ABSTRACT
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 cast from 24 wax-patterns were cemented to the corresponding dies. For all the coping-die assemblies cross-sectional technique was used to evaluate the marginal and internal fit at 15 points. The Student's t- test was used for statistical analysis [alpah=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-pattern fabrication produced copings with significantly better marginal and internal fit than CAD/CAM [machine-milled] technique. All the factors for 2 groups were standardized except wax pattern fabrication technique, therefore, only the conventional group results in copings with clinically acceptable margins of less than 120um