The present study was conducted to evaluate the effect of veneering
zirconia frameworks on the marginal and internal fit of zirconia based restorations.
Materials and methods: Forty natural premolars were prepared to receive all-ceramic
crowns. The forty premolars were divided into two groups according to the type of restoration.
Group (I) consisted of ten samples restored using monolithic zirconia crowns.
Group (II) consisted of thirty samples restored using veneered zirconia frameworks.
Group II was subdivided into three equal subgroups according to veneering technique.
Subgroup (IIA) veneered using manual layering technique, Subgroup (IIB) veneered
using Press-on technique and Subgroup (IIC) veneered using CAD-on technique. All
the finished crowns were cemented to their corresponding abutments then each tooth
was vertically sectioned bucco-lingually into 2 sections. Marginal, axial and occlusal
gaps were measured at seven defined points on each section using digital microscope.
Results: The significance level was set at Panalysis revealed that there was a significant difference between groups and
subgroups. The greatest mean value was recorded in subgroup IIA, veneered using
manual layering technique. Whereas the lowest mean value was recorded in subgroup
IIC, veneered using CAD-on technique. Regarding the internal gap statistical analysis
revealed that there was a significant difference. The greatest mean value was recorded
in group I (monolithic), whereas the lowest mean value was recorded in subgroup IIC,
veneered using CAD-on technique. Conclusion: Veneering zirconia frameworks using
the CAD-on technique produces superior marginal and internal adaptation of zirconia
based restorations.