Immobilization of phosphate monomers on collagen induces biomimetic mineralization.

BACKGROUND: Immobilization of phosphoproteins on type-I collagen via covalent binding may induce extra- and intrafibrillar mineralization. OBJECTIVE: This study tested the hypothesis that methacrylate phosphate esters immobilized on reconstituted type-I collagen can mimic the nucleating role of phosphoproteins. METHODS: Three functional monomers (MDP, GPDM and Phenyl-P) that differed in chemical structure and steric hindrances around the phosphate moiety were evaluated. Reconstituted type-I collagen was either left untouched (control) or treated by 5% monomer/ethanol for 20 s. All samples were incubated in simulated dentinal fluid as mineralizing medium at 37°C for 7 or 14 days. The extra- and intrafibrillar mineralization were examined by SEM and TEM/SAED crystallography, respectively. RESULTS: FT-IR spectroscopy showed that the phosphate groups were incorporated on reconstituted collagen, irrespective of their chemical structure. MDP immobilization induced dense growth of extrafibrillar mineral over time, while with GPDM- and Phenyl-P-immobilized collagen, mineralization was moderate and sparse, respectively. TEM/SAED evidence disclosed that intrafibrillar minerals exclusively occurred in MDP-immobilized collagen. CONCLUSIONS: Immobilization of MDP, which had the lowest steric hindrance, could induce significant biomimetic extra- and intrafibrillar mineralization; resembling the lowest level of hierarchy organization of dentin.

Color stability of adhesive resin cements after immersion in coffee.

OBJECTIVES: Marginal discoloration of luting cement may affect the appearance of esthetic restorations. This study evaluated the color stability of current adhesive resin cements after immersion in coffee. MATERIALS AND METHODS: Four dual-cured resin cements (Clearfil SA cement Automix Universal, Maxcem Elite Clear, Maxcem Elite Yellow, and RelyX Unicem2 Automix A2) and two chemical-cured resin cements (Super-Bond C&B Clear and Super-Bond C&B Esthetic) were examined. The CIE L*a*b* of 2.0-mm-thick disc-shaped specimens was measured using a spectrophotometer on a white background (n = 6). The color differences (∆E) after 1-day and 1-week immersion in 37 °C water or coffee were analyzed by two-way ANOVA by selecting immersion solution and product as main factors, followed by Tukey's HSD test (α = 0.05). Water sorption and solubility were also evaluated. RESULTS: The two-way ANOVA of the ∆Es suggested that the two main factors and their interaction were significant. The ∆Es after coffee immersion were significantly greater than those after water immersion, except for Super-Bond C&B Esthetic. The ∆Es after water immersion were not significantly different among the products; those of Maxcem Elite Clear and Maxcem Elite Yellow after coffee immersion were significantly greater than the others. The water sorption and solubility significantly correlated with the ∆Es. CONCLUSIONS: The ∆Es of the adhesive resin cements examined after 1-week coffee immersion were significantly different among the products. The product showing greater water sorption and solubility displayed greater color change. CLINICAL RELEVANCE: Adhesive resin cements should be carefully selected when the marginal appearance of the ceramic restoration is important.

Mechanical properties of composite resin blocks for CAD/CAM.

This study compared commercial composite resin blocks with one ceramic block for use in computer-aided design/computer aided manufacturing (CAD/CAM). Four composite resins, one composite ceramic, and one feldspar-ceramic block were investigated. Flexural strength (FS), flexural modulus (FM), and Vickers hardness (VH) were determined under three conditions: dry storage; immersion in water at 37°C for 7 days; and immersion in water at 37°C for 7 days followed by 10,000 thermocycles. After dry storage, FS ranged from 127 to 242 MPa, FM from 9.6 to 51.5 GPa, and VH from 64 to 455. Two-way ANOVA was performed for FS, FM and VH followed by Tukey's multiple comparison (α<0.05). Results demonstrated that the materials degraded after water immersion and thermocycling, but their properties were within the acceptable range for fabrication of single restorations according to the ISO standard for ceramics (ISO 6872:2008).

Effect of ultraviolet light irradiation and sandblasting treatment on bond strengths between polyamide and chemical-cured resin.

The aim of this study was to evaluate the effects of ultraviolet light (UV) irradiation and sandblasting treatment on the shear bond strength between polyamide and chemical-cured resin. Three types of commercial polyamides were treated using UV irradiation, sandblasting treatment, and a combining sandblasting and UV irradiation. The shear bond strength was measured and analyzed using the Kruskal-Wallis test (α=0.05). Comparing shear bond strengths without surface treatment, from 4.1 to 5.7 MPa, the UV irradiation significantly increased the shear bond strengths except for Valplast, whose shear bond strengths ranged from 5.2 to 9.3 MPa. The sandblasting treatment also significantly increased the shear bond strengths (8.0 to 11.4 MPa). The combining sandblasting and UV irradiation significantly increased the shear bond strengths (15.2 to 18.3 MPa) comparing without surface treatment. This combined treatment was considered the most effective at improving the shear bond strength between polyamide and chemical-cured resin.

Effect of ultraviolet light irradiation period on bond strengths between fiber-reinforced composite post and core build-up composite resin.

The aim of the present study was to characterize the effects of the ultraviolet light (UV) irradiation period on the bond strength of fiber-reinforced composite (FRC) posts to core build-up resin. Three types of FRC posts were prepared using polymethyl methacrylate, urethane dimethacrylate, and epoxy resin. The surfaces of these posts were treated using UV irradiation at a distance of 15 mm for 0 to 600 s. The pull-out bond strength was measured and analyzed with the Dunnett's comparison test (α=0.05). The bond strengths of the post surfaces without irradiation were 6.9 to 7.4 MPa; those after irradiation were 4.2 to 26.1 MPa. The bond strengths significantly increased after 15 to 120-s irradiation. UV irradiation on the FRC posts improved the bond strengths between the FRC posts and core build-up resin regardless of the type of matrix resin.

Effect of components and surface treatments of fiber-reinforced composite posts on bond strength to composite resin.

The aim of this study was to clarify the effect of the components and surface treatments of fiber-reinforced composite (FRC) posts on the durable bonding to core build-up resin evaluated using the pull-out and microtensile tests. Four types of experimental FRC posts, combinations of two types of matrix resins (polymethyl methacrylate and urethane dimethacrylate) and two types of fiberglass (E-glass and zirconia-containing glass) were examined. The FRC posts were subjected to one of three surface treatments (cleaned with ethanol, dichloromethane, or sandblasting). The bond strength between the FRC posts and core build-up resin were measured using the pull-out and microtensile tests before and after thermal cycling. The bond strengths obtained by each test before and after thermal cycling were statistically analyzed by three-way ANOVA and Tukey's multiple comparisons test (p<0.05). The bond strengths except for UDMA by the pull-out test decreased after thermal cycling. Regardless the test method and thermal cycling, matrix resins, the surface treatment and their interaction were statistically significant, but fiberglass did not. Dichloromethane treatment was effective for the PMMA-based FRC posts by the pull-out test, but not by the microtensile test. Sandblasting was effective for both PMMA- and UDMA-based FRC posts, regardless of the test method. The bond strengths were influenced by the matrix resin of the FRC post and the surface treatment. The bond strengths of the pull-out test showed a similar tendency of those of the microtensile test, but the value obtained by these test were different.