Characteristics, patterns, and prevalence of impacted mandibular second molars in Chinese Americans: A radiographic study

Introduction

Permanent mandibular second molar (MM2) eruption disturbances and impaction are relatively uncommon dental anomalies. However, its early diagnosis is necessary to prevent problems that could require multiple and complex treatments. The present study evaluates early radiographic characteristics, patterns, and prevalence of MM2 impactions.

Methods

Initial panoramic radiographs of 5,575 orthodontic patients aged 9-15 years (mean, 13 years) from Chinese American ethnic origin were examined for MM2 impaction and the presence of associated adjacent permanent mandibular third molar (MM3). These radiographs were analyzed according to gender, position, and type of angulation of impacted MM2s, the presence or absence and the stage of development of the adjacent MM3s.

Results

A prevalence of 2.4% for MM2 impaction was detected in 136 patients with 213 impacted MM2s in the Chinese American study group. Increased mesial angulation was present in most of the impacted MM2s (51%). MM3s were found adjacent to the impacted MM2s in 93.4% of the patients in various stages of development, and the most common stage was the half-crown (44%). Various patterns of the impacted MM2 adjacent to the permanent mandibular first molar were described and classified. Bilateral impactions were present more than unilateral.

Conclusions

A prevalence of 2.4% was detected for MM2 impaction in Chinese American orthodontic patients in New York City. Most of them presented an increased mesial angulation with their crowns in contact at the cementoenamel junction of the adjacent first molars. Third molars were detected developing distally or occlusally adjacent to most of the impacted second molars, but the possible involvement of the third molars in MM2 impaction is questionable. A new classification scheme for MM2 impaction into six patterns according to the level of contact with the adjacent first molars’ distal aspect is presented. Early radiographic detection, preventive and interceptive measures, and initiating orthodontic intervention should be considered for impacted MM2s.