Alteration of the intaglio surface of lithium disilicate glass-ceramic

Influence of additive and subtractive zirconia and lithium disilicate manufacturing on tensile bond strength and surface topography

STATEMENT OF PROBLEM

Although bonding is important for long-term clinical success, studies on the bonding of additively manufactured ceramics are sparse.

PURPOSE

The purpose of this in vitro study was to determine the influence of manufacturing methods, additive (LCM) versus subtractive (CAM). and ceramic materials, zirconia (ZrO2) and lithium disilicate (LiSi), on the tensile bond strength (TBS), failure mode, and surface roughness of ceramics.

MATERIAL AND METHODS

A total of 240 ceramic specimens (n=60/group; 2×2×10 mm) were prepared. Two additively manufactured (LCM-printed) ceramics, LiSi and ZrO2 (Lithoz), subtractively manufactured LiSi (IPS e.max CAD), and subtractively manufactured ZrO2 (KATANA Zirconia HTML PLUS) were evaluated. From each material, 40 specimens were bonded together (n=20 ceramic-ceramic specimens/group), and 20 specimens were bonded to equally sized human dentin specimens (n=20 ceramic-dentin specimens/group). The ZrO2 specimens were airborne-particle abraded (Al2O3, 50 µm, 0.1 MPa), and the LiSi specimens were etched with hydrofluoric acid. Then, a universal primer (Monobond Plus) was applied. After the dentin was coated with an etch-and-rinse adhesive (Syntac Classic), the specimens were bonded with luting composite resin (Variolink Esthetic DC), light polymerized for 40 seconds, thermally aged (10 000 cycles between 5 °C and 55 °C), tested for TBS, and statistically analyzed (1- and 3-way ANOVA and Weibull analysis). The ceramic surface was examined with scanning electron microscopy, and surface roughness was measured with digital microscopy before and after surface pretreatment.

RESULTS

TBS varied between 5.88 ±2.22 MPa and 6.34 ±2.26 MPa in the ceramic-dentin groups and 12.40 ±1.56 MPa and 18.82 ±5.92 MPa in the ceramic-ceramic groups. No significant difference was observed regarding the manufacturing method and material for different bonding conditions (P>.05). Additive and subtractive LiSi showed the highest reliability with m=18.27. The ceramic-ceramic specimens failed cohesively in the luting composite resin, whereas the ceramic-dentin specimens failed adhesively.

CONCLUSIONS

The manufacturing method and material used had little effect on bond strength values or surface properties. The recently introduced printed materials performed similarly to conventionally milled materials.

Microshear bond strength of resin cement to glass-ceramics after intaglio surface staining

STATEMENT OF PROBLEM

Applying stains to the intaglio surface of computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic ceramic restorations has been proposed as an option to help mask darkened substrates. However, little is known about the effects of this procedure on the adhesion between the resin cement and the ceramic.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of intaglio surface staining on the microshear bond strength between 2 CAD-CAM ceramics and a resin cement.

MATERIAL AND METHODS

Lithium disilicate (Gmax) and leucite-reinforced (Gpress) ceramic blocks were sectioned, crystalized when indicated, and polished. They received either none, 1, or 2 layers of ceramic stains and a glaze liquid mixture followed by a firing cycle. The surfaces of groups Gmax0, Gmax1, and Gmax2 were etched with 9% hydrofluoric acid etching (HF) for 20 seconds, and those of groups Gpress0 and Gpress1 were etched for 60 seconds. After rinsing and drying, a ceramic primer was applied and air-dried. Resin cement rods (n=24 per group) were built from a silicone mold. Specimens were stored in distilled water for 24 hours before microshear bond testing. Failure mode was observed under a digital microscope. Data were analyzed by using the Kruskal-Wallis and Mann-Whitney nonparametric tests (α=.05).

RESULTS

Intaglio staining negatively affected the microshear bond strength for both ceramics. A significant difference was observed between Gmax1 (3.5 ±1.73 MPa) and Gmax2 (3.7 ±2.1 MPa) when compared with Gmax0 (14.2 ±4.4 MPa) and also between GPress0 (25.7 ±5.1 MPa) and Gpress1 (1.8 ±2.7 MPa). No difference was observed between 1 and 2 stain layers for Gmax. Most failures were adhesive for Gmax0, mixed for Gpress, and cohesive within the stain layer for experimental groups.

CONCLUSIONS

Intaglio surface staining with a stain and glaze mixture caused a significant reduction in bond strength between resin cement and both ceramics tested.

Surface roughness and characteristics of CAD/CAM zirconia and glass ceramics after combined treatment procedures

BACKGROUND

The roughening of the inner surface of a fixed ceramic restoration is an important factor for the bonding process. The aim of this study is to investigate the effect of combined surface treatments (acid etching, air-abrasion and Er: YAG Laser) on surface roughness of CAD/CAM fabricated zirconia (ZrO₂) and lithium-disilicate glass ceramics (LDS).

METHODS

Sixty ZrO₂ (Ceramill Zi) and LDS (IPS e.max CAD) specimens, (5 mm in width, 5 mm in length and 1.5 mm in height) were fabricated using CAD/CAM and sintered according to the manufacturer's instructions. All specimens subjected to three surface treatment combinations; etching with 4% hydrofluoric acide (HF), airborne-particle abrasion with 110-μm alumina (Al₂O₃) (AP) and Er:YAG laser (Er:YAG) (Group A-HF + AP; Group B-Er:YAG + AP, and Group C-Er:YAG + HF). Perthometer was used to measure the surface roughness of the specimens before and after the tretments.

RESULTS

Group A presented the highest Ra (LDS 0.81 ± 0.27 and ZrO₂ 0.67 ± 0.21 after treatment) and Group C the lowest (LDS 0.45 ± 0.13 and ZrO₂ 0.26 ± 0.07, after treatment). Compared with before treatment, the Ra were significantly different only in Group A both ZrO₂ and LDS after treatment (p < 0.05). Qualitative SEM images suggested the surface topography of the ZrO₂ was smoother than the LDS. Less surface changes were observed in the Er:YAG combined procedures than HF + AP.

CONCLUSIONS

HF + AP was significantly succesful in modifying the ceramic surface. Er:YAG did not sufficiently promote the surface topography, even if combined with any other treatments. Overall, surface tretments on ZrO₂ not easier than LDS.