Novel Approach to Reliability Prediction Analysis of Dental Ceramic Materials

Objectives: 1) To test the hypothesis that clinical crowns which are correctly processed in the laboratory will have the same fractal dimension to that of ISO 6872 standard bend bars. 2) To test the hypothesis that quantitative fractography can be used on fractured crowns to determine stress at fracture.
Methods: A clinical study with 129 implant supported three-unit fixed dental prosthesis (FDPs) was conducted. Replicas of fractured 27 FDPs (17 ceramic-ceramic and 10 metal-ceramic) were made for fractographic analysis. Bend bars of the same material as the FDPs measuring 25 by 4 by 2 mm were made from fluoroapatite glass-ceramic (FGC) and leucite reinforced glass-ceramic (LRGC). Dynamic fatigue tests were performed at 0.05, 0.5, 5 and 50MPa/sec in water and 50MPa/sec in oil environment. The fractal dimension was obtained from both the fractured FDPs and bend bars using atomic force microscope (AFM) and FRACTAL software. The fracture origin was replicated by impression material first then replicated using epoxy material. The duplicate fracture origin on epoxy was scanned with AFM. The images were translated using MathCAD to the FRACTALS software. The fractal dimension was analyzed by Minkowski Cover (MC) method¹. Fractured FDPs and bars were examined using scanning electron microscopy to measure size of the fracture origin.
Results: The average stress at fracture was 52.2 ± 5.8 MPa for FGC and 67.1 ± 7.7 MPa for LRGC bars. The toughness was calculated as 0.69 ± 0.18 MPm^1/2 for FGC and 0.90 ± 0.14 MPm^1/2 for LRGC. The fractal dimensional increment was 0.11 ± 0.02 for FGC bridges and 0.13 ± 0.03 for FGC bars, and 0.12 ± 0.02 for LRGC bridges and 0.09 ± 0.01 LRGC bars. The stress at fracture for FDPs was 69.3 ± 21.5 MPa for FGC and 65.3 ± 21.5 MPa for LRGC.
Conclusions: We can use property data from bend bars to predict failure stress in clinically fixed dental prostheses.