A Measurement Protocol for the Marginal and Internal Fit of All-Ceramic Crowns.

Aims: To evaluate in vitro the influence of firing on marginal and internal fit of all-ceramic milled and pressed lithium-disilicate crowns. Materials and methods: One Standardized model with 1.6mm occlusal and 1.4mm axial reduction was used to fabricate 64 crowns. Using a factorial design, eight groups of lithium disilicate ceramics (n=8) using P=press, C=CAD/CAM, M=monolithic, O=coping, V=veneered, R=as produced: PMR, PMG, POR, PVG, CMR, CMG, COR, CVG. Crowns were produced and cemented on stone dies, then embedded in clear epoxy resin and sectioned into two plains. With a digital microscope, the distance between die and crowns was measured at the occlusal and axial walls. The horizontal/vertical fit at the finishing line of each section were measured as well. Results: For the marginal fit, the analysis shows that the influence of material and design was significant on horizontal and vertical margins, and the influence of finish was significant with horizontal but not vertical margins (p=0.09). For the internal fit, the analysis showed that the axial gap was significantly influenced by material and finish but not by design (p=0.44). Conclusions: With a few exceptions, horizontal and vertical marginal discrepancies were below 100 mu m. Additional firing increased the discrepancies.