Abstract
Objectives
To identify the TiO 2 phases of the root surface of commercially available titanium dental implants, subjected to various surface treatments.
Methods
The titanium implants studied were: Allfit (ALF), Ice (ICE), IMZ TPS (TPS), Laser Lok (LLK), Prima Connex (PRC), Ospol (OSP), Osseospeed TX (OSS), Osseotite Full (OTF), Replace Select (RPS), SLA (SLA) and Trilobe (TRB). The root parts of the implants (n:2) were analyzed by Raman microspectroscopy employing argon ion laser excitation (514.5 nm wavelength) and a 100 μm × 100 μm sampling area at two randomly selected sites.
Results
The spectra of OSP and RPS showed the characteristic peaks of anatase, with traces of rutile (RPS). Complex phases composed of anatase, rutile and amorphous TiO 2 were identified in ALF, ICE and LLK. Rutile and amorphous TiO 2 were found in PRC, OSS, OTF, TPS and TRB, whereas rutile and possibly brookite were traced in SLA. In all implants, except OSP and RPS, peaks assigned to organic impurities (CH 2 , CH 3 ) and carbonates were recorded. Ti 2 O 3 was identified in OTF, PRC and Al 2 O 3 in TRB.
Significance
Great variations in the TiO 2 polymorphs were registered among the implant root surfaces tested. Considering the important differences in the biological activity of these polymorphs, it can be concluded that provision of information regarding the TiO 2 state on implant surfaces should be a mandatory task for implant manufacturers.
1
Introduction
It has been long documented that the surface of titanium dental implants is covered by a thin oxide layer demonstrating low electron conductivity, excellent corrosion resistance and chemical stability, creating thus strong and durable interfaces with bone . The oxide layer is mainly composed of TiO 2 , with small contributions of TiO and Ti 2 O 3 located near the metal–oxide interface, along with other elements assigned to the oxidation procedure, surface conditioning treatments and environmental contamination . Although the fundamental biological role of TiO 2 in osseointegration has attracted a lot of interest, there is limited information for the structure of TiO 2 , especially on commercially available products.
TiO 2 occurs in nature in three crystalline polymorph phases: anatase (tetragonal), brookite (orthorhombic) and rutile (tetragonal), the latter being the stable equilibrium phase under all temperatures. Brookite, the rarest phase, is the largest one, with eight TiO 2 groups per crystal unit cell, anatase follows with four groups per unit cell and finally rutile with two groups per unit cell. In all phases a six-coordinated Ti participates in unit cells . Under the currently available TiO 2 synthetic routes, anatase, rutile or amorphous TiO 2 are produced depending on the conditions. It has been shown that upon heating, amorphous TiO 2 converts to anatase (<400 °C) and then to rutile (600–1000 °C) . The two crystalline phases, and especially anatase, have been the subject of many studies in photocatalysis and photon–electron transfer , hydrophilicity and biological decontamination capacity . Recently, these properties have been highlighted, as they may provide a synergistic effect to the wide range of the implant surface treatments used, for improved bone healing, osseointegration and decontamination of exposed surfaces.
Information on the TiO 2 phases on commercially available dental implant surfaces is extremely limited. It has been proposed that the rapid formation of the oxide layer during manufacturing leads to an amorphous TiO 2 layer on implant surfaces . Although it has been well documented that amorphous TiO 2 layer interacts with bone, hydroxyapatite does not readily grow on such a surface, since not all oxygen portions are ordered. In rutile and anatase, though, oxygen groups match better hydroxyl groups of hydroxyapatite, resulting in deposition of biomimetic apatite, which acts as a “bonding agent” for bone and may facilitate osseointegration . As these phases require additional treatments to be grown from native amorphous TiO 2 , a study hypothesis has been set that the various surface treatments performed on titanium implants to enhance osseointegration create anatase and rutile crystalline domains on implant surfaces. Therefore, the aim of this study was to analyze the structure of TiO 2 on representative types of commercially available titanium implants.
2
Materials and methods
The implants tested and the surface treatments employed according to their manufacturers are listed in Table 1 . The implants were analyzed as received (in sterile packages) under a Raman microscope (InVia, Renishaw, Glousestershire, UK) operated as follows: Ar + laser (514.5 nm), 50× magnification, 1800 grooves/mm grating, 100 μm slit size, 500 μm confocal hole, 5 (OSP, RPS)-50 mW (rest implants) intensity on target, 900–100 cm −1 wavenumber range, 4 cm −1 resolution, baseline correction and calibration based on the 520 cm −1 Raman peak of polycrystalline Si. The laser was focused at the middle of implant root region (between two successive flanks in serrated implants) and an area of 100 μm × 100 μm was scanned with 4 μm step scans to obtain an average spectrum of the region. For each of the implants tested (n:2 per product), two randomly selected root sites were analyzed. Spectra were considered identical when the Raman shifts of the peaks appeared at the same wavenumber and the relative intensities of the major peaks demonstrated less than 20% height difference. All spectra were peak fitted with PeakFit software (v4.12, SeaSolve Software Inc., Framingham, MA, USA) employing Pearson IV amplitude curve fitting (standard width per spectrum), after baseline correction (2nd derivative zero algorithm) and smoothening (FFT filtering). Raman spectra of amorphous and crystalline TiO 2 phases (anatase, brookite, rutile) along with Ti 2 O 3 and corundum (Al 2 O 3 ) were used as reference .
| Product | Code | Surface treatment a | Manufacturer |
|---|---|---|---|
| Allfit | ALF | Al 2 O 3 -blasted | Dr. Idhe Dental, Munich, Germany |
| Ice | ICE | Smooth machined | 3i, Palm Beach Gardens, FL, USA |
| IMZ TPS | TPS | Titanium plasma-sprayed | Friedrichsfeld, Mannheim, Germany |
| Laser Lok | LLK | Tricalcium phosphate/hydroxyapatite-blasted | Biohorizons, Birmingham, AL, USA |
| PrimaConnex | PRC | Calcium phosphate-blasted | Lifecore Biomedical, Chaska, MN, USA |
| Ospol | OSP | Calcium-anodized | Ospol, Malmö, Sweden |
| Osseospeed TX | OSS | Titanium oxide blasted/fluoride-treated | Astra Tech, Mölndal, Sweden |
| Osseotite Full | OTF | Acid-etched (double) | 3i, Palm Beach Gardens, FL, USA |
| Replace Select | RPS | Calcium phosphate-anodized | Nobel Biocare, Göteborg, Sweden |
| SLA | SLA | Al 2 O 3 -blasted/acid-etched | Institute Straumann, Basel, Switzerland |
| Trilobe | TRB | Al 2 O 3 -blasted | Southern Implants, Irene, S. Africa |
2
Materials and methods
The implants tested and the surface treatments employed according to their manufacturers are listed in Table 1 . The implants were analyzed as received (in sterile packages) under a Raman microscope (InVia, Renishaw, Glousestershire, UK) operated as follows: Ar + laser (514.5 nm), 50× magnification, 1800 grooves/mm grating, 100 μm slit size, 500 μm confocal hole, 5 (OSP, RPS)-50 mW (rest implants) intensity on target, 900–100 cm −1 wavenumber range, 4 cm −1 resolution, baseline correction and calibration based on the 520 cm −1 Raman peak of polycrystalline Si. The laser was focused at the middle of implant root region (between two successive flanks in serrated implants) and an area of 100 μm × 100 μm was scanned with 4 μm step scans to obtain an average spectrum of the region. For each of the implants tested (n:2 per product), two randomly selected root sites were analyzed. Spectra were considered identical when the Raman shifts of the peaks appeared at the same wavenumber and the relative intensities of the major peaks demonstrated less than 20% height difference. All spectra were peak fitted with PeakFit software (v4.12, SeaSolve Software Inc., Framingham, MA, USA) employing Pearson IV amplitude curve fitting (standard width per spectrum), after baseline correction (2nd derivative zero algorithm) and smoothening (FFT filtering). Raman spectra of amorphous and crystalline TiO 2 phases (anatase, brookite, rutile) along with Ti 2 O 3 and corundum (Al 2 O 3 ) were used as reference .
| Product | Code | Surface treatment a | Manufacturer |
|---|---|---|---|
| Allfit | ALF | Al 2 O 3 -blasted | Dr. Idhe Dental, Munich, Germany |
| Ice | ICE | Smooth machined | 3i, Palm Beach Gardens, FL, USA |
| IMZ TPS | TPS | Titanium plasma-sprayed | Friedrichsfeld, Mannheim, Germany |
| Laser Lok | LLK | Tricalcium phosphate/hydroxyapatite-blasted | Biohorizons, Birmingham, AL, USA |
| PrimaConnex | PRC | Calcium phosphate-blasted | Lifecore Biomedical, Chaska, MN, USA |
| Ospol | OSP | Calcium-anodized | Ospol, Malmö, Sweden |
| Osseospeed TX | OSS | Titanium oxide blasted/fluoride-treated | Astra Tech, Mölndal, Sweden |
| Osseotite Full | OTF | Acid-etched (double) | 3i, Palm Beach Gardens, FL, USA |
| Replace Select | RPS | Calcium phosphate-anodized | Nobel Biocare, Göteborg, Sweden |
| SLA | SLA | Al 2 O 3 -blasted/acid-etched | Institute Straumann, Basel, Switzerland |
| Trilobe | TRB | Al 2 O 3 -blasted | Southern Implants, Irene, S. Africa |
3
Results
Representative Raman spectra of the reference crystalline and amorphous TiO 2 phases, Ti 2 O 3 and of the endosseous part of the implants tested are presented in Figs. 1–12 . Based on the maximum intensity scale of the Raman peaks recorded, the implants were classified into three groups: Group A comprised of ICE, OTF, OSS, PRC and TRB, all demonstrating low Raman intensities (maximum peak scale <800 au, Figs. 2–6 ); Group B included ALF, LLK, TPS and SLA, with moderate intensities (maximum peak scale 1250 up to 6000 au, Figs. 7–10 ) and Group C incorporated OSP and RPS with high maximum peak intensities (>35,000 au, Figs. 11 and 12 ). Curve fitting greatly assisted in the deconvolution of the complex peak shape components, especially in low intensity spectra.
