Method: Our study substituted the nHAP filler (20nm from Berkeley Advanced Biomaterials) for equal weight of the commercial Fuji LC II powder to test a similar mechanical strengthening. Specimens of Fuji LC II were hand mixed (n=8) with standard capsule powder/liquid ratio (P/L =2.7g powder/1.0g liquid). Experimental specimens were modified by substituting 10% wt (0.27g) and 25%wt (0.675g) nHAP in Fuji LC II powder. Diametral tensile strength of each specimen (6mm dia./3mm thick) was evaluated at 24 hours. ANOVA, student-t and Newman-Keuls multiple comparison test were used to determine significant difference and rank order (p=0.05).
Result: The Diametral tensile strength for Fuji LC II capsules were measured as 34.4+/-3.6 MPa, hand mixed standard P/L strength(22.9+/-2.9 MPa), hand mixed with the 10% nHAP (24+/-3.1 MPa) and 25% nHAP (13.9+/-3.1 MPa). ANOVA of all measured strength groups and their multiple comparison test indicated that the standard mix and 10% nHAP had similar strengths, but the 25% nHAP was significantly weaker at p=0.05. The Fuji LC II capsule strength was significantly greater than the other groups. Fracture surfaces were analyzed for porosity.
Conclusion: The lower strengths for Fuji LC II may be related to the substitution of the resin monomers in Fuji LC II for some of the polyacrylic acid as compared to the Fuji I which has only polyacrylic acid. Also, the thicker 25% nHAP mix had larger voids.