A Novel Ion-releasing Low-shrinkage Restorative Composite Containing S-PRG Filler

Objectives: The aim of this study is to evaluate the characterization of a novel ion-releasing and low-shrinkage restorative composite containing S-PRG filler (Beautifil 2 LS, Shofu) and other restorative compsoites.
Methods: Polymerization shrinkages of a novel ion-releasing low-shrinkage restorative composite containing S-PRG filler (Beautifil 2 LS, Shofu) and commercially-available products (Filtek Supreme Ultra (FS, 3M ESPE), EsthetX HD (EX, Dentsply) and Herculite Ultra (HU, Kerr)) were calculated by following formula. Specific gravity of the material before and after light-curing was measured in conformity with ISO 17304.
Formula: Polymerization shrinkage (vol%) = ((D_after-D_before)/D_after) x 100
(D_before: Specific gravity of the material before light-curing, D_after: Specific gravity of the material after light-curing)
Polymerization shrinkage stress of these products was also measured by bonded disk method. Data of polymerization shrinkage and shrinkage stress were statistically analyzed (one-way ANOVA, Tukey’s test).
For evaluation of acid-neutralizing effect, light-cured disk specimens（15mm-diameter, 1mm-thickness） was immersed in lactic acid solution (5mL, pH=4.0, 37^oC), and time-dependent pH change in the test solution up to 12h was measured using a pH meter (pH METER F-22, Horiba Ltd.).
Results: LS showed significantly lower polymerization shrinkage stress than FS, EX and HU. Furthermore LS showed significantly lower polymerization shrinkage rate than EX and HU. Polymerization shrinkage rate of LS showed the lower value than FS, but it of between LS and FS was no significant different.
For acid neutralization evaluation, the pH values of lactic acid solutions shifted to the neutral region from 4.0 (initial) through 4.8 at 1 h to 5.9 at 24 h during the immersion of LS specimens.
In contrast, FS, EX, and HU specimens showed slightly pH change, maintaining the acidity of the test solution at 24h after the start of immersion.
Conclusions: LS showed low polymerization shrinkage rate and stress, it was anticipated to reduce the risk of contraction gap and white margin. Furthermore LS has acid-neutralizing capacity for containing S-PRG filler so that it is expected to reduce the risk of secondary caries on surround teeth.