Yuji Tsubota

Characteristics of low polymerization shrinkage flowable resin composites in newly-developed cavity base materials for bulk filling technique

The purpose of this study was to evaluate polymerization shrinkage and other physical properties of newly-developed cavity base materials for bulk filling technique, with the brand name BULK BASE (BBS). Polymerization shrinkage was measured according to ISO/FDIS 17304. BBS showed the significantly lowest polymerization shrinkage and significantly higher depth of cure than conventional flowable resin composites (p<0.05). The Knoop hardness, flexural strength and elastic modulus of that were significantly lower than conventional flowable resin composites (p<0.05). BBS had the significantly greatest filler content (p<0.05). SEM images of the surface showed failure of fillers. The lowest polymerization shrinkage was due to the incorporation of a new type of low shrinkage monomer, which has urethane moieties. There were no clear correlations between inorganic filler contents and polymerization shrinkage, flexural strength and elastic modulus. In conclusion, the low polymerization shrinkage of BBS will be useful for cavity treatment in dental clinics.

Effect of Eugenol-Containing Cements on the Bond Strength to Composite Core Resins.

The effect of eugenol-containing cements on the bond strength of three composite core resins to dentin were examined both before and after thermocycling.The following results were obtained.1. Dentin surfaces after removing eugenol-containing and eugenol-free cements with dental excavator were free of other cements by examining with the naked eye, however, from SEM observation a little cement remained on its surface.2. The remaining cements on the dentin surface influenced the bond strength of three composite core resins to dentin differently.3. Clearfil DC Core demonstrated the highest bond strength both before and after thermocycling. This means that Clearfil DC Core is little influenced by eugenol.4. Core Max II demonstrated comparatively high bond strength before thermocycling, however, after thermocycling it decreased significantly.5. The bond strength of Clearfil Photo Core was effected by some eugenol-containing cements both before and after thermocycling.