Stress Distribution In The Dental Surrounding Tissues Of The Abutments When The Titled Mandibular Molar As An Attachment Fixed Partial Denture Abutment: A Three-dimensional Finite Element Analysis

The tilted posterior teeth represent a clinical problem which frequently confronts the dentists. The most common offender is the lower second molar. Restoration of an edentulous space with a fixed partial denture when a tilted molar is involved presents the problem of attaining a common path of insertion for all abutments and excessive preparation for tilted molar. One mechanical method for solving the problem of a common path of insertion is the precision attachment. Attachment retained prosthesis is easily accepted by partially edentulous patients, due to its characteristics like good retention, stability, esthetics as well as little sense of foreign body. Attachment fixed partial denture, which was divided into two separate parts and each part will be inserted individually according to its own path and a retainer-receptacle attachment links the two parts into one rigid restoration in the oral cavity ,has become one of the idea therapeutic methods in the treating of the tilted mandibularmolar as an abutment The purpose of the task is to study stress distribution in the dental surrounding tissues of the titled mandibular molar as an attachment fixed partial denture abutment.The mandible is a kind of material which shows anisotropic characteristics in biomechanical function. But in the most of the past three dimensional finite elements models, the mandibles were regarded as an isotropic material. Another purpose of the task is to compare stress distribution in the surrounding tissues of the titled mandibular molar as an attachment fixed partial denture abutment when the mandible was regarded as an anisotropic or an isotropic material.Two three dimensional finite element models of attachment fixed partial denture in which the second molar were tilted 30 degrees toward the second premolar and its unrestored model were constructed by the combination of the Computer Tomographic(CT) scanning technology and Ansys software. Different static loads were applied.The stress distribution in the surrounding tissues of a titled mandibular molar ,before and after the restoration of attachment fixed bridge, the mandible regarded as an anisotropic or an isotropic material ,were compared and analyzed. Result: After restoration, when the mandible was regarded as an anisotropic material and vertical and oblique loads were applied ,the stress distribution in the surrounding tissues of the titled mandibular molar were modified and more adjacent to the axis of the tilted molar. After restoration, when the mandible was regarded as an isotropicmaterial, the trend of the stress change is the same as the anisotropic.When the mandible was regarded as an anisotropic and isotropic materialrespectively , the stress distribution in the periodontal ligament has no significant difference, but the difference of the stress distribution in the alveolar bone was great, especially applying horizontal loads. Conclusion: The restoration of the attachment fixed partial denture modified the stress distribution in the dental surrounding tissues of titled mandibular molar and favored the tilted molar at the aspect of mechanics. The increasing stress surrounding the second premolar can be shared by the teeth adjacent to it. After analyzing the stress distribution when the mandible was regarded as anisotropic and isotropic material, we can suppose that if we only study the periodontal ligament, the mandible can be assumed as an anisotropic material in order to simplify the calculation, but if alveolar bone was analyzed, the mandibular bone should be regarded as anisotropic material for analysis precision.