COMPARISON OF THE EFFECTS OF THREE PREPARATION DESIGNS: SHOULDER, CHAMFER AND DEEP CHAMFER IN THE PALATAL SURFACE ON RESISTANCE AGAINST BREAKAGE OF PORCELAIN LAMINATE VENEER

Statement of Problem: Porcelain laminate veneer is one of the most important restorations in dentistry because of stable esthetic and low destructive t echnique. But the main reason of failure in this treatment is porcelain fracture. Therefore, tooth preparation has an important role in fracture resistance of porcelain laminate veneer. Purpose: The aim of this in-vitro study was to compare the effect of tree preparation designs, shoulder and chamfer and heavy chamfer, on fracture strength of porcelain laminate veneer. Materials and Method: This experimental and in-vitro study was performed on 30 upper central teeth without fracture, carries or any problem. The teeth were divided into three-10 teeth groups. Then, the preparation design was performed perfectly. In the palatal surface s of the first group we used deep chamfer preparation design and the shoulder and the chamfer designs were performed for the second and third groups, respectively. Then the samples were put in instron machine with the angle of 30 degrees. The force rate which led to break in those samples was determined. The data were analysed usig t-test. Result: Resistance against breakage in the deep chamfer , shoulder and chamfer groups were 283.40 ± 17, 231.50 ± 25.61 and 254 ± 21.71 Newton, repectvely. No significant d i ffere n ce was found among the groups . Conclusion : The higher fracture resistance was observed in deep Chamfer/palatal over lap technique, so we prefer to use this kind of preparation for palatal extension of Porcelain Laminate Veneers . Key words: Chamfer, Shoulder, Deep Chamfer, Fracture resistance, Porcelain laminate veneer