[A three-dimensional study on alignment of upper permanent buccal teeth during the period of buccal teeth exchange].

Developmental changes of the buccal teeth segments on the longitudinal dentitions during the period of buccal teeth exchange and the factors having effect on their dimensional changes were investigated by using three groups: normal group, group with good alignment in spite of the premature loss of the second deciduous molar and the group resulting ultimately in bad alignment. The dimensional changes were observed as the positional changes of each buccal teeth, first permanent molars and permanent lateral incisors on the three dimensional coordinate, which was defined by the rugae, median raphe and papilla on the palate of the plaster model. As the result, the increment of the buccal arch segment placed between the permanent lateral incisor and the first permanent molar occurred mainly by the eruption of the permanent canine as well as of the first premolar in consequence of the forward and mesial migration of the permanent lateral incisor and in some cases backward migration of the first permanent molar by the eruption of the first premolar caused by the eruptive force of these permanent teeth. The decrement, on the contrary, was observed mainly by the eruption of the second premolar with the large forward migration of the first permanent molar. In the cases with a premature loss of the second deciduous molars, the increment of the segmental dimension was observed by the eruption of the second premolar, contrary to the normal group.