The Translucency of Glass Ceramics Cores Veneered with Different Ceramics

Objective: This study evaluated the translucency of glass ceramic core materials and the influence of different veneering ceramics on the translucency of bi-layered specimens. Method: Five samples of an experimental fluorcanasite glass ceramic (University of Sheffield) and lithium disilicate (e.max CAD, Ivoclar Vivadent) were prepared into discs of 0.5mm and 13mm diameter and ground to a p600 grit finish. In addition, three veneering ceramics (n=5) were prepared to the same dimensions: 50% feldspar and 50% leucite ceramic and a experimental multiple phase leucite ceramic, which both matched the coefficient of thermal expansion of the fluorcanasite, and a fluoroapatite veneering ceramic (e. max Ceram, Ivoclar Vivadent) recommended for use with the lithium disilicate. The discs were then analysed for total transmittance from 380-700nm using a spectrophotometer (Lambda 2, Perkin Elmer) with an integrating sphere. The core ceramic specimens were subsequently layered with appropriate veneering ceramic of 0.5mm thickness and the total transmittance measured as before. Statistical analysis was performed using the ANOVA test (P<0.05). Results: The average total transmittance (%) from 380 – 625nm was 72.5 for the fluorcanasite and 37.3 for the lithium disilicate (P<0.05). For the veneering ceramics, there were statistically significant differences between each group. The average total transmittances were: 82.5 for the feldspar/leucite; 75.3 for the multiphase leucite; and 66.4 for the fluoroapatite ceramic. When the fluorcanasite core was veneered with the feldspar/leucite, the average total transmittance was 72.3. With the multiple phase leucite/fluorcanasite specimens, this dropped to 68.9 but was not significantly different. The lithium disilicate veneered with the fluoroapatite ceramic showed a significantly lower average total transmittance of 41.8. Conclusion: The fluorcanasite core ceramic veneered with either the feldspar/leucite or multiple phase leucite ceramic showed significantly higher translucency in comparison to the lithium disilicate/fluoroapatite system.