Association between proximal caries and pulp canal obliteration in maxillary molars: A cone-beam computed tomography-based retrospective study

Abstract

Aim:

The aim of the study was to determine the correlation between proximal caries and pulp canal obliteration (PCO) in maxillary molars using cone-beam computed tomography (CBCT).

Materials and Methods:

This retrospective observational study analyzed 162 CBCT scans of maxillary molars with proximal caries (mesial or distal) obtained from patients aged 18–49 years. Two calibrated endodontists independently assessed the mesiobuccal (MB), distobuccal (DB), and palatal roots for the presence of PCO in sagittal, coronal, and axial planes using CBCT (<0.2 mm voxel size). Inter- and intra-observer reliability was evaluated using Cohen’s kappa. Associations between caries location and PCO were analyzed using Pearson’s Chi-square test or Fisher’s exact test and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated (P < 0.05).

Results:

PCO was observed in 21.2% (n = 34/162) of maxillary molars. Root-wise prevalence was the highest in the DB root (42%), followed by the MB (19.8%) and palatal roots (1.9%). No statistically significant association was found between caries location and PCO (MB: OR = 0.88, 95% CI: 0.41–1.92, P = 0.757; DB: OR = 0.55, 95% CI: 0.29–1.04, P = 0.064; palatal: OR = 0.39, 95% CI: 0.03–4.43, P = 0.434).

Conclusion:

Within the limitations of the study, PCO was frequently observed in maxillary molars with proximal caries, predominantly affecting the DB root irrespective of caries location. Females had higher predilection compared to males.

INTRODUCTION

Pulp canal obliteration (PCO) is a pulpal response, characterized by the progressive deposition of hard tissue-like substance within the root canal space. This phenomenon is usually seen following traumatic dental injuries but may also occur as a response to persistent irritation, including deep caries, restorative procedures, and orthodontic treatment. The prevalence of PCO due to dental trauma has been reported to range from 3.8% to 27.6%,[1,2] whereas caries-related PCO has been frequently seen in mandibular molars with 47%.[3] PCO generally starts within the pulp chamber space and progresses in the apical direction into root canal space through root canal orifices,[4] resulting in partial or complete obliteration depending on the stage of diagnosis and severity of stimulus.[5]

Clinically, teeth affected with PCO may be asymptomatic or symptomatic, exhibiting yellowish discoloration with reduced translucency due to tertiary dentin deposition based on the degree of obliteration. Nonetheless, when the symptoms are present, endodontic treatment is warranted. A success rate of 80% has been reported for nonsurgical endodontic treatment with PCO.[6] However, PCO presents a significant clinical challenge during access cavity preparation, canal orifice identification, and root canal negotiation, potentially resulting in iatrogenic errors.

Maxillary molars erupt at a younger age and have deep pits and fissures with increased tooth surface area, making them highly prone to caries.[7,8] Proximal surfaces of molars are difficult to clean and lead to proximal caries.[9] Pulp response to caries can vary between root canals within the single tooth,[10] making them an ideal model to observe the different stages of PCO. However, conventional two-dimensional radiographic evaluation of maxillary molars is more challenging due to overlapping structures and root canals may be partially visible or even radiographically invisible, which may further complicate endodontic diagnosis due to their complex root canal anatomy. Consequently, assessing the status of PCO in correlation to caries may enhance diagnostic accuracy, treatment outcome, and clinical relevance.

Cone-beam computed tomography (CBCT) offers three-dimensional multiplanar radiographic visualization of complex root canal systems which is more sensitive than routine periapical radiographs. CBCT imaging may enhance preoperative assessment and help clinicians to anticipate procedural difficulties during endodontic treatment. Endodontic diagnosis requires high spatial resolution of 0.2 mm or less.[11]

Previous studies have identified the correlation between the location of caries and PCO in mandibular molars, indicating the presence of PCO in the canals opposite to the carious lesion present.[3] However, root canal anatomy of maxillary teeth differs from the mandibular teeth. To date, no study has assessed the correlation between caries location and PCO in maxillary molars using CBCT imaging modality. Understanding root-specific susceptibility in maxillary molars has direct implications for access cavity design, canal negotiation strategies, and risk prediction of iatrogenic errors. Therefore, the aim of the study was to determine the correlation between caries location and PCO in maxillary molars using CBCT images. The null hypothesis stated that there is no correlation between the location of caries and PCO in maxillary molars.

MATERIALS AND METHODS

The study design was planned in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology guidelines. This study was a retrospective observational analysis on CBCT scans of maxillary molars teeth with proximal caries. The study was approved by the ethics committee (IEC/AIIMSA4996/03.10.2025). The institutional ethics committee waived the informed consent requirement due to the retroactive, noninterventional design.

A total of 1371 CBCT scans (Next Generation i-CAT; Imaging Sciences International, Hatfield, PA) of patients aged 18–49 years, from 2015 to 2025, were retrieved from the database of the institute following ethical approval. 1209 CBCT scans were excluded due to reasons including dental anomalies, mesio-occluso-distal caries, previous endodontic or restorative treatment, immature apices, grossly decayed teeth, and low image quality. One hundred and sixty-two scans with proximal caries (either mesial or distal) in maxillary molars were selected [Figure 1].

Figure 1.

Flowchart showing the selection process of cone-beam computed tomography scans

CBCT scans evaluation was done by reviewing 50 CBCT scans in collaboration with a maxillofacial radiologist to ascertain the absence and presence of calcifications within the root canals. Two endodontists (Y.P.K and A.S), as calibrated evaluators with substantial clinical experience evaluated the selected scans. The scan evaluation was conducted using CBCT multiplanar reconstruction mode, producing three-dimensional images (resolution <0.2 mm, FOV 8 cm × 8 cm) with the assistance of a maxillofacial radiologist to determine and obtain consensus on the location and extent of PCO. This was repeated after 1 week to check the reliability of the assessment. Inter-observer (0.82) and intra-observer (0.88) reliability was assessed using Cohen’s kappa statistics. CBCT scans were evaluated in a dimly lit setting on the 23.8-inch full high definition (1920 × 1080) display to enhance the image clarity and quality. The evaluators were permitted to adjust the brightness and contrast during the assessment. Only one maxillary molar per CBCT scan was considered as unit of analysis to avoid patient-level clustering. However, root-level observations within a tooth may not be fully independent. The mesiobuccal (MB), distobuccal (DB), and palatal roots of the selected tooth were separately evaluated for the presence or absence of calcifications within the root canal in both sagittal and coronal planes. For calibration in the sagittal plane, CBCT section was delineated at the level of the buccal roots and the assessment was done by dynamically moving the CBCT planes in an anteroposterior direction. In a similar manner, the CBCT section was positioned at the level of the palatal root for evaluation. For calibration in coronal plane, the CBCT scan was dynamically moved in the bucco-lingual direction for each root. The axial section was evaluated in an apico-coronal orientation from the cementoenamel junction to the root apex to examine root canal patency. PCO was graded as partial or complete obliteration of the root canal space along the root length on CBCT in any plane.

During any disagreement, the two observers conducted concurrent evaluations to achieve the consensus. If consensus was not reached, the final interpretation was made by the dental and maxillofacial radiologist. During the evaluation, the presence of calcified areas within the root canals was noted in datasheet. Demographic information of the patients, location of PCO present, and caries location was documented and analyzed. Figures 2 and 3 show the representative CBCT images of PCO.

Figure 2.

Sagittal section of maxillary molar showing mesial proximal caries and pulp canal obliteration in the distobuccal root with constricted root canals. Arrow points towards the narrowing of root canals (PCO). PC: Proximal caries, PCO: Pulp canal obliteration, MB: Mesiobuccal root, DB: Distobuccal root

Figure 3.

Coronal section of maxillary molar showing (a) presence of pulp canal obliteration (PCO) in the distobuccal root, (b) absence of PCO in the mesiobuccal root. Arrow points towards the narrowing of root canals (PCO). PC: Proximal caries, PCO: Pulp canal obliteration, MB: Mesiobuccal root, DB: Distobuccal root, P: Palatal root

Statistical analysis

Cross tabulation was performed to evaluate the association between PCO and caries location (mesial vs. distal) as well as gender. The Pearson Chi-square test was employed to assess statistical significance. For 2 × 2 tables, a continuity correction was applied, and when expected cell counts were <5, Fisher’s exact test was used. The strength of association was expressed as odds ratios (ORs) with 95% confidence intervals (CIs), obtained from the risk estimate procedure in SPSS (version 26, IBM Corp., Armonk, NY, USA). P < 0.05 was considered statistically significant.

RESULTS

A total of 162 CBCT scans were included in the study. PCO was noted in 21.2% of maxillary molars. Among 162 maxillary molars, the incidence of proximal caries was not significantly (P = 0.157) different at mesial (n = 90) and distal sites (n = 72). Table 1 indicates that in mesial proximal caries, the prevalence of PCO was higher in DB root (35.6%) compared to the MB root (18.9%) and palatal root (1.1%), although this difference was not statistical significance. Similarly, in the distal proximal caries, the prevalence of PCO was greater in DB root (50%) compared to MB root (20.8%) and palatal root (2.8%). The total prevalence of PCO was 42% in the DB root, 19.8% in the MB root, and 1.9% in the palatal root, regardless of the caries location.

Table 1.

Comparison of pulp canal obliteration prevalence between mesial and distal proximal caries across different roots of maxillary molars

Root type	Caries location	PCO absent, n (%)	PCO present, n (%)	Total, n (%)	χ2 (P)
Mesiobuccal	Mesial	73 (81.1)	17 (18.9)	90 (100)	χ2=0.095 P=0.757
	Distal	57 (79.2)	15 (20.8)	72 (100)
Distobuccal	Mesial	58 (64.4)	32 (35.6)	90 (100)	χ2=3.427 P=0.064
	Distal	36 (50.0)	36 (50.0)	72 (100)
Palatal	Mesial	89 (98.9)	1 (1.1)	90 (100)	χ2=0.611 P=0.434
	Distal	70 (97.2)	2 (2.8)	72 (100)

PCO: Pulp canal obliteration

The correlation between caries location (mesial vs. distal) and the presence of PCO was assessed individually for each root, as illustrated in Table 2. When compared to distal caries, mesial caries in the MB root showed similar odds of PCO (OR = 0.88; 95% CI: 0.41–1.92; P = 0.757), suggesting no statistical significance. Mesial caries in the DB root had lower odds of PCO than distal caries (OR = 0.55; 95% CI: 0.29–1.04); this difference was close to but not statistically significant (P = 0.064). Caries location and PCO in the palatal root exhibited no significant correlation (OR = 0.39; 95% CI: 0.03–4.43; P = 0.434). Overall, there was no association found between caries location and PCO in maxillary molars, although a trend toward higher PCO occurrence in DB root with distal caries was noted. The prevalence of PCO was analyzed across various patient demographics. PCO exhibited no significant difference between males and females. In MB root, PCO was more prevalent in females (24%) compared to males (16.1%), although this difference was not statistically significant (P = 0.207). In the DB root, PCO showed higher predilection in females (44%) (P = 0.628) than in males (40.2%), however, this difference was not statistically significant.

Table 2.

Odds ratio analysis showing the association between caries location (mesial vs. distal) and the presence of pulp canal obliteration in individual roots

Root	OR	95% CI	P
Mesiobuccal	0.88	0.41–1.92	0.757
Distobuccal	0.55	0.29–1.04	0.064
Palatal	0.39	0.03–4.43	0.434

OR: Odds ratio, CI: Confidence interval

DISCUSSION

The present study used CBCT imaging to evaluate the correlation between the location of proximal caries and site of PCO in maxillary molars. The null hypothesis was accepted, as no statistically significant correlation was observed between the location of caries and PCO. The results of the study suggest that regardless of caries location, higher prevalence of PCO was observed in the DB root, with a tendency toward increased occurrence with distal caries. The overall prevalence of PCO among teeth with proximal caries was 21.2%. When analyzed on a root wise basis, the DB root demonstrated the highest prevalence of PCO (42%), followed by the MB root (19.8%) and the palatal root (1.9%). The data reveal that the prevalence of PCO in maxillary molars is influenced by root-specific susceptibility rather than solely by caries site, indicating that specific roots may exhibit greater vulnerability to calcific alterations than others. Due to the very low prevalence of PCO in the palatal root, the estimated OR for palatal root should be interpreted with caution, as low event rates can lead to unstable estimates.

The results of the current study are in partial agreement with previous study done in mandibular molars, where the prevalence of PCO due to proximal caries has been reported as 47%.[3] Notably, PCO is commonly observed in the root canal opposite to the carious lesion in mandibular molars, indicating that the pulpal tissue is protecting itself from the stimulation by nearby dentin-pulp complexes. On the other hand, the results of our study in maxillary molars demonstrated that the DB canal is most affected irrespective of caries location, which may reflect anatomical and histological variations between maxillary and mandibular teeth.

Multiple factors could justify the higher predilection of the DB root for PCO. The DB root is typically smaller in diameter and has a narrower pulp canal compared to the MB and palatal roots. Narrower canals may experience accelerated or more pronounced calcific changes in response to irritation.[12] Second, fluctuation in vascular supply could influence the pulp’s reparative response. The pulp vascular network actively modulates tissue responses, with hypoxic stress enhancing angiogenic signaling that may influence reparative and calcific processes within the pulp tissue.[13,14] Third, maxillary molars endure different occlusal forces on each root. The DB root may experience stress patterns that promote tertiary dentin deposition or canal calcification, independent of caries.[15] The proximity to the furcation area and differences in dentinal tubule density may affect the dissemination of irritation and the ensuing odontoblastic response.[16] The trend toward significance (P ≈ 0.064) further substantiates the therapeutic relevance of this result, despite the absence of statistical significance. However, the absence of statistical significance does not exclude a biological association but may reflect limited power to detect the small effect sizes.

Prior studies indicated a 95% increase in the occurrence of PCO in carious teeth compared to caries-free and attrition-free teeth.[17] Different mechanisms such as release of growth factors,[18,19] T-lymphocyte stimulation, and migration of dendritic cells to odontoblastic layers from the sub-odontoblastic regions,[20] increase in neurogenic mediators like CGRP, substance P to stimulate BMPs,[21] were elucidated reasons on incidence of PCO in caries exposed teeth. Although these mechanisms provide plausible explanations, direct evidence linking these factors specifically to DB root PCO is limited.

In the present study, CBCT imaging played a vital role in identifying and evaluating PCO in maxillary molars. In contrast to traditional radiographs, CBCT offers high-resolution, three-dimensional views that enable the accurate assessment of root canal anatomy and minute calcifications.[22,23] Each root was examined in the sagittal, coronal, and axial planes to improve observer agreement and enabled root-wise analysis. Thus, the application of CBCT improved PCO assessment’s precision and repeatability, demonstrating its usefulness for both clinical endodontic diagnosis and research.

Sex-related differences were also observed, with females demonstrating a slightly higher frequency of PCO (24%) compared to males (16.1%). These findings are in partial agreement with previous studies[24,25] while this difference did not achieve statistical significance, it is suggested that hormonal, metabolic, or genetic factors may influence dentinogenesis and pulp responses. However, further studies with larger cohorts are required to validate this trend.

The present study focused on maxillary molars, a region relatively underexplored compared with mandibular molars, thereby addressing the existing gap in the literature and providing clinically relevant information for endodontic diagnosis and treatment planning. The root-wise analysis, rather than a tooth-level assessment, enabled a precise evaluation of differential pulpal responses within the same tooth. Furthermore, the use of high-resolution CBCT imaging allowed three-dimensional evaluation of root canal morphology and improved detection of PCO.

However, the present study has certain limitations such as lack of clinical correlation, age-related changes which may influence pulpal calcification. Multivariate regression was not performed due to limited sample size and event rate, to avoid model overfitting. Root-wise analysis may introduce intra-tooth correlation, potentially inflating Type I error, which was mitigated by conservative interpretation of results. The extent or depth of caries could not be reliably stratified due to the retrospective nature of CBCT imaging and absence of standardized caries grading, which may influence pulpal response. Exclusion of grossly decayed teeth may have led to underestimation of overall PCO prevalence, as advanced caries could potentially induce more pronounced pulpal calcification. Finally, restriction to a single geographical location may affect the generalizability of the findings.

From a clinical perspective, PCO presents significant challenges for endodontic treatment. Pulp chamber and root canal calcification may obscure canal orifices, complicate root canal negotiation, leading to iatrogenic errors. Therefore, early detection of PCO patterns using CBCT imaging can help in diagnosis and treatment planning, especially in high-risk cases such as maxillary molars with proximal caries. Based on the findings of the present study, special attention should be given to the DB root canal during diagnosis and treatment, as it is most likely to be affected. To validate these patterns and investigate the biological processes behind preferential obliteration in the DB root, future research should concentrate on multicentric prospective studies with larger populations and clinical correlation. In addition, investigating the role of systemic conditions and patient-related factors such as age, pulp vitality, and hormonal influences may provide further insights into the pathogenesis of PCO.

CONCLUSION

PCO was observed in a notable proportion of maxillary molars with proximal caries, predominantly affecting the DB root regardless of caries location. No significant correlation was found between caries site and PCO, suggesting root-specific anatomical factors may influence calcification. High-resolution CBCT allowed precise root-wise evaluation, enhancing diagnosis and treatment planning. These findings highlight the importance of careful assessment of the DB canal and the need for larger, multicentric studies with clinical correlation to further understand PCO.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.