Statement of Problem:
The accuracy of internal fit for subtractive CAD-CAM systems used in the fabrication of metal coping is still unclear.

Purpose:
This in vitro study compared the internal fit of casting metal core using conventional wax versus CAD wax.
Material and Methods:
Twenty four resin specimen dies were randomly divided into two groups according to method of metal coping construction using conventional (C) or CAD (D) wax. The silicon replica technique evaluated the internal fit using stereomicroscope at ×24 magnification; the thickness of the silicon layer was measured at 20 reference points on each specimen. Parametric data of internal gap width was analyzed using one-way ANOVA.
Results:
Different techniques of wax construction showed insignificant difference in internal gap values between specimens made with conventional (C) (103.89±40.39) and CAD (D) waxing (104.10±39.96).However, there was a significant difference between internal gap values measured at different sites.
Conclusions:
Both construction techniques of casting were considered reliable in production within a clinically acceptable range regarding internal fit.