Boundary of mandibular molar distalization in orthodontic treatment: A systematic review and meta-analysis

To explore the mandibular retromolar space length (MRSL), initial root-inner cortex contact percentage (IRCCP), and the various factors that influence mandibular molar distalization. Searches were undertaken in PubMed, EMBASE, Web of Science, Cochrane Library, Scopus, and grey literature (Google Scholar and OpenGrey) for eligible cross-sectional observational studies measuring the MRSL and IRCCP in healthy adult patients. The risk of bias and evidence quality were evaluated using the Joanna Briggs Institute's checklist and GRADE framework. Thirteen studies involving 1169 patients were included for qualitative synthesis. Seven of these studies were eligible for quantitative analysis. Meta-analysis showed that the mean MRSL at the subfurcation-6 mm plane in Asian normodivergent cases was 3.78 mm (95% confidence interval [CI]: 2.81-4.35; I² = 79.7%) for skeletal Class-I malocclusions, 3.02 mm (95% CI: 2.10-3.94; I² = 62.5%) for Class-II, and 4.43 mm (95% CI: 3.14-5.73; I² = 75.1%) for Class-III. The mean MRSL at the sub-cementoenamel junction (CEJ)-10 mm plane for Asian, Class-I, normodivergent cases was 3.28 mm (95% CI: 2.44-4.12; I² = 68.9%). The mean IRCCP for Asian, Class-I, normodivergent cases was 27.2% (95% CI: 0.22-0.32; I² = 0%). In Asian normodivergent cases, MRSL ranges from 3.28 to 4.43 mm with a 27.2% IRCCP for Class-I. Cone-beam computed tomography imaging is recommended for measuring the MRSL in the apex region particularly before molar distalization. Factors influencing MRSL and IRCCP include different races, skeletal patterns, facial types, and third-molar status.