Improvement on properties of experimental resin cements containing an iodonium salt cured under challenging polymerization conditions.

OBJECTIVE: The use of resin cements in clinical practice entails photopolymerization through prosthetic devices, which precludes light penetration. The objective of this study was to modify experimental resin cements (ERCs) with diphenyliodonium hexafluorophosphate (DPI) in an attempt to improve chemical and mechanical properties of materials cured with reduced irradiance and final radiant exposure. METHODS: A co-monomer base containing a 1:1 mass ratio of 2.2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) was prepared, with 1mol% of camphorquinone and 2mol% of ethyl 4-(dimethylamino)benzoate as initiator system. The resin was divided into 4 fractions according to the DPI concentrations (0, 0.5, 1 and 2mol%). The challenging polymerization condition was simulated performing the light activation (12, 23 and 46s) through a ceramic block (3mm thick). The irradiance was assessed with a calibrated spectrometer (1320mW/cm2), resulting in three levels of radiant exposure (0.58, 1.1 and 2.2J/cm2). The polymerization kinetics was evaluated in real-time using a spectrometer (Near-IR). Water sorption and solubility was analyzed and the cohesive strength of resins obtained through the microtensile test. Polymerization stress was assessed by Bioman method. RESULTS: Resins containing DPI had higher degree of conversion and rate of polymerization than the control (without DPI). The use of DPI reduced water sorption and solubility, and led to higher cohesive strength compared to resins without the iodonium salt. However, the stress of polymerization was higher for experimental resins with DPI. SIGNIFICANCE: Even under remarkably reduced irradiance, cements containing a ternary initiating system with an iodonium salt can present an optimal degree of conversion and chemical/mechanical properties.

In vitro assessment of the acid resistance of demineralized enamel irradiated with Er, Cr:YSGG and Nd:YAG lasers.

PURPOSE: This study's purpose was to evaluate the acid resistance of demineralized enamel irradiated with high-intensity lasers. METHODS: Enamel fragments were demineralized and treated as follows (N=10): Group 1-no treatment; Group 2-five percent sodium fluoride (NaF) varnish; Group 3-Er, Cr:YSGG laser (8.92 J/cm2, 0.5 W, 20 Hz, 30 seconds); Group 4-NaF and Er, Cr:YSGG laser; Group 5-Er, Cr:YSGG laser and NaF; Group 6-Nd:YAG laser (84.9 J/cm2, 0.5 W, 10 Hz, 30 seconds); Group 7-NaF and Nd:YAG laser; and Group 8-Nd:YAG laser and NaF. The samples were subjected to pH-cycling and assessed by microhardness (analysis of variance; α equals five percent) at different depths from the outer enamel surface. Samples were observed using polarized light microscopy (PLM) and scanning electron microscopy (SEM). RESULTS: There were no significant differences among the experimental groups in any of the subsurface layers evaluated. PLM observation revealed that the extent of demineralization of the irradiated samples was similar to the samples for Group 1 (control). SEM observation showed that irradiated surfaces were ablated and presented areas of melting. CONCLUSIONS: Laser irradiation, with or without applying five percent sodium fluoride, was not capable of increasing the enamel white spot lesions' acid resistance.

Improved polymerization efficiency of methacrylate-based cements containing an iodonium salt.

OBJECTIVE: This study evaluated the effect of adding diphenyliodonium hexafluorphosphate (DPI) as a third component of the free-radical photoinitiator system of model resin cements on their photopolymerization kinetics/stress and fundamental properties. METHODS: A model resin cement containing a 1:1 mass ratio of 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane and triethyleneglycol dimethacrylate was obtained. Camphorquinone (1 mol%) and 2-(dimethylamino)ethyl methacrylate (2 mol%) were added to monomer blend. Six mixtures were obtained by incorporation of 0 (control), 0.25, 0.5, 1, 2, or 4 mol% of DPI. The cements were loaded with a 60% mass fraction of silanated glass fillers. Polymerization kinetics (using Fourier-transform near-infrared spectroscopy), flexural strength and modulus, water uptake/solubility, and polymerization stress were assessed. Data were statistically analyzed using one-way ANOVA and Student-Newman-Keuls' test (P ≤ 0.05). RESULTS: In the DPI-modified materials, the onset of autodeceleration occurred earlier and at higher conversion compared with the control cement. The addition of DPI also led to a more active early-stage polymerization. The flexural modulus was generally higher for DPI-containing materials. Water uptake and solubility were generally lower for materials with DPI fractions ≥ 0.5%. Significant increase of polymerization stress was observed only in the group with 1 mol% of DPI compared with the control cement. SIGNIFICANCE: The effect of DPI on the photopolymerization reactivity of the cement is concentration-dependent; the use of DPI could result in better polymerization efficiency of resin-based cements.

Luting glass ceramic restorations using a self-adhesive resin cement under different dentin conditions.

OBJECTIVES: The aim of this study was to investigate the bond strength of ceramic restorations luted using a self-adhesive resin cement (RelyX Unicem, 3M ESPE) under different dentin conditions. MATERIAL AND METHODS: In the experimental groups, ceramic restorations were luted to bovine incisors with RelyX Unicem under the following conditions: [Dry dentin]: surface was dried using air stream for 15 s; [Moist dentin]: excess dentin moisture was removed with absorbent paper; [Bonding agent]: Clearfil SE Bond (Kuraray) self-etching adhesive system was previously applied to dentin. In the Control group, cementation was done using an etch-and-rinse adhesive (Excite DSC) and Variolink II resin cement (Ivoclar Vivadent). Photoactivation of the resin cements was performed with UltraLume LED 5 unit (Ultradent). The restorations (n=5 per group) were sectioned into beams and microtensile testing was carried out. Data were subjected to ANOVA and Tukey's test (p<0.05). Failure modes were classified under Scanning Electron Microscopic (SEM) (x120 magnification). RESULTS: The bond strength was dependent on the moisture status of the dentin. Bond strength in the "dry dentin group" was significantly lower than that of all other groups, which showed similar results. A predominance of mixed failures was detected for the control group, while a predominance of adhesive failures was observed for the "bonding agent" and "dry dentin" groups. The "moist dentin" group presented predominantly cohesive failures within the luting material. The previous application of a self-etching adhesive showed no significant effect. CONCLUSIONS: Only excess dentin moisture should be removed for the cementation of ceramic restorations with self-adhesive resin cements.

Surface/interface morphology and bond strength to glass ceramic etched for different periods.

This study evaluated the influence of etching periods on the surface/interface morphology and bond strength to glass ceramic with or without application of an unfilled resin after silane. Ceramic discs were divided into 12 groups, defined by etching time with 10% hydrofluoric acid: G1/G7--etching for 10 seconds, G2/G8--20 seconds; G3/G9--40 seconds; G4/G10--60 seconds; G5/G11--120 seconds and G6/G12--60 + 60 seconds. All the groups were silanated after etching and G7 - G12 received a layer of unfilled resin after silane. Microshear testing using resin cement was performed, with 12 resin cylinders tested per group. The data was submitted to two-way ANOVA and the Student-Newman-Keuls' test (p<0.05). Evaluation of the etching pattern and bonding interfaces was conducted by SEM. The bond strength means (MPa) were: 19.4 +/- 3.5, 22.3 +/- 5.1, 22.2 +/- 3.2, 17.8 +/- 2.1, 15.3 +/- 3.0 and 14.3 +/- 1.8 for G1-G6 and 17.4 +/- 4.8, 21.3 +/- 2.1, 21.1 +/- 2.3, 24.7 +/- 5.8, 20.4 +/- 2.2 and 18.5 +/- 4.6 for G7-G12. Poor etching was detected after 10 seconds of conditioning; whereas deep channels were extensively observed on surfaces etched for 120 and 60 + 60 seconds. Unfilled voids underlying the ceramic-cement interface were detected when only silane was applied. Full completion of the irregularities on G11 was detected using unfilled resin. When only silane was applied, the 60-second group and those etched for longer periods showed lower bond strengths. When both silane and unfilled resin were applied, all etching periods generally showed similar values. In conclusion, the etching period influenced the surface/interface topography and bond strength to ceramic. The application of unfilled resin was able to infiltrate all unfilled voids beneath the ceramic-cement interface, except on re-etched surfaces.

Luting glass ceramic restorations using a self-adhesive resin cement under different dentin conditions

OBJECTIVES: The aim of this study was to investigate the bond strength of ceramic restorations luted using a self-adhesive resin cement (RelyX Unicem, 3M ESPE) under different dentin conditions. MATERIAL AND METHODS: In the experimental groups, ceramic restorations were luted to bovine incisors with RelyX Unicem under the following conditions: [Dry dentin]: surface was dried using air stream for 15 s; [Moist dentin]: excess dentin moisture was removed with absorbent paper; [Bonding agent]: Clearfil SE Bond (Kuraray) self-etching adhesive system was previously applied to dentin. In the Control group, cementation was done using an etch-and-rinse adhesive (Excite DSC) and Variolink II resin cement (Ivoclar Vivadent). Photoactivation of the resin cements was performed with UltraLume LED 5 unit (Ultradent). The restorations (n=5 per group) were sectioned into beams and microtensile testing was carried out. Data were subjected to ANOVA and Tukey's test (p<0.05). Failure modes were classifed under Scanning Electron Microscopic (SEM) (x120 magnifcation). RESULTS: The bond strength was dependent on the moisture status of the dentin. Bond strength in the "dry dentin group" was signifcantly lower than that of all other groups, which showed similar results. A predominance of mixed failures was detected for the control group, while a predominance of adhesive failures was observed for the "bonding agent" and "dry dentin" groups. The "moist dentin" group presented predominantly cohesive failures within the luting material. The previous application of a self-etching adhesive showed no signifcant effect. CONCLUSIONS: Only excess dentin moisture should be removed for the cementation of ceramic restorations with self-adhesive resin cements.

Bonding to wet or dry deproteinized dentin: micro tensile bond strength and confocal laser micromorphology analysis

Aim: To investigate the influence of deproteinization and moisture condition (wet vs. dry) on the bond strength and micromorphology of resin-dentin bonding interfaces. Methods: Dentin surfaces were etched with 37% phosphoric acid for 15 s and rinsed with water. Four groups (n = 10) were tested: WET: dentin was left visibly moist; DRY: dentin was dried with compressed air; WET-D: dentin was deproteinized for 60 s using 10% NaOCl solution and left moist; DRY-D: dentin was deproteinized and dried. Prime&Bond 2.1 adhesive was applied and the teeth were restored with composite resin. Microtensile test was carried out after 24 h, and failure modes classified under magnification. Data were subjected to two-way ANOVAand Tukey’s test (P < 0.05). The bonding micromorphology was analyzed by confocal laser scanning microscopy. Results: The group DRY showed significantly lower bond strength (P < 0.05) than the other groups, which were similar to each other (P > 0.05). Adhesive failures were predominant. Analysis of micromorphology showed formation of a collagen-resin hybrid layer only for the non-deproteinizedgroups. Adhesive penetration into the dentinal tubules was deeper for the DRY-D compared to the WETD group. Conclusion: The bond strength was not dependent on the moisture condition and a more homogeneous hybridization was obtained when dentin was deproteinized.

Effects of ceramic thickness and curing unit on light transmission through leucite-reinforced material and polymerization of dual-cured luting agent.

This study investigated the influence of ceramic thickness and curing unit on light transmission through leucite-reinforced material and polymerization of a dual-cured resin luting agent. Discs of Empress Esthetic (Ivoclar Vivadent) of 0.7-, 1.4- and 2-mm thickness were prepared. Variolink II (Ivoclar Vivadent) was placed in a 1-mm-thick cylindrical mold, and light-activated through ceramic for 40 s, using QTH or LED units. The samples were divided into dual, light, and chemically-polymerized control groups. Knoop hardness indentations were made on the top and bottom surfaces. Data were subjected to split-plot design three-way ANOVA and Tukey's test (P < 0.05). The light spectrum transmitted through ceramic was obtained using a spectrometer. Samples activated through 1.4-and 2-mm-thick discs showed lower hardness than all others groups, except for the chemical control group. Dual and light-polymerized control samples showed similar hardness to those activated through the 0.7-mm ceramic, whereas chemically polymerized control samples showed similar hardness to those activated through 1.4- and 2-mm ceramics. No significant differences in hardness were detected between the curing units or between the top and bottom layers. No significant alteration in the light spectrum profile was observed for both units, irrespective of the ceramic thickness.