Abstract
We studied the relationship between the development of the first molar in its eruption locality during the period of deciduous dentition and changes in the eruption of the first molar in the jaw bone and examined the effect of the eruption locality size on the deciduous dentition. The material used in this study consisted of serial dental casts of the early and late stages of deciduous dentition and right and left oblique(45°)cephalograms of 26 caries-free children with clinically normal deciduous dentition (12 boys and 14 girls). Eruption locality on the serial dental casts was examined by moire topography, and the relationships between changes in eruption of the first molar, the size of the apical base and dental arch, and the interdental space volume were studied. The results obtained were as follows:
1) The use of moire topography facilitated determination of the precise volume and morphology of the eruption locality of the first molar.
2) The length of the eruption locality on the moire topograms increased by 2.11mm in the case of the maxilla and by 1.65 mm in the case of the mandible from the early stage to late stage of deciduous dentition.
3) The eruption locality volume increased by 58.86% in the case of the maxilla and by 24.13% in the case of the mandible from the early to late stages of the deciduous dentition.
4) With regard to mesial and distal positional changes in the highest portion of the eruption locality, both the maxilla and mandible tended to move distally. With respect to buccolingual positional changes, the highest portion of the eruption locality tended to move buccally in the maxilla and lingually in the mandible.
5) As far as the relationship between development of the eruption locality and changes in the eruption of the first molar are concerned, the eruption locality was completely formed in the maxilla with eruption of the first molar, and while the axial inclination of the first molar was related to the size of the eurption locality in the early stage of deciduous dentition in the mandible. There was, however, no such relationship in the late stage.
6) There was a relationship between the posterior development of the apical base and increase in eruption locality, but no clear relationship between the size of the dental arch and the interdental space.
7) It is important for occlusal guidance to take into consideration three-dimensional changes in the development of the first molar.
