The effect of occlusal surface relief of on marginal adaptation of metal frames in the metal-ceramic crowns

Abstract

Marginal adaptation of a cast crown is clearly crucial for the success of a cast restoration. Die spacers allow increased space for the cement between the tooth surface and the casting, reducing stress areas created during cementation.The effect of occlusal surface relief of dies on marginal adaptation of metal-ceramic frames has not been evaluated yet. Therefore the aim of this study was to evaluate the effect of occlusal surface relief of dies on marginal adaptation of metal-ceramic frames. Materials and Methods: Eighty caries free extracted third molar teeth selected. Standardized preparations for metal-ceramic crowns were obtained using a milling machine. Impressions and stone dies maked using die spacer in 2 manner: with and without relief of occlusal surface of the dies. The crowns were cast in a nickel chromium based metal ceramic alloy. After cementation, the teeth sectioned along the long axis. Vertical and horizontal discrepancies at 6 point of occlusal, buccal axial, lingual axial, shoulder and chamfer finish line and end of level were recorded after cementation for all specimens with stereoscope. Results:The buccal-axial gap in the dies with or without spacer using in the occlusal surface were 80.88 and 68.01? with standard deviation of 33.67 and 37.86, the cement thickness were 208.59 and 117.46? with SD of 71.7,47.72(p<0.0001), the lingual-axial gap were 86.69 and 72.22? with SD of 48.44 and 36.42, the gap of the shoulder margin were 106.67 and 81.88? with SD of 47.41 and 38.71(p<0.012), the gap of bevel margin were 50.44 and 39.31? with SD of 27.14 and 18.52 (p<0.035) and gap of chamfer finish line were 89.81 and 86.13? with SD of 44.91 and 37.84 respectively. Conclusion: Marginal gap and cement thickness values in the areas of Shoulder, bevel and occlusal surface, without relieving of occlusal surface of the die significantly reduced.