08 April 2020

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Bonding to Zirconia: is it clinically reliable?

Allegra Comba

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The use of zirconia in restorative dentistry has grown exponentially over the past decade. Early zirconia formulations were used for frameworks because of their high flexural strength and unaesthetic opacity. Through processing refinements, materials with increased translucency were introduced so that veneering with feldspathic porcelain was not required and the material could be used in monolithic form. Unfortunately, differently from silica-based ceramics, zirconia is a non etchable material, thus needing a different protocol to bond to the dental substrate. 
To better understand the Clinical efficacy of methods for bonding to zirconia,  Quigley et al. wrote a systematic review of the literature< with the purpose of critically appraise clinical studies investigating the survival rate of resin-bonded zirconia fixed partial dentures (FPDs), inlay retained zirconia FPDs, and zirconia veneers.

Materials and methods
The authors conducted the search in MEDLINE, EMBASE, PubMed, Web of Science, Scopus, Cochrane Library, and Google Scholar. Clinical studies of over 12 months duration involving bonded zirconia restorations between 1990 and July 2018 were reviewed. All suitable studies were assessed for quality using a “Questionnaire for selecting articles on Dental Prostheses”

Results
Eight studies were ultimately included. Three studies examined posterior inlay-retained FPDs with estimated survival rates of 12.1% at 10 years, 95.8% at 5 years, and 100% at 20 months. Five studies reviewed anterior, resin-bonded FPDs, all of which had a 3- to 10-year survival rate of 100%. Debonds occurred in all studies, but the prostheses could usually be rebonded.

Conclusions
This review aimed to collate and analyze the available clinical data on the survival rates of zirconia restorations that relied primarily on adhesive resin bonding for their success. Because of the lack of studies on posterior prostheses and their relative heterogeneity, a meta-analysis was not conducted. Based on the results obtained the authors concluded that:
 1. With correctly designed buccal and lingual PCRs (partial-coverage retainers) and minimal if any veneering porcelain, zirconia based, posterior, inlay-retained FPDs seem to have a high clinical survival rate. The role of bonding efficacy in this is unknown.
 2.  Anterior, cantilevered, resin-bonded zirconia FPDs also seem to have a high clinical survival rate. While these prostheses can debond, fracture of the entire prosthesis is unlikely, so they may be rebonded.
 3. To bond zirconia, the use of airborne-particle abrasion with 50-mm Al2O3 at 0.10 to 0.25 MPa in combination with a phosphate monomer containing adhesive resin is currently recommended. 
Rubber dami solation is also recommended during zirconia bonding.

For more information:  Clinical efficacy of methods for bonding to zirconia: A systematic review.