Designing, processing and characterisation of titanium cylinders with graded porosity: An alternative to stress-shielding solutions

Abstract

Bone resorption events and consequent failure of titanium implants are frequently related to stress-shielding problems, due to stiffness mismatch with respect to bone. This is a mechanical incompatibility problem, which is difficult to resolve because of the challenge of replacing highly anisotropic biomechanical systems, as is the case of dental implants. This work describes the designing, processing and characterisation of cylindrical titanium samples with a longitudinally graded porosity obtained by conventional powder-metallurgy techniques. The design concept used was biomimetic, based on the stiffness properties of the tissues to be in contact with titanium dental implants. Processing conditions were optimised in terms of different parameters: structural integrity, porosity and mechanical properties. The influence of sintering temperature was evaluated in search of optimum results under the above criteria. The behaviour of longitudinal porosity and Young’s modulus were consistent with the preliminary design concept from the original biomechanical system. Mechanical strength results were reasonably suitable for dental applications and they were favourably sensitive to increasing sintering temperature, due to a stronger adhesion between initial green layers of cylindrical samples. Results showed that it is possible to obtain a desired longitudinal gradient in Young’s modulus, as well as suitable yield strength values. The optimised processing described suggests that it is a plausible candidate for manufacturing dental implants with a good balance between reduced stress shielding and suitable mechanical strength, which encourages us to undertake further work along the same lines.