Effects of functional monomers and photo-initiators on the degree of conversion of a dental adhesive.

Besides functional and cross-linking monomers, dental adhesives contain a photo-initiator system for polymerization, thereby providing physico-mechanical strength to the adhesive-tooth interface. Few studies have investigated the effect of the functional monomer and polymerization-initiation system on the polymerization efficiency of the adhesive. Here, we tested the effect of two different functional monomers (MAC-10 vs. SR) and two photo-initiator systems, camphorquinone-amine (CQ) vs. borate (BO), on the degree of conversion (DC) of different adhesive formulations. The DC of the CQ-cured adhesive formulations was significantly affected by the MAC-10 monomer. This should be ascribed to the known inactivation of the amine co-initiator through acid-base reaction. However, the SR monomer did not decrease the DC, which could be attributed to a "gel effect" or the so-called "Trommsdorff-Norrish" phenomenon of enhanced DC with more viscous resins, and to the more favorable availability of CC double bonds. In contrast, the DC of the BO-cured adhesive formulations was not affected by any acidic monomer. It is concluded that the degree of conversion of an adhesive can be affected by the functional monomer, but this depends on the kind of photo-initiator system used. As bond durability depends, among other factors, on the strength and thus degree of conversion of the adhesive, potential interaction between adhesive ingredients and the photo-initiator system definitely needs to be studied further.

Bond strength of adhesives to dentin contaminated with smoker's saliva.

The purpose of this study was to determine the effects of contamination with smoker's and non-smoker's saliva on the bond strength of resin composite to superficial dentin using different adhesive systems. The interfacial structure between the resin and dentin was evaluated for each treatment using environmental scanning electron microscopy (ESEM). Freshly extracted human molars were ground with 600-grit SiC paper to expose the superficial dentin. Adhesives [One-Up-Bond-F-Plus (OUFP) and Adper-Prompt-L-Pop (APLP)] and resin composite (TPHSpectrum) were bonded to the dentin (n = 8/group, 180 total specimens) under five surface conditions: control (adhesive applied following manufacturers' instructions); saliva, then 5-s air dry, then adhesive; adhesive, saliva, 5-s air dry; adhesive, saliva, 5-s water rinse, 5-s air dry (ASW group); and adhesive, saliva, 5-s water rinse, 5-s air dry, reapply adhesive (ASWA group). After storage in water at 37 degrees C for 24 h, the specimens were debonded under tension at a speed of 0.5 mm/min. ESEM photomicrographs of the dentin/adhesive interfaces were taken. Mean bond strength ranged from 8.1 to 24.1 MPa. Fisher's protected least significant difference (P = 0.05) intervals for critical adhesive, saliva, and surface condition differences were 1.3, 1.3, and 2.1 MPa, respectively. There were no significant differences in bond strength to dentin between contamination by smoker's and nonsmoker's saliva, but bond strengths were significantly different between adhesive systems, with OUFP twice as strong as APLP under almost all conditions. After adhesive application and contamination with either smoker's or nonsmoker's saliva followed by washing and reapplication of the adhesive (ASWA group), the bond strength of both adhesive systems was the same as that of the control group.

Changes in color and staining of dental composite resins after wear simulation.

OBJECTIVES: The objectives were to measure the discoloration as well as the change in staining of composite resins after wear simulation. METHODS: Generalized wear simulation was performed with a three-body wear testing device for 400,000 cycles for six composite resins. A flat-planed stylus made with polyacetal resin was loaded perpendicularly under a load of 76-80 N. Color of nonworn and worn areas was measured with a spectrophotometer before and after staining with 0.5% methylene blue solution. Nonworn surface served as a control. Differences in color between nonworn and worn surfaces were calculated to indicate the change in color due to wear. Color change after staining with 0.5% methylene blue solution for nonworn and worn surfaces was calculated to observe the changes in staining. RESULTS: Color difference (DeltaE(*) (ab)) between nonworn and worn surfaces was in the range of 0.8-1.4 before staining, which increased to 1.1-3.9 after staining. Color change by staining with methylene blue in nonworn surface was 6.8-20.6, and that in worn surface was 5.2-17.8. Therefore, staining in nonworn surface was higher than that in worn surface (p < 0.05). Generalized wear simulation for approximately 3 years of clinical service resulted in acceptable color change before staining (DeltaE(*) (ab) < 3.3). After staining, color difference between nonworn and worn surface increased to not-acceptable value in one composite resin investigated.

Properties of a dental resin composite with a spherical inorganic filler.

This study compared the mechanical properties, generalized wear resistance and polymerization shrinkage of a resin composite filled with spherical inorganic filler to other commercial resin composites. Six dental resin composites were tested, including a submicron filled composite (Estelite sigma, Estelite), 1 nano-composite (Filtek Supreme, Supreme), 2 microfilled composites (Heliomolar; Renamel Microfill, Renamel) and 2 microhybrid composites (Esthet X Improved; Tetric Ceram). Compressive strength (CS), diametral tensile strength (DTS), flexural strength (FS), flexural modulus (FM), generalized wear resistance (WV) and polymerization shrinkage (PS) were evaluated for the 6 materials. The specimens were cured according to the manufacturers' instructions in appropriate molds, stored (37 degrees C water, 24 hours), then tested on an Instron testing machine (0.5 mm/minute). PS was tested according to the Archimedes method at 1, 24 and 48 hours continually after polymerization. Data were analyzed by analysis of variance. The results showed that CS values ranged from 252 to 298 MPa, DTS ranged from 35 to 54 MPa, FS from 73 to 140 MPa, FM from 4.8 to 11.1 GPa, WV from 0.037 to 0.086 mm(3) and PS at 24 hours from 2.17 to 3.96 vol%. Composite had statistically significant influence on the in vitro properties tested. Estelite performed similarly to nano-composite and microhybrid composites in mechanical properties and generalized wear resistance, while Estelite and Supreme had the lowest PS among the materials tested. The 2 microhybrid materials had similar properties, while the 2 microfilled composites were different for most properties tested. Overall, the microfilled composites had lower strength than the other composites except Renamel for CS. All the materials had a similar shrinkage pattern in that about 99% of shrinkage occurred in less than 24 hours.

Changes in gloss after simulated generalized wear of composite resins.

STATEMENT OF PROBLEM: Generalized wear of composite resins in the noncontact area may result in changes of gloss, which can influence esthetics of restorations. PURPOSE: The purpose of this study was to determine the changes in gloss of composite resins after generalized wear simulation. Surface roughness and amount of wear were measured for comparison. MATERIAL AND METHODS: Generalized wear simulation was performed with a wear tester for 400,000 cycles with 6 composite resins (Estelite Sigma, Esthet X improved, Filtek Supreme, Heliomolar, Renamel Microfill, and Tetric-Ceram). Composite resin was placed into a mold (8 mm in diameter, 3 mm in depth) in an acrylic resin block, and 8 specimens were prepared per group. A flat-planed stylus made with polyacetal was loaded perpendicularly. Gloss was measured after every 100,000 cycles with a glossmeter in gloss units (GU). Average surface roughness (R(a)) of each specimen before and after 400,000 cycles of wear was determined. The amount of wear was measured with a 3-dimensional profilometer. Changes in gloss were analyzed by repeated-measures analysis of variance, and mean values were compared by Fisher's PLSD interval (alpha=.05). RESULTS: Gloss was influenced by the number of wear cycles and the composite resin, and there was a significant interaction (P=.000) between the number of wear cycles and the brand of composite resin. There were no significant correlations between the wear depth and the gloss or changes in gloss after 400,000 cycles. CONCLUSION: Generalized wear simulation for approximately 3 years of clinical use resulted in gloss changes of 36 to 64 GU, and maximum wear depth was in the range of 35 to 75 mum. Change in gloss varied among the composite resins, but average surface roughness was not influenced by the various composite resins.