Nanoindentation tests to assess polymerization of resin-based luting cement.

OBJECTIVE: The optimal polymerization of resin-based luting cements plays a critical role in the long-term clinical success of dental prostheses and indirect restorations. This study investigated a mutual action between the conformational changes and mechanical properties of a dimethacrylate resin-based luting cement with and without pre-application of the acidic functional monomer 10-methacryloxydecyl dihydrogen phosphate. METHODS: Degree of conversion in the luting cement was measured using conventional infrared spectrophotometry. Mechanical properties of the luting cements were also evaluated by quasi-static and dynamic nanoindentation tests. RESULTS: The results of infrared spectrophotometry and nanoindentation testing were proportional in samples without functional monomer pretreatment. When considerable residual monomer remains within the final products, the mechanical properties of the resin-based luting cements could possibly be impaired. Although the apparent degree of conversion increased with a mixture of functional monomer, a reduction in the cross-linking polymer network may have resulted in the highest viscoelastic creep behavior of the luting cement. The time-dependent behaviors found in the nanoindentation tests likely resulted from linear polymerization chains of the functional monomer. SIGNIFICANCE: The application of an acidic functional monomer may affect the viscosity of resin-based luting cements. Quasi-static or dynamic nanoindentation is a useful tool for assessing the polymerization qualities of resin composites.

Combination treatment of tribochemical treatment and phosphoric acid ester monomer of zirconia ceramics enhances the bonding durability of resin-based luting cements.

The aim of the present study was to evaluate the bonding durability of resin-based luting cement to partially stabilized tetragonal zirconia (Y-TZP) achieved by combination treatment of tribochemical (TBC) treatment and two different phosphate acid ester monomers. Two phosphate acid ester monomers (EP: Epricord opaque primer, AZ: AZ primer) were applied to each surface modification followed by application of resin-based luting cement (Rely-X ARC). Bonding specimens were placed in deionized water at 37 degrees C and stored for 24 h. The other groups were subjected to 30,000 cycles of a thermal stress for the durability test. Shear bond tests were done using a universal testing machine at 1 mm/min. Shear bond strengths of combination treatments using EP and AZ on TBC treatment after thermal stress showed no significant difference (p>0.05) compared with those of storage after 24 h. Combination treatment using phosphoric acid ester monomer could achieve a durable bond.

Bonding strength of resin cement to silicate glass ceramics for dental CAD/CAM systems is enhanced by combination treatment of the bonding surface.

To increase the bond strength of CAD/CAM-fabricated, leucite-reinforced glass ceramics with a resin cement, the effects of the following were investigated: surface modification by tribochemical (TBC) treatment, followed by combined application of a silane coupling agent and a functional monomer as a primer. Bond strength was evaluated by a shear bond test. It was found that a silane coupling agent was useful for all the surfaces, particularly for the TBC-treated surface. This was because of the presence of a silica layer on the modified surface. The combination of a silane coupling agent and a functional monomer on the TBC surface allowed marked improvement in bonding, whereby the bonding endured 20,000 cycles of thermal cycling. Therefore, TBC treatment in combination with a silane coupling agent and a functional monomer as a primer substantially increased the bond strength of CAD/CAM-fabricated glass ceramics with resin cement, if the treatment conditions were appropriate.

Effect of sintering on the marginal and internal fit of CAD/CAM-fabricated zirconia frameworks.

The aim of this study was to investigate the effect of post-machining sintering on marginal and internal fit of CAD/CAM-fabricated zirconia frameworks. Single crown copings (A: abutment), three-unit bridge frameworks (APA, P: pontic), four-unit bridge frameworks (APPA), and five-unit bridge frameworks (A1P1A2P2A3) were fabricated with raw-stage zirconia blanks using a commercial CAD/CAM system (KATANA, Noritake Dental Supply Co. Ltd., Aichi, Japan). Crown copings and frameworks were cemented to their respective master abutment models, and thickness of the cement layer was measured at specific measuring points. Marginal and internal fit of both APA and APPA were within clinical acceptance. However, the marginal gap and thickness of the cement layer on the axial surface of the pontic side of APA and APPA were slightly higher than those of the non-pontic side. As for the marginal gap of A1P1A2P2A3 framework, it was superior to those of APA and APPA because the center abutment supported the framework to prevent distortion.

Fracture toughness measurement of dental ceramics using the indentation fracture method with different formulas.

This study examined fracture toughness (KIC) measurements obtained using the indentation fracture (IF) method with a view to improving their reliability. The KIC values of five dental ceramics were measured using the IF method with five different formulas, and the single-edge precracked beam (SEPB) method was used as a control. The elastic moduli of the dental ceramics were evaluated by dynamic hardness test. Load conditions of the dental ceramics that produced a median/radial crack for the IF method formulas were investigated. Based on the resultant c/a and P/c1.5 values, the indentation load (P) required for median/radial crack occurrence varied greatly from 29.4 to 196 N depending on the ceramic used. Among the five formulas, none of the KIC values obtained by the IF method with Miyoshi's formula differed significantly (p > 0.05) from the values obtained using SEPB method. These results suggested that, after an appropriate indentation load is determined, reliable KIC values for small dental ceramic specimens can be easily obtained using the IF method if Miyoshi's formula is used in combination with the dynamic hardness test.

Effect of Nd:YAG laser irradiation on shear bond strength of glass-lonomer luting cement to dentin surface.

PURPOSE: The purposes of this study were to evaluate the shear bond strength of luting glass-ionomer cement to a dentin surface treated by pulsed Nd:YAG laser irradiation, and to prove the hypothesis that the bond strength of glass-ionomer luting cement to dentin is favorably altered after Nd:YAG laser irradiation. MATERIALS AND METHODS: Sixty-four extracted human molars with an exposed flat dentin surface were divided into four groups (n = 16). After painting black ink on their surfaces, the teeth of groups 1, 2, and 3 were irradiated by an Nd:YAG laser at 1.064-microm wavelength at 1, 2, and 3 W, respectively; group 4 was untreated and served as a control. Some specimens of each group were used for morphologic and atomic analytic study, and the others were used for shear bond testing. The shear bond test was performed after cylindric titanium specimens were cemented with glass-ionomer cement on a circular dentin area and specimens were immersed in distilled water. The tested specimens were also morphologically investigated. RESULTS: Shear bond strength of group 3 was significantly higher than that of the control group. Morphologic observation of the cement-dentin interface showed good adaptation of the luting cement to laser-treated dentin. Analysis of atomic contents on the dentin surface showed a significant increase of calcium:phosphorus ratio after laser irradiation. CONCLUSION: The dentin surface was modified morphologically and chemically, and the shear bond strength of glass-ionomer luting cement to dentin was increased by Nd:YAG laser irradiation at 3 W.

Raman and IR studies on adsorption behavior of adhesive monomers in a metal primer for Au, Ag, Cu, and Cr surfaces.

6-[N-(4-vinylbenzyl)propylamino]-1,3,5-triazine-2,4-dithione (VBATDT) and 10-methacryloyloxydecyl dihydrogen phosphate (M10P) are functional monomers used for the surface treatment of dental alloys. The aim of our study was to clarify the role of a commercial metal primer containing both the monomers in adhesion between resin and various dental metals on a molecular level. We used surface-enhanced Raman scattering (SERS) and infrared reflection absorption (IRA) spectroscopy. An SERS measurement was performed with a 647 nm laser line for a mixture of aqueous Au colloid and the primer. IRA spectra were taken for cast films of the primer on Au, Ag, Cu, and Cr surfaces as a function of rinse time, and for self-assembled monolayer (SAM) films from dilute mixed solution of VBATDT and M10P. These spectra indicate that VBATDT in the primer is mainly chemisorbed on Au, Ag, and Cu surfaces with respect to thickness, whereas only M10P is adsorbed on Cr. We also examined the tensile bond strengths between resin and Au, Ag, Cu, and Cr plates treated by VBATDT, with and without M10P, and found that VBATDT effectively promotes the bond strength between resin and the metals except for Cr, whereas M10P is effective only for Cr. These adhesion characteristics are consistent with the chemisorbed species on each metal surface as shown in the spectroscopic evidence.