Prevalence of Class I, II and III skeletal relationships and its association with dental anomalies in an ethnic Chinese orthodontic population

Abstract

Objectives: To investigate the prevalence of skeletal Classes I, II and III in a Chinese orthodontic population, and determine its association with the prevalence of dental anomalies. Methods: This retrospective cross-sectional study was conducted on 2508 ethnic Chinese orthodontic patients aged 14 to 25 years who attended the Department of Orthodontics at the National Dental Centre Singapore. Radiographs, photographs and clinical records of the study sample were examined for the prevalence of dental anomalies in the permanent dentition, excluding third molars. The anteroposterior skeletal relationship was determined based on the A point–Nasion–B point angle measured from the lateral cephalogram, whereby Class I: A point–Nasion–B point = 3.6° ± 2.5° (1 standard deviation) that is 1.1° to 6.1°; Class II: A point–Nasion–B point greater than 6.1°; Class III: A point–Nasion–B point less than 1.1°. Logistic regression was used to determine the association between the anteroposterior skeletal relationship and the occurrence of various dental anomalies. Results: The prevalence of the anteroposterior skeletal relationship was: 49.5% Class I; 23.1% Class II; and 27.4% Class III. Class III patients had significantly lower odds of impacted teeth compared to Class I patients (odds ratio 0.608, 95% confidence interval 0.463–0.798; P =0.00009). There was no significant difference in the occurrence of the anomalies among the various anteroposterior skeletal types. Conclusions: The occurrence of impacted teeth was lower in Class III than Class I, while no significant differences were noted for hyperdontia, hypodontia, peg-shaped upper lateral incisors, transposition and double teeth. The occurrence of all investigated dental anomalies had no significant difference between Class II and Class I.