A calcium phosphate cement (CPC) sets to form hydroxyapatite and has been used in dental and craniofacial applications. However, when CPC was used in periodontal repair, tooth mobility resulted in the fracture and exfoliation of the brittle implants. The aim of this study was to develop CPC-chitosan lactate composites with higher strength and increased strain before failure. It was hypothesized that the incorporation of chitosan lactate would render CPC non-rigid with improved properties. Two-way ANOVA showed significant effects of chitosan lactate and powder:liquid ratio (p < 0.001) on flexural strength, strain-at-peak-load, work-of-fracture, and elastic modulus. At powder:liquid = 2, the strength (mean +/- SD; n = 6) at 20% chitosan lactate was 15.7 +/- 1.3 MPa, higher than 4.9 +/- 1.4 MPa of CPC without chitosan lactate. At powder:liquid = 1, the strain-at-peak-load was 0.2% for CPC without chitosan lactate; it increased to 15.8% for CPC containing 15% chitosan lactate. The work-of-fracture was increased by more than ten times. The novel strong and non-rigid CPC may provide compliance for tooth mobility without fracturing the implant, and may also extend the use of CPC into the repair of larger defects in stress-bearing locations.
Resin composites must be improved if they are to overcome the high failure rates in large stress-bearing posterior restorations. This study aimed to improve wear resistance via nano-silica-fused whiskers. It was hypothesized that nano-silica-fused whiskers would significantly improve composite mechanical properties and wear resistance. Nano-silicas were fused onto whiskers and incorporated into a resin at mass fractions of 0%-74%. Fracture toughness (mean +/- SD; n = 6) was 2.92 +/- 0.14 MPa.m(1/2) for whisker composite with 74% fillers, higher than 1.13 +/- 0.19 MPa.m(1/2) for a prosthetic control, and 0.95 +/- 0.11 MPa.m(1/2) for an inlay/onlay control (Tukey's at 0.95). A whisker composite with 74% fillers had a wear depth of 77.7 +/- 6.9 mum, less than 118.0 +/- 23.8 microm of an inlay/onlay control, and 172.5 +/- 15.4 microm of a prosthetic control (p < 0.05). Linear correlations were established between wear and hardness, modulus, strength, and toughness, with R = 0.95-0.97. Novel nano-silica-fused whisker composites possessed high toughness and wear resistance with smooth worn surfaces, and may be useful in large stress-bearing restorations.
Long-term water exposure may degrade polymer-matrix composites. This study investigated the water-aging of whisker composites. It was hypothesized that whiskers would provide stable and substantial reinforcement, and that whisker type would affect water-aging resistance. Silica-fused Si(3)N(4) and SiC whiskers were incorporated into a resin. The specimens were tested by three-point flexure and nano-indentation vs. water-aging for 1 to 730 days. After 730 days, SiC composite had a strength (mean +/- SD; n = 6) of 185 +/- 33 MPa, similar to 146 +/- 44 MPa for Si(3)N(4) composite (p = 0.064); both were significantly higher than 67 +/- 23 MPa for an inlay/onlay control (p < 0.001). Compared with 1 day, the strength of the SiC composite showed no decrease, while that of the Si(3)N(4) composite decreased. The decrease was due to whisker weakening rather than to resin degradation or interface breakdown. Whisker composites also had higher moduli than the controls. In conclusion, silica-fused whiskers bonded to polymer matrix and resisted long-term water attack, resulting in much stronger composites than the controls after water-aging.
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