A Prospective Study on the Effect of Oral Function on Natural Adaptation of Mandibular Molars during Maxillary Slow Expansion

Abstract

Maxillary lateral expansion is often the treatment of choice for narrowing of the dental arch width during the mixed dentition period. Although morphological changes in the maxilla and oral function before and after maxillary expansion treatment have been reported, few studies have focused on natural adaptation of the mandibular dental arch. Therefore, we investigated the relationship between the adaptation of the mandibular dentition and oral function in maxillary expansion treatment. Nineteen patients（9 boys and 10 girls; mean age, 8.9±1.1 y）diagnosed with narrow maxillary and mandibular dental arches were enrolled. Evaluations were performed at the initial examination（T1）and 3 and 6 months after the start of expansion（T2 and T3, respectively）. Oral morphology and function were compared before and after treatment. The masticatory patterns were divided into gliding and chopping types, and the amount of change in morphology and function before and after treatment was compared. Significant lateral expansion was observed in the mandibular dentition without the appliance. The maxillary first molar width increased significantly with expansion treatment. The mandibular first molar width increased for adapting to the maxillary dental arch expansion. Additionally, a positive correlation was observed between the width of the masticatory pathway at T1 and the amount of change in the width of the mandibular molars before and after treatment.　Thus, natural adaptation of the mandibular dentition after slow expansion treatment of the maxilla could have been influenced by the masticatory motion.