A novel technique using a composite disk under diametral compression was presented in a previous study for measuring the bond strength between intracanal posts and dentin. This study deals with the stress distribution within the composite disk to allow the bond strength to be calculated accurately. The effects of changing geometrical and material parameters on the post–dentin interfacial stress are also evaluated.
The finite element method with 3D models is used to analyze the stress distribution and to carry out the sensitivity analysis. Progressive post–dentin interfacial debonding is also simulated to better understand the failure process observed in experiments.
Material mismatch causes stress concentrations at the interfaces. The results are presented as correction factors to be used in conjunction with the analytical solution for a homogeneous disk. Comparison between the stresses at the post–dentin interface and those in dentin confirms that interfacial debonding will take place prior to fracture in the dentin.
The numerical solutions presented here will facilitate the adoption of the composite disk in diametral compression for bond strength measurement.
The diametral compression test, also known as the Brazilian disk test or indirect tensile test, is widely used to measure the tensile strength of elastic, brittle materials . It induces a tensile stress in the direction transverse to the applied compressive load which causes the disk specimen to split into 2 halves along the loaded diameter. Modified versions of the test have been applied to the measurement of fracture toughness , interfacial fracture problems , and layered structures . In a previous study , we demonstrated the viability of using a modified version of the diametral compression test, which used a resin composite disk containing a section of root dentin and an intracanal post in the center ( Fig. 1 a), to evaluate the bond strength between the intracanal post and dentin. Using acoustic emission and digital image correlation, we showed that, as required, failure of the disk was initiated from the post–dentin interface, which quickly resulted in whole disk fracture.
The detailed stress field within the homogeneous disk under diametral compression and factors that affect the failure load have been thoroughly discussed . Mathematical formulas (Eqs. (1)–(3) ) based on linear elasticity to describe the stress states within the disk have been given as :
σ x = − 2 p π t x 2 ( R − y ) β 1 4 + x 2 ( R + y ) β 2 4 − 1 2 R
σ y = − 2 p π t ( R − y ) 3 β 1 4 + ( R + y ) 3 β 2 4 − 1 2 R