Distally displaced premolars: A dental anomaly associated with palatally displaced canines.Am J Orthod Dentofacial Orthop. 2010 Sep; 138(3):318-22.AJ
The aim of this study was to evaluate the significance of association between distally displaced premolars (DDP) and palatally displaced canines (PDC) in the pattern of associated phenotypes of dental developmental disturbance.
A sample of 2811 subjects (mean age, 9 years 7 months +/- 1 year 3 months) was divided randomly into 2 groups. The first group of 500 subjects was the control group. The reference prevalence rates for the examined parameters were calculated for this group: DDP (measured with the distal angle theta and the premolar-molar angle gamma); PDC; and other dental anomalies, specifically, aplasia of the third molars, aplasia of the contralateral mandibular second premolar, aplasia of the maxillary lateral incisors, and small maxillary lateral incisors. Of the remaining 2311 subjects, the first 100 with a diagnosis of DDP of at least 1 mandibular second premolar comprised experimental group 1 (DDP group). In addition to sex distribution, the same variables that were examined in the control group were analyzed. In the subgroup with the concurrent DDP and PDC (experimental group 2, or DDP-PDC group), the presence of other dental anomalies was investigated. The prevalence rate for PDC in experimental group 1 was compared with that in the control group. The same was done for the prevalence rates for the 4 other dental anomalies in the PDC-DDP group (experimental group 2) vs the prevalence rates for these anomalies in the control group. All comparisons were performed with chi-square tests with the Yates correction (P <0.05), as were the comparisons between the sexes in experimental groups 1 and 2. The values for theta and gamma angles in experimental group 1 were compared with the values for these angles in experimental group 2, as well as with those in the control group. These statistical comparisons were made with analysis of variance (ANOVA) with the Bonferroni post-hoc test (P <0.05).
The prevalence rate for PDC in experimental group 1 (28%) was significantly greater than in the control group (4.2%) (P <0.01). Significantly greater prevalence rates for aplasia of the second premolars, aplasia of the maxillary lateral incisors, and small maxillary lateral incisors were found in the PDC-DDP group (experimental group 2) compared with the control group. Significant sex differences (P <0.01) were found in both experimental groups.
A significant relationship between distal displacement of unerupted mandibular second premolars and PDC was found. Because DDP is diagnosed earlier than PDC, it can be a developmental risk indicator for displaced maxillary permanent canines.