Impact of repeated heat-pressing on the microstructure and flexural strength of lithium disilicate glass-ceramics.

Background: The leftover material from the heat-pressing of IPS e.max Press ceramic is often discarded, despite some laboratories exploring its potential for reuse. However, there is a lack of data on the performance of IPS e.max Press ceramic when combined with the button portions. This study investigated the impact of repeated heat-pressing on the crystal structure and flexural strength of lithium disilicate glass-ceramic (LDGC). Methods: Specimens (N = 30, n = 10 per group) were categorized based on the number of heat-pressing cycles: G0 (control group, no heat-pressing), G1 (one cycle of heat-pressing), and G2 (two cycles of heat-pressing). The crystal structure of LDGC bars was characterized using X-ray diffraction (XRD). Flexural strength was tested, and microstructures were analyzed via scanning electron microscopy (SEM) and the ImageJ processing program. Data were analyzed using one-way analysis of variance (ANOVA), and multiple pairwise comparisons of means were performed with Tukey's post-hoc test. Results: G2 exhibited significantly lower flexural strength and crystallinity, as well as larger crystal size, compared to G1 and G0 (p < 0.05). Flexural strength values decreased significantly with an increased number of heat-pressing cycles. Conclusions: The mechanical properties of LDGC significantly degraded after repeated heat pressing. Therefore, it is not clinically advisable to repeatedly press the lithium disilicate ingot together with the leftover material. [ABSTRACT FROM AUTHOR]