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Association between mandibular third molar impaction pattern and mandibular crowding severity: a retrospective
Yuting Wang1,2,3, Linlin Zhu1,3,4, Lin Wang1,3,5
1State Key Laboratory Cultivation Base of Research, Prevention and Treatment for Oral Diseases Nanjing 210029, Jiangsu, China.
Objective:
This study analyzed mandibular third molar (M3M) impaction and its link to mandibular crowding.
Methods:
This retrospective study included 351 M3M patients (Oct 2023-Oct 2024), with 320 analyzed after exclusion. Outcome measures included mandibular full dentition crowding (MFDC), retromolar space of the mandible (RSM), impaction angle of the mandibular third molar (IAM3M), crown width of the mandibular third molar (CW-M3), eruption height of the mandibular third molar (EH-M3), adjacent distance between the mandibular second and third molars (AD-M2M3), and root curvature of the mandibular third molar (RC-M3). Spearman correlation and linear regression identified risk factors for mandibular crowding. Receiver operating characteristic (ROC) analysis evaluated radiographic indicators' predictive value for severe crowding (>8 mm).
Results:
Among 320 subjects, 487 impacted M3M were identified, 53.39% mesial, 20.12% horizontal, 16.22% vertical, 5.75% distal, and 4.52% buccal/lingual. Crowding severity was mild (34.38%), moderate (44.06%), and severe (21.56%). Severe crowding was most frequent in mesial (60.9%) and horizontal (26.1%) impactions, with other types below 10%. One-way ANOVA showed MFDC, IAM3M, CW-M3, and EH-M3 decreased, mesial > horizontal > distal > vertical > buccal/lingual (all P<0.05); RSM, AD-M2M3, and RC-M3 increased in the same sequence (all P<0.05). Spearman analysis revealed positive correlations between impaction type and MFDC (P<0.001). Linear regression identified mesial impaction, horizontal impaction, IAM3M>30°, and RSM<2.5 mm as independent risk factors for crowding (all P<0.05). IAM3M had the best predictive value for severe crowding (AUC=0.749, 95% CI: 0.703-0.795), followed by RSM (AUC=0.719, 95% CI: 0.665-0.773).
Conclusion:
M3M impaction worsens mandibular crowding, which offers clinical guidance.