Effect of Porous Microstructures on the Biomechanical Characteristics of a Root Analogue Implant: An Animal Study and a Finite Element Analysis.

Abstract

Full ceramic or metal custom-made root analogue implants (RAIs) are made by replicating the natural tooth geometry. However, it may lead to the stress shielding of the surrounding bone, and an RAI is unable to easily achieve primary stability. Therefore, to improve primary stability and reduce stress shielding, RAI porous structures are proposed. The purpose of this study was to evaluate the effect of porous microstructures on the biomechanical characteristics of the custom-made RAI. Porous and bulk titanium cylinders and porous RAI and conventional implants for in vivo tests were fabricated using a selective laser melting (SLM) technology. The elastic modulus and the compressive strength of porous titanium cylinders were evaluated. These samples were then implanted into rabbit femurs (cylinders) and beagle dog mandibles (RAI and conventional implants). A simplified three-dimensional geometry of the anterior maxilla of a patient was constructed. Then, based on the extracted standard template library (STL) data, five different RAI models were constructed: (A) smooth surface, (B) pit surface, (C) bulb surface, (D) threaded surface, and (E) porous surface. A conventional implant model was also constructed. A static load of 100 N was applied to the crown in the multivectoral direction. The results of the in vivo experiment confirmed that the porous structure decreased the elastic modulus of Ti6Al4V. Additionally, the implantation of the porous custom-made RAIs resulted in increased new bone ingrowth and decreased bone resorption compared to conventional implants. Moreover, the 3D finite element analysis suggested that the bone surrounding porous custom-made RAIs was subjected to a more uniform stress distribution, and the strain values of the surrounding bone were more conducive to bone formation. Based on these findings, a custom-made RAI with a porous surface accelerates bone formation and might reduce the stress-shielding effect.