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Wear behavior between zirconia and titanium as an antagonist on fixed dental prostheses
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2014 Biomed. Mater. 9 025005 (http://iopscience.iop.org/1748-605X/9/2/025005) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 202.28.191.34 This content was downloaded on 25/02/2015 at 15:33
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Biomedical Materials Biomed. Mater. 9 (2014) 025005 (8pp)
doi:10.1088/1748-6041/9/2/025005
Wear behavior between zirconia and titanium as an antagonist on fixed dental prostheses Tsunemichi Kanbara 1 , Hideshi Sekine 2,3 , Shinya Homma 1 , Yasutomo Yajima 1,3 and Masao Yoshinari 3 1
Department of Oral and Maxillofacial Implantology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan 2 Division of Oral Implant Service, Department of Clinical Oral Health Science, Tokyo Dental College, 2-9-18 Misakicho, Chiyoda-ku, Tokyo 101-0061, Japan 3 Division of Oral Implants Research, Oral Health Science Center, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan E-mail: [email protected] Received 22 July 2013, revised 11 November 2013 Accepted for publication 28 November 2013 Published 4 February 2014 Abstract
The aim of this in vitro study was to investigate the wear behavior of the abrader when tetragonal zirconia polycrystal (TZP), cp-titanium (CpTi) and Ti–6Al–4V alloy (TiAlV) were used as the antagonist on fixed dental prostheses (FDPs). Both hemisphere abrader and flat substrate specimens were prepared using TZP, CpTi and TiAlV. Two-body wear tests were performed in distilled water, and the wear volume of the abrader specimen was measured to evaluate the wear behavior. In addition, scanning microscopic observation and an electron probe micro-analysis were performed to elucidate the underlying mechanism of the wear. The wear volume of CpTi and TiAlV abrader specimens was approximately 20 times larger than that of TZP abrader specimen against all substrate specimens. This is due to the differences in hardness between the ultra-hardness of TZP and the comparatively low hardness of CpTi and TiAlV. The wear volume of CpTi and TiAlV abrader specimens against the TZP substrate was significantly smaller than for the CpTi and TiAlV substrates despite the hardness of TZP being much larger than those of CpTi and TiAlV. This phenomenon may be based on the adhesive wear mechanism. Elements of Ti, Al and V originating in the TiAlV substrate were detected adhering to the abrader CpTi specimen. These results suggest that FDPs of CpTi and TiAlV are susceptible to wear against not only TZP but also CpTi and TiAlV in contrast to TZP FDPs. Keywords: two-body wear, antagonist, zirconia, TZP, titanium, fixed dental prostheses
called monolithic TZP reconstructions. It is also reported that the monolithic TZP reconstructions show less enamel wear compared to porcelain antagonists [2–4]. In addition, the manufacturing costs could be reduced by automatic design and milling to a full-anatomical contour by computeraided design and manufacturing (CAD/CAM) technologies. The technique-sensitive veneering process would no longer be necessary, thus guaranteeing a more consistent quality of restoration. Accordingly, monolithic TZP reconstructions have been used despite the fact that the TZP is opaque
1. Introduction Tetragonal zirconia polycrystals (TZPs) are widely used in the dental field as materials for fixed dental prostheses (FDPs) due to their white color, and good mechanical and chemical properties. Though TZP frameworks have been veneered with translucent feldspathic or glass ceramic materials for aesthetic reasons, chipping of the veneering material has been frequently reported [1]. In order to overcome the chipping problem, it is possible today to produce TZP for FDPs without ceramic veneer, 1748-6041/14/025005+08$33.00
1
© 2014 IOP Publishing Ltd
Printed in the UK
T Kanbara et al
Biomed. Mater. 9 (2014) 025005
(a)
(b)
abrader substrate
Figure 1. (a) Experimental wear simulator. (b) Higher magnification of areas shown in rectangle in (a).
(non-translucent). Several manufacturers offer TZP material with improved aesthetic by adding coloring pigments [5]. Utilization of cp-titanium (CpTi) and Ti–6Al–4V alloy (TiAlV) for FDPs has also been increasing as the alternative material of precious alloys. In addition, CpTi and TiAlV have been used as the superstructure of an oral implant system, because FDPs with the same composition as the fixture (implant body) material could avoid the galvanic action between the superstructure and fixture with dissimilar metals for each. However, one concern associated with the use of monolithic TZP is the possible abrasiveness of CpTi and TiAlV on the restorations of FDPs. When these materials were used for the antagonist, excessive wear would occur. In particular, severe wear of FDPs made from CpTi and TiAlV is expected when TZP is used as an antagonist due to large differences in hardness between the two types of material. This has raised serious concerns that the wear may lead to a metal allergy originating in metal-wear debris [6–9] when these materials are used for FDPs. Therefore, the wear behavior between TZP and CpTi (TiAlV) as an antagonistic material on the FDPs would be of interest clinically. Concerning human enamel wear, several investigators have demonstrated that, in general, dental ceramic substrates cause greater abrasive wear of human enamel compared with dental alloys [10–12], even though the wear mechanism is unclear. However, less is also known about the wear behavior of TZP for dental applications. While some basic studies of zirconia–zirconia combinations have shown catastrophic wear [13], others have demonstrated excellent wear resistance [14, 15], mainly due to different test conditions. Recently, the wear behavior of TZP against CpTi and/or TiAlV was reported, under the assumption of wear between TZP implant abutments and Ti retaining screws [16]. They reported that CpTi and TiAlV were more susceptible to wear by both TZP and CpTi (TiAlV) in contrast to TZP. This report, however,
Table 1. Materials used in this study.
Material
Manufacturer
Yttria-stabilized Tosoh tetragonal zirconia polycrystals (TZ-3YB-E) Cp-titanium Tokyo Titanium Ti–6Al–4V alloy Tokyo Titanium
Composition (mass%)
Code
ZrO2: balanced, Y2O3: 5.16, Al2O3: 0.25
TZP
Ti > 99.0 Ti : balanced, Al: 6.2, V:4.2
CpTi TiAlV
did not evaluate the wear behavior of antagonists for FDPs. Furthermore, there were no reports about the wear behavior between TZP and titanium as an antagonist on FDPs. The aim of this in vitro study is focused on the wear behavior of the abrader when TZP, CpTi and TiAlV were used as the antagonist on FDPs using a two-body wear test. 2. Experimental details 2.1. Materials
Three kinds of materials, yttria-stabilized tetragonal zirconia polycrystal (Y-TZP, TZ-3YB-E, sintered density of 6.07 g cm−3, Tosoh, Tokyo, Japan), commercially pure titanium (CpTi, grade 4, Tokyo Titanium, Saitama, Japan) and Ti–6Al–4V alloy (TiAlV, grade 5, Tokyo Titanium, Saitama, Japan), were used in this study as shown in table 1. Each material was used for the abraders or the substrates that corresponded to abraders, as shown in figures 1(b) and 2(a). 2.2. Making the abrader specimen
The cylindrical abrader specimen with one hemispherical end (10 mm in length and 5 mm in diameter with a radius of curvature of 5 mm) was prepared using a CAD/CAM 2
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(a)
P=10N
2.6. Statistical analysis
(b)
Abrader specimen
For the statistical analysis, an analysis of variance (ANOVA) was used for the wear volume in the wear test, followed by the Scheffe test for a post hoc comparison between groups.
S
ϕ=5mm
3. Results r=5mm
3.1. SEM observation of worn surfaces of abrader specimens (c)
Representative SEM images of worn surfaces of abrader specimens are shown in figures 3–5. When TZP was used as the abrader specimen (figure 3), comparatively small circles caused by the wear against TZP, CpTi and TiAlV substrates were observed under low magnification (left). Small grains that were originated by a row of material of the TZP were randomly observed under high magnification (right, arrows). When CpTi was used as the abrader specimen (figure 4), the diameter of worn surfaces was larger than that of TZP abraders (figure 3), and the wear morphologies were altered depending on the substrate specimens. In addition, the peripheral morphology of the abraded circles was different against between TZP substrate and CpTi substrate, that is, a very sharp periphery was recognized when TZP was used as the substrate specimen (arrow in figure 4 upper). On the contrary, when CpTi was used as the substrate specimen (arrow in figure 4 middle), irregular peripheries were observed, suggesting that some fraction of the substance had been pulled off. When TiAlV was used as the abrader specimen (figure 5), the wear morphologies had a similar tendency as the CpTi abrader specimen, although the size of the abraded circle was larger than with the CpTi abrader.
Substrate specimen S
V Figure 2. (a) Schematic illustrations of the wear test. (b) Wear area
(S) of the worn surface of the abrader specimen observed with SEM. (c) Wear volume (V) of the abrader specimen.
machine (DENTAL CAD/CAM GN-1, GC, Tokyo, Japan). These specimens were finally polished with 6 μm diamond pastes. 2.3. Making the substrate specimen
Disks of 13 mm in diameter and 1 mm in thickness were prepared as the substrate specimens, and these specimens were also polished with 6 μm diamond pastes. Both abrader and substrate specimens showed mirror-like surfaces with less than 0.1 μm of surface roughness (Ra). 2.4. Wear test and measurement of abrader wear volume
Wear tests were performed using an experimental wear simulator as shown in figure 1 according to previous studies [16, 17]. As seen in figure 2(a), each abrader specimen was moved back and forth on the substrate specimen over a distance of 3 mm for 30 000 cycles at a speed of 90 cycles min−1 and with a vertical load of 10 N. The test was carried out at room temperature with distilled water circulated through a water chamber in order to remove abrasion debris. After 30 000 cycles of wear test, the worn surfaces of abrader specimens were observed using a scanning microscope (SEM, SU-6600, HITACHI, Hitachi, Japan) as shown in figure 2(b). Subsequently, the wear area (S) of the abrader specimen was measured using an image analyzer (HDS-N1, HIROYA, Tokyo, Japan), and finally the wear volume (V) was calculated (figure 2(c)). Five specimens were used for each combination.
3.2. Wear volume of abrader specimens
The wear volume of abrader specimens against various substrate specimens is shown in figures 6 and 7. A significantly small wear area was recognized in TZP abraders compared to CpTi and TiAlV abraders. The wear behavior of substrate specimens showed the same tendency as those of abrader specimens besides the comparative large wear volume on the TiAlV abrader compared to the CpTi abrader against TZP substrates. Figure 6 shows the wear volume of TZP abrader specimens against various substrate specimens. A quite small wear volume was recognized against all substrates, and no significant difference in wear volume was recognized among the substrates. Figure 7 shows the wear volume of CpTi and TiAlV abrader specimens against various substrate specimens. The wear volume of CpTi and TiAlV abraders was approximately 20 times larger than that of the TZP abrader specimen (figure 6). The wear volume of CpTi and TiAlV abraders against the TZP substrate was significantly smaller than against CpTi and TiAlV substrates (P < 0.05). The wear volume of the TiAlV abrader specimen showed a large wear volume, the same as that of CpTi abraders. The wear volume of the TiAlV
2.5. Electron probe micro-analysis
A characteristic x-ray image analysis of the abrader specimens was performed to identify abraded particles that had adhered to the abrader specimens from the substrate specimens using an electron probe micro-analyzer (EPMA, JXA-8200, JEOL, Tokyo, Japan). 3
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Abrader : TZP Substrate: TZP
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
Abrader : TZP Substrate: CpTi
Abrader : TZP Substrate: TiAlV
Figure 3. Representative SEM images of the worn surfaces of abrader specimens (TZP) against various substrates.
Abrader : CpTi Substrate: TZP
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
Abrader : CpTi Substrate: CpTi
Abrader : CpTi Substrate: TiAlV
Figure 4. Representative SEM images of the worn surfaces of abrader specimens (CpTi) against various substrates. 4
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Abrader : TiAlV Substrate: TZP
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm 2 µm
500 µm
50 µm
2 µm
Abrader : TiAlV Substrate: CpTi
Abrader : TiAlV Substrate: TiAlV
Figure 5. Representative SEM images of the worn surfaces of abrader specimens (TiAlV) against various substrates.
Figure 6. Mean wear volume of the TZP abrader specimen against various substrate specimens. Standard deviations are shown by error bars. Identical letters indicate no significant difference (p > 0.05).
Figure 7. Mean wear volume of CpTi and TiAlV abrader specimens against various substrate specimens. Standard deviations are shown by error bars. Different letters indicate significant differences (p < 0.05).
abrader specimen against TZP substrate was significantly smaller than against CpTi and TiAlV substrates (P < 0.05). Table 2 shows multiple comparisons between groups on the wear volume of abrader specimens. The wear volumes of TZP abraders were significantly smaller than those of CpTi and TiAlV abraders. The wear volumes of CpTi and TiAlV abraders against TZP substrates were significantly smaller than those against CpTi and TiAlV substrates.
3.3. EPMA analysis
Characteristic x-ray images of the worn surface of the TZP abrader specimen against the CpTi substrate are shown in figure 8. An optical image of the TZP abrader specimen with black-colored staining after the wear test is also given in figure 8. Ti element was identified as the abraded particles that had adhered to abrader specimens from the CpTi substrate 5
T Kanbara et al
Biomed. Mater. 9 (2014) 025005
SEM
Optical image
1 mm
Figure 8. Characteristic x-ray images of the worn surface of the TZP abrader specimen against CpTi substrate. An optical image of the TZP abrader specimen with black-colored staining after the wear test is also given in the figure.
SEM
Figure 9. Characteristic x-ray images of the worn surface of the CpTi abrader specimen against the TiAlV substrate. 6
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Table 2. Multiple comparisons between groups on the wear volume of abrader specimens.
TZP/TZP TZP/CpTi TZP/TiAlV CpTi/TZP CpTi/CpTi CpTi/TiAlV TiAlV/TZP TiAlV/CpTi TiAlV/TiAlV TZP/TZP TZP/CpTi TZP/TiAlV CpTi/TZP CpTi/CpTi CpTi/TiAlV TiAlV/TZP TiAlV/CpTi TiAlV/TiAlV
–
– –
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
–
∗
– –
– –
∗
∗
∗
–
Abrader/substrate: –: NS, ∗ : P < 0.05, ∗∗ : P < 0.01.
(arrows). Figure 9 shows characteristic x-ray images of the worn surface of the CpTi abrader specimen against the TiAlV substrate. Elements of Al and V as well as Ti originating in the TiAlV substrate were detected adhering to the CpTi abrader specimen (arrows).
this study. The previous study revealed that the coefficient of friction between CpTi and CpTi showed a higher value than the CpTi/TZP combination, showing that a strong adhesive interaction had occurred on the CpTi/CpTi combination [16]. This is also supported by SEM observation of the worn surfaces on the CpTi/CpTi combination (figure 4, lower left, arrow), in which irregular shapes at the peripheral morphology had resulted from eroded particles from the substrate specimens adhering to the abrader specimens. Another underlying mechanism can be linked to the microstructure of TZP. The grain size of TZP is less than 0.5 μm with a homogenous distribution of crystal sizes and orientations. The grain size is an important parameter, which determines the surface topography and the tribological behavior of the materials. The fine grain size of TZP may lead to very smooth surfaces after polishing, leading to its lower susceptibility to the antagonist wear behavior. In the present study, a comparatively large wear volume on the TiAlV abrader specimen was shown compared to the CpTi abrader specimen against TZP substrates. Though the reason for these results is still unclear, the existence of a βphase in TiAlV in contrast to the homogeneous structure of CpTi is possibly responsible for the abrasion behavior. In the EPMA analysis, the Ti element was detected on the TZP abrader specimen when CpTi was used as the substrate. In addition, elements of Al and V originating in the TiAlV substrate were detected adhering to the CpTi abrader specimen, showing that the worn particles of CpTi and TiAlV had attached to the opposite specimens, which would represent a hazard to health due to the presence of metal particles. On the other hand, TZP was less susceptible to wear by either TZP or titanium. Thus, it would be better to carry out metal-free restoration using TZP in FDPs in order to successfully avoid any metal allergy originating from worn particles. In the present study, we used opaque (non-translucent) monolithic TZP that has been increasingly used as FDPs without veneering ceramics due to the reduced enamel wear compared to the porcelain antagonist. However, using a translucent TZP is more appropriate in the interest of aesthetic dental treatments. Further study is necessary to clarify the wear behavior using a translucent TZP instead of conventional opaque TZP that is used in this study. In this study, the wear behavior of the hemisphere abrader specimens was evaluated assuming the cusp abrasion on the FDPs. However, in order to elucidate the wear
4. Discussion The aim of this study was to estimate the wear behavior when TZP and titanium (Ti and Ti alloy) were used for the antagonist on FDPs using a two-body wear test. In this study, the wear behavior was evaluated by estimating the wear volume of the abrader specimen as the antagonist according to the previous reports [2–5]. Silva et al evaluated the volumetric loss of lithium disilicate glassceramic and TZP restorations in an in vivo study [18]. Kim et al also evaluated the wear volume of the abrader specimens using feldspathic porcelain cusp as well as the cusp of the premolar teeth in an in vitro study [2]. Accordingly, the use of an abrader specimen with a hemisphere is considered to be beneficial for evaluating the wear behavior between antagonists. The TZP abrader specimen showed quite a small wear volume against all substrate specimens in this study. In contrast, the wear volume of CpTi and TiAlV abrader specimens was approximately 20 times larger than that of the TZP abrader specimen against all substrate specimens. This is considered mainly to be due to the differences in hardness between the TZP and CpTi (TiAlV) that have a hardness (Hv) of 1356, 177 and 256 on TZP, CpTi and TiAlV, respectively [16]. This indicates that the operating mechanism of wear between the CpTi (TiAlV) and the TZP was abrasive wear due to the ultra-hardness of the TZP. In the present study, the wear volume of CpTi and TiAlV abrader specimens against the TZP substrate was significantly smaller than CpTi and TiAlV substrates although the hardness of TZP was much larger than those of CpTi and TiAlV. These phenomena can be explained by the adhesive wear mechanism [19]. Adhesive wear appears when two bodies slide over each other, or are pressed into one another, which enhances material transfer between the two surfaces. In the contact, fragments of one surface are pulled off and adhere to the other, due to the strong adhesive interaction between two surfaces with similar physicochemical properties such as metal to metal [20, 21]. This supposition is supported by the differences in the coefficient of friction between the materials used in 7
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¨ [5] Stawarczyk B, Ozcan M, Schmutz F, Trottmann A, Roos M and H¨ammerle C H F 2013 Two-body wear of monolithic, veneered and glazed zirconia and their corresponding enamel antagonists Acta. Odontol. Scand. 71 102–12 [6] Uo M, Asakura K, Yokoyama A, Ishikawa M, Tamura K, Totsuka Y, Akasaka T and Watari F 2007 X-ray absorption fine structure (XAFS) analysis of titanium-implanted soft tissue Dent. Mater. J. 26 268–73 [7] Egusa H, Ko N, Shimazu T and Yatani H 2008 Suspected association of an allergic reaction with titanium dental implants a clinical report J. Prosthet. Dent. 100 344–7 [8] Witt J D and Swann M 1991 Metal wear and tissue response in failed titanium alloy total hip replacements J. Bone Joint Surg. Br. 73 559–63 [9] Sicilia A, Cuesta S, Coma G, Arregui I, Guisasola C, Ruiz E and Maestro A 2008 Titanium allergy in dental implant patients a clinical study on 1500 consecutive patients Clin. Oral Implants Res. 19 823–35 [10] Seghi R R, Rosenstiel S F and Bauer P 1991 Abrasion of human enamel by different dental ceramics in vitro J. Dent. Res. 70 221–5 [11] Hacker C H, Wagner W C and Razzoog M E 1996 An in vitro investigation of the wear of enamel on porcelain and gold in saliva J. Prosthet. Dent. 75 14–7 [12] Metzler K T, Woody R D, Miller A W 3rd and Miller B H 1999 In vitro investigation of the wear of human enamel by dental porcelain J. Prosthet. Dent. 81 356–64 [13] Oonishi H, Ueno M, Okimatsu H and Amino H 1996 Investigation of the wear behavior of ceramic on ceramic combinations in total hip prosthesis Bioceramics: Proc. 9th Int. Symp. on Ceramics in Medicine vol 9 ed T Nakamura, F Miyaji and T Kokubo (Kldlington: Pergamon) pp 503–6 [14] Willmann G, Fruh H J and Pfaff H G 1996 Wear characteristics of sliding pairs of zirconia (Y-TZP) for hip endoprostheses Biomaterials 17 2157–62 [15] Clarke I C, Good V, Yamamoto K, Schroeder D and Gustafson A 2000 High wear resistance of alumina and zirconia ceramic combinations in THR wear study Trans. 6th World Biomaterials Congress Workshop#7 8 [16] Kanbara T, Yajima Y and Yoshinari M 2011 Wear behavior of tetragonal zirconia polycrystal versus titanium and titanium alloy Biomed. Mater. 6 021001 [17] Takarabe M 1982 An experimental study on sliding-induced abrasion of natural teeth and materials used for crowns Shikwa Gakuho 82 949–1004 in Japanese [18] Silva N R F A, Thompson Van P, Valverde G B, Paulo G, Powers J M, Farah J W and Esquivel-Upshaw J 2011 Comparative reliability analyses of zirconium oxide and lithium disilicate restorations in vitro and in vivo J. Am. Dent. Assoc. 142 (Suppl. 2) 4S–9S [19] Kato K 2002 Classification of wear mechanisms/models Proc. Inst. Mech. Eng. J 216 349–55 [20] Rodrigues D C, Urban R M, Jacobs J J and Gilbert J L 2009 In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants J. Biomed. Mater. Res. B 88 206–19 [21] Hallab N J, Messina C, Skipor A and Jacobs J J 2004 Differences in the fretting corrosion of metal-metal and ceramic-metal modular junctions of total hip replacements J. Orthop. Res. 22 250–9
phenomena, both contacting surfaces should be analyzed. The wear behavior of the substrate specimens was evaluated previously under the assumption of wear between TZP implant abutments and the titanium retaining screws on the dental implant treatment [16]. The results of the present study showed the same tendency as those of the previous study besides the comparative large wear volume on the TiAlV abrader compared to the CpTi abrader against TZP substrate in this study. Accordingly, it is confirmed by both previous and current studies that the operating mechanism of the wear for the CpTi/TZP combination was abrasive wear, whereas that of the CpTi/CpTi combination was adhesive wear. The two-body wear test was used to evaluate the wear behavior in this study. However, this test method does not truly simulate the clinical chewing situation. The wear behavior using the chewing simulator with thermo-mechanical loading and simultaneous thermal stress should be addressed [5]. In conclusion, the results in the present study showed that titanium FDPs (CpTi and TiAlV) are susceptible to wear against not only TZP but also CpTi and TiAlV in contrast to TZP FDPs. It should be noted that a wear volume of 0.53 mm3 on the CpTi abrader against the CpTi substrate is equivalent to 190 μm of cusp height reduction on the FDPs, which may influence the vertical dimension on the occlusion. Therefore, the results of this study may provide useful information to the clinical application of zirconia and titanium FDPs from the point of view of cusp abrasion. Acknowledgments This research was supported partly by an Oral Health Science Center Grant HRC7 from Tokyo Dental College and a Project for Private Universities: matching fund subsidy from MEXT (Ministry of Education, Culture, Sports, Science and Technology of Japan, 2006–2011). References [1] Sailer I, Feh´er A, Filser F, Gauckler L J, L¨uthy H and H¨ammerle C H F 2007 Five-year clinical results of zirconia frameworks for posterior fixed partial dentures Int. J. Prosthodont. 20 383–8 [2] Kim M J, Oh S H, Kim J H, Ju S W, Seo D G, Jun S H, Ahn J S and Ryu J J 2012 Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains J. Dent. 40 979–88 [3] Mitov G, Heintze S D, Walz S, Woll K, Muecklich F and Pospiech P 2012 Wear behavior of dental Y-TZP ceramic against natural enamel after different finishing procedures Dent. Mater. 28 909–18 [4] Preis V, Weiser F, Handel G and Rosentritt M 2013 Wear performance of monolithic dental ceramics with different surface treatments Quintessence Int. 44 393–405
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Wear behavior between zirconia and titanium as an antagonist on fixed dental prostheses
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2014 Biomed. Mater. 9 025005 (http://iopscience.iop.org/1748-605X/9/2/025005) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 202.28.191.34 This content was downloaded on 25/02/2015 at 15:33
Please note that terms and conditions apply.
Biomedical Materials Biomed. Mater. 9 (2014) 025005 (8pp)
doi:10.1088/1748-6041/9/2/025005
Wear behavior between zirconia and titanium as an antagonist on fixed dental prostheses Tsunemichi Kanbara 1 , Hideshi Sekine 2,3 , Shinya Homma 1 , Yasutomo Yajima 1,3 and Masao Yoshinari 3 1
Department of Oral and Maxillofacial Implantology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan 2 Division of Oral Implant Service, Department of Clinical Oral Health Science, Tokyo Dental College, 2-9-18 Misakicho, Chiyoda-ku, Tokyo 101-0061, Japan 3 Division of Oral Implants Research, Oral Health Science Center, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan E-mail: [email protected] Received 22 July 2013, revised 11 November 2013 Accepted for publication 28 November 2013 Published 4 February 2014 Abstract
The aim of this in vitro study was to investigate the wear behavior of the abrader when tetragonal zirconia polycrystal (TZP), cp-titanium (CpTi) and Ti–6Al–4V alloy (TiAlV) were used as the antagonist on fixed dental prostheses (FDPs). Both hemisphere abrader and flat substrate specimens were prepared using TZP, CpTi and TiAlV. Two-body wear tests were performed in distilled water, and the wear volume of the abrader specimen was measured to evaluate the wear behavior. In addition, scanning microscopic observation and an electron probe micro-analysis were performed to elucidate the underlying mechanism of the wear. The wear volume of CpTi and TiAlV abrader specimens was approximately 20 times larger than that of TZP abrader specimen against all substrate specimens. This is due to the differences in hardness between the ultra-hardness of TZP and the comparatively low hardness of CpTi and TiAlV. The wear volume of CpTi and TiAlV abrader specimens against the TZP substrate was significantly smaller than for the CpTi and TiAlV substrates despite the hardness of TZP being much larger than those of CpTi and TiAlV. This phenomenon may be based on the adhesive wear mechanism. Elements of Ti, Al and V originating in the TiAlV substrate were detected adhering to the abrader CpTi specimen. These results suggest that FDPs of CpTi and TiAlV are susceptible to wear against not only TZP but also CpTi and TiAlV in contrast to TZP FDPs. Keywords: two-body wear, antagonist, zirconia, TZP, titanium, fixed dental prostheses
called monolithic TZP reconstructions. It is also reported that the monolithic TZP reconstructions show less enamel wear compared to porcelain antagonists [2–4]. In addition, the manufacturing costs could be reduced by automatic design and milling to a full-anatomical contour by computeraided design and manufacturing (CAD/CAM) technologies. The technique-sensitive veneering process would no longer be necessary, thus guaranteeing a more consistent quality of restoration. Accordingly, monolithic TZP reconstructions have been used despite the fact that the TZP is opaque
1. Introduction Tetragonal zirconia polycrystals (TZPs) are widely used in the dental field as materials for fixed dental prostheses (FDPs) due to their white color, and good mechanical and chemical properties. Though TZP frameworks have been veneered with translucent feldspathic or glass ceramic materials for aesthetic reasons, chipping of the veneering material has been frequently reported [1]. In order to overcome the chipping problem, it is possible today to produce TZP for FDPs without ceramic veneer, 1748-6041/14/025005+08$33.00
1
© 2014 IOP Publishing Ltd
Printed in the UK
T Kanbara et al
Biomed. Mater. 9 (2014) 025005
(a)
(b)
abrader substrate
Figure 1. (a) Experimental wear simulator. (b) Higher magnification of areas shown in rectangle in (a).
(non-translucent). Several manufacturers offer TZP material with improved aesthetic by adding coloring pigments [5]. Utilization of cp-titanium (CpTi) and Ti–6Al–4V alloy (TiAlV) for FDPs has also been increasing as the alternative material of precious alloys. In addition, CpTi and TiAlV have been used as the superstructure of an oral implant system, because FDPs with the same composition as the fixture (implant body) material could avoid the galvanic action between the superstructure and fixture with dissimilar metals for each. However, one concern associated with the use of monolithic TZP is the possible abrasiveness of CpTi and TiAlV on the restorations of FDPs. When these materials were used for the antagonist, excessive wear would occur. In particular, severe wear of FDPs made from CpTi and TiAlV is expected when TZP is used as an antagonist due to large differences in hardness between the two types of material. This has raised serious concerns that the wear may lead to a metal allergy originating in metal-wear debris [6–9] when these materials are used for FDPs. Therefore, the wear behavior between TZP and CpTi (TiAlV) as an antagonistic material on the FDPs would be of interest clinically. Concerning human enamel wear, several investigators have demonstrated that, in general, dental ceramic substrates cause greater abrasive wear of human enamel compared with dental alloys [10–12], even though the wear mechanism is unclear. However, less is also known about the wear behavior of TZP for dental applications. While some basic studies of zirconia–zirconia combinations have shown catastrophic wear [13], others have demonstrated excellent wear resistance [14, 15], mainly due to different test conditions. Recently, the wear behavior of TZP against CpTi and/or TiAlV was reported, under the assumption of wear between TZP implant abutments and Ti retaining screws [16]. They reported that CpTi and TiAlV were more susceptible to wear by both TZP and CpTi (TiAlV) in contrast to TZP. This report, however,
Table 1. Materials used in this study.
Material
Manufacturer
Yttria-stabilized Tosoh tetragonal zirconia polycrystals (TZ-3YB-E) Cp-titanium Tokyo Titanium Ti–6Al–4V alloy Tokyo Titanium
Composition (mass%)
Code
ZrO2: balanced, Y2O3: 5.16, Al2O3: 0.25
TZP
Ti > 99.0 Ti : balanced, Al: 6.2, V:4.2
CpTi TiAlV
did not evaluate the wear behavior of antagonists for FDPs. Furthermore, there were no reports about the wear behavior between TZP and titanium as an antagonist on FDPs. The aim of this in vitro study is focused on the wear behavior of the abrader when TZP, CpTi and TiAlV were used as the antagonist on FDPs using a two-body wear test. 2. Experimental details 2.1. Materials
Three kinds of materials, yttria-stabilized tetragonal zirconia polycrystal (Y-TZP, TZ-3YB-E, sintered density of 6.07 g cm−3, Tosoh, Tokyo, Japan), commercially pure titanium (CpTi, grade 4, Tokyo Titanium, Saitama, Japan) and Ti–6Al–4V alloy (TiAlV, grade 5, Tokyo Titanium, Saitama, Japan), were used in this study as shown in table 1. Each material was used for the abraders or the substrates that corresponded to abraders, as shown in figures 1(b) and 2(a). 2.2. Making the abrader specimen
The cylindrical abrader specimen with one hemispherical end (10 mm in length and 5 mm in diameter with a radius of curvature of 5 mm) was prepared using a CAD/CAM 2
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(a)
P=10N
2.6. Statistical analysis
(b)
Abrader specimen
For the statistical analysis, an analysis of variance (ANOVA) was used for the wear volume in the wear test, followed by the Scheffe test for a post hoc comparison between groups.
S
ϕ=5mm
3. Results r=5mm
3.1. SEM observation of worn surfaces of abrader specimens (c)
Representative SEM images of worn surfaces of abrader specimens are shown in figures 3–5. When TZP was used as the abrader specimen (figure 3), comparatively small circles caused by the wear against TZP, CpTi and TiAlV substrates were observed under low magnification (left). Small grains that were originated by a row of material of the TZP were randomly observed under high magnification (right, arrows). When CpTi was used as the abrader specimen (figure 4), the diameter of worn surfaces was larger than that of TZP abraders (figure 3), and the wear morphologies were altered depending on the substrate specimens. In addition, the peripheral morphology of the abraded circles was different against between TZP substrate and CpTi substrate, that is, a very sharp periphery was recognized when TZP was used as the substrate specimen (arrow in figure 4 upper). On the contrary, when CpTi was used as the substrate specimen (arrow in figure 4 middle), irregular peripheries were observed, suggesting that some fraction of the substance had been pulled off. When TiAlV was used as the abrader specimen (figure 5), the wear morphologies had a similar tendency as the CpTi abrader specimen, although the size of the abraded circle was larger than with the CpTi abrader.
Substrate specimen S
V Figure 2. (a) Schematic illustrations of the wear test. (b) Wear area
(S) of the worn surface of the abrader specimen observed with SEM. (c) Wear volume (V) of the abrader specimen.
machine (DENTAL CAD/CAM GN-1, GC, Tokyo, Japan). These specimens were finally polished with 6 μm diamond pastes. 2.3. Making the substrate specimen
Disks of 13 mm in diameter and 1 mm in thickness were prepared as the substrate specimens, and these specimens were also polished with 6 μm diamond pastes. Both abrader and substrate specimens showed mirror-like surfaces with less than 0.1 μm of surface roughness (Ra). 2.4. Wear test and measurement of abrader wear volume
Wear tests were performed using an experimental wear simulator as shown in figure 1 according to previous studies [16, 17]. As seen in figure 2(a), each abrader specimen was moved back and forth on the substrate specimen over a distance of 3 mm for 30 000 cycles at a speed of 90 cycles min−1 and with a vertical load of 10 N. The test was carried out at room temperature with distilled water circulated through a water chamber in order to remove abrasion debris. After 30 000 cycles of wear test, the worn surfaces of abrader specimens were observed using a scanning microscope (SEM, SU-6600, HITACHI, Hitachi, Japan) as shown in figure 2(b). Subsequently, the wear area (S) of the abrader specimen was measured using an image analyzer (HDS-N1, HIROYA, Tokyo, Japan), and finally the wear volume (V) was calculated (figure 2(c)). Five specimens were used for each combination.
3.2. Wear volume of abrader specimens
The wear volume of abrader specimens against various substrate specimens is shown in figures 6 and 7. A significantly small wear area was recognized in TZP abraders compared to CpTi and TiAlV abraders. The wear behavior of substrate specimens showed the same tendency as those of abrader specimens besides the comparative large wear volume on the TiAlV abrader compared to the CpTi abrader against TZP substrates. Figure 6 shows the wear volume of TZP abrader specimens against various substrate specimens. A quite small wear volume was recognized against all substrates, and no significant difference in wear volume was recognized among the substrates. Figure 7 shows the wear volume of CpTi and TiAlV abrader specimens against various substrate specimens. The wear volume of CpTi and TiAlV abraders was approximately 20 times larger than that of the TZP abrader specimen (figure 6). The wear volume of CpTi and TiAlV abraders against the TZP substrate was significantly smaller than against CpTi and TiAlV substrates (P < 0.05). The wear volume of the TiAlV abrader specimen showed a large wear volume, the same as that of CpTi abraders. The wear volume of the TiAlV
2.5. Electron probe micro-analysis
A characteristic x-ray image analysis of the abrader specimens was performed to identify abraded particles that had adhered to the abrader specimens from the substrate specimens using an electron probe micro-analyzer (EPMA, JXA-8200, JEOL, Tokyo, Japan). 3
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Abrader : TZP Substrate: TZP
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
Abrader : TZP Substrate: CpTi
Abrader : TZP Substrate: TiAlV
Figure 3. Representative SEM images of the worn surfaces of abrader specimens (TZP) against various substrates.
Abrader : CpTi Substrate: TZP
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm
Abrader : CpTi Substrate: CpTi
Abrader : CpTi Substrate: TiAlV
Figure 4. Representative SEM images of the worn surfaces of abrader specimens (CpTi) against various substrates. 4
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Abrader : TiAlV Substrate: TZP
500 µm
50 µm
2 µm
500 µm
50 µm
2 µm 2 µm
500 µm
50 µm
2 µm
Abrader : TiAlV Substrate: CpTi
Abrader : TiAlV Substrate: TiAlV
Figure 5. Representative SEM images of the worn surfaces of abrader specimens (TiAlV) against various substrates.
Figure 6. Mean wear volume of the TZP abrader specimen against various substrate specimens. Standard deviations are shown by error bars. Identical letters indicate no significant difference (p > 0.05).
Figure 7. Mean wear volume of CpTi and TiAlV abrader specimens against various substrate specimens. Standard deviations are shown by error bars. Different letters indicate significant differences (p < 0.05).
abrader specimen against TZP substrate was significantly smaller than against CpTi and TiAlV substrates (P < 0.05). Table 2 shows multiple comparisons between groups on the wear volume of abrader specimens. The wear volumes of TZP abraders were significantly smaller than those of CpTi and TiAlV abraders. The wear volumes of CpTi and TiAlV abraders against TZP substrates were significantly smaller than those against CpTi and TiAlV substrates.
3.3. EPMA analysis
Characteristic x-ray images of the worn surface of the TZP abrader specimen against the CpTi substrate are shown in figure 8. An optical image of the TZP abrader specimen with black-colored staining after the wear test is also given in figure 8. Ti element was identified as the abraded particles that had adhered to abrader specimens from the CpTi substrate 5
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SEM
Optical image
1 mm
Figure 8. Characteristic x-ray images of the worn surface of the TZP abrader specimen against CpTi substrate. An optical image of the TZP abrader specimen with black-colored staining after the wear test is also given in the figure.
SEM
Figure 9. Characteristic x-ray images of the worn surface of the CpTi abrader specimen against the TiAlV substrate. 6
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Table 2. Multiple comparisons between groups on the wear volume of abrader specimens.
TZP/TZP TZP/CpTi TZP/TiAlV CpTi/TZP CpTi/CpTi CpTi/TiAlV TiAlV/TZP TiAlV/CpTi TiAlV/TiAlV TZP/TZP TZP/CpTi TZP/TiAlV CpTi/TZP CpTi/CpTi CpTi/TiAlV TiAlV/TZP TiAlV/CpTi TiAlV/TiAlV
–
– –
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
–
∗
– –
– –
∗
∗
∗
–
Abrader/substrate: –: NS, ∗ : P < 0.05, ∗∗ : P < 0.01.
(arrows). Figure 9 shows characteristic x-ray images of the worn surface of the CpTi abrader specimen against the TiAlV substrate. Elements of Al and V as well as Ti originating in the TiAlV substrate were detected adhering to the CpTi abrader specimen (arrows).
this study. The previous study revealed that the coefficient of friction between CpTi and CpTi showed a higher value than the CpTi/TZP combination, showing that a strong adhesive interaction had occurred on the CpTi/CpTi combination [16]. This is also supported by SEM observation of the worn surfaces on the CpTi/CpTi combination (figure 4, lower left, arrow), in which irregular shapes at the peripheral morphology had resulted from eroded particles from the substrate specimens adhering to the abrader specimens. Another underlying mechanism can be linked to the microstructure of TZP. The grain size of TZP is less than 0.5 μm with a homogenous distribution of crystal sizes and orientations. The grain size is an important parameter, which determines the surface topography and the tribological behavior of the materials. The fine grain size of TZP may lead to very smooth surfaces after polishing, leading to its lower susceptibility to the antagonist wear behavior. In the present study, a comparatively large wear volume on the TiAlV abrader specimen was shown compared to the CpTi abrader specimen against TZP substrates. Though the reason for these results is still unclear, the existence of a βphase in TiAlV in contrast to the homogeneous structure of CpTi is possibly responsible for the abrasion behavior. In the EPMA analysis, the Ti element was detected on the TZP abrader specimen when CpTi was used as the substrate. In addition, elements of Al and V originating in the TiAlV substrate were detected adhering to the CpTi abrader specimen, showing that the worn particles of CpTi and TiAlV had attached to the opposite specimens, which would represent a hazard to health due to the presence of metal particles. On the other hand, TZP was less susceptible to wear by either TZP or titanium. Thus, it would be better to carry out metal-free restoration using TZP in FDPs in order to successfully avoid any metal allergy originating from worn particles. In the present study, we used opaque (non-translucent) monolithic TZP that has been increasingly used as FDPs without veneering ceramics due to the reduced enamel wear compared to the porcelain antagonist. However, using a translucent TZP is more appropriate in the interest of aesthetic dental treatments. Further study is necessary to clarify the wear behavior using a translucent TZP instead of conventional opaque TZP that is used in this study. In this study, the wear behavior of the hemisphere abrader specimens was evaluated assuming the cusp abrasion on the FDPs. However, in order to elucidate the wear
4. Discussion The aim of this study was to estimate the wear behavior when TZP and titanium (Ti and Ti alloy) were used for the antagonist on FDPs using a two-body wear test. In this study, the wear behavior was evaluated by estimating the wear volume of the abrader specimen as the antagonist according to the previous reports [2–5]. Silva et al evaluated the volumetric loss of lithium disilicate glassceramic and TZP restorations in an in vivo study [18]. Kim et al also evaluated the wear volume of the abrader specimens using feldspathic porcelain cusp as well as the cusp of the premolar teeth in an in vitro study [2]. Accordingly, the use of an abrader specimen with a hemisphere is considered to be beneficial for evaluating the wear behavior between antagonists. The TZP abrader specimen showed quite a small wear volume against all substrate specimens in this study. In contrast, the wear volume of CpTi and TiAlV abrader specimens was approximately 20 times larger than that of the TZP abrader specimen against all substrate specimens. This is considered mainly to be due to the differences in hardness between the TZP and CpTi (TiAlV) that have a hardness (Hv) of 1356, 177 and 256 on TZP, CpTi and TiAlV, respectively [16]. This indicates that the operating mechanism of wear between the CpTi (TiAlV) and the TZP was abrasive wear due to the ultra-hardness of the TZP. In the present study, the wear volume of CpTi and TiAlV abrader specimens against the TZP substrate was significantly smaller than CpTi and TiAlV substrates although the hardness of TZP was much larger than those of CpTi and TiAlV. These phenomena can be explained by the adhesive wear mechanism [19]. Adhesive wear appears when two bodies slide over each other, or are pressed into one another, which enhances material transfer between the two surfaces. In the contact, fragments of one surface are pulled off and adhere to the other, due to the strong adhesive interaction between two surfaces with similar physicochemical properties such as metal to metal [20, 21]. This supposition is supported by the differences in the coefficient of friction between the materials used in 7
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¨ [5] Stawarczyk B, Ozcan M, Schmutz F, Trottmann A, Roos M and H¨ammerle C H F 2013 Two-body wear of monolithic, veneered and glazed zirconia and their corresponding enamel antagonists Acta. Odontol. Scand. 71 102–12 [6] Uo M, Asakura K, Yokoyama A, Ishikawa M, Tamura K, Totsuka Y, Akasaka T and Watari F 2007 X-ray absorption fine structure (XAFS) analysis of titanium-implanted soft tissue Dent. Mater. J. 26 268–73 [7] Egusa H, Ko N, Shimazu T and Yatani H 2008 Suspected association of an allergic reaction with titanium dental implants a clinical report J. Prosthet. Dent. 100 344–7 [8] Witt J D and Swann M 1991 Metal wear and tissue response in failed titanium alloy total hip replacements J. Bone Joint Surg. Br. 73 559–63 [9] Sicilia A, Cuesta S, Coma G, Arregui I, Guisasola C, Ruiz E and Maestro A 2008 Titanium allergy in dental implant patients a clinical study on 1500 consecutive patients Clin. Oral Implants Res. 19 823–35 [10] Seghi R R, Rosenstiel S F and Bauer P 1991 Abrasion of human enamel by different dental ceramics in vitro J. Dent. Res. 70 221–5 [11] Hacker C H, Wagner W C and Razzoog M E 1996 An in vitro investigation of the wear of enamel on porcelain and gold in saliva J. Prosthet. Dent. 75 14–7 [12] Metzler K T, Woody R D, Miller A W 3rd and Miller B H 1999 In vitro investigation of the wear of human enamel by dental porcelain J. Prosthet. Dent. 81 356–64 [13] Oonishi H, Ueno M, Okimatsu H and Amino H 1996 Investigation of the wear behavior of ceramic on ceramic combinations in total hip prosthesis Bioceramics: Proc. 9th Int. Symp. on Ceramics in Medicine vol 9 ed T Nakamura, F Miyaji and T Kokubo (Kldlington: Pergamon) pp 503–6 [14] Willmann G, Fruh H J and Pfaff H G 1996 Wear characteristics of sliding pairs of zirconia (Y-TZP) for hip endoprostheses Biomaterials 17 2157–62 [15] Clarke I C, Good V, Yamamoto K, Schroeder D and Gustafson A 2000 High wear resistance of alumina and zirconia ceramic combinations in THR wear study Trans. 6th World Biomaterials Congress Workshop#7 8 [16] Kanbara T, Yajima Y and Yoshinari M 2011 Wear behavior of tetragonal zirconia polycrystal versus titanium and titanium alloy Biomed. Mater. 6 021001 [17] Takarabe M 1982 An experimental study on sliding-induced abrasion of natural teeth and materials used for crowns Shikwa Gakuho 82 949–1004 in Japanese [18] Silva N R F A, Thompson Van P, Valverde G B, Paulo G, Powers J M, Farah J W and Esquivel-Upshaw J 2011 Comparative reliability analyses of zirconium oxide and lithium disilicate restorations in vitro and in vivo J. Am. Dent. Assoc. 142 (Suppl. 2) 4S–9S [19] Kato K 2002 Classification of wear mechanisms/models Proc. Inst. Mech. Eng. J 216 349–55 [20] Rodrigues D C, Urban R M, Jacobs J J and Gilbert J L 2009 In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants J. Biomed. Mater. Res. B 88 206–19 [21] Hallab N J, Messina C, Skipor A and Jacobs J J 2004 Differences in the fretting corrosion of metal-metal and ceramic-metal modular junctions of total hip replacements J. Orthop. Res. 22 250–9
phenomena, both contacting surfaces should be analyzed. The wear behavior of the substrate specimens was evaluated previously under the assumption of wear between TZP implant abutments and the titanium retaining screws on the dental implant treatment [16]. The results of the present study showed the same tendency as those of the previous study besides the comparative large wear volume on the TiAlV abrader compared to the CpTi abrader against TZP substrate in this study. Accordingly, it is confirmed by both previous and current studies that the operating mechanism of the wear for the CpTi/TZP combination was abrasive wear, whereas that of the CpTi/CpTi combination was adhesive wear. The two-body wear test was used to evaluate the wear behavior in this study. However, this test method does not truly simulate the clinical chewing situation. The wear behavior using the chewing simulator with thermo-mechanical loading and simultaneous thermal stress should be addressed [5]. In conclusion, the results in the present study showed that titanium FDPs (CpTi and TiAlV) are susceptible to wear against not only TZP but also CpTi and TiAlV in contrast to TZP FDPs. It should be noted that a wear volume of 0.53 mm3 on the CpTi abrader against the CpTi substrate is equivalent to 190 μm of cusp height reduction on the FDPs, which may influence the vertical dimension on the occlusion. Therefore, the results of this study may provide useful information to the clinical application of zirconia and titanium FDPs from the point of view of cusp abrasion. Acknowledgments This research was supported partly by an Oral Health Science Center Grant HRC7 from Tokyo Dental College and a Project for Private Universities: matching fund subsidy from MEXT (Ministry of Education, Culture, Sports, Science and Technology of Japan, 2006–2011). References [1] Sailer I, Feh´er A, Filser F, Gauckler L J, L¨uthy H and H¨ammerle C H F 2007 Five-year clinical results of zirconia frameworks for posterior fixed partial dentures Int. J. Prosthodont. 20 383–8 [2] Kim M J, Oh S H, Kim J H, Ju S W, Seo D G, Jun S H, Ahn J S and Ryu J J 2012 Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains J. Dent. 40 979–88 [3] Mitov G, Heintze S D, Walz S, Woll K, Muecklich F and Pospiech P 2012 Wear behavior of dental Y-TZP ceramic against natural enamel after different finishing procedures Dent. Mater. 28 909–18 [4] Preis V, Weiser F, Handel G and Rosentritt M 2013 Wear performance of monolithic dental ceramics with different surface treatments Quintessence Int. 44 393–405
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