Decrease and increase in residual ridges after extraction of teeth in monkeys (part I).

The purpose of this study is to prevent and control the reduction of residual ridges. The subjects used in this study consisted of 19 crab-eating monkeys which were divided into four groups according to the extraction area. These categories are 1U0L group (extracted on M1), 1U5L group (extracted on M1 and M3M2M1P2P1), 0U5L group (extracted on M3M2M1P2P1), and 5U1L group (extracted on M3M2M1P3P1 and M1). Impressions were taken before the extraction. Further impressions were taken at three week, six week, three month, six month, one year, and two year intervals after the extraction in order to observe morphological changes. Casts were made immediately thereafter and the cross-sectional areas of the residual ridges were measured by a standardized method with the aid of a Kubuskraniophor and a diagraph. The measurements taken of the right side, which was operated on, and the left side, which served as the control, were compared in order to observe changes in the form of the edentulous area. The results were as follows: 1) Increase in the Residual Ridge Areas: It is highly significant that the measurements of the M1 section of the 1U5L group and the M1 section of the 5U1L group gradually decreased until the sixth week, and then began to increase until the areas were approximately equivalent to the measurements of the areas before the extraction after a two-year period. This may be due to the fact that along with the elongation of the neighboring teeth, the alveolar bone grew to such an extent that the resorption rate was surpassed. 2) Decrease in the Residual Ridges Areas: With the exception of the above-mentioned sections, almost all of other sections responded in the expected manner, that is, there was a sharp decrease in the areas of these sections. The decrease took place rapidly. Seventy to 80% of the total loss occurring over the two-year period took place in the first three months. After a sharp decline in the initial three-month period, the process continued at a slow pace. This gradual decrease after a short period of rapid decrease typifies the standard pattern of the edentulous resorption process.