Reducing composite restoration polymerization shrinkage stress through resin modified glass-ionomer based adhesives.

BACKGROUND: The aim of this study was to determine whether employing resin modified glass-ionomer based adhesives can reduce polymerization contraction stress generated at the interface of restorative composite adhesive systems. METHODS: Five resin based adhesives (G Bond, Optibond-All-in-One, Optibond-Solo, Optibond-XTR and Scotchbond-Universal) and two resin modified glass-ionomer based adhesives (Riva Bond-LC, Fuji Bond-LC) were analysed. Each adhesive was applied to bond restorative composite Filtek-Z250 to opposing acrylic rods secured within a universal testing machine. Stress developed at the interface of each adhesive-restorative composite system (n = 5) was calculated at 5-minute intervals over 6 hours. RESULTS: The resin based adhesive-restorative composite systems (RBA-RCS) demonstrated similar interface stress profiles over 6 hours; initial rapid contraction stress development (0-300 seconds) followed by continued contraction stress development ≤0.02MPa/s (300 seconds - 6 hours). The interface stress profile of the resin modified glass-ionomer based adhesive-restorative composite systems (RMGIBA-RCS) differed substantially to the RBA-RCS in several ways. Firstly, during 0-300 seconds the rate of contraction stress development at the interface of the RMGIBA-RCS was significantly (p < 0.05) lower than at the interface of the RBA-RCS. Secondly, at 300 seconds and 6 hours the interface contraction stress magnitude of the RMGIBA-RCS was significantly (p < 0.05) lower than the stress of all assessed RBA-RCS. Thirdly, from 300 seconds to 6 hours both the magnitude and rate of interface stress of the RMGIBA-RCS continued to decline over the 6 hours from the 300 seconds peak. CONCLUSIONS: The use of resin modified glass-ionomer based adhesives can significantly reduce the magnitude and rate of polymerization contraction stress developed at the interface of adhesive-restorative composite systems.

Marginal adaptation and micro-porosity of class II restorations of a high copper amalgam and a palladium-free gallium-based alloy.

The aim of the current investigation was to compare the marginal adaptation and internal porosity of a gallium (Ga)-based alloy (Galloy) with a high copper amalgam (Permite C DP) when used in moderately sized conventional class II cavities. Ten dentists placed two restorations of each material in standardized class II cavities in typodont teeth set in a phantom head. The proximal surfaces of the restored teeth were subsequently examined using an optical microscope and colour photographs were taken. The teeth were then serially sectioned before being re-examined microscopically and re-photographed. Three dentists rated the photographs of the restorations on two occasions, 2 weeks apart, for marginal adaptation and internal porosity using a six and five point scoring criteria, respectively. Inter- and intra-examiner agreements were assessed with weighted kappa statistics. The Ga-based alloy exhibited inferior marginal adaptation and a significantly higher level of porosity and internal defects compared with the dental amalgam. Marginal defects were mainly concentrated at the gingival third of the proximal boxes for both alloys. The poor marginal adaptation and extensive internal porosity detected for the Ga-based alloy was attributed to the difficulty in the alloy condensation related mainly to the 'stickiness' of the alloy to the condensers and to the rapid change in the plasticity of the alloy during condensation. This could possibly be a factor in the post-operative complications reported with the clinical use of this alloy.

Influence of bonding agent composition on flexural properties of an Ultra-High Molecular Weight Polyethylene Fiber-Reinforced Composite.

This study evaluated the influence of seven commercially available bonding agents on the flexural properties of an Ultra High Molecular Weight Polyethylene (UHMWPE) Fiber-Reinforced Composite (FRC). Nine groups (n=10 per group) of flexural strength specimens were prepared from an indirect composite reinforced with UHMWPE fiber and cured according to manufacturers' instructions (Groups A to I). Group I was a fiber-reinforced negative control without any bonding agent resination. A tenth group (Group J) was a positive control group prepared using indirect composite alone. The fiber reinforcement material for Groups A to H was resinated with one of the seven different bonding agents. Group H used the same bonding agent as for Group G specimens. However, the fiber was silanized before bonding agent application for Group G specimens. Specimens were stored wet for 24 hours at 37 degrees C before measuring flexural strength and modulus in three-point bend at a crosshead speed of 1 mm/minute. Scanning Electron Microscopy (SEM) was employed to assess the fiber-resin interface of representative samples. The mean (SD) flexural strength of the test groups impregnated by the bonding agents ranged from 169 (37) to 266 (39) MPa. Statistical analysis of the flexural strength data using one-way ANOVA revealed significant (p<0.05) differences between the test groups. There was catastrophic fiber/composite failure in the positive control group that had a mean flexural strength of 75 (8) MPa. Silane pre-treatment of UHMWPE fiber before impregnation with the bonding agent significantly reduced the flexural strength (p<0.05).

Handling characteristics of a palladium-free gallium-based alloy compared with a high copper dental amalgam in a simulated clinical trial.

The aim of the current study was to compare the handling characteristics of a palladium-free gallium-based alloys (Galloy) with those of a high-copper amalgam (Permite C). The study had a particular interest in the evaluation of the direct placement delivery system used with both alloys. Ten dentists participated in the current study. Each placed two amalgam and two gallium-based alloy restorations in conventional class II cavities prepared in acrylic typodont teeth. None of the participating dentists had used the direct placement delivery system or had any previous experience with gallium-based alloy and no practice was allowed beforehand. The restorations were evaluated according to the following criteria: ease of loading the cavity (delivery system), ease of condensation, capacity to produce and sustain contact area, ease of carving, resistance to damage during removal of the matrix band, overall quality of the restoration and the available working time. Each criterion was given a score on a scale of 1-5 (1: very poor, 2: poor, 3: fair, 4: good, 5: very good). The results showed no statistically significant difference in the evaluated criteria between the two alloys (P > 0.05) except for criterion number 2 (ease of condensation, P=0.0005).

The influence of fibre placement and position on the efficiency of reinforcement of fibre reinforced composite bridgework.

The effect of placement of ultra-high molecular weight polyethylene (UHMWPE) fibres on the flexural properties and fracture resistance of a direct dental composite was investigated. The UHMWPE fibres are increasingly being used for the reinforcement of laboratory fabricated resin composite crown and bridgework. The aim of this study was to assess the effect of a commonly used laboratory fabrication variable on the in vitro strength of beam shaped specimen simulating a three-unit fixed bridge. Four groups (10 specimens per group) of Herculite XRV were prepared for flexural modulus and strength testing after reinforcement with UHMWPE fibres. Two groups of control specimens were prepared without any fibre reinforcement. Half the specimen groups were stored in distilled water and the other groups were stored dry, both at 37 degrees C for 2 weeks before testing. The results of this study showed that placement of fibre at or slightly away from the tensile side improved the flexural properties of the composite in comparison with the unreinforced control specimen groups whilst the mode of failure differed according to fibre position. Scanning electron microscope (SEM) investigation revealed that placement of the fibre slightly away from the tensile side favoured crack development and propagation within the resin bridging the interfibre spaces in addition to debonding parallel to the direction of fibre placement. Laboratory fabrication variables may effect the strength of fibre reinforced bridgework significantly.