Pre-eruptive Factors of Tooth Rotation and Axial Inclination

¹ Forsyth Dental Infirmary and Department of Oral Pediatrics, Tufts University School of Dental Medicine, Boston, Massachusetts.

This investigation was undertaken to determine the pre-eruptive causes of rotation and the axial inclinations of the lower premolars. Angular measurements were obtained directly from the study models and radiographs with the aid of an arm protractor. From 503 longitudinal case records, 180 cases of the lower first premolars and 211 cases of the lower second premolars were selected for study.

In Group I, the normal sample, less than 3° of mean rotation was found in both erupting first and second premolars. The mean axial inclinations were 88.9° for the first premolars and 92.76° for the second premolars.

In Group II, the mean rotations were 6.26° for the first premolars and 11.9° for the second premolars. The differences of the means were found to be significant at the 1 per cent level of confidence when compared with the means of the normal sample. The mean axial inclinations were 88.31° and 93.29° for the first and second premolars, respectively, and no significant difference was found between the means of Groups I and II.

In Group III, the mean rotations were 11.71° for the first premolars and 23.57° for the second premolars. The mean differences between this group and the normal sample, were found to be significant at the 1 per cent level of confidence. It was also found that cases which had lesions in the deciduous molar root area for more than one year showed significantly greater mean rotations than those which had lesions for less than one year. The means of axial inclination were 88.44° for the first premolars and 91.74° for the second premolars.

In Group IV, the mean rotations were 12.66° and 25.59° for the first and second premolars, respectively. The mean differences between this group and Group I were also found to be significant at the 1 per cent level of confidence. The mean axial inclinations were 83.71° and 88.00° for the first and second premolars, respectively. These mean axial inclinations were found to be significantly different at the 1 per cent level of confidence when compared with the normal group.

In general, it was found that the lower first and second premolars had a characteristic tendency to rotate in a mesial direction. This tendency, as well as the severity of rotation, was found to be greater in second premolars than the first premolars.

It was concluded that (1) the preservation of a deciduous molar with apical pathology is contraindicated, and (2) the extraction of the lower first permanent molar prior to the eruption of adjacent premolars should be avoided, if possible.

This article has been cited by other articles:

				L. B. Messer, J. T. Cline, and N. W. Korf Long Term Effects of Primary Molar Pulpotomies on Succedaneous Bicuspids Journal of Dental Research, February 1, 1980; 59(2): 116 - 123. [Abstract] [PDF]