Inferior Alveolar Nerve Proximity in Mandibular Molar Distalization: Implications for Orthodontic Treatment Planning

Samantha Hsien-Chu Mao, Department of Orthodontics, Kaohsiung Chang Gung Memorial Hospital and Chang Gung, University College of Medicine, Kaohsiung, Taiwan
Chia-Hsuan Chan, Department of Orthodontics, Kaohsiung Chang Gung Memorial Hospital and Chang Gung, University College of Medicine, Kaohsiung, Taiwan
Yu-Jen Chang, Department of Orthodontics, Kaohsiung Chang Gung Memorial Hospital and Chang Gung, University College of Medicine, Kaohsiung, Taiwan
Shiu-Shiung Lin, Department of Orthodontics, Kaohsiung Chang Gung Memorial Hospital and Chang Gung, University College of Medicine, Kaohsiung, Taiwan
Chen-Feng Cheng, Department of Orthodontics, Kaohsiung Chang Gung Memorial Hospital and Chang Gung, University College of Medicine, Kaohsiung, Taiwan
Te-Ju Wu, Department of Orthodontics, Kaohsiung Chang Gung Memorial Hospital and Chang Gung, University College of Medicine, Kaohsiung, TaiwanFollow

Abstract

Purpose: This study aimed to clarify the anatomical boundaries of mandibular molar distalization, emphasizing the risk of inferior alveolar nerve (IAN) contact. Patients and Methods: In total, 30 skeletal Class III patients undergoing orthognathic surgery (59 mandibular hemi-arches) were analyzed using pretreatment three-dimensional (3D) computed tomography scans. The shortest horizontal distance between the mandibular second molar and the inferior alveolar canal (M2-IAC) was measured at multiple depths below the cementoenamel junction, along with the distance to the lingual cortical plate (M2-MLC). Samples were categorized by vertical facial pattern (low-, normal-, and high-angle case). Simulated distalization cases predicting IAN contact were recorded. Results: Potential IAN contact after full distalization of the second molar was observed in 8 of 59 mandibular sides (13.6%). High-angle cases occurred most frequently (25%), followed by low-angle (16.7%) and normal-angle (3.7%) cases. In most cases, M2-MLC was shorter than M2-IAC, indicating that the lingual cortex would be reached before the nerve; however, in four cases M2-IAC was shorter, suggesting that the nerve would be contacted first. Typically, the distal root apex was the initial point of IAN contact. Conclusion: In Class III skeletal patients, due to the sufficient buffer zone between the mandibular second molar and the IAC, the nerve is seldom the limitation of molar distalization. However, if a larger-than-5 mm molar distalization is attempted, a careful evaluation should be made beforehand, especially those with hyperdivergent (high-angle) skeletal patterns, which showed minimal clearance between the molar root and the IAN. These results highlight the importance of 3D imaging and careful planning to prevent possible IAN impacts during mandibular molar distalization.

Recommended Citation

Mao, Samantha Hsien-Chu; Chan, Chia-Hsuan; Chang, Yu-Jen; Lin, Shiu-Shiung; Cheng, Chen-Feng; and Wu, Te-Ju () "Inferior Alveolar Nerve Proximity in Mandibular Molar Distalization: Implications for Orthodontic Treatment Planning," Taiwanese Journal of Orthodontics: Vol. 38: Iss. 1, Article 2.
https://doi.org/10.38209/2708-2636.1393
Available at: https://www.tjo.org.tw/tjo/vol38/iss1/2