J Mater Sci: Mater Med (2015) 26:71 DOI 10.1007/s10856-015-5405-7
BIOCOMPATIBILITY STUDIES
In vivo degradation of orthodontic miniscrew implants: surface analysis of as-received and retrieved specimens Masahiro Iijima • Takeshi Muguruma • Masahiro Kawaguchi • Yoshitaka Yasuda Itaru Mizoguchi
•
Received: 27 February 2014 / Accepted: 6 November 2014 Ó Springer Science+Business Media New York 2015
Abstract This study investigated in vivo degradation of Ti–6Al–4V alloy miniscrew implants. Miniscrew implants were placed in patients, and the surfaces were studied upon retrieval by scanning electron microscopy, microscale X-ray photoelectron spectroscopy, elastic recoil detection analysis and nanoindentation testing. Bone-like structures were formed on the retrieved specimens. The hardness and elastic modulus of the surfaces of the retrieved specimens were significantly lower than the as-received specimens, although no statistically significant differences were observed for the hardness and elastic modulus in the bulk region. Thick organic over-layer containing carbon, oxygen, and nitrogen, with the thickness greater than 50 nm, covered the retrieved specimens, and higher concentrations of hydrogen were detected in the retrieved specimens compared with the as-received specimens. Minimal degradation of the bulk mechanical properties of miniscrew implants was observed after clinical use, although precipitation of bone-like structures, formation of a carbonaceous contamination layer, and hydrogen absorption were observed on the surfaces of miniscrew implants.
M. Iijima (&) T. Muguruma I. Mizoguchi Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, Japan e-mail: [email protected] M. Kawaguchi Commercialization Support Department Advanced Analysis and Development Sector, Tokyo Metropolitan Industrial Technology Research Institute, Tokyo, Japan Y. Yasuda Yasuda Orthodontic Office, Nishinomiya, Hyogo, Japan
1 Introduction In dentistry, the use of implants to replace missing teeth is common, and the concept of direct bone-to-implant contact, defined as osseointegration, has been established [1]. In clinical orthodontics, Roberts et al. [2] reported the use of a dental implant as an skeletal anchorage without the need for patient compliance for tooth movement in orthodontic treatment; however, their technique requires a surgical procedure, is costly, and difficult to hygiene control. Thus, miniscrew implants introduced by Kanomi [3] have gained popularity, because their small size allows for more placement sites in the oral cavity, less discomfort for patients, an easy surgical procedure, and low cost [4–6]. A disadvantage of currently available miniscrew implants is their relatively low success rate (80–87 %) [7], which is attributable to several factors related to the interface between the miniscrew implant and surrounding bone [4–6, 8]. Fracture of miniscrew implants during placement and removal is also a concern. Recent clinical studies have reported that approximately 2–7 % of miniscrew implants fracture during placement or removal [5, 9]. Miniscrew implant fracture is a serious problem for orthodontists and patients, because it can be difficult to remove implant fragments embedded in the bone. If bone-toimplant apposition is of osseointegration, then fracture of the miniscrew implant may be caused by torqueing during removal. Fluoride-containing products, such as toothpaste and mouthrinse, are commonly used in dentistry to prevent dental caries. However, fluoride ions in the product may combine with hydrogen ions to form hydrogen fluoride (HF), which attacks the protective surface oxide of titanium alloys used for implants. Hydrogen embrittlement of titanium or titanium alloys through the use of fluoride-containing products lead to brittle fracture of titanium products
123
71
Page 2 of 7
J Mater Sci: Mater Med (2015) 26:71
experimental protocol (Number 85; July 10th, 2013), and all subjects provided written informed consent to participate in this study. Ten as-received miniscrew implants of the same type were used for control specimens.
[10, 11]. Hydrogen absorption by and subsequent embrittlement of nickel–titanium orthodontic wires have also been reported [10, 12]. Little information on the in vivo degradation of dental implant biomaterials is available; thus, interest in postretrieval analysis has recently increased in biomaterials sector. Such studies provide critical information on the performance of the materials in which they are intended to function [13, 14]. In the present study, retrieved miniscrew implants made from titanium alloy Ti–6Al–4V were investigated to evaluate the changes in their characteristics after clinical use. The surfaces of the miniscrew implants were morphologically studied by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and the compositional changes (surface contaminants) were examined using microscale X-ray photoelectron spectroscopy (micro-XPS) and elastic recoil detection analysis (ERDA). To the best of our knowledge, this is the first study that has investigated hydrogen absorption in orthodontic miniscrew implants using ERDA.
2.2 Morphological observation and compositional analysis for the screw threads by SEM and EDS All miniscrew implants were examined before and after clinical use without sputter-coated surfaces by SEM (S3500N, Hitachi, Tokyo, Japan) at 15 kV. Low-magnification SEM images about tip regions were obtained for each implant. Five locations on each specimen were randomly selected for compositional analysis using EDS (S-3500N, Hitachi). EDS analysis was performed at a working distance of 15 mm. 2.3 Nanoindentation testing for evaluating mechanical properties at the heads of the miniscrew implants The heads of five representative as-received and five representative retrieved miniscrew implants were examined with nanoindentation testing. The miniscrew implants were fixed on the specimen stage with adhesive resin (Superbond Orthomite, Sun Medical, Shiga, Japan). All nanoindentation testing was carried out at 28 °C (ENT-1100a, Elionix, Tokyo, Japan) using a Berkovich indenter. Three peak loads of 0.5, 100 and 500-mN were used. The hardness and elastic modulus of the miniscrew implant specimens were calculated using the software provided with the nanoindentation apparatus (Nano indentation tester software, Elionix). Linear extrapolation methods (ISO Standard 14577) were used for the unloading curve between 95 and 70 % of the maximum test force to calculate the elastic modulus.
2 Materials and methods 2.1 Materials Titanium alloy (Ti–6Al–4V) miniscrew implants were used in the present study (AbsoAnchor SH-1413-07, Dentos, Daegu, Korea). The dimensions of the implants were as follows: 1.3-mm tip diameter, 1.4-mm neck side diameter, and 7-mm length. Ten miniscrew implants were manually placed in patients using a hand-driver at the buccal region between the second premolar and the first molar without drilling of a pilot hole; the miniscrew implants were immediately loaded with approximately 150 g after placement. The list of patients with the duration of intraoral service and age of implant placement is summarized in Table 1. After clinical use, the implants were carefully removed by application of torque with a hand-driver, and were collected for study. The duration of intraoral service was between 54 and 513 days. The retrieved miniscrew implants were rinsed with ultra-pure de-ionized water and alcohol prior to further study. The ethics committee of the Health Sciences University of Hokkaido approved the Table 1 List of patients
123
2.4 Depth-dependent surface compositional analysis of the heads of the miniscrew implants by microXPS and ERDA The surface and in-depth composition of ten as-received and ten retrieved miniscrew implants was evaluated. The surfaces of the specimen heads were analyzed using microXPS (Quantera II, Ulvac-Phi, Kanagawa, Japan) employing
Patient
Gender
Duration of intraoral service (days)
Age of implant placement
A
Female
220
22 years 0 month
B
Female
54
21 years 9 months
C
Female
217
18 years 3 months
D
Female
513
18 years 0 month
E
Female
329
19 years 8 months
J Mater Sci: Mater Med (2015) 26:71
Page 3 of 7
71
A statistical analysis was performed using PASW Statistics (version 18.0J for Windows, IBM, Armonk, NY, USA). The maximum indentation depth, hardness, and elastic modulus of the retrieved and as-received miniscrews were not normally distributed (Levene test). A Kruskal–Wallis test was applied to determine whether significant differences existed among the groups. The Mann–Whitney U test was also used for the two independent groups, and the Bonferroni correction was applied (P \ 0.05).
use. All retrieved implants showed signs of debris and contaminations on their surfaces. Fractured screw tips and stripped screw threads after clinical use were not observed. The formation of bone-like structures was observed on the surface of some specimens after clinical use (A1, A2, C2, D1, D2, E1, E2). In addition to titanium, aluminum, and vanadium, small amounts of calcium and phosphorus were detected by EDS on the surfaces of the retrieved miniscrews (Table 2). Figure 2 presents the mechanical properties (maximum depth, hardness, and elastic modulus) of the as-received and retrieved miniscrew implants measured using nanoindentation testing. The analysis depths from the specimen surfaces obtained from three indentation loads (0.5, 100, and 500-mN) were approximately 50, 1,000, and 2,400 nm, respectively. With a 0.5-mN load, the hardness and elastic modulus values of the retrieved miniscrew implants were significantly lower than those of the as-received specimens. At a 100-mN load, the elastic modulus of the retrieved miniscrew was significantly lower than that of the as-received specimens. At a 500-mN load, no statistically significant differences were observed in the hardness and elastic modulus of the retrieved and as-received miniscrew implants. Figure 3 shows the dependence of the concentrations of individual elements on the sputtering depth for the asreceived and retrieved miniscrew implants obtained using XPS. XPS indicated the presence of Ti, N, O, and C as the main elements on the surfaces of all specimens. Wide-scan XPS spectra (not shown) indicated that the surface oxide film of the as-received miniscrews mainly consisted of TiO2 with a thickness of approximately 10 nm (5 nm/min for SiO2). The main difference between the as-received and retrieved miniscrew implants was that thicker organic overlayer containing carbon, oxygen, and nitrogen, with the thickness greater than 50 nm, covered the retrieved specimens. High-concentration of O and C were detected on the surface of the retrieved implants, and the amount decreased with increasing in depth. On the other hand, the amounts of N for the retrieved implants increased with increasing in depth. Figure 4 shows the average hydrogen depth profile observed using ERDA for the as-received and retrieved miniscrew implants. Higher concentration of H was detected in the retrieved implants surfaces as compared to the as-received implant surfaces. Up to a depth of 60 nm, higher concentrations of hydrogen were observed in the retrieved miniscrew implants.
3 Results
4 Discussion
Figure 1 shows SEM photomicrographs of ten miniscrew implants before (as-received) and after (retrieved) clinical
Since its development by Kanomi [3], the anchorage system with miniscrew implant has been widely accepted in
Al Ka radiation at 25-W beam power. The pressure of the main chamber was maintained at less than 1 9 10-6 Pa. Measurements on a 100-lm2 area of the miniscrew heads were conducted from 0 to 1,100 eV with a step size of 0.2 eV. The counting time was 20 ms at each step, and the number of sweeps was five, i.e., the total counting time was 100 ms at each step. Argon ion sputtering was used for depth profiling measurements. The ion sputtering area was 2 9 2 mm2 and the measurements were accomplished at the center of the area. The sputtering rate of SiO2 layer under same conditions was 5 nm/min. The relative atomic concentrations of the elements at each depth were calculated from the ratios of the element area intensities. High-resolution ERDA (HRBS1000, Kobelco, Hyogo, Japan) was used for depth profiling of the hydrogen content in miniscrews. The ion type, acceleration voltage, incident angle, and scattering angle were N?, 500 kV, 67.5° and 45.6°, respectively. The main chamber was maintained less than 1 9 10-5 Pa during the measurements. A multichannel plate was used as the detector in this study. A beam of 500 keV N? ions was irradiated against the surface of the implants and hydrogen ions recoiled at 45.6° were measured by the 90° sector type magnetic spectrometer. To reject the scattered N?ions, a mylar foil was set in front of a multi-channel plate detector. The energy of hydrogen ions recoiled from the surface region of the implants was *61 keV. Amorphous carbon materials with 20 at.% hydrogen were used as standard sample. The standard sample were also measured under same measurement conditions. The hydrogen contents of the miniscrew implants were compared with that of standard sample, and then the depth profile of the contents could be calculated because the change in the energy of the hydrogen ions corresponds to the theoretical position of the depth from the surface. 2.5 Statistical analysis
123
71
Page 4 of 7
J Mater Sci: Mater Med (2015) 26:71
Fig. 1 SEM photomicrographs of miniscrew implants before and after clinical use. The first and second rows show side-view images. The third and fourth rows show upper-view images
Table 2 Composition of the miniscrew implant surfaces (wt%)
Determined by EDS analysis
Elements
Al
P
Ti
V
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Before use
6.73
0.58
–
–
–
–
89.45
0.69
3.83
0.52
After use
5.92
1.67
0.14
0.12
1.16
3.29
89.54
2.65
3.24
0.49
modern clinical orthodontics, and many case reports using this system have been published [15, 16]. However, few studies on the basic material properties of miniscrew implants exist. In addition, fracture of miniscrew implants during placement and removal [5, 9], as well as relatively low survival rates during clinical use, have been reported [7]. These issues might be attributable to changes in the physical properties of the bulk material and/or surface composition. Eliades and colleagues [14] characterized retrieved miniscrew implants from five patients and reported that the bulk structure deduced from Vickers microhardness measurements was not altered by long-term clinical application. However, their SEM observations indicated morphological changes on the miniscrew implant surfaces with integuments, including calcium–phosphate precipitation on the surface. The present study was designed to analyze the compositional surface changes (surface contaminants) in more detail, including hydrogen absorption by the retrieved miniscrew implants. To the best of our knowledge, hydrogen absorption of orthodontic miniscrew miniscrew implants has not been previously reported.
123
Ca
The formation of bone-like structures was observed by SEM on the surfaces of some retrieved specimens, and small amounts of calcium and phosphorus were also detected. These observations are in agreement with previous findings by Eliades and colleagues [14]. Previous studies reported torquing forces of 7.3–13.5 Ncm [17] and 10.8 Ncm (average value) [18] during placement and removal, respectively. Another study that compared the torsional properties of commercially available miniscrew implants reported average torque values of 24.2–26.1 Ncm for the fracture of titanium alloy implants [19]. Thus, a higher safety factor for the strength of miniscrew implants is suggested, because bone-to-implant integration by bone apposition onto the surface of the implants may be influenced by the torquing load during implant removal. Torque values during placement and removal were not measured in this study and are thus suggested for future research. XPS results indicated the base alloy was covered by contamination layer with a thickness greater than 50 nm containing carbon, oxygen, and nitrogen on the retrieved miniscrew implants. This layer was organic in nature, presumable protein-related. In addition, the hardness and
J Mater Sci: Mater Med (2015) 26:71
Fig. 2 Comparison of the mechanical properties of the as-received and retrieved miniscrew implants specimens measured using nanoindentation testing. The upper, middle, and lower portions of the figure show the results obtained under 0.5, 100, and 500-mN loads. The short horizontal bars in the boxes correspond to median values;
Page 5 of 7
71
50 % of all values are within the boxes. The bottom and top of each box indicate the lower and upper quartiles, respectively. The vertical lines represent the value ranges. *P \ 0.05 by the Mann–Whitney U-test; ns indicates nonsignificance
Fig. 3 XPS depth profiles of the as-received and retrieved miniscrew implants. Full of the horizontal axis would regard about 50 nm of the depth due to the sputtering rate of SiO2, i.e., 5 nm/min
elastic modulus measured on the surfaces of the retrieved miniscrew implants using nanoindentation testing were significantly lower than those of the as-received specimens. On the other hand, no statistically significant differences
were observed in the bulk mechanical properties (2,400 nm from the surface) of the as-received and retrieved miniscrew implants, thereby suggesting that long-term clinical use of the implants under continuous load will not cause
123
71
Page 6 of 7
J Mater Sci: Mater Med (2015) 26:71
513 days for patient D and 329 days for patient E). However, the duration did not influence the results of surface analysis. Degradation of the mechanical properties of the miniscrew implants was not observed after more than 513 days of clinical use. However, surface changes, precipitation of bone-like structures, formation of a carbonaceous contamination layer, and hydrogen absorption were observed. Therefore, the reuse of miniscrew implants is not recommended, because surface changes in the implants may lead to inappropriate tissue response and prevent osseointegration.
Fig. 4 ERDA depth profiles of the as-received and retrieved miniscrew implants
work hardening that would affect the mechanical properties. Hydrogen absorption by titanium or titanium alloys from fluoride-containing dental products causes hydrogen embrittlement and brittle fracture of titanium products [10– 12]. In the current study, patients used a NaF-containing toothpaste (950 ppm) daily; other fluoride-containing products such as mouth rinse and bracket bonding material were not used. Higher concentrations of hydrogen were detected on the surfaces of the retrieved miniscrew implants compared to the as-received specimens. Fluoride ions from dental products combine with hydrogen ions in the oral environment to form HF, which enabled hydrogen absorption on the surfaces of the miniscrew implants. However, as noted above, the nanoindentation test results indicated no statistical significant differences in the bulk mechanical properties (2,400 nm from the surface) between the as-received and retrieved miniscrew implants. Therefore, surface-absorbed hydrogen did not significantly influence the bulk mechanical properties in the present investigation. In the present study, surface of static regions were analyzed, although the damage of fretting (wear) might be partially introduced. Fretting between miniscrew implant and bone might accelerate the nucleation and early growth of fatigue cracks that propagate and may cause fracture of the miniscrew implant [20]. The surface analysis for fretted regions should be worthwhile to elucidate the influence of fretting and breakage of the passive oxide film and subsequent re-passivation. No miniscrew implants used in the present study fractured during placement, clinical use, or removal. Thus, a more detailed investigation of failed and fractured miniscrew implants is suggested for future research. The duration of intraoral service varied in this study (220 days for patient A, 54 days for patient B, 217 days for patient C,
123
5 Conclusions The formation of bone-like structures was observed on the surfaces of miniscrew implants for some specimens. EDS analysis indicated that the retrieved specimens contained small amounts of calcium and phosphorus in addition to titanium, aluminum, and vanadium. The hardness and elastic modulus of the surfaces of retrieved miniscrew implants were significantly lower than those of the as-received specimens, although no statistically significant differences in the hardness and elastic modulus of the bulk regions were observed. Organic-related deposits, with layers containing carbon, oxygen, and nitrogen, were detected on the retrieved miniscrew implants; the thickness of the layer was more than 50 nm. Higher concentrations of hydrogen were found on the surfaces of the retrieved miniscrew implants compared to the as-received specimens. Acknowledgments This study was partially supported by the Research Project of the Research Institute of Personalized Health Sciences, Health Sciences University of Hokkaido.
References 1. Branemark PI, Aspegren K, Breine U. Microcirculatory studies in man by high resolution vital microscopy. Angiology. 1964;15: 329–32. 2. Roberts WE, Smith RK, Zilberman Y, Mozary PG, Smith RS. Osseous adaptation to continuous loading of rigid endosseous implants. Am J Orthod. 1984;86:95–111. 3. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod. 1997;31:763–7. 4. Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, Takano-Yamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2003;124:373–8. 5. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2006;130:18–25. 6. Kuroda S, Yamada K, Deguchi T, Hashimoto T, Kyung HM, Takano-Yamamoto T. Root proximity is a major factor for screw
J Mater Sci: Mater Med (2015) 26:71
7.
8.
9.
10.
11.
12.
13.
failure in orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2007;131(Supp 1):S68–73. Scha¨tzle M, Ma¨nnchen R, Zwahlen M, Lang NP. Survival and failure rates of orthodontic temporary anchorage devices: a systematic review. Clin Oral Implants Res. 2009;20:1351–9. Deguchi T, Yabuuchi T, Hasegawa M, Garetto LP, Roberts WE, Takano-Yamamoto T. Histomorphometric evaluation of cortical bone thickness surrounding miniscrew for orthodontic anchorage. Clin Inplant Dent Res. 2009;13:197–205. Buchter A, Wiechmann D, Koerdt S, Wiesmann HP, Piffko J, Meyer U. Load-related implant reaction of mini-implants used for orthodontic anchorage. Clin Oral Impl Res. 2005;16:473–9. Yokoyama K, kaneko K, Moroyama K, Asaoka K, Sakai J, Nagumo M. Hydrogen embrittlement of Ni–Ti superelastic alloy in fluoride solution. J Biomed Mater Res A. 2003;65A:182–7. Rodrigues DC, Urban RM, Jacobs JJ, Gilbert JL. In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants. J Biomed Mater Res B Appl Biomater. 2009;88:206–19. Zinelis S, Eliades T, Pandis N, Eliades G, Bourauel C. Why do nickel-titanium archwires fracture intraorally? Fractograpic analysis and failure mechanism of in vivo fractured wires. Am J Orthod Dentofacial Orthop. 2007;132:84–9. Esposito M, Lausmaa J, Hirsch JM, Thomsen P. Surface analysis of failed oral titanium implants. J Biomed Mater Res. 1999;48: 559–68.
Page 7 of 7
71
14. Eliades T, Zinelis S, Papadopoulos MA, Eliades G. Characterization of retrieved orthodontic miniscrew implant. Am J Orthod Dentofacial Orthop. 2009;135:10.e1–7. 15. Bae SM, Kyung HM. Mandibular molar intrusion with miniscrew anchorage. J Clin Orthod. 2006;40:107–8. 16. Ishihara Y, Kuroda S, Sugawara Y, Balam TA, Takano-Yamamoto T, Yamashiro T. Indirect usage of miniscrew anchorage to intrude overerupted mandibular incisors in a class II patient with a deep overbite. Am J Orthod Dentofacial Orthop. 2013;143: S113–24. 17. Motoyoshi M, Hirabayashi M, Uemura M, Shimizu N. Recommended placement torque when tightening an orthodontic miniimplant. Clin Oral Implants Res. 2006;17:109–14. 18. Chen YJ, Chen YH, Lin LD, Yao CC. Removal torque of miniscrews used for orthodontic anchorage-a preliminary report. Int J Oral Maxillofac Implants. 2006;21:283–9. 19. Iijima M, Muguruma T, Brantley WA, Okayama M, Yuasa T, Mizoguchi I. Torsional properties and microstructures of miniscrew implants. Am J Orthod Dentofacial Orthop. 2008;134: 333.e1–6. 20. Hoeppner DW, Chandrasekaran V. Fretting in orthopedic implants: a review. Wear. 1994;173:189–97.
123
BIOCOMPATIBILITY STUDIES
In vivo degradation of orthodontic miniscrew implants: surface analysis of as-received and retrieved specimens Masahiro Iijima • Takeshi Muguruma • Masahiro Kawaguchi • Yoshitaka Yasuda Itaru Mizoguchi
•
Received: 27 February 2014 / Accepted: 6 November 2014 Ó Springer Science+Business Media New York 2015
Abstract This study investigated in vivo degradation of Ti–6Al–4V alloy miniscrew implants. Miniscrew implants were placed in patients, and the surfaces were studied upon retrieval by scanning electron microscopy, microscale X-ray photoelectron spectroscopy, elastic recoil detection analysis and nanoindentation testing. Bone-like structures were formed on the retrieved specimens. The hardness and elastic modulus of the surfaces of the retrieved specimens were significantly lower than the as-received specimens, although no statistically significant differences were observed for the hardness and elastic modulus in the bulk region. Thick organic over-layer containing carbon, oxygen, and nitrogen, with the thickness greater than 50 nm, covered the retrieved specimens, and higher concentrations of hydrogen were detected in the retrieved specimens compared with the as-received specimens. Minimal degradation of the bulk mechanical properties of miniscrew implants was observed after clinical use, although precipitation of bone-like structures, formation of a carbonaceous contamination layer, and hydrogen absorption were observed on the surfaces of miniscrew implants.
M. Iijima (&) T. Muguruma I. Mizoguchi Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, Japan e-mail: [email protected] M. Kawaguchi Commercialization Support Department Advanced Analysis and Development Sector, Tokyo Metropolitan Industrial Technology Research Institute, Tokyo, Japan Y. Yasuda Yasuda Orthodontic Office, Nishinomiya, Hyogo, Japan
1 Introduction In dentistry, the use of implants to replace missing teeth is common, and the concept of direct bone-to-implant contact, defined as osseointegration, has been established [1]. In clinical orthodontics, Roberts et al. [2] reported the use of a dental implant as an skeletal anchorage without the need for patient compliance for tooth movement in orthodontic treatment; however, their technique requires a surgical procedure, is costly, and difficult to hygiene control. Thus, miniscrew implants introduced by Kanomi [3] have gained popularity, because their small size allows for more placement sites in the oral cavity, less discomfort for patients, an easy surgical procedure, and low cost [4–6]. A disadvantage of currently available miniscrew implants is their relatively low success rate (80–87 %) [7], which is attributable to several factors related to the interface between the miniscrew implant and surrounding bone [4–6, 8]. Fracture of miniscrew implants during placement and removal is also a concern. Recent clinical studies have reported that approximately 2–7 % of miniscrew implants fracture during placement or removal [5, 9]. Miniscrew implant fracture is a serious problem for orthodontists and patients, because it can be difficult to remove implant fragments embedded in the bone. If bone-toimplant apposition is of osseointegration, then fracture of the miniscrew implant may be caused by torqueing during removal. Fluoride-containing products, such as toothpaste and mouthrinse, are commonly used in dentistry to prevent dental caries. However, fluoride ions in the product may combine with hydrogen ions to form hydrogen fluoride (HF), which attacks the protective surface oxide of titanium alloys used for implants. Hydrogen embrittlement of titanium or titanium alloys through the use of fluoride-containing products lead to brittle fracture of titanium products
123
71
Page 2 of 7
J Mater Sci: Mater Med (2015) 26:71
experimental protocol (Number 85; July 10th, 2013), and all subjects provided written informed consent to participate in this study. Ten as-received miniscrew implants of the same type were used for control specimens.
[10, 11]. Hydrogen absorption by and subsequent embrittlement of nickel–titanium orthodontic wires have also been reported [10, 12]. Little information on the in vivo degradation of dental implant biomaterials is available; thus, interest in postretrieval analysis has recently increased in biomaterials sector. Such studies provide critical information on the performance of the materials in which they are intended to function [13, 14]. In the present study, retrieved miniscrew implants made from titanium alloy Ti–6Al–4V were investigated to evaluate the changes in their characteristics after clinical use. The surfaces of the miniscrew implants were morphologically studied by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and the compositional changes (surface contaminants) were examined using microscale X-ray photoelectron spectroscopy (micro-XPS) and elastic recoil detection analysis (ERDA). To the best of our knowledge, this is the first study that has investigated hydrogen absorption in orthodontic miniscrew implants using ERDA.
2.2 Morphological observation and compositional analysis for the screw threads by SEM and EDS All miniscrew implants were examined before and after clinical use without sputter-coated surfaces by SEM (S3500N, Hitachi, Tokyo, Japan) at 15 kV. Low-magnification SEM images about tip regions were obtained for each implant. Five locations on each specimen were randomly selected for compositional analysis using EDS (S-3500N, Hitachi). EDS analysis was performed at a working distance of 15 mm. 2.3 Nanoindentation testing for evaluating mechanical properties at the heads of the miniscrew implants The heads of five representative as-received and five representative retrieved miniscrew implants were examined with nanoindentation testing. The miniscrew implants were fixed on the specimen stage with adhesive resin (Superbond Orthomite, Sun Medical, Shiga, Japan). All nanoindentation testing was carried out at 28 °C (ENT-1100a, Elionix, Tokyo, Japan) using a Berkovich indenter. Three peak loads of 0.5, 100 and 500-mN were used. The hardness and elastic modulus of the miniscrew implant specimens were calculated using the software provided with the nanoindentation apparatus (Nano indentation tester software, Elionix). Linear extrapolation methods (ISO Standard 14577) were used for the unloading curve between 95 and 70 % of the maximum test force to calculate the elastic modulus.
2 Materials and methods 2.1 Materials Titanium alloy (Ti–6Al–4V) miniscrew implants were used in the present study (AbsoAnchor SH-1413-07, Dentos, Daegu, Korea). The dimensions of the implants were as follows: 1.3-mm tip diameter, 1.4-mm neck side diameter, and 7-mm length. Ten miniscrew implants were manually placed in patients using a hand-driver at the buccal region between the second premolar and the first molar without drilling of a pilot hole; the miniscrew implants were immediately loaded with approximately 150 g after placement. The list of patients with the duration of intraoral service and age of implant placement is summarized in Table 1. After clinical use, the implants were carefully removed by application of torque with a hand-driver, and were collected for study. The duration of intraoral service was between 54 and 513 days. The retrieved miniscrew implants were rinsed with ultra-pure de-ionized water and alcohol prior to further study. The ethics committee of the Health Sciences University of Hokkaido approved the Table 1 List of patients
123
2.4 Depth-dependent surface compositional analysis of the heads of the miniscrew implants by microXPS and ERDA The surface and in-depth composition of ten as-received and ten retrieved miniscrew implants was evaluated. The surfaces of the specimen heads were analyzed using microXPS (Quantera II, Ulvac-Phi, Kanagawa, Japan) employing
Patient
Gender
Duration of intraoral service (days)
Age of implant placement
A
Female
220
22 years 0 month
B
Female
54
21 years 9 months
C
Female
217
18 years 3 months
D
Female
513
18 years 0 month
E
Female
329
19 years 8 months
J Mater Sci: Mater Med (2015) 26:71
Page 3 of 7
71
A statistical analysis was performed using PASW Statistics (version 18.0J for Windows, IBM, Armonk, NY, USA). The maximum indentation depth, hardness, and elastic modulus of the retrieved and as-received miniscrews were not normally distributed (Levene test). A Kruskal–Wallis test was applied to determine whether significant differences existed among the groups. The Mann–Whitney U test was also used for the two independent groups, and the Bonferroni correction was applied (P \ 0.05).
use. All retrieved implants showed signs of debris and contaminations on their surfaces. Fractured screw tips and stripped screw threads after clinical use were not observed. The formation of bone-like structures was observed on the surface of some specimens after clinical use (A1, A2, C2, D1, D2, E1, E2). In addition to titanium, aluminum, and vanadium, small amounts of calcium and phosphorus were detected by EDS on the surfaces of the retrieved miniscrews (Table 2). Figure 2 presents the mechanical properties (maximum depth, hardness, and elastic modulus) of the as-received and retrieved miniscrew implants measured using nanoindentation testing. The analysis depths from the specimen surfaces obtained from three indentation loads (0.5, 100, and 500-mN) were approximately 50, 1,000, and 2,400 nm, respectively. With a 0.5-mN load, the hardness and elastic modulus values of the retrieved miniscrew implants were significantly lower than those of the as-received specimens. At a 100-mN load, the elastic modulus of the retrieved miniscrew was significantly lower than that of the as-received specimens. At a 500-mN load, no statistically significant differences were observed in the hardness and elastic modulus of the retrieved and as-received miniscrew implants. Figure 3 shows the dependence of the concentrations of individual elements on the sputtering depth for the asreceived and retrieved miniscrew implants obtained using XPS. XPS indicated the presence of Ti, N, O, and C as the main elements on the surfaces of all specimens. Wide-scan XPS spectra (not shown) indicated that the surface oxide film of the as-received miniscrews mainly consisted of TiO2 with a thickness of approximately 10 nm (5 nm/min for SiO2). The main difference between the as-received and retrieved miniscrew implants was that thicker organic overlayer containing carbon, oxygen, and nitrogen, with the thickness greater than 50 nm, covered the retrieved specimens. High-concentration of O and C were detected on the surface of the retrieved implants, and the amount decreased with increasing in depth. On the other hand, the amounts of N for the retrieved implants increased with increasing in depth. Figure 4 shows the average hydrogen depth profile observed using ERDA for the as-received and retrieved miniscrew implants. Higher concentration of H was detected in the retrieved implants surfaces as compared to the as-received implant surfaces. Up to a depth of 60 nm, higher concentrations of hydrogen were observed in the retrieved miniscrew implants.
3 Results
4 Discussion
Figure 1 shows SEM photomicrographs of ten miniscrew implants before (as-received) and after (retrieved) clinical
Since its development by Kanomi [3], the anchorage system with miniscrew implant has been widely accepted in
Al Ka radiation at 25-W beam power. The pressure of the main chamber was maintained at less than 1 9 10-6 Pa. Measurements on a 100-lm2 area of the miniscrew heads were conducted from 0 to 1,100 eV with a step size of 0.2 eV. The counting time was 20 ms at each step, and the number of sweeps was five, i.e., the total counting time was 100 ms at each step. Argon ion sputtering was used for depth profiling measurements. The ion sputtering area was 2 9 2 mm2 and the measurements were accomplished at the center of the area. The sputtering rate of SiO2 layer under same conditions was 5 nm/min. The relative atomic concentrations of the elements at each depth were calculated from the ratios of the element area intensities. High-resolution ERDA (HRBS1000, Kobelco, Hyogo, Japan) was used for depth profiling of the hydrogen content in miniscrews. The ion type, acceleration voltage, incident angle, and scattering angle were N?, 500 kV, 67.5° and 45.6°, respectively. The main chamber was maintained less than 1 9 10-5 Pa during the measurements. A multichannel plate was used as the detector in this study. A beam of 500 keV N? ions was irradiated against the surface of the implants and hydrogen ions recoiled at 45.6° were measured by the 90° sector type magnetic spectrometer. To reject the scattered N?ions, a mylar foil was set in front of a multi-channel plate detector. The energy of hydrogen ions recoiled from the surface region of the implants was *61 keV. Amorphous carbon materials with 20 at.% hydrogen were used as standard sample. The standard sample were also measured under same measurement conditions. The hydrogen contents of the miniscrew implants were compared with that of standard sample, and then the depth profile of the contents could be calculated because the change in the energy of the hydrogen ions corresponds to the theoretical position of the depth from the surface. 2.5 Statistical analysis
123
71
Page 4 of 7
J Mater Sci: Mater Med (2015) 26:71
Fig. 1 SEM photomicrographs of miniscrew implants before and after clinical use. The first and second rows show side-view images. The third and fourth rows show upper-view images
Table 2 Composition of the miniscrew implant surfaces (wt%)
Determined by EDS analysis
Elements
Al
P
Ti
V
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Before use
6.73
0.58
–
–
–
–
89.45
0.69
3.83
0.52
After use
5.92
1.67
0.14
0.12
1.16
3.29
89.54
2.65
3.24
0.49
modern clinical orthodontics, and many case reports using this system have been published [15, 16]. However, few studies on the basic material properties of miniscrew implants exist. In addition, fracture of miniscrew implants during placement and removal [5, 9], as well as relatively low survival rates during clinical use, have been reported [7]. These issues might be attributable to changes in the physical properties of the bulk material and/or surface composition. Eliades and colleagues [14] characterized retrieved miniscrew implants from five patients and reported that the bulk structure deduced from Vickers microhardness measurements was not altered by long-term clinical application. However, their SEM observations indicated morphological changes on the miniscrew implant surfaces with integuments, including calcium–phosphate precipitation on the surface. The present study was designed to analyze the compositional surface changes (surface contaminants) in more detail, including hydrogen absorption by the retrieved miniscrew implants. To the best of our knowledge, hydrogen absorption of orthodontic miniscrew miniscrew implants has not been previously reported.
123
Ca
The formation of bone-like structures was observed by SEM on the surfaces of some retrieved specimens, and small amounts of calcium and phosphorus were also detected. These observations are in agreement with previous findings by Eliades and colleagues [14]. Previous studies reported torquing forces of 7.3–13.5 Ncm [17] and 10.8 Ncm (average value) [18] during placement and removal, respectively. Another study that compared the torsional properties of commercially available miniscrew implants reported average torque values of 24.2–26.1 Ncm for the fracture of titanium alloy implants [19]. Thus, a higher safety factor for the strength of miniscrew implants is suggested, because bone-to-implant integration by bone apposition onto the surface of the implants may be influenced by the torquing load during implant removal. Torque values during placement and removal were not measured in this study and are thus suggested for future research. XPS results indicated the base alloy was covered by contamination layer with a thickness greater than 50 nm containing carbon, oxygen, and nitrogen on the retrieved miniscrew implants. This layer was organic in nature, presumable protein-related. In addition, the hardness and
J Mater Sci: Mater Med (2015) 26:71
Fig. 2 Comparison of the mechanical properties of the as-received and retrieved miniscrew implants specimens measured using nanoindentation testing. The upper, middle, and lower portions of the figure show the results obtained under 0.5, 100, and 500-mN loads. The short horizontal bars in the boxes correspond to median values;
Page 5 of 7
71
50 % of all values are within the boxes. The bottom and top of each box indicate the lower and upper quartiles, respectively. The vertical lines represent the value ranges. *P \ 0.05 by the Mann–Whitney U-test; ns indicates nonsignificance
Fig. 3 XPS depth profiles of the as-received and retrieved miniscrew implants. Full of the horizontal axis would regard about 50 nm of the depth due to the sputtering rate of SiO2, i.e., 5 nm/min
elastic modulus measured on the surfaces of the retrieved miniscrew implants using nanoindentation testing were significantly lower than those of the as-received specimens. On the other hand, no statistically significant differences
were observed in the bulk mechanical properties (2,400 nm from the surface) of the as-received and retrieved miniscrew implants, thereby suggesting that long-term clinical use of the implants under continuous load will not cause
123
71
Page 6 of 7
J Mater Sci: Mater Med (2015) 26:71
513 days for patient D and 329 days for patient E). However, the duration did not influence the results of surface analysis. Degradation of the mechanical properties of the miniscrew implants was not observed after more than 513 days of clinical use. However, surface changes, precipitation of bone-like structures, formation of a carbonaceous contamination layer, and hydrogen absorption were observed. Therefore, the reuse of miniscrew implants is not recommended, because surface changes in the implants may lead to inappropriate tissue response and prevent osseointegration.
Fig. 4 ERDA depth profiles of the as-received and retrieved miniscrew implants
work hardening that would affect the mechanical properties. Hydrogen absorption by titanium or titanium alloys from fluoride-containing dental products causes hydrogen embrittlement and brittle fracture of titanium products [10– 12]. In the current study, patients used a NaF-containing toothpaste (950 ppm) daily; other fluoride-containing products such as mouth rinse and bracket bonding material were not used. Higher concentrations of hydrogen were detected on the surfaces of the retrieved miniscrew implants compared to the as-received specimens. Fluoride ions from dental products combine with hydrogen ions in the oral environment to form HF, which enabled hydrogen absorption on the surfaces of the miniscrew implants. However, as noted above, the nanoindentation test results indicated no statistical significant differences in the bulk mechanical properties (2,400 nm from the surface) between the as-received and retrieved miniscrew implants. Therefore, surface-absorbed hydrogen did not significantly influence the bulk mechanical properties in the present investigation. In the present study, surface of static regions were analyzed, although the damage of fretting (wear) might be partially introduced. Fretting between miniscrew implant and bone might accelerate the nucleation and early growth of fatigue cracks that propagate and may cause fracture of the miniscrew implant [20]. The surface analysis for fretted regions should be worthwhile to elucidate the influence of fretting and breakage of the passive oxide film and subsequent re-passivation. No miniscrew implants used in the present study fractured during placement, clinical use, or removal. Thus, a more detailed investigation of failed and fractured miniscrew implants is suggested for future research. The duration of intraoral service varied in this study (220 days for patient A, 54 days for patient B, 217 days for patient C,
123
5 Conclusions The formation of bone-like structures was observed on the surfaces of miniscrew implants for some specimens. EDS analysis indicated that the retrieved specimens contained small amounts of calcium and phosphorus in addition to titanium, aluminum, and vanadium. The hardness and elastic modulus of the surfaces of retrieved miniscrew implants were significantly lower than those of the as-received specimens, although no statistically significant differences in the hardness and elastic modulus of the bulk regions were observed. Organic-related deposits, with layers containing carbon, oxygen, and nitrogen, were detected on the retrieved miniscrew implants; the thickness of the layer was more than 50 nm. Higher concentrations of hydrogen were found on the surfaces of the retrieved miniscrew implants compared to the as-received specimens. Acknowledgments This study was partially supported by the Research Project of the Research Institute of Personalized Health Sciences, Health Sciences University of Hokkaido.
References 1. Branemark PI, Aspegren K, Breine U. Microcirculatory studies in man by high resolution vital microscopy. Angiology. 1964;15: 329–32. 2. Roberts WE, Smith RK, Zilberman Y, Mozary PG, Smith RS. Osseous adaptation to continuous loading of rigid endosseous implants. Am J Orthod. 1984;86:95–111. 3. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod. 1997;31:763–7. 4. Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, Takano-Yamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2003;124:373–8. 5. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2006;130:18–25. 6. Kuroda S, Yamada K, Deguchi T, Hashimoto T, Kyung HM, Takano-Yamamoto T. Root proximity is a major factor for screw
J Mater Sci: Mater Med (2015) 26:71
7.
8.
9.
10.
11.
12.
13.
failure in orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2007;131(Supp 1):S68–73. Scha¨tzle M, Ma¨nnchen R, Zwahlen M, Lang NP. Survival and failure rates of orthodontic temporary anchorage devices: a systematic review. Clin Oral Implants Res. 2009;20:1351–9. Deguchi T, Yabuuchi T, Hasegawa M, Garetto LP, Roberts WE, Takano-Yamamoto T. Histomorphometric evaluation of cortical bone thickness surrounding miniscrew for orthodontic anchorage. Clin Inplant Dent Res. 2009;13:197–205. Buchter A, Wiechmann D, Koerdt S, Wiesmann HP, Piffko J, Meyer U. Load-related implant reaction of mini-implants used for orthodontic anchorage. Clin Oral Impl Res. 2005;16:473–9. Yokoyama K, kaneko K, Moroyama K, Asaoka K, Sakai J, Nagumo M. Hydrogen embrittlement of Ni–Ti superelastic alloy in fluoride solution. J Biomed Mater Res A. 2003;65A:182–7. Rodrigues DC, Urban RM, Jacobs JJ, Gilbert JL. In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants. J Biomed Mater Res B Appl Biomater. 2009;88:206–19. Zinelis S, Eliades T, Pandis N, Eliades G, Bourauel C. Why do nickel-titanium archwires fracture intraorally? Fractograpic analysis and failure mechanism of in vivo fractured wires. Am J Orthod Dentofacial Orthop. 2007;132:84–9. Esposito M, Lausmaa J, Hirsch JM, Thomsen P. Surface analysis of failed oral titanium implants. J Biomed Mater Res. 1999;48: 559–68.
Page 7 of 7
71
14. Eliades T, Zinelis S, Papadopoulos MA, Eliades G. Characterization of retrieved orthodontic miniscrew implant. Am J Orthod Dentofacial Orthop. 2009;135:10.e1–7. 15. Bae SM, Kyung HM. Mandibular molar intrusion with miniscrew anchorage. J Clin Orthod. 2006;40:107–8. 16. Ishihara Y, Kuroda S, Sugawara Y, Balam TA, Takano-Yamamoto T, Yamashiro T. Indirect usage of miniscrew anchorage to intrude overerupted mandibular incisors in a class II patient with a deep overbite. Am J Orthod Dentofacial Orthop. 2013;143: S113–24. 17. Motoyoshi M, Hirabayashi M, Uemura M, Shimizu N. Recommended placement torque when tightening an orthodontic miniimplant. Clin Oral Implants Res. 2006;17:109–14. 18. Chen YJ, Chen YH, Lin LD, Yao CC. Removal torque of miniscrews used for orthodontic anchorage-a preliminary report. Int J Oral Maxillofac Implants. 2006;21:283–9. 19. Iijima M, Muguruma T, Brantley WA, Okayama M, Yuasa T, Mizoguchi I. Torsional properties and microstructures of miniscrew implants. Am J Orthod Dentofacial Orthop. 2008;134: 333.e1–6. 20. Hoeppner DW, Chandrasekaran V. Fretting in orthopedic implants: a review. Wear. 1994;173:189–97.
123
