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[Root surface area. Part 2. The change of the root surface area corresponding with periodontal tissue reduction].

The purpose of this investigation was to study the relation between the level of existing periodontal supporting tissues when involved with periodontal disease and the area of root surface. The root length from cemento-enamel junction to the apex of the root was divided into four equal parts. The root surface area of each divided part was measured by the method described in the part I. The result were as follows : 1) In upper and lower premolars the proportion of the root surface area of each divided part to total root surface area decreased with approaching to the apex. In other teeth than premolars the part of a quarter to half length of the root from cemento-enamel junction was the largest of all the four divided apex to a quarter length of the apex was the smallest. 2) The proportion of the root surface area corresponding with the distance from the apex to each divided part decreased more in upper and lower premolars than in any other teeth. 3) The root surface area from half length of the apex was approximately 43-44 % of the total root surface area. 4) The first and the second premolars in upper and lower were similar to each other in their total root surface area and in root surface area corresponding with the distance from the apex to each divided part. 5) The canine tooth in upper and lower jaws has the largest remaining root surface area corresponding with the decrease in attachment level of all the single rooted teeth.