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Mandibular second molar impaction. Part I: Genetic traits and characteristics
Yehoshua Shapira1, Tamar Finkelstein, Nir Shpack
1Department of Orthodontics, Maurice and Gabriela Goldshleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel. shapi@netvision.net.il
Summary
Mandibular second molar (MM2) impaction shows a genetic link, with higher prevalence in Chinese-Americans. Reduced mesial root length is a key factor in MM2 impaction development.
Area of Science:
- Orthodontics
- Genetics
- Oral Surgery
Background:
- Mandibular second molar (MM2) impaction requires accurate diagnosis for effective orthodontic treatment.
- Investigating genetic predispositions and distinct characteristics of MM2 impaction is crucial.
Purpose of the Study:
- To examine a potential genetic trait in MM2 impaction across two distinct populations.
- To identify and define specific characteristics associated with MM2 impaction.
Main Methods:
- Panoramic radiographs of 6,500 patients (Israeli and Chinese-American, aged 11-15) were analyzed.
- Twelve specific dental and skeletal characteristics were compared between impacted and non-impacted sides.
Main Results:
- MM2 impaction occurred in 1.8% of subjects, with higher prevalence in Chinese-Americans (2.3%) than Israelis (1.4%).
- Chinese-Americans exhibited more bilateral MM2 impactions (45%) compared to Israelis (27%).
- Unilateral impaction correlated with reduced mandibular arch dimensions, shorter MM2 mesial root length, and altered molar angulations.
Conclusions:
- Evidence suggests an autosomal genetic trait contributes to MM2 impaction, with higher penetrance in the Chinese-American population.
- Deficient mesial root length of the MM2 is identified as a primary developmental factor in impaction.
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