Enhanced Hardness of Osseointegrated Bone by Titanium Surface Roughness

Objectives: Mechanisms underlying advantageous anchorage of roughened titanium implants have not been completely identified. This study aimed at investigating the effect of titanium and its surface roughness on hardness and elasticity modulus of peri-implant bone using nano-indentation technology.

Methods: Rectangular titanium implants with an inner chamber were placed into the femurs of 12 Sprague-Dawley rats. Six rats received implants with a machined surface, and six rats received implants with a dual acid-etched (DAE) surface. At week 4, the femurs from six rats were harvested and sawed along the long axis of the implants. Implant and bone were then carefully dissociated, having the osseointegration interface exposed. The other six femurs were sawed along the implant chamber openings and ground to obtain the transverse section of the implant chamber with de novo bone formation inside.  Tissue hardness and elasticity modulus were measured at the osseointegration interface and inner peri-implant bone using a nano-indenter. Femoral trabecular and cortical bone from additional three untreated rats served as a reference control. A 1-way analysis of variance (ANOVA; P<0.05) followed by Bonferroni multiple comparison tests was used to determine the effect of specimen types on the variables.

Results: Hardness and elastic modulus at the osseointegration interface and peri-implant inner bone associated to the DAE surface were 3 times and 2 times greater, respectively, than those for the machined surface (p<0.0001). The hardness and elastic modulus for the DAE surface were equivalent to those of the cortical bone which showed 4 times greater hardness and 6 times greater elastic modulus than the trabecular bone  (p<0.0001).

Conclusions: The bone tissue around the DAE titanium was harder and stiffer than that around the machined surface both at osseointegration interface and inner peri-implant bone. The hardness and elastic modulus of acid-etched surface-associated bone were equivalent to those of cortical bone.