Effect of water storage on ultimate tensile strength and mass changes of universal adhesives.

BACKGROUND: The aim of the present study was to evaluate the influence of water storage on micro tensile strength (µTS) and mass changes (MC) of two universal adhesives. MATERIAL AND METHODS: 10 disk-shaped specimens were prepared for each adhesive; Scotchbond Universal (SCU) All-Bond Universal (ABU) and Adper Single Bond 2 (SB2). At the baseline and after 1 day and 28 days of water storage, their mass were measured and compared to estimate water sorption and solubility. For µTS test, 20 dumbbell shaped specimens were also prepared for each adhesive in two subgroups of 1 day and 28 days water storage. RESULTS: MC was significantly lower for SCU and ABU than SB2 (P < 0.05) at both time intervals. In all three adhesives, the MC was significantly lower at 28 days compared to that at 1 day (P < 0.05). Similarly, µTS was significantly higher for SCU and ABU than SB2 at both storage intervals (P < 0.05). After 28 days, µTS increased significantly for universal adhesives (P < 0.05). CONCLUSIONS: MC and µTS of adhesives were both material and time dependent when stored in water; both universal adhesives showed less water sorption and higher values of µTS than the control group. Key words:Absorption, dental adhesives, dentin-bonding agents, solubility, tensile strength.

Effect of decontamination on micro-shear bond strength of silorane-based composite increments.

AIM: The aim of the present study was to evaluate the micro-shear bond strength of silorane-based composites after saliva/blood decontamination. METHODS: A transparent mold (1 × 2 × 1 cm) was used to make 11 flat, silorane-based composite blocks. One block served as the control. After contamination, the blocks were treated as follows: group 1: 10-s air spray; group 2: 10-s water spray + 10-s air spray; group 3: 10-s water spray + 10-s air spray + 10-s etching with phosphoric acid; group 4: 10-s air spray + 10-s etching + bonding; group 5: 10-s water spray + 10-s air spray + 10-s etching + bonding; and groups 6-10: treated the same as groups 1-5, the only difference being that blood was used instead of saliva. Ten tubes (0.7 mm × 1 mm) containing silorane-based composites were attached to each decontaminated block and light cured for 40 s. After 24-h storage in distilled water, specimens were tested under micro-shear loading at a cross-head speed of 0.5 mm/min. Data were analyzed using one-way anova and Tukey's honest significant difference (HSD) test (P < 0.05). RESULTS: One-way anova showed significant differences in the micro-shear bond strength among the experimental groups (P < 0.001). Tukey's HSD test revealed that the bond strengths in groups 5, 9, and 10 were similar to the control group (P > 0.05). CONCLUSION: Decontamination by water and air spray, etching, and bonding was effective in restoring the bond strength of silorane-based composite increments.

Temperature Rise Induced by Light Curing Unit Can Shorten Enamel Acid-Etching Time.

OBJECTIVES: The aim of this in-vitro study was to assess the thermal effect of light emitting diode (LED) light curing unit on the enamel etching time. MATERIALS AND METHODS: Three treatment groups with 15 enamel specimens each were used in this study: G1: Fifteen seconds of etching, G2: Five seconds of etching, G3: Five seconds of etching plus LED light irradiation (simultaneously). The micro shear bond strength (µSBS) of composite resin to enamel was measured. RESULTS: The mean µSBS values ± standard deviation were 51.28±2.35, 40.47±2.75 and 50.00±2.59 MPa in groups 1, 2 and 3, respectively. There was a significant difference between groups 1 and 2 (P=0.013) and between groups 2 and 3 (P=0.032) in this respect, while there was no difference between groups 1 and 3 (P=0.932). CONCLUSION: Simultaneous application of phosphoric acid gel over enamel surface and light irradiation using a LED light curing unit decreased enamel etching time to five seconds without compromising the µSBS.

Microshear bond strength of composite resins to enamel and porcelain substrates utilizing unfilled versus filled resins.

BACKGROUND: Failures such as marginal discoloration and composite chipping are still the problems of tooth-colored restorations on the substrate of enamel and porcelain, which some of these problems are consequently as a result of failures in the bonding layer. Using filled resin has been recently introduced to increase the bond strength of this layer. The aim of this study was to compare the microshear bond strength (µ-SBS) of composite resins to enamel incubated in periods of 24 h and 9 months and porcelain with unfilled resin and flowable composites (filled resin). MATERIALS AND METHODS: In this in vitro study, two groups of 75 enamel samples with different storage times (24 h and 9 months) and a group of 75 porcelain samples were used. They were divided into 5 experimental groups of 15 samples in each. Composite cylinders in tygon tubes were bonded on the surface of acid-etched enamel and pretreated porcelain. Wave, Wave MV, Wave HV, Grandioflow and Margin Bond were used as bonding agents. The µ-SBS was measured at the speed of 1.0 mm/min. The bond strengths were analyzed with one-way analysis of variance (ANOVA) test followed by Tukey test. P < 0.05 was selected as the level of statistical significance in this study. RESULTS: The results showed that for enamel (24 h), the µ-SBS of the Wave MV and Wave HV groups were significantly lower than the Margin Bond group. Tukey test indicated the absence of a significant difference between the µ-SBS of the Wave group and the Margin Bond group. However, the µ-SBS of the Grandioflow group was significantly higher than the one for the Margin Bond as a bonding agent. In enamel (9 months), there was a significant difference between the Grandioflow and Margin Bond groups. Regarding bonding to the porcelain the one-way ANOVA test did not show a significant difference among the groups. CONCLUSION: This study revealed that flowable composites (filled resins) can be used instead of unfilled resins in bonding composite resins to enamel and porcelain substrates.