Fracture-resistant monolithic dental crowns.

OBJECTIVE: To quantify the splitting resistance of monolithic zirconia, lithium disilicate and nanoparticle-composite dental crowns. METHODS: Fracture experiments were conducted on anatomically-correct monolithic crown structures cemented to standard dental composite dies, by axial loading of a hard sphere placed between the cusps. The structures were observed in situ during fracture testing, and critical loads to split the structures were measured. Extended finite element modeling (XFEM), with provision for step-by-step extension of embedded cracks, was employed to simulate full failure evolution. RESULTS: Experimental measurements and XFEM predictions were self-consistent within data scatter. In conjunction with a fracture mechanics equation for critical splitting load, the data were used to predict load-sustaining capacity for crowns on actual dentin substrates and for loading with a sphere of different size. Stages of crack propagation within the crown and support substrate were quantified. Zirconia crowns showed the highest fracture loads, lithium disilicate intermediate, and dental nanocomposite lowest. Dental nanocomposite crowns have comparable fracture resistance to natural enamel. SIGNIFICANCE: The results confirm that monolithic crowns are able to sustain high bite forces. The analysis indicates what material and geometrical properties are important in optimizing crown performance and longevity.

[Preliminary application of injectable calcium phosphate cement/poly (lactic-co-glycolic acid) microspheres for extraction site preservation].

OBJECTIVE: To investigate the feasibility of extraction site preservation using injectable calcium phosphate cement (CPC) combine with poly (lactic-co-glycolic acid) (PLGA) microspheres. METHODS: Immediate extraction defects models were created in canine mandibles, and the defects were filled with CPC/PLGA (experimental group, E) , Bio-Oss (positive control, P), non-treatment (blank control, B) respectively. Dogs were sacrificed after 4, 8, 12 weeks post operation. Statistical analysis were conducted using SPSS 19. RESULTS RESULTS: of radiological observation showed that there were not significantly different between groups in 4 and 8 week (P > 0.05). After 12 week,E (114.9 ± 8.4) were not significantly different compared with P (117.4 ± 12.1) (P > 0.05) , both were significantly higher than B (95.0 ± 12.6) (P < 0.05) . Histology examination showed that at 4 week following surgery, the result of newly formed bone was as follow, P[ (87.5 ± 1.5) %] > B[(78.7 ± 2.7)%] > E[(69.2 ± 1.8)%] (P < 0.05). At 8, 12 week, results of P[(94.0 ± 2.3)% and (93.5 ± 1.9) %] and E[ (94.7 ± 1.1) % and (96.0 ± 0.9) %] were better than those of B[ (76.8 ± 3.0)% and (87.0 ± 2.4)%] (P < 0.05). CONCLUSIONS: The effect of CPC/PLGA repair immediate alveolar ridge defects is the same as that of Bio-Oss, and CPC/PLGA can be used as a material in extraction site preservation.