A comparative study of gonial angle and growth of the lower third molar in cleft lip and palate. An orthopantomographical study.

In children and young adults with cleft lip and palate, the gonial angle, the angle between the lower second molar and the mandibular plane, the angle between the longitudinal axes of the second and third molars as well as the timing of the development of the third molar were investigated on the right and left side from orthopantomograms. The results were compared with the corresponding results in a noncleft Finnish material. The series consisted of 100 randomly selected subjects aged from 10 to 24 years, 57 males and 43 females. One to three orthopantomograms were available for each subject, totalling 201. The results were examined in a cross-sectional and longitudinal material. The right and left gonial angles were not found to differ in the different cleft groups. Among subjects with cleft lip and palate the gonial angle was found to be larger in the different age groups than the corresponding values in the comparison material. In both materials, the gonial angle was found to decrease between the ages of 10 and 15 years. In males with cleft lip and palate the decrease in this angle, however, continued up to the age of 19. The anterior angle between the longitudinal axis of the lower second molar and the mandibular base line was about 10 degrees larger than in the comparison material, being slightly larger than that in the Angle's Class III occlusion type in the comparison material. When examined by degrees of development the development of the lower third molar was delayed approx. 0.9 years in males and 1.6 years in females compared with the corresponding times in the comparison material.