Comparison the Marginal and Internal Fit of Metal Copings Cast From Wax Patterns Fabricated By Cad/Cam and Conventional Wax Up Techniques

Statement of problem: metal-ceramic crowns are most commonly used as the complete coverage restorations in clinical daily use. disadvantages of conventional handmade wax-patterns introduce some alternative ways by means of cad/cam technologies.purpose: this study compares the marginal and internal fit of copings cast from cad/cam and conventional fabricated wax-patterns.materials and method: twenty-four standardized brass dies were prepared and randomly divided into 2 groups according to the wax-patterns fabrication method (cad/cam technique and conventional method) (n=12). all the wax-patterns were fabricated in a standard fashion by means of contour, thickness and internal relief (m1- m12: representative of cad/cam group, c1-c12: representative of conventional group). cad/cam milling machine (cori tec 340i; imes-icore gmbh, eiterfeld,germany) was used to fabricate the cad/cam group wax-patterns. the copings castfrom 24 wax-patterns were cemented to the corresponding dies. for all the coping-dieassemblies cross-sectional technique was used to evaluate the marginal and internal fitat 15 points. the student’s t- test was used for statistical analysis (α=0.05).results: the overall mean (sd) for absolute marginal discrepancy (amd) was 254.46(25.10) um for cad/cam group and 88.08(10.67) um for conventional group (control).the overall mean of internal gap total (igt) was 110.77(5.92) um for cad/cam group and 76.90 (10.17) um for conventional group. the student’s t-test revealed significant differences between 2 groups. marginal and internal gaps were found to be significantly higher at all measured areas in cad/cam group than conventional group (p< 0.001).conclusion: within limitations of this study, conventional method of wax-patternfabrication produced copings with significantly better marginal and internal fit thancad/cam (machine-milled) technique. all the factors for 2 groups were standardizedexcept wax pattern fabrication technique, therefore, only the conventional group resultsin copings with clinically acceptable margins of less than 120um.