Clinical performance of zirconia crowns Tartaglia GM et al. single or multiple tooth- or implant-supported crowns. As the published literature on zirconia-core crowns for implants is limited, further investigations with more extensive follow-up periods are necessary. In particular, due to the problem of fatigue fractures with all-ceramic prostheses,1,3,13,14,17 a longer observation period is necessary.19 This is especially warranted for rehabilita- tions in young patients who likely exert greater bite forces on their prostheses. In conclusion, zirconia-core crowns appear to be a good clinical solution for both single- and multiple-unit pros- theses, as they were shown to exhibit favorable aesthetic and functional properties. The marginal fit of these prostheses should be improved, as should the teamwork with the dental hygienist. Overall patient satisfaction was good, and the percentage of failures was limited in this clinical follow-up study. Undoubtedly, further longitudinal analyses are necessary, and the clinical performance of prosthetic reconstructions should be assessed five years after their placement.19 AUTHOR CONTRIBUTIONS Tartaglia GM was responsible for the concept, design, execution, and interpretation of the study. Sidoti E was responsible for the bibliographic review, execution, and interpretation of the study. Sforza C was responsible for the concept, design, statistical analysis, and interpretation of the study. REFERENCES 1. Sundh A, Molin M, Sjogren G. Fracture resistance of yttrium oxide partially stabilized zirconia all-ceramic bridges after veneering and mechanical fatigue testing. Dent Mater. 2005;21:476–82, doi: 10.1016/j. dental.2004.07.013. 2. Denry I, Kelly JR. State of the art of zirconia for dental applications. Dent Mater. 2008;24:299-307, doi: 10.1016/j.dental.2007.05.007. 3. Manicone P, Iommetti P, Raffaelli L. An overview of zirconia ceramics: Basic properties and clinical applications J Dent. 2007;35:819-26. 4. Piconi C, Maccauro G. Zirconia as a ceramic biomaterial. Biomaterials. 1999;20:1–25, doi: 10.1016/S0142-9612(98)00010-6. 5. Schley JS, Heussen N, Reich S, Fischer J, Haselhuhn K, Wolfart S. Survival probability of zirconia-based fixed dental prostheses up to 5 yr: a systematic review of the literature. Eur J Oral Sci. 2010;118:443-50, doi: 10.1111/j.1600-0722.2010.00767.x. 6. Luthardt RG, Holzhuter M, Sandkuhl O, Herold V, Schnapp JD, Kuhlisch E, et al. Reliability and properties of ground Y-TZP-zirconia ceramics. J Dent Res. 2002;81:487–91, doi: 10.1177/154405910208100711. 7. Sailer I, Fehe´r A, Filser F, Gauckler LJ, L u¨thy H, Ha¨mmerle CH. Five- year clinical results of zirconia frameworks for posterior fixed partial dentures. Int J Prosthodont. 2007;20:383-8. 8. C¸ehreli MC, Ko¨ kat AM, Akc¸a K. CAD/CAM Zirconia vs. slip-cast glass- infiltrated Alumina/Zirconia all-ceramic crowns: 2-year results of a randomized controlled clinical trial. J Appl Oral Sci. 2009;17:49-55, doi: 10.1590/S1678-77572009000100010. CLINICS 2011;66(12):2063-2070 9. Christensen GJ. Porcelain-fused-to-metal versus zirconia-based ceramic restorations, 2009. J Am Dent Ass. 2009;140:1036-9. 10. Papaspyridakos P, Lal K. Complete arch implant rehabilitation using subtractive rapid prototyping and porcelain fused to zirconia prosthesis: a clinical report. J Prosthet Dent. 2008;100:165-72, doi: 10.1016/S0022- 3913(08)00110-8. 11. Vult von Steyern P, Carlson P, Nilner K. All-ceramic fixed partial dentures designed according to the DC-Zirkon technique. A 2-year clinical study. J Oral Rehabil. 2005;32:180-7, doi: 10.1111/j.1365-2842. 2004.01437.x. 12. Wolfart S, Harder S, Eschbach S, Lehmann F, Kern M. Four-year clinical results of fixed dental prostheses with zirconia substructures (Cercon): end abutments vs. cantilever design. Eur J Oral Sci. 2009;117:741-9, doi: 10.1111/j.1600-0722.2009.00693.x. 13. Shah K, Holloway JA, Denry IL. Effect of coloring with various metal oxides on the microstructure, color, and flexural strength of 3Y-TZP. J Biomed Mater Res B Appl Biomater. 2008;87B:329–37, doi: 10.1002/jbm. b.31107. 14. Papanagiotou HP, Morgano SM, Giordano RA, Pober R. In vitro evaluation of low-temperature aging effects and finishing procedures on the flexural strength and structural stability of Y-TZP dental ceramics. J Prosthet Dent. 2006;96:154-64, doi: 10.1016/j.prosdent.2006.08.004. 15. Encke BS, Heydecke G, Wolkewitz M, Strub JR. Results of a prospective randomized controlled trial of posterior ZrSiO(4)-ceramic crowns. J Oral Rehabil. 2009;36:226-35, doi: 10.1111/j.1365-2842.2008.01918.x. 16. Ortorp A, Kihl ML, Carlsson GE. A 3-year retrospective and clinical follow-up study of zirconia single crowns performed in a private practice. J Dent. 2009;37:731-6. 17. Att W, Grigoriadou M, Strub JR. ZrO2 three-unit fixed partial dentures: comparison of failure load before and after exposure to a mastication simulator. J Oral Rehabil. 2007;34:282-90, doi: 10.1111/j.1365-2842.2006. 01705.x. 18. Kohorst P, Herzog TJ, Borchers L, Stiesch-Scholz M. Load-bearing capacity of all-ceramic posterior four-unit fixed partial dentures with different zirconia frameworks. Eur J Oral Sci. 2007;115:161-6, doi: 10. 1111/j.1600-0722.2007.00429.x. 19. Raigrodski AJ, Chiche GJ, Potiket N, Hochstedler JL, Mohamed SE, Billiot S, et al. The efficacy of posterior three-unit zirconium-oxide-based ceramic fixed partial dental prostheses: a prospective clinical pilot study. J Prosthet Dent. 2006;96:237-44, doi: 10.1016/j.prosdent.2006.08.010. 20. Bandlish RB, McDonald AV, Setchell DJ. Assessment of the amount of remaining coronal dentine in root-treated teeth. J Dent. 2006;34:699-708, doi: 10.1016/j.jdent.2006.01.002. 21. Ferrario VF, Tartaglia GM, Galletta A, Grassi GP, Sforza C. The influence of occlusion on jaw and neck muscle activity: a surface EMG study in healthy young adults. J Oral Rehabil. 2006;33:341-8, doi: 10.1111/j.1365- 2842.2005.01558.x. 22. Hickel R, Roulet JF, Bayne S, Heintze SD, Mjo¨ r IA, Peters M, et al. Recommendations for conducting controlled clinical studies of dental restorative materials. Clin Oral Invest. 2007;11:5-33, doi: 10.1007/s00784- 006-0095-7. 23. Hickel R, Peschke A, Tyas M, Mjo¨ r I, Bayne S, Peters M, et al. FDI World Dental Federation: clinical criteria for the evaluation of direct and indirect restorations—update and clinical examples. Clin Oral Invest. 2010;14:349–66, doi: 10.1007/s00784-010-0432-8. 24. Ferrario VF, Marciandi PV, Tartaglia GM, Dellavia C, Sforza C. Neuromuscular evaluation of post-orthodontic stability: an experimental protocol. Int J Adult Orthodon Orthognath Surg. 2002;17:307-13. 25. Di Palma E, Gasparini G, Pelo S, Tartaglia GM, Chimenti C. Activities of masticatory muscles in patients after orthognathic surgery. J Craniomaxillofac Surg. 2009;37:417-20, doi: 10.1016/j.jcms.2009.05.004. 2070