Malposition of unerupted mandibular second premolar associated with agenesis of its antimere

Aberrant tooth positions--such as infraocclusion, mesially ectopic maxillary first molar, palatally displaced canine, tooth transposition, and tooth rotation--are gaining attention as variables in a putative, genetically related pattern of dental anomalies. This study, using panoramic roentgenograms, was undertaken to measure the angular position of the unerupted mandibular second premolar (MnP2) in children. The experimental subjects were 17 children with an unerupted MnP2 and agenesis of the other MnP2, a likely indicator of site-specific genetic disturbance. An age/sex-matched control-reference group was similarly measured for comparison. The hypothesis tested was that the unerupted, developing MnP2 teeth in the experimental subjects would show measurably greater malpositions than those of the control sample. The results indicated a 10 degrees increase in distoangular inclination for the unerupted MnP2 in the agenesis sample; this was a highly significant difference statistically (P = .003), compared with the MnP2 inclinations in the control sample. These findings, associating exaggerated distoangular malposition of the unerupted MnP2 in children with agenesis of the contralateral MnP2, identify a new phenotype of dental developmental disturbance to add to the accumulated evidence supporting shared genetic mechanisms for dental anomaly patterns.