Relationships among apical surface area, impaction level, and age in impacted mandibular third molars: a CBCT study

This study investigated the association between the apical surface area measurement (ASAM) of impacted mandibular third molars (IMTM) and chronological age at varying impaction levels, as well as ASAM differences among levels.

A total of 446 IMTM (227 right, 219 left) from 257 Malaysian patients aged 15.0 to 25.9 years were included and grouped into 0.9-year intervals. All CBCT images were analysed using Mimics and 3-matic software (Materialise NV, Belgium, version 21.0) to calculate the apical surface area. Impaction level was categorised according to the Pell and Gregory classification system. Spearman's correlation and Welch's ANOVA were conducted to assess the relationship between ASAM and age and to compare ASAM across the four levels (A, B, modified B/C, and C). Differences between left and right IMTM were assessed using an independent t-test, and analysed with SPSS (version 26).

ASAM showed an inverse correlation with age (ρ = -0.89, ρ² = 0.79), with a median of 4.86 mm² (IQR: 2.35-11.92). The steepest decline was observed between 17-18 years, followed by a plateau from 21 years onwards. Left and right IMTM were not statistically different (p = 0.53) and subsequently pooled. ASAM increased with impaction depth; however, only level C exhibited significantly larger ASAM than levels A and B (p < 0.001), with an effect size of ω² = 0.13, indicating a notable delay in maturation.

This study demonstrates the relationship between ASAM in IMTM and age, with potential applicability in dental age estimation. However, caution is advised for level C impactions, as the estimated age may be biased.