JPOR-260; No. of Pages 3 journal of prosthodontic research xxx (2014) xxx–xxx

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Letter to the Editor Update zirconia restorations

Keywords: Zirconia Zirconia all-ceramic restoration Full zirconia restoration Polishing Wear

Dear Editor, Zirconia has excellent mechanical strength, biocompatibility, and esthetics as a material for prosthetic appliances in all ceramic restorations. It has been used as a framework because of its low light transmittance, however esthetic porcelain, for facing, needs to be applied to the framework. This porcelain is associated with serious clinical problems such as chipping and fracture. A study has indicated that long-term clinical results of zirconia all-ceramic crowns are equivalent to those of porcelain-fused-to-cast crowns [1]. However, long-term clinical studies of zirconia all-ceramic crown are still inadequate as compared with porcelainfused-to-cast crown, and further research is needed [2]. Full zirconia restoration may become widely used in the future if its light transmittance can be improved. The effect of full zirconia restoration on abrasion of antagonistic teeth is an issue of great clinical significance from the standpoint of prolonged stability and safety of the occlusion when zirconia is used for the occlusal surface. In the Evening Session ‘‘Update Zirconia Restorations’’, the 123rd Annual Meeting of Japan Prosthodontic Society 2014, three speakers who have been engaged in research on zirconia restoration made a presentation, and we had a fruitful discussion. The followings are the outline of the presentation and the discussion:

1. Clinical study report of zirconia all-ceramic restorations Retrospective record evaluation and clinical examination of patients treated with zirconia all-ceramic crowns were performed. Five dentists of the Department of Fixed

Prosthodontics of the Tohoku University Hospital treated the patients. 106 crowns were made using cercon1 smart ceramics (DeguDent) and veneered with low-fusing porcelain. The crowns were performed during the follow-up period from 2004 to 2012. Data (differences of ratio) were analyzed by x2 test to assess possible associations with chipping. The results are shown in Table 1. Eight crowns showed chipping of the veneering porcelain, whereas none of the crowns exhibited fracture of the zirconia framework. No exposure of the zirconia frame interface was noticed; chip fractures were exclusively within the veneer porcelain. In 6 out of the 8 crowns chipping occurred within the first year after seating, proving enhanced risk for fracturing in early stages during service. Issue of this report with regards to chipping occurrence was occlusion factors, appropriate clearance, and cementing using dedicated primer. Physically, they include the slow heating rate of porcelain firing, excessively large porcelain thickness arising because of poor frame design. A prospective study is expected to carry out in the future that takes these factors into consideration.

2. Wear performance of bovine tooth enamel against translucent tetragonal zirconia polycrystals after different surface treatments Recently, highly translucent tetragonal zirconia polycrystals (TZPs) that achieve improved esthetic results have been introduced. Several translucent TZP products have already been used for clinical applications. However, there is little information about the wear behavior between translucent monolithic TZP and tooth enamel. The aim of this study was to investigate the wear performances of bovine tooth enamel (BTE) against translucent TZP compared to that of feldspar porcelain and the influence of surface treatments of translucent TZP by the two-body wear test. Translucent TZP and feldspar porcelain were used as hemisphere abrader specimens with a radius of curvature of 5 mm; flat BTE surfaces were used as substrate specimens. The cross-sectional area of the worn surfaces of the substrates and the wear volume of the antagonist abraders were measured. Surface roughness, hardness and coefficient of friction as well as scanning

Please cite this article in press as: Takeichi T. Update zirconia restorations. J Prosthodont Res (2014),

JPOR-260; No. of Pages 3


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Table 1 – Associated attributes and the presence or absence of chipping. Chipping % (n) 


Gender Female Male

95 (91) 70 (7)

5 (5) 30 (3)

Age group 20–39 40–59 60–

95 (20) 90 (44) 94 (34)

5 (1) 10 (5) 6 (2)

Type of tooth Incisor Premolar Molar Cement Glass ionomer Resin Resin-reinforced glass ionomer y




0.006 100 (56) 82 (23) 86 (19)

0 (0) 18 (5) 14 (3)

92 (57) 96 (23) 90 (18)

8 (5) 4 (1) 10 (2)


x2 test.

electron microscopy (SEM) observations and electron probe microanalyzer analyses were also performed to investigate the underlying mechanism of wear. The results suggested that BTE is less susceptible to wear when translucent TZP is used as the antagonist in contrast to the use of feldspar porcelain, and that surface treatment of the TZP abraders significantly influenced the wear of BTE substrates.

3. The effect of polishing and finishing procedures on full zirconia restoration The wear of antagonists depends on the material used: material’s factors such as fracture toughness, internal pores, and surface flaws and/or defects may induce accelerated wear of antagonists [3]. The surface textures also play an important role in wear of antagonists. Previous studies reported that the wear of enamel opposite to well-polished monolithic zirconia surface showed less than that of enamel to enamel [4,5]. On the other hand, glazed zirconia using glazing materials showed the increase of surface roughness after loading due to the loss of glazing layer [4–6]. Surface roughness after polished with diamond paste and glazing, zirconia showed smoother than feldspathic porcelain. Moreover, no statistical difference was found between the surface roughness values of polished with diamond paste and glazing. These results indicated that zirconia might have a possibility to produce smooth surface after occlusal adjustment and loading. Stawarczyk et al. reported that the SEM images after loading test showed increase in the form of cracks on the enamel antagonist [6]. This result suggests that disadvantage of full zirconia restorations caused by the discrepancy of hardness. Further investigation is required for this point.

This symposium provided a good opportunity not only to understand the latest research results about zirconia all-ceramic restoration and full zirconia restoration but also to inform clinicians about clinical applications. In addition, clinical application and research on this theme have the potential to improve prosthodontic care and are, therefore, promising avenues of further study.


[1] Ozer F, Mante FK, Chiche G, Saleh N, Takeichi T, Blatz MB. A retrospective survey on long-term survival of posterior zirconia and porcelain-fused-to-metal crowns in private practice. Quintessence Int 2014;45:31–8. [2] Takeichi T, Katsoulis J, Blatz MB. Clinical outcome of single porcelain-fused-to-zirconium dioxide crowns: a systematic review. J Prosthet Dent 2013;110:455–61. [3] Oh WS, Delong R, Anusavice KJ. Factors affecting enamel and ceramic wear: a literature review. J Prosthet Dent 2002;87:451–9. [4] Janyavula S, Lawson N, Cakir D, Beck P, Ramp LC, Burgess JO. The wear of polished and glazed zirconia against enamel. J Prosthet Dent 2013;109:22–9. [5] Burgess JO, Janyavula S, Lawson NC, Lucas TJ, Cakir D. Enamel wear opposing polished and aged zirconia. Oper Dent 2014;39:189–94. ¨ zcan M, Schmutz F, Trottmann A, Roos M, [6] Stawarczyk B, O Ha¨mmerie CH. Two-body wear of monolithic, veneered and glazed zirconia and their corresponding enamel antagonists. Acta Odontol Scand 2013;71:102–12.

Takuro Takeichi DDS, PhD 1,* Department of Fixed Prosthodontics, School of Dentistry, Aichi Gakuin University, 2-11, Suemoridori, Chikusa, Nagoya, Aichi 464-8651, Japan Shoko Miura DDS, PhD Shin Kasahara DDS, PhD Hiroshi Egusa DDS, PhD Division of Molecular and Regenerative Prosthodontics, Graduate School of Dentistry, Tohoku University, Japan Mai Hara DDS, PhD Toru Sato DDS, PhD Department of Crown & Bridge Prosthodontics, Tokyo Dental College, Japan Masao Yoshinari DDS, PhD Division of Oral Implants Research, Oral Health Science Center, Tokyo Dental College, Japan Tetsurou Odatsu DDS, PhD Department of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University, Japan Ikuya Watanabe DDS, PhD Department of Dental and Biomedical Materials Science, Graduate School of Biomedical Sciences, Nagasaki University, Japan

Please cite this article in press as: Takeichi T. Update zirconia restorations. J Prosthodont Res (2014),

JPOR-260; No. of Pages 3


journal of prosthodontic research xxx (2014) xxx–xxx

Takashi Sawase DDS, PhD Department of Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University, Japan


Coordinator of the Evening Session 3 ‘‘Update Zirconia Restorations’’, The 123rd Annual Meeting of Japan Prosthodontic Society. 11 September 2014


Corresponding author. Tel.: +81 52 759 2156; fax: +81 52 759 2156 E-mail address: [email protected] (T. Takeichi) 1883-1958/# 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.

Please cite this article in press as: Takeichi T. Update zirconia restorations. J Prosthodont Res (2014),

Update zirconia restorations.

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