Statement of Problem: Sprue design is a factor that controls the velocity and adequate supply of metal to the mold. Currently various manufacturers recommend different sprue design, which have not been advocated in textbooks and literature is lacking for their routine applications. Purpose: The purpose of the present study was to evaluate the marginal fit and surface roughness by comparing between four sprue Design. Materials and Methods: Part I of the study determined marginal fit of base ceramometal crowns with the use of phosphate bonded investment. Stainless steel metal die was used and four sprue shapes (Group A cylinder, Group B Square, Group C bottle neck D conical) were evaluated. 40 stone die were made, 10 wax patterns for each sprue design were waxed up, invested with phosphate bonded investment material and castings done with centrifugal casting machine by the same operator under standardized protocols. The casting coreFit on the respective die and .margin on digital microscope evaluation. Data were tabulated and statistically analyzed with 1 way ANOVA followed By Student‘t’ test.Part IIused AFM microscope to evaluate the surface roughness of casting disc made with same techniques as Part I. Results: For margin gap: The results differed significantly (P <0.0001) ) between the Groups with maximum defects in the castings of Group A followed in decreasing order by Group B, Group C and Group D. When comparing between the Groups (P <0.05) the gap in Groups B, C and D was significantly lower than Group A. For surface roughness results differed significantly (P <0.0001) ) between the Groups with maximum defects(roughness) in the castings of Group C followed in decreasing order by Group A, Group B and Group D. When comparing between the Groups (P <0.05) the defects in Groups C and A was significantly higher than Group Band D. Conclusion: Conical with flared point of attachment sprues produced most satisfactory margin fit and surface roughness, meanwhile the cylinder without reservoir produced maximum defect in margin gap and surface roughness.
