29 September 2020

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Fixed dental prostheses: which is the gold standard material?

Alessandra Abbà

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Metal ceramic has always been the golden standard for implant‐supported reconstructions in the past and the most investigated material in literature, but nowadays the application of all-ceramics, in particular zirconia, as restorative material for implant‐supported single crowns (SCs) and fixed dental prostheses (FDPs) has increased. In fact, thanks to the CAD/CAM technology, it allows the use of less expensive materials and faster manufacturing procedure. 

 There are two main type of zirconia restorations: bilayer, in which zirconia constitutes the core of the structure and is covered by a ceramic veneer, or single layer, in which the prosthesis is entirely made in monolithic zirconia. zirconia  core with porcelain coverage guarantees an optimal aesthetics but an higher risk of chipping. On the other hand, monolithic zirconia avoids this problem but until a few years ago it showed not satisfying aesthetic outcomes due to the opacity of the material. Recent modifications in composition and structure seem to solve this problem giving to monolithic zirconia  a superior translucency. zirconia  restorations exhibit considerable advantages: flexural strength, more conservative dental preparation, minimal wear on the antagonists, lower treatment costs and time.

Selection of the most appropriate material for each restoration remains a challenge for the clinicians. Although zirconia  tend to be the most used in the last period, long‐term behavior and their impact on the survival and complication rates of implant‐supported reconstructions, still remains an open question and further evaluations will be necessary as well as comparisons with gold standard in order to establish a standard of care.

This is the reason why the Authors realized this review published in 2018, with the aim to analyze survival and technical, biologic and aesthetic complications  rates of the zirconia‐ceramic and/or monolithic zirconia  implant‐supported multiple‐unit FDPs, as compared to the golden‐standard, the metal ceramics implant‐supported multiple‐unit FDPs.  

Materials and Methods
Randomized controlled clinical trials, prospective cohort studies and retrospective case series on implant‐supported FDP s with a mean follow‐up of at least 3  years, were selected for the review and failures and complications  rates were then analyzed.  

Results
The first group consisted of 932 metal‐ceramic FDPs with a mean follow‐up of 6.3 years and the second group of 175 zirconia  FDPs and a mean follow‐up time of 5.1 years.  

SURVIVAL:
 -From meta‐analysis data it is highlighted that 15 out of the 932 metal ceramics implant‐supported FDPs originally inserted were lost. 5‐year survival rate for metal ceramics implant‐supported FDPs results to be 98.7% (95% CI: 96.8%–99.5%).  
 -From the 175 zirconia  implant‐supported FDPs, nine were lost. For this group, 5‐year survival rate for zirconia  implant‐supported FDPs was 93.0% (95% CI: 90.6%–94.8%).  
 -The difference in survival rates between metal ceramics and zirconia FDPs reached statistical significance (p  < 0.001).  

SUCCESS:
 - Three studies including 371 metal ceramics  implant‐supported FDPs reported on the total number of FDPs with biological or technical complication. The estimated 5‐year complication  rate for metal ceramics  FDPs was 15.1% (95% CI: 11.2%–20.4%).
- None of the included studies on zirconia  implant‐supported FDPs reported on the total number of complication or the number of FDPs free of all complication.  

TECHNICAL COMPLICATIONS:
 -The total number of complication  found at the metal ceramics FDPs was 15.1% (95% CI: 11.2%–20.4%).
 -None of the studies on the zirconia ‐ceramic FDPs reported the total number of complication.
 -Thirteen studies with 781 metal ceramics implant‐supported FDPs estimated a 5‐year rate of pronounced ceramic fractures and chippings to be 11.6% compared with a significantly higher (p  < 0.001) rate for extensive fracture and chipping for zirconia implant‐supported FDPs of 50%, reported in a small study with only 13 zirconia implant‐supported FDPs.       

BIOLOGICAL COMPLICATIONS:
-5‐year rate of peri‐implantitis or soft tissue complication was estimated to be 3.1% for metal ceramics implant‐supported FDPs. 
- based on one study reporting on 73 FDPs, 5-year rate for zirconia  implant‐supported FDPs  is 10,1%.
-biological complication  was estimated to be significantly (p = 0.030) higher for zirconia  implant‐supported FDPs  

Conclusions
 Data emerged from this review reveal that for implant‐supported FDP s, metal ceramics seems to remain the golden standard. Due to the pronounced risk of chipping and fractures, veneered zirconia  should not be considered as first choice material. Monolithic zirconia  instead should be considered as an alternative, but further study about its potential are necessary.

For additional information:  A Systematic Review of the Survival and Complication Rates of Zirconia-Ceramic and Metal-Ceramic Multiple-Unit Fixed Dental Prostheses