The association between the anatomical features of teeth and the pathogenesis of periodontitis is well-documented. This study aimed to evaluate the influence of the mesial concavity of the maxillary first premolar on periodontal clinical indices and alveolar bone resorption rates. Employing a cross-sectional design, in 226 patients with periodontitis, we used cone beam computed tomography(CBCT) to examine the mesial concavity and alveolar bone resorption of 343 maxillary first premolar. Periodontal clinical indicators recorded by periodontal probing in the mesial of the maxillary first premolar in patients with periodontitis. Our findings indicate that the presence of mesial concavity at the cemento-enamel junction of the maxillary first premolar was not significantly influenced by either tooth position or patient sex (p > 0.05). Nonetheless, the mesial concavity at the cemento-enamel junction of the maxillary first premolar was found to exacerbate alveolar bone resorption and the inflammatory condition (p < 0.05). We infer that the mesial concavity at the cemento-enamel junction of the maxillary first premolar may contribute to localized alveolar bone loss and accelerate the progression of periodontal disease.
These authors contributed equally: Feng Chen, Qi Liu, and Xinyue Liu.
Periodontitis is an inflammatory disease that leads to the destruction of alveolar bone and periodontal ligaments, with dental plaque identified as the primary etiological agent[
The anatomical intricacies of the maxillary first premolar set it apart from other molars due to its varied morphology, which complicates periodontal treatment and poses a challenge for patient home care. A notable feature of the maxillary first premolar in individuals with periodontitis is the mesial concavity[
Although mesial concavity can be visualized and precisely measured post-extraction, the availability of first premolars is often limited due to loss primarily from orthodontic treatments or periodontitis, resulting in a sample size that lacks broader representation. This limitation has historically impeded research in this area. Cone-beam computed tomography (CBCT) effectively compensates for this shortfall. CBCT provides clear images across axial, sagittal, and coronal planes, eliminating structural superimposition and enhancing visualization of the target anatomy [
Previous investigations have established that mesial concavity influences the outcome of endodontic therapy and plays a pivotal role in dental restorations[
In this study, 343 maxillary first premolar teeth were analyzed, comprising 167 from the right side and 176 from the left. Of the right maxillary first premolars, 68.9% (n = 115) exhibited mesial concavity, while on the left, the prevalence was 62.5% (n = 110). The mean angles of mesial concavity for the right and left maxillary first premolars were 150.5 ± 9.59° and 152.3 ± 9.06°, respectively. No significant statistical differences were observed in the incidence or angle of mesial concavity between the right and left maxillary first premolars (p > 0.05).
Sex-based variation in the distribution of maxillary first premolar mesial concavity was also explored. The sample consisted of teeth from 177 females and 166 males. mesial concavity was present in 62.9% (n = 115) of male and 62.1% (n = 110) of female patients. Further analysis of the mean angle of mesial concavity by sex revealed angles of 150.3° for males and 152.5° for females, with these differences not reaching statistical significance (p > 0.05). The pertinent data is summarized in Table 1.
Table 1 Incidence of proximal mesial concavity of maxillary first premolar in positions and sex.
Group Number Number of occurrences Percentage (%) The mean angle (Mean ± SD) Position Left 176 110 62.5 152.3 ± 9.06 Right 167 115 68.9 150.5 ± 9.59 – – 0.21 0.13 sexs Male 166 115 69.2 150.3 ± 10.24 Female 177 110 62.1 152.5 ± 8.35 – – 0.22 0.17
Clinical attachment loss (CAL) measurements for the maxillary first premolar were taken prior to initiating basic periodontal treatment. In patients with mesial concavity, the mean CAL was 3.48 ± 1.56 mm on the buccal side and 3.29 ± 1.38 mm on the palatal side. Conversely, in patients lacking mesial concavity, the mean CAL was 3.06 ± 0.91 mm on the buccal aspect and 3.22 ± 1.22 mm on the palatal aspect. The data revealed that the mean buccal CAL was greater in premolars with mesial concavity compared to those without, although this difference was not observed on the palatal side. Notably, the difference in buccal CAL associated with mesial concavity was statistically significant (p < 0.05). These findings are detailed in Table 2.
Table 2 Clinical attachment loss (CAL) of the first premolars without/with concavity (Mean ± SD).
Clinical attachment loss (CAL) Dental with concavity Dental without concavity Buccal 3.48 ± 1.56 3.06 ± 0.91 0.02 Palatal 3.29 ± 1.38 3.22 ± 1.22 0.40
Mesial Plaque Index (PI) values were recorded for patients who had not received basic periodontal treatment. Among periodontitis patients with mesial concavity, 11.1% exhibited a PI score of 0, 38.2% had a score of 1, and 41.8% had a score of 2. In contrast, for periodontitis patients without mesial concavity, the scores were distributed as follows: 25.4% had a PI score of 0, 38.1% had a score of 1, and 28.0% had a score of 2. Specifically, PI scores of 0 on the mesial aspect of the first premolar with concavity were 9%, compared to 8% for those without concavity. The influence of mesial concavity on PI was statistically significant (p < 0.05). These results are detailed in Table 3.
Table 3 Plaque index of the maxillary first premolars without/with mesial concavity.
The plaque index was 0 The plaque index was 1 The plaque index was 2 The plaque index was 3 With mesial concavity 25 (11.1%) 86 (38.2%) 94 (41.8%) 20 (9%) 0.03 Without mesial concavity 30 (25.4%) 45 (38.1%) 33 (28.0%) 10 (8%)
Bleeding on Probing (BOP) was also assessed prior to basic periodontal treatment. The percentage of bleeding upon probing the mesial buccal aspect of the maxillary first premolar with concavity was 49.3%, compared to 37.2% when the concavity was absent. The impact of mesial concavity on BOP was statistically significant (p < 0.05). However, when probing the mesial palatal aspect, BOP was recorded at 43.5% for premolars with concavity and 35.5% for those without concavity. In this case, mesial concavity did not significantly affect the rate of palatal bleeding (p > 0.05). These findings are presented in Table 4.
Table 4 Effect of mesial concavity on palatal and buccal percentage of bleeding on probing.
Palatal Buccal Bleeding on probing No bleeding on probing Percentage (%) Bleeding on probing No bleeding on probing Percentage (%) Dental with concavity 98 127 43.5 111 114 49.3 Dental without concavity 42 76 35.5 44 74 37.2 – – 0.15 – – 0.03
Similarly, at the patient's initial visit, the gingival index (GI) of the patient's mesial maxillary first premolar was observed and the gingival index was recorded. Within the periodontitis group suffering from mesial concavity, 20.4% exhibited a GI index of 0, 36.0% a GI index of 1, 29.8% a GI index of 2, and 13.8% a GI index of 3. However, for periodontitis patients without mesial concavity, the scores were distributed as follows:22.0% had a PI score of 0, 49.2% had a score of 1, 17.8% had a score of 2, and 11.0% a GI index of 3. The statistical results showed that GI was higher in patients with mesial concavity(p < 0.05). The specific data are shown in Table 5.
Table 5 Gingival index of the maxillary first premolars without/with mesial concavity.
The gingival Index was 0 The gingival Index was 1 The gingival Index was 2 The gingival Index was 3 With mesial concavity 46 (20.4%) 81 (36.0%) 67 (29.8%) 31 (13.8%) 0.04 Without mesial concavity 31 (22.0%) 54 (49.2%) 21 (17.8%) 12 (11.0%)
In patients with periodontitis, cone-beam computed tomography (CBCT) images provide precise measurements of alveolar bone height, facilitating the assessment of alveolar bone loss. Our analysis indicates that mesial concavity exacerbates alveolar bone resorption on the buccal aspect of the first premolar. Across all age groups, the difference in the rate of buccal alveolar bone loss associated with concavity was statistically significant (p < 0.05), while the rate of palatal alveolar bone resorption was not significantly affected (p > 0.05). These findings are illustrated in Table 6.
Table 6 Impact of mesial concavity on buccal and palatal alveolar bone absorbs.
Age group (years) The buccal alveolar bone absorbs (Mean ± SD%) The palatal alveolar bone absorbs(Mean ± SD%) Dental with Dental without concavity Dental with concavity Dental without concavity ≤ 30 8.63 ± 7.45 5.54 ± 5.50 0.04 5.70 ± 9.09 5.80 ± 6.35 0.46 31–40 15.1 ± 13.62 8.58 ± 6.10 0.03 11.97 ± 14.07 7.58 ± 5.91 0.57 41–50 18.29 ± 10.33 11.48 ± 7.92 0.04 12.65 ± 10.53 13.10 ± 10.69 0.61 ≥ 51 23.06 ± 12.11 15.34 ± 7.62 0.01 19.18 ± 15.01 15.14 ± 7.68 0.76
Using clinical attachment loss as a criterion, we graded 225 maxillary first premolar teeth: clinical attachment loss of 1–2 mm was classified as mild periodontitis, clinical attachment loss of 3–4 mm as moderate periodontitis, and clinical attachment loss of more than 5 mm as severe periodontitis[
Table 7 The severity of periodontitis in the maxillary first premolars with the degree of mesial concavity (Mean ± SD).
Group Number The mean Angle of mesial concavity Mild periodontitis 64 154.3 ± 6.2 Mild periodontitis 0.02 Moderate periodontitis Moderate periodontitis 111 150.5 ± 9.5 Mild periodontitis 0.04 Severe periodontitis Severe periodontitis 50 149.9 ± 10.1 Moderate periodontitis 1 Severe periodontitis
In the present study, we investigated the prevalence of mesial concavity at the cemento-enamel junction in patients with periodontitis and examined its impact on the disease. Our findings indicate a high prevalence of mesial concavity among patients with periodontitis, with no statistically significant differences in distribution based on tooth position or sex. Moreover, we demonstrated that mesial concavity contributes to increased inflammation and alveolar bone resorption in these patients, thus exacerbating periodontal disease, which is an advancement over previous research.
Mesial concavity, also recognized as furcal or developmental concavity, is commonly observed at the cemento-enamel junction[
Food particles and bacterial plaque are prone to accumulate in mesial concavities, facilitating calculus formation[
CAL serves as a critical metric for gauging periodontitis severity[
Periodontal disease can lead to the resorption of alveolar bone, manifesting various alterations in bone architecture[
There are limitations in this study that warrant consideration. Firstly, while we relied on CAL, BOP, PI, and GI as markers of gingival inflammation and periodontal health, potential biases from our sample size—which was not large and was ethnically homogeneous—could not be overlooked. Our investigation focused solely on the impact of mesial concavity on periodontal health of the maxillary first premolar, without delving into the underlying mechanisms. Future research will address whether the microbial profile associated with concave maxillary first premolars differs and whether it influences inflammation levels in the mesial area.
In conclusion, our study establishes a connection between the mesial concavity of the maxillary first premolar and periodontitis. Periodontists should give special attention to this anatomical feature during routine treatment to enhance plaque removal, as mesial concavity is implicated in clinical attachment loss and alveolar bone resorption. Consequently, a thorough understanding of root anatomy is advocated, as it is a crucial prognostic factor in periodontal disease management.
There was a 0.7 CAL difference with a 0.3 standard deviation between patients with and without mesial concavity, according to the literature[
This study was conducted in strict adherence to the protocols of a cross-sectional study and met all operational specifications. Informed consent was obtained from all participating patients. The research received ethical approval from the ethics committee of the affiliated hospital of Hangzhou Normal University (Approval No. 2022(E2)-KS-107). Patients who underwent CBCT at the Center for Stomatology, Affiliated Hospital of Hangzhou Normal University, between November 2021 and March 2023 were considered for inclusion. Specific criteria for inclusion were: (
Graph: Figure 1Flow chart of the study design.
Periodontal clinical data were collected by an experienced periodontist. The periodontal status of the maxillary first premolar was assessed at six sites using a periodontal probe (Hu-Friedy; PCPUNC156, America), and clinical parameters such as PD, CAL, BOP, PI, and GI were recorded. A consistent force of 20 g was applied to measure PD from the gingival margin in millimeters on the mesial buccal and palatal sides of the maxillary first premolar. CAL was calculated as the sum of PD and the gingival margin level in cases of gingival recession(h) or as the difference between PD and the gingival margin level(h) when the gingival margin covered the CEJ (Fig. 2). Mesial PI was scored from 0 to 3[
Graph: Figure 2CAL (clinical attachment loss); PD = (probing depth); h = gingival margin level.
Images were captured using a CBCT scanner (Galileos, Sirona, Germany) equipped with a proven hybrid 3D solution, featuring an optimal 8 × 8 cm cylindrical volume at a resolution of 160 µm. A Sirona Dental System (D-64625 Bensheim, Germany) was used, operating at 85 kVp and 7 mA. The images were acquired and displayed on a 17-in. personal computer (PC) monitor, allowing for the visualization of transverse slices in the axial, coronal, and sagittal planes. Image reconstruction was processed using the GALAXIS 1.9 software (SICAT GmbH & Co. KG, Bonn, Germany).
The full texts of all potentially eligible articles were independently reviewed by two authors (Xinyue Liu and Feng Chen). Data from studies meeting the inclusion criteria were extracted and tabulated using a standardized data collection form. Any discrepancies between the authors were resolved through discussion to achieve consensus.
CBCT images that satisfied the inclusion criteria were analyzed and quantified by two periodontal experts (Feng Chen and Qi Liu), with the data recorded in a standardized table. In cases of disagreement, a third periodontal specialist was consulted. The inter-rater agreement was confirmed utilizing the Kappa test, ensuring the reliability of measurements.
The evaluation and measurement protocol for each CBCT image involved documenting the incidence and angle of mesial concavity in maxillary first premolars of patients with periodontitis. The measuring point for mesial concavity was at the enamel-cementum junction. The angle was determined by connecting the most convex points on the buccal and lingual sides with the most concave midpoint. The angle of mesial concavity ascertained from the axial image is depicted in Fig. 3.
Graph: Figure 3The angle of mesial concavity identified from the axial segment image.
As demonstrated in Fig. 4, axial views at the enamel-cementum junction revealed the pulp chamber, while sagittal views intersecting its center and coronal views at either the buccal or palatal side provided insights into the alveolar bone condition. Reference points utilized were the apical point (A), the CEJ point (B), and the alveolar ridge point (C). A parallel line to point B (B1) and point A (A1) were projected to establish a line from B to A1, parallel to the coronal plane. Line L extended from B to C, and line H from B1 to A1. The extent of bone loss on the buccal or palatal side of the maxillary first premolar was calculated using the formula [(L − 2 mm)/(H − 2 mm)] × 100%[
Graph: Figure 4The apical point (A); cementum-enamel junction (CEJ) point (B); the alveolar ridge point (C); B1 was parallel to B; A1 was parallel to A; H was the line of B to C; L was the line of B1 to A1.
Statistical analysis was performed using the IBM SPSS Statistics software (version 24.0 for Windows). The association between tooth location and sex with the presence of mesial concavity in periodontitis patients was evaluated using the chi-squared test. The influence of mesial concavity on the gingival index, plaque index, and percentage of bleeding on probing in periodontitis patients was evaluated using the chi-squared test. The influence of mesial concavity on clinical attachment loss was examined using independent sample t-tests. The Mann–Whitney U test was applied to assess the impact of root concavity on the degree of bone loss and the severity of periodontitis in the maxillary first premolars with the degree of mesial concavity. The significance level was established at α = 0.05.
All study procedures involving human participants were in compliance with the ethical standards of the Declaration of Helsinki and its later amendments, as well as other relevant ethical guidelines. The research received ethical approval from the Ethics Committee of Hangzhou Normal University Hospital (Approval No. 2022(E2)-KS-107). Prior to enrollment in the study, participants were informed about the research objectives and procedures and provided written informed consent. Consent for the publication of identifiable images was obtained from all participants. Informed consent was acquired from each patient or their legal guardians for inclusion in the study.
The authors deny any conflicts of interest related to this study.
F.C. and Q.L. drafted the manuscript. L.J.Z. and C.D. designed the study and edited the manuscript. Q.F and X.Y.L. performed the statistical analysis. R.L., K.X.Z., B.X.Z., and Z.S. collected the data and contributed to the analysis of the results. All authors read and approved the manuscript.
This study was funded by Affiliated Hospital of Hangzhou Normal University, Hangzhou Normal University, China (2021YN148, 2021YN003), Affiliated Hospital of Hangzhou Normal University, Hangzhou Normal University, China (Z20200046).
On reasonable request, the corresponding author will provide the datasets created and/or used in the current study.
The authors declare no competing interests.
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