Fit of pressed crowns fabricated from two CAD-CAM wax pattern process plans: A comparative in vitro study

Statement of problem. Subtractive and additive computer-aided design and computer-aided manufacturing (CAD-CAM) wax pattern processing are 2 methods of fabricating a pressed ceramic crown. Whether a subtractive milled wax pattern or a pattern from the microstereolithography additive process produces lithium disilicate crowns with better marginal and internal fit is unclear. Materials and methods. Ten silicone impressions were made for a prepared canine tooth. Each die received 2 lithium disilicate (IPS e.max) copings, 1 from milled wax blocks and 1 from additive wax. The replica technique was used to measure the fit by scanning electron microscopy at x80 magnification. Collected data were analyzed using the paired Student t test for the marginal and internal fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed rank test was used (alpha=.05). Results. The mean marginal, axial, and occlusal fit showed no significant differences when the 2 CAD-CAM manufacturing processes were compared (P>.05). For the marginal fit, the mean (+/- SD) values were 105.1 mu m +/- 39.6 with the milled process and 126.2 mu m +/- 25.2 for the additive process. The mean values were 98.1 mu m +/- 26.1 for the axial fit in the milled process and 106.8 mu m +/- 21.2 in the additive process. For the occlusal fit, median values (interquartile interval) were 199.0 mu m (141.5 to 269.9) for subtractive manufacturing and 257.2 mu m (171.6 to 266.0) for micro-SLA manufacturing. Conclusions. No significant difference was found between the fit of the 2 techniques. The mean values of axial and occlusal median values were 10 and 5 to 6 times greater than machine's nominal values.