Biomechanical and Histomorphometrical Evaluation of TiZr Alloy Implants: An in vivo Study in the Rabbit Ryo Jimbo, DDS, PhD;* Yoshihito Naito, DDS, PhD;† Silvia Galli, DDS;‡ Simon Berner, MS, PhD;§ Michel Dard, DDS, PhD;¶,§ Ann Wennerberg, LDS, PhD**
ABSTRACT Background: Clinically, there is a demand for mechanically stronger alloyed implants; however, not much evidence exists with regard to these materials. Purpose: To test the osseointegration property of TiZr1317 implants in a rabbit model. Materials and Methods: Hydrophilic titanium–zirconium alloy (TiZr1317) implants with sand-blasted and acid-etched surface (test) and hydrophilic cpTi implants with the same treatment (control) were placed pairwise in the hind limbs (two in each tibia and one in each femur) of 36 Swedish lop-eared rabbits. After 2, 4, and 12 weeks (n = 12/time point), the bone samples were subjected to removal torque (RTQ, proximal tibia and femur) and histologic/histomorphometric (distal tibia) testings. Results: The control presented significantly higher RTQ than the test at 2 weeks (55 vs 36 Ncm). No differences were observed for other time points. The test presented higher mean BIC than the control (19.25 vs 13.89 %) at 4 weeks; however, there were no statistical differences for the following time point tested in vivo.The new bone area was significantly higher for the test at 4 weeks in the marrow areas. Conclusion: The TiZr1317 implants presented comparable biologic outcomes to that of the cpTi implants through a 12-week evaluation period. KEY WORDS: animal study, bone-implant interface, histological analysis
INTRODUCTION
survival and success rates after more than 5 years in function.1,2 Historically, the commercially pure titanium (c.p. Ti, Grade 1–4) has been used as an implant material and, to this date, dominates the market. One of the major reasons for selection of titanium as an implant material owes to its biocompatibility. Titanium is suggested to be a biocompatible material since the outermost layer is spontaneously oxidized in air.3 Additionally to the biocompatibility aspect, the titanium has been clinically successful due to its excellent mechanical properties. It can be said in general that the mechanical properties of the titanium is enough to withstand repetitive occlusal forces. However, in cases such as patients with a limited alveolar ridges or limited space such as the anterior region of the mandible, narrow-diameter implants are regarded as one clinical alternative. However, some questions remain as to whether the narrowed titanium implant can withstand
Oral implant treatment has in the full or partial edentulous jaws proven to be a predictable concept, with high *Associate professor, Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden; †assistant professor, Department of Oral and Maxillofacial Prosthodontics and Oral Implantology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan; ‡doctoral candidate, Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden; §senior researcher, Institut Straumann AG, Basel, Switzerland; ¶adjunct professor, Department of Periodontics, New York University College of Dentistry, New York, NY, USA; **professor and chair, Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden Corresponding Author: Prof. Ryo Jimbo, Department of Prosthodontics, Faculty of Odontology, Malmö University, 205 06 Malmö, Sweden; e-mail: [email protected] © 2015 Wiley Periodicals, Inc. DOI 10.1111/cid.12305
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Osseointegration Property of TiZr Alloy Implants
functional forces as the diameter directly influences the fatigue strength.4,5 One common approach to overcome these problems is strengthening the mechanical properties of the titanium by alloying it with other metals, and this strategy has indeed increased the elastic modulus or fatigue strength by adjusting the optimized ratio of various metals.6–9 In implant dentistry, the titanium 6-aluminium 4-vanadium (Ti6Al4V) alloy has commonly been used as an alternative that could be utilized as an implant bulk material. To date, some portion of the commercially available implants are available in this form of alloy; however, the Ti6Al4V has been regarded as a difficult material to roughen probably because of its hardness and etching procedures not being suitable for Ti6Al4V. This has been described by Wennerberg and Albrektsson that some of the commercially available Ti6Al4V surface possesses a surface roughness below the recommended surface roughness.10 Furthermore, the biocompatibility of the Ti6Al4V material used for dental implants has not come to a general consensus in in vivo studies11,12; however, it must be stressed that these implants actually have some clinical reports affirming their acceptable prognosis.13,14 In such a background, a new implant produced with titanium–zirconium alloy (TiZr1317, 83–87% titanium, 13–17% zirconium, Roxolid®, Institut Straumann AG, Basel, Switzerland) has been introduced in the market. Mechanical tests of it have shown higher tensile, fatigue strength, and loading stress compared with pure titanium implants and the biological outcomes not presenting negative responses.15–17 More interestingly, Bernhard and colleagues has reported that the TiZr1317 alloy has a monophasic α-structure like titanium, and furthermore, the TiZr1317 allows to perform surface modification using the conventional sand-blasting and acid-etching procedures, which results in topography similar to that of the surface modified c.p. Ti.18 Thus, it was of great interest to understand whether the microtextured TiZr1317 implant surface would present similar osseointegration properties as compared with the c.p. Ti surface with the same surface treatment procedure, which has been reported to present enhanced bone apposition to the implant.19,20 The aim of this study was to test the null hypothesis that microtextured TiZr1317 implants compared with its counterpart, the micro-textured c.p. Ti implants (grade 4), would present comparable bone tissue response by means of biomechanical (removal torque [RTQ]) and
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histomorphometric measurements after 2, 4, and 12 weeks of healing in a rabbit hind leg model in vivo. MATERIALS AND METHODS Implants One hundred eleven Roxolid SLActive® implants (test group, Institut Straumann AG, 3.3 mm in diameter, 8 mm long) consisting from 13% to 17% zirconium (TiZr1317) and 111 control implants with a hydrophilic sand-blasted and acid-etched surface (control group, Institut Straumann AG, 3.3 mm in diameter, 8 mm long, Ti SLActive®, Institut Straumann AG) were used in the study for topographical characterization, RTQ testing, and histologic/histomorphometric testing. The number of implants assigned to each evaluation will be stated in the following sections. Topographic Analysis In order to evaluate the surface topography of the two implant groups, an optical interferometer (MicroXam, ADE Phase Shift Technology, Inc., Tucson, AZ, USA) was utilized. Three implants from each type were randomly selected, dried with gentle airflow, and measured on three thread tops, three thread valleys, and three flanks. The measuring area was 260 × 200 μm2, and prior to the parameter calculation, a Gaussian filter (filter size of 50 × 50 μm2) was applied. The following three different parameters suggested by Wennerberg and Albrektsson21 that would describe most efficiently the surface topography of the implant were selected: Sa = average height deviation from a mean plane, measured in micrometers and represents a pure height descriptive parameter. Sds = density of summits, measured in number of peaks per square micrometers and represents a pure spatial parameter. Sdr = developed surface area, measured in % enlargement compared with a totally plane reference area (equal to the measured area). Three-dimensionally reconstructed images of the surfaces were obtained with the Mountain Map software (Digital Surf, Besançon, France) and were used for qualitative evaluation. Chemical Characterization The chemical composition of the sample surface (outermost 5–10 nm) was determined by x-ray
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photoelectron spectroscopy (XPS). The XPS spectra were acquired on a PHI5000 VersaProbe spectrometer (ULVAC-PHI, INC., Chigasaki, Japan) equipped with a focused scanning monochromatic Al-K_ source (1486.6 eV). The photoelectrons were detected at an angle of 45° to the surface normal. The measurements were performed with a spot size of 200 μm. Three implants from the same batch used in the animal surgery were measured for each material. The implants were removed from the container, rinsed under running, ultrapure water, and blown dry in a stream of nitrogen prior to the measurements. Animals and Surgical Procedures Thirty-six Swedish lop-eared rabbits of mixed sexes (mean body weight, 3.5 kg) were used in this study. The study was approved by the Lund University animal ethics committee. Preoperatively, the surgical sites (i.e., both the tibia and the femur) were shaved and disinfected with 70% ethanol and 70% chlorhexidine. The animals were anesthetized by a mixed intramuscular injection consisting of 0.15 mL/kg medetomidine (1 mg/mL Dormitor, Orion Pharma, Sollentuna, Sweden) and 0.35 mL/kg ketamine hydrochloride (50 mg/mL Ketalar, Pfizer AB, Sollentuna, Sweden). Lidocaine hydrochloride (Xylocaine, AstraZeneca AB, Södertälje, Sweden) was injected for local anaesthetic purposes. Thereafter, two implants in the tibia (proximal and distal) and one implant in the femur were placed on both hind legs (total six implants per rabbit). The implants (control, Ti SLActive; test, Roxolid SLActive) were always placed in a pairwise manner (left to right). However, the side they were placed (left or right) were randomized. After cover screw connection, the surgical sites were sutured layer-by-layer using a bioresorbable suture (4-0 Vicryl, Ethicon, Auneau, France). After 2, 4, and 12 weeks of healing, the rabbits were euthanized (n = 12 per time point) with an overdose of sodium pentobarbital (60 mg/mL Apoteksbolaget AB, Stockholm, Sweden), and the bone samples were removed en bloc. RTQ Test After a thorough soft tissue removal of the bone implant samples, the cover screws were removed, and the implants placed in the femur and the proximal tibia were subjected to RTQ testing with an electrically con-
trolled RTQ unit.12 In brief, the peak (maximum) RTQ was recorded in which the values were transmitted at a frequency of 100 Hz to a computer. Histological and Histomorphometrical Evaluation The distally placed implants were subjected to histologic/histomorphometric tests. The dissected bone-implant blocks were placed in 4% formaldehyde for 24 h. After fixation, and trimming, all samples were subjected to dehydration in a series of ethanol (70– 100%) and infiltration in resin (30–100%), which was performed under constant vacuuming and thereafter were embedded in light curing-resin (Technovit 7200 VLC, Heraeus Kulzer, Wehrheim, Germany). The embedded resin blocks were subjected to nondecalcified cut and grind sectioning. In brief, a central section of each sample was prepared using the EXAKT™ cutting and grinding equipment (EXAKT, Norderstedt, Germany) to a final thickness of approximately 20 μm. After polishing, the sections were finally stained with a mixed solution of toluidine blue and pyronin G. The histological observation were performed using a light microscope (Eclipse ME600, Nikon, Sendai, Japan), and the histomorphometrical data were analyzed with image analysis software (ImageJ v. 1.43u, National Institute of Health, Bethesda, MD); the outcomes were calculated in an excel software (Microsoft Co, Redmond, WA) as follows: 1) Bone-to-implant contact (BIC): Percentage was calculated by measuring distance of the bone in direct contact to the implant surface and was divided by the entire length of the implant placed in the bone. The percentage of bone length in contact with the surfaces in the cortical and marrow regions was also calculated. 2) New bone area (NBA): Percentage was calculated by measuring the area inside a thread occupied by newly formed bone, which is deeply stained, whereas the mother bone or the so-called existing cortical or trabecular bone is stained light blue, both in the cortical and marrow area, and was divided by the entire area of the thread. Statistical Power and Analysis The number of animals per time point was considered in relation to the size of the sample in the study and to
Osseointegration Property of TiZr Alloy Implants
TABLE 1 Mean Values for Sa, Sdr, and Sds (SD) for Topographical Analyses of Implants with Interferometer
SLActive Roxolid p Value*
Sa μm
Sds 1/μm2
Sdr %
1.45 (0.2) 1.53 (0.2) .1
0.07 (0.005) 0.06 (0.008) .002
75.73 (10.23) 52.56 (11.00) .003
*p Values for Sa and Sdr were obtained with independent samples t-test for mean comparison; p value for Sds was obtained with independent samples Mann–Whitney test.
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regarding the density of summits in square micrometers (Sds) and the developed surface ratio in % (Sdr), as presented in Table 1. No significant differences were confirmed for the average height deviation in micrometers (Sa) (p > .05). The descriptive images for both surfaces are presented in Figure 1. The investigation of samples by interferometer showed no qualitative differences in the morphology of the surface between both implants. XPS
the effect size. Prior to the animal study, a power analysis was conducted, and the statistical power between 60% and 80% was achieved for all evaluations. The number 12 rabbits were therefore decided based on this power analysis and also based on the ethical considerations included in the approved ethical application to minimize the number of animals as much as possible. For the interferometer measurements, independent samples Student t-test was used to compare the mean values of Sa and Sdr of the control and test groups, while independent samples Mann–Whitney test was used to compare the mean values of Sds between the two groups. The RTQ and histomorphometrical outcomes of test and control samples were compared using Wilcoxon Signed Rank for paired samples. For all tests, a significance threshold of 0.05 was used, and SPSS (IBM, Armonk, NY, USA) software was used for the analyses.
The chemical composition of the Ti and Roxolid (RXD) SLActive implants as determined by XPS is shown in Table 2. The two types of implants presented similar surface chemistry except for the Zr that was detected only for the test implants. Low levels of carbon contamination of about 10% were detected for both implants.
RESULTS
The histological observation showed that the bone around the implant presented normal healing at all time points observed, and no qualitative differences could be observed between the control and test groups (Figure 3). In brief, at 2 weeks, the cortical mother bone was in close
Topographical Analyses Topographical analyses of the implants with the interferometer showed a statistically significant difference
RTQ Test The only statistical significance seen was for the femur after a healing period of 2 weeks, where control implants (RTQ = 55 Ncm) presented significantly higher RTQ than test implants (36 Ncm, p = .012, Figure 2A). For the other groups, the mean values were higher for the control implants; however, there were no statistical differences (Figure 2, A and B). Histologic and Histomorphometrical Evaluation
Figure 1 Descriptive three-dimensional images (A) SLActive (B) Roxolid from the interferometer measurements (scan area: 260 × 200 μm).
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TABLE 2 Apparent Normalized Atomic Concentration (%) of the Elements Detected by XPS Implants
Ti SLActive-1 Ti SLActive-2 Ti SLActive-3 RXD SLActive-1 RXD SLActive-2 RXD SLActive-3
Ti (%)
Zr (%)
O (%)
N (%)
C (%)
Na (%)
Al (%)
23.9 24.2 24.7 22.0 21.6 22.2
0.0 0.0 0.0 3.6 3.7 3.7
60.1 59.5 60.4 60.3 59.0 60.3
1.4 1.3 1.4 0.6 1.0 0.5
11.7 11.8 10.5 10.0 11.7 10.0
0.0 0.2 0.2 0.0 0.0 0.0
3.1 2.9 2.6 3.5 3.0 3.3
contact with the implant surface, whereas woven bone formation could already be observed in the marrow regions. At 4 weeks, the newly formed bone in the marrow region had further matured and the bone had formed along the implant surface, and the maturation continued even at 12 weeks of healing. The cortical bone seemed to have undergone a bone resorption and apposition process, where some of the bone that was in close contact to the implant had resorbed, and thereafter, the newly formed bone filled the resorbed space (Figure 3). No statistical differences in the BIC in the cortical area were observed throughout the observation periods (Figure 4A), whereas in the bone marrow area, the test group had higher mean BIC than the control group (19.25% and 13.89%, respectively, p = .05225); however, there were no statistical differences between the groups throughout the observation period in vivo (Figure 4B). The NBA was significantly higher for the test group at 4 weeks in the marrow areas (p = .02686, Figure 5). No statistical differences could be observed for all other
time points despite the higher mean values for the test group (Figure 5). DISCUSSION The aim of this study was to test the null hypothesis that Roxolid SLActive (test) and Ti SLActive (control) implants would present comparable bone tissue response after 2, 4, and 12 weeks healing in the tibia/femur of rabbits. The results from RTQ and BIC indicated that both implants successfully osseointegrated; however, the healing kinetics was different for the two implants as previously suggested.22 The results confirm the outcomes of the previously conducted studies testing the two different implants23,24; however, the information obtained here was of interest since three different time points (initial phase, midphase, and bone remodeling phase) were chosen and tested so that the bone healing properties of the two different implant groups could be illustrated. In brief, the mean RTQ values were higher (although no significant difference) for the control implants especially in the femur; however, at later stages, these differences in mean values diminished for both
Figure 2 Results from the removal torque tests at different time points (A) in the femur, and (B) in the tibia.
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Figure 3 Histological micrographs of the bone tissue formed around the control and test implants after 2, 4, and 12 weeks of healing in vivo both in the cortical and marrow regions.
bone types. In the histomorphometrical evaluation, there was a difference in healing process especially evident in the marrow areas at 4 weeks with the test group presenting higher osseointegration; however, the differences between the two groups diminished after 12 weeks.
Since the implants placed in the current study received no forms of vertical dynamic loading, and both implants were treated in a similar manner after manufacturing (i.e., stored in 0.9% NaCl),25 it is speculated that one of the major reasons for the obtained
Figure 4 Graph presenting the bone-to-implant contact (BIC) at 2, 4, and 12 weeks for both control and test groups in the (A) cortical and (B) in the marrow regions.
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Figure 5 Graph presenting the new bone area (NBA) at 2, 4, and 12 weeks for both control and test groups in the (A) cortical and (B) in the marrow regions. Asterisk represents a statistical significance.
results are an outcome of the differences in surface topography. In detail, the statistically significant difference in Sds (number of summits in μm: 2) and Sdr (the developed surface ratio in %) was confirmed with the control implants possessing overall a rougher surface topography than the test implants. It has been suggested that the optimal Sa value to obtain good bone response is between 1.0 and 2.0 μm, which is the so-called moderately roughened implant surface.20 Although the surface roughening procedure applied for the commercially pure Ti can also be applied for the TiZr1317, it is a general consensus that no surfaces can be identical if the base substrate is different. As expected, the XPS detected that there exists a difference in the outermost surface, which was the Zr composition for the TiZr alloy surface. To date, there is a lack of evidence with regard to the effect of Zr existence as compared with the Ti only; however, literature both in vitro and in vivo suggests that both materials and related alloys are biocompatible.26,27 However, as suggested by Yamano and colleagues, the differences in chemical elements have the possibility to induce distinct cellular responses, and this could be one of the reasons why a different osseointegration pathway was observed, although this had no significant effect on the outcomes.28 Overall, it can be suggested that despite the fact that some of the surface topographical parameters presented significant differences, and the chemistry may have added some differences in the healing cascade, the differences may not be clinically relevant as both implants can be classified as moderately roughened implants with comparable surface morphology and with proven biocompatibility. Therefore, the
results of the biomechanical, histomorphometrical, and surface topographical characterization suggest that comparable biologic outcomes can be expected for the TiZr1317 implants to the conventional c.p. Ti implants and is in accordance to previous investigations.15,29 This may be of great clinical interest as the improved mechanical property of the implant may expand the clinical application range of the implant treatment even in sites with thin alveolar ridges or in lower anterior defects. Although long-term clinical reports do not exist to date, several studies suggest that the clinical outcomes after prosthetic connection are promising,30–32 and the smaller diameter, but stronger mechanical characteristic, of the implant seems to benefit especially in the interforaminal region.31,33 Although it is suggested that both Ti and TiZr alloy small diameter implants function comparably in clinical situations in terms of marginal bone stability and peri-implant tissue status,31 it is of note to understand that the peri-implant bone strain under lateral loading significantly decreases for the TiZr implants.34 Thus, further studies are necessary to validate the long-term effect of the binary TiZr1317 alloy; however, the implant is suggested to function as comparable with the standard c.p. Ti implants. CONCLUSION The TiZr1317 alloy implants presented comparable biomechanical and histological outcomes to that of the c.p. Ti implants through a 12-week evaluation period in rabbit bone; thus, the initial hypothesis was accepted.
Osseointegration Property of TiZr Alloy Implants
ACKNOWLEDGEMENTS This study was fully funded by Institut Straumann AG, Basel, Switzerland. The authors acknowledge Marcel Obrecht for the technical and administrative assistance throughout the study. REFERENCES 1. Mertens C, Steveling HG. Early and immediate loading of titanium implants with fluoride-modified surfaces: results of 5-year prospective study. Clin Oral Implants Res 2011; 22:1354–1360. 2. Adell R, Eriksson B, Lekholm U, Branemark PI, Jemt T. Long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxillofac Implants 1990; 5:347–359. 3. Sawase T, Jimbo R, Wennerberg A, Suketa N, Tanaka Y, Atsuta M. A novel characteristic of porous titanium oxide implants. Clin Oral Implants Res 2007; 18:680–685. 4. Veltri M, Ferrari M, Balleri P. One-year outcome of narrow diameter blasted implants for rehabilitation of maxillas with knife-edge resorption. Clin Oral Implants Res 2008; 19:1069–1073. 5. Allum SR, Tomlinson RA, Joshi R. The impact of loads on standard diameter, small diameter and mini implants: a comparative laboratory study. Clin Oral Implants Res 2008; 19:553–559. 6. Taddei EB, Henriques VAR, Silva CRM, Cairo CAA. Production of new titanium alloy for orthopedic implants. Mater Sci Eng C 2004; 24:683–687. 7. Davidson JA, Mishra AK, Kovacs P, Poggie RA. New surfacehardened, low-modulus, corrosion-resistant Ti-13Nb-13Zr alloy for total HIP arthroplasty. Biomed Mater Eng 1994; 4:231–243. 8. Semlitsch M, Weber H, Streicher R, Schon R. Joint replacement components made of hot-forged and surface-treated Ti-6Al-7Nb alloy. Biomaterials 1992; 13:781–788. 9. Li SJ, Yang R, Niinomi M, Hao YL, Cui YY. Formation and growth of calcium phosphate on the surface of oxidized Ti-29Nb-13Ta-4.6Zr alloy. Biomaterials 2004; 25:2525– 2532. 10. Wennerberg A, Albrektsson T. On implant surfaces: a review of current knowledge and opinions. Int J Oral Maxillofac Implants 2010; 25:63–74. 11. Stenport VF, Johansson CB. Evaluations of bone tissue integration to pure and alloyed titanium implants. Clin Implant Dent Relat Res 2008; 10:191–199. 12. Johansson CB, Jimbo R, Stefenson P. Ex vivo and in vivo biomechanical test of implant attachment to various materials: introduction of a new user-friendly removal torque equipment. Clin Implant Dent Relat Res 2012; 14:603– 611.
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13. Teixeira ER, Wadamoto M, Akagawa Y, Kimoto T. Clinical application of short hydroxylapatite-coated dental implants to the posterior mandible: a five-year survival study. J Prosthet Dent 1997; 78:166–171. 14. Östman P-O, Wennerberg A, Albrektsson T. Immediate occlusal loading of NanoTite™ PREVAIL® implants: a prospective 1-year clinical and radiographic study. Clin Implant Dent Relat Res 2010; 12:39–47. 15. Gottlow J, Dard M, Kjellson F, Obrecht M, Sennerby L. Evaluation of a new titanium-zirconium dental implant: a biomechanical and histological comparative study in the mini pig. Clin Implant Dent Relat Res 2012; 14:538–545. 16. Thoma DS, Jones AA, Dard M, Grize L, Obrecht M, Cochran DL. Tissue integration of a new titaniumzirconium dental implant: a comparative histologic and radiographic study in the canine. J Periodontol 2011; 82:1453–1461. 17. Grandin HM, Berner S, Dard M. A review of titanium zirconium (TiZr) alloys for use in endosseous dental implants. Materials 2012; 5:1348–1360. 18. Bernhard N, Berner S, De Wild M, Wieland M. The binary TiZr Alloy – a newly developed Ti alloy for use in dental implants. Forum Implantol 2009; 5:30–39. 19. Wennerberg A, Jimbo R, Stubinger S, Obrecht M, Dard M, Berner S. Nanostructures and hydrophilicity influence osseointegration: a biomechanical study in the rabbit tibia. Clin Oral Implants Res 2013; 25:1041–1050. 20. Buser D, Broggini N, Wieland M, et al. Enhanced bone apposition to a chemically modified SLA titanium surface. J Dent Res 2004; 83:529–533. 21. Wennerberg A, Albrektsson T. Effects of titanium surface topography on bone integration: a systematic review. Clin Oral Implants Res 2009; 20:172–184. 22. Wen B, Zhu F, Li Z, Zhang P, Lin X, Dard M. The osseointegration behavior of titanium-zirconium implants in ovariectomized rabbits. Clin Oral Implants Res 2014; 25:819–825. 23. Saulacic N, Bosshardt DD, Bornstein MM, Berner S, Buser D. Bone apposition to a titanium-zirconium alloy implant, as compared to two other titanium-containing implants. Eur Cell Mater 2012; 23:273–286, discussion 286– 278. 24. Kämmerer PW, Palarie V, Schiegnitz E, Hagmann S, Alshihri A, Al-Nawas B. Vertical osteoconductivity and early bone formation of titanium-zirconium and titanium implants in a subperiosteal rabbit animal model. Clin Oral Implants Res 2014; 25:774–780. 25. Wennerberg A, Svanborg LM, Berner S, Andersson M. Spontaneously formed nanostructures on titanium surfaces. Clin Oral Implants Res 2013; 24:203–209. 26. Welander M, Abrahamsson I, Berglundh T. The mucosal barrier at implant abutments of different materials. Clin Oral Implants Res 2008; 19:635–641.
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27. Correa DRN, Vicente FB, Donato TAG, Arana-Chavez VE, Buzalaf MAR, Grandini CR. The effect of the solute on the structure, selected mechanical properties, and biocompatibility of Ti-Zr system alloys for dental applications. Mater Sci Eng C 2014; 34:354–359. 28. Yamano S, Ma AK, Shanti RM, Kim SW, Wada K, Sukotjo C. The influence of different implant materials on human gingival fibroblast morphology, proliferation, and gene expression. Int J Oral Maxillofac Implants 2011; 26:1247–1255. 29. Anchieta RB, Baldassarri M, Guastaldi F, et al. Mechanical property assessment of bone healing around a titaniumzirconium alloy dental implant. Clin Implant Dent Relat Res 2013; 2014 Dec; 16(6):913–919. doi: 10.1111/cid.12061. Epub 2013 Mar 25. 30. Al-Nawas B, Domagala P, Fragola G, et al. A prospective non-interventional study to evaluate survival and success of reduced diameter implants made from titaniumzirconium alloy. J Oral Implantol 2014 Mar 25. [Epub ahead of print].
31. Quirynen M, Al-Nawas B, Meijer HJA, et al. Small-diameter titanium Grade IV and titanium-zirconium implants in edentulous mandibles: three-year results from a doubleblind, randomized controlled trial. Clin Oral Implants Res 2014 Apr 9. doi: 10.1111/clr.12367. [Epub ahead of print]. 32. Chiapasco M, Casentini P, Zaniboni M, Corsi E, Anello T. Titanium-zirconium alloy narrow-diameter implants (Straumann Roxolid®) for the rehabilitation of horizontally deficient edentulous ridges: prospective study on 18 consecutive patients. Clin Oral Implants Res 2012; 23:1136– 1141. 33. Al-Nawas B, Brägger U, Meijer HJA, et al. Double-blind randomized controlled trial (RCT) of titanium-13Zirconium versus titanium grade IV small-diameter bone level implants in edentulous mandibles – results from a 1-year observation period. Clin Implant Dent Relat Res 2012; 14:896–904. 34. Wu AY-J, Hsu J-T, Huang H-L. An in vitro biomechanical evaluation of a new commercial titanium-zirconium alloy dental implant. Implant Dent 2014; 23:534–538.
ABSTRACT Background: Clinically, there is a demand for mechanically stronger alloyed implants; however, not much evidence exists with regard to these materials. Purpose: To test the osseointegration property of TiZr1317 implants in a rabbit model. Materials and Methods: Hydrophilic titanium–zirconium alloy (TiZr1317) implants with sand-blasted and acid-etched surface (test) and hydrophilic cpTi implants with the same treatment (control) were placed pairwise in the hind limbs (two in each tibia and one in each femur) of 36 Swedish lop-eared rabbits. After 2, 4, and 12 weeks (n = 12/time point), the bone samples were subjected to removal torque (RTQ, proximal tibia and femur) and histologic/histomorphometric (distal tibia) testings. Results: The control presented significantly higher RTQ than the test at 2 weeks (55 vs 36 Ncm). No differences were observed for other time points. The test presented higher mean BIC than the control (19.25 vs 13.89 %) at 4 weeks; however, there were no statistical differences for the following time point tested in vivo.The new bone area was significantly higher for the test at 4 weeks in the marrow areas. Conclusion: The TiZr1317 implants presented comparable biologic outcomes to that of the cpTi implants through a 12-week evaluation period. KEY WORDS: animal study, bone-implant interface, histological analysis
INTRODUCTION
survival and success rates after more than 5 years in function.1,2 Historically, the commercially pure titanium (c.p. Ti, Grade 1–4) has been used as an implant material and, to this date, dominates the market. One of the major reasons for selection of titanium as an implant material owes to its biocompatibility. Titanium is suggested to be a biocompatible material since the outermost layer is spontaneously oxidized in air.3 Additionally to the biocompatibility aspect, the titanium has been clinically successful due to its excellent mechanical properties. It can be said in general that the mechanical properties of the titanium is enough to withstand repetitive occlusal forces. However, in cases such as patients with a limited alveolar ridges or limited space such as the anterior region of the mandible, narrow-diameter implants are regarded as one clinical alternative. However, some questions remain as to whether the narrowed titanium implant can withstand
Oral implant treatment has in the full or partial edentulous jaws proven to be a predictable concept, with high *Associate professor, Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden; †assistant professor, Department of Oral and Maxillofacial Prosthodontics and Oral Implantology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan; ‡doctoral candidate, Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden; §senior researcher, Institut Straumann AG, Basel, Switzerland; ¶adjunct professor, Department of Periodontics, New York University College of Dentistry, New York, NY, USA; **professor and chair, Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden Corresponding Author: Prof. Ryo Jimbo, Department of Prosthodontics, Faculty of Odontology, Malmö University, 205 06 Malmö, Sweden; e-mail: [email protected] © 2015 Wiley Periodicals, Inc. DOI 10.1111/cid.12305
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functional forces as the diameter directly influences the fatigue strength.4,5 One common approach to overcome these problems is strengthening the mechanical properties of the titanium by alloying it with other metals, and this strategy has indeed increased the elastic modulus or fatigue strength by adjusting the optimized ratio of various metals.6–9 In implant dentistry, the titanium 6-aluminium 4-vanadium (Ti6Al4V) alloy has commonly been used as an alternative that could be utilized as an implant bulk material. To date, some portion of the commercially available implants are available in this form of alloy; however, the Ti6Al4V has been regarded as a difficult material to roughen probably because of its hardness and etching procedures not being suitable for Ti6Al4V. This has been described by Wennerberg and Albrektsson that some of the commercially available Ti6Al4V surface possesses a surface roughness below the recommended surface roughness.10 Furthermore, the biocompatibility of the Ti6Al4V material used for dental implants has not come to a general consensus in in vivo studies11,12; however, it must be stressed that these implants actually have some clinical reports affirming their acceptable prognosis.13,14 In such a background, a new implant produced with titanium–zirconium alloy (TiZr1317, 83–87% titanium, 13–17% zirconium, Roxolid®, Institut Straumann AG, Basel, Switzerland) has been introduced in the market. Mechanical tests of it have shown higher tensile, fatigue strength, and loading stress compared with pure titanium implants and the biological outcomes not presenting negative responses.15–17 More interestingly, Bernhard and colleagues has reported that the TiZr1317 alloy has a monophasic α-structure like titanium, and furthermore, the TiZr1317 allows to perform surface modification using the conventional sand-blasting and acid-etching procedures, which results in topography similar to that of the surface modified c.p. Ti.18 Thus, it was of great interest to understand whether the microtextured TiZr1317 implant surface would present similar osseointegration properties as compared with the c.p. Ti surface with the same surface treatment procedure, which has been reported to present enhanced bone apposition to the implant.19,20 The aim of this study was to test the null hypothesis that microtextured TiZr1317 implants compared with its counterpart, the micro-textured c.p. Ti implants (grade 4), would present comparable bone tissue response by means of biomechanical (removal torque [RTQ]) and
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histomorphometric measurements after 2, 4, and 12 weeks of healing in a rabbit hind leg model in vivo. MATERIALS AND METHODS Implants One hundred eleven Roxolid SLActive® implants (test group, Institut Straumann AG, 3.3 mm in diameter, 8 mm long) consisting from 13% to 17% zirconium (TiZr1317) and 111 control implants with a hydrophilic sand-blasted and acid-etched surface (control group, Institut Straumann AG, 3.3 mm in diameter, 8 mm long, Ti SLActive®, Institut Straumann AG) were used in the study for topographical characterization, RTQ testing, and histologic/histomorphometric testing. The number of implants assigned to each evaluation will be stated in the following sections. Topographic Analysis In order to evaluate the surface topography of the two implant groups, an optical interferometer (MicroXam, ADE Phase Shift Technology, Inc., Tucson, AZ, USA) was utilized. Three implants from each type were randomly selected, dried with gentle airflow, and measured on three thread tops, three thread valleys, and three flanks. The measuring area was 260 × 200 μm2, and prior to the parameter calculation, a Gaussian filter (filter size of 50 × 50 μm2) was applied. The following three different parameters suggested by Wennerberg and Albrektsson21 that would describe most efficiently the surface topography of the implant were selected: Sa = average height deviation from a mean plane, measured in micrometers and represents a pure height descriptive parameter. Sds = density of summits, measured in number of peaks per square micrometers and represents a pure spatial parameter. Sdr = developed surface area, measured in % enlargement compared with a totally plane reference area (equal to the measured area). Three-dimensionally reconstructed images of the surfaces were obtained with the Mountain Map software (Digital Surf, Besançon, France) and were used for qualitative evaluation. Chemical Characterization The chemical composition of the sample surface (outermost 5–10 nm) was determined by x-ray
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photoelectron spectroscopy (XPS). The XPS spectra were acquired on a PHI5000 VersaProbe spectrometer (ULVAC-PHI, INC., Chigasaki, Japan) equipped with a focused scanning monochromatic Al-K_ source (1486.6 eV). The photoelectrons were detected at an angle of 45° to the surface normal. The measurements were performed with a spot size of 200 μm. Three implants from the same batch used in the animal surgery were measured for each material. The implants were removed from the container, rinsed under running, ultrapure water, and blown dry in a stream of nitrogen prior to the measurements. Animals and Surgical Procedures Thirty-six Swedish lop-eared rabbits of mixed sexes (mean body weight, 3.5 kg) were used in this study. The study was approved by the Lund University animal ethics committee. Preoperatively, the surgical sites (i.e., both the tibia and the femur) were shaved and disinfected with 70% ethanol and 70% chlorhexidine. The animals were anesthetized by a mixed intramuscular injection consisting of 0.15 mL/kg medetomidine (1 mg/mL Dormitor, Orion Pharma, Sollentuna, Sweden) and 0.35 mL/kg ketamine hydrochloride (50 mg/mL Ketalar, Pfizer AB, Sollentuna, Sweden). Lidocaine hydrochloride (Xylocaine, AstraZeneca AB, Södertälje, Sweden) was injected for local anaesthetic purposes. Thereafter, two implants in the tibia (proximal and distal) and one implant in the femur were placed on both hind legs (total six implants per rabbit). The implants (control, Ti SLActive; test, Roxolid SLActive) were always placed in a pairwise manner (left to right). However, the side they were placed (left or right) were randomized. After cover screw connection, the surgical sites were sutured layer-by-layer using a bioresorbable suture (4-0 Vicryl, Ethicon, Auneau, France). After 2, 4, and 12 weeks of healing, the rabbits were euthanized (n = 12 per time point) with an overdose of sodium pentobarbital (60 mg/mL Apoteksbolaget AB, Stockholm, Sweden), and the bone samples were removed en bloc. RTQ Test After a thorough soft tissue removal of the bone implant samples, the cover screws were removed, and the implants placed in the femur and the proximal tibia were subjected to RTQ testing with an electrically con-
trolled RTQ unit.12 In brief, the peak (maximum) RTQ was recorded in which the values were transmitted at a frequency of 100 Hz to a computer. Histological and Histomorphometrical Evaluation The distally placed implants were subjected to histologic/histomorphometric tests. The dissected bone-implant blocks were placed in 4% formaldehyde for 24 h. After fixation, and trimming, all samples were subjected to dehydration in a series of ethanol (70– 100%) and infiltration in resin (30–100%), which was performed under constant vacuuming and thereafter were embedded in light curing-resin (Technovit 7200 VLC, Heraeus Kulzer, Wehrheim, Germany). The embedded resin blocks were subjected to nondecalcified cut and grind sectioning. In brief, a central section of each sample was prepared using the EXAKT™ cutting and grinding equipment (EXAKT, Norderstedt, Germany) to a final thickness of approximately 20 μm. After polishing, the sections were finally stained with a mixed solution of toluidine blue and pyronin G. The histological observation were performed using a light microscope (Eclipse ME600, Nikon, Sendai, Japan), and the histomorphometrical data were analyzed with image analysis software (ImageJ v. 1.43u, National Institute of Health, Bethesda, MD); the outcomes were calculated in an excel software (Microsoft Co, Redmond, WA) as follows: 1) Bone-to-implant contact (BIC): Percentage was calculated by measuring distance of the bone in direct contact to the implant surface and was divided by the entire length of the implant placed in the bone. The percentage of bone length in contact with the surfaces in the cortical and marrow regions was also calculated. 2) New bone area (NBA): Percentage was calculated by measuring the area inside a thread occupied by newly formed bone, which is deeply stained, whereas the mother bone or the so-called existing cortical or trabecular bone is stained light blue, both in the cortical and marrow area, and was divided by the entire area of the thread. Statistical Power and Analysis The number of animals per time point was considered in relation to the size of the sample in the study and to
Osseointegration Property of TiZr Alloy Implants
TABLE 1 Mean Values for Sa, Sdr, and Sds (SD) for Topographical Analyses of Implants with Interferometer
SLActive Roxolid p Value*
Sa μm
Sds 1/μm2
Sdr %
1.45 (0.2) 1.53 (0.2) .1
0.07 (0.005) 0.06 (0.008) .002
75.73 (10.23) 52.56 (11.00) .003
*p Values for Sa and Sdr were obtained with independent samples t-test for mean comparison; p value for Sds was obtained with independent samples Mann–Whitney test.
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regarding the density of summits in square micrometers (Sds) and the developed surface ratio in % (Sdr), as presented in Table 1. No significant differences were confirmed for the average height deviation in micrometers (Sa) (p > .05). The descriptive images for both surfaces are presented in Figure 1. The investigation of samples by interferometer showed no qualitative differences in the morphology of the surface between both implants. XPS
the effect size. Prior to the animal study, a power analysis was conducted, and the statistical power between 60% and 80% was achieved for all evaluations. The number 12 rabbits were therefore decided based on this power analysis and also based on the ethical considerations included in the approved ethical application to minimize the number of animals as much as possible. For the interferometer measurements, independent samples Student t-test was used to compare the mean values of Sa and Sdr of the control and test groups, while independent samples Mann–Whitney test was used to compare the mean values of Sds between the two groups. The RTQ and histomorphometrical outcomes of test and control samples were compared using Wilcoxon Signed Rank for paired samples. For all tests, a significance threshold of 0.05 was used, and SPSS (IBM, Armonk, NY, USA) software was used for the analyses.
The chemical composition of the Ti and Roxolid (RXD) SLActive implants as determined by XPS is shown in Table 2. The two types of implants presented similar surface chemistry except for the Zr that was detected only for the test implants. Low levels of carbon contamination of about 10% were detected for both implants.
RESULTS
The histological observation showed that the bone around the implant presented normal healing at all time points observed, and no qualitative differences could be observed between the control and test groups (Figure 3). In brief, at 2 weeks, the cortical mother bone was in close
Topographical Analyses Topographical analyses of the implants with the interferometer showed a statistically significant difference
RTQ Test The only statistical significance seen was for the femur after a healing period of 2 weeks, where control implants (RTQ = 55 Ncm) presented significantly higher RTQ than test implants (36 Ncm, p = .012, Figure 2A). For the other groups, the mean values were higher for the control implants; however, there were no statistical differences (Figure 2, A and B). Histologic and Histomorphometrical Evaluation
Figure 1 Descriptive three-dimensional images (A) SLActive (B) Roxolid from the interferometer measurements (scan area: 260 × 200 μm).
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TABLE 2 Apparent Normalized Atomic Concentration (%) of the Elements Detected by XPS Implants
Ti SLActive-1 Ti SLActive-2 Ti SLActive-3 RXD SLActive-1 RXD SLActive-2 RXD SLActive-3
Ti (%)
Zr (%)
O (%)
N (%)
C (%)
Na (%)
Al (%)
23.9 24.2 24.7 22.0 21.6 22.2
0.0 0.0 0.0 3.6 3.7 3.7
60.1 59.5 60.4 60.3 59.0 60.3
1.4 1.3 1.4 0.6 1.0 0.5
11.7 11.8 10.5 10.0 11.7 10.0
0.0 0.2 0.2 0.0 0.0 0.0
3.1 2.9 2.6 3.5 3.0 3.3
contact with the implant surface, whereas woven bone formation could already be observed in the marrow regions. At 4 weeks, the newly formed bone in the marrow region had further matured and the bone had formed along the implant surface, and the maturation continued even at 12 weeks of healing. The cortical bone seemed to have undergone a bone resorption and apposition process, where some of the bone that was in close contact to the implant had resorbed, and thereafter, the newly formed bone filled the resorbed space (Figure 3). No statistical differences in the BIC in the cortical area were observed throughout the observation periods (Figure 4A), whereas in the bone marrow area, the test group had higher mean BIC than the control group (19.25% and 13.89%, respectively, p = .05225); however, there were no statistical differences between the groups throughout the observation period in vivo (Figure 4B). The NBA was significantly higher for the test group at 4 weeks in the marrow areas (p = .02686, Figure 5). No statistical differences could be observed for all other
time points despite the higher mean values for the test group (Figure 5). DISCUSSION The aim of this study was to test the null hypothesis that Roxolid SLActive (test) and Ti SLActive (control) implants would present comparable bone tissue response after 2, 4, and 12 weeks healing in the tibia/femur of rabbits. The results from RTQ and BIC indicated that both implants successfully osseointegrated; however, the healing kinetics was different for the two implants as previously suggested.22 The results confirm the outcomes of the previously conducted studies testing the two different implants23,24; however, the information obtained here was of interest since three different time points (initial phase, midphase, and bone remodeling phase) were chosen and tested so that the bone healing properties of the two different implant groups could be illustrated. In brief, the mean RTQ values were higher (although no significant difference) for the control implants especially in the femur; however, at later stages, these differences in mean values diminished for both
Figure 2 Results from the removal torque tests at different time points (A) in the femur, and (B) in the tibia.
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Figure 3 Histological micrographs of the bone tissue formed around the control and test implants after 2, 4, and 12 weeks of healing in vivo both in the cortical and marrow regions.
bone types. In the histomorphometrical evaluation, there was a difference in healing process especially evident in the marrow areas at 4 weeks with the test group presenting higher osseointegration; however, the differences between the two groups diminished after 12 weeks.
Since the implants placed in the current study received no forms of vertical dynamic loading, and both implants were treated in a similar manner after manufacturing (i.e., stored in 0.9% NaCl),25 it is speculated that one of the major reasons for the obtained
Figure 4 Graph presenting the bone-to-implant contact (BIC) at 2, 4, and 12 weeks for both control and test groups in the (A) cortical and (B) in the marrow regions.
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Figure 5 Graph presenting the new bone area (NBA) at 2, 4, and 12 weeks for both control and test groups in the (A) cortical and (B) in the marrow regions. Asterisk represents a statistical significance.
results are an outcome of the differences in surface topography. In detail, the statistically significant difference in Sds (number of summits in μm: 2) and Sdr (the developed surface ratio in %) was confirmed with the control implants possessing overall a rougher surface topography than the test implants. It has been suggested that the optimal Sa value to obtain good bone response is between 1.0 and 2.0 μm, which is the so-called moderately roughened implant surface.20 Although the surface roughening procedure applied for the commercially pure Ti can also be applied for the TiZr1317, it is a general consensus that no surfaces can be identical if the base substrate is different. As expected, the XPS detected that there exists a difference in the outermost surface, which was the Zr composition for the TiZr alloy surface. To date, there is a lack of evidence with regard to the effect of Zr existence as compared with the Ti only; however, literature both in vitro and in vivo suggests that both materials and related alloys are biocompatible.26,27 However, as suggested by Yamano and colleagues, the differences in chemical elements have the possibility to induce distinct cellular responses, and this could be one of the reasons why a different osseointegration pathway was observed, although this had no significant effect on the outcomes.28 Overall, it can be suggested that despite the fact that some of the surface topographical parameters presented significant differences, and the chemistry may have added some differences in the healing cascade, the differences may not be clinically relevant as both implants can be classified as moderately roughened implants with comparable surface morphology and with proven biocompatibility. Therefore, the
results of the biomechanical, histomorphometrical, and surface topographical characterization suggest that comparable biologic outcomes can be expected for the TiZr1317 implants to the conventional c.p. Ti implants and is in accordance to previous investigations.15,29 This may be of great clinical interest as the improved mechanical property of the implant may expand the clinical application range of the implant treatment even in sites with thin alveolar ridges or in lower anterior defects. Although long-term clinical reports do not exist to date, several studies suggest that the clinical outcomes after prosthetic connection are promising,30–32 and the smaller diameter, but stronger mechanical characteristic, of the implant seems to benefit especially in the interforaminal region.31,33 Although it is suggested that both Ti and TiZr alloy small diameter implants function comparably in clinical situations in terms of marginal bone stability and peri-implant tissue status,31 it is of note to understand that the peri-implant bone strain under lateral loading significantly decreases for the TiZr implants.34 Thus, further studies are necessary to validate the long-term effect of the binary TiZr1317 alloy; however, the implant is suggested to function as comparable with the standard c.p. Ti implants. CONCLUSION The TiZr1317 alloy implants presented comparable biomechanical and histological outcomes to that of the c.p. Ti implants through a 12-week evaluation period in rabbit bone; thus, the initial hypothesis was accepted.
Osseointegration Property of TiZr Alloy Implants
ACKNOWLEDGEMENTS This study was fully funded by Institut Straumann AG, Basel, Switzerland. The authors acknowledge Marcel Obrecht for the technical and administrative assistance throughout the study. REFERENCES 1. Mertens C, Steveling HG. Early and immediate loading of titanium implants with fluoride-modified surfaces: results of 5-year prospective study. Clin Oral Implants Res 2011; 22:1354–1360. 2. Adell R, Eriksson B, Lekholm U, Branemark PI, Jemt T. Long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxillofac Implants 1990; 5:347–359. 3. Sawase T, Jimbo R, Wennerberg A, Suketa N, Tanaka Y, Atsuta M. A novel characteristic of porous titanium oxide implants. Clin Oral Implants Res 2007; 18:680–685. 4. Veltri M, Ferrari M, Balleri P. One-year outcome of narrow diameter blasted implants for rehabilitation of maxillas with knife-edge resorption. Clin Oral Implants Res 2008; 19:1069–1073. 5. Allum SR, Tomlinson RA, Joshi R. The impact of loads on standard diameter, small diameter and mini implants: a comparative laboratory study. Clin Oral Implants Res 2008; 19:553–559. 6. Taddei EB, Henriques VAR, Silva CRM, Cairo CAA. Production of new titanium alloy for orthopedic implants. Mater Sci Eng C 2004; 24:683–687. 7. Davidson JA, Mishra AK, Kovacs P, Poggie RA. New surfacehardened, low-modulus, corrosion-resistant Ti-13Nb-13Zr alloy for total HIP arthroplasty. Biomed Mater Eng 1994; 4:231–243. 8. Semlitsch M, Weber H, Streicher R, Schon R. Joint replacement components made of hot-forged and surface-treated Ti-6Al-7Nb alloy. Biomaterials 1992; 13:781–788. 9. Li SJ, Yang R, Niinomi M, Hao YL, Cui YY. Formation and growth of calcium phosphate on the surface of oxidized Ti-29Nb-13Ta-4.6Zr alloy. Biomaterials 2004; 25:2525– 2532. 10. Wennerberg A, Albrektsson T. On implant surfaces: a review of current knowledge and opinions. Int J Oral Maxillofac Implants 2010; 25:63–74. 11. Stenport VF, Johansson CB. Evaluations of bone tissue integration to pure and alloyed titanium implants. Clin Implant Dent Relat Res 2008; 10:191–199. 12. Johansson CB, Jimbo R, Stefenson P. Ex vivo and in vivo biomechanical test of implant attachment to various materials: introduction of a new user-friendly removal torque equipment. Clin Implant Dent Relat Res 2012; 14:603– 611.
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13. Teixeira ER, Wadamoto M, Akagawa Y, Kimoto T. Clinical application of short hydroxylapatite-coated dental implants to the posterior mandible: a five-year survival study. J Prosthet Dent 1997; 78:166–171. 14. Östman P-O, Wennerberg A, Albrektsson T. Immediate occlusal loading of NanoTite™ PREVAIL® implants: a prospective 1-year clinical and radiographic study. Clin Implant Dent Relat Res 2010; 12:39–47. 15. Gottlow J, Dard M, Kjellson F, Obrecht M, Sennerby L. Evaluation of a new titanium-zirconium dental implant: a biomechanical and histological comparative study in the mini pig. Clin Implant Dent Relat Res 2012; 14:538–545. 16. Thoma DS, Jones AA, Dard M, Grize L, Obrecht M, Cochran DL. Tissue integration of a new titaniumzirconium dental implant: a comparative histologic and radiographic study in the canine. J Periodontol 2011; 82:1453–1461. 17. Grandin HM, Berner S, Dard M. A review of titanium zirconium (TiZr) alloys for use in endosseous dental implants. Materials 2012; 5:1348–1360. 18. Bernhard N, Berner S, De Wild M, Wieland M. The binary TiZr Alloy – a newly developed Ti alloy for use in dental implants. Forum Implantol 2009; 5:30–39. 19. Wennerberg A, Jimbo R, Stubinger S, Obrecht M, Dard M, Berner S. Nanostructures and hydrophilicity influence osseointegration: a biomechanical study in the rabbit tibia. Clin Oral Implants Res 2013; 25:1041–1050. 20. Buser D, Broggini N, Wieland M, et al. Enhanced bone apposition to a chemically modified SLA titanium surface. J Dent Res 2004; 83:529–533. 21. Wennerberg A, Albrektsson T. Effects of titanium surface topography on bone integration: a systematic review. Clin Oral Implants Res 2009; 20:172–184. 22. Wen B, Zhu F, Li Z, Zhang P, Lin X, Dard M. The osseointegration behavior of titanium-zirconium implants in ovariectomized rabbits. Clin Oral Implants Res 2014; 25:819–825. 23. Saulacic N, Bosshardt DD, Bornstein MM, Berner S, Buser D. Bone apposition to a titanium-zirconium alloy implant, as compared to two other titanium-containing implants. Eur Cell Mater 2012; 23:273–286, discussion 286– 278. 24. Kämmerer PW, Palarie V, Schiegnitz E, Hagmann S, Alshihri A, Al-Nawas B. Vertical osteoconductivity and early bone formation of titanium-zirconium and titanium implants in a subperiosteal rabbit animal model. Clin Oral Implants Res 2014; 25:774–780. 25. Wennerberg A, Svanborg LM, Berner S, Andersson M. Spontaneously formed nanostructures on titanium surfaces. Clin Oral Implants Res 2013; 24:203–209. 26. Welander M, Abrahamsson I, Berglundh T. The mucosal barrier at implant abutments of different materials. Clin Oral Implants Res 2008; 19:635–641.
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27. Correa DRN, Vicente FB, Donato TAG, Arana-Chavez VE, Buzalaf MAR, Grandini CR. The effect of the solute on the structure, selected mechanical properties, and biocompatibility of Ti-Zr system alloys for dental applications. Mater Sci Eng C 2014; 34:354–359. 28. Yamano S, Ma AK, Shanti RM, Kim SW, Wada K, Sukotjo C. The influence of different implant materials on human gingival fibroblast morphology, proliferation, and gene expression. Int J Oral Maxillofac Implants 2011; 26:1247–1255. 29. Anchieta RB, Baldassarri M, Guastaldi F, et al. Mechanical property assessment of bone healing around a titaniumzirconium alloy dental implant. Clin Implant Dent Relat Res 2013; 2014 Dec; 16(6):913–919. doi: 10.1111/cid.12061. Epub 2013 Mar 25. 30. Al-Nawas B, Domagala P, Fragola G, et al. A prospective non-interventional study to evaluate survival and success of reduced diameter implants made from titaniumzirconium alloy. J Oral Implantol 2014 Mar 25. [Epub ahead of print].
31. Quirynen M, Al-Nawas B, Meijer HJA, et al. Small-diameter titanium Grade IV and titanium-zirconium implants in edentulous mandibles: three-year results from a doubleblind, randomized controlled trial. Clin Oral Implants Res 2014 Apr 9. doi: 10.1111/clr.12367. [Epub ahead of print]. 32. Chiapasco M, Casentini P, Zaniboni M, Corsi E, Anello T. Titanium-zirconium alloy narrow-diameter implants (Straumann Roxolid®) for the rehabilitation of horizontally deficient edentulous ridges: prospective study on 18 consecutive patients. Clin Oral Implants Res 2012; 23:1136– 1141. 33. Al-Nawas B, Brägger U, Meijer HJA, et al. Double-blind randomized controlled trial (RCT) of titanium-13Zirconium versus titanium grade IV small-diameter bone level implants in edentulous mandibles – results from a 1-year observation period. Clin Implant Dent Relat Res 2012; 14:896–904. 34. Wu AY-J, Hsu J-T, Huang H-L. An in vitro biomechanical evaluation of a new commercial titanium-zirconium alloy dental implant. Implant Dent 2014; 23:534–538.
