To assess the 5-year survival of metal-ceramic and all-ceramic tooth-supported single crowns (SCs) and to describe the incidence of biological, technical and esthetic complications.
Medline (PubMed), Embase, Cochrane Central Register of Controlled Trials (CENTRAL) searches (2006–2013) were performed for clinical studies focusing on tooth-supported fixed dental prostheses (FDPs) with a mean follow-up of at least 3 years. This was complimented by an additional hand search and the inclusion of 34 studies from a previous systematic review . Survival and complication rates were analyzed using robust Poisson’s regression models to obtain summary estimates of 5-year proportions.
Sixty-seven studies reporting on 4663 metal-ceramic and 9434 all-ceramic SCs fulfilled the inclusion criteria. Seventeen studies reported on metal-ceramic crowns, and 54 studies reported on all-ceramic crowns. Meta-analysis of the included studies indicated an estimated survival rate of metal-ceramic SCs of 94.7% (95% CI: 94.1–96.9%) after 5 years. This was similar to the estimated 5-year survival rate of leucit or lithium-disilicate reinforced glass ceramic SCs (96.6%; 95% CI: 94.9–96.7%), of glass infiltrated alumina SCs (94.6%; 95% CI: 92.7–96%) and densely sintered alumina and zirconia SCs (96%; 95% CI: 93.8–97.5%; 92.1%; 95% CI: 82.8–95.6%). In contrast, the 5-year survival rates of feldspathic/silica-based ceramic crowns were lower ( p < 0.001). When the outcomes in anterior and posterior regions were compared feldspathic/silica-based ceramic and zirconia crowns exhibited significantly lower survival rates in the posterior region ( p < 0.0001), the other crown types performed similarly. Densely sintered zirconia SCs were more frequently lost due to veneering ceramic fractures than metal-ceramic SCs ( p < 0.001), and had significantly more loss of retention ( p < 0.001). In total higher 5 year rates of framework fracture were reported for the all-ceramic SCs than for metal-ceramic SCs.
Survival rates of most types of all-ceramic SCs were similar to those reported for metal-ceramic SCs, both in anterior and posterior regions. Weaker feldspathic/silica-based ceramics should be limited to applications in the anterior region. Zirconia-based SCs should not be considered as primary option due to their high incidence of technical problems.
All-ceramic fixed dental prostheses (FDPs) are considered an established treatment alternative to metal-ceramic FDPs in daily clinical practice. The main reason to use of the all-ceramics instead of metal-ceramics is based on more favorable esthetics . All-ceramic materials mimic very naturally the optical properties of teeth. Another more recent factor influencing the choice of materials and leading to an increasing use of all-ceramics is treatment costs, mostly due to the pronounced raise of the costs for high precious metals like gold .
The main shortcoming of the firstly introduced ceramics like, e.g. feldspathic glass ceramic, yet, was low mechanical stability, which limited the indications for all-ceramic reconstructions to anterior regions and to single-unit FDPs . In the past years, numerous new dental ceramic materials were developed with the aim to increase the overall stability of the all-ceramic reconstructions, while still maintaining the esthetic benefit. Among those materials, leucite or lithium-disilicate leucit or lithium-disilicate reinforced glass ceramics and oxide ceramics such as alumina and zirconia appeared to be very promising for different indications. Reconstructions made of these more recently developed ceramics were placed at posterior sites and even included multiple-unit FDPs .
Subsequently performed clinical studies confirmed the assumption that these mechanically more stable ceramic materials would perform better than the firstly developed ones when used for tooth-borne FDPs. The clinical outcomes of the more recent ceramics were far better than the ones of the first generation of dental ceramics . A systematic review of the literature demonstrated significantly higher survival rates of SCs, e.g. made out of leucit or lithium-disilicate reinforced glass ceramics compared to SCs made out of feldspathic ceramics (95.4% vs. 87.5%). Tooth-borne SCs made out of densely sintered alumina exhibited the highest survival rates (96.4%) compared to all other all-ceramic SCs. Furthermore, all-ceramic crowns exhibited similar survival rates as metal-ceramic crowns (93.3% vs. 95.6%) . In conclusion, improvements in terms of material properties such as mechanical stability of the ceramics had a positive effect on the clinical outcomes of all-ceramic reconstructions.
The clinical follow-up of the studies on all-ceramic FDPs, however, was rather short. At time of the above-mentioned systematic review a limited amount of studies was available, most of the published studies did not exceed 5 years of clinical follow-up. In order to be able to draw clinical conclusions with respect to the outcomes of all-ceramic reconstructions, more clinical research with longer observation periods was needed. In addition, the available clinical research indicated that despite of all material improvements catastrophic fractures remained to be one major issue of all-ceramic reconstructions. In addition, this problem was more often found in the posterior region, or for multiple-unit FDPs where high load occurred .
Hence, until recently, it was not possible to recommend all-ceramic single or multiple-unit FDPs as clinically equivalent treatment alternative to metal ceramic FDPs. Metal-ceramics remained to be the “gold standard” type of reconstruction. Yet, a high number of new manuscripts of all-ceramic and metal-ceramic single- and multiple-unit FDPs was published since the previously mentioned systematic review. The more recent studies either reported on the all-ceramic or metal-ceramic FDPs analyzed before but with longer observation periods, or on new all-ceramic FDPs made out of improved ceramic materials.
Therefore, the aim of the present systematic review was to analyze the outcomes of all-ceramic and metal-ceramic FDPs, i.e. of single crowns and of multiple-unit FDPs, and to assess whether or not all-ceramic FDPs achieve similar long-term results as FDPs made out of metal-ceramics.
The objectives of this systematic review, therefore, were:
To update the previous systematic review on tooth-supported FDPs with an additional literature search including retrospective and prospective studies from 2007 to 2013.
To obtain overall robust estimates of the long-term survival and complication rates of all-ceramic crowns over an observation period of at least 3 years.
To compare the survival and complication rates of all-ceramic crowns with the ones of metal-ceramic crowns (gold standard).
The present part 1 of the review presents the outcomes of all-ceramic versus metal-ceramic single crowns. Part 2 of the review analyzed the outcomes of the multiple-unit FDPs.