Abstract
The purpose of the present study was to investigate the relationship of occlusal contacts from an early to later stage of the 1st permanent molars. The subjects examined in the study were 13 children ranging from the early (mean age 6.5 years. ) to the later stage (mean age 7.7 years. ). Two cast models and occlusal bites were obtained and the interocclusal relationship was then evaluated by using the “Occlusogram” computed image analyzing system. The main system consisted of a CCD camera (PX-390A, PIAS), personal computer (PC-9801RX, NEC), image analyzer (LA-525MS, PIAS) and digitizer (D3110, PIAS). A CCD camera standardized at the right angle to the measuring plane of cast 250 mm apart. The sampling image was input into the personal computer, and an image analyzer and digitizer were then used for analysis.
The accuracy of the system was evaluated first and the items measured were; The number of occlusal contact, the area of occlusal contact and the displacement of the centroid of occlusal contact shown on either 2nd primary molars.
The following results were obtained;
1) The accuracy based on distance between the CCD camera and model was 200 mm: 0.096%,250 mm: -0.106%,300 mm: 0.276%,350 mm: 0.326%in that order.
2) The mean numbers of occlusal contact points of the 1st and 2nd primary molars were noticed, while those of the 1st permanent molars significantly increased from 1.3 to 3.3 point (p<0.01) during the early and later eruptive stages of the 1st permanent molar.
3) The mean area (mm2) of occlusal contacts of the 1st and 2nd primary molars did not show any difference during the eruptive period of the 1st permanent molar. However, those of the 1st permanent molars significantly increased from 0.69 to 2.29 mm2 (p<0.01).
4) The centroid of occlusal contact of the lower 2nd ipsilateral primary molars was displaced disto-buccaly while the 1st permanent molars was erupting. The mean length and angle of the displacement of the centroid on the occlusal contact of the 2nd primary molar were 1.11 mm and 54.46°in the left and 1.09 mm and 61.88° in the right side.
Based on this data the mesio-lingual movement of 2nd primary molars due to the erupting 1st molar was suggested.
