Evaluation of Acid Resistance for Novel Machinable Lithium Disilicate Glass-Ceramics

Objectives: Recently, lithium disilicate glass-ceramic restorations, especially fabricated by CAD/CAM technology, have become popular. As dental restorative materials, they are used for long term in intraoral environment. Thus, chemical durability is an important property for aesthetics and physical properties. We have developed novel machinable lithium disilicate glass-ceramics, which doesn’t require crystallization firing after grinding. The aim of this study was to evaluate the acid resistance for the lithium disilicate glass-ceramics compared to other machinable lithium disilicate glass-ceramics.
Methods: Three test groups were prepared, 1) LiSi block (GC, LS), 2) e.max CAD (Ivoclar Vivadent, EM), 3) CEREC Tessera (Dentsply-Sirona, TE). Flat specimens with 15×13×2mm dimensions were cut out from the blocks, and EM and TE were heat-treated for crystallization or glazing according to the manufacturer’s instruction. After that, these samples were polished by DP-Paste P1/4μm (Struers). These specimens were immersed in 4vol% acetic acid aq at 80 degrees celsius for 1week. Gloss decreasing rate (VG-7000, NIPPON DENSHOKU INDUSTRIES) were measured and amount of dissolution were calculated from sample weight before and after immersion (n=3). One way ANOVA and dunnett test was used to assess the significant difference (p<0.05).
Results: Gloss decreasing rate for LS shown in below table was the significantly smallest in these samples. Amount of dissolution for LS was also significantly lower than other samples. These findings indicated that LS was able to maintain glossiness by high acid resistance.
Conclusions: Acid resistance of LS is greater than other samples, including EM which has been used in clinical practice for a long time. Thus, it is considered that LS is useful for dental restorative material over the long term.