Effects of ethanol concentrations of acrylate-based dental adhesives on microtensile composite-dentin bond strength and hybrid layer structure of a 10 wt% polyhedral oligomeric silsesquioxane (POSS)-incorporated bonding agent

Novel Multifunctional Spherosilicate-Based Coupling Agents for Improved Bond Strength and Quality in Restorative Dentistry

The aim of this study was to investigate the restorative connections of composite materials after fracture, under controlled conditions of treating the materials with novel, spherosilicate-based (SS) primers bearing both methacryl (MA) and trimethoxysilyl (TMOS) groups. The chemistry of methacrylate group insertion and reactive groups hydrolysis has been studied with the aid of ¹H NMR (Nuclear Magnetic Resonance) spectroscopy. The light-cured resin composites were repaired by activating the connection site with the obtained primers and, for comparison, a silane (methacryloxypropyltrimethoxysilane, MATMOS) as a conventional coupling agent bearing the same reactive groups. The resistance of such a joint was tested in a three-point bending test after 24 h and 28 days period of sample conditioning. The effect of bond application was also studied, showing that spherosilicate-based primers may be used more effectively than MATMOS for two-step (primer-composite) restorative process, while for silane, the three-step process with bond application is crucial for satisfactory joint quality. The joint failure mode was determined by microscopic analysis and it was found that SS-4MA-4TMOS and SS-2MA-6TMOS application resulted in mostly composite, and not joint, failure. After 28 days of conditioning, the flexural strength of the joint repaired with SS-4MA-4TMOS was at 94% of the neat, solid material under the same procedure. However, the strength of the neat composite was observed to decline during the conditioning process by ~30%. The joint behavior was explained on the basis of the gradual hydrolysis effect (the greatest decrease being observed for silane).

The influence of nanofillers on the properties of ethanol-solvated and non-solvated dental adhesives

Objectives

The aim of this study was to evaluate the influence of different concentrations of nanofillers on the chemical and physical properties of ethanol-solvated and non-solvated dental adhesives.

Materials and Methods

Eight experimental adhesives were prepared with different nanofiller concentrations (0, 1, 2, and 4 wt%) and 2 solvent concentrations (0% and 10% ethanol). Several properties of the experimental adhesives were evaluated, such as water sorption and solubility (n = 5, 20 seconds light activation), real-time degree of conversion (DC; n = 3, 20 and 40 seconds light activation), and stability of cohesive strength at 6 months (CS; n = 20, 20 seconds light activation) using the microtensile test. A light-emitting diode (Bluephase 20i, Ivoclar Vivadent) with an average light emittance of 1,200 mW/cm² was used.

Results

The presence of solvent reduced the DC after 20 seconds of curing, but increased the final DC, water sorption, and solubility of the adhesives. Storage in water reduced the strength of the adhesives. The addition of 1 wt% and 2 wt% nanofillers increased the polymerization rate of the adhesives.

Conclusions

The presence of nanofillers and ethanol improved the final DC, although the DC of the solvated adhesives at 20 seconds was lower than that of the non-solvated adhesives. The presence of ethanol reduced the strength of the adhesives and increased their water sorption and solubility. However, nanofillers did not affect the water sorption and strength of the tested adhesives.

Effect of heat treatment and addition of 4-META to silane on microtensile bond strength of IPS e.max CAD ceramic to resin cement

BACKGROUND

Silane promotes bonding between ceramic and resin cement. Silane function could be improved by heat treatment and adding 4-Methacryloxyethyl trimellitate anhydride (4-META). The aim of this study was to assess the effect of heat treatment and adding 4-META to silanes on the microtensile bond strength of IPS e.max CAD ceramic and resin cement.

MATERIALS AND METHODS

In this in vitro study, 32 IPS e.max CAD blocks (6 mm × 6 mm × 4 mm) were randomly divided into 8 groups of 4. The ceramic surfaces were etched by 10% hydrofluoric (HF) for 20 s, and Clearfil Ceramic Primer Plus, Clearfil Porcelain Bond Activator (CPA) +4-META, CPA + Clearfil SE Bond (CPA + SE), and Bis-Silane with and without Oven drying at 100°C for 5 min were applied on the ceramic surfaces as silanes, and then, the ceramics were bonded to composite disks by dual-cured resin cements. Ultimately, a total of 120 sticks ( 1 mm × 1 mm × 8 mm) were subjected to microtensile bond strength test (15 sticks from each group) and the failure types were assessed by stereomicroscope at 40x. Data were analyzed by two-sided analysis of variance test and Student's t-test the P values were considered to be < 0.05.

RESULTS

The Bis Silane group (two bottles) showed maximum bond strength (P = 0.009). Heat treatment significantly reduced the bond strength in Bis Silane (P = 0.0001); but, in other groups, it did not show significant effect on the bond strength. Adding 4-META to CPA did not significantly affect the microtensile bond strength of IPS e.max CAD ceramic to resin cement, and there was no difference in mode of failure between groups.

CONCLUSION

The effect of silane type was significant on the microtensile bond strength of the ceramic to resin cement. The effect of 4-META on the bond strength was not significant. The interaction between silane type and heat treatment on the bond strength of ceramic to resin cement was also significant.