Usama Nassar DDS MS
Survival rates of short-unit, zirconia-based fixed dental prostheses (FDP) appear promising, but improved veneering systems are required to decrease chipping; however, we need more randomized controlled trials to evaluate FDPs with more units.
In adults, what are the 5-year survival rates and complication-free rates of ceramic zirconia-based FDPs based on technical and biological considerations?
Three reviewers independently searched one electronic literature database (MEDLINE: PubMed) to identify clinical studies published between January 1999 and November 2009 in German and English languages. They complemented this search by manually searching within the references of selected full-text articles plus two German-language journals. They included prospective clinical trials with follow-up exams that had a mean of at least three years, survival and failures reported and description of technical and biological complications and repair. Excluded studies contained inlay or implant- retained prostheses, single crowns, esthetic aspects or patient satisfaction, same patient cohorts used multiple times, and in vitro studies. They described, but did not analyze, periodontal parameters and marginal gaps. They defined "survival" as the FPD still being in situ at the end of the observation period. "Failure" included every type of complication that led to prostheses removal. Technical complications included: chipping of porcelain, framework fracture, and loss of retention. Biological complication included: caries, loss of vitality, endodontic issues, and fracture of abutment tooth. They fitted a Poisson regression model with a logarithmic like-function and logarithm of total exposure time as an offset variable to the data in order to obtain a 95% confidence interval for all included studies. They used SAS software to analyze survival rates and corresponding 95% confidence limits.
Out of 399 titles found by the database search, the reviewers selected nine clinical studies that dealt with survival of the FPDs and met all inclusion/exclusion criteria. In these nine studies, 330 FDPs of different span length were initially inserted, and 33 FDPs were defined as dropouts. The mean follow-up period of the 297 remaining FDPs was 3.57 years. The 5-year mean survival rate was 94.29% (95% CI: 58.98-99.32%) for all FDPs. The five -year complication-free rate was 76.41% (95% CI: 42.42-91.60%). For biological complications, the five -year complication-free rate was 91.72% (95% CI: 59.19-98.53).
Short-span posterior zirconia frameworks are stable. The zirconia veneering technique should be improved, since chipping was the most frequent complication. The reviewers found limited value in assessing long-span and cantilevered FDPs. To provide guidelines for these restorations, randomized controlled clinical trials using a meta-analysis are needed.
Source of Funding:
Source of funding was not specified.
Importance and Context:
In vitro testing of different zirconia systems have shown no significant effects on fracture load for three-unit FDPs. Currently, zirconia-based core materials have become popular due to their excellent mechanical properties and high biocompatibility. Since there are no literature reviews that solely discuss zirconia rather than all types of ceramic FDPs, the five -year clinical survival rates of zirconia FDPs and incidences of technical and biological complications need to be evaluated.
Strengths and Weaknesses of the Systematic Review:
The review asked a clear question regarding the survival rates of zirconia FDPs. Although the three reviewers independently searched only one electronic database, they supplemented this electronic search with a manual one. They resolved disagreements by discussion. The studies provided details of the electronic search, such as key words and MESH headings, and fairly presented the characteristics of the included studies. The authors presented a succinct comparison of biological and technical survival rates of each included study. The review did not provide a quality assessment of the individual studies nor any evidence of using "grey literature" in the inclusion criteria. The reviewers included only studies with English and German languages. They did not discuss publication bias. The survival rate was evaluated irrespective of the number of units in the FDPs, design or location in the oral cavity.
Strengths and Weaknesses of the Evidence:
The authors reported the individual study results in tables, but they did not elaborate on outliers, leaving reasons for isolated occurrences of high chipping rates unknown. The review succeeded in showing high overall survival rate for short-unit zirconia FDPs; however, the nine studies reported the use of different veneering and ceramic systems. Furthermore, identification of the evaluation criteria for complications was not clear in some of the studies. One study included comparisons of cantilever to end-abutment FDPs. The reviewers did not categorize the location of any restoration in the mouth.
Implications for Dental Practice:
Implications for Dental Practice: This systematic review, based on nine small prospective cohort studies, suggests that the mean five -year overall survival rate of short-unit zirconia-based FDPs of 94% is promising. The technical five-year complication-free rate--with material chipping as the main complication-- was 76%, implying a need for improvement of the veneering system. A more recent systematic review, based on an RCT and 11 prospective cohorts with three year follow up, also concluded that zirconia FDPs are acceptable and may serve as an alternative to metal ceramic prostheses.1 Another systematic review, based on 13 studies on zirconia and two studies comparing zirconia to metal supported FDPs with three-year follow up, concluded that veneer chipping was higher in zirconia FDPs and clinical studies are needed to evaluate fabrication techniques.2 Longer-term randomized controlled clinical trials of zirconia-based FPDs are needed to evaluate their survival rates in comparison with other materials such as metal-ceramic restorations. 1. Raigrodski AJ, Hillstead MB, Meng GK, Chung K-H. Survival and complications of zirconia-based fixed dental prostheses: A systematic review J Prosthet Dent 2012;107:170-7, 2012. 2. Henitze SD, Rousson V. Survival of zirconia- and metal-supported fixed dental prostheses: a systematic review. Int J Prosthodont 2010;23(6):493-502. *Support for this Critical Summary was provided by a grant from the Canadian Institutes of Health Research*