Effect of unfilled resins and a silane primer on bonding between layers of a light-activated composite resin veneering material

Repairability of cross-linked biopolymers

Repair of biopolymers is a critical issue, especially with aged restorations. Obtaining a chemical bond to the repair surface might solve this problem. We hypothesized that certain repair liquids are suitable to establish a strong bond to an artificially aged dimethacrylate-based biopolymer for temporary restorations. Specimens made of a self-curing temporary crown-and-bridge material were prepared and thermocycled for 7 days (5000x, 5-55 degrees C). Cylinders made of light-curing composites (n=10) were bonded onto the specimen surface, either after grinding or after the application of 4 different experimental repair liquids (Bis-GMA:TEGDMA mixture=bonding, methylmethacrylate=MMA, bonding & acetone, bonding & MMA). A shear bond strength test was performed 24 hrs after repair. The highest bond strength was obtained with the bonding & acetone liquid (20.1+/-2.2 MPa). The use of MMA significantly affected the bond strength (6.8+/-1.9 MPa). MMA is inadequate as a repair liquid on aged composite-based biopolymers.

Hydrolytic stability of composite repair bond

The hydrolytic stability of composite repairs is a desirable property. In the present study, the composite repair microtensile bond strength, failure mode distribution, and nanoleakage occurrence before and after thermocycling were evaluated. Standardized, 1-month-old composite substrates were roughened, cleaned, and randomly assigned to seven groups according to the intermediate agent applied. Resin-based, silane-based, and combined silane/adhesive coupling agents were investigated. The same resin composite as the substrate was used for repair. For each group, repaired samples were wet stored for 24 h (37 degrees C) or thermocycled (5,000 cycles, 5-55 degrees C). Failure mode and silver nitrate penetration were examined by stereomicroscopy. Intermediate agent, experimental condition, and their interaction were significant factors. Hydrophobic flowable composites resulted in statistically higher repair strengths, lower occurrence of adhesive failures, and good quality interfacial coupling without any silver uptake in both conditions. Light-curing, hydrophilic resin monomer-based intermediate agents, although not affected by thermocycling, showed a more pronounced silver penetration. The composite repair strength of a self-curing silane/adhesive agent was significantly affected by thermal stresses, despite the absence of silver uptake. A prehydrolized silane agent recorded the lowest repair strength, with minimal or no evidence of interfacial silver impregnation after thermocycling. In conclusion, flowability and hydrophobic nature can be considered important properties when selecting intermediate agents for composite repair.

Effect of Intermediate Agents and Pre-heating of Repairing Resin on Composite-repair Bonds

The combination of a flowable composite as an intermediate agent and a repairing material at a temperature of 23°C or 37°C prior to light curing may be recommended as a simple, suitable procedure to provide higher bond strengths and uniform composite-to-composite interfacial adaptation.

Microtensile bond strength testing of luting cements to prefabricated CAD/CAM ceramic and composite blocks

OBJECTIVES

To investigate the Microtensile bond strength (microTBS) and failure mode of resin cements bonded to composite and ceramic CAD/CAM blocks following various surface treatments.

METHODS

Paradigm composite blocks and Cerec Vitablocs received three surface treatments following the control treatment of surface grinding with 600 SiC grit. (1) Application of adhesive resin (Adh), (2) etching with hydrofluoric acid and silanization (HF+S) or (3) combination of the previous two treatments (HF+S+Adh). Three resin cements (Tetric Flow, Nexus 2, RelyX ARC) were applied to these surfaces and built-up in layers. After 24 h water storage at 37 degrees C, the non-trimming version of microTBS test was used to produce 1 mm(2) microbars. The Microbars were subjected to a tensile load using a modified testing device. The broken specimens were examined with a stereomicroscope and SEM to determine the failure mode.

RESULTS

All control and adhesive treated groups of the ceramic substrate showed premature debonding during cutting. The overall mean microTBS for the three resin cements bonded to ceramic following HF+S and HF+S+Adh surface treatment, was 27 and 29.2 MPa and for the resin cements bonded to composite substrate was 42.3 and 54.2 MPa, respectively. The mode of failure was 98% adhesive with composite as a substrate and 68% mixed failures with ceramic as a substrate.

CLINICAL SIGNIFICANCE

CAD/CAM restorations fabricated from processed composite blocks may have advantage over the ceramic blocks with regard to the higher bond strength with resin cements.

In vitro evaluation of marginal and internal adaptation after occlusal stressing of indirect class II composite restorations with different resinous bases

Composite inlays are indicated for large cavities, which frequently extend cervically into dentin. The purpose of this study was to compare in vitro the marginal and internal adaptation of class II fine hybrid composite inlays (Herculite, Kerr) made with or without composite bases, having different physical properties. Freshly extracted human molars were used for this study. The base extended up to the cervical margins on both sides and was made from Revolution (Kerr), Tetric flow (Vivadent), Dyract (Detrey-Dentsply) or Prodigy (Kerr), respectively. Before, during and after mechanical loading (1 million cycles, with a force varying from 50 to 100 N), the proximal margins of the inlay were assessed by scanning electron microscopy. Experimental data were analysed using non-parametric tests. The final percentages of marginal tooth fracture varied from 30.7% (no base) to 37.6% (Dyract). In dentin, percentages of marginal opening varied from 9.2% (Tetric Flow) to 30.1% (Prodigy), however, without significant difference between base products. Mean values of opened internal interface with dentin varied from 11.06% (Tetric Flow) to 28.15% (Prodigy). The present results regarding dentin adaptation confirmed that the physical properties of a base can influence composite inlay adaptation and that the medium-rigid flowable composite Tetric Flow is a potential material to displace, in a coronal position, proximal margins underneath composite inlays.

Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites

STATEMENT OF PROBLEM

Enhancement of bond strength between new and old composite usually requires increasing the surface roughness to promote mechanical interlocking and coating of old composite with unfilled resin bonding agents to advance surface wetting and chemical bonding.

PURPOSE

The purpose of this study was to evaluate the effect of combinations of surface treatments and bonding agents on the shear bond strength between new and old composite.

MATERIAL AND METHODS

Six surface treatments, two bonding agents, and an untreated control comprised 18 different subgroups.

RESULTS

The use of unfilled resin, alone or combined with silane, was the most effective procedure to enhance the shear bond strength of the repaired composite specimens, irrespective of the surface pretreatment processes. Silanation and unfilled resin slightly but not significantly improved the repair strength compared with unfilled resin alone.

CONCLUSIONS

Different combinations of surface treatments and bonding agents affect shear bond strength differently. The highest shear bond strength values were achieved by grinding the surface with green Carborundum stone or sandblasting, whereas the lowest values were obtained with hydrofluoric acid as the surface treatment agent.