Vertical changes following first premolar extractions.

Orthodontic treatment involving the extraction of first premolars has been implicated in the dental literature as an etiologic factor in the development of temporomandibular joint (TMJ) disorders. Authors have proposed that the extraction of first premolars causes a decrease in the vertical dimension of occlusion. The purpose of this study was to investigate the validity of this claim. Records of 45 Class I, nonextraction cases and 38 Class I, first premolar extraction cases were obtained. The pretreatment and posttreatment cephalographs were digitized, and several cephalometric variables were examined to evaluate the vertical changes occurring as a result of orthodontic treatment. Statistical analysis of the data revealed no significant differences between the vertical changes occurring in the extraction and nonextraction groups. On average, orthodontic treatment in both groups produced an increase in the cephalometric vertical dimensions that were examined.