OBJECTIVES: This study aimed to quantitatively evaluate the therapeutic effect of decompression on mandibular cystic lesions using three-dimensional volumetric analysis and investigate factors influencing volume reduction patterns. METHODS: A retrospective cohort of 44 patients with mandibular cystic lesions, including 12 unicystic ameloblastomas (UAB), 12 odontogenic keratocysts (OKC), and 20 nonkeratinizing cysts (NKC), was analyzed. Volumetric measurements before and after decompression were obtained using Three- dimensional (3D) Slicer software and CBCT data. Outcome variables included absolute volume reduction (AVR), absolute speed of shrinkage (ASS), relative reduction in volume (RRV), and relative speed of shrinkage (RSS). Predictor variables were patient age, gender, presence of impacted teeth, mandibular ramus involvement, preoperative volume, and decompression duration. Statistical analyses were performed, with significance set at P ≤ 0.05. RESULTS: Significant volume reductions were observed across all groups post-decompression (P <
0.01). Preoperative volume correlated positively with AVR and ASS (P <
0.05). Decompression duration was inversely related to RSS (P <
0.05) and positively related to RRV in OKC and NKC groups (P <
0.05). Other variables showed no significant associations (P >
0.05). CONCLUSIONS: Decompression effectively reduces mandibular cystic lesion volume, with preoperative size and duration of decompression being key influencing factors. Three-dimensional volumetric analysis provides detailed, reliable evaluation of treatment efficacy, enhancing clinical monitoring and decision-making.