A comparison of resin-modified glass-ionomer and resin composite polymerisation shrinkage stress in a wet environment.
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 (5mm diameter×30mm) 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 1.00mm 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 40s and the plastics cup was filled with ambient temperature water. To determine polymerisation shrinkage stress (σpol) three specimens of each material were tested for a 6-h period to determine mean maximum σpol (MPa), σpol rate (MPa/s) and final σpol (MPa). ANOVA and post hoc Tukey tests were used to determine significant differences between means.


RESULTS
The highest mean maximum σpol of (5.4±0.5) MPa was recorded for RMGIC and (4.8±1.0) MPa for composite. The lowest mean final σpol of (0.8±0.4) MPa was recorded for RMGIC. For mean maximum σpol,σpol rate and final σpol 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.


CONCLUSIONS
When comparing mean σpol, maximum σpol, and σpol rates between individual RMGIC and composite materials significant differences (p<0.05) were observed. However when comparing the group RMGIC to composite no significant differences (p>0.05) were observed. The null hypothesis that there is no difference in the short term σpol of RMGIC materials when compared to composite materials is only partly rejected.


CONCLUSIONS
Limited information is available on the comparison of RMGIC and resin composite σpol levels. This study provides information on the short term levels in a wet environment and will assist in understanding the initial σpol rates RMGIC place in cavities.
Melbourne Dental School, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia. Electronic address: j.cheetham@student.unimelb.edu.au.
Joshua J
JJ
Cheetham
Joseph E A
JE
Palamara
Martin J
MJ
Tyas
Michael F
MF
Burrow
D005898:Glass / Q000737:chemistry*; D008422:Materials Testing; D058105:Polymerization; D011108:Polymers / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water
D011108:Polymers; D012117:Resins, Synthetic; D014867:Water
Polymerisation contraction stress; Polymerisation shrinkage stress; Resin composite; Resin-modified glass-ionomer