Prevalence of Short Dental Roots in Four Ethnic Groups in an Orthodontic Population

Root resorption is the most frequent unwanted side-effect of orthodontic treatment and occurs in all patients to various degrees. A number of factors have been found to be associated with root resorption including dental anomalies, syndromes, variations in dental anatomy, gender, orthodontic mechanics, disturbances during development, and genetic polymorphisms. Past research has found that developmentally short dental roots, or teeth with certain anomalies, are at increased risk of root resorption during orthodontic treatment. Past research has also found that maxillary incisors are more predisposed to root resorption during orthodontic treatment than other teeth. Developmentally short roots may develop from three mechanisms: disturbances during development, resorption of previously well-formed roots, or genetics. Short root anomaly is a genetic condition where bilateral maxillary incisors and less commonly canines and premolars have a crown to root ratio of at least 1:1.6. These teeth are at a 41.1% increased of experiencing root resorption during orthodontic treatment. Two previous studies mentioned that the prevalence of developmentally short dental roots may differ between races, but neither investigated if one or more ethnic groups have a higher prevalence of developmentally short dental roots. The purpose of the current study was to investigate if a significant relationship exists between ethnicity and short dental roots. In addition, hypotheses were stated that Hispanics have a higher prevalence of short dental roots than Caucasians, African Americans, and Asian; females have a higher prevalence of short dental roots than males. The experimental groups consisted of 30 Caucasians, 30 Hispanics, 30 African Americans, and 26 Asian patients that presented to University of Illinois Department of Orthodontics for treatment. The subjects had to satisfy specific inclusion criteria to be included in the study. Maxillary and mandibular central and lateral incisors, and 2nd premolars, were measured on periapical radiographs. The actual root length and relative root length values along with the subjects ethnicity was recorded. The data was first tested for normality. Two way analysis of variance tests were done using ethnic group and gender as factors for all teeth. Scheffe tests were used to isolate pair-wise differences among groups, and interactions between groups were shown graphically. The results of this study found that Asians had the shortest dental root lengths for all teeth measured, except the maxillary 2nd premolar. Statistically significant differences in root length were found between ethnic groups for the maxillary central incisor, mandibular central and lateral incisors, and mandibular 2nd premolar. Significant differences in relative root length values between the ethnic groups were found for the maxillary central incisor and 2nd premolar. In general, Caucasians and Hispanics had larger relative root length values, and African Americans and Asians had smaller relative root length values, but these differences were not always statistically significant. One exception was that Caucasians were found to have the smallest relative root length value for the maxillary 2 nd premolar. Statistically significant differences between genders were found for the maxillary central and lateral incisors, and mandibular central incisor and 2nd premolar root lengths; the maxillary central incisor and 2nd premolar relative root lengths. Females had shorter roots than their male counterparts within each ethnic group.