Toward optimizing dental implant performance: Surface characterization of Ti and TiZr implant materials

Graphical abstract

Highlights

  • Ti and TiZr implant surfaces are studied to further insight into osseointegration.

  • Data are acquired from substrates subjected to SLA and SLActive surface treatments.

  • All substrates exhibit surface films with near TiO 2 stoichiometry.

  • No evidence is found for discrete ZrO x phases on TiZr implant surfaces.

Abstract

Objective

Targeting understanding enhanced osseointegration kinetics, the goal of this study was to characterize the surface morphology and composition of Ti and TiZr dental implant substrates subjected to one of two surface treatments developed by Straumann. These two treatments are typically known as SLA and SLActive , with the latter resulting in more rapid osseointegration.

Methods

A range of techniques was applied to characterize four different substrate/surface treatment combinations ( Ti SLA , Ti SLActive , TiZr SLA , and TiZr SLActive ). Contact angle measurements established their hydrophilic/hydrophobic nature. Surface morphology was probed with scanning electron microscopy. X-ray diffraction, Raman μ-spectroscopy, and X-ray photoelectron spectroscopy were used to elucidate the composition of the near-surface region.

Results

Consistent with previous work, surface morphology was found to differ only at the nanoscale, with both SLActive substrates displaying nano-protrusions. Spectroscopic data indicate that all substrates exhibit surface films of titanium oxide displaying near TiO 2 stoichiometry. Raman μ-spectroscopy reveals that amorphous TiO 2 is most likely the only phase present on Ti SL A , whilst rutile-TiO 2 is also evidenced on Ti SLActive , TiZr SLA , and TiZr SLActive . For TiZr alloy substrates, there is no evidence of discrete phases of oxidized Zr. X-ray photoelectron spectra demonstrate that all samples are terminated by adventitious carbon, with it being somewhat thicker (∼1 nm) on Ti SL A and TiZr SLA .

Significance

Given previous in vivo studies, acquired data suggest that both nanoscale protrusions, and a thinner layer of adventitious carbon contribute to the more rapid osseointegration of SLActive dental implants. Composition of the surface oxide layer is apparently less important in determining osseointegration kinetics.

Introduction

Osseointegration, defined as ‘ the formation of a direct interface between an implant and bone without soft tissue interposition at the optical microscopy level ’ , is key to the success of dental implant procedures. On this basis much effort has been expended to enhance the osseointegration performance of such implants through surface engineering . Optimizing surface morphology and composition are primary targets, as there is a general consensus that these two factors can impact significantly upon the osseointegration process . Indeed, significant progress has been made in this area, with current dental implants far out performing their predecessors . There is, however, still the potential for further improvement through understanding gained from detailed knowledge of the implant surfaces. Here, we contribute to this topic through a systematic study of the surface morphology and composition of a series of technically pertinent substrates. The focus is on comparing Ti and TiZr implant substrates, subjected to processing developed by Straumann (Institut Straumann AG, Basel, Switzerland) for their range of commercial dental implants.

Straumann fabricate dental implants from both commercially pure Ti (c.p.-Ti) and TiZr alloy (13–17 wt% Zr). Subsequent to machining, the implants undergo one of two rather similar surface treatments to enhance osseointegration . The first of these approaches, which leads to the so-called SLA surface, involves sandblasting, followed by acid etching. The implant is then cleaned and sterilized under ambient atmospheric conditions and stored in air within sterile packaging. The second method, which results in the SLActive surface, merely differs in the sterilization and storage steps, i.e., it is cleaned and sterilized in an inert atmosphere, and stored in sterile saline solution. This apparently minor modification, however, results in significant improvement in the kinetics of osseointegration, significantly reducing the time to reach a state where the implant is able to safely bear loads .

Regarding the enhanced osseointegration properties of SLActive implants relative to SLA , substantial effort has been applied to gain insight into this phenomenon . It is well established that following implantation a significantly higher bone-implant contact area is achieved for SLActive implants during the first one to two months after insertion , and that they also perform better in extraction testing during this period . Consistent with this difference in performance, it is reported that SLActive and SLA implants display distinct initial bio-responses in pertinent in vivo/vitro environments . Notably, SLActive surfaces enhance interfacial blood coagulation and fibrin scaffold deposition , which in turn promote the attachment and differentiation of osteoblasts .

To further understand the performance of SLA and SLActive implants, a number of researchers have engaged in studies to identify pertinent surface properties/characteristics, focusing primarily on Ti substrates . Macroscopically, it has been established that the SLActive surface is super-hydrophilic, whereas the SLA surface is hydrophobic in nature . This observation is generally perceived to indicate that super-hydrophilicity and more rapid osseointegration kinetics are intimately related . As to the origin of these improvements in hydrophilicity/osseointegration, it has been suggested that the reduced amount of surface (adventitious) carbon found on SLActive substrates may underpin these two phenomena, although this result is disputed . An alternative explanation for this variation in surface functionality is the presence of nanoscale structures on the SLActive surface, which are absent from SLA implant material ; microscopically, SLActive and SLA substrates display very similar morphologies . More recent results suggest that both a low degree of surface carbon contamination and nanoscale structures are likely requirements for the more rapid osseointegration exhibited by SLActive substrates , although they may impact upon different steps in the osseointegration process . More explicitly, it is suggested that the nanoscale structures enhance the rate of blood protein adsorption, whilst hydrophilicity enhances subsequent blood coagulation.

Besides the surface characteristics mentioned above (i.e., nanostructures and reduced adventitious carbon) being the origin of the more rapid osseointegration of SLActive implants, other possibilities also require consideration. For example, the identity of surface oxide phases may play an important role, although to date this topic has attracted relatively little attention . Given this particular knowledge gap, the underpinning hypothesis motivating this study was that the SLA and SLActive treatments of Ti and TiZr substrates lead to distinct surface oxide terminations. Hence, the aim of this study was to characterize the surface oxides on Ti and TiZr substrates with SLA and SLActive treatments. To this end, a combination of Raman μ-spectroscopy and X-ray photoelectron spectroscopy (XPS) have been employed, supported by contact angle goniometry, scanning electron microscopy (SEM), and grazing incidence X-ray diffraction (GIXRD). Some of these measurements have been performed previously on analogous substrates , but this is the first study where such an array of complementary characterization techniques have been systematically applied and consistently interpreted. The data acquired from the TiZr alloy are particularly noteworthy, as very limited effort has been applied to characterize the surface of this substrate previously .

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Nov 22, 2017 | Posted by in Dental Materials | Comments Off on Toward optimizing dental implant performance: Surface characterization of Ti and TiZr implant materials
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