Three-dimensional Finite Analysis Of The Stress In First Mandibular Molar With Composite Class Ⅰ Restoration When Different Cement Bases Were Used

In this experiment, the first permanent mandibular molar with classⅠcompositerestoration was chosen to study. The variety of magnitude and location of stressesunder physical load in the remaining tooth structure and restorations resulting fromchanging the liquid/powder mixing ratio, the thickness and the combination of basecements were studied quantificationally by establishing the 3-D finite elementmodels. The possible damage to the remaining tooth structure and compositerestorations was also analysed..This study was divided into three parts①Testing elastic moduli andpoisson'ratios of base cements. Light-cured calcium hydroxide(Ultra-blend plus),glass-ionomer (Vitrebond)with mixing ratios of 1:1,3:4,4:3 and self-cured calciumhydroxide (Dycal) with the same ratios were made into cylindrical form withdimensions 12mm height and 5ram diameter., 5 samples in each group, 35 in total,were tested and calculated the mean value and standard deviation. The result showedthe elastic moduli of base cements in various mixing ratios were different, whichhad the statistic significance.②Establishing the three dimensional finite element models of the first permanentmandibular molar with classⅠcavity. Micro-CT was used to scan the firstpermanent mandibular molar with normal shape and little attrition. 475 CT imageswith slice thickness of 20μm were gained, which were used to construct the three dimensional finite element models of the first permanent mandibular molar withclassⅠcavity of 4mm deep. The total number of elements was 132848 with 27616nodes. The type of element was tetrahedron C3D4.③Stress analysis of tooth structure, restoration and base cement when differentmaterials were used. The variety of magnitude and location of maximal principalstress, minimal principal stress and maximal Von Mises stress in each group underphysical load of 250N on central fossa in the remaining tooth structure, restorationand base cement resulting from changing the liquid/powder mixing ratio, thethickness and the combination of base cements were studied. The result showed themagnitude and location of stress in restored tooth made no differences when themixing ratio of Vitrebond and Dycal were changed. Whatever basing cement wereused, the peak stresses in restored tooth were located on the interface betweenmaterials,material and tooth tissue. So the fracture was possibly initiated on theinterface. In clinic, if Vitrebond or Dycal was used as base, the distribution of stressin restored tooth was best when its thickness was 0.5mm or 1.0mm. If Dycal orUltra-blend plus was used as capping material, Vitrebond as basing material, thedistribution of stress was best when their thickness were both 0.5mm. In order toprevent the fracture of tooth or restoration, in the treatment of deep caries, the basecements, the elastic moduli of which were proximal to the dentin and restoration,should be chosen as far as possible.