical surgery (1.9%), endodontic-periodontic infections (0.2%), apical cementicles (0.2%), and palatal gingival groove (\u0026lt;\u0026thinsp;0.1%). Reported causes of failure after initial apical surgery include beveled root resections that expose infected dentinal tubules, leakage or dislodgement of retrofilling materials, and untreated isthmi or accessory canals not addressed during the first procedure. Modern microsurgery techniques and imaging have substantially improved outcomes in these resurgery scenarios, with success rates approaching those of primary microsurgery [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The relatively low proportion of failed apical surgeries observed in this study is encouraging. The concept of \u0026ldquo;modern endodontic microsurgery\u0026rdquo; emerged in the late 1990s and early 2000s [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] and gained broader acceptance in the following decade. Because many of the initial surgeries in this cohort were already performed using modern protocols, this likely contributed to the reduced frequency of failures requiring resurgery.\u003c/p\u003e \u003cp\u003eOur study showed a high frequency of post-related indications in the maxillary arch, particularly maxillary anterior teeth (140/304, 46.1%) and maxillary premolars (120/308, 39.0%). This distribution is consistent with radiographic surveys reporting that posts are placed more often in the maxilla\u0026mdash;especially in maxillary anterior and premolar teeth [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In addition, uncleaned accessory canals were common indications in both maxillary molars (150/559, 26.8%) and mandibular molars (152/353, 43.1%), likely reflecting the high prevalence of isthmus anatomy\u0026mdash;between mesiobuccal-1 and mesiobuccal-2 canals in maxillary molars and between the mesiobuccal and mesiolingual canals in mandibular molars\u0026mdash;which complicates complete debridement during nonsurgical treatment [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo our knowledge, no prior clinical investigations have directly evaluated whether routine use of LAI influences the subsequent incidence of EMS. Existing research has focused primarily on antimicrobial efficacy, smear-layer and debris removal, or short-term clinical outcomes such as postoperative pain, rather than on long-term surgical incidence [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The present study design represents a time-period comparison of surgical incidence rather than a cause-and-effect analysis at the level of individual teeth. Moreover, separated instrument and root fracture\u0026mdash;indications unlikely to be influenced by LAI\u0026mdash;showed no period-related change, supporting the specificity of the uncleaned accessory canal association. The rise in calcification is addressed separately below through a biologic-lag interpretation. Together, these analyses strengthen the overall robustness of our findings. Nevertheless, the results remain associational and warrant confirmation in prospective, tooth-level studies.\u003c/p\u003e \u003cp\u003eThe EdgePRO\u0026trade; system is an Er,Cr:YSGG laser device (2780 nm) designed for intracanal disinfection during root canal treatment with LAI. Its mechanism of action involves rapid heating and vaporization of the irrigant, which generates expanding and collapsing vapor bubbles. The collapse of these bubbles produces acoustic and shock waves that propagate through the canal system, thereby enhancing the removal of microbes and debris from complex root canal anatomy. Among the 15 indications for EMS, the two most likely to be influenced by LAI are primarily, uncleaned accessory canal and secondarily, excessive calcification. The impact of LAI on cleaning accessory anatomy (lateral canals, isthmi, apical ramifications) is supported by multiple studies [\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. While LAI does not directly remove calcified dentin, the enhanced irrigant penetration and hydrodynamic agitation\u0026mdash;together with improved smear-layer/debris removal in constricted canal portions\u0026mdash;may secondarily assist canal negotiation in some cases by revealing micro-anatomic pathways that instruments can subsequently follow. In our study, the proportion of EMS cases performed for uncleaned accessory canals significantly decreased from 28.6% in the BLT group to 17.7% in the ALT group. This reduction suggests that improved intracanal disinfection with LAI may have reduced the need for surgery related to untreated accessory anatomy.\u003c/p\u003e \u003cp\u003eIn contrast, the proportion of EMS performed for excessive calcification increased from 10.8% in the BLT period to 17.3% in the ALT period. This pattern is biologically plausible as LAI does not mechanically remove calcified dentin and has limited direct effect on hard calcific obstructions. The increase, however, is noteworthy. Because pulp-canal calcifications are known to increase with patient age [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], we compared mean and median ages between the BLT and ALT groups to exclude age as a potential confounder for the observed rise in calcification-related EMS. The mean ages (56.5 vs 56.2 years) and median ages (58 years in both groups) were nearly identical, indicating that the age distribution between periods was well-matched and unlikely to explain the differential increase in calcification-related surgical indications. One theory of a likely driver is a lagged rise in pulp canal obliteration (PCO) associated with parafunctional loading during the COVID-19 pandemic. Chronic functional stress has been linked to pulpal calcification [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], and pandemic-era reports document increased cracked teeth consistent with elevated bruxism/clenching and deferred care [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Notably, PCO is typically recognized\u0026thinsp;\u0026ge;\u0026thinsp;1 year after the inciting insult and can progress over multiple years [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Taken together, a biologic lag from the 2020\u0026ndash;2021 pandemic stressor to radiographically evident calcification aligns with the higher ALT frequency. Thus, while LAI may or may not improve nonsurgical debridement in some calcified cases, any potential benefit was likely outweighed by a time-shifted increase in the underlying calcification burden, yielding a greater relative proportion of calcification-related EMS in the ALT period.\u003c/p\u003e \u003cp\u003eIn our study, apical cysts accounted for 12.4% (n\u0026thinsp;=\u0026thinsp;207) of EMS cases. A landmark histopathologic study by Nair et al. examined 256 extracted teeth with persistent apical periodontitis and reported that 15% were periapical cysts, of which 9% were true cysts and 6% were pocket cysts [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. True cysts are self-sustaining lesions that may persist despite adequate nonsurgical treatment, whereas pocket cysts are usually dependent on intraradicular infection and may resolve following conventional root canal therapy. A key limitation of surgical biopsy specimens is that histopathology cannot reliably distinguish between true and pocket cysts, because once the lesion is removed, its anatomic relationship to the root canal system is lost and the pathologist can only evaluate the cystic sac in isolation. Nair\u0026rsquo;s study overcame this limitation by examining extracted teeth with the periapical tissues intact, preserving the continuity between the root canal system and the lesion and allowing for more definitive classification. This diagnostic limitation highlights the complexity of assigning a single definitive etiology to apical cysts and underscores the need to interpret biopsy findings in the broader clinical and radiographic context. Accordingly, the 12.4% incidence of apical cysts in our cohort is likely more comparable to the overall 15% reported by Nair et al. than to the 9% incidence of true cysts alone. The proportion of true apical cysts within our cohort cannot be determined, as histopathologic analysis alone does not allow this distinction.\u003c/p\u003e \u003cp\u003eIn this study, \u0026ldquo;unknown etiology\u0026rdquo; denotes cases in which recognized indications (e.g., extraradicular infection, cystic pathosis, fractures, procedural mishaps, or identifiable untreated anatomy) were not evident, yet symptoms and/or the periapical radiolucency persisted. The literature describes non-infectious mechanisms that can sustain periapical inflammation despite adequate orthograde treatment, notably cholesterol crystal aggregates that elicit a foreign-body giant-cell response and, more rarely, true foreign-body reactions to endogenous or exogenous material (e.g., sealer components). These processes are seldom distinguishable without surgical access and histopathologic examination, which explains why some clinically \u0026ldquo;unknown\u0026rdquo; cases proceed to EMS after conservative options are exhausted [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this large private practice cohort of 1,672 EMS cases, among 15 different possible indications, the most frequent were uncleaned accessory canal, post-related challenges, and excessive calcification. The incidence of uncleaned accessory canal\u0026ndash;related surgeries significantly decreased after the introduction of LAI suggesting improved nonsurgical debridement. In contrast, calcification-related surgeries increased, which may reflect broader etiologic factors such as stress-associated pulpal changes during the COVID-19 pandemic rather than a direct effect of LAI. Failed apical surgery was a rare indication, a finding consistent with improved outcomes associated with modern EMS. Other uncommon indications, such as apical cementicles, palatal gingival groove, and endodontic-periodontic infections, remain infrequent and are unlikely to be influenced by advances in EMS. LAI may indirectly aid nonsurgical debridement of accessory anatomy, and in this study was associated with a lower proportion of EMS for uncleaned accessory canals after adoption. By contrast, calcification-related EMS increased across periods\u0026mdash;likely reflecting a time-lagged rise in COVID-19-related PCO rather than a direct LAI effect. Future tooth-level, prospective studies are needed to establish causality and to clarify whether LAI influences the downstream need for EMS.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval:\u003c/strong\u003e This study received an Institutional Review Board (IRB) waiver of authorization (IRB Study No.: 1401656). All procedures were in accordance with the ethical standards of the 1964 Helsinki Declaration and its later amendments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent:\u003c/strong\u003e Informed consent was waived by the IRB due to the retrospective, de-identified nature of the data.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest:\u003c/strong\u003e The authors declare they have no financial or non-financial interests to disclose.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e No funds, grants, or other support were received.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution:\u003c/strong\u003e [Omitted for blind review].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability:\u003c/strong\u003e De-identified data is available from the corresponding author upon reasonable request\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSetzer FC (2022) Present status and future directions: surgical endodontics. Int Endod J 55:16\u0026ndash;34\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSetzer FC, Walter C, Sharma P, Petkovic-Curcin A, Kim S (2019) Outcome of crown and root resection: a systematic review. J Endod 45:13\u0026ndash;19\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu SY, Cheng HL, Chen YH, Hsieh YD (2021) A long-term treatment outcome of intentional replantation: modern technique, viability and survival. J Endod 47:1234\u0026ndash;1242\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaito T, Ogiso B, Sato T, Takahashi S (2020) Treatment of inflammatory external root resorption with endodontic microsurgery, apicoectomy, and mineral trioxide aggregate restoration: a case report. Jpn Endod Assoc J 41:193\u0026ndash;197\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSetzer FC, Shah SB, Kohli MR, Karabucak B, Kim S (2010) Outcome of endodontic surgery: a meta-analysis\u0026mdash;Part 1: comparison of traditional root-end surgery and endodontic microsurgery. J Endod 36:1757\u0026ndash;1765\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTortorici S, Difalco P, Caradonna L, Tet\u0026egrave; S (2014) Traditional endodontic surgery versus modern technique: a 5-year controlled clinical trial. J Craniofac Surg 25:804\u0026ndash;807\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRicucci D, Siqueira JF Jr, R\u0026ocirc;\u0026ccedil;as IN (2015) Extraradicular infection as the cause of persistent symptoms: a case series. J Endod 41:265\u0026ndash;273\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evon Arx T, H\u0026auml;nni S (2015) Clinical and radiographic assessment of predictors for healing one year after periapical surgery. J Endod 41:589\u0026ndash;598\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTawil PZ, Trope M (2020) The endodontic\u0026ndash;restorative connection: a 15-year systematic review of longitudinal clinical studies. J Endod 46(5S):S2\u0026ndash;S13\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVenskutonis T, Plotino G, Tocci L, Gambarini G (2014) Periapical and endodontic status scale using cone-beam computed tomography. J Endod 40:652\u0026ndash;658\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDiVito E, Peters OA, Peters CI (2014) Effect of laser-activated irrigation on smear layer and debris removal: a scanning electron microscope study. J Endod 40:151\u0026ndash;154\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFahim YZ, Ghali RM, Hashem AA, El-Khodary HM, El-Ashry SH, El-Boghdadi RM (2024) The efficacy of 2780-nm Er,Cr:YSGG and 940-nm diode lasers in root canal disinfection: a randomized clinical trial. Clin Oral Investig 28:3589\u0026ndash;3597\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuter B, Suter V, Lussi A (2019) The effectiveness of laser-activated irrigation compared with conventional irrigation in root canal disinfection: a systematic review. Int Endod J 52:1663\u0026ndash;1675\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeire MA, Van Acker J, Coenye T, De Moor RJ (2024) Principle and antimicrobial efficacy of laser-activated irrigation. Int Endod J 57:1021\u0026ndash;1034\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSabeti M, Kazemipoor M, Karimi A, Asgary S (2025) Comparison of ultrasonically activated irrigation and laser-activated irrigation on postoperative endodontic pain: a randomized clinical trial. J Endod 51:123\u0026ndash;129\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbramovitz I, Better H, Shacham A, Shlomi B, Metzger Z (2002) Case selection for apical surgery: a retrospective evaluation of associated factors and rationale. J Endod 28:527\u0026ndash;530\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRicucci D, Siqueira JF Jr (2010) Fate of the tissue in lateral canals and apical ramifications in response to pathologic conditions and treatment procedures. J Endod 36:1\u0026ndash;15\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVertucci FJ (2005) Root canal morphology and its relationship to endodontic procedures. Endod Top 10:3\u0026ndash;29\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZuolo ML, Ferreira MO, Gutmann JL (2005) Prognosis in periradicular surgery: a meta-analysis. Int Endod J 38:521\u0026ndash;526\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTavares PM, C\u0026acirc;ndido MS, Souza E et al (2020) Surgical management of endodontic failures due to calcifications and technical difficulties. Dent Press Endod 10:52\u0026ndash;61\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim D, Ku H, Nam T, Shin SJ, Kim E (2018) Outcome of endodontic micro-resurgery: a retrospective study with propensity-matched comparison to primary microsurgery. J Endod 44:183\u0026ndash;189\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTaschieri S, Del Fabbro M, Testori T, Francetti L, Weinstein RL (2007) Endodontic reoperation using an endoscope and microsurgical instruments: a prospective clinical study. Int Endod J 40:186\u0026ndash;193\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim S, Rethnam S (1997) Modern endodontic surgery concepts and practice: a review. Dent Clin North Am 41:481\u0026ndash;497\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlmaghrabi J, Alesawi A, Attar E, Alshali S (2022) Radiographic analysis of posts performed by undergraduate dental students: a cross-sectional study. Clin Cosmet Investig Dent 14:37\u0026ndash;43\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKiefner P, Connert T (2017) Treatment of calcified root canals in older people. Gerodontology 34:285\u0026ndash;292\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMalhotra N, Mala K (2013) Calcific metamorphosis: literature review and clinical strategies. Dent Update 40:48\u0026ndash;60\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFarias Z, Sousa J, Faria C, Vieira J, Sobral A, Silveira M (2023) Pulpal calcifications in orthodontically moved teeth: a scoping review. J Clin Exp Dent 15:e773\u0026ndash;e780\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNosrat A, Yu P, Verma P, Dianat O, Wu D, Fouad AF (2022) Was the COVID-19 pandemic associated with an increased rate of cracked teeth? J Endod 48:1241\u0026ndash;1247\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcCabe PS, Dummer PMH (2012) Pulp canal obliteration: an endodontic diagnosis and treatment challenge. Int Endod J 45:177\u0026ndash;197\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndreasen FM, Zhijie Y, Thomsen BL, Andersen PK (1987) Occurrence of pulp canal obliteration after luxation injuries in the permanent dentition. Endod Dent Traumatol 3:103\u0026ndash;115\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNair PN, Pajarola G, Luder HU (1996) Types and incidence of human periapical lesions obtained with extracted teeth. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 81:93\u0026ndash;102\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDuncan HF et al (2023) Treatment of pulpal and apical disease: The European Society of Endodontology (ESE) S3-level clinical practice guideline. Int Endod J 56:239\u0026ndash;314\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbramovitz I, Better H, Shacham A, Shlomi B, Metzger Z (2002) Case selection for apical surgery: a retrospective evaluation of associated factors and rationale. J Endod 28:527\u0026ndash;530\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTorabinejad M, Corr R, Handysides R, Shabahang S (2009) Outcomes of nonsurgical retreatment and endodontic surgery: a systematic review. J Endod 35:930\u0026ndash;937\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"clinical-oral-investigations","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cloi","sideBox":"Learn more about [Clinical Oral Investigations](http://link.springer.com/journal/784)","snPcode":"784","submissionUrl":"https://submission.nature.com/new-submission/784/3","title":"Clinical Oral Investigations","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Endodontic microsurgery (EMS), Laser-activated irrigation (LAI), Er,Cr:YSGG laser, Before-Laser Treatment (BLT), After-Laser Treatment (ALT)","lastPublishedDoi":"10.21203/rs.3.rs-8761178/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8761178/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjectives\u003c/h2\u003e \u003cp\u003eTo characterize indications for endodontic microsurgery (EMS) in a large private practice cohort and compare indication distributions before and after adoption of laser-activated irrigation (LAI) in non-surgical treatment.\u003c/p\u003e\u003ch2\u003eMaterials and Methods\u003c/h2\u003e \u003cp\u003eA retrospective cohort of consecutive EMS cases (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1,672) treated by six endodontists (April 2019\u0026ndash;August 2025) was analyzed. Two periods were prespecified: Before-Laser Treatment (BLT) and After-Laser Treatment (ALT) following implementation of an Er,Cr:YSGG intracanal LAI protocol (August 2022). Each surgical tooth was assigned one or two predefined reasons. Proportions were compared between periods with Pearson\u0026rsquo;s χ\u0026sup2; test and 95% Wald confidence intervals.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe most frequent indications overall were uncleaned accessory canal (22.7%), large post (22.3%) and excessive calcification (14.4%). Surgeries for uncleaned accessory canals decreased from 28.6% (219/767) in BLT to 17.7% (160/905) in ALT (difference\u0026thinsp;\u0026minus;\u0026thinsp;10.9 percentage points; 95% CI\u0026thinsp;\u0026minus;\u0026thinsp;14.9 to \u0026minus;\u0026thinsp;6.8; P \u0026lt; .001). Surgeries for excessive calcification increased from 10.8% (83/767) to 17.3% (157/905) (difference\u0026thinsp;+\u0026thinsp;6.5 percentage points; 95% CI\u0026thinsp;+\u0026thinsp;3.2 to +\u0026thinsp;9.8; P \u0026lt; .001).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eIn this practice-based cohort, LAI adoption was associated with fewer EMS for uncleaned accessory canals. By contrast, calcification-related EMS increased, a pattern compatible with delayed pulp-canal obliteration rather than a direct LAI effect. Causal inference is limited by the time-period design.\u003c/p\u003e\u003ch2\u003eClinical Relevance\u003c/h2\u003e \u003cp\u003eThe adoption of laser-activated irrigation (LAI) in non-surgical endodontics may reduce the necessity for subsequent microsurgery related to uncleaned accessory anatomy. Conversely, clinicians should anticipate a continued or increasing burden of calcification-related cases, potentially influenced by broader factors like pandemic-associated stress.\u003c/p\u003e","manuscriptTitle":"Endodontic Microsurgery in Private Practice: Indications and Time-Period Trends Before and After Adoption of Laser-Activated Irrigation - A Retrospective Cohort Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-19 11:48:22","doi":"10.21203/rs.3.rs-8761178/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-02-17T08:48:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-03T22:22:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-03T22:22:06+00:00","index":"","fulltext":""},{"type":"submitted","content":"Clinical Oral Investigations","date":"2026-02-02T06:05:18+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"clinical-oral-investigations","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cloi","sideBox":"Learn more about [Clinical Oral Investigations](http://link.springer.com/journal/784)","snPcode":"784","submissionUrl":"https://submission.nature.com/new-submission/784/3","title":"Clinical Oral Investigations","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"9c7bb877-00a3-4ef0-b88a-691b4dd1e3b0","owner":[],"postedDate":"February 19th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-19T11:48:22+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-19 11:48:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8761178","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8761178","identity":"rs-8761178","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}