Determinations of strength of synthetic hydroxyapatite ceramic implants

To study the physical strengths of various types of synthetic high porosity hydroxyapatite plates, we constructed samples of a fixed shape, 8 X 25 mm in size, with varying degrees of thickness (3 to 10 mm) and porosity (40, 50, and 60 percent), as well as samples with varying degrees of curvature and samples constructed with computer-aided design-computer-aided manufacturing (CAD-CAM) technology based on a real-size model made with laser lithography from computed tomography data. The strength of the samples was studied with the three-point bending test and crush tests. Studies showed that strength decreases with increasing porosity and increases with increasing thickness. In addition, results of testing plates of varying shapes and degrees of curvature revealed that the effects of these variations were small and that when the width and thickness were held constant, changing the curvature of the entire unit (from a height of 20 to 30 mm) or altering both sides had no remarkable effect on strength. On the other hand, strength testing of plates of various shapes and thicknesses constructed from clinical computed tomography data revealed that minimum optimization of the parameters was achieved when plates had a porosity of about 40 percent and a thickness of about 8 mm.