Thesis & Dissertations

Statement of problem: Although metal ceramic restorations with porcelain margin have solved the esthetics of such restorations still the unsupported labial porcelain margin led to decrease in fracture strength at margin. Purpose: The objective of this study was to evaluate the color differences and fracture resistance between conventional and two labial finish lines design of collarless metal-ceramic crowns. Materials and Methods: Two different acrylic teeth preparation were investigated. Group  was the conventional collarless preparation design with one labial finish line and group  was preparation with two labial finish lines. 30 collarless porcelain fused to metal (PFM) crowns were fabricated according to the preparation design and divided into 15 crowns for each group. Using an Easyshade spectrophotometer, delta E (ΔE) color difference was calculated between the collarless crowns in comparison to the corresponding A1 shade tab. The (ΔEs) obtained were assessed based on ΔE = 2.7 which represent the color difference that could not be detected by human eye and considered clinically not perceivable. Then the two tested groups were subjected to fracture resistance test using Instron universal testing machine with crosshead speed of 0.5 mm/min. Acrylic disk about a 3 mm thickness was placed between the plunger tip and the occlusal surfaces of the crowns. Vertical load was applied until catastrophic porcelain fracture occurred. Result: A statistical significant differences in color were calculated between the two groups (P= .023), which suggested that group  with the smaller ΔE = 1.52 value achieved a more accurate color match compared to the group  ΔE = 2.08. Fracture resistance test revealed no significant differences between the two tested groups (P > .05). Conclusion: Within the limitation of this study, it could be concluded that restorations with optimum esthetics can be fabricated with new clinical and laboratory technique set up. The new collarless PFM crowns preparation design can be a guide for proper placement and extension of labial shoulder porcelain. Keywords: Collarless, Porcelain, Ceramic, Metal, Margin, Preparation, Color, Shade, Spectrophotometer