Abstract
BACKGROUND: Most existing difficulty indices for impacted mandibular third molar (IMTM) surgery rely predominantly on radiographic criteria and often underrepresent clinical and systemic contributors to surgical difficulty. We aimed to develop and internally assess a multidimensional clinical–radiographic difficulty score and to examine its association with operation time as a pragmatic criterion measure. METHODS: This prospective observational study was conducted in a single oral and maxillofacial surgery unit using consecutive sampling. The difficulty instrument comprised systemic (3 binary items), radiographic (9 ordinal/binary items), and clinical (6 ordinal/binary items) components, summed to yield a total difficulty score. The primary outcome was operation time (minutes). Continuous variables are reported as mean ± SD and median (IQR). Operation time was compared across predefined difficulty groups using Kruskal–Wallis testing with Bonferroni-adjusted Mann–Whitney U post-hoc comparisons. Criterion-related validity was examined using Spearman correlations with bootstrap confidence intervals. Multivariable linear regression with heteroskedasticity-robust standard errors was used to adjust for age, sex, tooth side, and surgeon experience. Discrimination for prolonged surgery (≥ 75th percentile of operation time) was assessed with ROC analysis. RESULTS: A total of 215 cases were analyzed. Mean operation time was 13.08 ± 6.64 min, and mean total difficulty score was 16.16 ± 2.24. Operation time differed across difficulty categories (Kruskal–Wallis H = 14.29, p < 0.001). Total score showed a low but significant association with operation time (Spearman ρ = 0.266, p < 0.001). In multivariable regression, total score remained independently associated with operation time (β = 0.811 min per 1-point increase, p < 0.001), while surgeon experience was associated with shorter operation time (β=−0.450 min per year, p < 0.001). ROC analysis showed modest discrimination for prolonged surgery (AUC = 0.661). CONCLUSIONS: In this single-center cohort, the proposed multidomain score showed preliminary internal evidence of criterion-related and known-groups validity and may support preoperative risk stratification and planning. External validation and objective reliability testing (inter-rater/test–retest) are warranted. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12903-026-07970-y.