Abstract
Osseointegrated implants inserted in the temporal bone are a vital component of bone-anchored hearing systems (BAHS). Despite low implant failure levels, early loading protocols and simplified procedures necessitate the application of implants which promote bone formation, bone bonding and biomechanical stability. Here, screw-shaped, commercially pure titanium implants were selectively laser ablated within the thread valley using an Nd:YAG laser to produce a microtopography with a superimposed nanotexture and a thickened surface oxide layer. State-of-the-art machined implants served as controls. After eight weeks’ implantation in rabbit tibiae, resonance frequency analysis (RFA) values increased from insertion to retrieval for both implant types, while removal torque (RTQ) measurements showed 153% higher biomechanical anchorage of the laser-modified implants. Comparably high bone area (BA) and bone-implant contact (BIC) were recorded for both implant types but with distinctly different failure patterns following biomechanical testing. Fracture lines appeared within the bone ~30–50 μm from the laser-modified surface, while separation occurred at the bone-implant interface for the machined surface. Strong correlations were found between RTQ and BIC and between RFA at retrieval and BA. In the endosteal threads, where all the bone had formed de novo, the extracellular matrix composition, the mineralised bone area and osteocyte densities were comparable for the two types of implant. Using resin cast etching, osteocyte canaliculi were observed directly approaching the laser-modified implant surface. Transmission electron microscopy showed canaliculi in close proximity to the laser-modified surface, in addition to a highly ordered arrangement of collagen fibrils aligned parallel to the implant surface contour. It is concluded that the physico-chemical surface properties of laser-modified surfaces (thicker oxide, micro- and nanoscale texture) promote bone bonding which may be of benefit in situations where large demands are imposed on biomechanically stable interfaces, such as in early loading and in compromised conditions.
Highlights
For more than 30 years, osseointegrated implants inserted in the temporal bone have served as an important component of bone-anchored hearing systems (BAHS) [1]
In the search for an explanation of this observation, we evaluated the amount of new bone and the bone-implant contact, the extracellular matrix composition and the structure at the implant surface, as well as the stiffness of the bone-implant unit
The present study shows that osseointegration was attained for two macroscopically similar yet differently structured titanium surfaces
Summary
For more than 30 years, osseointegrated implants inserted in the temporal bone have served as an important component of bone-anchored hearing systems (BAHS) [1]. An increase in implant failures has been reported in young patients, as well as in patients > 60 years of age, possibly related to reduced blood flow in the bone [6]. Clinical conditions such as osteogenesis imperfecta, corticosteroid medication and irradiation have been implicated in higher rates of failure [7]. For this reason, despite the overall low incidence of implant failure, ranging between 2% and 17% in mixed populations (depending on the follow-up time) [1], there is a need to understand the mechanisms of failure, as well as to explore novel measures to improve the clinical performance of these devices. Implant surfaces that incorporate well-defined nanotopography stimulate osseointegration in vivo [15]
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