journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Available online at www.sciencedirect.com
www.elsevier.com/locate/jmbbm
Research Paper
Two-body wear comparison of zirconia crown, gold crown, and enamel against zirconia Min-Seok Kwona, Sang-Yeob Ohb,n, Sung-Am Choa,nn a
Department of Prosthodontics, School of Dentistry, Kyungpook National University, South Korea School of Automotive Engineering, Kyungpook National University, South Korea
b
art i cle i nfo
ab st rac t
Article history:
Problem statement: Full zirconia crowns have recently been used for dental restorations
Received 19 September 2014
because of their mechanical properties. However, there is little information about their
Received in revised form
wear characteristics against enamel, gold, and full zirconia crowns.
6 November 2014
Purpose: The purpose of this study was to compare the wear rate of enamel, gold crowns,
Accepted 10 November 2014
and zirconia crowns against zirconia blocks using an in vitro wear test.
Available online 20 March 2015
Materials and methods: Upper specimens were divided into three groups: 10 enamels (group
Keywords:
1), 10 gold crowns (group 2, Type III gold), and 10 zirconia crowns (group 3, PrettausZirkon
Zirconia
9H, Zirkonzahn, Italy). Each of these specimens was wear tested against a zirconia block
Wear
(40 30 3 mm3) as a lower specimen (30 total zirconia blocks). Each specimen of the
Enamel
groups was abraded against the zirconia block for 600 cycles at 1 Hz with 15 mm front-to-
Fixed partial dentures
back movement on an abrading machine. Moreover, the load applied during the abrading test was 50 N, and the test was performed in a normal saline emulsion for 10 min. Threedimensional images were taken before and after the test, and the statistical analysis was performed using the Krushal–Wallis test and Mann–Whitney test (p ¼0.05). Results: The mean volume loss of group 1 was 0.47 mm3, while that of group 2 and group 3 was 0.01 mm3. Conclusion: The wear volume loss of enamels against zirconia was higher than that of gold and zirconia crowns. Moreover, according to this result, zirconia crowns are not recommended for heavy bruxers. & 2015 Elsevier Ltd. All rights reserved.
n Correspondence to: School of Automotive Engineering, Kyungpook National University, 2559 Gyeongsang-Daero, Sangju, Gyung-Buk 742-711, South Korea. Fax: þ82 54 530 1409. nn Correspondence to: College of Dentistry, Kyung-Pook National University, 2175 Dalgubeoldae-Ro, Jung-Gu, 700-412 Dae-Gu, South Korea. Fax: þ82 53 427 0778. E-mail addresses: [email protected] (S.-Y. Oh), [email protected], [email protected] (S.-A. Cho).
http://dx.doi.org/10.1016/j.jmbbm.2014.11.029 1751-6161/& 2015 Elsevier Ltd. All rights reserved.
22
1.
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Introduction
There are many diverse esthetic materials used in dental restorations. While metal–ceramic and all-ceramic restorations have been used in dental clinics for fixed partial dentures (Raigrodski, 2004) there are still some clinical limitations in using metal–ceramic and all-ceramic restorations. Ceramic breakage, gingival discoloration, allergic reactions, and false-teeth sensations are the primary deficiencies in the case of metal–ceramic restorations (Christensen, 2009). Though all-ceramic restorations have better esthetic points than metal–ceramic restorations, they still have limited use for posterior fixed partial dentures because of the low fracture resistance and low flexural strength. To improve the mechanical deficiencies, several newly developed ceramic materials and zirconia have been used for posterior fixed partial dentures (Raigrodski, 2004). To overcome these limitations, zirconia was introduced to use dental restorations because zirconia has a high fracture resistance via transformation toughening mechanisms and is a bio-compatible material (Piconi and Maccauro, 1999). Initially, zirconia could be used as a coping material because of its opacity and could be useful for highly loaded restorations (Tinschert et al., 2001). Porcelain layered on the zicronia coping is known as a veneering ceramic, which has the potential to withstand occlusal forces applied in the posterior region and can represent alternatives for replacing metal ceramics (Att et al., 2007; Conrad et al., 2007). Despite the good results of veneering ceramic (Att et al., 2007), veneering ceramic still suffers from chipping of the layering ceramic (Christensen, 2008; Christensen and Ploeger, 2010; Ashkanani et al., 2008). However, full zirconia crowns showed higher strength, easier laboratory procedures, and no chipping compared to the zirconia ceramic restorations (Jang et al., 2011). Several experiments about enamel wear against zirconia were reported because the wear rate is one of the important
requisites for restoration material (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012; Janyavula et al., 2013). According to these reports, full zirconia was less abrasive than porcelain (Jung et al., 2010; Mitov et al., 2012). Concerning the wear test methods, there were no reports on simple reciprocal enamel wear against zirconia. Therefore, the purpose of this study was to compare the simple reciprocal wear rate of enamel, gold crowns, and full zirconia crowns against zirconia blocks using an in vitro wear test. The null hypothesis of this study was that wear quantity against zirconia would be same regardless of experimental subjects.
2.
Materials and methods
2.1.
Lower specimens
Thirty rectangular zirconia specimens (40 30 3 mm3) were prepared with zirconia blocks according to the manufacturer instructions (Prettaus Zirkon 9H,Zirkonzahn,Italy) and bonded in acrylic resin mold (58 38 3.5 mm3) with resin cement (RelyX U200, 3M ESPE, Germany) (Fig. 1C). The zirconia specimens had no glazing process, and the surfaces were polished first with zirconia polishing kits (Magic KIT Zir, Sungwon Dental, Korea) and then high polished by a cotton wheel with polishing compound (Legabril Diamond, Fegramed GmBH, Germany). Then lower specimens were engaged with screws at the wear test machine (Fig. 2).
2.2.
Upper specimens
2.2.1.
Group 1 (enamel specimens)
Ten enamel specimens were obtained from the functional cusps of unrestored premolars that had been recently extracted. Each specimen was trimmed with high-speed diamond bur before it was embedded in a titanium holder (Fig. 1A).
Fig. 1 – (A) Three specimens: zirconia crown, gold crown, and tooth. (B) A zirconia crown is cemented in implant abutment analogs before being embedding in titanium holders with autopolymerized resin. (C) Lower specimen: the rectangular zirconia block was attached to an acrylic plate with resin cement. (D) Schematic diagram of the wear test.
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
23
Fig. 2 – Wear test machine. (A) Lower specimen. (B) Position of lower and upper specimen during the wear test. Testing conditions: 50 N load, 1.5-cm back-and forth-movement, 1 Hz, 600 cycles.
2.2.2.
Group 2 (gold crown specimens)
Ten lower premolar shaped gold crowns were made with type III gold. Ten abutment replicas (CAN45SL, Dentium, Korea) were used with laboratory dies, and the gold crowns were cemented to the abutment replicas with resin cement (RelyX U200, 3M ESPE, Germany) (Fig. 1A).
2.2.3.
Group 3 (zirconia crown specimens)
Ten premolar-shaped zirconia crowns were made with Prettau (Prettaus Zirkon 9H, Zirkonzahn, Italy); they were highly polished without glazing. Ten abutment replicas (CAN45SL, Dentium, Korea) were used with laboratory dies, and the zirconia crowns were cemented to the abutment replicas with resin cement (RelyX U200, 3M ESPE, Germany) (Fig. 1B).
2.3.
Titanium holders
The upper specimens were connected to the wear-test machine using titanium holders (Fig. 1B).The outer diameter and length of the titanium holders was 8 mm and 20 mm, respectively.The inner diameter and hole depth of the titanium holders was 7 mm and 17 mm, respectively. The enamel specimens and the cemented components of the zirconia and gold crown specimens were embedded in the titanium holders with acrylic resin (Ostron,GC Cooperation, Tokyo, Japan).
2.4.
Wear test
The wear test was performed with a wear-test machine (TE77 Auto, Plint Tribology, England). The upper specimens were fixed in the upper specimen holder, and the lower specimens were fixed in the lower specimen housing with screws (Fig. 2). The test was run for 600 cycles at 1 Hz under 50 N load, where the length of the back and forth movement was 15 mm. All tests were performed for 10 min at room temperature, and normal saline was applied in the lower specimen housing (Fig. 1D).
2.5.
Volume loss measurement
All upper specimens were scanned before and after the test using the Ceramill CAD/CAM system (Amanngirrbach
Corporation, Austria). The volume loss of upper specimens was calculated with image analysis software (SolidWorks 2012, DS SolidWorks, USA), and the dimension of wear faces of upper specimens was calculated with image analysis software (Image J, Wayne Rasband, USA). Representative lower specimens from each test group were examined with a scanning electron microscope (SEM; S-4300, Hitachi, Japan) at both 40 and 300 magnification.
2.6.
Statistical analysis
The data was statistically analyzed using statistical software (IMB SPSS 20.0 for Windows, SPSS Inc., USA). The Kruskal– Wallis test, which is a one-way analyses of variance (ANOVA) test,was used to determine statistically significant differences,while the differences among groups were analyzed using the Mann–Whitney test (p40.05).
3.
Results
The wear rate of group 1 was much higher than that of group 2 and group 3.The volumetric loss images of the upper specimens are presented in Fig. 3, and the volumetric loss images of the upper specimens are presented in Fig. 4.There were significant differences between group 1 and group 2 and between group 1 and group 3; however, there was no significant difference between group 2 and group 3. The mean enamel volume loss of group 1 was 0.47 mm3, and the mean volume loss of group 2 and group 3 was 0.01 mm3(Fig. 5). The mean wear dimensions of group 1, group 2, and group 3 were 3.52 mm2, 0.58 mm2, and 0.47 mm2. The SEM images of the tested lower specimens at 40 and 300 magnifications are presented in Fig. 6. The wear track line appeared only on the lower specimen of zirconia group and there were some fragments found at the lower specimen of enamel and gold groups. The results of Kruskal–Wallis test and Mann–Whitney test are summarized in Table 1.
4.
Discussion
The purpose of this study was to evaluate the simple reciprocal wear rate of enamel opposing monolithic zirconia
24
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Fig. 3 – Height change of specimensbefore (left) and after (right) for A, enamel, B, gold crown, and C, zirconia crown.
and the enamel wear opposing the monolithic zirconia was much higher than that of gold crowns or zirconia crowns. Therefore, the null hypothesis was rejected. Many investigations of dental restoration materials have been performed for clinical use. Most investigation tested the fracture strength and wear rate because dental restoration materials must endure occlusal forces and have similar wear rate as natural enamel (Tinschert et al., 2001; Att et al., 2007; Ashkanani et al., 2008; Jang et al., 2011; Jung et al., 2010; Mitov et al., 2012; Manicone et al., 2007; Oh et al., 2002; Heintze et al., 2008; Albashaireh et al., 2010; Jagger and Harrison, 1994; Wang et al., 2012; Seghi et al., 1991; Hudson et al., 1995; Jacobi et al., 1991; Kadokawa et al., 2006; Elmaria et al., 2006).
Att et al. (2007) reported that yttria tetragonal zirconia polycrystal (Y-TZP) all-ceramic fixed partial dentures (FPDs) had the potential to withstand physiological occlusal forces applied in the posterior region and could be alternatives for replacing porcelain-fused-to-metal (PFM) restorations (Tinschert et al., 2001). Some authors reported that the wear rate of zirconia is lower than that of porcelain and similar to that of natural enamel (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012). The experimental conditions of these investigations are variable depending on the applied load, loading methods, cycling number, wear distance, and the application of the two-body or three-body test (Jung et al., 2010; Mitov et al., 2012; Kim et al.,
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
25
Fig. 4 – Volumetric change images of specimens for A, enamel, B, gold crown, and C, zirconia crown.
Fig.5 – Mean volume loss of each group. 2012; Albashaireh et al., 2010; Jagger and Harrison, 1994; Wang et al., 2012; Seghi et al., 1991; Hudson et al., 1995; Jacobi et al., 1991; Kadokawa et al., 2006). The applied load of other researches are vary from 0.65 N to 75 N (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012; Heintze et al., 2008; Kadokawa et al., 2006; Elmaria et al., 2006; Krejci et al., 1993; Krejci et al., 1994) and we were supposed to use 49 N load because it was the most used load in wear
researches. But it is possible to set five multiple N through our wear test machine and we chose approximate value 50 N which belongs to masticatory load range (Att et al., 2007). At the beginning of our experiments, PFMs were included in one of the test groups. However, it was impossible to test PFMs due to severe porcelain fracture in our experimental conditions. For this reason, PFMs were excluded from our study. We performed several earlier tests to select the cycling number with tooth and zirconia block. We selected the cycling number when vertical height loss was 0.5 mm because the wear tendency of enamel was beyond our expectation. Various factors cause tooth wear and these factors consist of surface finish, physical factors, microstructural factors, and chemical degradation (Oh et al., 2002). Regarding surface finish, in the case of zirconia and porcelain, polished surfaces showed less enamel wear than glazed surfaces (Heintze et al., 2008; Albashaireh et al., 2010; Jagger and Harrison, 1994; Wang et al., 2012; Sabrah et al., 2013). The physical factors include hardness, frictional resistance, and fracture toughness (Oh et al., 2002).
26
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Fig. 6 – The SEM images of the lower specimens against three groups at 40 magnification (left) and 300 magnification (right). (A and B) Lower specimen surface of the enamel group. (C and D) Lower specimen surface of the gold group. (E and F) Lower specimen surface of the zirconia group. White arrows indicate the wear track line. Table 1 – Mean value and standard deviations of the wear dimension and volume loss of each group.
Wear face dimension (mm2) Volume loss(mm3)
Group 1 (n¼ 10)
Group 2 (n ¼10)
Group 3 (n ¼10)
X2
p-Value
3.5971.04a 0.4770.23a
0.5970.59b 0.0170.01b
0.4770.07b 0.0170.25b
23.49 20.20
o0.001n o0.001n
ab n
Mann–Whitney test. Kruskal–Wallis test.
In the case of ceramics, harder materials were more resistant to surface scratching and retained their polished surface for a long time. Thus, for porcelain and zirconia, there was less enamel wear in highly polished surfaces than in glazed or rough surface (Seghi et al., 1991). For these reasons, we polished the zirconia crowns and lower zirconia block with zirconia polishing kits. In our experiment, the enamel wear opposing the monolithic zirconia was much higher than that of gold crowns or zirconia crowns. This result was contrary to other results that
the wear of the polished zirconia is similar to that of natural enamel (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012). The sliding distances of other studies are shorter and the distances vary from 0.3 mm to 6.0 mm under similar load (Jung et al., 2010; Hudson et al., 1995), whereas the sliding distance of our study was 15 mm but the cycle number is lower than others. We believe the greater sliding distance affected the wear of enamel and the hardness and the roughness of the polished zirconia also would have affected the result (Seghi et al., 1991).
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
However, some results of our experiment were coincident to other studies. The low wear rate of zirconia opposing zirconia and the low wear rate of gold crowns were both similar to other studies (Albashaireh et al., 2010; Seghi et al., 1991; Jacobi et al., 1991). The reason that gold crowns show less wear was likely due to the ductility of the gold alloy (Kadokawa et al., 2006). Some authors reported that gold is a good material for restorations other than esthetic restorations because of its wear rate against enamel (Jacobi et al., 1991). In the SEM images, the wear track line was not clearly identified, and some fragments caused by wear test were observed in the lower specimens of the enamel and gold crown group (group 2). No remarkable differences were observed between polished and wear test areas. However, longitudinal wear track lines and surface deformations were observed in the lower specimen of the zirconia crown group. These results indicate that zirconia maintains its surface when it opposes both enamel and gold restorations. However, when it opposes hard materials like zirconia, its surface is abraded and deformed. According to many reports on bite force, the maximal bite force ranges from 17 N up to 698 N (Gibbs et al., 1981; Anderson, 1956; Morneburg and Proschel, 2002; Abreu et al., 2014; Owais et al., 2013; Helkimo et al., 1977; Van Der Bilt et al., 2008; Serra and Manns, 2013)and Gibbs et al. (1981) reported that the bite force of chewing exceeded 260 N. However, we applied a 50 N bite force in our experiments. When zirconia crowns were used for restorations, loads over 50 N would be applied to its counterpart. If monolithic crowns opposing enamel were used for heavy bruxers or patients that habitually clench their teeth, the opposing teeth would be severely abraded because of higher bite force (Stober et al., 2014). Kadokawa et al. (2006) reported that the mean wear values of the porcelain in the three-body condition were significantly smaller than those in the two-body condition when porcelain opposed composite resin or enamel, regardless of the porcelain surface condition. Therefore, we will perform a three-body condition test of our experiment with glycerin medium in the future. Jang et al. (2011) reported that zirconia crowns with 0.5 mm occlusal thickness showed similar strength to PFM and that zirconia crowns over 2.0 mm thickness had the fracture strength to endure occlusal force by inhibiting crack growth and propagation. This means monolithic zirconia is an adequate restoration material when tooth-colored restorations are needed for those who lack occlusal clearance. To restore posterior missing teeth with monolithic zirconia, we should consider an occlusal scheme of a patient and opposing tooth. If a patient has a canine protected occlusion and opposing gold crown, monolithic zirconia crowns and bridge will be good choices for posterior fixed partial dentures. For the long-term success of monolithic zirconia, further investigation regarding the low-temperature degradation of zirconia is required. This low-temperature degradation is aging by slow surface transformation to the stable monoclinic phase in the presence of water or water vapor, which decreases the
27
mechanical properties of zirconia and increases the surface roughness (Chevalier, 2006; Christel et al., 1989).
5.
Conclusion
We report the following results in this study: 1. In a simple reciprocation wear-test against zirconia, enamels were more abraded than gold or zirconia crowns. 2. The wear of gold crowns was not significantly different with that of zirconia crowns. This shows that gold crown is a good restoration option for non-esthetic usage. 3. Zirconia crowns are not recommended for heavy bruxers.
Acknowledgments This research was supported by the Kyung-Pook National University ResearchFund, (Grant no. 2013).
r e f e r e nc e s
Abreu, Roge´rio Alexandre Modesto de, M.D., Pereira, Furtado, F., Prado, G.P.R., Junior, W.M., Ferreira, L.M., 2014. Masticatory efficiency and bite force in individuals with normal occlusion. Arch. Oral Biol. 59, 1065–1074. Albashaireh, Z.S., Ghazal, M., Kern, M., 2010. Two-body wear of different ceramic materials opposed to zirconia ceramic. J. Prosthet. Dent. 104, 105–113. Anderson, D.J., 1956. Measurement of stress in mastication. I. J. Dent. Res. 35, 664–670. Ashkanani, H.M., Raigrodski, A.J., Flinn, B.D., Heindl, H., Mancl, L.A., 2008. Flexural and shear strengths of ZrO2 and a high-noble alloy bonded to their corresponding porcelains. J. Prosthet. Dent. 100, 274–284. Att, W., Stamouli, K., Gerds, T., Rudolf Strub, J., 2007. Fracture resistance of different zirconium dioxide three-unit allceramic fixed partial dentures. Acta Odontol. 65, 14–21. Chevalier, J., 2006. What future for zirconia as a biomaterial? Biomaterials 27, 535–543. Christel, P., Meunier, A., Heller, M., Torre, J., Peille, C., 1989. Mechanical properties and short-term in vivo evaluation of yttrium-oxide-partially-stabilized zirconia. J. Biomed. Mater. Res. 23, 45–61. Christensen, G., 2008. PFM vs. zirconia restorations—how are they comparing clinically. Clin. Rep. 1, 1–2. Christensen, G., 2009. Porcelain-fused-to-metal versus zirconiabased ceramic restorations, 2009. J. Am. Dent. Assoc. 140, 1036–1039. Christensen, R.P., Ploeger, B.J., 2010. A clinical comparison of zirconia, metal and alumina fixed-prosthesis frameworks veneered with layered or pressed ceramic: a three-year report. J. Am. Dent. Assoc. 141, 1317–1329. Conrad, H.J., Seong, W., Pesun, I.J., 2007. Current ceramic materials and systems with clinical recommendations: a systematic review. J. Prosthet. Dent. 98, 389–404. Elmaria, A., Goldstein, G., Vijayaraghavan, T., Legeros, R.Z., Hittelman, E.L., 2006. An evaluation of wear when enamel is opposed by various ceramic materials and gold. J. Prosthet. Dent. 96, 345–353. Gibbs, C.H., Mahan, P.E., Lundeen, H.C., Brehnan, K., Walsh, E.K., Holbrook, W.B., 1981. Occlusal forces during chewing and
28
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
swallowing as measured by sound transmission. J. Prosthet. Dent. 46, 443–449. Heintze, S., Cavalleri, A., Forjanic, M., Zellweger, G., Rousson, V., 2008. Wear of ceramic and antagonist—a systematic evaluation of influencing factors in vitro. Dent. Mater. 24, 433–449. Helkimo, E., Carlsson, G.E., Helkimo, M., 1977. Bite force and state of dentition. Acta Odontol. 35, 297–303. Hudson, J.D., Goldstein, G.R., Georgescu, M., 1995. Enamel wear caused by three different restorative materials. J. Prosthet. Dent. 74, 647–654. Jacobi, R., Shillingburg Jr., H.T., Duncanson Jr., M.G., 1991. A comparison of the abrasiveness of six ceramic surfaces and gold. J. Prosthet. Dent. 66, 303–309. Jagger, D., Harrison, A., 1994. An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel. J. Prosthet. Dent. 72, 320–323. Jang, G., Kim, H., Choe, H., Son, M., 2011. Fracture strength and mechanism of dental ceramic crown with zirconia thickness. Procedia Eng. 10, 1556–1560. Janyavula, S., Lawson, N., Cakir, D., Beck, P., Ramp, L.C., Burgess, J.O., 2013. The wear of polished and glazed zirconia against enamel. J. Prosthet. Dent. 109, 22–29. Jung, Y., Lee, J., Choi, Y., Ahn, J., Shin, S., Huh, J., 2010. A study on the in-vitro wear of the natural tooth structure by opposing zirconia or dental porcelain. J. Adv. Prosthodont. 2, 111–115. Kadokawa, A., Suzuki, S., Tanaka, T., 2006. Wear evaluation of porcelain opposing gold, composite resin, and enamel. J. Prosthet. Dent. 96, 258–265. Kim, M., Oh, S., Kim, J., Ju, S., Seo, D., Jun, S., et al., 2012. Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains. J. Dent. 40, 979–988. Krejci, I., Lutz, F., Reimer, M., Heinzmann, J., 1993. Wear of ceramic inlays, their enamel antagonists, and luting cements. J. Prosthet. Dent. 69, 425–430. Krejci, I., Mueller, E., Lutz, F., 1994. Effects of thermocycling and occlusal force on adhesive composite crowns. J. Dent. Res. 73, 1228–1232. Manicone, P.F., Rossi Iommetti, P., Raffaelli, L., 2007. An overview of zirconia ceramics: basic properties and clinical applications. J. Dent. 35, 819–826.
Mitov, G., Heintze, S.D., Walz, S., Woll, K., Muecklich, F., Pospiech, P., 2012. Wear behavior of dental Y-TZP ceramic against natural enamel after different finishing procedures. Dent. Mater. 28, 909–918. Morneburg, T.R., Proschel, P.A., 2002. Measurement of masticatory forces and implant loads: a methodologic clinical study. Int. J. Prosthodont. 15, 20–27. Oh, W., DeLong, R., Anusavice, K.J., 2002. Factors affecting enamel and ceramic wear: a literature review. J. Prosthet. Dent. 87, 451–459. Owais, A.I., Shaweesh, M., Abu Alhaija, E.S., 2013. Maximum occusal bite force for children in different dentition stages. Eur. J. Orthod. 35, 427–433. Piconi, C., Maccauro, G., 1999. Zirconia as a ceramic biomaterial. Biomaterials 20, 1–25. Raigrodski, A.J., 2004. Contemporary materials and technologies for all-ceramic fixed partial dentures: a review of the literature. J. Prosthet. Dent. 92, 557–562. Sabrah, A.H., Cook, N.B., Luangruangrong, P., Hara, A.T., Bottino, M.C., 2013. Full-contour Y-TZP ceramic surface roughness effect on synthetic hydroxyapatite wear. Dent. Mater. 29, 666–673. Seghi, R.R., Rosenstiel, S.F., Bauer, P., 1991. Abrasion of human enamel by different dental ceramics in vitro. J. Dent. Res. 70, 221–225. Serra, C., Manns, A., 2013. Bite force measurements with hard and soft bite surfaces. J. Oral Rehabil. 40, 563–568. Stober, T., Bermejo, J., Rammelsberg, P., Schmitter, M., 2014. Enamel wear caused by monolithic zirconia crowns after 6 months of clinical use. J. Oral Rehabil. 41, 314–322. Tinschert, J., Natt, G., Mautsch, W., Augthun, M., Spiekermann, H., 2001. Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study. Int. J. Prosthodont. 14, 231–238. Van Der Bilt, A., Tekamp, A., Van Der Glas, H., Abbink, J., 2008. Bite force and electromyograpy during maximum unilateral and bilateral clenching. Eur. J. Oral Sci. 116, 217–222. Wang, L., Liu, Y., Si, W., Feng, H., Tao, Y., Ma, Z., 2012. Friction and wear behaviors of dental ceramics against natural tooth enamel. J. Eur. Ceram. Soc. 32, 2599–2606.
Available online at www.sciencedirect.com
www.elsevier.com/locate/jmbbm
Research Paper
Two-body wear comparison of zirconia crown, gold crown, and enamel against zirconia Min-Seok Kwona, Sang-Yeob Ohb,n, Sung-Am Choa,nn a
Department of Prosthodontics, School of Dentistry, Kyungpook National University, South Korea School of Automotive Engineering, Kyungpook National University, South Korea
b
art i cle i nfo
ab st rac t
Article history:
Problem statement: Full zirconia crowns have recently been used for dental restorations
Received 19 September 2014
because of their mechanical properties. However, there is little information about their
Received in revised form
wear characteristics against enamel, gold, and full zirconia crowns.
6 November 2014
Purpose: The purpose of this study was to compare the wear rate of enamel, gold crowns,
Accepted 10 November 2014
and zirconia crowns against zirconia blocks using an in vitro wear test.
Available online 20 March 2015
Materials and methods: Upper specimens were divided into three groups: 10 enamels (group
Keywords:
1), 10 gold crowns (group 2, Type III gold), and 10 zirconia crowns (group 3, PrettausZirkon
Zirconia
9H, Zirkonzahn, Italy). Each of these specimens was wear tested against a zirconia block
Wear
(40 30 3 mm3) as a lower specimen (30 total zirconia blocks). Each specimen of the
Enamel
groups was abraded against the zirconia block for 600 cycles at 1 Hz with 15 mm front-to-
Fixed partial dentures
back movement on an abrading machine. Moreover, the load applied during the abrading test was 50 N, and the test was performed in a normal saline emulsion for 10 min. Threedimensional images were taken before and after the test, and the statistical analysis was performed using the Krushal–Wallis test and Mann–Whitney test (p ¼0.05). Results: The mean volume loss of group 1 was 0.47 mm3, while that of group 2 and group 3 was 0.01 mm3. Conclusion: The wear volume loss of enamels against zirconia was higher than that of gold and zirconia crowns. Moreover, according to this result, zirconia crowns are not recommended for heavy bruxers. & 2015 Elsevier Ltd. All rights reserved.
n Correspondence to: School of Automotive Engineering, Kyungpook National University, 2559 Gyeongsang-Daero, Sangju, Gyung-Buk 742-711, South Korea. Fax: þ82 54 530 1409. nn Correspondence to: College of Dentistry, Kyung-Pook National University, 2175 Dalgubeoldae-Ro, Jung-Gu, 700-412 Dae-Gu, South Korea. Fax: þ82 53 427 0778. E-mail addresses: [email protected] (S.-Y. Oh), [email protected], [email protected] (S.-A. Cho).
http://dx.doi.org/10.1016/j.jmbbm.2014.11.029 1751-6161/& 2015 Elsevier Ltd. All rights reserved.
22
1.
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Introduction
There are many diverse esthetic materials used in dental restorations. While metal–ceramic and all-ceramic restorations have been used in dental clinics for fixed partial dentures (Raigrodski, 2004) there are still some clinical limitations in using metal–ceramic and all-ceramic restorations. Ceramic breakage, gingival discoloration, allergic reactions, and false-teeth sensations are the primary deficiencies in the case of metal–ceramic restorations (Christensen, 2009). Though all-ceramic restorations have better esthetic points than metal–ceramic restorations, they still have limited use for posterior fixed partial dentures because of the low fracture resistance and low flexural strength. To improve the mechanical deficiencies, several newly developed ceramic materials and zirconia have been used for posterior fixed partial dentures (Raigrodski, 2004). To overcome these limitations, zirconia was introduced to use dental restorations because zirconia has a high fracture resistance via transformation toughening mechanisms and is a bio-compatible material (Piconi and Maccauro, 1999). Initially, zirconia could be used as a coping material because of its opacity and could be useful for highly loaded restorations (Tinschert et al., 2001). Porcelain layered on the zicronia coping is known as a veneering ceramic, which has the potential to withstand occlusal forces applied in the posterior region and can represent alternatives for replacing metal ceramics (Att et al., 2007; Conrad et al., 2007). Despite the good results of veneering ceramic (Att et al., 2007), veneering ceramic still suffers from chipping of the layering ceramic (Christensen, 2008; Christensen and Ploeger, 2010; Ashkanani et al., 2008). However, full zirconia crowns showed higher strength, easier laboratory procedures, and no chipping compared to the zirconia ceramic restorations (Jang et al., 2011). Several experiments about enamel wear against zirconia were reported because the wear rate is one of the important
requisites for restoration material (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012; Janyavula et al., 2013). According to these reports, full zirconia was less abrasive than porcelain (Jung et al., 2010; Mitov et al., 2012). Concerning the wear test methods, there were no reports on simple reciprocal enamel wear against zirconia. Therefore, the purpose of this study was to compare the simple reciprocal wear rate of enamel, gold crowns, and full zirconia crowns against zirconia blocks using an in vitro wear test. The null hypothesis of this study was that wear quantity against zirconia would be same regardless of experimental subjects.
2.
Materials and methods
2.1.
Lower specimens
Thirty rectangular zirconia specimens (40 30 3 mm3) were prepared with zirconia blocks according to the manufacturer instructions (Prettaus Zirkon 9H,Zirkonzahn,Italy) and bonded in acrylic resin mold (58 38 3.5 mm3) with resin cement (RelyX U200, 3M ESPE, Germany) (Fig. 1C). The zirconia specimens had no glazing process, and the surfaces were polished first with zirconia polishing kits (Magic KIT Zir, Sungwon Dental, Korea) and then high polished by a cotton wheel with polishing compound (Legabril Diamond, Fegramed GmBH, Germany). Then lower specimens were engaged with screws at the wear test machine (Fig. 2).
2.2.
Upper specimens
2.2.1.
Group 1 (enamel specimens)
Ten enamel specimens were obtained from the functional cusps of unrestored premolars that had been recently extracted. Each specimen was trimmed with high-speed diamond bur before it was embedded in a titanium holder (Fig. 1A).
Fig. 1 – (A) Three specimens: zirconia crown, gold crown, and tooth. (B) A zirconia crown is cemented in implant abutment analogs before being embedding in titanium holders with autopolymerized resin. (C) Lower specimen: the rectangular zirconia block was attached to an acrylic plate with resin cement. (D) Schematic diagram of the wear test.
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
23
Fig. 2 – Wear test machine. (A) Lower specimen. (B) Position of lower and upper specimen during the wear test. Testing conditions: 50 N load, 1.5-cm back-and forth-movement, 1 Hz, 600 cycles.
2.2.2.
Group 2 (gold crown specimens)
Ten lower premolar shaped gold crowns were made with type III gold. Ten abutment replicas (CAN45SL, Dentium, Korea) were used with laboratory dies, and the gold crowns were cemented to the abutment replicas with resin cement (RelyX U200, 3M ESPE, Germany) (Fig. 1A).
2.2.3.
Group 3 (zirconia crown specimens)
Ten premolar-shaped zirconia crowns were made with Prettau (Prettaus Zirkon 9H, Zirkonzahn, Italy); they were highly polished without glazing. Ten abutment replicas (CAN45SL, Dentium, Korea) were used with laboratory dies, and the zirconia crowns were cemented to the abutment replicas with resin cement (RelyX U200, 3M ESPE, Germany) (Fig. 1B).
2.3.
Titanium holders
The upper specimens were connected to the wear-test machine using titanium holders (Fig. 1B).The outer diameter and length of the titanium holders was 8 mm and 20 mm, respectively.The inner diameter and hole depth of the titanium holders was 7 mm and 17 mm, respectively. The enamel specimens and the cemented components of the zirconia and gold crown specimens were embedded in the titanium holders with acrylic resin (Ostron,GC Cooperation, Tokyo, Japan).
2.4.
Wear test
The wear test was performed with a wear-test machine (TE77 Auto, Plint Tribology, England). The upper specimens were fixed in the upper specimen holder, and the lower specimens were fixed in the lower specimen housing with screws (Fig. 2). The test was run for 600 cycles at 1 Hz under 50 N load, where the length of the back and forth movement was 15 mm. All tests were performed for 10 min at room temperature, and normal saline was applied in the lower specimen housing (Fig. 1D).
2.5.
Volume loss measurement
All upper specimens were scanned before and after the test using the Ceramill CAD/CAM system (Amanngirrbach
Corporation, Austria). The volume loss of upper specimens was calculated with image analysis software (SolidWorks 2012, DS SolidWorks, USA), and the dimension of wear faces of upper specimens was calculated with image analysis software (Image J, Wayne Rasband, USA). Representative lower specimens from each test group were examined with a scanning electron microscope (SEM; S-4300, Hitachi, Japan) at both 40 and 300 magnification.
2.6.
Statistical analysis
The data was statistically analyzed using statistical software (IMB SPSS 20.0 for Windows, SPSS Inc., USA). The Kruskal– Wallis test, which is a one-way analyses of variance (ANOVA) test,was used to determine statistically significant differences,while the differences among groups were analyzed using the Mann–Whitney test (p40.05).
3.
Results
The wear rate of group 1 was much higher than that of group 2 and group 3.The volumetric loss images of the upper specimens are presented in Fig. 3, and the volumetric loss images of the upper specimens are presented in Fig. 4.There were significant differences between group 1 and group 2 and between group 1 and group 3; however, there was no significant difference between group 2 and group 3. The mean enamel volume loss of group 1 was 0.47 mm3, and the mean volume loss of group 2 and group 3 was 0.01 mm3(Fig. 5). The mean wear dimensions of group 1, group 2, and group 3 were 3.52 mm2, 0.58 mm2, and 0.47 mm2. The SEM images of the tested lower specimens at 40 and 300 magnifications are presented in Fig. 6. The wear track line appeared only on the lower specimen of zirconia group and there were some fragments found at the lower specimen of enamel and gold groups. The results of Kruskal–Wallis test and Mann–Whitney test are summarized in Table 1.
4.
Discussion
The purpose of this study was to evaluate the simple reciprocal wear rate of enamel opposing monolithic zirconia
24
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Fig. 3 – Height change of specimensbefore (left) and after (right) for A, enamel, B, gold crown, and C, zirconia crown.
and the enamel wear opposing the monolithic zirconia was much higher than that of gold crowns or zirconia crowns. Therefore, the null hypothesis was rejected. Many investigations of dental restoration materials have been performed for clinical use. Most investigation tested the fracture strength and wear rate because dental restoration materials must endure occlusal forces and have similar wear rate as natural enamel (Tinschert et al., 2001; Att et al., 2007; Ashkanani et al., 2008; Jang et al., 2011; Jung et al., 2010; Mitov et al., 2012; Manicone et al., 2007; Oh et al., 2002; Heintze et al., 2008; Albashaireh et al., 2010; Jagger and Harrison, 1994; Wang et al., 2012; Seghi et al., 1991; Hudson et al., 1995; Jacobi et al., 1991; Kadokawa et al., 2006; Elmaria et al., 2006).
Att et al. (2007) reported that yttria tetragonal zirconia polycrystal (Y-TZP) all-ceramic fixed partial dentures (FPDs) had the potential to withstand physiological occlusal forces applied in the posterior region and could be alternatives for replacing porcelain-fused-to-metal (PFM) restorations (Tinschert et al., 2001). Some authors reported that the wear rate of zirconia is lower than that of porcelain and similar to that of natural enamel (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012). The experimental conditions of these investigations are variable depending on the applied load, loading methods, cycling number, wear distance, and the application of the two-body or three-body test (Jung et al., 2010; Mitov et al., 2012; Kim et al.,
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
25
Fig. 4 – Volumetric change images of specimens for A, enamel, B, gold crown, and C, zirconia crown.
Fig.5 – Mean volume loss of each group. 2012; Albashaireh et al., 2010; Jagger and Harrison, 1994; Wang et al., 2012; Seghi et al., 1991; Hudson et al., 1995; Jacobi et al., 1991; Kadokawa et al., 2006). The applied load of other researches are vary from 0.65 N to 75 N (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012; Heintze et al., 2008; Kadokawa et al., 2006; Elmaria et al., 2006; Krejci et al., 1993; Krejci et al., 1994) and we were supposed to use 49 N load because it was the most used load in wear
researches. But it is possible to set five multiple N through our wear test machine and we chose approximate value 50 N which belongs to masticatory load range (Att et al., 2007). At the beginning of our experiments, PFMs were included in one of the test groups. However, it was impossible to test PFMs due to severe porcelain fracture in our experimental conditions. For this reason, PFMs were excluded from our study. We performed several earlier tests to select the cycling number with tooth and zirconia block. We selected the cycling number when vertical height loss was 0.5 mm because the wear tendency of enamel was beyond our expectation. Various factors cause tooth wear and these factors consist of surface finish, physical factors, microstructural factors, and chemical degradation (Oh et al., 2002). Regarding surface finish, in the case of zirconia and porcelain, polished surfaces showed less enamel wear than glazed surfaces (Heintze et al., 2008; Albashaireh et al., 2010; Jagger and Harrison, 1994; Wang et al., 2012; Sabrah et al., 2013). The physical factors include hardness, frictional resistance, and fracture toughness (Oh et al., 2002).
26
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
Fig. 6 – The SEM images of the lower specimens against three groups at 40 magnification (left) and 300 magnification (right). (A and B) Lower specimen surface of the enamel group. (C and D) Lower specimen surface of the gold group. (E and F) Lower specimen surface of the zirconia group. White arrows indicate the wear track line. Table 1 – Mean value and standard deviations of the wear dimension and volume loss of each group.
Wear face dimension (mm2) Volume loss(mm3)
Group 1 (n¼ 10)
Group 2 (n ¼10)
Group 3 (n ¼10)
X2
p-Value
3.5971.04a 0.4770.23a
0.5970.59b 0.0170.01b
0.4770.07b 0.0170.25b
23.49 20.20
o0.001n o0.001n
ab n
Mann–Whitney test. Kruskal–Wallis test.
In the case of ceramics, harder materials were more resistant to surface scratching and retained their polished surface for a long time. Thus, for porcelain and zirconia, there was less enamel wear in highly polished surfaces than in glazed or rough surface (Seghi et al., 1991). For these reasons, we polished the zirconia crowns and lower zirconia block with zirconia polishing kits. In our experiment, the enamel wear opposing the monolithic zirconia was much higher than that of gold crowns or zirconia crowns. This result was contrary to other results that
the wear of the polished zirconia is similar to that of natural enamel (Jung et al., 2010; Mitov et al., 2012; Kim et al., 2012). The sliding distances of other studies are shorter and the distances vary from 0.3 mm to 6.0 mm under similar load (Jung et al., 2010; Hudson et al., 1995), whereas the sliding distance of our study was 15 mm but the cycle number is lower than others. We believe the greater sliding distance affected the wear of enamel and the hardness and the roughness of the polished zirconia also would have affected the result (Seghi et al., 1991).
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
However, some results of our experiment were coincident to other studies. The low wear rate of zirconia opposing zirconia and the low wear rate of gold crowns were both similar to other studies (Albashaireh et al., 2010; Seghi et al., 1991; Jacobi et al., 1991). The reason that gold crowns show less wear was likely due to the ductility of the gold alloy (Kadokawa et al., 2006). Some authors reported that gold is a good material for restorations other than esthetic restorations because of its wear rate against enamel (Jacobi et al., 1991). In the SEM images, the wear track line was not clearly identified, and some fragments caused by wear test were observed in the lower specimens of the enamel and gold crown group (group 2). No remarkable differences were observed between polished and wear test areas. However, longitudinal wear track lines and surface deformations were observed in the lower specimen of the zirconia crown group. These results indicate that zirconia maintains its surface when it opposes both enamel and gold restorations. However, when it opposes hard materials like zirconia, its surface is abraded and deformed. According to many reports on bite force, the maximal bite force ranges from 17 N up to 698 N (Gibbs et al., 1981; Anderson, 1956; Morneburg and Proschel, 2002; Abreu et al., 2014; Owais et al., 2013; Helkimo et al., 1977; Van Der Bilt et al., 2008; Serra and Manns, 2013)and Gibbs et al. (1981) reported that the bite force of chewing exceeded 260 N. However, we applied a 50 N bite force in our experiments. When zirconia crowns were used for restorations, loads over 50 N would be applied to its counterpart. If monolithic crowns opposing enamel were used for heavy bruxers or patients that habitually clench their teeth, the opposing teeth would be severely abraded because of higher bite force (Stober et al., 2014). Kadokawa et al. (2006) reported that the mean wear values of the porcelain in the three-body condition were significantly smaller than those in the two-body condition when porcelain opposed composite resin or enamel, regardless of the porcelain surface condition. Therefore, we will perform a three-body condition test of our experiment with glycerin medium in the future. Jang et al. (2011) reported that zirconia crowns with 0.5 mm occlusal thickness showed similar strength to PFM and that zirconia crowns over 2.0 mm thickness had the fracture strength to endure occlusal force by inhibiting crack growth and propagation. This means monolithic zirconia is an adequate restoration material when tooth-colored restorations are needed for those who lack occlusal clearance. To restore posterior missing teeth with monolithic zirconia, we should consider an occlusal scheme of a patient and opposing tooth. If a patient has a canine protected occlusion and opposing gold crown, monolithic zirconia crowns and bridge will be good choices for posterior fixed partial dentures. For the long-term success of monolithic zirconia, further investigation regarding the low-temperature degradation of zirconia is required. This low-temperature degradation is aging by slow surface transformation to the stable monoclinic phase in the presence of water or water vapor, which decreases the
27
mechanical properties of zirconia and increases the surface roughness (Chevalier, 2006; Christel et al., 1989).
5.
Conclusion
We report the following results in this study: 1. In a simple reciprocation wear-test against zirconia, enamels were more abraded than gold or zirconia crowns. 2. The wear of gold crowns was not significantly different with that of zirconia crowns. This shows that gold crown is a good restoration option for non-esthetic usage. 3. Zirconia crowns are not recommended for heavy bruxers.
Acknowledgments This research was supported by the Kyung-Pook National University ResearchFund, (Grant no. 2013).
r e f e r e nc e s
Abreu, Roge´rio Alexandre Modesto de, M.D., Pereira, Furtado, F., Prado, G.P.R., Junior, W.M., Ferreira, L.M., 2014. Masticatory efficiency and bite force in individuals with normal occlusion. Arch. Oral Biol. 59, 1065–1074. Albashaireh, Z.S., Ghazal, M., Kern, M., 2010. Two-body wear of different ceramic materials opposed to zirconia ceramic. J. Prosthet. Dent. 104, 105–113. Anderson, D.J., 1956. Measurement of stress in mastication. I. J. Dent. Res. 35, 664–670. Ashkanani, H.M., Raigrodski, A.J., Flinn, B.D., Heindl, H., Mancl, L.A., 2008. Flexural and shear strengths of ZrO2 and a high-noble alloy bonded to their corresponding porcelains. J. Prosthet. Dent. 100, 274–284. Att, W., Stamouli, K., Gerds, T., Rudolf Strub, J., 2007. Fracture resistance of different zirconium dioxide three-unit allceramic fixed partial dentures. Acta Odontol. 65, 14–21. Chevalier, J., 2006. What future for zirconia as a biomaterial? Biomaterials 27, 535–543. Christel, P., Meunier, A., Heller, M., Torre, J., Peille, C., 1989. Mechanical properties and short-term in vivo evaluation of yttrium-oxide-partially-stabilized zirconia. J. Biomed. Mater. Res. 23, 45–61. Christensen, G., 2008. PFM vs. zirconia restorations—how are they comparing clinically. Clin. Rep. 1, 1–2. Christensen, G., 2009. Porcelain-fused-to-metal versus zirconiabased ceramic restorations, 2009. J. Am. Dent. Assoc. 140, 1036–1039. Christensen, R.P., Ploeger, B.J., 2010. A clinical comparison of zirconia, metal and alumina fixed-prosthesis frameworks veneered with layered or pressed ceramic: a three-year report. J. Am. Dent. Assoc. 141, 1317–1329. Conrad, H.J., Seong, W., Pesun, I.J., 2007. Current ceramic materials and systems with clinical recommendations: a systematic review. J. Prosthet. Dent. 98, 389–404. Elmaria, A., Goldstein, G., Vijayaraghavan, T., Legeros, R.Z., Hittelman, E.L., 2006. An evaluation of wear when enamel is opposed by various ceramic materials and gold. J. Prosthet. Dent. 96, 345–353. Gibbs, C.H., Mahan, P.E., Lundeen, H.C., Brehnan, K., Walsh, E.K., Holbrook, W.B., 1981. Occlusal forces during chewing and
28
journal of the mechanical behavior of biomedical materials 47 (2015) 21 –28
swallowing as measured by sound transmission. J. Prosthet. Dent. 46, 443–449. Heintze, S., Cavalleri, A., Forjanic, M., Zellweger, G., Rousson, V., 2008. Wear of ceramic and antagonist—a systematic evaluation of influencing factors in vitro. Dent. Mater. 24, 433–449. Helkimo, E., Carlsson, G.E., Helkimo, M., 1977. Bite force and state of dentition. Acta Odontol. 35, 297–303. Hudson, J.D., Goldstein, G.R., Georgescu, M., 1995. Enamel wear caused by three different restorative materials. J. Prosthet. Dent. 74, 647–654. Jacobi, R., Shillingburg Jr., H.T., Duncanson Jr., M.G., 1991. A comparison of the abrasiveness of six ceramic surfaces and gold. J. Prosthet. Dent. 66, 303–309. Jagger, D., Harrison, A., 1994. An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel. J. Prosthet. Dent. 72, 320–323. Jang, G., Kim, H., Choe, H., Son, M., 2011. Fracture strength and mechanism of dental ceramic crown with zirconia thickness. Procedia Eng. 10, 1556–1560. Janyavula, S., Lawson, N., Cakir, D., Beck, P., Ramp, L.C., Burgess, J.O., 2013. The wear of polished and glazed zirconia against enamel. J. Prosthet. Dent. 109, 22–29. Jung, Y., Lee, J., Choi, Y., Ahn, J., Shin, S., Huh, J., 2010. A study on the in-vitro wear of the natural tooth structure by opposing zirconia or dental porcelain. J. Adv. Prosthodont. 2, 111–115. Kadokawa, A., Suzuki, S., Tanaka, T., 2006. Wear evaluation of porcelain opposing gold, composite resin, and enamel. J. Prosthet. Dent. 96, 258–265. Kim, M., Oh, S., Kim, J., Ju, S., Seo, D., Jun, S., et al., 2012. Wear evaluation of the human enamel opposing different Y-TZP dental ceramics and other porcelains. J. Dent. 40, 979–988. Krejci, I., Lutz, F., Reimer, M., Heinzmann, J., 1993. Wear of ceramic inlays, their enamel antagonists, and luting cements. J. Prosthet. Dent. 69, 425–430. Krejci, I., Mueller, E., Lutz, F., 1994. Effects of thermocycling and occlusal force on adhesive composite crowns. J. Dent. Res. 73, 1228–1232. Manicone, P.F., Rossi Iommetti, P., Raffaelli, L., 2007. An overview of zirconia ceramics: basic properties and clinical applications. J. Dent. 35, 819–826.
Mitov, G., Heintze, S.D., Walz, S., Woll, K., Muecklich, F., Pospiech, P., 2012. Wear behavior of dental Y-TZP ceramic against natural enamel after different finishing procedures. Dent. Mater. 28, 909–918. Morneburg, T.R., Proschel, P.A., 2002. Measurement of masticatory forces and implant loads: a methodologic clinical study. Int. J. Prosthodont. 15, 20–27. Oh, W., DeLong, R., Anusavice, K.J., 2002. Factors affecting enamel and ceramic wear: a literature review. J. Prosthet. Dent. 87, 451–459. Owais, A.I., Shaweesh, M., Abu Alhaija, E.S., 2013. Maximum occusal bite force for children in different dentition stages. Eur. J. Orthod. 35, 427–433. Piconi, C., Maccauro, G., 1999. Zirconia as a ceramic biomaterial. Biomaterials 20, 1–25. Raigrodski, A.J., 2004. Contemporary materials and technologies for all-ceramic fixed partial dentures: a review of the literature. J. Prosthet. Dent. 92, 557–562. Sabrah, A.H., Cook, N.B., Luangruangrong, P., Hara, A.T., Bottino, M.C., 2013. Full-contour Y-TZP ceramic surface roughness effect on synthetic hydroxyapatite wear. Dent. Mater. 29, 666–673. Seghi, R.R., Rosenstiel, S.F., Bauer, P., 1991. Abrasion of human enamel by different dental ceramics in vitro. J. Dent. Res. 70, 221–225. Serra, C., Manns, A., 2013. Bite force measurements with hard and soft bite surfaces. J. Oral Rehabil. 40, 563–568. Stober, T., Bermejo, J., Rammelsberg, P., Schmitter, M., 2014. Enamel wear caused by monolithic zirconia crowns after 6 months of clinical use. J. Oral Rehabil. 41, 314–322. Tinschert, J., Natt, G., Mautsch, W., Augthun, M., Spiekermann, H., 2001. Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study. Int. J. Prosthodont. 14, 231–238. Van Der Bilt, A., Tekamp, A., Van Der Glas, H., Abbink, J., 2008. Bite force and electromyograpy during maximum unilateral and bilateral clenching. Eur. J. Oral Sci. 116, 217–222. Wang, L., Liu, Y., Si, W., Feng, H., Tao, Y., Ma, Z., 2012. Friction and wear behaviors of dental ceramics against natural tooth enamel. J. Eur. Ceram. Soc. 32, 2599–2606.
