L. Virginia Powell DMD, GPR
When evaluated after a five-year period, all-ceramic crowns placed on natural posterior teeth fail at a higher rate than those placed on anterior teeth, with molar crowns fracturing at a significantly higher rate than those placed on premolar teeth.
This is a comprehensive review of heterogeneous clinical trials, combined without quality assessment. It concluded that all-ceramic crowns fabricated with currently used materials demonstrate relatively low fracture rates, with molar crown fractures being more frequent than those on premolar or anterior teeth.
What is the 5-year fracture incidence of all-ceramic crowns placed on natural tooth structure and how does it compare among tooth types?
Review authors searched four databases using broad search terms for articles published between 1990 and May 2011 in English and Chinese. They manually searched the bibliographies of selected articles and the table of contents of selected journals. Inclusion criteria required that studies be either prospective or retrospective with at least a three-year follow-up and report details regarding materials and tooth type. Authors excluded questionnaires, chart reviews, case studies, animal studies, and in vitro studies. They also excluded studies in which restorations were placed on implants only and those that reported results solely for indirect restorations other than all-ceramic full crowns. Two reviewers independently determined study acceptance and data collection. Disagreements were resolved after discussion. Review authors contacted study authors for missing data; they made no formal attempt to assess the quality of the included studies. They calculated annual and 5-year fracture rates using Poisson regression methods. Authors classified fractures as either "core" or "veneer" when possible.
The authors selected 37 articles for review from an initial pool of 5,600 records, resulting in a total tooth count of 5,207. Only two studies were randomized controlled trials. Ceramic crown materials included: sintered alumina crowns (8 studies/700 crowns, Procera AllCeram); glass-infiltrated crowns (10 studies/1,054 crowns, In-Ceram Alumina and Spinell); feldspathic porcelain crowns (6 studies/193 crowns, Vita Mark II); lithium disilicate-reinforced crowns (4 studies/397 crowns, IPS e.max and IPS Empress 2); leucite-reinforced glass ceramic (6 studies/1,129 crowns, IPS Empress, Finesse); and zirconia-based crowns (2 studies/233 crowns, Lava Zirconia, Porcera Zirconia) . Five studies (1,501 teeth) that reported the fracture rate for glass-ceramic crowns (Dicor, Cerestore, Hi-ceram) were segregated for separate analysis because their fracture rate was high and the materials are no longer used . These studies were, however, included in the principal analysis.
The combined 5-year overall fracture incidence rate (for both core and veneer fractures) for all studies was 7.7 percent for all studies. When the glass-ceramic crowns were excluded, the modified 5-year overall fracture rate was 4.4 percent. The difference between posterior teeth (modified 5-year overall, 5.4 percent) and anterior teeth (modified 5-year overall, 3.0 percent) was statistically significant (p < 0.001 calculated on annual rates). Further, the modified analysis determined that molar crowns demonstrated a significantly higher fracture rate than that of premolar crowns (8.1 percent vs. 3.0 percent, p < 0.001, calculated on annual rates). Core fractures followed a similar, significant trend; veneer fractures did as well although results were not significant.
The authors concluded that all-ceramic crowns demonstrated an acceptable rate of fracture over 5 years; that posterior crowns fractured at a higher rate than anterior crowns; and that molar crowns fractured at a higher rate than premolar crowns.
Source of Funding:
This study was supported by grants from the National Natural Science Foundation of China and Fundamental Research Funds for the Central Universities of China.
Importance and Context:
Patients' expectations for esthetic dental restorations can be high. All-ceramic crowns offer the best chance for excellent esthetics. As most of these materials are relatively new, at least when compared to the gold standard of porcelain-fused-to-metal crowns, determining their failure rate is essential to describing the risks, benefits, and restorative treatment options to the patient.
Strengths and Weaknesses of the Systematic Review:
The reviewers designed a thorough and broad search strategy and established a priori inclusion and exclusion criteria. Two reviewers independently determined which studies met the criteria and reconciled any disagreements. No population demographics were reported, and the data may have been easier to follow with graphic representation. The authors did not evaluate the studies for risk of bias, and only addressed heterogeneity descriptively in a limited manner. However, ceramic systems that are quite different were combined, perhaps inappropriately. If the crowns had been stratified by technique, it appears that crowns fabricated by CAD/CAM and hot pressing may fail at different rates.
Strengths and Weaknesses of the Evidence:
The evidence included only two randomized clinical trials. Head-to-head trials comparing the different types of all-ceramic crowns were also few in number, and trials often reported outcome variables that had limited clinical usefulness. For example, not all fractures require a redo of the procedure. Further, crowns fabricated by a veneering technique may not be as likely to require a redo if partial fracture occurs and the tooth is located in the posterior regions where esthetics is less of a concern. Some of the ceramic systems were obsolete; however, frequent changes in materials make it difficult to conduct a clinically relevant trial of longer-term outcomes.
Implications for Dental Practice:
All-ceramic crowns placed on natural tooth structure will fail at a higher rate when placed on posterior teeth. How the fracture rate varies among the different all-ceramic techniques and materials, and how the fracture rate of all-ceramic crowns compares to that of the gold standard, porcelain-fused-to-metal, has yet to be determined. References: 1. Bona AD, Kelly JR. The Clinical Success of All-Ceramic Restorations. JADA 2008; 139(suppl 4):8S-13S. 2. Griggs, JA. Recent Advances in Materials for All-Ceramic Restorations. Dent Clin North Am 2007; 51(3):713viii.