Three-dimensional Finite Element Analysis Of The First Permanent Mandibular Molar With Class â…  Composite Restorations

Restoration of caries lesion is the most basal and common treatment in restorative dentistry. However, it is also a subtle therapy. Remaining tooth structure, occlusal force, cavity design and selection of the restorative materials must all be taken into account. For many reasons, the failure of dental restorations occurs commonly. How to improve the successful rate of restoration of caries lesion is the concern of caries research.In this experiment, the first permanent mandibular molar with class I composite restorations was chosen to study. The variety of magnitude and location of stresses in the remaining tooth structure and composite restorations resulting from the change of occlusal force, cavity design and base was studied quantificationally by establishing the three dimensional finite element models . The possible damage to the remaining tooth structure and composite restorations was also analysed.The study was divided into three parts according to the designed factors. (1) In part one, static loads were applied vertically or obliquely into the occlusal of the same three dimensional finite element model. The magnitude of occlusal load was 50N, 100N, 150N respectively. The magnitude and distribution of maximum Von Mises stress and maximum principal stress in enamel, dentine and composite restorations were compared. (2) In pare two, six different three dimensional finite element models were generated and the dimension of class I cavity in each model differed. A static occlusal load of 100N was vertically applied in each model and the distribution ofmaximum Von Mises stress and maximum tensile stress in enamel and composite restorations were compared. (3) In part three, four different three dimensional finite element models were generated. The base material or base thickness was different in each model. A static occlusal load of 100N was vertically applied in each model and the distribution of maximum Von Mises stress and maximum tensile stress in enamel and composite restorations were compared.The results showed: (1) The magnitude of maximum Von Mises stress and maximum principal stress in enamel, dentine and composite restorations all increased as the occlusal loads increased regardless of the direction of the occlusal loads. The peak stresses in enamel and composite restorations were much higher than those in dentin. When occlusal loads were vertically applied, the stresses in enamel and composite restorations were comparatively lower and compressive stress was dominant. The distribution of the stress was equable. However, the stresses in enamel and composite restorations were much higher and the distribution of the stress was not equable when occlusal loads were obliquely applied. The tensile stress in the interface between enamel and composite restorations increased remarkably. The peak stress of composite restorations located in the surface of composite restorations and decreased from the surface to the bottom. (2) When the width of class I cavity was invariable, the magnitude of maximum Von Mises stress and maximum tensile stress in enamel and composite restorations increased as the depth of cavity increased. Similarly, when the depth of class I cavity was invariable, the magnitude of peak stresses also elevated as the width of cavity increased. But width of cavity was the more critical factor governing the stress elevation in enamel and composite restorations. (3) When zinc phosphate cement was used as the base material, the magnitude of maximum Von Mises stress and maximum tensile stress in enamel and composite restorations were comparatively lower than those of glass ionomer cement and the stress distribution were more equable. From the point of view of base thickness, the magnitude of maximum Von Mises stress and maximum tensile stress in enamel and compositerestorations decreased as base thickness increased.