Changes to Dyract restorative resin immersed in various media

To examine changes in weight, strength, fluoride release, and surface changes to the polyacid-modified resin composite Dyract after immersion in various media for periods up to 16 weeks.

Properties investigated were change in weight, strength, release of fluoride ions, and surface changes. Specimens were immersed in reverse osmosis deionized water (ROW) and in acetate buffer solutions containing calcium hydrogen orthophosphate. The acetate media were of pH3, pH5 and pH7. All solutions were maintained at 37 degrees C without agitation. Solutions were changed weekly and retained for fluoride analysis and specimens were weighed each week. After periods of 1, 2, 3, 4, 8, 12 and 16 weeks, some specimens were subjected to shear punch testing and SEM examination.

All specimens except those in pH3 medium gained weight for the first 2-5 weeks after which weight was lost until all specimens weighed less than at the commencement of the study. The specimens in pH3 medium lost considerable weight from weeks 1 and 2. SEM examination showed disintegration of the surface of all specimens examined. Fluoride release peaked at 1 week in all specimens except those in pH3 medium. Fluoride release was highest in pH3 media (approximately 46 ppm) after 1 week and remained high for 7 weeks, after which it was reduced to about 50% of the initial release. Specimens stored in ROW and pH5 media released approximately 5 ppm after 1 week, and this was reduced to approximately 1 ppm (pH7) and 2 ppm (ROW) by week 6.