The impaction of the mandibular third molar is one of the most common dental problems and is important because of its potential impact on the second molar.[1] The most common oral disease worldwide is dental caries, and an estimated 2.5 billion people worldwide have untreated caries.[2] Distal caries of the second molar of the mandible is worthy of special consideration as it can form in a relatively inaccessible region, go undetected clinically, and may ultimately affect a tooth with a favourable long-term prognosis.[3] The presence of impacted third molars in the mandible can be a factor in this process, as teeth create areas to collect plaque between the third and second molars and reduce the ability for good oral hygiene, causing longer bacterial buildup.[1]

The angulation and the position of the impacted tooth have a strong association with distal caries in relation to third molar impaction.[4] Mandibular third molars are classified by Winter's classification, which specifies vertical, mesioangular, horizontal, distoangular, and other less common classifications.[5] There is a growing body of evidence that a mesioangular and horizontally positioned third molar is especially significant, due to the potential for the crown to contact or approach the distal surface of the second molar and provide a space for food impaction and the formation of cariogenic biofilm.[6] In a recent systematic review and meta-analysis, 13,788 patients were included, and the overall rate of distal caries adjacent to impacted mandibular third molars was found to be 29.89%, with the highest association seen with mesioangular impaction (43.37%).[7] Likewise, one study in 2024 using CBCT showed that 19.5% of second molars adjacent to impacted third molars had distal caries, whereas only 3.5% of the non-impaction group had distal caries; mesioangular impaction of the third molar was found to be a significant risk factor.[8]

Recent evidence has also highlighted that the sequence of impaction could have clinical utility in identifying second molars that are at higher risk. In a 2025 cross-sectional study of 1,594 eligible panoramic radiographs, 37% had impacted third molars, and 19.56% of impacted third molars were associated with distal caries in the second molar, with mesioangular impaction being a significant factor in increasing the risk of caries.[9] A more recent study found carious lesions in 39.35% of impacted mandibular third molars, especially with mesioangular, level A, and class I impactions.[10] This study suggests that the risk is not equal among all affected 3rd molars and that just knowing that a 3rd molar is impacted may not be enough to assess how clinically relevant is the specific angulation of that impaction.[10]

Although the evidence is growing, the clinical relevance of the individual Winter's classifications to distal caries of adjacent mandibular second molars is clinically significant, especially in populations where routine dental attendance and assessment of preventive measures may be limited. The most strongly associated impaction patterns with distal caries may be helpful in identifying high-risk second molars, aid in radiographic assessment of second molars, inform prevention strategies and individual decisions for monitoring or removal of third molars. Thus, the purpose of this study was to investigate the relationship between Winter's impacted mandibular third molar classifications and the presence of distal caries in adjacent mandibular second molars.

A cross-sectional analytical study was done in the Oral and maxillofacial surgery Department. The study was conducted over a period of six from November, 2025 to April 2026. The sample size was determined based on the OpenEpi version 3.01 based on reported prevalence of 19.56% distal caries in impacted mandibular third molars.[9] The calculated minimum sample size using a 95% confidence level, expected prevalence of 19.56%, and an absolute precision of 5% was 267 cases. A non-probability consecutive sampling technique was used. Patients older than 18 years of age, both male and female, whose mandibular third molar was impacted and which had a clinically and/or radiographically recognizable adjacent second molar were eligible for inclusion. Diagnostic-quality panoramic radiographs were needed that included the full crown and necessary portions of the roots of the mandibular second and third molars. Mandibular third molars that were impacted were categorized based on Winter's classification as vertical, mesioangular, horizontal, or distoangular. The second molar adjacent was examined for the presence or absence of distal caries. Patients with missing second molars, previous distal fillings, extensive restorations covering the distal surface, grossly destroyed teeth, and teeth that were not well visualized radiographically or with poor quality radiographs were excluded. Previous orthodontic treatment which involved the area of the lower molars, patients with developmental dental anomalies, patients with jaw pathology, patients with syndromes that affect tooth development, patients with a history of trauma or surgery in the area of the lower molars were also excluded. They were similar to the criteria those used in recent studies to assess the impact of third molars and second molar caries. Demographic and clinical data were then collected on a structured data collection proforma, after securing ethical approval and informed consent. Age and sex of the participants were recorded. As a routine part of a participant's dental examination, a panoramic radiograph was acquired or retrieved. The third molar was considered impacted if it had not been able to reach the occlusal plane and its angulation was classified based on Winter's classification. Radiographic measurements showed the angle between the long axes of the second and third molars of the mandible, and the third molar was classified as vertical, mesioangular, horizontal, or distoangular. The second molar on the opposite side (mandibular second molar) was then inspected for caries on the distal surface. Caries detected clinically and radiographically was noted as present or absent in the distal caries category. A radiographic assessment was used if available, with standardised digital panoramic images being taken under similar viewing conditions. Intra-observer agreement was evaluated by re-examining a subset of radiographs after a period of time. In cases where two examiners were used, differences in opinion were solved by discussion and consensus. Recent CBCT-based studies also employed the standard approach of Winter's classification and distal caries and showed that there was a significantly higher prevalence of distal caries in impacted third molar compared to non-impacted third molar sites. The numbers obtained were input and analysed with IBM SPSS Statistics. Data for continuous variables (age) were summarised as mean ± SD or median with IQR, and frequencies and percentages were presented for categorical variables (gender, Winter's classification, presence of distal caries). The Pearson chi-square test and Fisher's exact test was used to evaluate the association between Winter's classification and distal caries in the adjacent mandibular second molar. Distal caries prevalence was compared between the vertical, mesioangular, horizontal and distoangular groups of impactions. A binary logistic regression was then conducted to see if Winter's classification predicted distal caries after controlling for the other potential confounding factors including age and gender. Odds ratios (ORs) with 95% confidence intervals (CIs) were given. A p value of < 0.05 was statistically significant.

A total of 267 participants/radiographic sites were included, with a mean age of 27.8 ± 6.4 years. The majority were aged 25–34 years (47.2%), followed by 18–24 years (37.8%), while 15.0% were aged ≥35 years. The study population was 54.3% male and 45.7% female. (Table 1)

The most common Winter's types were mesioangular impaction (44.6%), vertical impaction (31.1%), horizontal impaction (18.0%) and distoangular impaction (6.4%). (Table 2)

Distal caries of the adjacent mandibular second molar was detected in 76 (28.5%) sites, while 191 (71.5%) sites did not show any evidence of distal caries. (Table 3)

A significant association was observed between Winter’s classification and distal caries (χ²=17.02, p<0.001). The most common impaction types were mesioangular (39.5%), horizontal (29.2%), vertical (15.7%) and distoangular (11.8%). (Table 4)

The mean age of the participants with distal caries was significantly higher than the mean age of the participants without caries

(p=0.011). However, gender was not significantly associated with distal caries (p=0.428). (Table 5)

In multivariable logistic regression, mesioangular impaction was independently associated with distal caries with affected sites having about threefold the odds of caries as compared to vertical impaction (p=0.001) after controlling for age and gender. Age was also independently associated with distal caries (p=0.031), but gender, horizontal impaction and distoangular impaction were not significant factors. (Table 6)

Table 1. Demographic characteristics of the study participants (n=267)

Table 2. Distribution of impacted mandibular third molars according to Winter’s classification (n=267)

Table 3. Prevalence of distal caries in adjacent mandibular second molars (n=267)

Table 4. Association between Winter’s classification and distal caries in adjacent mandibular second molars

Table 5. Comparison of age and gender according to presence of distal caries

Table 6. Binary logistic regression analysis of factors associated with distal caries

The present study revealed that there was a significant correlation between Winter's classification of impacted mandibular third molars and distal caries of adjacent mandibular second molars. Distal caries was diagnosed in 28.5% of the evaluated sites, being the highest frequency in mesioangular impactions (39.5%), horizontal (29.2%), vertical (15.7%) and distoangular (11.8%) impactions. Additionally, mesioangular impaction was an independent risk factor for the presence of distal caries when adjusted for age and sex. The results are congruent with the hypothesis that the caries risk of the second molar is associated with the shape of the impacted third molar. Overall, the rate of distal caries in this study was similar to that which has been recently reported. Jin et al., 2021, studied 500 panoramic radiographs and found that 37.6% of the mandibular second molars adjacent to impacted third molars had distal caries, with angulation of <80° and shallower impaction depth being independent factors associated with caries.[11] Likewise, Hur et al. evaluated 2,642 mandibular second molar teeth adjacent to impacted third molar teeth, and found 12.2% of the teeth had distal caries; age, third molar angulation, Winter's classification, contact point at the cementoenamel junction, and Pell–Gregory classification were identified as significant predictors.[12] These differences may have resulted from variation in case selection, definition of impaction, and the type of impaction pattern included in the Hur et al. study, since our study was specifically focused on impacted mandibular third molar sites.[12] Our study also showed mesioangular impaction was the more common pattern, with distal caries being more strongly associated with the same compared to the comparative clinical study done by Prasanna Kumar et al in 2021. They studied 341 patients and found that 50.1% had mesioangular impaction, which was significantly associated with dental caries in the adjacent second molar, which occurred in 32.2% of the cases with mesioangular impaction.[1] A similar pattern was found in our study, with 39.5% of the mesioangular impactions having distal caries. This higher prevalence in our study might be explained by differing population characteristics, diagnostic methods, or by our outcome being limited to distal caries only. This was also confirmed by Le et al. (2022) who examined 446 pairs of second and third molars in the mandible, and found the distal caries prevalence to be 50.67% for third molars with mesial or horizontal impaction. After sex adjustment, they found multivariable associations of distal caries with mesial angulation, vertical position, and horizontal position. Age was also an important predictor. Their prevalence rate was significantly higher than that of our study (28.5%), however the direction of association was similar such as with mesial angulation, the risk was increased. The difference could be due to the intentional selection of mesially and horizontally impacted third molars, which are more likely to cause a plaque-retentive contact area in close proximity to the second molar.[13] Our results are corroborated by evidence from Pakistan. In a study of 151 patients, Iqbal et al. (2022) reported that distal caries of second molar was more common with mesioangular impaction pattern of third molar (42.4%), and more common with vertical impaction (41.7%).[14] Alsaegh et al. (2022) also investigated the validity of Winter's and Pell–Gregory classifications in relation to the presence of carious lesions of adjacent second molars when examining 2,000 orthopantomograms of Emiratis. They found that the pattern and location of the impacted third molars correlated with caries development in the adjacent second molars, which further underscores the need to assess impacted tooth characteristics rather than just noting the presence of an impacted tooth. Their results match our own, which further validates the clinical significance of Winter's classification as a simple radiologic method for determining potentially hazardous third molars.[15] The association that we found in this study is also in line with the results of Toedtling et al. (2023), who examined the radiographically observed surface caries around the distal surfaces of mandibular third molars. They concentrated on anatomical and radiographic factors associated with distal caries and pointed out the significance of the position of the third molar in assessing the risk to the adjacent second molar.[3] In a large Polish radiological study of 2,488 panoramic radiographs, Poszytek and Górski found significantly higher risk of dental and periodontal lesions associated with partially impacted third molars, with horizontal and mesioangularly positioned third molars showing the highest risks. Our findings are biologically plausible because of the studies that describe the difficulty of mechanical cleaning of the distal surface of the second molar, food stagnation, and plaque accumulation when the mesioangular orientation is present.[16] The present results were confirmed by a recent study from China using CBCT in 2024. Zhou et al. analyzed 552 CBCT scans and observed that 19.5% of second molars with impacted third molars had distal caries, while 3.5% of non-impacted second molars had distal caries. Mesioangular impaction was strongly associated with distal caries (OR 11.22), as was position A and type I ramus relationship. Our adjusted odds ratio of 3.28 is similar to the mesioangular angulation effect observed in the aforementioned study. The smaller association value could be explained due to the fact that imaging modality was used, since CBCT offers a more detailed three-dimensional view of the contact relation and early carious changes compared to panoramic radiography.[8] Another study by Demyati et al. (2024) found that carious lesions are also a serious problem with impacted third molars, with 39.35% of impacted third-molar cases being associated with carious lesions. Mesioangular, level A, and Class I impactions had an especially high occurrence of distal caries of the adjacent second molar. This observation is very similar to our finding that the highest-risk Winter category was mesioangular impaction. These results, combined, suggest that mesioangular orientation might serve as a helpful indicator for closer attention to be paid to the development of second molars in a clinical setting, suggesting a need for more surveillance with appropriate x-rays.[10] The 2025 cross-sectional research study by Arandi and Jarrar is especially supportive of our findings due to the similarity of the methodology with that of the current study. In 19.56% of the impacted mandibular third molars, distal caries in the adjacent second molar was found in 1,594 panoramic radiographs. Mesioangular impaction significantly affected the likelihood of distal caries, age was an important predictor, and there was no significant relationship with the likelihood of distal caries and gender. In similar fashion, our study showed that there was a significant relationship between mesioangular impaction and gender was not significantly related to caries. The prevalence in our study was 28.5 % which was higher than the prevalence reported by Arandi and Jarrar (19.56 %), but this is possibly due to the differences in the population characteristics, clinical setting, sampling process and radiographic assessment.[9] The results are corroborated by the systematic review and meta-analysis published by Revuelta-Cortés et al. in 2025, which pooled the data regarding the incidence of distal caries of impacted mandibular third molars. Overall distal caries prevalence was reported around 29.89% and mesioangular impaction showed the highest prevalence of around 43.37%. The overall prevalence (28.5%) was also very similar to the pooled estimate and the prevalence (39.5%) of mesioangular impactions was similarly consistent with the higher risk found in the meta-analysis. This is a pooled contemporary evidence agreement that enhances the validity of the current results.[17] Limitations There were a number of limitations to the present study. Because of its cross sectional structure, a temporal or causal relationship between the impaction of mandibular third molars and the presence of distal caries of the second molar was not established. The results may not be generalizable to other tertiary care dental hospitals because they came from non-probability consecutive sampling from one hospital. Radiographic assessment was mostly based on panoramic radiographs, which could have underestimated small or early distal caries lesions when compared with bitewing and/or CBCT. Dietary patterns, oral hygiene practices, smoking, fluoride exposure, frequency of dental visits and socioeconomic status were not assessed as potential confounding factors. Moreover, only limited Winter's classifications were evaluated and anatomical variables such as Pell–Gregory classification, cementoenamel-junction distance and contact-point position were not considered.

Distal caries of adjacent mandibular second molars was highly correlated with Winter's classification. The highest prevalence of distal caries was with mesioangular impaction, and this was found to be independent of age and gender after adjustments. The results indicate that mesioangular impacted mandibular third molar should be evaluated carefully in both clinical and radiographic evaluations to detect the presence of second molars that are at higher risk for distal caries. Multicenter studies with inclusion of other anatomical, behavioral and oral hygiene variables are recommended to develop more comprehensive risk-prediction models.

1. Prasanna Kumar, D., et al., Pathologies associated with second mandibular molar due to various types of impacted third molar: a comparative clinical study. Journal of maxillofacial and oral surgery, 2022. 21(4): p. 1126-1139.
2. Qin, X., H. Zi, and X. Zeng, Changes in the global burden of untreated dental caries from 1990 to 2019: A systematic analysis for the Global Burden of Disease study. Heliyon, 2022. 8(9).
3. Toedtling, V., T. Forouzanfar, and H.S. Brand, Parameters associated with radiographic distal surface caries in the mandibular second molar adjacent to an impacted third molar. BMC Oral Health, 2023. 23(1): p. 125.
4. Yıldırım, H. and M. Büyükgöze-Dindar, Investigation of the prevalence of impacted third molars and the effects of eruption level and angulation on caries development by panoramic radiographs. Medicina oral, patología oral y cirugía bucal, 2022. 27(2): p. e106.
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6. Hadziabdic, N., et al., The clinical and radiological evaluation of impacted third molar position, crown and root morphology. Acta Medica Academica, 2023. 52(2): p. 77.
7. Revuelta-Cortes, P., et al., Prevalence of distal caries in second molar associated with impacted mandibular third molar and the position and level of impaction: a systematic review and meta-analysis. Clinical oral investigations, 2025. 29(1): p. 83.
8. Zhou, W., et al., Cone-beam computed tomographic investigation of the association between impacted mandibular third molars and the development of distal caries in adjacent second molars in a Chinese population. Heliyon, 2024. 10(23).
9. Arandi, N.Z. and A. Jarrar, Association between mandibular third molar impactions and distal carious lesions on the adjacent second molars: A cross-sectional study. Journal of International Medical Research, 2025. 53(3): p. 03000605251324489.
10. Demyati, A.K., Patterns of mandibular third molar impaction and its relationship with distal caries in the adjacent mandibular second molars: A retrospective study. The Saudi Dental Journal, 2024. 36(12): p. 1544-1548.
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