The marginal gap and internal fit of monolithic crowns milled with different luting spaces

Three of the more promising materials for CAD/CAM restorations are Zirconia (VITA Zahnfabrik, Germany), Enamic (VITA Zahnfabrik, Germany), and the composite material Brilliant Crios (Coltene, Switzerland). Zirconia has been tested for the marginal gap and internal fit; Enamic and Crios have not been tested for marginal gap and internal fit and no studies have tested the effect of different luting spaces. A standardised crown preparation on a typodont mandibular first molar tooth was scanned and imaged (CEREC CAD/CAM, Germany). The marginal gap was measured using a Reflex microscope in both two- and three-dimensions. The internal fit was calculated using the properties of the luting agent and the surface area of the preparation. The 3D measurements were significantly higher, but only on average 10µm higher. The marginal gaps of the crowns milled with a 200µm luting space were significantly smaller than for those milled with a 100µm luting space. The smallest mean gap was recorded by Enamic at 31.7µm followed by Crios at 32.5µm, and Zirconia at 33.1µm. All of these measurements are well within acceptable clinical limits. All crowns milled, regardless of the luting space used, provided excellent marginal and internal fit, well within clinically acceptable parameters. The 3D measurements are more clinically relevant than 2D measurements. The smallest marginal gaps were found in the crowns milled with a 200µm luting space. However, this can present problems with non-axial seating and so it may be advisable to use the 100µm luting space parameter