Impacted mandibular third molars are among the most frequently encountered dental developmental abnormalities and represent a common reason for dental radiographic assessment and oral surgical referral. Although many impacted third molars remain asymptomatic, their presence may be associated with a variety of pathological consequences affecting the third molar itself or adjacent anatomical structures.¹ One clinically important complication is external root resorption of the adjacent mandibular second molar. Root resorption may remain asymptomatic for an extended period and can compromise the long-term prognosis of the affected second molar when substantial root structure is lost. Early recognition of patients at increased risk may therefore facilitate appropriate monitoring and timely intervention.²

The likelihood of root resorption appears to be influenced by the spatial relationship between the impacted third

molar and adjacent second molar.³ Third-molar angulations is particularly important, with horizontally and mesioangularly impacted teeth frequently reported to have a closer relationship with the distal aspect of the second molar. The depth of impaction and degree of contact between the third molar and second-molar root may further influence the likelihood of resorptive changes.⁴ Several radiographic studies have reported an association between impacted mandibular third molars and distal root resorption of adjacent second molars. However, reported prevalence estimates vary considerably according to population characteristics, imaging modality, diagnostic criteria and the characteristics of the impacted teeth.^3-6

Three-dimensional imaging may identify resorptive lesions that are not readily apparent on conventional panoramic radiographs. Nevertheless, panoramic radiography remains widely used for initial assessment because of its accessibility, relatively low radiation exposure and ability to provide an overview of the mandibular dentition.⁵ The identification of radiographic characteristics associated with root resorption is particularly relevant in treatment planning. If specific patterns of impaction are associated with substantially increased risk, patients with such features may benefit from closer radiographic surveillance or consideration of earlier surgical management.⁶

Therefore, the present study was designed to determine the prevalence of adjacent second-molar root resorption associated with impacted mandibular third molars and to evaluate the relationship between root resorption and third-molar angulation, depth, classification and radiographic contact with the adjacent second molar.

A cross-sectional radiographic study was designed to evaluate the association between impacted mandibular third molars and external root resorption of adjacent mandibular second molars. For the panoramic radiographs containing 250 impacted mandibular third molars were evaluated. Patients were included if the mandibular third molar was impacted and the adjacent second molar was fully visible on the panoramic radiograph. Radiographs with severe distortion, poor image quality, extensive pathology obscuring the root surface or previous surgical removal of the adjacent second molar were excluded. Each mandibular third molar was evaluated for its angulation relative to the long axis of the adjacent second molar and classified according to Winter's classification as vertical, mesioangular, horizontal or distoangular. The depth of impaction was assessed using the Pell and Gregory classification. The relationship between the third molar and the adjacent second-molar root was also recorded as no contact, close contact or apparent overlap/contact. External root resorption was defined radiographically as an irregular loss or reduction in the external contour of the adjacent second-molar root attributable to the impacted third molar. Both the presence and absence of resorption were recorded. Age and Gender were also recorded. Where both mandibular third molars were present and eligible, each tooth was assessed according to the predefined radiographic criteria. All radiographic assessments were performed using standardized viewing conditions. For reliability assessment, a subset of radiographs was re-evaluated after an appropriate interval, and intraobserver agreement was determined using Cohen's kappa statistic. Ethical approval was obtained from the institution vide # IRB-01AED-3377. Categorical variables were presented as frequencies and percentages. Associations between root resorption and categorical radiographic variables were assessed using the chi-square test. Variables demonstrating significant associations in univariable analysis were subsequently entered into a multivariable logistic regression model. Adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Statistical significance was set at p<0.05.

A total of 250 impacted mandibular third molars were evaluated. The mean age of the patients was 27.4 ± 5.8 years, with an age range of 18–42 years. There were 132 (52.8%) males and 118 (47.2%) females. Radiographic evidence of external root resorption involving the adjacent mandibular second molar was identified in 38 (15.2%) cases, while 212 (84.8%) showed no evidence of resorption (Table 1).

Table 1. Demographic characteristics of the study population

Root resorption was most frequently associated with horizontal impaction, occurring in 13 of 53 cases (24.5%), followed by mesioangular impaction in 18 of 99 cases (18.2%). Resorption was observed in 6 of 85 vertically impacted third molars (7.1%) and 1 of 26 distoangular impactions (3.8%). The association between third-molar angulation and adjacent second-molar root resorption was statistically significant (p<0.001) (Table 2).

Table 2. Root resorption according to third-molar angulation

Root resorption was also significantly associated with the depth of impaction. Resorption occurred in 23 (21.8%) of the 106 third molars positioned at or below the cervical level of the adjacent second molar, compared with 15 (9.4%) of 144 more superficially positioned third molars (p=0.002) (Table 3).

Table 3. Root resorption according to impaction depth

The spatial relationship between the impacted third molar and second-molar root demonstrated an even stronger association. Root resorption was identified in 25 (30.5%) cases in which close contact or apparent overlap with the second-molar root was present, compared with 13 (7.7%) cases without close contact (p<0.001) (Table 4).

Table 4. Root resorption according to relationship with second-molar root

Pell and Gregory classification was also significantly associated with root resorption. Resorption was more frequent among Class II and Class III impactions than Class I impactions (p=0.018). However, the association with ramus relationship was weaker than that observed for third-molar angulation and direct root contact. Age was modestly higher among patients with root resorption than among those without resorption (29.1 ± 6.2 vs. 27.1 ± 5.7 years; p=0.041). No statistically significant association was observed between sex and root resorption (p=0.638).

In multivariable logistic regression, horizontal impaction remained independently associated with root resorption (adjusted OR=3.86, 95% CI: 1.61–9.24; p=0.003). Close contact or apparent overlap between the impacted third molar and second-molar root was also independently associated with increased risk (adjusted OR=4.72, 95% CI: 2.01–11.08; p<0.001). Greater impaction depth remained a significant predictor (adjusted OR=2.41, 95% CI: 1.12–5.19; p=0.024) (Table 5).

Table 5. Multivariable logistic regression for predictors of root resorption

The present study identified radiographic evidence of adjacent second-molar root resorption in 38 (15.2%) of impacted mandibular third molars. The most important finding was that root resorption was significantly associated with third-molar angulation, impaction depth and close radiographic contact with the adjacent second-molar root. Horizontal impaction and close contact remained independent predictors after adjustment for potential confounding factors. The prevalence observed in the present study is broadly comparable with previous radiographic investigations, although reported rates vary substantially. Differences in prevalence are expected because studies use different imaging modalities, age groups and definitions of root resorption. Panoramic radiography may also underestimate subtle or buccally/lingually located resorptive defects compared with cone-beam computed tomography (CBCT). Therefore, the 38 (15.2%) prevalence observed in the present cohort should be interpreted within the context of the imaging modality and diagnostic criteria. The strong association between horizontal impaction and root resorption is consistent with previous research. Horizontally impacted third molars frequently lie in direct proximity to the distal cervical or middle root region of the second molar, creating a mechanical and anatomical relationship that may predispose to resorption. Studies using panoramic radiography and CBCT have repeatedly identified horizontal or mesioangular third molars as important radiographic patterns associated with adjacent second-molar root resorption.7-9 The present study found root resorption in 24.5% of horizontally impacted teeth, compared with 18.2% of mesioangular, 7.1% of vertical and 3.8% of distoangular impactions (p<0.001). This gradient is clinically meaningful because it suggests that third-molar angulation may help clinicians identify patients requiring closer assessment. However, angulation should not be considered in isolation because the actual three-dimensional relationship between the third molar and second-molar root may be more important than angulation alone. The particularly strong association between close contact/overlap and root resorption supports this interpretation. In the present study, resorption occurred in 30.5% of cases with close contact or apparent overlap compared with only 7.7% of cases without close contact. After adjustment, close contact remained the strongest independent predictor, with an adjusted OR of 4.72. This finding is consistent with the concept that direct anatomical proximity between the impacted third molar and the second-molar root is a major determinant of resorptive risk.10-12 Previous CBCT-based investigations by Arandi et al. (2025)13 have similarly emphasized the importance of three-dimensional contact and relative positioning. In particular, resorption may be more readily identified when the third molar is positioned directly against the distal aspect of the second molar. This may explain why studies using CBCT sometimes report higher prevalence than panoramic radiographic studies. The present study also demonstrated a significant association between greater impaction depth and root resorption. Resorption occurred in 21.8% of teeth positioned at or below the cervical level of the second molar compared with 9.4% of more superficially positioned teeth. Deeper impaction may increase the likelihood of prolonged and intimate contact with the adjacent second-molar root. Previous radiographic studies conducted by Arandi et al. (2025)13 have also identified increased depth as a potential risk factor, although the strength of this relationship varies between populations. Pell and Gregory classification showed a significant association with root resorption in the present study, but the association was weaker than that observed for angulation and direct root contact. This finding is important because Pell and Gregory classification primarily describes the relationship of the third molar to the ramus and occlusal plane, whereas root resorption is more directly influenced by the spatial relationship between the third molar and second-molar root. Thus, classification systems may be useful for overall surgical assessment but may not fully predict root resorption risk. The present study also found a modest association between age and root resorption. Patients with resorption were slightly older than those without resorption. Previous studies have reported conflicting findings regarding age. Increasing age may provide a longer period during which pathological interaction can develop, but age is also strongly associated with changes in third-molar position and the decision to retain or remove impacted teeth.14,15 Therefore, the observed relationship should not be interpreted as evidence that age independently causes root resorption. No significant association was found between sex and root resorption. This finding is consistent with the biological nature of the condition, which is primarily related to anatomical and spatial relationships rather than sex-specific factors. Where previous studies have identified differences between males and females, these may partly reflect differences in sample composition, age distribution or third-molar characteristics.16

The present study identified radiographic evidence of adjacent second-molar root resorption in 38 (15.2%) of impacted mandibular third molars. The most important finding was that root resorption was significantly associated with third-molar angulation, impaction depth and close radiographic contact with the adjacent second-molar root. Horizontal impaction and close contact remained independent predictors after adjustment for potential confounding factors. The prevalence observed in the present study is broadly comparable with previous radiographic investigations, although reported rates vary substantially. Differences in prevalence are expected because studies use different imaging modalities, age groups and definitions of root resorption. Panoramic radiography may also underestimate subtle or buccally/lingually located resorptive defects compared with cone-beam computed tomography (CBCT). Therefore, the 38 (15.2%) prevalence observed in the present cohort should be interpreted within the context of the imaging modality and diagnostic criteria.

The strong association between horizontal impaction and root resorption is consistent with previous research. Horizontally impacted third molars frequently lie in direct proximity to the distal cervical or middle root region of the second molar, creating a mechanical and anatomical relationship that may predispose to resorption. Studies using panoramic radiography and CBCT have repeatedly identified horizontal or mesioangular third molars as important radiographic patterns associated with adjacent second-molar root resorption.7-9

The present study found root resorption in 24.5% of horizontally impacted teeth, compared with 18.2% of mesioangular, 7.1% of vertical and 3.8% of distoangular impactions (p<0.001). This gradient is clinically meaningful because it suggests that third-molar angulation may help clinicians identify patients requiring closer assessment. However, angulation should not be considered in isolation because the actual three-dimensional relationship between the third molar and second-molar root may be more important than angulation alone. The particularly strong association between close contact/overlap and root resorption supports this interpretation. In the present study, resorption occurred in 30.5% of cases with close contact or apparent overlap compared with only 7.7% of cases without close contact. After adjustment, close contact remained the strongest independent predictor, with an adjusted OR of 4.72. This finding is consistent with the concept that direct anatomical proximity between the impacted third molar and the second-molar root is a major determinant of resorptive risk.10-12

Previous CBCT-based investigations by Arandi et al. (2025)13 have similarly emphasized the importance of three-dimensional contact and relative positioning. In particular, resorption may be more readily identified when the third molar is positioned directly against the distal aspect of the second molar. This may explain why studies using CBCT sometimes report higher prevalence than panoramic radiographic studies. The present study also demonstrated a significant association between greater impaction depth and root resorption. Resorption occurred in 21.8% of teeth positioned at or below the cervical level of the second molar compared with 9.4% of more superficially positioned teeth. Deeper impaction may increase the likelihood of prolonged and intimate contact with the adjacent second-molar root. Previous radiographic studies conducted by Arandi et al. (2025)13 have also identified increased depth as a potential risk factor, although the strength of this relationship varies between populations.

Pell and Gregory classification showed a significant association with root resorption in the present study, but the association was weaker than that observed for angulation and direct root contact. This finding is important because Pell and Gregory classification primarily describes the relationship of the third molar to the ramus and occlusal plane, whereas root resorption is more directly influenced by the spatial relationship between the third molar and second-molar root. Thus, classification systems may be useful for overall surgical assessment but may not fully predict root resorption risk. The present study also found a modest association between age and root resorption. Patients with resorption were slightly older than those without resorption. Previous studies have reported conflicting findings regarding age. Increasing age may provide a longer period during which pathological interaction can develop, but age is also strongly associated with changes in third-molar position and the decision to retain or remove impacted teeth.14,15 Therefore, the observed relationship should not be interpreted as evidence that age independently causes root resorption.

No significant association was found between sex and root resorption. This finding is consistent with the biological nature of the condition, which is primarily related to anatomical and spatial relationships rather than sex-specific factors. Where previous studies have identified differences between males and females, these may partly reflect differences in sample composition, age distribution or third-molar characteristics.16

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