Effects of post material and cement on stress distribution by using finite element analysis and in vitro fracture test

Abstract

A comparative study on the stress distribution of an endodontically treated maxillary incisor has been carried out by three dimensional stress analyses using the Finite Element Method. The role of post material and cement rigidity on reliability of endodontic restorations is discussed. Methods: A 3D FEM model of a central maxillary incisor with 2 mm surviving dentinal walls was created. The following parameters were studied: 3 loading conditions, 3 different luting cements, 4 post materials when present, and absence of post. The teeth were constructed with 5 different techniques: steel, titanium, glass fiber, zirconium posts with composite cores and composite restoration without post. Three luting cements with different elastic moduli were discussed. The structural efficiency of restorations has been evaluated under 3 different loading conditions (mastication, bruxism and impact). In this study the validity of the FEM model was controlled by an in vitro test. Twenty five recently extracted caries free, human maxillary central incisors with similar root sizes were divided into 5 groups. Endodontic treatment was subsequently performed and post core restorations were prepared and porcelain restorations were fabricated. Fracture strengths and modes of failure were determined by universal testing machine. Results and significance: There were significant differences between post systems, cements. The stresses decreased with the post material in order of steel, zirconium, titanium, glass fiber. Minimum stress values were obtained with the glass fiber post bonded with an adhesive resin cement with low elastic modulus. In functional loading, maximum equivalent stress mostly occurs at the vestibular side of the cement layer. Horizontal loading from the buccal aspect increased and vertical loads decreased the maximum stress. There was correlation between the results of FEM and fracture test results.