Zirconium dental restoration survival: limited evidence

Conventional high-noble-alloy-based porcelain-fused-to-metal (PFM) restorations have good long-term survival rates. However all-ceramic restorations have good aesthetics and biocompatibility. The development of Yttrium oxide-stabilised tetragonal zirconium dioxide polycrystal (Y-TZP) ceramics commonly referred to as zirconium has extended the application of ceramic dental restorations.

The aim of this review was to summarise the clinical performance of tooth- or implant-supported zirconia-based fixed dental prostheses (FDPs).

Methods

Searches were conducted in PubMed, the Cochrane Library and Science Direct for studies presenting clinical results on tooth- or implant-supported FDPs with a substructure made of Y-TZP. Electronic searches were supplemented with hand searches of the journals; International Journal of Prosthodontics, Journal of Oral Rehabilitation, International Journal of Oral & Maxillofacial Implants and Clinical Oral Implants Research. Two reviewers independently selected studies.

Failure was defined as restoration having been removed.
Success was defined as an FDP that remained unchanged and did not require any intervention over the observation period.
Survival was defined as the FDP remaining in situ at the examination visit with one or more modifications.
Technical complications included fracture of the framework, fracture or chipping of the veneering ceramic, marginal gap, discoloration and loss of retention and abutment tooth fracture that did not lead to failure.

Results

27 studies were included, only 5 of which were randomised.
23 studies reported on 887 tooth-supported FDPs and 4 studies on 72 implant-supported FDPs.
Follow-up periods ranged from 2-11 years.
10 studies reported on 20 FDPs or fewer.
The cumulative 5-year survival rate of
- implant-supported zirconia-based FDPs was 100%
- tooth-supported zirconia-based FDPs was 93.3%.
Commonest reasons for failure were veneering material fracture, framework fracture and caries.
The cumulative 5-year (technical) complication rate
- implant-supported zirconia-based FDPs was 30.5%
- tooth-supported zirconia-based FDPs was 27.6%

Conclusions

The authors concluded:

The results suggest that the 5-year survival rate is excellent for implant-supported zirconia-based FDPs, despite the incidence of complications, and acceptable for tooth-supported zirconia-based FDPs. These results are, however, based on a relatively small number of studies, especially for the implant-supported FDPs. The vast majority of the studies are not controlled clinical trials and have limited follow-up. Thus, interpretation of the results should be made with caution. Well-designed studies with large patient groups and long follow-up times are needed before general recommendations for the use of zirconia-based restorations can be provided.

Commentary

The search strategy for this review involved three databases as well as hand searches but no formal quality assessment of the included studies has been conducted and only 5 of the included studies were randomised. While the authors state that the majority of the included studies were prospective it is not easy to confirm this from the material presented. Many of the studies were small and there was no minimum follow up period stated and only 4 of the included studies had a follow up period of more than 5 years. The quality of the available evidence is therefore low and these findings should be viewed cautiously and as the authors suggest larger well-designed studies with longer follow up periods are needed.