The effect of two buffer solutions on wear resistance and mechanical properties of chairside lithium silicate glass-ceramic materials

Objective: To compare the impact of neutral and acidic environments on wear of lithium silicate glass-ceramics (LSGC) with and without crystallization firing after manufacturing. Materials and Methods: Eight square-shaped specimens (7 × 7 × 2 mm) were manufactured from four commercially available LSGC and opposed by steatite antagonists in a chewing simulator. Of these four LSGC materials, two were tested twice: one in both fired and unfired states, and another was additionally opposed by zirconia antagonists. Zirconia served as a control both as specimen/substrate and as antagonist/abrader. This resulted in a total of 56 specimens being exposed. The wear test was performed while specimens were immersed in a neutral (pH 7) or an acidic (pH 3) buffer solution for 250,000 cycles with a 5 kg load and 1 mm sliding movement. Laser scanning microscopy and optical profilometry were used to quantify and evaluate wear. The same specimens were used for Raman microscopy, Vickers hardness and fracture toughness tests. Data were analyzed with 1-way ANOVA. Scanning electron microscopy was used to investigate the wear process. Results: The neutral buffer solution was more detrimental to the wear of all LSGC materials compared to the acidic buffer solution. The wear mechanism caused by steatite antagonists differed from the wear mechanism caused by zirconia antagonists. Significance: Environmental conditions play a major role in the wear performance of LSGC. Fully crystallized LSGC materials (factory crystallized) exhibit similar susceptibility to environmental changes as LSGC materials requiring crystallization firing.