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.