27 - Dentine Analogue Materials for Ceramic Crown Fatigue Test: A Reliability Study.

To seek dentine analogue materials that could reliably replace human dentine in ceramic crown fatigue test. Two dentine analogue materials, woven glass fibre-filled epoxy (NEMA grade G10, International Paper, Hampton, SC, USA; G10) and glass fiber-reinforced polyamide-nylon (30% glass fiber reinforced polyamide-nylon 6,6, Goodfellow Cambridge Limited, Huntingdon, England; RPN), were used as substrates and compared with human extracted teeth (HD). Beam-shaped specimens were prepared and tested with three-point bending test in anti-plane longitudinal direction to determine the flexural strength and elastic modulus (n=10). Nanohardness (n=3) was tested on the beam specimens. Abutment-shaped substrates were prepared and restored with monolithic lithium disilicate crowns (n=10) and then subjected to wet cyclic loading in a step-stress manner (500 N initial load, 100 N step size, 100,000 cycles per step) with a 20 Hz frequency. Mechanical and fatigue test data were statistically analyzed using Kruskal-Wallis one-way ANOVA and post-hoc comparisons (α=0.05). Survival probability estimation was performed by Mantel-Cox Log-Rank test with 95% confidence intervals (CI). For the fatigue failure load (FFL) and the number of cycles until failure (NCF), Weibull modulus (m), characteristic strength (η), and load for 10% failure probability (B10) with 90% CI were calculated using the median-rank regression method. Finite Element Models of the fatigue test were established for stress distribution analysis and lifetime prediction. Fractographic observations were qualitatively analyzed. The flexural strength in descending order was HD (164.27±14.24 MPa), G10 (116.48±5.93 MPa), and RPN (86.73±3.56 MPa), which showed significant difference (p<0.001). No significant difference was observed in the flexural moduli of three materials (p=0.377) and the nanohardness between HD and RPN (p=0.749). G10 and RPN presented comparable mean FFL and NCF with human dentine (p=0.237 and 0.294, respectively). The Mantel-Cox Log-Rank test revealed similar survival probabilities of crowns restored with three substrate materials (p=0.055). However, the Weibull modulus (m) of RPN (13.57 for FFL, 9.46 for NCF) was significantly higher than those of G10 (2.87 for FFL, 1.91 for NCF), i.e. RPN is a more reliable dentine analogue material than G10. FEA analysis presented a correlation with the experimental results, such that RPN showed a closer stress distribution to dentine. Dentine analogue materials with similar elastic properties and fatigue performance to human dentine can reliably replace human dentine as substrate in ceramic crown fatigue test. [Display omitted] [ABSTRACT FROM AUTHOR]