IADR Abstract Archives
Influence of Thermal Processing on Shades of Dental Zirconia
Objectives: Unprecedented strength, low abrasion, excellent esthetics and cementation properties gained zirconia a significant share of use for crowns and bridgework. In recent years more attention has focused on enhancing esthetic appearance. Major improvements to translucency, better match to shade references and the addition of a natural fluorescence effect has been achieved (Lava Esthetic). This study investigates the influence of thermal processing steps used for glazing and veneering on the final shade. A praseodymium doped zirconia was used as a model material.
Methods: Discs of pre-sintered Lava Plus 3Y TZP zirconia were immersed for 2min in a solution of 0.80wt.% praseodymium acetate, 2.25wt.% polyethylene glycol 35000 and 1.30wt.% triammonium citrate in water. After drying for 12h at air under ambient conditions, subsequent sintering at 1450°C for 2h in a Lava Therm furnace and polishing with a 9µm diamond paste samples of 1mm height and 13mm diameter were received. These discs were heat treated in a Austromat 3001, Dekema, dental furnace under vacuum for 2min at varying temperatures from 600 to 1050°C (n=2 each temperature). Shade parameters (L*a*b*) were determined on a Color I7, X-Rite, spectrophotometer, in remission mode before and after heat treatment, DeltaE values were calculated accordingly.
Results: Fig. 1 exhibits the DeltaE values compared to the as sintered state related to the applied firing temperature. DeltaE values of <1, showing a not visible difference are obtained at temperatures up to 800°C whereas at higher temperatures varying DeltaE values generally >2 indicating a visible difference are observed.
Conclusions: The resulting shade of praseodymium doped zirconia depends on the firing temperature used for applying glaze and veneer. Though investigations were made using a simplified model material, this study indicates the importance of thoroughly defining the firing conditions in order to obtain a constant dental shade.
Methods: Discs of pre-sintered Lava Plus 3Y TZP zirconia were immersed for 2min in a solution of 0.80wt.% praseodymium acetate, 2.25wt.% polyethylene glycol 35000 and 1.30wt.% triammonium citrate in water. After drying for 12h at air under ambient conditions, subsequent sintering at 1450°C for 2h in a Lava Therm furnace and polishing with a 9µm diamond paste samples of 1mm height and 13mm diameter were received. These discs were heat treated in a Austromat 3001, Dekema, dental furnace under vacuum for 2min at varying temperatures from 600 to 1050°C (n=2 each temperature). Shade parameters (L*a*b*) were determined on a Color I7, X-Rite, spectrophotometer, in remission mode before and after heat treatment, DeltaE values were calculated accordingly.
Results: Fig. 1 exhibits the DeltaE values compared to the as sintered state related to the applied firing temperature. DeltaE values of <1, showing a not visible difference are obtained at temperatures up to 800°C whereas at higher temperatures varying DeltaE values generally >2 indicating a visible difference are observed.
Conclusions: The resulting shade of praseodymium doped zirconia depends on the firing temperature used for applying glaze and veneer. Though investigations were made using a simplified model material, this study indicates the importance of thoroughly defining the firing conditions in order to obtain a constant dental shade.
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