Australasian Dentist Magazine Sept-Oct 2021

Category 82 Australasian Dentist clinical ester zirconia primer such as 10-MDP (eg, Z-Prime™ Plus, BISCO), 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 self priming 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 resin modified 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. Case Examples 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 dentine 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. Conclusion 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 Propermanagement 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. u About the Author Gary Alex, DMD Private Practice, Huntington, New York; Accredited Member, American Academy of Cosmetic Dentistry; Member, International Association for Dental Research Fig 9 Fig 6 Fig 7 Fig 8 Fig 11 Fig 10 Fig 12 Fig 9 through Fig 12. When good resistance and retention form are present, zirconia restorations do not require bonding. After sandblasting, they can be placed with ion-releasing cements. Fig 9: Preparations for a three-unit fixed partial denture that demonstrate good resistance and retention form. Fig 10: Monolithic zirconia restoration with ovoid pontic. Fig 11: The case was cemented with a conventional RMGI. Fig 12: The finished case immediate post cementation. Fig 6 through Fig 8. Missing tooth #25 was replaced with a single-wing #26 high-strength zirconia resin bonded bridge. The intaglio surface of the wing was sandblasted and treated with zirconia primer to maximize adhesion to the zirconia. To strengthen adhesion to the tooth, enamel and exposed dentin were etched (total-etch) and a universal adhesive was placed prior to the wing being bonded to the lingual of #26.