Analysis of body mass index, the mandible, and dental alveolar arch factors in prediction of mandibular third molar impaction: a pilot study.

AIM The aim of this study was to determine how some physical characteristics can be used to predict the occurrence of impacted mandibular third molars. BACKGROUND While the concept of prophylactic removal of the asymptomatic erupting or impacted mandibular third molar has generated much controversy over the years, new theories of therapeutic surgical removal of the erupting tooth and therapeutic agenesis of the tooth bud are emerging. However, there are a few studies that address the anthropometric factors that could predict an impacted mandibular third molar. METHODS AND MATERIALS The study included Nigerian patients of both genders who were at least 16 years of age. A total of 83 subjects participated in the study; there were 44 (53 percent) females and 39 (47 percent) males. RESULTS Eighty-one (97.6 percent) of the participants were between 16 and 23 years old, while 2 (2.4 percent) were between 30 and 39 years old, of which 44 (53 percent) were women and 39 (47 percent) were men. There were 38 (45.8 percent) cases of impaction and 45 (54.2 percent) cases of unimpacted third molar. The mean and standard deviation values of BMI for the two groups in males and females were 21.10±1.90, 22.40±2.70 and 22.00±2.40, 22.30±1.99 respectively, with no significant difference, p>0.05, CI 95%. The two determinant factors of impaction were mandibular length and the difference between alveolar arch length (p=0.04) and total teeth size. Both of these variables had significant inverse correlations with impaction values of p=0.04 and p=0.003, respectively. The prediction values were 59 percent for mandibular length and 81.9 percent for differences between mandibular length and teeth sizes, respectively. The synthesized prediction value by the two determinant factors is 75.6 percent.The subjects were divided into two categories: presence of impaction (Group 1) and absence of impaction (Group 2). Impaction of the mandibular third molar was assessed by clinical and radiographic evaluation. Body mass index (BMI) of each subject was determined by measuring the body weight (BW) and body height (BH), then dividing the weight of the body by the square of the height. The mandibular index (MI) was assessed by measuring the length and width of the mandible (MW). It was calculated by dividing the width of the mandible by the length of the mandible. The mandibular length (ML) consisted of the total teeth sizes of the three anterior teeth, the two premolars, and the first and second molars. These dimensions were measured with a divider/ruler and recorded. The anterior-posterior distance of the arch from the midline to the retromolar pad (alveolar arch length) also was measured. CONCLUSION The prediction of mandibular third molar impaction was mainly dependent on two factors: the length of the mandible and the difference between arch length and total teeth size. CLINICAL SIGNIFICANCE Small mandible, small dental arch, and large teeth are risk factors that are strongly associated with the occurrence of impacted third molars.