In proceeding with orthodontic treatment, the prediction for the shape, growth rate and growth direction of mandible plays a major role to set up the treatment plan and determine its period and prognosis. Various approaches being made so far have shown that the linear and angular measurement using lateral cephalograms are relatively accurate to estimate them
This study was purposed to find the shape of mandible more clearly by preventing the overlap of the Condyle head area which appears in lateral cephalogram, and to estimate its growth rate by comparing the growth quantity and ratio via lateral area measurement.
This experimental was performed against 40 patients total, of which Class I of 14, Class II of 9 and Class III of 17 consist. Wide open lateral cephalograms of 40 patients were taken over average period of 4 Year 3 Months, then the linear and angular measurements were carried out with 11 itemized lists. Autocad R14 application program was utilized to draw their appearance, measure and compare their lateral area.
As a result of study, conclusions were made as follows;
1. Mandibular´body length (gonion-menton) tended to increase in order of CITI,.CI and CH, and Mandibular body length of CIII group had a tendency to grow twice faster than that of CII group.
2. In lateral ifems such ah Go-Me, A-Cd, B-Cp, E-F and G-H, CIII showed a significant increase on the year-average quantity and rate of the growth, and especially apparent difference was observed in CHI group rather than CH group.
3. For the 4 Year 3 Months period, the year-average growth quantity of lateral area of the mandible was 1.0 cm2 for Class I, 0.8 cm2 for Class II and 1.4 cm 22 for Class III, which corresponds to 11.9%, 11.8% and 20.3% of growth ratio respectively. Thus, growth ratio almost 2 times more than other groups was observed in group CIII while growth ratio between group CI and CH has little difference.
4. Considering the results as above, it can be proposed that the difference in size of the mandible between groups is caused by the difference in the growth rate and growth quantity of the mandible, which generated in the middle of growth, rather than the difference in size of congenital jaw-bone.
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