Keys to Successful Placement of Zirconia Restorations
Gary Alex, DMD
Abstract: The many positive characteristics of zirconia have made this material a popular choice in indirect dentistry. This article focuses on the placement of zirconia restorations, highlighting proper principles and techniques for successful outcomes. Such issues as sandblasting, the use of primers and cleaning agents, and whether to cement or bond are discussed, and case examples are presented.
Zirconia has seen a dramatic increase in use and popularity in dentistry over the past several years.1 This restorative material has many positive attributes, including high flexural strength (from five to more than 10 times that of conventional porcelain-fused-to-metal [PFM] restorations2-4) and a superior fracture toughness compared to lithium-disilicate and PFM restorations.5 Zirconia can be bonded or conventionally cemented and, contrary to what many dentists believe, is wear-friendly to the opposing dentition when properly polished.6-8 Zirconia restorations are compatible with CAD/CAM technology and can be milled full contour to maximize strength or layered with stacked or pressed ceramics for optimal esthetics. (Note: The author has written a detailed and in-depth essay on zirconia's physical properties, surface optimization, and cementation options aimed at enhancing clinicians' understanding of the principles and techniques for the placement of zirconia restorations demonstrated in this article,9 and readers are referred to it. See No. 9 in the Reference list.)
Sandblasting Zirconia Prior to Placement
The author strongly suggests-and this is well supported in the literature10-13-that the intaglio surface of zirconia restorations be particle-abraded (sandblasted) prior to placement regardless of what type of conventional or resin-based cement is used. However, certain caveats are in order. First, care should be taken not to use excessive blasting pressures that might cause undue physical damage and/or tetragonal to monolithic phase transformation of the zirconia surface (both of which can reduce physical properties). Also, particle size and type should be considered, because, generally speaking, the larger (more massive) and harder the particle the greater the force it imparts as it hits the target surface. Some studies have shown that traditional high-strength zirconia can be safely and effectively sandblasted with 30 μm to 50 μm aluminous oxide using a blast pressure of 1.5-2.0 bar (approximately 20 psi to 30 psi) from a distance of 2 cm to 3 cm.13-15 When dealing with translucent zirconia (5 mol % yttria concentration) blasting pressures should be in the lower range (20 psi) to minimize any surface damage that could lead to a reduction in physical properties. The author prefers to sandblast the intaglio surface of zirconia restorations after try-in and any adjustments, just before cementation/bonding (Figure 1).
Zirconia Primers and Zirconia Cleaning Agents
In situations where the dentist wants maximum retention/adhesion between zirconia and tooth tissues (eg, minimally retentive preparations, zirconia winged bridges, etc) some type of bonding protocol using a resin-based cement in conjunction with a zirconia primer is required. The primer can take the form of a separately applied solution that contains a phosphate ester zirconia primer such as 10-MDP (eg, Z-Prime™ Plus, BISCO, bisco.com), or a resin cement can be used that incorporates a zirconia primer directly in its chemical makeup (Figure 2 through Figure 4).
If when trying in a zirconia restoration the intaglio surface is contaminated by saliva, phosphate ions from the saliva will bind to and occupy the same reactive sites that zirconia primers require for chemical interactions. This competition for reaction sites greatly decreases the efficacy of zirconia primers, thus it is necessary for these sites to be "freed up" to allow the primer to function optimally. This can be done by sandblasting the restoration after saliva contamination and/or using a strongly alkaline cleaning solution (eg, ZirClean®, BISCO).
Cement or Bond?
In clinical situations where there is a lack of resistance and retention form, and maximum adhesion is required, zirconia restorations should be treated with a zirconia primer and bonded into place with resin cement (Figure 5). Although dentists often prefer dual-cure self-etching selfpriming resin cements because no separate bonding agent needs to be placed on the tooth, it should be noted that the highest bond to tooth structure is achieved by using resin cements in conjunction with a separately placed bonding agent.16-18 Resin-based cements used in conjunction with a bonding agent have a distinct advantage over resinmodified glass ionomers (RMGIs) and other conventional cements with regard to bonding restorations on or in minimally retentive preparations in that their bond to both tooth tissues and zirconia is more durable and predictable.13,19,20 Moreover, resin-based cements may be advantageous when working with translucent zirconia or zirconia restorations with minimal occlusal thickness, because these cements allow for better stress distribution when loaded, may inhibit crack formation, and generally optimize overall assembly strength.21 If the preparation(s) has adequate resistance and retention form, then ion-releasing cements that often are easier to use and clean, such as RMGI, are good options.
In Case 1 (Figure 6 through Figure 8) the missing tooth No. 25 was replaced with a single-wing (No. 26) high-strength zirconia resin-bonded bridge. To maximize adhesion to the zirconia the intaglio surface of the wing was sandblasted and treated with a zirconia primer (Z-Prime™ Plus, BISCO). To maximize adhesion to the tooth tissues, enamel and any exposed dentin were etched with phosphoric acid (total-etch), followed by the placement of a universal adhesive (All-Bond Universal®, BISCO). The wing was then bonded to the lingual of No. 26 with a dual-cure resin cement (Duo-Link Universal™, BISCO).
Case 2 (Figure 9 through Figure 12) is an example of a situation where there was good resistance and retention form, and retention was not an issue. In such cases, zirconia restorations do not have to be bonded in, but, after sandblasting, can be placed with ion-releasing cements such as RMGI or TheraCem®(BISCO), which generally are easier to clean and work with.
A common misconception is that dentists cannot bond to zirconia. The fact is zirconia surfaces can be bonded to very predictably and durably using a combination of sandblasting, a phosphate ester primer such as 10-MDP, and an appropriate resin-based cement.9 Proper management of both the zirconia substrate and tooth tissues is crucial for predictable and durable clinical outcomes. As a general rule the intaglio surface of all zirconia restorations should be particle-abraded (sandblasted) and a zirconia primer placed (typically, a phosphate ester like 10-MDP). However, this is not true in every situation, and the use of a separate zirconia primer is contraindicated or unnecessary with some materials. In this regard, manufacturer instructions and recommendations should be followed precisely for best results. It is incumbent on all clinicians to familiarize themselves with optimal cementation options and protocols when placing zirconia restorations.
This article was commercially supported by BISCO.
About the Author
Gary Alex, DMD
Private Practice, Huntington, New York; Accredited Member,
American Academy of Cosmetic Dentistry; Member,
International Association for Dental Research
1. Makhija SK, Lawson NC, Gilbert GH, et al. Dentist material selection for single-unit crowns: findings from the National Dental Practice-Based Research Network. J Dent. 2016;55:40-47.
2. Fischer J, Stawarczyk B, Hämmerle CH. Flexural strength of veneering ceramics for zirconia. J Dent. 2008;36(5):316-321.
3. Matsuzaki F, Sekine H, Honma S, et al. Translucency and flexural strength of monolithic translucent zirconia and porcelain-layered zirconia. Dent Mater J. 2015;34(6):910-917.
4. Kayahan ZO. Monolithic zirconia: A review of the literature. Biomedical Research.2016;27(4):1427-1436.
5. Ritzberger C, Apel E, Höland W, et al. Properties and clinical application of three types of dental glass-ceramics and ceramics for CAD-CAM technologies. Materials (Basel). 2010;3(6):3700-3713.
6. Burgess JO, Janyavula S, Lawson NC, et al. Enamel wear opposing polished and aged zirconia. Oper Dent. 2014;39(2):189-194.
7. Daou EE. Esthetic prosthetic restorations: reliability and effects on antagonist dentition. Open Dent J.2015;9:473-481.
8. Esquivel-Upshaw JF, Kim MJ, Hsu SM, et al. Randomized clinical study of wear of enamel antagonists against polished monolithic zirconia crowns. J Dent. 2018;68:19-27.
9. Alex G. Zirconia - separating fact from fiction. Oral Health. 2019;July:60-61. https://www.oralhealthgroup.com/features/zirconiaseparating-fact-from-fiction/#. Accessed January 27, 2021.
10. Kim BK, Bae HE, Shim JS, Lee KW. The influence of ceramic surface treatments on the tensile bond strength of composite resin to all-ceramic coping materials. J Prosthet Dent. 2005;94(4):357-362.
11. Yi YA, Ahn JS, Park YJ, et al. The effect of sandblasting and different primers on shear bond strength between yttria-tetragonal zirconia polycrystal ceramic and a self-adhesive resin cement. Oper Dent. 2015;40(1):63-71.
12. Barragan G, Chasqueira F, Arantes-Oliveria S, Portugal J.Ceramic repair: influence of chemical and mechanical surface conditioning on adhesion to zirconia. Oral Health Dent Manag. 2014;13(2):155-158.
13. Zandparsa R, Talua NA, Finkelman MD, Schaus SE. An in vitro comparison of shear bond strength of zirconia to enamel using different surface treatments. J Prosthodont.2014;23(2):117-123.
14. Hallmann L, Ulmer P, Wille S, et al. Effect of surface treatments on the properties and morphological change of dental zirconia. J Prosthet Dent. 2016;115(3):341-349.
15. Skienhe H, Habchi R, Ounsi H, et al. Evaluation of the effect of different types of abrasive surface treatment before and after zirconia sintering on its structural composition and bond strength with resin cement. Biomed Res Int. 2018;2018:1803425.
16. Barcellos DC, Batista GR, Silva MA, et al. Evaluation of bond strength of self-adhesive cements to dentin with or without application of adhesive systems. J Adhes Dent. 2011;13(3):261-265.
17. Chen C, He F, Burrow MF, Xie H. Bond strengths of two self-adhesive resin cements to dentin with different treatments. J Med Biol Eng. 2011;31(1):73-77.
18. Pisani-Proença J, Erhardt MC, Amaral R, et al. Influence of different surface conditioning protocols on microtensile bond strength of self-adhesive resin cements to dentin. J Prosthet Dent. 2011;105(4):227-235.
19. Kern M. Bonding to oxide ceramics-laboratory testing versus clinical outcome. Dent Mater. 2015;31(1):8-14.
20. Tanis MC, Akay C, Karakis D. Resin cementation of zirconia ceramics with different bonding agents. Biotechnol Biotechnol Equip. 2015;29(2):363-367.
21. McLaren E, Burgess J, Brucia J. Cubic-containing zirconia: Is adhesive or conventional cementation best? Compend Contin Educ Dent. 2008;29(5):282-284.