Highlights
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Effects of instrumentation on anatase and titanium surface integrity were evaluated.
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Nanosized anatase surfaces are more prone to abrasive treatments than pure titanium.
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Abrasive surface alterations may not correlate with complete loss of functionality.
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Plastic tipped instruments, air flow device and rubber cup did not harm integrity.
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This study suggests to avoid certain instruments for nanocoated implants.
Abstract
Objective
To determine in vitro the loss of integrity caused on photocatalytic anatase coated implant surfaces by clinical instrumentation through changes in surface topography and loss of functionality.
Methods
Anatase-coated titanium discs were treated with diamond burs, polishers, plastic and metal hand instruments, air scaler and air flow devices. The pressure exerted through instrumentation was measured online. Surface topography was evaluated through scanning electron microscopy and contact profilometry, surface function through hydrophilization capacity upon UV-A activation.
Results
Treatment with diamond burs and instruments with metal tips resulted in an increase of roughness. Use of silicone polishers led to smoothening, which was more pronounced on the anatase surface. Plastic instruments, the air abrasive system and rubber cups left the surfaces intact. Functionality was partially lost on surfaces subjected to hand instruments and completely lost upon diamond burs and silicone polishers.
Significance
The integrity of functional nanocoatings depends on the applied instrumentation. Air flow device, rubber cup with polishing paste and plastic tipped instruments prevent damage on these nanosurfaces and may be preferably used when decontaminating anatase and other nanocoatings in a clinical setting.
1
Introduction
The role of micron-, submicron- and nanoscale roughness and surface wettability on both early osseointegration and prevention of early implant failure have been extensively researched . While inflammation of the peri-implant tissue is regarded to be a main factor associated with late implant failure , the reported epidemiology varies greatly within the literature, with numbers of affected implants ranging between 12% and 43% . A later study suggested as many as 10% of implants and 20% of patients to be affected , yet smaller incidences were reported more recently . Thus, there is still uncertainty regarding the incidence of peri-implantitis.
Although no direct link between the implant surface structure and peri-implant inflammation could be identified , the process is clearly related to biofilm formation, which largely depends on surface roughness and surface free energy .
While mucosal inflammation is reversible and can be treated non-surgically by means of oral hygiene, prophylaxis and decontamination , progression into peri-implantitis may, if untreated, ultimately lead to implant loss. Due to the etiological relevance of bacterial colonization, therapeutic intervention aims at debridement and disinfection of the implant surface. Usually, a combination of conservative and surgical intervention is suggested . The latter involves open flap surgery, different mechanical debridement methods and chemical decontamination . On areas where bone is lost around the threads and apical shift of the soft tissue has occurred, thread reduction as well as contouring and smoothening of the surface are recommended .
Although many studies reported effects of mechanical treatment and cleaning methods on different titanium surfaces , the impact such treatments may have on advanced functional nanocoatings is unknown.
Anatase, a semiconductive crystalline modification of titanium dioxide (TiO 2 ), has recently been proposed as a multifunctional nanocoating for dental implants. Upon ultraviolet-(UV-)A illumination, anatase thin films form free radicals as well as active oxygen species on their surface that decompose organic hydrocarbon contaminations and convert lower wettable surfaces to superhydrophilicity . In recent years, the important role of hydrophilicity for improvements in the cascade of reactions towards osseointegration as well as possible synergistic effects of combined hydrophilic and nanoscaled surfaces could be shown . UV-A illuminated anatase has been proven to photocatalytically decompose adsorbed organic films such as model albumin films and macromolecular human pellicle films which offer important binding sites for early bacterial colonizers . Therefore, photofunctionalized implant surfaces might provide a possible means for the treatment of peri-implant infections both by a more effective surface decontamination and by enhanced re-osseointegration through improved wettability.
The aim of this study was to analyze the effect of professional hygiene and peri-implantitis treatment procedures on anatase-coated titanium surfaces compared to commercially pure (c.p.) titanium in terms of changes to surface topography and photo-functionality. A main question to be answered was whether anatase coatings can still be hydrophilized or even superhydrophilized upon UV-A, and thus would remain functional after therapeutic treatments. Additionally, this study aimed to evaluate which treatments should be preferred and which avoided when dealing with such nanocoatings in a clinical application.
2
Materials and methods
2.1
Preparation of titanium and anatase samples
99.6% titanium foils (Ti000430 titanium foil, Goodfellow, Bad Nauheim, Germany), prepared as discs (1 mm thick, 10 mm diameter, ground to 1200 grit), were coated with a 500 nm TiO 2 anatase layer by reactive pulse magnetron sputtering in bipolar pulse mode with a frequency of 20 kHz. To achieve maximum photocatalytic activity, exclusive growth of the anatase phase was favored against rutile . Pure anatase composition of such thin films has been confirmed in a previous publication through XRD . Uncoated titanium discs served as reference implant material.
2.2
Surface characterization
The morphologies of the untreated control surfaces and those that underwent instrumentation were analyzed qualitatively by scanning electron microscopy (Quanta FEG250, FEI, Eindhoven, Netherlands) with magnifications varying from 300× to 30.000× at high vacuum, an accelerating voltage of 10 kV and Spot 3. Special sample preparation like sputtering or cleaning was not required. The titanium samples were grounded low resistive with a copper strip. For quantitative surface characterization, a mechanical contact profilometer (Perthometer S6P, Perthen Instruments, Mahr, Göttingen, Germany) with a 2-μm diamond stylus was used. For each sample, an area of 3 mm × 8 mm was measured, resulting in 21 profiles with a sampling length of 8 mm. The data obtained was further processed with Mountainsmap 7.0 (Digital Surf, Besançon, France). From the primary profiles, an area of 3 mm × 3 mm in the center of the specimen was selected for further analysis. The mean roughness parameter Ra, calculated complying with ISO 4287, was chosen for the quantitative analysis of surface topographical changes upon wear. To control the functionality of the anatase layer, contact angle measurement was used. Apparent static contact angles of 2 μL drops of ultrapure water (Simplicity 185, Millipore, Schwalbach, Germany) were analysed by means of a high-resolution drop shape analysis system (DSA 10-MK 2, Kruess, Hamburg, Germany) using DSA calculation software (version 1.90.0.11, Kruess).
2.3
UV treatment
Surface activation and hydrophilization was initialized by UV light (>315 nm, peak 382 nm, 25 mW/cm 2 ) applied in a UV-box (UVACube 100, Hoenle, Graefelfing, Germany) for 10 min. Illumination was performed on reference samples which were not included in the instrumentation process as well as on treated samples. Prior to UV irradiation and experimental use the specimens were ultrasonically cleaned by 2-propanol 70% (AppliChem, Darmstadt, Germany) and stored in darkness for 2–4 weeks in closed glass petri-dishes under ambient atmosphere without ventilation to achieve comparable (hydro)carbon contamination and increased water contact angles of around 40° . Then, the therapeutic treatment methods described below were applied to the surfaces and the samples were again stored for two weeks to allow re-hydrophobization. After storing, pre- and post-illumination contact angle measurements were performed to gain information on the direct effect of the different treatment procedures on the respective surface functionality. Last, to study possible differences in the wettability after cleaning, all samples were again ultrasonically cleaned by 2-propanol 70% and stored for further two weeks in darkness before final pre- and post-illumination contact angles were measured.
2.4
Therapeutic treatment procedures
Out of the large number of available methods used for prophylaxis and supra- as well as subgingival anti-inflammatory therapy, the following were selected for testing. Each procedure was applied on three titanium and three anatase-coated titanium specimens, respectively, in the described manner: Spherical shaped red diamond burs with fine grain of 50 μm and yellow diamond burs with extra fine grain size of 30 μm (Omnident, Rodgau Nieder-Roden, Germany) in combination with a red high-speed contra-angle handpiece (KaVo IntraLux, KaVo, Biberach, Germany) were used for 10 s at 40.000 rpm with water cooling. Brownie and Greenie silicone polishers (SHOFU DENTAL GmbH, Ratingen, Germany) as well as a Pro-Cup rubber cup in combination with a fluoride-free prophy paste (Cleanic mint), both Kerr GmbH (Rastatt, Germany), were used in combination with a green contra-angle handpiece (KaVo IntraLux) for 20 s with 5000 rpm and without water cooling. For manual instrumentation, a metal curette No 11/12 and a Columbia H6/H7 plastic curette (both HuFriedy Leimen, Germany) were selected and applied 20 times per specimen. Furthermore, an Air Scaler system (KaVo Sonicflex) with a metal tip (Scaler No 5) and a plastic PEEK tip (Sonicflex Implant) for 20 s with output level 2 was used. Finally, an Air-flow device (KaVo PROPHYflex ® 3) in combination with a sodium bicarbonate powder (ProphyPowder, KaVo) was applied from a distance of 0.5 cm for 20 s.
The pressure exerted during instrumentation was measured with a force sensor (Lorenz Messtechnik GmbH, Altdorf, Germany).
2.5
Statistical analysis
Data were expressed by means and standard deviations (SD). Normal distribution was tested by use of the Shapiro–Wilk-test and non-parametric statistical tests were applied. For the comparison of two groups the Mann–Whitney-U-test was used; for more factors, the Kruskal–Wallis-test was performed. For all tests, p < 0.05 was considered statistically-significant (calculated by JMP 11.2.0, SAS Institute, Cary, NC, USA).
2
Materials and methods
2.1
Preparation of titanium and anatase samples
99.6% titanium foils (Ti000430 titanium foil, Goodfellow, Bad Nauheim, Germany), prepared as discs (1 mm thick, 10 mm diameter, ground to 1200 grit), were coated with a 500 nm TiO 2 anatase layer by reactive pulse magnetron sputtering in bipolar pulse mode with a frequency of 20 kHz. To achieve maximum photocatalytic activity, exclusive growth of the anatase phase was favored against rutile . Pure anatase composition of such thin films has been confirmed in a previous publication through XRD . Uncoated titanium discs served as reference implant material.
2.2
Surface characterization
The morphologies of the untreated control surfaces and those that underwent instrumentation were analyzed qualitatively by scanning electron microscopy (Quanta FEG250, FEI, Eindhoven, Netherlands) with magnifications varying from 300× to 30.000× at high vacuum, an accelerating voltage of 10 kV and Spot 3. Special sample preparation like sputtering or cleaning was not required. The titanium samples were grounded low resistive with a copper strip. For quantitative surface characterization, a mechanical contact profilometer (Perthometer S6P, Perthen Instruments, Mahr, Göttingen, Germany) with a 2-μm diamond stylus was used. For each sample, an area of 3 mm × 8 mm was measured, resulting in 21 profiles with a sampling length of 8 mm. The data obtained was further processed with Mountainsmap 7.0 (Digital Surf, Besançon, France). From the primary profiles, an area of 3 mm × 3 mm in the center of the specimen was selected for further analysis. The mean roughness parameter Ra, calculated complying with ISO 4287, was chosen for the quantitative analysis of surface topographical changes upon wear. To control the functionality of the anatase layer, contact angle measurement was used. Apparent static contact angles of 2 μL drops of ultrapure water (Simplicity 185, Millipore, Schwalbach, Germany) were analysed by means of a high-resolution drop shape analysis system (DSA 10-MK 2, Kruess, Hamburg, Germany) using DSA calculation software (version 1.90.0.11, Kruess).
2.3
UV treatment
Surface activation and hydrophilization was initialized by UV light (>315 nm, peak 382 nm, 25 mW/cm 2 ) applied in a UV-box (UVACube 100, Hoenle, Graefelfing, Germany) for 10 min. Illumination was performed on reference samples which were not included in the instrumentation process as well as on treated samples. Prior to UV irradiation and experimental use the specimens were ultrasonically cleaned by 2-propanol 70% (AppliChem, Darmstadt, Germany) and stored in darkness for 2–4 weeks in closed glass petri-dishes under ambient atmosphere without ventilation to achieve comparable (hydro)carbon contamination and increased water contact angles of around 40° . Then, the therapeutic treatment methods described below were applied to the surfaces and the samples were again stored for two weeks to allow re-hydrophobization. After storing, pre- and post-illumination contact angle measurements were performed to gain information on the direct effect of the different treatment procedures on the respective surface functionality. Last, to study possible differences in the wettability after cleaning, all samples were again ultrasonically cleaned by 2-propanol 70% and stored for further two weeks in darkness before final pre- and post-illumination contact angles were measured.
2.4
Therapeutic treatment procedures
Out of the large number of available methods used for prophylaxis and supra- as well as subgingival anti-inflammatory therapy, the following were selected for testing. Each procedure was applied on three titanium and three anatase-coated titanium specimens, respectively, in the described manner: Spherical shaped red diamond burs with fine grain of 50 μm and yellow diamond burs with extra fine grain size of 30 μm (Omnident, Rodgau Nieder-Roden, Germany) in combination with a red high-speed contra-angle handpiece (KaVo IntraLux, KaVo, Biberach, Germany) were used for 10 s at 40.000 rpm with water cooling. Brownie and Greenie silicone polishers (SHOFU DENTAL GmbH, Ratingen, Germany) as well as a Pro-Cup rubber cup in combination with a fluoride-free prophy paste (Cleanic mint), both Kerr GmbH (Rastatt, Germany), were used in combination with a green contra-angle handpiece (KaVo IntraLux) for 20 s with 5000 rpm and without water cooling. For manual instrumentation, a metal curette No 11/12 and a Columbia H6/H7 plastic curette (both HuFriedy Leimen, Germany) were selected and applied 20 times per specimen. Furthermore, an Air Scaler system (KaVo Sonicflex) with a metal tip (Scaler No 5) and a plastic PEEK tip (Sonicflex Implant) for 20 s with output level 2 was used. Finally, an Air-flow device (KaVo PROPHYflex ® 3) in combination with a sodium bicarbonate powder (ProphyPowder, KaVo) was applied from a distance of 0.5 cm for 20 s.
The pressure exerted during instrumentation was measured with a force sensor (Lorenz Messtechnik GmbH, Altdorf, Germany).
2.5
Statistical analysis
Data were expressed by means and standard deviations (SD). Normal distribution was tested by use of the Shapiro–Wilk-test and non-parametric statistical tests were applied. For the comparison of two groups the Mann–Whitney-U-test was used; for more factors, the Kruskal–Wallis-test was performed. For all tests, p < 0.05 was considered statistically-significant (calculated by JMP 11.2.0, SAS Institute, Cary, NC, USA).
3
Results
3.1
Surface morphology
Fig. 1 a shows the magnetron sputtered polycrystalline anatase film on the c.p. titanium substrate. The evaluation of the SEM pictures showed that the diamond burs completely removed the anatase coatings, reaching the titanium substrate in depth. The traces of this instrumentation can be visualized already at very low magnifications ( Fig. 1 b). Although the margins of the treated area appeared slightly distorted, no shearing of the anatase-coating could be detected ( Fig. 1 b, c). The resulting surface damage was comparable to that on the titanium specimens. Use of the metal curette also caused anatase removal and disclosure of the underlying titanium substrate. The metal curette caused a rectangular, sharp etched fracture pattern. However, some areas, mostly located between the traces of two strokes, were still intact, with an overall sharp and straight transitional zone and no signs of shearing ( Fig. 1 d, e). Treatment with the sonic scaler with metal tip also caused significant damage to the anatase surface. While the titanium substrate was not visible in the treated areas, the surface appeared compressed and glossed with an extensive loss of anatase and displacements at the edges ( Fig. 1 f). Again, no indications of shearing could be detected. Polishing with the Brownie silicone polisher led to a surface largely comparable to that of the polished pure titanium, with anatase residues visible only in some areas ( Fig. 1 g). Use of the Greenie, on the other hand, also resulted in a smoothened surface but did not reach the bottom of most substrate surface irregularities, thus leaving more anatase intact ( Fig. 1 h). The treatment with a plastic curette ( Fig. 1 i, j) and an air scaler with a plastic tip ( Fig. 1 k, l) did not inflict any visible damage on both anatase and titanium surfaces; in some areas, deposition of additional material was visible. An intact anatase surface was also found in the specimens treated with air powder abrasive and the rubber cup, although minor deposits of debris were noted ( Fig. 1 m, n).
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