A study to compare the internal fitness and marginal gap between single crowns and crowns within three-unite bridge of zirconia substructure fabricated by cad-cam system : an in vitro study

Abstract EN

Background: The aim of this in vitro study was to compare the marginal gap and internal fitness between single crowns and the crowns within three-unit bridges of zirconium fabricated by CAD-CAM system.

Materials and methods: Standard model from Ivoclar Company was used as pattern to simulate three-unit bridge (upper first molar and upper first premolar) as abutments used to fabricate stone models, eight single crowns of molar, and eight of three units bridges.

Crowns and bridges fabricated by CAD-CAM system were cemented on their respective stone models then sectioned at the mid-point bucco-lingually and mesio-distally and examined under stereomicroscope.

Results: The marginal gap in both the crown and bridge were within the acceptable value 120μm, one –way ANOVA showed that there was significant differences in the internal gape among the areas.

Independent t- Test showed there were significant differences between the molar single crowns and molar within bridges in all areas in concern to marginal and internal fitness.

Conclusions: The marginal and internal gaps were in the bridge higher than those in the crowns.

The areas of sloped surfaces such as chamfer area, occlusal area and cusp tip had high gap values in compare with area of flat surface such as axial wall and when the surface area of abutment increased, the marginal and internal gaps of abutment was increase.