Influence of Sintering Parameters on the Mechanical Behaviour of Lithium Disilicate Glass Ceramics: An In-Vitro Study

This study investigates the effect of different sintering parameters on the surface roughness and fracture resistance of different CAD/CAM lithium disilicate ceramics before and after thermocycling and simulated toothbrushing. Sixty lithium disilicate ceramic samples were categorized according to ceramic type (AMB: Amber Mill, ECAD: IPS e.max CAD) and level of translucency (LT: low and HT: high) into four groups: AMB_LT, AMB_HT, ECAD_LT and ECAD_HT. Specimens were prepared to 2 mm thickness, crystallized, polished, and subjected to thermocycling to simulate five years of clinical aging. Simulated toothbrushing was performed using a soft-bristled mechanical brushing system under controlled force and strokes. Surface roughness was assessed using a profilometer before and after brushing, and fracture resistance was measured using a universal testing machine. Data were statistically evaluated using paired <i>t</i>-tests, one-way ANOVA with Bonferroni post hoc correction (<i>p</i> ≤ 0.05). LT lithium disilicate specimens exhibited significantly smoother surfaces than high-translucency counterparts. After thermocycling and brushing simulation, all groups showed a statistically significant increase in surface roughness, ranging between 0.239 ± 0.012 μm (AMB_LT) and 0.486 ± 0.014 μm (ECAD_HT). In terms of fracture resistance, the highest values were recorded for ECAD_HT (636 ± 8.29 N), and the lowest in the AMB_HT group (546.3 ± 21.9 N) with significant differences observed between materials and translucency levels. Sintering parameters and artificial aging significantly influenced the surface roughness and fracture resistance of lithium disilicate ceramics. Low-translucency variants demonstrated smoother surfaces and higher strength than high-translucency groups, while all materials exhibited increased roughness after aging. These findings provide guidance for the selection of lithium disilicate ceramics, balancing esthetic and mechanical requirements in anterior and posterior restorations.