Abstract
Objectives
The aim of this cone-beam computed tomography (CBCT)-based retrospective study was to evaluate the age-related prevalence of closed apices in permanent maxillary and mandibular second molars in a Turkish pediatric and adolescent population. Additionally, potential sex-related differences in closed apices were investigated.
Materials and methods
This study included 357 individuals (714 teeth) aged 12–21 years whose CBCT scans were retrieved from the digital archive. The apical status of permanent second molars was evaluated three-dimensionally using multiplanar reconstruction. According to root development, teeth were classified into two groups: those with closed apices in all roots and those with at least one open apex. Age was categorized into seven groups (12–12.99, 13–13.99, 14–14.99, 15–15.99, 16–16.99, 17–17.99, and ≥ 18 years). Associations between closed apices, age, and sex were analyzed using Pearson’s chi-square test and Fisher’s exact test (p < 0.05).
Results
The prevalence of closed apices increased markedly with age in both jaws. Rates were low in the 12–12.99 age group (maxillary 2.1%; mandibular 5.4%), exceeded 60% by 14–14.99 years, and approached completion by 16–16.99 years, reaching 100% in individuals aged ≥ 18 years. Overall, no statistically significant difference was observed between permanent maxillary and mandibular second molars (p > 0.05). However, in the 13–13.99 and 14–14.99 age groups, females demonstrated significantly higher rates of closed apices than males in both jaws; in the 15–15.99 age group, this difference was significant only for permanent maxillary second molars (p < 0.05).
Conclusion
Closed apices in permanent second molars show a marked age-related increase and tend to occur earlier in females than in males during certain adolescent age groups. These findings support the use of closed apices in second molars as a reliable indicator for both endodontic treatment planning and forensic age estimation.
Clinical relevance
Knowledge of the relationship between age and sex and the rates of closed apices in permanent second molars play an important role in both forensic dentistry and in endodontic and pediatric treatment planning.
Keywords: Closed apices, Permanent second molars, CBCT, Mandible, Maxilla
Introduction
Forensic age estimation and the assessment of dental maturity are important in both medico-legal decision-making and clinical dentistry. The need for age estimation in living individuals has increased in recent years, particularly in migration-related cases and legal proceedings involving minors, where conclusions must rely on objective and evidence-based biological indicators [1]. Dental development is considered a reliable marker of biological age because tooth mineralization follows a genetically regulated sequence and is relatively resistant to short-term environmental influences [2].
Closed apices represent one of the most clinically and forensically relevant milestones of dental development, reflecting the completion of root formation. Clinically, differentiating between open and closed apices is essential because immature permanent teeth with open apices present thin dentinal walls, wide apical foramina, and an increased risk of fracture. Accordingly, treatment planning depends on root maturity: apexogenesis may be indicated when pulp vitality is preserved, whereas necrotic immature teeth often require apexification or regenerative endodontic procedures [3, 4].
From a forensic perspective, adolescence represents a challenging period for age estimation because many teeth have completed crown formation, limiting observable developmental changes. Traditional dental age estimation has therefore relied on staging systems such as those proposed by Moorrees, Nolla, and Demirjian, with modifications introduced to improve population-specific accuracy [5–9]. Methods focusing on apical development, such as Cameriere’s open apices approach, further emphasize the forensic value of root maturation during adolescence [10].
Third molars are frequently used in adolescent age estimation but show high variability and population differences. Therefore, attention has shifted to alternative markers, including mandibular permanent second molars, as their eruption and root maturation overlap with legally relevant adolescent thresholds [11]. Evidence based on panoramic radiographs indicates strong associations between second molar development and chronological age, especially around the 14-year threshold [12, 13]. Since closed apices represent the final developmental stage, they may provide a clearer and clinically interpretable endpoint; a forensic study reported that closed apices in mandibular second molars may assist in differentiating adolescents between 14 and 16 years [11].
However, panoramic radiography has limitations such as distortion, magnification, and posterior anatomical superimposition, which may reduce accuracy when evaluating transitional apical stages. Cone-beam computed tomography (CBCT) enables three-dimensional multiplanar visualization and a more precise assessment of apical morphology, potentially providing more accurate reference data regarding the chronology of closed apices. Dental maturity also varies by sex and population, with females typically maturing earlier, emphasizing the need for population-specific datasets [12]. Our group previously demonstrated the feasibility of CBCT-based assessment of the chronology of closed apices in first permanent molars, supporting the value of three-dimensional reference data for clinical and forensic applications [14].
Therefore, the aim of this CBCT-based retrospective study was to evaluate the age distribution and prevalence of closed apices in permanent maxillary second molars and permanent mandibular second molars in a Turkish pediatric and adolescent population, and to assess potential sex-related differences in the timing of closed apices.
Materials and methods
This retrospective cross-sectional study was conducted using CBCT scans retrieved from the digital archive of the Department of Oral and Maxillofacial Radiology, Izmir Katip Çelebi University, Türkiye. The informed consent to use of data was obtained from all patient and legal guardian of minor regarding the use of their radiologic data for scientific research. This study was approved by the Izmir Katip Celebi University Non-Interventional Clinical Studies Institutional Review Board (Approval number: 121/2024) and was performed in full accordance with Declaration of Helsinki, as revised in 2013.
Based on a previous CBCT-based study on closed apices of permanent molars, an a priori power analysis was performed using G*Power software (version 3.1.9.7; Franz Faul, Universität Kiel, Kiel, Germany). Assuming an effect size of w = 0.286, an alpha level of 0.05, and a desired power of 0.80, the minimum required sample size was calculated to be 97. The final sample of the present study included 357 individuals, exceeding the minimum required sample size.
CBCT scans belonging to individuals aged 12–21 years were screened. Eligibility criteria were defined to ensure clear visualization of the mandibular permanent second molar apices and to minimize factors that could affect root development. Participants who were between 12 and 21 years of age at the time of CBCT acquisition, had at least one mandibular permanent second molar present, and had CBCT images of sufficient diagnostic quality for the evaluation of apical morphology were included in the study. The study sample was randomly selected from eligible CBCT records. CBCT scans were excluded in the presence of missing mandibular second molars, previous endodontic treatment of mandibular second molars, periapical lesions, cystic lesions, internal or external root resorption affecting the apical region, tooth anomalies, severe malformations or developmental disorders affecting dental maturation, extensive restorations, or artifacts obscuring the apical region, and poor image quality (motion artifacts or inadequate resolution) preventing accurate evaluation. After application of the eligibility criteria, 357 individuals were included in the final sample.
Data collection and image evaluation
No additional CBCT scans were obtained for the purposes of this study, and only retrospectively archived records were evaluated. All CBCT images were acquired using a NewTom 5G CBCT system (QR srl, Verona, Italy). In the imaging protocol, the tube voltage was fixed at 110 kVp, and the tube current was adjusted within a range of 1–20 mA. The voxel size was set at 0.15 mm, and the field of view (FOV) was 12 × 8 cm. The acquired images were reconstructed using the multiplanar reconstruction (MPR) technique to ensure standardization. To ensure standardization, the long axes of the roots were reoriented to be perpendicular to the axial plane and parallel to the other planes during reconstruction. All data were collected and evaluated by a single oral and maxillofacial radiologist with more than ten years of experience. To assess intra-examiner reproducibility, a random sample of 25 CBCT images was re-examined after an interval of 2 weeks. The intra-examiner reliability demonstrated excellent agreement (kappa value = 0.97) [15].
The individuals included in the study were categorized according to sex and age. The age groups were divided into seven categories: 12–12.99, 13–13.99, 14–14.99, 15–15.99, 16–16.99, 17–17.99, and 18 years and older. Within the scope of the study, the root apices of the maxillary and mandibular second molars were analyzed in three different anatomical planes. To eliminate ambiguity in the classification of closed apices, the final decision was based on the consensus of two specialists: an oral and maxillofacial radiologist and a pediatric dentist. The teeth were classified into two groups according to root development. Teeth with at least one open root apex were defined as “teeth with open apices,” whereas teeth in which all root apices were closed were recorded as “teeth with closed apices” (Figs. 1 and 2).
Fig. 1.
Different CBCT sections of a second permanent mandibular molar are shown. In the upper panel, white arrows indicate closed apices in the axial (A), sagittal (B), and coronal (C) sections, whereas in the lower panel, open apices are observed in the axial (D), sagittal (E), and coronal (F) sections
Fig. 2.
Different CBCT sections of a second permanent maxillary molar are shown. In the upper panel, white arrows indicate closed apices in the axial (A), coronal (B), and sagittal (C) sections, whereas in the lower panel, open apices are observed in the axial (D), coronal (E), and sagittal (F) sections
Statistical analysis
Data entry and all statistical analyses were performed using IBM SPSS Statistics version 26.0 (IBM Corp., Armonk, NY, USA). The Pearson Chi-square test and Fisher’s exact test were used to examine associations between apical closure, age, and gender. Multivariate logistic regression analysis was performed to evaluate the effects of the independent variables (age and gender) on apical closure in maxillary and mandibular second molars. A p-value of < 0.05 was considered statistically significant.
Results
A total of 357 individuals and 714 teeth were included in the study. Of the participants, 54.6% were female (n = 195) and 45.4% were male (n = 162). Analysis of the age distribution demonstrated that the sample was relatively balanced across the age range of 12 to 18 years and older, with each age group representing approximately 13.2% to 16.0% of the total sample. The highest number of participants was observed in the 13–13.99 age group (n = 57, 16.0%), whereas the lowest number was recorded in the 18 years and older group (n = 47, 13.2%). When the age distribution was evaluated according to sex, equal numbers of female and male participants were observed only in the 14–14.99 age group (n = 26). In all other age groups, the number of female participants was higher than that of males (Table 1).
Table 1.
Age and gender distribution of the participants
| Age Group (years) |
Gender | Total | ||||
|---|---|---|---|---|---|---|
| Female | Male | |||||
| N | % | N | % | N | % | |
| 12-12.99 | 27 | 7.6% | 23 | 6.4% | 50 | 14.0% |
| 13-13.99 | 29 | 8.1% | 28 | 7.8% | 57 | 16.0% |
| 14-14.99 | 26 | 7.3% | 26 | 7.3% | 52 | 14.6% |
| 15-15.99 | 31 | 8.7% | 22 | 6.2% | 53 | 14.8% |
| 16-16.99 | 29 | 8.1% | 21 | 5.9% | 50 | 14.0% |
| 17-17.99 | 26 | 7.3% | 22 | 6.2% | 48 | 13.4% |
| ≥ 18 | 27 | 7.6% | 20 | 5.6% | 47 | 13.2% |
| Total | 195 | 54.6% | 162 | 45.4% | 357 | 100.0% |
The overall closed apices rates of permanent second molars were found to be quite low in the 12–12.99 age group (maxillary 2.1%; mandibular 5.4%). A marked increase in closed apices rates was observed in the 13–13.99 age group, reaching 43.9% in maxillary molars and 38.1% in mandibular molars. In the 14–14.99 age group, closed apices rates exceeded 60% in both tooth groups (maxillary 66.0%; mandibular 61.2%).
In the 15–15.99 age group, closed apices rates continued to increase, reaching 77.9% in maxillary molars and 84.0% in mandibular molars. In the 16–16.99 age group, the rates were 97.0% for maxillary molars and 96.0% for mandibular molars. In the 18 years and older group, all apices (100%) were closed in both maxillary and mandibular permanent second molars (Table 2). Furthermore, when the closed apices rates of maxillary and mandibular second molars were compared between jaws, no statistically significant difference was observed across age groups (p > 0.05) (Table 2).
Table 2.
Proportion of closed apices for permanent second maxillary and mandibular molars by age group
| Age Groups (years) |
Maxillary Molars | Mandibular Molars | p | ||
|---|---|---|---|---|---|
| N | % | N | % | ||
| 12-12.99 | 2 | 2.1% | 5 | 5.4% | 0.273 |
| 13-13.99 | 47 | 43.9% | 43 | 38.1% | 0.376 |
| 14-14.99 | 66 | 66.0% | 63 | 61.2% | 0.474 |
| 15-15.99 | 81 | 77.9% | 89 | 84.0% | 0.262 |
| 16-16.99 | 97 | 97.0% | 96 | 96.0% | 1 |
| 17-17.99 | 92 | 98.9% | 95 | 99.0% | 1 |
| ≥ 18 | 94 | 100.0% | 93 | 100.0% | 1 |
Table 3 presents the root-based closed apices rates of permanent second molars according to age groups. The closed apices rates of maxillary molar roots demonstrated variability between 12 and 15.99 years of age. For mandibular second molars, closed apices rates were higher in the mesial roots than in the distal roots within the 12–15.99 age range.
Table 3.
Proportion of closed apices for each root of permanent molars by age group
| Age Group (years) |
Maxillary Molar | Mandibular Molar | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Mesiobuccal Root | Distobuccal Root | Palatal Root | Mesial Root | Distal Root | ||||||
| N | % | N | % | N | % | N | % | N | % | |
| 12-12.99 | 4 | 4.2% | 2 | 2.1% | 2 | 2.1% | 10 | 10.8% | 5 | 5.4% |
| 13-13.99 | 49 | 45.8% | 52 | 48.6% | 48 | 44.9% | 49 | 43.4% | 45 | 39.8% |
| 14-14.99 | 70 | 70.0% | 70 | 70.0% | 66 | 66.0% | 73 | 70.9% | 63 | 61.2% |
| 15-15.99 | 84 | 80.8% | 84 | 80.8% | 81 | 77.9% | 91 | 85.8% | 89 | 84.0% |
| 16-16.99 | 98 | 98.0% | 98 | 98.0% | 98 | 98.0% | 98 | 98.0% | 98 | 98.0% |
| 17-17.99 | 92 | 98.9% | 92 | 98.9% | 92 | 98.9% | 95 | 99.0% | 95 | 99.0% |
| ≥ 18 | 94 | 100.0% | 94 | 100.0% | 94 | 100.0% | 93 | 100.0% | 93 | 100.0% |
In mandibular second molars, the closed apices rate in the 13–13.99 age group was 50.0% in females and 25.5% in males, and this difference was statistically significant (p = 0.007). Similarly, in the 14–14.99 age group, the closed apices rate was 71.2% in females and 51.0% in males, with a statistically significant difference between sexes (p = 0.036) (Table 4).
Table 4.
Proportion of open and closed apices for permanent second mandibular molars by age group according to gender
| Age Group (years) |
Gender | P | Total | ||
|---|---|---|---|---|---|
| Female N (%) | Male N (%) | ||||
| 12-12.99x | Open Apex | 46a (92.0%) | 42a (97.7%) | 0.369 | 88 (94.6%) |
| Closed Apex | 4a (8.0%) | 1a (2.3%) | 5 (5.4%) | ||
| 13-13.99y | Open Apex | 29a (50.0%) | 41b (74.5%) | 0.007** | 70 (61.9%) |
| Closed Apex | 29a (50.0%) | 14b (25.5%) | 43 (38.1%) | ||
| 14-14.99y | Open Apex | 15a (28.8%) | 25b (49.0%) | 0.036* | 40 (38.8%) |
| Closed Apex | 37a (71.2%) | 26b (51.0%) | 63 (61.2%) | ||
| 15-15.99y | Open Apex | 7a (11.3%) | 10a (22.7%) | 0.114 | 17 (16.0%) |
| Closed Apex | 55a (88.7%) | 34a (77.3%) | 89 (84.0%) | ||
| 16-16.99x | Open Apex | 1a (1.7%) | 3b (7.1%) | 0.307 | 4 (4.0%) |
| Closed Apex | 57a (98.3%) | 39a (92.9%) | 96 (96.0%) | ||
| 17-17.99x | Open Apex | 0a (0.0%) | 1a (2.3%) | 0.458 | 1 (1.0%) |
| Closed Apex | 52a (100.0%) | 43a (97.7%) | 95 (99.0%) | ||
| ≥ 18 | Open Apex | 0 (0.0%) | 0 (0.0%) | - | 0 (0.0%) |
| Closed Apex | 53a (100.0%) | 40a (100.0%) | 93 (100.0%) | ||
Each subscript letter denotes a subset of gender categories according to age groups whose column proportions do not differ significantly from each other at the 0.05 level
x= Fisher’s exact test
y= Chi-square test
The significance level was set to P < 0.05. *: P < 0.05. **:P < 0.01
In maxillary second molars, the closed apices rate in the 13–13.99 age group was 53.6% in females and 33.3% in males, and this difference was statistically significant (p = 0.035). In the 14–14.99 age group, a statistically significant difference between sexes was also observed (p = 0.011). In the 15–15.99 age group, the closed apices rate was 78.0% in females and 54.0% in males. Similarly, in the 16–16.99 age group, the closed apices rate in maxillary second molars was 85.5% in females and 66.7% in males, with females demonstrating significantly higher rates (p = 0.023) (Table 5). In the remaining age groups, although closed apices rates were higher in females than in males for both maxillary and mandibular permanent second molars, these differences were not statistically significant (p > 0.05) (Tables 4 and 5).
Table 5.
Proportion of open and closed apices for permanent second maxillary molars by age group according to gender
| Age Group (years) |
Gender | P | Total | ||
|---|---|---|---|---|---|
| Female N (%) | Male N (%) | ||||
| 12-12.99x | Open Apex | 48a (96.0%) | 46a (100.0%) | 0.496 | 94 (97.9%) |
| Closed Apex | 2a (4.0%) | 0a (0.0%) | 2 (2.1%) | ||
| 13-13.99y | Open Apex | 26a (46.4%) | 34b (66.7%) | 0.035* | 60 (56.1%) |
| Closed Apex | 30a (53.6%) | 17b (33.3%) | 47 (43.9%) | ||
| 14-14.99y | Open Apex | 11a (22.0%) | 23b (46.0%) | 0.011* | 34 (34.0%) |
| Closed Apex | 39a (78.0%) | 27b (54.0%) | 66 (66.0%) | ||
| 15-15.99y | Open Apex | 9a (14.5%) | 14b (33.3%) | 0.023* | 23 (22.1%) |
| Closed Apex | 53a (85.5%) | 28b (66.7%) | 81 (77.9%) | ||
| 16-16.99x | Open Apex | 3a (5.2%) | 0a (0.0%) | 0.262 | 3 (3.0%) |
| Closed Apex | 55a (94.8%) | 42a (100.0%) | 97 (97.0%) | ||
| 17-17.99x | Open Apex | 0a (0.0%) | 1a (2.3%) | 0.462 | 1 (1.1%) |
| Closed Apex | 50a (100.0%) | 42a (97.7%) | 92 (98.9%) | ||
| 18 ≥ | Open Apex | 0 (0.0%) | 0 (0.0%) | - | 0 (0.0%) |
| Closed Apex | 54a (100.0%) | 40a (100.0%) | 94 (100.0%) | ||
Each subscript letter denotes a subset of gender categories according to age groups whose column proportions do not differ significantly from each other at the 0.05 level
x= Fisher’s exact test
y= Chi-square test
The significance level was set to P < 0.05. *: P < 0.05
Age and sex were evaluated as potential predictors of closed apices in the maxillary and mandibular second molars using multivariate logistic regression analysis. In the maxillary second molars, age was significantly associated with closed apices (p < 0.001), with the probability of having closed apices increasing as age increased (OR = 0.250; 95% CI: 0.203–0.309). Sex was also a significant predictor in the maxillary group, where females were approximately 2.38 times more likely to exhibit closed apices compared to males (OR = 2.376; 95% CI: 1.471–3.836; p < 0.001) (Table 6).
Table 6.
Multivariate logistic regression analysis of the effects of age and gender on apical closure of maxillary and mandibular second molars
| Tooth | Variable | B | S.E. | Wald | P | OR | 95% CI |
|---|---|---|---|---|---|---|---|
| Second Maxillary Molar | Age | -1.385 | 0.108 | 165.731 | < 0.001* | 0.250 | 0.203–0.309 |
| Gender | 0.865 | 0.244 | 12.524 | < 0.001* | 2.376 | 1.471–3.836 | |
| Second Mandibular Molar | Age | -1.394 | 0.108 | 167.053 | < 0.001* | 0.248 | 0.201–0.307 |
| Gender | 0.983 | 0.244 | 16.230 | < 0.001* | 2.672 | 1.656–4.310 |
B Beta coefficient, S.E. Standard Error, Wald Wald statistic, OR Odds ratio, CI Confidence interval
The significance level was set at P < 0.05. *: P < 0.001
Similarly, in the mandibular second molars, age showed a significant association with closed apices (p < 0.001), with the probability of having closed apices increasing with advancing age (OR = 0.248; 95% CI: 0.201–0.307). Sex was also a significant predictor in this group, with females having approximately 2.67 times higher odds of closed apices than males (OR = 2.672; 95% CI: 1.656–4.310; p < 0.001). Overall, these findings indicate that both age and sex significantly influence the closed apices process in second molar teeth (Table 6).
Discussion
Teeth exhibit high resistance to environmental factors due to their durable mineralized structure [16]. The analysis of structural and biological changes occurring within this resilient tissue is based on morphological, radiographic, histological, and biochemical methods. Owing to developmental differences, dental age estimation is generally evaluated within three main periods: the prenatal–neonatal–early postnatal period, the childhood–adolescent period, and adulthood. Each period requires specific parameters and distinct assessment methodologies [17–19].
The use of teeth for age and sex determination is one of the most widely accepted and reliable methods in forensic odontology. Periapical and panoramic radiographs used for this purpose provide important evidence for identification and age estimation due to their non-invasive nature and ease of application. These imaging methods provide data on the monitoring of tooth germs, assessment of mineralization stages, determination of crown completion, and analysis of tooth eruption processes [11, 17, 19–22]. However, recent literature reports that the use of CBCT in the assessment of dental maturation provides higher accuracy compared with panoramic radiographs [23].
In light of the aforementioned considerations, the present study was designed to investigate age-related variations in closed apices rates of mandibular and maxillary permanent second molars in a Turkish subpopulation using CBCT imaging, and to contribute updated reference data to the existing literature Furthermore, potential sex-related differences in closed apices were systematically evaluated in order to provide clinically and forensically relevant insights.
In previous studies, mandibular canines and third molars have generally been preferred for age estimation and developmental assessment [24–26]. However, the fact that root formation and closed apices of mandibular canines are typically completed around the age of 13 represents a limitation, as it hinders the monitoring of active growth processes that continue until approximately 16–17 years of age. On the other hand, the high frequency of agenesis in third molars within the human dentition raises concerns regarding the reliability of this parameter [27]. For these reasons, the present study aimed to determine the age- and sex-specific closed apices rates of permanent second molars, which offer an advantage due to their prolonged developmental period extending into later adolescence.
Almeida et al. [28] reported that mineralization of mandibular second molars tends to occur at a more advanced stage compared with their maxillary counterparts. However, the present study found no statistically significant difference in closed apices between permanent second molars of the two jaws (p > 0.05). This observation, indicating the absence of developmental differences between the jaws, is consistent with studies conducted in Korean [29] and Northern Chinese [30] populations. The results of our study indicate that the development of closed apices in permanent second molars occurs synchronously in both jaws, with similar closed apex rates observed across age groups in both maxillary and mandibular teeth.
Balaraj et al. [11] demonstrated the presence of sex-related differences in the closed apices of permanent second molars. In their study, closed apices were reported to occur at an earlier age in females, with 95% achieving closure at approximately 14 years and 9 months, whereas in males, 94.0% closure was observed at around 15 years and 5 months. Furthermore, the maximum age at which an open apex could still be detected was reported as 15 years and 11 months in females and 17 years in males, thereby defining the upper developmental limits of the process. Consistent with the literature, the findings of the present study indicate that closed apices rates of both maxillary and mandibular second molars increase markedly after the age of 14.
The present study demonstrated that in the 13–13.99 and 14–14.99 age groups, the rate of closed apices in permanent second molars of both jaws was significantly higher in females compared with males (p < 0.05). Similarly, in the 15–15.99 age group, the developmental stage of maxillary permanent second molars was more advanced in females than in males, and the prevalence of closed apices was also significantly higher in females within this group (p < 0.05). These findings are consistent with those reported by Balaraj et al. [11], who indicated that dental development is completed earlier in females than in males.
Kumar et al. [27] reported that in male individuals, the Demirjian Index (DI) stages of mandibular second molars were more advanced compared with skeletal maturation stages, suggesting that dental development progresses more rapidly than skeletal development. In contrast, in the present study, when chronological age was considered, the closed apices rates of mandibular second molars in males were significantly lower than those in females in the 13–13.99 and 14–14.99 age groups (p < 0.05). Although this finding appears to be inconsistent with the literature, it may be attributed to methodological differences between studies. Furthermore, since closure of the apical foramen represents the final stage of dental maturation, sex-specific differences in developmental rates may become more pronounced at this terminal stage.
Singh et al. [31] reported that permanent mandibular second molars can be used as a reliable parameter for dental age estimation. In their study, evaluation was performed using the Nolla method on intraoral periapical radiographs; however, maxillary second molars were excluded from the analysis. The authors stated that, due to the superimposition of surrounding anatomical structures in the maxillary region, root development in these teeth could not be assessed with sufficient accuracy [31]. In contrast, the present study employed CBCT imaging, which eliminates the risk of superimposition and provides three-dimensional visualization. Owing to this methodological advantage, closed apices of maxillary second molars were also included in the analyses, unlike the limitations reported in previous literature.
The clinical relevance of closed apices extends beyond their value as a developmental parameter. The status of the apex—whether open or closed—is a critical determinant in endodontic treatment planning [32]. After tooth eruption, root development and closure of the apex are typically completed within approximately three years. During this period, teeth are more vulnerable to traumatic injuries and environmental influences. Trauma affecting immature teeth may interrupt root development, and the presence of open apices renders endodontic procedures technically more complex and demanding [33–35]. In teeth with open apices, the wide apical foramen increases procedural risks, including irrigant extrusion, difficulties in working length determination, and challenges in obturation [33, 35–37]. In contrast, the presence of a well-defined apical constriction in teeth with closed apices is a key factor contributing to improved treatment outcomes and predictability.
Therefore, an increased prevalence of closed apices in certain age groups indicates that conventional endodontic approaches may be more feasible within those age ranges. The findings of the present study, demonstrating significantly higher closed apices rates in females within specific age groups, suggest that a more mature apical morphology may be encountered in females compared with males of the same chronological age. This may have important implications for treatment selection, particularly in cases involving traumatic injuries or necrotic immature teeth.
Evidence from the literature indicates that dental development may vary across different ethnic and population groups. A substantial proportion of these studies have employed the Demirjian method and panoramic radiography [38–41]. In multi-ethnic cohort studies, children of Moroccan, Turkish, African, and Asian descent have been reported to show dental development that is either advanced or delayed by approximately 2–5 months compared with children of European descent [39]. Similarly, differences of approximately 5 months between Chinese and Caucasian populations, and around 8 months in Afro-descendant groups, have been reported [40].
In contrast, some studies have reported no statistically significant or clinically relevant differences between ethnic groups; for example, in Finnish and Somali populations, similar timing of mandibular tooth development has been demonstrated based on Demirjian stages [38]. Therefore, the use of population-specific reference data is recommended in forensic and clinical practice. In particular, the limited availability of data on ethnic variation in CBCT-based parameters such as closed apices of mandibular second molars further highlights the importance of the present study.
This study has several limitations that should be acknowledged. First, the dynamic progression of closed apices was not assessed longitudinally; only cross-sectional data from specific age groups were evaluated. Therefore, age-related or developmental changes should be interpreted with caution. Longitudinal studies following the same individuals throughout growth periods may provide a more accurate understanding of craniofacial developmental dynamics. Second, the sample was derived from a single-center CBCT archive and represents a Turkish subpopulation, which may limit the generalizability of the findings to other ethnic or geographic populations. Finally, apical status was classified dichotomously as open or closed apices, and intermediate developmental stages were not analyzed. This approach may have limited the detailed assessment of developmental variations, particularly during transitional periods.
Conclusion
This retrospective CBCT-based study demonstrated that the prevalence of closed apices in permanent second molars increases markedly with age in a Turkish pediatric and adolescent population. A significant rise in the prevalence of closed apices was observed particularly after the age of 14. Furthermore, in the 13–14.99 age range, the prevalence of closed apices in both mandibular and maxillary permanent second molars was significantly higher in females compared with males. Additionally, in the 15–15.99 age group, maxillary permanent second molars exhibited significantly higher prevalence of closed apices in females.
The findings suggest that closed apices in second molars may serve as a reliable and clinically interpretable indicator for both endodontic treatment planning and forensic age estimation. The three-dimensional assessment provided by CBCT enables a more precise evaluation of apical morphology and contributes population-specific reference data to the literature. Nevertheless, future multicenter studies incorporating probability-based statistical models in diverse populations are needed to further enhance the predictive value of this parameter in forensic applications.
Acknowledgements
Not applicable.
Abbreviations
- B
Beta coefficient
- CBCT
Cone-beam computed tomography
- 95%CI
Confidence interval
- DI
Demirjian Index
- FOV
Field of view
- MPR
Multiplanar reconstruction
- OR
Odds ratio
- SE
Standard Error
Authors' contributions
Conceptualization: F.K., N.Y., M.C.E., I.G., and E.A.; methodology: E.H., F.K., N.Y. and M.C.E.; software: E.H. and F.K.; validation: E.H. and F.K.; formal analysis: E.H., F.K. and M.C.E.; investigation: E.H., F.K., N.Y. and M.C.E.; resources: F.K. and I.G.; data curation: F.K. and E.A.; writing—original draft preparation: E.H., F.K., N.Y. and M.C.E.; writing—review and editing: E.H. and F.K.; visualization: E.H. and M.C.E.; supervision: E.H. and F.K. All authors have read and agreed to the published version of the manuscript.
Funding
No funding was obtained for this study.
Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study was approved by the Izmir Katip Celebi University Non-Interventional Clinical Studies Institutional Review Board (Approval number: 121/2024) and was performed in full accordance with Declaration of Helsinki, as revised in 2013. Written informed consent was obtained from all participants.
Consent for publication
Not applicable.
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.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.