A Three-dimensional Finite Element Analysis Of The Tilted Mandibular Molar As A Fixed Bridge Abutment

With the development of prosthodontics, fixed partial denture (FPD)has become the first choice of those patients with missing teeth due to its particular advantages. However, it is frequently found that the adjacent teeth may tilt mesially if they are not restored in time, especially the second mandibular molar with the lost first molar. Although Tylman has insisted that it was inappropriate to choose those teeth tilted over 24 degrees as bridge abutments, many scholars have made researches about this issue in order to improve the application of such teeth. With these work as basis, this subject is to compare the stress distribution of dental supporting structures of a tilted mandibular molar as an abutment before and after the restoration of three-unit fixed partial denture (mandibular second premolar to second molar) and to evaluate the influence of different tilting angles on the stress distribution of the molar abutments using software of finite element analysis, by this means, in order to accumulate some biomechanical information for the restoration oftilted molar and provide some reference for clinical practice on indications and prognosis.This research can be divided into four parts as follows:1. Construction of A three-dimensional finite element analysis model of three-unit mandibular fixed partial dentureThe objective is to construct a three-dimensional finite element analysis model of three-unit mandibular fixed partial denture. One three-dimensional finite element model of 3-unit fixed partial denture was constructed by the combination of the Computerized Tomography (CT) scanning technology and ANSYS software. The model has good geometry similarity and can be deleted, rotated, incised, and added easily according to different demands. The model constructed by the CT scanning technology and software can simulate the natural condition and facilitate the further biomechanical research.2. Stress distribution in the dental surrounding tissues of the tilted mandibular molar as a fixed bridge abutment before andafter restorationThe objective is to compare the stress distribution in the dentalsurrounding tissues of a tilted mandibular molar before and after the restoration of three-unit fixed partial denture using finite element analysis. Five three-dimensional finite element models of 3-unit fixed partial denture in which the second molar were tilted different degrees toward the second premolar and their unrestored models were constructed with the basis of previous part. A vertical load was applied to the central fossa of the second molar. Compare the stress distribution between two models. Results indicated that theintroduction of a fixed partial denture decreased the stress in the bone mesial to the root and adjacent to the apex of the tilted molar and increased the stress surrounding the second premolar. The placement of the fixed partial denture modified the stress distribution around the roots of the tilted molar abutment and favored the tilted molar at the aspect of mechanics.3. Stress distribution in the dental surrounding tissue of normal mandibular second molarApply the axial pain threshold of the mandibular second molar to it before restoration and take the stress in dental alveolar bone as the threshold in this subject.That will provide some reference for the research on stress distribution of the abutment with different tilting angles.4. Stress distribution in the dental surrounding tissues of the tilted mandibular molar as bridge abutment with different tilting degreesThe objective is to evaluate the influence of different tilting angles on the stress distribution of the molar abutments using finite element analysis to look for the scope of restoration of tilted abutment. Five three-dimensional finite element models of 3-unit fixed partial dentures in which the second molars were tilted different degrees toward the second premolar were constructed. A same vertical load was applied to the second molar on the central fossa in each case. Compare...