Shrinkage Stress and Microleakage of a Resin-Based Calcium Phosphate Cement

Successful pulp capping depends on the ability of a material to seal exposures or near exposures from bacteria.  A resin-based calcium phosphate cement developed for pulp capping has demonstrated favorable mechanical properties, moderate dentin adhesion, and remineralizing capability in vitro and in vivo.  OBJECTIVE: This study evaluated the polymerization shrinkage stress and microleakage characteristics of a second generation resin-based calcium phosphate cement, termed RCPC2, in comparison to currently used materials.  METHODS: Shrinkage stress determination:  Samples (n=10) of 3 materials [RCPC2, VLC Dycal (Caulk Dentsply) and Vitrebond (3M)] were mixed, placed between 2 quartz rods (6 mm in diameter) mounted in a Tensometer.  The 1.2 mm thick specimens were subjected to visible light (quartz halogen) polymerization for 60 s.  Shrinkage stress was quantified (MPa) and recorded via a cantilever beam deflection method.  Microleakage determination:  De-identified human molars were divided into 3 groups (n=8), dentin cavities prepared (3.0 mm diameter x 1.5 mm depth) and either RCPC2, VLC Dycal, or Vitrebond placed according to manufacturer's instructions.  All teeth were thermocycled (2000 cycles, 5/55°C, 30 s dwell), immersed in 50% aqueous AgNO₃ (2 h), rinsed, and placed in developer (3 h).  Teeth were sectioned longitudinally through the middle of the preparation and evaluated for staining under a stereo light microscope (Wild/Leica MZ16).  Data was analyzed using ANOVA and Tukey post hoc analysis (a=0.05).  RESULTS: Shrinkage Stress:  RCPC2 (1.96±0.20 MPa) exhibited significantly greater shrinkage stress (p<0.001) than either VLC Dycal (0.76±0.12 MPa) or Vitrebond (1.36±0.18 MPa).  Microleakage:  All VLC Dycal and Vitrebond samples de-bonded from dentin during thermocycling rendering microleakage determination impossible.  CONCLUSION: RCPC2 was the only material to withstand thermocycling and exhibited acceptably low microleakage.  RCPC2 appears to be a clinically acceptable material for use as a pulp capping agent. Supported by NIDCR Grant Number R21DE13298, ADAF, USN NNMC.2006.0132 and NIST.