No abstract

The first aim of this study was to devise a meaningful, objective, and reproducible method of measuring premolar rotation on study casts. A new method of measurement was devised, using standardized arch forms as the reference line superimposed on the study casts. The method error of the difference in two determinations was calculated as +/- 2.95 degrees. Using this method, premolar rotations were measured on study casts at 15 years of 203 children enrolled in the Nittedal Growth Study. Histograms of the frequency distribution for each premolar were drawn and the mean rotations compared. Correlation coefficients were then calculated to determine if any intra-quadrant, intra-arch, or inter-arch relationships existed. Significant correlations were found between contra-lateral teeth in the same arch (P less than 0.001) and to a lesser degree between premolars in the same quadrant. Significant inter-arch correlation was found between left upper and lower second premolars (P less than 0.001). Surprisingly, some cross-arch relationships were found between the upper left second premolar and lower right second premolar (P less than 0.001), and between the upper right second premolar and lower left second premolar (P less than 0.01). It is suggested that aetiological factors in premolar rotation are genetic and, to a lesser extent, local factors. The significant correlation found between the upper and lower left second premolars suggests that occlusal factors may have a role to play.

The aim of this study was to investigate whether the rotation of teeth changed from the point of eruption until the established dentition. The first 50 cases with adequate records enrolled in the Belfast Growth Study were selected, and the premolar rotation was measured at the point of eruption and again at age 15 in the established dentition. All premolars in a quadrant with early loss of the deciduous predecessors, early loss of the first permanent molars or absence of premolars, were disregarded. The results showed that the second premolars in both the upper and lower arches which erupted rotated had a tendency to improve over the observed period. Upper and lower first premolars which erupt rotated show the same tendency to improve, but to a lesser extent and less frequently than the second premolars. There seemed to be cases where a premolar deteriorated over the period, especially the first premolars.

Discontinuation of orthodontic treatment is associated with a reduced level of treatment outcome.

No abstract