A comparison of resin-modified glass-ionomer and resin composite polymerisation shrinkage stress in a wet environment.

Abstract Objective The aim of this study was to investigate the polymerisation shrinkage stress under water of four resin-modified glass-ionomers and three resin composite materials. Methods Transparent acrylic rods (5 mm diameter×30 mm) were prepared and secured into drill chucks connected to a universal testing machine. A plastics cup was placed around the lower rod and a distance of 1.00 mm was established between the prepared surfaces which provided a C-factor of 2.5. For composite only, an adhesive layer (Scotchbond Universal Adhesive) was placed on the rod ends and cured to achieve a bond with the rod end. Materials were placed between the rods and a strain gauge extensometer was installed. Materials were light cured for 40 s and the plastics cup was filled with ambient temperature water. To determine polymerisation shrinkage stress ( σ pol ) three specimens of each material were tested for a 6-h period to determine mean maximum σ pol (MPa), σ pol rate (MPa/s) and final σ pol (MPa). ANOVA and post hoc Tukey tests were used to determine significant differences between means. Results The highest mean maximum σ pol of (5.4±0.5) MPa was recorded for RMGIC and (4.8±1.0) MPa for composite. The lowest mean final σ pol of (0.8±0.4) MPa was recorded for RMGIC. For mean maximum σ pol, σ pol rate and final σ pol there were significant differences between materials within groups, although no significant difference ( p >0.05) was observed when comparing the RMGIC group to the composite group. Conclusion When comparing mean σ pol, maximum σ pol, and σ pol rates between individual RMGIC and composite materials significant differences ( p p >0.05) were observed. The null hypothesis that there is no difference in the short term σ pol of RMGIC materials when compared to composite materials is only partly rejected. Relevance Limited information is available on the comparison of RMGIC and resin composite σ pol levels. This study provides information on the short term levels in a wet environment and will assist in understanding the initial σ pol rates RMGIC place in cavities.