Micro-Indentation Method for Material Selection for Dental Restorations

Objectives: Accessories (stain/glaze, veneering, and add-on) selection play an important role in all ceramic and press over metal (POM) restorations. The stress profile on an actual restoration with different stain/glaze, veneering, and add-on will be different depending on their properties. The purpose of this study was to use a micro-indentation approach on a posterior restoration to assess the nature of stress (compressive vs. tensile) in the restoration after stain/ glaze, veneering, and add-on is baked on to it.
Methods: A new class of glass-ceramic material called Obsidian from Glidewell Laboratories was studied. Four different paint stains and three spray glaze with different CTE range of 9.8-12.9x10^-6/K were applied on three different Obsidian restorations “CAD/CAM, Obsidian Pressed Monolithic, and POM” with CTE range from 12.2-13.4x10^-6/K. In addition, veneer and add-on with CTE of 11.7x10^-6/K were built on obsidian all-ceramic crown. The thermal stability of restorations after firing cycle was investigated for crack morphology. Posterior restoration specimens with stain/glaze, veneering and add-on were precision cut, polished and tested using Vickers micro-indentation at different loads ranging from 10N-20N. Three indentation areas were considered, just below stain/glaze surface, margin area and close to cementation area. Indentation cracks for each load level were introduced on the target surface and optical microscopy was used to analyze the indentation crack morphology and propagation mechanism which is suggestive of tensile and compressive stresses.
Results: The results demonstrate that the thermal residual stress due to the application of stain/glaze, veneering, and add-on material greatly influences the indentation crack stability of all ceramic and POM restorations.
Conclusions: This study shows that there are still considerable prospects for improving dental ceramics. Micro-indentation on actual restorations might help better understand the stresses generated due to accessories which can then be used for prudent accessory selection for dental restorations.