Changes in the curve of Spee with treatment and at 2 years posttreatment.

The purposes of this study were to determine pretreatment skeletal and dental patterns related to curve of Spee depth, evaluate changes in the curve of Spee with treatment and the effects on dentofacial structures, and determine factors associated with the stability of the curve of Spee after treatment. Lateral cephalograms and dental casts were evaluated for 24 white male and 26 white female patients at pretreatment, posttreatment, and at least 2 years postretention. All patients had mandibular permanent second molars and premolars erupted and in occlusion. The following variables were correlated with increased pretreatment curve of Spee depth: low Frankfort-mandibular plane angle, deep overbite, increased overjet, and Class II molar malocclusion. No significant differences were found in pretreatment curve depth between male and female patients or between right and left sides. Leveling the curve of Spee was accomplished by uprighting the molars, extruding the premolars, and intruding or flaring the incisors. Extraction and nonextraction cases demonstrated no significant differences in the amount of curve relapse. Increased curve relapse was correlated with postretention increases in overbite, irregularity index, and patients given removable retainers. Overall, the curve of Spee was relatively stable after treatment, with only a 16% relapse of the leveled curve.