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Published on: February 23, 2024
Evaluation of retromolar space for mandibular molar distalization: A retrospective cross-sectional CBCT study of
Yuke Shi1, Hong Zhou1, Shangyou Wen1
1State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases & Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
Objectives:
This study aimed to examine the available retromolar space for mandibular molar distalization and its influencing factors and evaluate the diagnostic accuracy of panoramic radiography in assessing retromolar space compared to cone-beam computed tomography (CBCT).
Methodology:
This retrospective cross-sectional study included 126 eligible patients (252 sides) between January 2020 and December 2023. Mesiodistal and buccolingual angulations of second molars (M7MDA and M7BLA), mesiodistal angulations of third molars (M8MDA), ANB and SN-MP, and the distance between the second molar crown and the anterior border of the ramus (M7RamusPa) were measured. Retromolar space was measured at different horizontal planes (cementoenamel junction, mid-root, and apex) intersected by different buccolingual sections (buccal, middle, and lingual). The diagnostic accuracy of panoramic radiography was compared with CBCT.
Results:
Of the 126 participants (mean age 25.06±6.28 years), 252 sides were analyzed. Retromolar space was the smallest at the apical lingual site (Apex-L). Linear mixed-effects modelling revealed that the Apex-L space was significantly associated with M7DRamusPa (β=0.34, P<0.001), M8MDA (β=0.27, P=0.001), and hypodivergent vertical pattern (β=1.01, P<0.001), but not with M7MDA or M7BLA (both P>0.05). The positive predictive values of panoramic radiography for available retromolar space were 0.99 (95% CI: 0.95-1.00), 0.77 (0.70-0.84), and 0.61 (0.55-0.67) for hypodivergent, normodivergent, and hyperdivergent patients, respectively.
Conclusions:
The lingual cortex at the apical level is the anatomic limit for mandibular molar distalization. Distal crown tipping and buccal root torque of the mandibular second molar are recommended. Panoramic radiography underestimates and overestimates available retromolar space among hypodivergent and hyperdivergent subjects, respectively, versus CBCT. This study was approved by the Ethics Committee of the West China School of Stomatology, Sichuan University (approval number: WCHSIRB-D-2022-469) and supported by the Angelalign Clear Aligner Research Programme (grant no. SDTS21-1-18). The authors declare no conflict of interest, as the funders played no role in the study design, data collection/analysis or preparation of the manuscript.
