The clinical success of tooth‐ and implant‐supported zirconia‐based fixed dental prostheses. A systematic review

The aim was to make an inventory of the current literature on the clinical performance of tooth‐ or implant‐supported zirconia‐based FDPs and analyse and discuss any complications. Electronic databases, PubMed.gov, Cochrane Library and Science Direct, were searched for original studies reporting on the clinical performance of tooth‐ or implant‐supported zirconia‐based FDPs. The electronic search was complemented by manual searches of the bibliographies of all retrieved full‐text articles and reviews, as well as a hand search of the following journals: International Journal of Prosthodontics, Journal of Oral Rehabilitation, International Journal of Oral & Maxillofacial Implants and Clinical Oral Implants Research. The search yielded 4253 titles. Sixty‐eight potentially relevant full‐text articles were retrieved. After applying pre‐established criteria, 27 studies were included. Twenty‐three studies reported on tooth‐supported and 4 on implant‐supported FDPs. Five of the studies were randomised, comparing Y‐TZP‐based restorations with metal–ceramic or other all‐ceramic restorations. Most tooth‐supported FDPs were FDPs of 3–5 units, whereas most implant‐supported FDPs were full arch. The majority of the studies reported on 3‐ to 5‐year follow‐up. Life table analysis revealed cumulative 5‐year survival rates of 93·5% for tooth‐supported and 100% for implant‐supported FDPs. For tooth‐supported FDPs, the most common reasons for failure were veneering material fractures, framework fractures and caries. Cumulative 5‐year complication rates were 27·6% and 30·5% for tooth‐ and implant‐supported FDPs, respectively. The most common complications were veneering material fractures for tooth‐ as well as implant‐supported FDPs. Loss of retention occurred more frequently in FDPs luted with zinc phosphate or glass–ionomer cement compared to those luted with resin cements. 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.     

Clinical performance of long-span zirconia frameworks for fixed dental prostheses: 5-year results

The purpose of this prospective cohort study was to assess the performance of tooth-supported, long-span, zirconia fixed dental prostheses (FDPs). Thirty FDPs with span lengths from 36 to 46 mm (mean 40·33 mm), with 4-7 units and with connector dimensions ～9 mm(2) were inserted (19 in the posterior region, 11 including anterior teeth) using glass-ionomer cement. The performance of the FDPs was assessed (aesthetic evaluation, failures, hypersensitivity/tooth vitality, secondary caries, pocket depth, decementation, and chipping) at baseline and after 5 years. Cox regression analysis was performed to identify risk factors. There were 16 failures after 5 years. Framework fracture occurred for two FDPs, four FDPs had to be re-cemented, one abutment tooth had to be treated endodontically, one abutment tooth fractured and cohesive failure of the veneer occurred for eight. Four FDPs had to be replaced, so survival was 82%. The aesthetics were rated as excellent by the patients at baseline and good at the 5-year recall. Cox regression analysis showed that both length [P = 0·05, exp(B) = 1·22] and location [P = 0·019, exp(B) = 4·09] of the FDP were risk factors for failure. Compared with the previously published 2-year results, the incidence of complications increased dramatically. Additionally, it was shown that long-span FDPs in the molar region are at greater risk of failure than FDPs in the anterior region.     

Four‐year clinical results of fixed dental prostheses with zirconia substructures (Cercon): end abutments vs. cantilever design

The purpose of this prospective study was to evaluate the clinical outcome of three‐ to four‐unit posterior all‐ceramic fixed dental prostheses (FDPs) made of yttria‐stabilized tetragonal zirconia‐polycrystal ceramic frameworks (CerconBase; Degudent). Fifty‐eight restorations were placed in 48 patients. Twenty‐four FDPs had an end abutment design (EAD) replacing 3 premolars and 21 molars. Thirty‐four FDPs had a cantilever design (CD) replacing 11 premolars and 23 molars. The frameworks had a minimum proximal connector dimension of 3 × 3 mm. The fixed dental prostheses were cemented with glass‐ionomer cement after air‐abrading the inner crown surfaces. Three FDPs were defined as drop‐outs. The mean observation period was 48 ± 7 months for the EAD (21 patients/24 FDPs) and 50 ± 14 months for the CD (25 patients/31 FDPs). The 4‐yr survival rate, according to the Kaplan–Meier analyses, was 96% for the EAD and 92% for the CD. The technical complication rate was 13% for the EAD and 12% for the CD, and the biological complication rate was 21% for the EAD and 15% for the CD. For none of the analyses were significant differences found between both groups. After 4 yr the clinical outcome of three‐ to four‐unit posterior FDPs with EAD and CD was promising.     

All-ceramic inlay-retained fixed dental prostheses for replacing posterior missing teeth: A systematic review

Purpose

To evaluate the current status of all-ceramic inlay-retained fixed dental prostheses (CIR-FDPs) for the replacement of posterior teeth.

Load-bearing capacity of all-ceramic posterior inlay-retained fixed dental prostheses

The purpose of this in vitro study was to compare the quasi-static load-bearing capacity of all-ceramic resin-bonded three-unit inlay-retained fixed dental prostheses (IRFDPs) made from computer-aided design/computer-aided manufacturing (CAD/CAM)-manufactured yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) frameworks with two different connector dimensions, with and without fatigue loading. Twelve IRFDPs each were made with connector dimensions 3 × 3 mm² (width × height) (control group) and 3 × 2 mm² (test group). Inlay-retained fixed dental prostheses were adhesively cemented on identical metal-models using composite resin cement. Subgroups of six specimens each were fatigued with maximal 1,200,000 loading cycles in a chewing simulator with a weight load of 25 kg and a load frequency of 1.5 Hz. The load-bearing capacity was tested in a universal testing machine for IRFDPs without fatigue loading and for IRFDPs that had not already fractured during fatigue loading. During fatigue testing one IRFDP (17%) of the test group failed. Under both loading conditions, IRFDPs of the control group exhibited statistically significantly higher load-bearing capacities than the test group. Fatigue loading reduced the load-bearing capacity in both groups. Considering the maximum chewing forces in the molar region, it seems possible to use zirconia ceramic as a core material for IRFDPs with a minimum connector dimension of 9 mm². A further reduction of the connector dimensions to 6 mm² results in a significant reduction of the load-bearing capacity.     

Ten-year outcome of three-unit fixed dental prostheses made from monolithic lithium disilicate ceramic

BackgroundThe authors conducted a prospective study to evaluate the long-term outcome of crown-retained fixed dental prostheses (FDPs) made from monolithic lithium disilicate ceramic (IPS e.max Press, Ivoclar Vivadent, Schaan, Liechtenstein).MethodsFaculty dentists at the Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Germany, placed 36 three-unit FDPs in 28 patients to replace six anterior and 30 posterior teeth. The proximal connector size (height and width) was 4 × 3 millimeters for anterior FDPs and 4 × 4 mm for posterior FDPs. FDPs were cemented either conventionally with glass ionomer cement (n = 19) or adhesively with resin-based composite (n = 17). Patients made annual recall visits.ResultsThe mean (standard deviation) observation period was 121 (12.8) months. FDPs' survival rate (survival being defined as remaining in place either with or without complications) was 100 percent after five years and 87.9 percent after 10 years, and their success rate (success being defined as remaining unchanged and free of complications) was 91.1 percent after five years and 69.8 percent after 10 years. The cementation method did not affect the outcome.ConclusionThree-unit FDPs made from monolithic lithium disilicate ceramic showed five- and 10-year survival and success rates that were similar to those of conventional metal-ceramic FDPs.Clinical ImplicationsIf the manufacturer's recommendations are followed, three-unit FDPs made from monolithic lithium disilicate ceramic may be a safe alternative to metal-ceramic FDPs regardless of the cementation method used.     

Survival and failure modes: platform‐switching for internal and external hexagon cemented fixed dental prostheses

This study evaluated the probability of survival (reliability) of platform‐switched fixed dental prostheses (FDPs) cemented on different implant–abutment connection designs. Eighty‐four‐three‐unit FDPs (molar pontic) were cemented on abutments connected to two implants of external or internal hexagon connection. Four groups (n = 21 each) were established: external hexagon connection and regular platform (ERC); external hexagon connection and switched platform (ESC); internal hexagon and regular platform (IRC); and internal hexagon and switched platform (ISC). Prostheses were subjected to step‐stress accelerated life testing in water. Weibull curves and probability of survival for a mission of 100,000 cycles at 400 N (two‐sided 90% CI) were calculated. The beta values of 0.22, 0.48, 0.50, and 1.25 for groups ERC, ESC, IRC, and ISC, respectively, indicated a limited role of fatigue in damage accumulation, except for group ISC. Survival decreased for both platform‐switched groups (ESC: 74%, and ISC: 59%) compared with the regular matching platform counterparts (ERC: 95%, and IRC: 98%). Characteristic strength was higher only for ERC compared with ESC, but not different between internal connections. Failures chiefly involved the abutment screw. Platform switching decreased the probability of survival of FDPs on both external and internal connections. The absence in loss of characteristic strength observed in internal hexagon connections favor their use compared with platform‐switched external hexagon connections.     

Fracture resistance of zirconia‐based all‐ceramic crowns after bur adjustment

Intra‐oral grinding is often required to optimize occlusion of all‐ceramic restorations. The effect of burs of different grit size on the fracture resistance of veneered zirconia crowns was investigated in this study. Forty‐eight standardized zirconia copings were produced. The ceramic veneer was designed with a positive ellipsoidal defect on the palatal aspect of the crowns. To simulate adjustment of dental restorations by burs, this palatal defect was removed by use of three different diamond‐coated burs with grit sizes 46, 107, or 151 μm (fine, medium, or coarse, respectively). Each different grit size of bur was used to grind 16 crowns. All crowns were then polished and surface roughness was measured. Half of the specimens underwent thermomechanical aging (10,000 thermocycles between 6.5°C and 60°C) and 1.2 million cycles of chewing simulation (F = 108 N). A linear regression model was computed to test the effect of aging and grinding grit size at a level of significance of α = 0.05. Fracture loads increased with decreasing grit size. Grit size and aging had a significant effect on the fracture resistance of the crowns. Use of fine and coarse burs for intra‐oral adjustments resulted in different fracture resistance of veneered zirconia crowns. Coarse burs should be avoided in the final stage of grinding before polishing.     

Fractographic features of glass‐ceramic and zirconia‐based dental restorations fractured during clinical function

Fractures during clinical function have been reported as the major concern associated with all‐ceramic dental restorations. The aim of this study was to analyze the fracture features of glass‐ceramic and zirconia‐based restorations fractured during clinical use. Twenty‐seven crowns and onlays were supplied by dentists and dental technicians with information about type of cement and time in function, if available. Fourteen lithium disilicate glass‐ceramic restorations and 13 zirconia‐based restorations were retrieved and analyzed. Fractographic features were examined using optical microscopy to determine crack initiation and crack propagation of the restorations. The material comprised fractured restorations from one canine, 10 incisors, four premolars, and 11 molars. One crown was not categorized because of difficulty in orientation of the fragments. The results revealed that all core and veneer fractures initiated in the cervical margin and usually from the approximal area close to the most coronally placed curvature of the margin. Three cases of occlusal chipping were found. The margin of dental all‐ceramic single‐tooth restorations was the area of fracture origin. The fracture features were similar for zirconia, glass‐ceramic, and alumina single‐tooth restorations. Design features seem to be of great importance for fracture initiation.     

Clinical performance of extended zirconia frameworks for fixed dental prostheses: two-year results

Summary  The purpose of this prospective cohort study was to assess the performance of tooth-supported, extended zirconia, fixed dental prostheses (FDPs). Thirty FDPs with span-lengths between 36 and 46 mm (mean: 40·33 mm), four to seven units and with connector dimensions of ∼9 mm² were inserted (19 in the posterior region, 11 including anterior teeth) using glass–ionomer cement and assessed (aesthetic evaluation, failures, hypersensitivity/tooth vitality, secondary caries, pocket depth, decementation and chipping) at baseline and after 2 years. Differences between baseline and 2-year recall were analysed using the Wilcoxon signed-rank test for matched pairs. There were five failures. One FDP revealed a core fracture at the base of the connector, probably caused by a damage induced during fabrication. Two FDPs had to be recemented, one abutment tooth had to be treated endodontically and one cohesive failure of the veneer was observed. There were no significant changes of pocket depth and hypersensitivity between baseline and 2-year recall. The aesthetics were rated as excellent by the patients at both baseline and recall. Two year clinical results of extended zirconia based FDPs with 9 mm² connectors are promising.     

Fracture load of tooth-implant-retained zirconia ceramic fixed dental prostheses: effect of span length and preparation design

Objectives: Evaluation of the effect of different span length and preparation designs on the fracture load of tooth–implant‐supported fixed dental prostheses (TIFDPs) manufactured from yttrium‐stabilized zirconia frameworks. Material and methods: Forty‐eight TIFDPs were manufactured using a CAD/CAM system and veneered with a press ceramic. Rigidly mounted implants (SLA, diameter 4.1 mm, length 10 mm) in the molar region with a titanium abutment were embedded in PMMA bases pairwise with premolars. All premolars were covered with heat‐shrink tubing to simulate physiological tooth mobility. Six different test groups were prepared (a) differing in the preparation design of the premolar (inlay [i]; crown [c]), (b) the material of the premolar (metal [m]; natural human [h]) and (c) the length of the TIFDPs (3‐unit [3]; 4‐unit [4]). All TIFDPs underwent thermomechanical loading (TCML) (10,000 × 6.5°/60°; 6 × 10⁵× 50 N). The load to fracture (N) was measured and fracture sites were evaluated macroscopically. Results: None of the restorations failed during TCML. The mean fracture loads (standard deviations) were 1,522 N (249) for the 3‐unit, inlay‐retained TIFDPs on a metal abutment tooth (3‐im), 1,910 N (165) for the 3‐cm group, 1,049 N (183) for group 4‐im, 1,274 N (282) for group 4‐cm, 1,229 N (174) for group 4‐ih and 911 N (205) for group 4‐ch. Initial damages within the veneering ceramic occurred before the final failure of the restoration. The corresponding loads were 24–52% lower than the fracture load values. Conclusions: All restorations tested could withstand the mastication forces expected. Fracture‐load values for 3‐ and 4‐unit inlay–crown and crown–crown‐retained TIFDPs should spur further clinical investigation.