[Longitudinal study of dental arch forms, with special reference to normal and malocclusions]

The purpose of the present study was to investigate the developmental changes of dental arch forms by using longitudinal materials. The data was derived from dental casts and roentgenographic cephalograms collected from a longitudinal growth study of Japanese children from the age of 5 to 15 years. The materials were divided into three groups of occlusion at the time that the children had full permanent dentitions as follows; normal occlusion group (N-group; N = 19), Angle's class I crowding group (CR-group; N = 11), Angle's class II malocclusion group (CL2-group; N = 7). In addition, members of these groups were classified into three developmental stages as follows; deciduous, mixed and permanent dentition. The developmental changes in dental arch forms were analyzed from metrical measurements of dental casts and roentgenographic cephalograms. The measurements, such as dental arch lengths, widths, amount of interdental space or crowding, mesiodistal crown diameters, overjet and overbite, were obtained from dental casts, and those of incisor inclination angles and ANB angles were from roentgenographic cephalograms. Finally, principal component analysis was performed to clarify the developmental changes of dental arch forms in the series of longitudinal data. The results were as follows; 1. A method was devised for drawing dental arch forms directly from dental casts using compasses, sliding calipers and rulers. 2. Dental arch lengths and widths of the CR-group were uniformly smaller from the deciduous to permanent stages than those of the N-group. 3. The CL2-group showed nearly the same sizes of arch lengths and widths as the N-group at the deciduous stage. Nevertheless, these dimensions of the CL2-group increased considerably and showed larger sizes of arch lengths and widths than the N-group in mixed and permanent stages except in the case of maxillary arch widths. 4. The sum of mesiodistal crown diameters of the CR-group were quite similar to those of the N-group in all three stages. On the other hand, the CL2-group tended to be larger in both arches than the N-group in all stages. 5. So far as the deciduous stage is concerned, the amount of interdental space was significantly larger in the N-group than in the other two groups. 6. Throughout all stages, there were no significant differences in the maxillary central incisor inclination angles among the three groups, while the CR-group tended to show lingual inclination of the mandibular central incisor compared with the other two groups.(ABSTRACT TRUNCATED AT 400 WORDS)