Yu-Sung Choi

Microtensile bond strength and micromorphologic analysis of surface-treated resin nanoceramics

PURPOSE The aim of this study was to evaluate the influence of different surface treatment methods on the microtensile bond strength of resin cement to resin nanoceramic (RNC). MATERIALS AND METHODS RNC onlays (Lava Ultimate) (n=30) were treated using air abrasion with and without a universal adhesive, or HF etching followed by a universal adhesive with and without a silane coupling agent, or tribological silica coating with and without a universal adhesive, and divided into 6 groups. Onlays were luted with resin cement to dentin surfaces. A microtensile bond strength test was performed and evaluated by one-way ANOVA and Tukey HSD test (α=.05). A nanoscratch test, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy were used for micromorphologic analysis (α=.05). The roughness and elemental proportion were evaluated by Kruskal–Wallis test and Mann–Whitney U test. RESULTS Tribological silica coating showed the highest roughness, followed by air abrasion and HF etching. After HF etching, the RNC surface presented a decrease in oxygen, silicon, and zirconium ratio with increasing carbon ratio. Air abrasion with universal adhesive showed the highest bond strength followed by tribological silica coating with universal adhesive. HF etching with universal adhesive showed the lowest bond strength. CONCLUSION An improved understanding of the effect of surface treatment of RNC could enhance the durability of resin bonding when used for indirect restorations. When using RNC for restoration, effective and systemic surface roughening methods and an appropriate adhesive are required.

Effect of ceramic material and resin cement systems on the color stability of laminate veneers after accelerated aging

Statement of problem. Laminate veneers are susceptible to color change during clinical service. Studies that compare the effects of different ceramic and resin cement systems on color stability are lacking. Purpose. The purpose of this in vitro study was to evaluate the color stability of laminate veneers after accelerated aging using different ceramic and resin cement systems. Material and methods. Ceramic specimens (N=168; shade A1; thickness, 0.50 ±0.05 mm; diameter, 10.00 ±0.10 mm) were prepared using nanofluorapatite and lithium disilicate (high translucency [HT] to low translucency [LT]) ceramics. Light‐polymerizing (LP) cements were classified by brightness (high or low). Dual‐polymerizing cements were classified by composition (base‐only [DB] or base‐catalyst [DC]) for comparison of color stability on the basis of polymerization type. DB cement was light‐polymerizing, whereas DC cement was dual‐polymerizing. They were further classified by shade (transparent, white, or yellow [n=7, each]). Color difference (&Dgr;E) values were obtained by spectrophotometric quantification of L* (lightness), a* (green‐red), and b* (blue‐yellow) values before and after aging. The Kruskal‐Wallis, Mann‐Whitney U, Wilcoxon signed rank, and Bonferroni post hoc tests were used for statistical analysis. Results. After specimens were subjected to accelerated aging, HT ceramic specimens luted with yellow‐shade DC cement exhibited the greatest color change (&Dgr;E=2.11), whereas HT and LT ceramic specimens luted with low‐brightness LP cement exhibited the least color change (&Dgr;E=1.37). In HT ceramic specimens, which exhibited the greatest color change of the 3 ceramic types, transparent shade cement exhibited significantly lower &Dgr;E values than the other shades with DB (P<.001) and DC cements (P=.010). High‐brightness cement exhibited significantly higher &Dgr;E values than low‐brightness cement when used with NF (P=.017), HT (P<.001), and LT (P<.001) ceramics. The &Dgr;E values of DB cement were not always lower than those of DC cement. For all specimens, the aging of laminate veneers decreased the L* values and increased the a* and b* values. Conclusions. Ceramic and resin‐cement systems affected the color stability of laminate veneers. Relative to other ceramics, HT lithium disilicate ceramics exhibited greater color changes upon aging. For HT ceramics, the use of transparent shade resin cement is recommended. The lower the brightness of resin cement, the higher the color stability of veneers. For luting of 0.5‐mm‐thick laminate veneers with dual‐polymerizing cement, light polymerization did not yield better color stability than dual polymerization over time.