DECREASE AND INCREASE IN RESIDUAL RIDGES AFTER EXTRACTION OF TEETH IN MONKEYS (PART II).

The goal of this study is to reveal (1) the rate of elongation of upper alveolar process after loss of antagonistic teeth, and (2) a change in residual ridge area after extraction of upper elongated teeth. The subjects used in this study were seven crab-eating monkeys, which were divided into two groups; 0U5L group (extracted on M3M2M1P2P1) and 5U5L group (extracted on M3M2M1P2P1 and two years later M3M2M1P2P1). Three monkeys were in each group. In order to observe the morphological changes, impressions were taken before the extraction and at fixed intervals of three weeks, six weeks, three months, six months, one year, two years, and three years (only in the 5U5L group) after the extraction. Casts were made immediately thereafter. Then the changes in the height and cross-sectional area of the alveolar process or the residual ridge were measured. The method was the same as that described in Part I. The results were as follows: 1) 0U5L group: In the first six week period after extraction of antagonistic teeth, the height of the upper alveolar process increased rapidly, and thereafter continued to increase over the two year period. Also the change in the cross sectional area displayed the same tendency as the growth in the height of the alveolar process. 2) 5U5L group: In the first three week period after extraction of the elongated teeth, height of the residual ridge decreased rapidly, and from then on, decreased gradually over the next three year period. However, even after the decrease in height over the three year period, the height of the residual ridge was still greater than the process before elongation of the teeth. The residual ridge area displayed the typical pattern of “rapid decrease followed by a gradual decrease”. However, even after three years the area was still slightly greater than that before the elongation. Thus it is clear that, unlike the decrease in height and area of the residual ridge following extraction of normally occluded teeth, the decrease in the elongated ridge appeared to be difficult