Australasian Dentist Magazine Sept-Oct 2021

Category 80 Australasian Dentist 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. Z irconia 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] restora­ tions 2-4 ) 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 technologyandcanbemilled full contour to maximise strength or layered with stacked or pressed ceramics for optimal aesthetics. (Note: The author has written a detailed and in-depth essay on zirconia’s physical properties, surface optimisation, 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 literature 10-13 – 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 Keys to Successful Placement of Zirconia Restorations clinical By Gary Alex, DMD Fig 1. The author suggests clinicians sandblast the intaglio surface of zirconia restorations after try-in and any adjustments, prior to cementation/ bonding. Fig 2 Fig 4 Fig 3 Fig 5 Fig 2 through Fig 4. To maximize adhesion to zirconia when using a resin cement the intaglio surface should be sandblasted and treated with a zirconia primer (Fig 2). In this case, the primer was dried with a warm-air drier (Fig 3) prior to the placement of a dual-cure resin cement (Fig 4). If the cement already contains a zirconia primer, such as 10-MDP, a separately applied primer may not be necessary. Fig 5. When there is a lack of resistance and retention form, as in this single-wing zirconia resin-bonded bridge, the intaglio surface may be sandblasted, treated with a zirconia primer and bonded into place with resin cement.