1983 Volume 25 Issue 1 Pages 117-143
In order to obtain satisfactory clinical success in the treatment of periodontally affected multi-rooted teeth the importance of studying their anatomical characteristics and the specific features of furcation involvements has been emphasized.
The purpose of this study is to investigate the different states of stress being distributed in the remaining surrounding alveolar bone according to the different levels of bone resorption, when occlusal force worked on a multi-rooted teeth. Especially the action of levers might operate more effectively when the occlusal force worked on the involved side of the multi-rooted teeth with intraosseous defect, because it has a longer mesio-distal or wider bucco-lingual dimension.
A two-dimensional model copy based on the anatomical relationships of the mandibular first molar and the periodontal supporting structures served as the material. Eight different load directions and seven different vertical levels of intraosseous resorption were assumed as the experimental parameter. The qualitative and quantitative stress distribution were investigated using the photoelastic experiment and the finite element method.
From the results obtained from the seven steps of bone resorption; ranging from the physiologic case to that with the defect beyond the interradicular septum; four load directions proved practically enough to represent the load direction working on the mandibular first moalr. These are: the load directed to the mesial cusp, the oblique mesial incline of the mesial cusp, the distal cusp and the central fossa. From the calculated stress distribution and stress value, the following could be concluded:
A) Physiological alveolar bone level.
In the photoelastic experiment, strong stress concentration was seen in the root apex, and a wide stress distribution was found around the inter-radicular septum. Using the finite element method, the stress values induced in the surrounding alveolar bone were calculated.
1) In the mesial alveolar bone, the crest showed the minimum stress, and the area one third from root apex showed the maximum stress.
2) In the mesial side of the furcation, the area right beneath the furcation showed the minimum stress, and the area around the root apex showed the maximum stress.
3) In the distal side of the furcation, the area right beneath the furcation showed the minimum stress and the area one half from the root apex showed the maximum stress.
4) In the distal alveolar bone, the crest showed the minimum stress, and the area one third from the root apex to one fourth from the root apex showed the maximum stress.
Furthermore, of all the measurements, the furcation area showed the minimum stress.
B) Mesial alveolar bone resorption.
In the photoelastic experiment, the stress concentration of the apex decreased and the stress distribution of the interradicular space became intensive. In the finite element method, the increase of stress value was moderate until bone resorption reached to one third of the root length, but with further bone resorption the stress value showed a marked increase.
C) Resorption of the interradicular septum.
In the photoelastic experiment, the stress concentration of the root apex increased. In the finite element method, the increase of stress value was moderate until resorption of the interradicular septum reached to one third of the root length, but with further bone resorption, the stress value showed a marked increase.
These results show that in accordance with the alveolar bone resorption, there is a marked change in the stress distribution pattern of the remaining alveolar bone aroundd the multi-rooted teeth.
