بررسی برخی عوامل آناتومیک مؤثر بر احتمال نهفتگی دندان آسیای سوم فک پایین

Introduction: Mandibular third molar impaction can sometimes be associated with pathological phenomena such as caries, pericoronitis and cystic lesions. The aim of this study was determination of some anatomic factors, including gonial, alpha and beta angles and Ganss ratio for predicting mandibular third molar impaction. Material and methods: In this cross-sectional descriptive/analytical study, 98 panoramic radiographs of patients, aged 20‒30, were divided into two groups of erupted and mesioangularly impacted third molars. Inclination of the third molar to the second molar (beta angle), third molar angle to the base of the mandible (alpha angle), the distance between the most distal point of the second molar to the anterior border of the ramus (Ganss ratio), and the angle between the posterior border of the ramus and lower border of mandible (gonial angle) were recorded. Data were analyzed by t-test using SPSS 11.5 (α=0.05). Results: Means of gonial angles in the mesioangularly impacted and erupted groups were 122.8° and 122.5°, respectively, with no significant differences (p value = 0.66). Means of beta and alpha angles and Ganss ratios in the erupted group on the right side were 42.64°, 86.11° and 1.24 and in the mesioangularly impacted group they were 21.48°, 70.85° and 0.82. Means of beta and alpha angles and Ganss ratio on the left side in the erupted group were 9.26° and 94.1° and 1.22 and in the impacted group they were 25.7° and 71.25° and 0.82 (p value < 0.001). Conclusion: Alpha and beta angles and Ganss ratios were appropriate discriminative factors for predicting impaction of mandibular third molars. The means of Ganss ratios and beta angle were higher in the impacted group and the alpha angle was greater in the erupted group. Gonial angle could not be a suitable discriminative factor for predicting the impaction of third molars. It appears by determining alpha and beta angles and Ganss ratio on panoramic radiographs at 20 years of age it is possible to predict eruption status of third molars. Key words: Impacted tooth, Panoramic radiography, Third molar