Prevalence of gingival recession and its associated risk factors in the mandibular central incisors of Chinese patients following fixed orthodontic treatment: a retrospective study.

Prevalence of gingival recession and its associated risk factors in the mandibular central incisors of Chinese patients following fixed orthodontic treatment: a retrospective study - PMC Skip to main content An official website of the United States government Here's how you know Here's how you know Official websites use .gov A .gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock ( Lock Locked padlock icon ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites. Search Log in Dashboard Publications Account settings Log out Search… Search NCBI Primary site navigation Search Logged in as: Dashboard Publications Account settings Log in Search PMC Full-Text Archive Search in PMC Journal List User Guide PERMALINK Copy As a library, NLM provides access to scientific literature. 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Learn more: PMC Disclaimer | PMC Copyright Notice BMC Oral Health . 2026 Mar 7;26:670. doi: 10.1186/s12903-026-08013-2 Search in PMC Search in PubMed View in NLM Catalog Add to search Prevalence of gingival recession and its associated risk factors in the mandibular central incisors of Chinese patients following fixed orthodontic treatment: a retrospective study Xiaoyan Li Xiaoyan Li 1 Department of Orthodontics, Hebei Medical University Third Hospital, No. 139 Ziqiang Road, Shijiazhuang, Hebei Province 050051 PR China Find articles by Xiaoyan Li 1, ✉ , Zichuan Zhang Zichuan Zhang 2 Department of Stomatology, Bethune International Peace Hospital, Shijiazhuang, Hebei Province PR China Find articles by Zichuan Zhang 2 , Cheng Jia Cheng Jia 1 Department of Orthodontics, Hebei Medical University Third Hospital, No. 139 Ziqiang Road, Shijiazhuang, Hebei Province 050051 PR China Find articles by Cheng Jia 1 Author information Article notes Copyright and License information 1 Department of Orthodontics, Hebei Medical University Third Hospital, No. 139 Ziqiang Road, Shijiazhuang, Hebei Province 050051 PR China 2 Department of Stomatology, Bethune International Peace Hospital, Shijiazhuang, Hebei Province PR China ✉ Corresponding author. Received 2025 Jun 26; Accepted 2026 Feb 25; Collection date 2026. © The Author(s) 2026 Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/ . PMC Copyright notice PMCID: PMC13081519  PMID: 41795082 Abstract Objectives This retrospective study was designed to describe and compare the prevalence and severity of gingival recession (GR) in the mandibular central incisor region. Additionally, it sought to identify potential risk factors associated with GR. Methods According to the selection criteria, a total 286 Chinese patients who had completed fixed orthodontic treatment between January 2019 to March 2024, 123 males (43.0%) and 163 females (57.0%), were included in the study. The following parameters were assessed: gingival recession depth (GRD), gingival biotype (GBT), keratinized gingival width (KGW), incisor-mandibular plane angle (IMPA), and labial alveolar bone thickness at the alveolar ridge crest, middle, and apical region (LBT-crest, LBT-mid, LBT-apex). Data were obtained anonymously from the pre-treatment (T0) and post-treatment (T1) archival records. Based on the difference in IMPA between T1 and T0, subjects were categorized into protrusion and retrusion groups. Statistical analyses were performed using the independent sample t-test, Mann-Whitney U test, and Pearson’s chi-square test. Logistic regression analyses identified the risk factors for GR. Receiver operating characteristic (ROC) curves were employed to determine the optimal cut-off values for the high-risk factors of GR. Results There were 75 subjects (26.2%) with GR and 211 participants (73.8%) without GR at T1, all of whom had ideal gingival margin positions at T0. The protrusion group had a significantly higher GRD (0.31 ± 0.52 mm) than the retrusion group (0.06 ± 0.12 mm, P < 0.05). However, no significant difference in the occurrence rate of GR was observed between the two groups ( P > 0.05). Compared to GR patients, non-GR subjects exhibited statistically lower ∆IMPA values, higher KGW, LBT-crest, LBT-mid, and LBT-apex. Furthermore, statistically significant associations was found between the occurrence of GR following orthodontic treatment and GBT, KGW and LBT-crest. The optimal cut-off values for KGW (T0), KGW (T1), LBT-crest (T0), and LBT-crest (T1) were 2.70 mm, 2.23 mm, 0.72 mm, and 0.73 mm, respectively. Conclusions Thin GBT, narrow KGW, and thin LBT-crest may increase the risk of GR. A minimum LBT-crest of 0.72 mm and KGW of 2.70 mm prior to orthodontic treatment may effectively prevent the occurrence of GR. Keywords: Orthodontic treatment, Gingival recession, Alveolar Bone Loss, Retrospective studies, ROC curve Background Gingival recession(GR), a disturbing and prevalent periodontal disease, is described as the apical displacement of the marginal gingiva relative to the cementum-enamel junction(CEJ) [ 1 , 2 ]. According to reports, 50% of people aged 18–64 years and 88% of people aged 65 years or older had at least one recession site, which is more common in the mandible than the maxilla and on labial surfaces rather than lingual/palatal surfaces [ 2 ]. Romandini et al. also found that over 90% of American adults had mid-buccal GR, with the majority of them occurring in the aesthetic zone [ 3 ]. Under the condition of attachment loss and root surface exposure, patients may develop signs and symptoms including dental plaque accumulation, gingival inflammation, unaesthetic appearance, dentin hypersensitivity, and carious or noncarious cervical lesions, seriously affecting the patients’ daily life [ 2 – 4 ]. Although there is no consensus on the pathogenesis of GR, several predisposing and precipitating factors have been suggested according to previous literatures [ 3 , 4 ], for example, poor oral hygiene with dental plaque accumulation, gingival inflammation and periodontal disease, traumatic mechanical toothbrushing, abnormal tooth position, aberrant frenal attachment, absence of attached gingiva, thin gingiva biotype, dental malocclusion, occlusal trauma, bone dehiscences and bone fenestration, as well as advanced age and smoking. In addition, orthodontic treatment had also been considered to be an iatrogenic factor related to GR, which had been widely discussed and remained controversial until today [ 5 , 6 ]. A recent systematic review indicated that mandibular incisor teeth were the most susceptible to GR [ 7 ], which might be due to thin or nonexistent alveolar bone covering the labial surface of their roots and small or absent keratinized gingiva [ 8 , 9 ]. The potential mechanism is that excessive labially tipping movement or bodily movement with uncontrolled orthodontic forces may cause roots to migrate close to or through the labial alveolar cortical plates, resulting in bone dehiscence or fenestration [ 9 – 11 ]. In the absence of appropriate alveolar bone support, the marginal gingiva may move apically, exposing the root surface. It had been demonstrated that following fixed orthodontic treatment, the labial gingival recession depth (GRD) of the anterior teeth increased by approximately 0.2 mm for per 1° increase in inclination [ 12 ]. Despite extensive research focusing on the correlation between labial movement of mandibular incisor teeth during orthodontic treatment and GR, there is a scarcity of literature investigating the relationship between lingual movement of mandibular incisors and GR, particularly among Chinese individuals. Therefore, the objective of the current retrospective study was to describe and compare the prevalence and severity of GR in the mandibular central incisor region with labial or lingual tooth movement following fixed orthodontic treatment, as well as identify potential risk factors associated with GR. This study’s findings may be helpful in providing insightful information about prevention and treatment strategies for GR. Methods Study design This retrospective study with a non-probabilistic sampling was designed and performed in compliance with the World Medical Association Declaration of Helsinki and was approved by the Ethics Committee of Hebei Medical University Third Hospital (Project No.W2022-070-1). After receiving a detailed explanation of the study’s objectives and methods, all candidates or their guardians signed an informed consent form for the anonymous use of their archival records. Sample size estimation The sample size calculation was based on a two-sided hypothesis, with a significance level (α) of 5% and a test power (1-β) of 90%. The Z α/2 and Z β values were 1.96 and 1.28, respectively, corresponding to a 95% confidence interval. Based on our pilot study findings, we estimated a 30% prevalence rate (P) of GR in the lower central incisors, with a permissible error (δ) of 10%. To account for a potential dropout rate, we increased the theoretical sample size by 30%, resulting in a final sample size of 286 participants. The sample size was calculated according to the following formula: Inclusion and exclusion criteria The study sample were selected from the pool of Chinese patients who had completed their orthodontic treatment with fixed appliances from January 2019 to March 2024 at the Department of Orthodontics of Hebei Medical University Third Hospital. The inclusion criteria were as follows: (1) patients having received straight-wire orthodontic treatment with prescription Damon Self-Ligating brackets across all the orthodontic procedures; (2) patients aged 13–24 years old at the beginning of orthodontic treatment; (3) patients with no missing teeth and no obvious abnormal tooth morphology; (4) patients with healthy periodontium, without signs of hypertrophied or inflamed gingiva in the mandibular incisors in the initial or final intraoral photographs; (5) patients with no gingival recession or restorations in the region of the lower incisors prior to orthodontic treatment; (6) patients with permanent teeth erupted up to first molars prior to orthodontic treatment and none of the four lower permanent incisors extracted before and during treatment; (7) patients having complete sets of high-quality pre- and post-treatment clinical records, including intraoral photographs, lateral cephalometric radiographs, and dental plaster models; The exclusion criteria were as follows: (1) patients with congenital craniofacial anomalies (e.g. cleft lip and palate); (2) patients with bad habits (e.g. smoking, alcoholism, or intravenous drug abuse); (3) patients in pregnancy or lactation; (4) patients having taken any antibiotics within the past 6 months; (5) patients with a history of maxillofacial or dental trauma, periodontal surgical or orthodontic treatment in the lower anterior teeth; (6) patients with a history orthognathic surgery or in a treatment plan including complex surgical procedures in the anterior area of mandible; (7) patients with systemic diseases (e.g. hypertension, hyperthyroidism or diabetes) or taking medications that could affect the gingival condition and periodontal status. Observation indicators and evaluation methods To ensure blinding, all the archival records of patients were anonymized and assigned unique identification numbers. The primary materials used to evaluate GR included pre-treatment (T0) and post-treatment (T1) intraoral photographs, lateral cephalometric radiographs, and dental plaster models. Information pertaining to gender, age, Angle classification, treatment duration, treatment type (extraction or non-extraction) were also extracted from the patients’ clinical records. All patients received oral hygiene instructions (such as toothbrushing with Charter’s technique at least three times per day, daily flossing, water flosser, and interdental brush) before orthodontic treatment and during follow-up visits to minimize the risk of gingivitis. If patients experienced symptoms such as swollen or red gums, or bleeding while brushing their teeth, they should rinse their mouths with a 0.2% chlorhexidine solution. Rinse with 10 mL of solution for 1 min, three times a day, for a total duration of one week. The clinical mesiodistal width of the dental crown was measured at the incisal edge of the maxillary central incisor in the plaster model, which was used to calculate the actual gingival recession depth (GRD) and keratinized gingival width (KGW) observed in the intraoral photographs. All model measurements were performed using a digital caliper with an accuracy of 0.01 mm (Hangzhou Hantoo Enterprises, Hangzhou, China). To minimize inaccuracy, each measurement was repeatedly performed three times at 24-hour intervals and the mean value was used as the final result. After importing the pre- and post-treatment frontal intraoral photographs into Photoshop software (version 2020, Adobe Systems Incorporated, San Jose, CA, USA), both of GRD and KGW were assessed and calculated (Fig. 1 ). The position of the gingival margin on the labial surface of the mandibular central incisor was defined as the distance between the lowest point of the gingival margin and the CEJ. If the CEJ was not visible, a value of 0 mm was recorded. The GRD was calculated by subtracting the pre-treatment value from the post-treatment value. A positive GRD value indicated GR, and the mandibular central incisor with greater GRD was selected for study. KGW was defined as the distance between the most apical point of the gingival margin and the mucogingival junction on the mid-labial aspect of the tooth. The results of them were recorded to the nearest 0.01 mm. Due to different magnification of each intraoral photograph, the values of GRD and KGW need to be corrected according to the following equation : Fig. 1. Open in a new tab Intraoral photographs of mandibular central incisors used to evaluate GRD and KGW. GRD: Red lines; KGW: Black lines; T0: Pre-treatment; T1: Post-treatment Gingival biotype (GBT) was assessed based on visual inspection of tooth crown morphology and capillary transparency in intraoral photographs [ 13 ]. The gingival tissue was classified as thin if it exhibited triangular crowns, interproximal contacts near the incisal edge, and clearly visible contours of the tooth root and capillary network. Conversely, it was classified as thick if it exhibited square-shaped crowns, larger interproximal contacts located more apically, and invisible contours of the tooth root and capillary network. The GBT of the mandibular central incisor with greater GRD was recorded in this research. The inclination and position of mandibular central incisors were evaluated using lateral cephalometric radiographs obtained at T0 and T1. After importing these cephalograms into Winceph version 9.0 software (Rise Corporation, Sakuragaok acho, Shibuy aku, Tokyo, Japan), the following landmarks were identified and traced: incisal edge (IE) and apex (AP) of the mandibular central incisor, menton (the lowest point of the mandibular symphysis, Me), and gonion (the most inferior posterior point of the mandibular angle, Go). The line connecting IE and AP was considered as the long axis of the lower central incisor, and the line connecting Me and Go represented the mandibular plane. The incisor-mandibular plane angle (IMPA) was defined as the angle between the long axis of the lower central incisor and the mandibular plane, indicating the inclination of this tooth relative to the mandible plane. The change in inclination of the lower central incisors during orthodontic treatment was determined by calculating the difference between the IMPA at T1 and T0. A positive ∆IMPA value indicated labial inclination (proclination), while a negative value indicated lingual inclination (retroclination). In addition to the IMPA, the labial alveolar bone thickness (LBT) in different regions was also assessed using the software (Fig. 2 ). The detailed measurement items were as follows: (1) LBT-crest: the distance from the labial root surface to the cortical plate at the alveolar ridge crest; (2) LBT-mid: the distance from the labial root surface to the cortical plate at the middle root area; (3) LBT-apex: the distance from the labial root surface to the cortical plate at the apical region. All data were recorded to the nearest 0.01° or 0.01 mm. Participants were categorized into protrusion or retrusion group based on which way the mandibular central incisor moved or inclined after receiving orthodontic treatment. Fig. 2. Open in a new tab Lateral cephalometric radiographs with landmarks used to assess the IMPA, LBT-crest, LBT-mid, and LBT-apex All measurements were conducted by a single calibrated orthodontist to minimize potential bias. In addition, twenty subjects from each group were randomly selected, and all the variables (GRD, IMPA, KGW, LBT-crest, LBT-mid, LBT-apex) were measured twice by the same examiner within 30 days. To determine the intra-observer reliability, the intraclass correlation coefficient (ICC) was calculated. The value of ICC ranged from 0.98 to 0.87, indicating excellent reliability. As a dichotomous variable, the GBT of the twenty individuals was also evaluated twice within a 30-day interval, and the results showed good consistency (kappa = 0.91). Statistical analysis All descriptive and comparative statistical analyses of the aforementioned variables were performed using the SPSS software package (Statistical Package for Social Sciences, version 25.0, SPSS Inc., Chicago, IL, USA). The normal distribution assumption was confirmed with the Kolmogorov-Smirnov test. Descriptive statistics were presented as mean ± standard deviation for normally distributed quantitative variables and median (Interquartile Range, IQR) for skewed distributions. These were statistically compared using independent sample t-tests and Mann-Whitney U tests, respectively. Categorical variables or nominal variables were expressed as frequencies or percentages and compared through Pearson’s chi-square test. Univariate and multivariate logistic regression analyses were carried out to identify risk factors for GR, with an odds ratio (OR) and 95% confidence intervals (CI). In the models, the absence or presence of GR per patient, the GBT (thick or thin), and treatment type (extraction or non-extraction) were converted to binary variables. Potential confounding variables included gender, age, and Angle classification. Receiver operating characteristic (ROC) analysis was performed to evaluate the predictive capacities of high-risk predictors for GR, based on logistic regression results, using the area under the ROC curve (AUC) and determining the optimal cut-off value. A two-sided P -value of less than 0.05 was considered to be statistically significant. Results This study enrolled 286 Chinese patients who completed orthodontic treatment, comprising 123 males (43.0%) and 163 females (57.0%). Among the participants, 153 individuals were under 18 years of age (53.5%), while 133 were 18 years or older (46.5%). The median age was 18 years, with an age range of 13 to 24 years. A total of 150 patients completed orthodontic treatment without extractions. Additionally, 84 patients underwent bilateral extraction of mandibular first premolars, 29 patients underwent bilateral extraction of mandibular second premolars, and 23 patients had extraction of the first premolar on one side along with the second premolar on the contralateral side, based on varying occlusal relationships of the first molars. The distributions of gender, age, GBT, Angle classification, and duration of treatment were all well-matched between the two groups ( P > 0.05). In contrast, the percentage of extraction versus non-extraction treatments varied significantly across the two groups ( P < 0.05). None of the included patients had GR prior to undergoing orthodontic treatment, but 75 patients (26.2%) with GR were discovered following orthodontic therapy. No significant difference in the occurrence rate of GR was observed between the two groups ( P > 0.05) (Table 1 ). The GRD in the protrusion group was 0.31 ± 0.52 mm, significantly higher than that of the retrusion group (0.06 ± 0.12 mm, P < 0.05). Additionally, patients with GR in the protrusion group exhibited a statistically greater GRD (1.06 ± 0.32 mm) compared to those with GR in the retrusion group (0.26 ± 0.10 mm, P < 0.05). Table 1. Basic characteristics of the study population Total ( N = 286) Protrusion group ( N = 145) Retrusion group ( N = 141) P Gender Male 123 65 58 0.528 Female 163 80 83 Angle classification Class 1 166 81 85 0.449 Class 2 120 64 56 Treatment type Extraction 136 24 112 0.000 Non-extraction 150 121 29 Gingival biotype (GBT) Thick 183 97 86 0.298 Thin 103 48 55 Gingival Recession (GR) Absence 211 102 109 0.181 Presence 75 43 32 Age(Median(IQR), years) Pre-treatment (T0) 18 (16,21) 18 (15,21) 0.674 Post-treatment (T1) 20 (18,24) 21 (18,24) 0.729 Duration of treatment (Median(IQR), months) 22 (19,29) 26 (23,29) 0.054 Open in a new tab IQR Interquartile Range Table 2 summarizes the number of patients with thick and thin GBT, along with their tooth extraction status. The significantly different distribution of GBT indicated a potential association between GBT and GR. In contrast, tooth extraction did not appear to be a predisposing factor for GR. Table 2. Distribution of gingival biotype (GBT) and treatment type in mandibular central incisors Protrusion group ( N = 145) Retrusion group ( N = 141) Absence of GR Presence of GR P Absence of GR Presence of GR P GBT Thick 76 21 0.003 78 8 0.000 Thin 26 22 31 24 Treatment type Extraction 18 6 0.585 87 25 0.835 Non-extraction 84 37 22 7 Open in a new tab Table 3 shows that patients with GR had a significantly higher ∆IMPA value compared to those without GR, regardless of whether they were in the protrusion or retrusion group. In addition, patients without GR exhibited significantly higher KGW, LBT-crest, LBT-mid, and LBT-apex compared to those with GR. In the protrusion group, KGW and LBT-crest were significantly higher at T0 compared to T1, while LBT-apex was lower at T0 in both patients with and without GR. No significant differences were observed in LBT-mid between T0 and T1 for either GR or non-GR patients. In the retrusion group, KGW was significantly higher at T0 compared to T1 for both patients with and without GR. However, no significant differences were found in LBT-crest and LBT-mid between T0 and T1 for either GR or non-GR patients. Additionally, no significant difference in LBT-apex was found in patients without GR between T0 and T1. Conversely, patients with GR exhibited significantly higher LBT-apex at T0 compared to T1. Table 3. Descriptive statistics of potential predictors in the study population GR Protrusion group ( N = 145) Retrusion group ( N = 141) T0 T1 P T0 T1 P ∆IMPA (°) Absence( N = 211) 2.50 ± 1.49 — -3.75 ± 3.56 — Presence( N = 75) 4.87 ± 1.74 — -5.82 ± 4.57 — P 0.000 0.008 KGW (mm) Absence( N = 211) 3.42 ± 0.46 3.28 ± 0.47 0.000 3.39 ± 0.53 3.27 ± 0.45 0.000 Presence( N = 75) 2.04 ± 0.38 1.72 ± 0.40 0.000 2.01 ± 0.43 1.76 ± 0.43 0.000 P 0.000 0.000 0.000 0.000 LBT-crest (mm) Absence( N = 211) 0.96 ± 0.29 0.82 ± 0.27 0.000 0.98 ± 0.25 1.00 ± 0.28 0.058 Presence( N = 75) 0.66 ± 0.22 0.45 ± 0.22 0.000 0.40 ± 0.18 0.37 ± 0.13 0.104 P 0.000 0.000 0.000 0.000 LBT-mid (mm) Absence( N = 211) 1.35 ± 0.42 1.43 ± 0.47 0.093 1.47 ± 0.38 1.49 ± 0.41 0.365 Presence( N = 75) 1.00 ± 0.30 0.96 ± 0.36 0.354 0.84 ± 0.27 0.90 ± 0.29 0.122 P 0.000 0.000 0.000 0.000 LBT-apex (mm) Absence( N = 211) 3.81 ± 0.66 4.92 ± 0.78 0.000 3.52 ± 0.77 3.45 ± 0.86 0.102 Presence( N = 75) 3.08 ± 0.50 3.84 ± 0.55 0.000 2.77 ± 0.72 2.62 ± 0.77 0.000 P 0.000 0.000 0.000 0.000 Open in a new tab Univariate and multivariate logistic regression analyses were performed by using the occurrence of GR following orthodontic treatment as the dependent variable (0 for without GR, 1 for with GR). The independent variables included gender, age, GBT, Angle classification, treatment type, duration of orthodontic treatment, the ∆IMPA between T0 and T1, as well as the values of KGW, LBT-crest, LBT-mid, and LBT-apex at both T0 and T1. Pre- and post- treatment ages of patients were transformed into categorical variables in the regression analyses, with a cutoff value of 18 years (0 for under 18 years, 1 for above 18 years). Furthermore, gender, GBT, Angle classification, and treatment type were also recorded as dichotomous variables. As presented in Table 4 , the univariate analysis revealed significant associations between the occurrence of GR after orthodontic treatment and GBT, KGW (at T0 and T1), and LBT-crest (at T0 and T1). This suggested that patients with thin GBT, narrow KGW, and thin LBT-crest prior to treatment were at a higher risk of developing GR. No statistically significant correlations were established between other factors and the incidence of GR. After adjusting for several potential confounders, including gender, age, and Angle classification, variables with P < 0.05 in univariate analyses were included in the multivariate model. Furthermore, the multivariate analysis yielded results consistent with those of the univariate analysis. Table 4. Logistic regression models demonstrating the relationships of potential predictors with gingival recession Univariate model Multivariate model COR 95%CI P AOR 95%CI P Gender 1.334 0.747 ~ 2.381 0.330 - - - Age (T0) 0.566 0.265 ~ 1.209 0.142 - - - Age (T1) 0.595 0.242 ~ 1.462 0.258 - - - Angle classification 1.610 0.764 ~ 3.390 0.211 - - - Treatment type 0.823 0.341 ~ 1.987 0.665 - - - Duration of treatment 1.054 0.989 ~ 1.123 0.106 - - - GBT 0.212 0.118 ~ 0.381 0.000 0.208 0.115 ~ 0.377 0.000 ∆IMPA 1.189 0.952 ~ 1.483 0.126 - - - KGW (T0) 0.003 0.000 ~ 0.021 0.000 4249.966 93.490 ~ 193199.966 0.000 LBT-crest (T0) 0.006 0.000 ~ 0.407 0.017 1327.077 2.843 ~ 619493.410 0.022 LBT-mid (T0) 0.634 0.039 ~ 10.386 0.749 - - - LBT-apex (T0) 0.577 0.206 ~ 1.614 0.295 - - - KGW (T1) 0.003 0.000 ~ 0.029 0.000 1804.889 50.576 ~ 64410.800 0.000 LBT-crest (T1) 0.002 0.000 ~ 0.435 0.023 7134.363 2.027 ~ 25109475.567 0.033 LBT-mid (T1) 0.257 0.017 ~ 3.971 0.330 - - - LBT-apex (T1) 0.614 0.251 ~ 1.504 0.286 - - - Open in a new tab COR Crude odds ratio, AOR Adjusted odds ratio, CI Confidence intervals ROC analysis was performed for predictors with a P -value < 0.05 in the logistic regression analysis, as presented in Table 5 . All variables were found to be significant predictors of GR ( P < 0.05). The AUC values for KGW (T0), KGW (T1), LBT-crest (T0), and LBT-crest (T1) were 0.977, 0.985, 0.868, and 0.920, respectively, indicating that these predictors demonstrated excellent accuracy in predicting GR. All predictors demonstrated high sensitivity and specificity based on the cut-off values. The ROC curves are illustrated in Fig. 3 . Table 5. ROC analysis of high-risk predictors for gingival recession Cut-Off Value Sensitivity (%) Specificity (%) AUC (95% CI) P KGW (T0) 2.70 mm 92.9 94.7 0.977 (0.956 ~ 0.998) 0.000 KGW (T1) 2.23 mm 99.1 93.3 0.985 (0.969 ~ 1.000) 0.000 LBT-crest (T0) 0.72 mm 82.9 73.3 0.868 (0.822 ~ 0.913) 0.000 LBT-crest (T1) 0.73 mm 76.8 90.7 0.920 (0.888 ~ 0.951) 0.000 Open in a new tab ROC Receiver Operating Characteristic, AUC Area Under the ROC Curve Fig. 3. Open in a new tab ROC curves of KGW (T0, T1) and LBT-crest (T0, T1) for predicting GR Discussion The increasing public interest in facial aesthetics has led to a higher demand for orthodontic treatment, which can enhance both masticatory function and oral health. Concurrently, gingival recession (GR), a potential adverse effect of orthodontic tooth movement, has garnered significant attention. In our study, the prevalence of GR after orthodontic treatment was 26.2%, with an average GRD of 0.31 mm in the protrusion group and 0.06 mm in the retrusion group. Compared to GR patients, non-GR patients exhibited significantly lower ∆IMPA values and higher KGW, LBT-crest, LBT-mid, and LBT-apex. Additionally, only GBT, KGW, and LBT-crest were significantly associated with the occurrence of GR following orthodontic treatment according to the results of the univariate and multivariate logistic regression analyses. This indicated that patients with thin GBT, narrow KGW, and thin LBT-crest prior to treatment are at a higher risk of developing GR. The archival records of the patients included in this study contained only lateral cephalograms and did not include cone-beam computed tomography (CBCT) images. In the lateral cephalometric radiograph, the central incisors are the most anterior teeth in the arch, which facilitates accurate measurement of their IMPA and LBT. The lingual surfaces of the mandibular anterior teeth are adjacent to the duct openings of the sublingual and submandibular glands. These surfaces are difficult to clean and susceptible to dental calculus formation, potentially leading to gingivitis and GR. This condition may affect the final research outcomes. Consequently, this study focused solely on evaluating the prevalence and severity of GR on the labial surfaces of the mandibular central incisors. There is a consensus in the literature that the ideal method to measure GRD is direct measurement in the mouth [ 8 , 9 ]. However, because the present study was a retrospective investigation, relevant information was not included in the patients’ medical records. Previous research primarily employed plaster models or intraoral photographs to evaluate GR [ 8 , 9 , 14 – 16 ]. The use of plaster models may be problematic due to the inappropriate expansion rate of impression materials and inadequate preservation environments, which may lead to inaccurate measurements. In addition, plaster models are prone to wear and fragility, resulting in many unreadable and missing teeth [ 17 ]. Even though there may be measurement bias due to varying orientations of intraoral photographs, this method is still considered preferable for assessing GR. In our study, all intraoral photographs were carefully selected to ensure consistent orientation, complete exposure of the gingival margin of the mandibular incisors, and the absence of inflammation and gingival edema. The literature consensus indicates that the development of GR is associated with individual age, with its prevalence and severity increasing as age advances [ 9 – 11 , 14 ]. However, the effect of gender on GR still remains controversial [ 11 , 14 , 17 , 18 ]. Renkema et al. reported that neither gender nor extraction treatment was associated with the development of GR in the mandibular central incisors [ 11 ]. In contrast, Pernet et al. [ 14 ] and Mazurova et al. [ 18 ] demonstrated that the frequency of GR was higher in males than in females, opposing the findings of Ramos et al. [ 17 ]. These divergent results may be explained by various factors, including oral hygiene quality, smoking habits, and the force applied to periodontal tissues during tooth brushing [ 17 ]. Therefore, the two groups in this study were made as compatible and similar as possible regarding age, gender, treatment duration, initial Angle classification of malocclusion, and GBT, which may be crucial for the development of GR following orthodontic treatment. Tooth extraction is commonly performed in orthodontic treatment to create additional space for crowded dentition, typically accompanied by lingual movement of the anterior teeth. Consequently, the retrusion group included more participants who underwent tooth extraction compared to the protrusion group in the present study. Findings from Li et al. [ 16 ] and Ji et al. [ 19 ] indicated that the prevalence of GR after orthodontic treatment was higher in patients who had undergone tooth extraction compared to those who did not. This may be due to a greater range of tooth movement, a longer treatment duration, and challenges in maintaining oral hygiene. However, there was no significant difference in the incidence rate of GR between the two groups in this study, which aligns with the findings of Renkema et al. [ 11 ]. This may be explained by the fact that when soft and hard tissues surrounding the teeth are subjected to external forces, whether tension or pressure, stress absorption may occur, potentially leading to GR. To the best of our knowledge, differing conclusions remain regarding the correlation between incisor retroclination and the development of GR. Both Lee et al. [ 12 ] and Kalina et al. [ 20 ] reported a significantly greater reduction in GRD in patients with retroclined incisors compared to those with proclined teeth. Saab et al. [ 9 ] also suggested that incisor retraction may reduce the risk of developing GR. This may be attributed to incisor retraction increasing labial alveolar bone height and KGW, potentially leading to the migration of the gingival edge towards the crown. However, Vasconcelos et al. [ 21 ] thought that incisor retroclination was more strongly correlated with GR than the proclination of lower incisors. And Chen et al. [ 22 ] observed significant GR in the lower anterior region following the retraction of mandibular incisors in patients with narrow alveolar bone plates and a thin phenotype. In our study, no significant difference was found in the occurrence rate of GR between the two groups. Although the average GRD of patients in the protrusion group was significantly greater than that in the retrusion group, both of them remained below 0.5 mm. The minimal clinically important difference (MCID) is a crucial indicator for assessing the clinical significance of study results. It represents the smallest change in a clinical outcome that a patient considers important and can be calculated using distribution-based methods, anchor-based methods, and the Delphi method [ 23 ]. Currently, there is no established MCID value for GR. Given that the GR values in this study were very small and did not affect the patients’ appearance or cause discomfort, the authors concluded that the difference in GRD values between the two groups lacks clinical significance. Additionally, the average ∆IMPA value in patients with GR was significantly higher than in those without GR, regardless of whether they belonged to the protrusion or retrusion group. However, ∆IMPA was not significantly associated with the occurrence of GR following orthodontic treatment according to the result of the univariate logistic regression analyses, which aligns with the findings of Gül et al. [ 24 ]. This suggests that the occurrence of GR may not be related to the direction of movement of the lower anterior teeth. Gingival biotype (GBT) can be classified into two categories: thin fan-shaped gingiva and thick platform gingiva, depending on factors such as gingival margin, keratinized gingiva width, crown shape, gingiva papilla height, and the contact points of adjacent teeth [ 19 ]. The thin biotype is characterized by delicate soft tissue with minimal attachment and a thickness of less than 1.5 mm, whereas the thick biotype features dense, fibrotic soft tissue with substantial attachment and a thickness of 2 mm or greater [ 12 ]. Various methods have been introduced to evaluate GBT, including visual inspection, probe transparency, transgingival probing, ultrasonic devices, and cone beam computed tomography (CBCT) [ 6 , 12 , 13 ]. In this study, visual inspection was employed to identify the GBT of the mandibular central incisors using frontal intraoral photographs. Although visual inspection is not an ideal method due to its uncertain accuracy and repeatability, it remains the only feasible and satisfactory approach for the retrospective design. Until now, the role of GBT in the development of GR is still a debatable topic [ 5 , 6 , 12 , 13 ]. Both Alsalhi et al. [ 6 ] and Lee et al. [ 12 ] found no significant correlation between GBT and GR. However, Ashfaq et al. [ 5 ] and Antanavičienė et al. [ 13 ] concluded that a thin GBT may increase the risk of buccal GR during orthodontic treatment, aligning with our findings. Recently, Alkan et al. [ 25 ] found no significant relationship between sagittal tooth movement (STM) and changes in KGW, which is consistent with our findings. In the present study, the KGW was significantly higher at T0 than at T1 for both GR and non-GR patients, irrespective of the direction of orthodontic tooth movement. Fleming et al. [ 26 ] suggested that a keratinized attached gingival tissue width of just 1 mm may be adequate to withstand orthodontic stresses. They recommended performing periodontal surgical procedures prior to orthodontic treatment, especially in cases of recession defects with minimal attached gingival width (< 1 mm). In contrast, Sawan NM et al. [ 27 ] proposed that teeth with a KGW of ≥ 2 mm can withstand orthodontic forces and prevent GR. In our study, the mean KGW of patients without GR was greater than 3 mm at both T0 and T1, significantly exceeding that of GR patients in both the protrusion and retrusion groups. The ROC analysis indicated that the optimal cut-off values of KGW at T0 and T1 were 2.70 mm and 2.23 mm, respectively, demonstrating excellent AUC values. These results were aligned with the findings of Sawan NM et al. [ 27 ]. As a supporting tissue of the gingiva, the thickness of the alveolar bone is likely closely related to the development of GR. In our study, non-GR patients exhibited significantly higher LBT-crest, LBT-mid, and LBT-apex compared to GR patients in both protrusion and retrusion groups. In contrast, Pernet et al. [ 14 ] found no significant association between the width of the alveolar bone process at the crest, middle, or apex and the onset of buccal or lingual recessions. This may be attributed to the measurement of alveolar process thickness in their study, which included the lingual and labial gingiva, alveolar bone, periodontal membrane, and root. It is known that one side of the alveolar bone becomes thinner due to pressure, while the opposite side thickens due to tension during STM. Therefore, the total thickness of both the labial and lingual gingiva, as well as the alveolar bone, remains constant before and after orthodontic treatment. Additionally, Lee et al. [ 12 ] suggested that initial labial alveolar bone thickness did not affect labial GR. In their study, alveolar bone thickness was measured at 4 mm below the CEJ, similar to the intermediate positions of LBT-crest and LBT-mid in our study. Logistic regression analysis revealed a significant relationship between LBT-crest and the occurrence of GR following orthodontic treatment, while no statistically significant correlation was found between LBT-mid and GR. According to the results of the ROC analysis, a minimum LBT-crest of 0.72 mm may be adequate to withstand orthodontic stresses and prevent the occurrence of GR. Recently, Küçükoğlu et al. [ 28 ] evaluated alveolar trabecular changes in the mandibular anterior and premolar regions, both with and without GR, during the post-orthodontic retention period. They employed fractal dimension (FD) analysis to quantitatively assess trabecular changes in alveolar bone by capturing the self-similarity of gray value variations. The results indicated a significant decrease in FD values in the mandibular anterior region with GR, while changes in the premolar region were minimal and not statistically significant. FD analysis is a well-established method for detecting subtle changes in bone microarchitecture, including reductions in internal trabecular structure, reshaping of connecting trabeculae, and thinning of the cortical bone. Therefore, FD analysis should be utilized in future research to evaluate subtle changes in alveolar bone microarchitecture during orthodontic treatment and their potential relationship with GR. Orthodontic tipping movements are more prevalent than translational movements in anterior teeth, regardless of whether they move labially or lingually. During tipping movements, the crown moves in the opposite direction to the root, with the rotation centered in the middle of the root. Consequently, no significant difference in LBT-mid was observed between T0 and T1 in both the protrusion and retrusion groups. In the protrusion group, LBT-crest was larger and LBT-apex was lower at T0 compared to T1. This could be explained that the root cervical region approached the labial cortical bone, leading to bone absorption and thinning due to compressive stress. Conversely, the root apex moved away from the labial cortical bone, resulting in bone growth and thickening due to the tensile stress. Nonetheless, no significant differences in LBT-crest were observed between T0 and T1 in the retrusion group. This may be attributed to stress resorption of the labial alveolar bone caused by external forces, while the pulling effect of the periodontium contributed to an increase in the thickness of the labial alveolar bone. There were several limitations involved in the current investigation, which may have contributed to potential deviations within the research findings. Firstly, the retrospective design with a non-probabilistic sampling of this study lacked randomization and blinding, potentially increasing the risk of bias. Secondly, all participants were drawn from a single medical center, which may have skewed the study results and restricted the generalizability of these findings. Thirdly, relevant data were collected only from initial and final tooth positions, without progress records of tooth movement during treatment, limiting the assessment of the total displacement. Fourthly, while a calibration formula was provided for intraoral photograph measurements, such as GRD and KGW, it relies entirely on plaster models. Consequently, the drawbacks of plaster models, including inappropriate expansion rates, susceptibility to wear and fragility, may introduce potential bias in the final results. Fifthly, although the intraclass correlation coefficient (ICC) for the variables (GRD, IMPA, KGW, LBT-crest, LBT-mid, and LBT-apex) demonstrated excellent reliability, the lack of inter-examiner reliability assessment may also be a limitation of this study. This assessment will be addressed in future research. Furthermore, there were no records of oral hygiene, brushing habits, and periodontal status assessment, which may be contributing factors to GR. Therefore, to identify the potential contributing factors for GR during orthodontic tooth movement, well-controlled prospective studies with meticulous clinical examinations before, during, and after treatment should be conducted across multiple medical centers. Additionally, the amount of GR should be measured clinically in future prospective studies instead of relying on study models or intraoral photographs. Conclusions Despite these limitations, several inferences can be drawn from the findings of this study. There were 75 patients (26.2%) developed GR in the mandibular central incisor region following fixed orthodontic treatment, who had ideal gingival margin positions at pre-treatment. The occurrence of GR may not be related to the direction of movement of the lower anterior teeth. Although there was a statistically significant difference in GRD between the two groups, this difference lacked clinical significance. Thin GBT, narrow KGW, and thin LBT-crest prior to orthodontic treatment may increase the risk of GR. When external forces are applied, whether tension or pressure, absorption occurs in the soft and hard tissues surrounding the teeth, potentially leading to GR. A minimum LBT-crest of 0.72 mm and KGW of 2.70 mm prior to orthodontic treatment may effectively prevent the occurrence of GR. Acknowledgements Not applicable. Clinical trial number Not applicable. Abbreviations CEJ Cementum-enamel Junction KGW Keratinized Gingival Width GR Gingival Recession GRD Gingival Recession Depth GBT Gingival Biotype IMPA Incisor-Mandibular Plane Angle LBT-crest Labial alveolar bone thickness at the alveolar ridge crest LBT-mid Labial alveolar bone thickness at the middle root area LBT-apex Labial alveolar bone thickness at the apical region IE Incisal Edge AP Apex Me Menton Go Gonion ICC Intraclass Correlation Coefficient COR Crude Odds Ratio AOR Crude Odds Ratio CBCT Cone Beam Computed Tomography STM Sagittal Tooth Movement ROC Receiver Operating Characteristic AUC Area Under the ROC Curve Authors’ contributions Xiaoyan Li: Conceptualization, Methodology, Investigation, Validation, Software, Formal analysis, Data curation, Writing - original draft; Zichuan Zhang: Validation, Software, Data analysis, Visualization, Writing - review & editing; Cheng Jia: Methodology, Project administration, Supervision, Validation.All authors reviewed and approved the manuscript. Funding This work was supported by the Medical Science Research Project of Hebei Province (Project No. 20221169). Data availability No datasets were generated or analysed during the current study. Declarations Ethics approval and consent to participate Ethics approval was obtained from the Ethics Committee of Hebei Medical University Third Hospital (Project No.W2022-070-1). All the phases of the study were carried out following the principles of the Helsinki Declaration for Research on Human Subjects. Written informed consent was obtained from all candidates or their guardians. Consent for publication Written informed consent for information about the patients to be published was obtained from all the study participants or their guardians. Competing interests The authors declare no competing interests. Footnotes Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. References 1. Abdel-Fatah R, Saleh W. 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