Objectives:
It is important for restorative paste to be sufficiently condensable for forming posterior occlusal surfaces. We have developed a new ion-releasing posterior restorative material with excellent condensability, which contains S-PRG filler based on Pre-Reacted Glass-ionomer (PRG) technology. This study aimed to evaluate its polymerization shrinkage and acid-neutralizing effect.
Methods:
Four posterior restorative materials were used: S-PRG filler-containing condensable restorative material (BEP, Shofu), and as controls, commercially-available condensable restorative materials, SureFil (S, DENTSPLY), Prodigy Condensable (P, Kerr), and Heliomolar HB (H, Ivoclar Vivadent). Specific gravity of each restorative material was measured using a gas pycnometer (Accupyc 1330, Micromeritics) before (Dbefore) and after (Dafter) light-curing of each material, and then its polymerization shrinkage(PS) was calculated by the following equation: PS(vol%)=(1-Dbefore/Dafter)x100. Data of PS were statistically analyzed (one-way ANOVA, Tukey's test).
For evaluation of acid-neutralizing effect, each light-cured disc specimen (15mm-diameter, 1mm-thickness) was immersed in lactic acid solution (5mL, pH=4.0, 37ºC), and time-dependent pH change in the test solution was measured up to 24h after the start of immersion using a pH meter (pH METER F-22, Horiba Ltd.).
Results:
-BEP showed significantly lower polymerization shrinkage than S, P and H.
-For acid neutralization evaluation, the pH values of lactic acid solutions shifted to the neutral region from 4.0 (initial) through 4.9 (at 1h) to 6.0 (at 24h) during the immersion of BEP. In contrast, S and P showed considerably less pH increase than BEP, and H exhibited almost no pH change from initial to 24h time point.
| BEP | S | P | H |
Polymerization shrinkage (vol%) | 1.72(0.1)a | 2.80(0.2)b | 2.66(0.1)b,c | 2.46(0.1)c |
Mean (SD) Values with the same superscript were not significantly different (p>0.01).
Conclusions:
Low polymerization shrinkage observed in BEP was anticipated to reduce the risk of contraction gaps and white margins even when the bulk placement technique is used. Furthermore, BEP's acid-neutralizing capacity was expected to reduce the risk of secondary caries on surrounding teeth.