Clinical fit of four‐unit zirconia posterior fixed dental prostheses

The objective of this clinical study was to assess the internal and marginal accuracy of computer‐aided design/computer‐aided manufacturing (CAD/CAM)‐generated four‐unit all‐ceramic posterior fixed dental prostheses (FDPs). The data were compared with the results of three‐unit metal‐ceramic and all‐ceramic FDPs that were obtained in a previous study. Twenty‐four patients were provided with all‐ceramic posterior four‐unit FDPs made from semisintered blank zirconia material. Prior to definitive insertion the accuracy was evaluated using a replica technique with a light body silicone that was stabilized with a heavy body material. The replica samples were examined using microscopy. The median marginal gap of the 24 four‐unit FDPs was 77 μm. The median gap widths were 87 μm at the midaxial wall, 167 μm at the axio‐occlusal transition of the abutments, and 170 μm at centro‐occlusal location. Although the marginal accuracy of the four‐unit FDPs differed significantly from that of the three‐unit metal‐ceramic FDPs (median 54 μm), the values obtained were clinically satisfactory and showed that semisintered zirconia blanks could be used for the fabrication of four‐unit FDPs.     

Eight-year outcome of posterior inlay-retained all-ceramic fixed dental prostheses

Aim

The main goal of this prospective clinical study was to evaluate the outcome of inlay-retained fixed dental prostheses (FDPs) made from heat-pressed lithium-disilicate glass-ceramic.

Methods

Forty-five FDPs were placed in 42 patients (21 women, mean age 36.1 years and 21 men, mean age 42.0 years). The FDPs replaced 4 premolars and 19 molars in the maxilla and 4 premolars and 18 molars in the mandible. Preparations were performed in accordance with general principles for ceramic inlay restorations. Five of the 45 FDPs were hybrid-retained restorations, i.e. one abutment tooth with an inlay retainer and one with a full crown retainer.All FDPs were pressed in one piece using lithium-disilicate ceramic (IPS e.max Press, Ivoclar Vivadent). The minimum dimensions for the proximal connector were 4 mm in height and 4 mm in width (16 mm²) with a minimum occlusal ceramic thickness of 1.5 mm. The surfaces of the inlay retainer were conditioned by etching with hydrofluoric acid 5% and silane application. Standard adhesive luting techniques were performed using a dentin adhesive (Syntac Classic, Ivoclar Vivadent) and a resin composite (Variolink II, Ivoclar Vivadent). Clinical follow-up examinations were performed annually.

Results

The mean observation periods were 70 months (minimum 4, maximum 123 months). Twenty-seven FDPs (60%) failed during the observation period and had to be replaced. The Kaplan–Meier survival rate for inlay-retained FDPs was 57% after 5 years and 38% after 8 years, while for hybrid-retained FDPs it was 100% after 5 and 60% after 8 years.

Conclusions

Inlay-retained FDPs made from lithium-disilicate ceramic present a high clinical failure rate and therefore cannot be recommended.     

Influence of Preliminary Damage on the Load‐Bearing Capacity of Zirconia Fixed Dental Prostheses

Purpose: The objective of this investigation was to evaluate the influence of differently shaped preliminary cuts in combination with artificial aging on the load‐bearing capacity of four‐unit zirconia fixed dental prostheses (FDPs). Materials and Methods: Forty frameworks were fabricated from white‐stage zirconia blanks (InCeram YZ, Vita) by means of a computer‐aided design/computer‐aided manufacturing system (Cerec inLab, Sirona). Frameworks were divided into four homogeneous groups with ten specimens each. Prior to veneering, frameworks of two groups were “damaged” by defined saw cuts of different dimensions, to simulate accidental flaws generated during shape cutting. After the veneering process, FDPs, with the exception of a control group without preliminary damage, were subjected to thermal and mechanical cycling (TMC) during 200 days storage in distilled water at 36°C. Following the aging procedure, all specimens were loaded until fracture, and forces at fracture were recorded. The statistical analysis of force at fracture data was performed using two‐way ANOVA, with the level of significance chosen at 0.05. Results: Neither type of preliminary mechanical damage significantly affected the load‐bearing capacity of FDPs. In contrast, artificial aging by TMC proved to have a significant influence on the load‐bearing capacity of both the undamaged and the predamaged zirconia restorations (p < 0.001); however, even though load‐bearing capacity decreased by about 20% due to simulated aging, the FDPs still showed mean load‐bearing capacities of about 1600 N. Conclusions: The results of this study reveal that zirconia restorations have a high tolerance regarding mechanical damages. Irrespective of these findings, damage to zirconia ceramics during production or finishing should be avoided, as this may nevertheless lead to subcritical crack growth and, eventually, catastrophic failure. Furthermore, to ensure long‐term clinical success, the design of zirconia restorations has to accommodate the decrease in load‐bearing capacity due to TMC in the oral environment.     

Effect of veneering technique on the fracture resistance of zirconia fixed dental prostheses

Summary To compare the fracture resistance of zirconia 3‐unit posterior fixed dental prostheses (FDPs) frameworks veneered with different veneering materials and techniques before and after artificial ageing. Forty‐eight zirconia 3‐unit FDPs, representing a missing first molar, were adhesively cemented on human teeth. The zirconia frameworks were randomly distributed according to the veneering materials and techniques into three groups, each containing 16 samples: group LV (layering technique/Vintage ZR), group LZ (layering technique/ZIROX) and group PP (CAD/CAM and press‐over techniques/PressXZr). Half of each group was artificially aged through dynamic loading and thermocycling to simulate 5 years of clinical service. Afterwards, all specimens were tested for fracture resistance using compressive load. An analysis of variance (anova ) was used to assess the effect of veneering ceramic and artificial ageing on fracture resistance (P < 0·05). Except for one minor cohesive chipping in group LV1, all specimens survived artificial ageing. The mean fracture resistance values (in Newton) of different non‐aged (± s.d.)/aged (± s.d.) groups were as follows: LV0 2034 (± 401)/LV1 1625 (± 291); LZ0 2373 (± 718)/LZ1 1769 (± 136); and PP0 1959 (± 453)/PP1 1897 (± 329). Artificial ageing significantly reduced the fracture resistance in groups veneered with the layering technique (P < 0·05), whereas no significant effect was found in specimens veneered with the CAD/CAM and press‐over techniques. All tested systems have the potential to withstand occlusal forces applied in the posterior region. The combination of the CAD/CAM and press‐over techniques for the veneering process improved the overall stability after artificial ageing, relative to the layering technique.     

Marginal Gap,Internal Fit,and Fracture Load of Leucite‐Reinforced Ceramic Inlays Fabricated by CEREC inLab and Hot‐Pressed Techniques

Purpose: This in vitro study was designed to evaluate and compare the marginal gap, internal fit, and fracture load of resin‐bonded, leucite‐reinforced glass ceramic mesio‐occlusal‐distal (MOD) inlays fabricated by computer‐aided design/manufacturing (CAD/CAM) or hot pressing. Materials and Methods: Fifty caries‐free extracted human molars were prepared for standardized MOD inlays. Impressions of each specimen were made and poured using type IV dental stone. Dies were randomly divided into two equal groups. Twenty‐five ceramic inlays were fabricated by the hot‐pressed technique using IPS Empress leucite‐reinforced glass ceramics, and the other 25 ceramic inlays were produced by CAD/CAM technology using ProCAD leucite‐reinforced ceramic blocks and CEREC inLab facilities. Inlays were bonded to the teeth using a dual‐cured resin cement. The specimens were stored in distilled water at 37°C for 24 hours and then thermocycled for 5000 cycles. The marginal gap measurements were taken with a stereomicroscope. Specimens in each group of inlay systems were randomly divided into two subgroups of 10 and 15 specimens each. Ten specimens in each subgroup were sectioned mesiodistally for evaluation of the internal fit. The fracture load of specimens in the second subgroup (n = 15) of the two inlay systems was determined under compressive load in a universal testing machine. Data were analyzed using Student's t‐test at a significance level of p < 0.05. Results: The mean marginal and internal gap size in both IPS Empress and ProCAD inlays were less than 100 μm; however, the marginal gap for the IPS Empress restorations was significantly higher than that of ProCAD restorations (p < 0.05). There was no significant difference in the mean internal fit or the fracture load between the two glass ceramic inlays (p > 0.05). Conclusions: The leucite‐reinforced glass ceramic inlay restorations fabricated by CEREC inLab (CAD/CAM) and the hot‐pressed technique provided clinically acceptable marginal and internal fit with comparable fracture loads after luting.     

Evaluation of zirconium-oxide-based ceramic single-unit posterior fixed dental prostheses (FDPs) generated with two CAD/CAM systems compared to porcelain-fused-to-metal single-unit posterior FDPs: a 5-year clinical prospective study

Purpose: The purpose of this prospective clinical study was to determine the success rate of single‐unit posterior fixed dental prostheses (FDPs) with zirconia copings generated with two CAD/CAM systems, compared to porcelain‐fused‐to‐metal (PFM) single‐unit posterior FDPs after 5 years of function. Materials and Methods: From 2005 to 2006, 60 patients who needed a single‐unit FDP on a first molar in the mandibular jaw (left or right) in a private office setting were included in this study. The 60 first mandibular molars were randomly divided into three groups (n = 20): in the control group (group C), 20 PFM FDPs were included. In the other two groups CAD/CAM technology was used for the fabrication of the zirconium‐oxide copings: 20 single‐unit posterior FDPs with zirconia copings were generated with the Procera system (group P, Nobel Biocare); 20 single‐unit posterior FDPs with zirconia copings were generated with the Lava system (group L, 3M ESPE). For the ANOVA follow‐up data, the clinical life table method was applied. The statistical analysis was performed using two nonparametric tests, the log‐rank test for k‐groups and the Fisher exact test. Results: No statistically significant difference in the clinical outcome of zirconia–ceramic FDPs of both groups (P and L) evaluated together and metal–ceramic posterior single FDPs was found at 5 years of function; however, clinical data showed that technical problems, such as extended fracture of the veneering ceramic, tended to occur more frequently in the zirconia–ceramic FDP groups. The difference in the frequency of failure was statistically significant only in the comparison of groups C and P. Conclusions: Even if no statistically significant difference in the clinical outcome of zirconia–ceramic FDPs of both groups (P and L) considered together and metal–ceramic posterior single FDPs was found at 5 years of function, clinical data showed that the two zirconia–ceramic FDP groups tended to have more frequent clinical problems: for this reason all the clinical and technical variables related to the use of zirconia–ceramic FDPs generated with CAD/CAM systems should be carefully considered prior to all treatment procedures.     

Fracture behaviour of zirconia ceramic cantilever fixed dental prostheses in vitro

Objective. Evaluation of the fracture resistance of all-ceramic cantilever fixed dental prostheses (FDPs) manufactured from zirconia frameworks and veneered with a press ceramic. Material and Methods. Two mandibular premolars were prepared either with a box inlay cavity or with a full crown chamfer preparation and then duplicated. 40-three-unit cantilever FDPs replacing one premolar, with a group size of eight for each design, were manufactured. In group i-i the cantilever FDPs were retained by two inlays, in group i-c by an inlay–crown combination, and in group c-c by two crowns. The frameworks in groups i-c-R and c-c-R were reinforced by an additional shoulder on the oral side of the zirconia frameworks. All FDPs were subjected to thermal cycling (TC) and 600,000 cycles of mechanical loading (ML) with 50 N. The load to fracture was measured and fracture sites were evaluated. Results. The mean fracture values ranged from 172 N to 792 N. Fracture-strength values were significantly lower for the i-i retained FDPs than for the i-c and c-c combinations. There was no significant effect of the reinforcing shoulder in groups i-c-R and c-c-R. For FDPs with a crown on the terminal tooth, fractures were usually within the distal wall of the distal crown. Conclusions. Inlay–inlay retained cantilever FDPs cannot withstand the mastication forces expected. Fracture load values for inlay–crown and crown–crown-retained FDPs encourage further clinical investigation. The mode of fracture indicates that reinforcement of the distal crown wall might enhance fracture resistance.     

Effect of finish line design on stress distribution in bilayer and monolithic zirconia crowns: a three‐dimensional finite element analysis study

This study evaluated the influence of different finish line designs and abutment materials on the stress distribution of bilayer and monolithic zirconia crowns using three‐dimensional finite element analysis (FEA). Three‐dimensional models of two types of zirconia premolars – a yttria‐stabilized zirconia framework with veneering ceramic and a monolithic zirconia ceramic – were used in the analysis. Cylindrical models with the finish line design of the crown abutments were prepared with three types of margin curvature radius (CR): CR = 0 (CR0; shoulder margin), CR = 0.5 (CR0.5; rounded shoulder margin), and CR = 1.0 (CR1.0; deep chamfer margin). Two abutment materials (dentin and brass) were analyzed. In the FEA model, 1 N was loaded perpendicular to the occlusal surface at the center of the crown, and linear static analysis was performed. For all crowns, stress was localized to the occlusal loading area as well as to the axial walls of the proximal region. The lowest maximum principal stress values were observed when the dentin abutment with CR0.5 was used under a monolithic zirconia crown. These results suggest that the rounded shoulder margin and deep chamfer margin, in combination with a monolithic zirconia crown, potentially have optimal geometry to minimize occlusal stress.     

Effect of occlusal thickness design on the fracture resistance of endocrowns restored with lithium disilicate ceramic and zirconia

目的 探讨二硅酸锂陶瓷和氧化锆制作的下颌第一磨牙髓腔固位冠的面厚度设计对抗折性能的影响。方法 根据修复设计（冠部材料及厚度）的不同,将24个下颌第一磨牙树脂仿真牙随机分成4组,每组6个。二硅酸锂2 mm组：采用二硅酸锂陶瓷制作修复体,面厚度2 mm,固位体长4 mm;二硅酸锂4 mm组：采用二硅酸锂陶瓷制作修复体,面厚度4 mm,固位体长2 mm;氧化锆2 mm组：采用氧化锆制作修复体,面厚度2 mm,固位体长4 mm;氧化锆4 mm组：采用氧化锆制作修复体,面厚度4 mm,固位体长2 mm。使用树脂水门汀粘接系统（RelyX Ultimate Clicker）粘接后,冷热循环10 000次。将万能试验机与牙长轴呈135°,位移速度0.5 mm·min^-1,在颊尖加载,测定抗折力及折裂方式,并用SPSS 15.0软件进行方差分析和多重比较。结果 二硅酸锂2 mm组、二硅酸锂4 mm组、氧化锆2 mm组、氧化锆4 mm组的抗折力分别为（890.54±83.41）、（2 320.87±728.57）、（2 258.05±557.66）和（3 847.70±495.99）N。氧化锆4 mm组的抗折力最高,二硅酸锂2 mm组的抗折力最低。结论 磨牙髓腔固位冠使用氧化锆较二硅酸锂陶瓷有更高的抗折力,增加修复体面厚度可提高抗折力,但基牙折裂风险也增加。     

Fracture load and chewing simulation of zirconia and stainless‐steel crowns for primary molars

Aesthetic alternatives to stainless‐steel crowns for restoring primary molars attain growing interest. We studied the mechanical properties of prefabricated zirconia crowns and conventional crowns. Three brands of prefabricated zirconia crowns were compared with computer‐aided design/computer‐aided manufacturing (CAD/CAM) zirconia crowns, preveneered stainless‐steel crowns, and conventional stainless‐steel crowns regarding: (i) fracture load under each of three conditions [no pretreatment, artificial aging in saliva for 12 wk, and after chewing simulation/thermocycling (1.68 × 10⁶ cycles/5–55°C)]; and (ii) survival rate during chewing simulation, considering decementation, fracture, chipping, fatigue cracks, and occlusal holes. Without pretreatment, the prefabricated zirconia crowns showed mean fracture load values between 893 N and 1,582 N, while the corresponding values for CAD/CAM zirconia crowns and preveneered stainless‐steel crowns were 2,444 N and 6,251 N. Preveneered stainless‐steel crowns showed significantly lower fracture loads after artificial aging (5,348 N after saliva aging; 3,778 N after chewing simulation) than without artificial aging, whereas the fracture load of zirconia crowns was not influenced negatively. The survival rate of the different groups of zirconia crowns and preveneered stainless‐steel crowns during chewing simulation was 100%, but only 41.7% for the stainless‐steel crowns. These in‐vitro data suggest that prefabricated zirconia crowns are aesthetically and durable alternatives to stainless‐steel crowns for primary molars.     

Influence of different preparation forms on the loading-bearing capacity of zirconia cantilever FDPs. A laboratory study

PurposeTo investigate the impact of inlay design and number of retainer wings on the failure load of all-ceramic resin-bonded inlay-retained cantilever fixed dental prostheses (IRCFDPs) made from a computer-aided design/computer-aided manufacturing (CAD/CAM) yttrium-oxide partially-stabilized zirconia framework(Y-TZP).MethodsSixty-four extracted human first molars were divided according to preparation design into four groups. Teeth were provided with IRCFDPs representing a premolar pontic and a retainer of variable design: (R1S) shallow inlay/one lingual retainer wing, (R2S) shallow inlay/two retainer wings (lingual/buccal), (R1D) deep inlay/one lingual retainer wing and (R2D) deep inlay/two retainer wings (lingual/buccal). All IRCFDPs were cemented using adhesive resin. Quasi-static fracture strength (QSFS) was tested for 32 specimens after 3 days in a universal testing machine (UTM). The other specimens were stored in a water bath (150 days/37 °C) and thermocycled (37,500 times, 5–55 °C); then exposed to dynamic loading in a chewing simulator (50 N/1,200,000 cycles).ResultsThe median QSFS (N) for the different designs were: R1S:105.1, R1D:167.5, R2S:147.9, R2D:232.3. The number of retainer wings had a statistically significant influence on the fracture load of both groups, whereas the inlay design had an impact only in the double-retainer wing group. Under dynamic loading, lower failure loads within all groups were reported except for the group R2S. The number of retainer wings continued to significantly influence the failure loads of both groups, whereas no influence of inlay design could be revealed.ConclusionsDouble-retainer IRCFDPs showed promising results for replacing single premolars. The inlay design seems to have no significant influence on the fracture strength of these restorations.     

Comparison of fracture-load values of cantilevered FDPs

Abstract

Objective. Evaluation of the effect of different framework designs and of fatigue on the fracture-load values of cantilevered fixed dental prostheses (FDPs). The load values were compared with those for lithium disilicate ceramic and metal–ceramic FDPs. Materials and methods. Fifty cantilevered FDPs were manufactured using a zirconia framework veneered with a feldspathic ceramic. Ten FDPs were made from a lithium disilicate ceramic and 10 were designed as metal–ceramic FDPs. All FDPs were anchored by two premolar crowns to replace a missing premolar. Twenty of the 50 zirconia FDPs were regarded as the control groups; these were divided into two groups—with and without fatigue. The other 30 zirconia FDPs were divided into three test groups with different framework designs. The load to fracture was measured and fracture sites were identified. The Kruskal–Wallis test and the Mann–Whitney U-test were used for statistical analysis. Results. Most of the all-ceramic FDPs fractured within the distal wall of the terminal crown abutment. The mean fracture-load ranged between 346–493 N for the FDPs with the 0.7 mm framework. Mean values for the three zirconia test groups ranged from 529–590 N. Reinforcement of the framework resulted in significantly higher fracture-loads than for the control group. Values for lithium disilicate restorations were significantly lower than those for the test groups and the values for the metal–ceramic group were significantly higher than those for the test groups. Conclusion. Although reinforcement of the distal crown core might enhance the fracture resistance of all-ceramic cantilever FPDs, they cannot yet be unreservedly recommended for clinical use.     

Fracture analysis of randomized implant-supported fixed dental prostheses

Objective

Fractures of posterior fixed dental all-ceramic prostheses can be caused by one or more factors including prosthesis design, flaw distribution, direction and magnitude of occlusal loading, nature of supporting infrastructure (tooth root/implant), and presence of adjacent teeth. This clinical study of implant-supported, all-ceramic fixed dental prostheses, determined the effects of (1) presence of a tooth distal to the most distal retainer; (2) prosthesis loading either along the non-load bearing or load bearing areas; (3) presence of excursive contacts or maximum intercuspation contacts in the prosthesis; and (4) magnitude of bite force on the occurrence of veneer ceramic fracture.

Methods

89 implant-supported FDPs were randomized as either a three-unit posterior metal–ceramic (Au–Pd–Ag alloy and InLine POM, Ivoclar, Vivadent) FDP or a ceramic–ceramic (ZirCAD and ZirPress, Ivoclar, Vivadent) FDP. Two implants (Osseospeed, Dentsply) and custom abutments (Atlantis, Dentsply) supported these FDPs, which were cemented with resin cement (RelyX Universal Cement). Baseline photographs were made with markings of teeth from maximum intercuspation (MI) and excursive function. Patients were recalled at 6 months and 1–3 years. Fractures were observed, their locations recorded, and images compared with baseline photographs of occlusal contacts.

Conclusion

No significant relationship existed between the occurrence of fracture and: (1) the magnitude of bite force; (2) a tooth distal to the most distal retainer; and (3) contacts in load-bearing or non-load-bearing areas. However, there was a significantly higher likelihood of fracture in areas with MI contacts only.

Clinical significance

Because of the absence of a periodontal ligament, this clinical study demonstrates that there is a need to evaluate occlusion differently with implant-supported prostheses than with natural tooth supported prostheses. Implant supported prostheses should have minimal occlusion and lighter contacts than those supported by natural dentition.

Clinical Trials.gov No

K23 D2007-46.     

In vitro chipping behaviour of all‐ceramic crowns with a zirconia framework and feldspathic veneering: comparison of CAD/CAM‐produced veneer with manually layered veneer

The purpose of this in vitro study was to assess the breaking load of zirconia‐based crowns veneered with either CAD/CAM‐produced or manually layered feldspathic ceramic. Thirty‐two identical zirconia frameworks (Sirona inCoris ZI, mono L F1), 0·6 mm thick with an anatomically shaped occlusal area, were constructed (Sirona inLab 3.80). Sixteen of the crowns were then veneered by the use of CAD/CAM‐fabricated feldspathic ceramic (CEREC Bloc, Sirona) and 16 by the use of hand‐layered ceramic. The CAD/CAM‐manufactured veneer was attached to the frameworks by the use of Panavia 2.0 (Kuraray). Half of the specimens were loaded until failure without artificial ageing; the other half of the specimens underwent thermal cycling and cyclic loading (1·2 million chewing cycles, force magnitude F_max = 108 N) before the assessment of the ultimate load. To investigate the new technique further, finite element (FE) computations were conducted on the basis of the original geometry. Statistical assessment was made by the use of non‐parametric tests. Initial breaking load was significantly higher in the hand‐layered group than in the CAD/CAM group (mean: 1165·86 N versus 395·45 N). During chewing simulation, however, 87·5% (7/8) of the crowns in the hand‐layered group failed, whereas no crown in the CAD/CAM group failed. The CAD/CAM‐produced veneer was significantly less sensitive to ageing than the hand‐layered veneer.     

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.     

Five‐year results of a prospective randomised controlled clinical trial of posterior computer‐aided design–computer‐aided manufacturing ZrSiO4‐ceramic crowns

The aim of this prospective randomised controlled clinical trial was to evaluate the clinical outcome of shrinkage‐free ZrSiO₄‐ceramic full‐coverage crowns on premolars and molars in comparison with conventional gold crowns over a 5‐year period. Two hundred and twenty‐three patients were included and randomly divided into two treatment groups. One hundred and twenty‐three patients were restored with 123 ZrSiO₄‐ceramic crowns, and 100 patients received 100 gold crowns, which served as the control. All crowns were conventionally cemented with glass–ionomer cement. After an observation period of 6, 12, 24, 36, 48 and 60 months, the survival probability (Kaplan–Meier) for the shrinkage‐free ZrSiO₄‐ceramic crowns was 98·3%, 92·0%, 84·7%, 79% and 73·2% and for the gold crowns, 99%, 97·9%, 95·7%, 94·6% and 92·3%, respectively. The difference between the test and control group was statistically significant (P = 0·0027). The gold crowns showed a better marginal integrity with less marginal discoloration than the ceramic crowns. The most common failure in the ceramic crown group was fracture of the crown. The 60‐month results of this prospective randomised controlled clinical trial suggest that the use of these shrinkage‐free ZrSiO₄‐ceramic crowns in posterior tooth restorations cannot be recommended.     

Three-year clinical prospective evaluation of zirconia-based posterior fixed dental prostheses (FDPs)

This clinical study evaluated posterior three-unit fixed dental prostheses (FDPs) made of zirconia substructures veneered with pressable glass–ceramic. Nineteen patients received 21 FDPs replacing either the second premolar, first molar, or second molar. The FDPs were cemented with glass ionomer. Recall examinations were performed every 12 months. The mean service time of the FDP was 40 months. At 30 months, one maxillary FDP exhibited zirconia framework fracture at a thinned occlusal area of the abutment. Loss of retention led to the removal of one FDP after 38 months. The Kaplan–Meier survival probability was 90.5% after 40 months for all types of failures and 95.2% concerning framework fractures. The overpressing technique appears to be reliable in terms of the veneering material. However, one framework fracture was observed in this study.     

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.     

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.     

Practice‐based clinical evaluation of metal–ceramic and zirconia molar crowns: 3‐year results

This practice‐based study evaluates the clinical performance of conventionally luted metal–ceramic and zirconia molar crowns fabricated with pronounced anatomical core design and a prolonged cooling period of the veneering porcelain. Fifty‐three patients were treated from 07/2008 until 07/2009 with either metal–ceramic crowns (MCC) (high‐noble alloy + low‐fusing porcelain) or zirconia crowns (Cercon System, DeguDent, Germany). Forty‐nine patients (30 women/19 men) with 100 restorations (metal–ceramic: 48/zirconia: 52, mean observational period: 36·5 ± 6 months) participated in a clinical follow‐up examination and were included in the study. Time‐dependent survival (in situ criteria), success (event‐free restorations) and chipping rates (defects of the veneering ceramics) were calculated according to the Kaplan–Meier method and analysed in relation to the crown fabrication technique, using a Cox regression model (P < 0·05). Three complete failures (metal–ceramic: 1, zirconia: 2) were recorded (survival rate after 3 years: metal–ceramic: 97·6%, zirconia: 95·2%). Of the metal–ceramic restorations, 90·9% remained event‐free (two ceramic fractures, one endodontic treatment), whereas the success rate for the zirconia was 86·8% (two ceramic fractures, one endodontic treatment, one secondary caries). No significant differences in survival (P = 0·53), success (P = 0·49) and ceramic fracture rates (P = 0·57) were detected. The combination of a pronounced anatomical core design and a modified firing of the veneering porcelain for the fabrication of zirconia molar crowns resulted in a 3‐year survival, success and chipping rate comparable to MCC.