Methods: Two types of fillers were used: nCaF2 with a diameter of 53 nm, and glass particles of 1.4 µm. Four composites were fabricated with fillers of: (1) 0% nCaF2 + 65% glass; (2) 10% nCaF2 + 55% glass; (3) 20% nCaF2 + 45% glass; (4) 30% nCaF2 + 35% glass. Three commercial materials were also tested. Specimens were subjected to thermal-cycling between 5°C and 60°C for 105 cycles, three-body wear for 4x105 cycles, and water-aging for 2 years.
Results: After thermal-cycling, the nCaF2 nanocomposites had flexural strengths in the range of 100-150 MPa, 5 times higher than the 20-30 MPa for resin-modified glass ionomer (RMGI). The wear scar depth showed an increasing trend with increasing nCaF2 filler. Wear of nCaF2 nanocomposites was within the range of wear for commercial controls. Water-aging decreased the strength of all materials. At 2 years, flexural strength was 94 MPa for nanocomposites with 10% nCaF2, 60 MPa with 20% nCaF2, and 48 MPa with 30% nCaF2. They are 3-6 fold higher than the 15 MPa for RMGI (p<0.05). SEM revealed air bubbles and cracks in RMGI, while composite control and nCaF2 nanocomposites appeared dense and solid.
Conclusions: Combining nCaF2 with glass particles yielded nanocomposites with long-term mechanical properties that were comparable to those of a commercial composite with little F release, and much better than those of RMGI controls. These strong long-term properties, together with their F-release being comparable to RMGI as previously reported, indicate that the nCaF2 nanocomposites are promising for load-bearing and caries-inhibiting restorations. Supported by NIH DE14190 and DE17974 (HX).
Keywords: Aging, Composites, Nanoparticles, Polymers and Wear
See more of: Dental Materials 7: Polymer-based Materials-Physical Properties and Performance