CAD/CAM Zirconia vs. slip-cast glass-infiltrated Alumina/Zirconia all-ceramic crowns: 2-year results of a randomized controlled clinical trial

Optical properties of recycled zirconia for dental applications

STATEMENT OF PROBLEM

While waste zirconia can be recycled, whether the optical properties of recycled zirconia match those of commercially available zirconia is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the optical properties of recycled zirconia by assessing its color, translucency, and opalescence across different thicknesses and shades.

MATERIAL AND METHODS

Sixty specimens were prepared from 3 mol% yttria-stabilized tetragonal zirconia polycrystal blocks (Lava Plus; 3M ESPE) (group C); 60 other specimens were prepared from waste blocks of the same zirconia (group R). The specimens were further categorized into 4 subgroups (n=15) based on their thicknesses (1.0 mm or 1.5 mm) and shades (A1 or A3). Specimen color was measured with a spectrophotometer (Easyshade Advance 4.0; Vita ZahnFabrik). The parameters of color difference (ΔE00), translucency (TP), contrast ratio (CR), and opalescence (OP) were calculated. Grain size analysis was performed using scanning electron microscopy. Data were analyzed with analysis of variance (ANOVA) (α=.05).

RESULTS

Significant differences in translucency and opalescence were observed between groups C and R in all specimens (P<.001). Group R exhibited a range of TP (4.89 to 11.27), CR (0.74 to 0.91), and OP (3.36 to 8.65) values. The ΔE00 values between groups C and R ranged from 13.99 to 21.31. Both thickness and shade significantly affected the ΔE00 values (P<.001). The grain size in group C was not significantly different from that in group R (F=0.364, df=1, P=.555). The TP and OP values of group R decreased with increasing thickness (P<.001).

CONCLUSIONS

Recycled zirconia was less translucent and opalescent than commercially available zirconia. The color difference between commercially available and recycled zirconia exceeded the acceptable threshold, even when using the same staining procedure. Recycled zirconia exhibited reduced translucency and opalescence with increasing thickness.

Comparison of subcritical growth parameters of a Y-TZP obtained via cyclic or dynamic fatigue tests

OBJECTIVE

The objective of this study was to 1) compare the stress corrosion coefficient (n) of a Y-TZP obtained by two fatigue tests: cyclic and dynamic and 2) evaluate the effect of frequency in the characteristic lifetime and the existence of interaction between the cyclic fatigue and slow crack growth.

METHODS

A total of 145 Y-TZP specimens were produced in accordance with the manufacturer's instructions. These specimens, measuring 4.0 × 3.0 × 25.0 mm, were used for dynamic (n = 70) and cyclic fatigue tests (n = 75). The specimens were obtained from CAD/CAM blocks, sectioned, and sintered in a furnace at 1530 °C with a heating rate of 25 °C/min. They were tested in their "as-sintered" form without any additional surface treatment. The fatigue tests were conducted using a four-point bending to obtain the slow crack growth parameters (n). The cyclic fatigue test was also conducted in two frequencies (2 and 10 Hz), using stress levels between 350 and 600 MPa. Data from these tests were analyzed using ASTM C 1368-00 formulas and Weibull statistics. Scanning electron microscope (SEM) was used for fracture surface analysis to identify the origin of the fracture. Critical defect size was measured and used, along with flexural strength values, to estimate fracture toughness. Dynamic fatigue test data were used to obtain subcritical crack growth (SCG) parameters and perform Weibull statistical analysis. The cyclic fatigue data were used in the General Log-linear Model equation using the ALTA PRO software. Data were analyzed using one-way ANOVA followed by Tukey post-hoc tests and Student's t-test at a significance level of p ≤ 0.05.

RESULTS

In the dynamic fatigue test, the values obtained for σfo and n were 667 and 54, respectively. This parameter indicates how the strength of the material diminishes over time due to internal cracks. The Weibull parameters obtained from the same test results were m = 7.9, σ0 = 968, 9 and σ5% = 767, which indicates the reliability of the material. The Weibull parameters obtained by cyclic fatigue were statistically similar for the two frequencies used, the m* was 0.17 (2 Hz) and 0.21 (10 Hz); characteristic lifetimes (η) were 1.93 × 106 and 40,768, respectively. The n values obtained by cyclic fatigue were 48 and 40 at frequencies of 2 and 10 Hz, respectively. There was no effect of the frequency, the stress level or the interaction of the two in the Y-TZP lifetime, when analysed by General Log Linear Model.

SIGNIFICANCE

the n values obtained by cyclic and dynamic fatigue tests showed no statistically significant difference and the effect of frequency in the characteristic lifetime and the existence of interaction between the cyclic fatigue and subcritical growth were not observed in the tested specimens.

Retrospective clinical study of 1472-unit monolithic zirconia restorations with feather-edge margins realized with digital workflow

OBJECTIVES

To evaluate the clinical performance of monolithic zirconia restorations with feather-edge margins fabricated by digital impressions.

MATERIALS AND METHODS

All participants that present monolithic zirconia restorations with feather-edge margins realized with digital workflow were evaluated during scheduled periodontal maintenance between February and September 2022 according to predetermined inclusion criteria. Clinical performance was assessed using the modified USPHS and periodontal parameters. Overall survival was calculated for monolithic zirconia restorations. Technical and biologic complications were reported. Descriptive statistical analysis and life-table analyses were performed for all data.

RESULTS

A total of 1472 monolithic zirconia FDPs (1279 on abutments and 193 on pontics) placed in 1189 patients (982 males and 490 females) from February 2017 to September 2020 were analyzed. The mean follow-up was 44 months (range 36-61 months), and the overall survival rate was 98.5%. There were 931 single crowns, 96 were 3-unit FDPs, 33 were 4-unit FDPs, 11 were 5-unit FDPs, and 6-unit FDPs. Three single crowns had irreparable cracks, and 6 single crowns and one 4-unit FDP were fractured. One 3-unit FDP failed due to tooth fracture and 5 single crowns failed due to endodontic failure. The loss of retention was noted in 25 monolithic zirconia FDPs and hypersensitivity in 44 single crowns. Biologic complications were uncommon.

CONCLUSIONS

Based on the results and its limitations, the monolithic zirconia FPDs and digital impressions represent a favorable prosthetic treatment similar to that reported with other margin designs CLINICAL RELEVANCE: Monolithic zirconia restorations on vertical-margin abutments fabricated using a digital workflow demonstrate excellent clinical performance. The digital clinical workflow without the use of a cast means a reduction in costs, steps, and operating time.

Clinical outcomes of tooth-supported monolithic zirconia vs. porcelain-veneered zirconia fixed dental prosthesis, with an additional focus on the cement type: a systematic review and meta-analysis

PURPOSE

To compare the failure rates and the prevalence of technical complications between full-coverage tooth-supported monolithic zirconia (MZ) and porcelain-veneered zirconia (PVZ) fixed dental prosthesis, based on a systematic literature review.

METHODS

An electronic search was performed in three databases, supplemented by hand searching. Several statistical methods were used.

RESULTS

Seventy-four publications reported 6370 restorations (4264 PVZ; 2106 MZ; 8200 abutment teeth; 3549 patients), followed up until 152 months. A total of 216 prostheses failed, and survival was statistically significant different between groups. PVZ had higher occurrence of complications than MZ; the difference was especially greater for either minor or major chipping. The difference in prevalence of either minor or major chipping was statistically significant for PVZ prostheses between cementation with glass ionomer and adhesive resin cement (higher), adhesive resin and resin-modified glass ionomer cement (RMGIC, higher), and between RMGIC (higher) and glass ionomer cement. For MZ the difference was significant only for minor chipping between RMGIC (higher) and adhesive resin cement. Abutment teeth to PVZ prostheses more often lost vitality. Decementation was not observed with RMGIC. Air abrasion did not seem to clinically decrease the decementation risk. The 5-year difference in the occurrence of minor or major chipping between MZ and PVZ prostheses was statistically significant, but nor for catastrophic fracture.

CONCLUSION

Tooth-supported PVZ prostheses present higher failure and complication rates than MZ prosthesis. The difference in complications is striking when it comes to chipping.

CLINICAL RELEVANCE

Awareness of the outcome differences between different types of zirconia prostheses is important for clinical practice.

Do tooth-supported zirconia restorations present more technical failures related to fracture or loss of retention? Systematic review and meta-analysis

OBJECTIVES

This systematic review was performed to determine the main cause of technical failure of tooth-supported zirconia crowns and fixed partial dentures (FPDs), categorizing them as fracture/chipping or loss of retention/decementation.

MATERIALS AND METHODS

Electronic and manual searches were performed for randomized clinical trials, prospective clinical trials, and prospective cohort studies that reported the technical failure rates of zirconia restorations. The Cochrane Collaboration risk-of-bias tool and Newcastle-Ottawa scale were used to assess the quality of the studies.

RESULTS

Fifty-two studies were included and most of them had unclear risk of bias. Considering all reported fractures/chipping, for veneered crowns with 1 to 3 years of follow-up, the relative risk (RR) of fracture in relation to loss or retention was 3.95 (95% CI 1.18-13.23; p = 0.03). For 4 to 6 years of follow-up, the RR was 5.44 (95% CI 1.41-20.92; p = 0.01). For veneered FPDs with 1 to 3 years of follow-up, the RR was 5.98 (95% CI 2.31-15.01; p = 0.0002). For 4 to 6 years of follow-up, the RR was 3.70 (95% CI 1.63-8.41; p = 0.002). For 7 years or more of follow-up, the RR was 3.45 (95% CI 1.84-6.46; p = 0.0001). When only framework fractures were considered, there were no significant differences for the RR in all follow-up periods (p > 0.05).

CONCLUSIONS

Higher RR for fracture/chipping in relation to decementation for veneered zirconia crowns and FPDs at all follow-up times. For framework fractures, no difference was observed between the risk of failure of the restoration due to fracture or decementation.

CLINICAL RELEVANCE

Zirconia crowns and FPDs showed relatively high success and survival rates. However, considering the technical failures, there is approximately four times higher chance of fracture/chipping than loss of retention for both single and multi-unit tooth-supported veneered zirconia restorations.

Long-term clinical performance and complications of zirconia-based tooth- and implant-supported fixed prosthodontic restorations: A summary of systematic reviews

OBJECTIVES

To present an overview on systematic reviews on prosthodontic zirconia restorations and to discuss long-term complications as well as information on anatomical and functional changes to the masticatory system.

DATA/SOURCES

MEDLINE, EMBASE, Trip medical, and Cochrane Library databases were searched for systematic reviews up to February 2021. Bias was assessed and clinical survival and complications were analyzed.

STUDY SELECTION

38 eligible articles published between 2006 and 2021 were included. The reviews were based on 128 in vivo studies on approximately 10,000 zirconia restorations. 5-year cumulative survival rates varied between 91.2% and 95.9% for tooth-supported (TS) single crowns (SC), 89.4% and 100% for TS multi-unit fixed dental prostheses (FDP), 97.1% and 97.6% for implant-supported (IS) SCs and 93.0% and 100% for IS FDPs. Chipping was the most often technical complication, followed by framework fracture, loss of retention, marginal discrepancies/discoloration, occlusal roughness and abutment/screw loosening. Color mismatch was the only esthetic complication. Biological complications were caries, endodontic complications, tooth fracture, periodontal disease, abrasion/attrition, persisting pain, high sensitivity, peri‑implantitis and soft tissue issues. Patients with bruxism were only examined sporadically.

CONCLUSIONS

5-year results for zirconia restorations were satisfactory. The predominant technical problem of veneering fractures could be overcome with adapted design or fabrication and application of monolithic restorations, but reviews of clinical studies on this subject are rare. The impact of zirconia restorations on the masticatory system remains unclear.

CLINICAL SIGNIFICANCE

Zirconia restorations are experiencing a rapidly increasing use in dental practice. Being highly wear-resistant, hard and durable, it can be assumed that they do not follow natural abrasion and changes in the masticatory system. Possible long-term effects on the stomatognathic system as a whole should therefore be considered.

Comparison of Mechanical Properties of Chairside CAD/CAM Restorations Fabricated Using a Standardization Method

The aim of this in vitro study was to investigate the fracture resistance, fracture failure pattern, and fractography of four types of chairside computer-aided design/computer-aided manufacturing (CAD/CAM) restoration materials in teeth and titanium abutments fabricated using a standardization method. An artificial mandibular left first premolar prepared for all-ceramic crown restoration was scanned. Forty extracted mandibular molars and cylindrical titanium specimens were milled into a standardized shape. A total of eighty CAD/CAM restoration blocks were milled into a crown and twenty pieces of each lithium disilicate (LS), polymer-infiltrated-ceramic-network (PICN), resin nano ceramic (RNC), and zirconia-reinforced lithium silicate (ZLS) materials were used. Crowns were bonded to abutments, and all specimens underwent thermal cycling treatment for 10,000 cycles. Fracture resistance was measured using a universal testing machine and fracture failure patterns were analyzed using optical microscopy and scanning electron microscopy. Statistical differences were analyzed using appropriate ANOVA, Tukey HSD post hoc tests, and independent sample t-tests (α = 0.05). The results indicated that, in both teeth abutments and titanium abutments, the fracture resistances showed significantly the highest values in LS and the second highest in ZLS (p < 0.05). The fracture resistances based on teeth abutments and titanium abutments were significantly different in all the CAD/CAM restoration materials (p < 0.05). There are statistically significant correlations between the types of materials and the types of abutments (p < 0.05). Each of the different materials showed different fracture failure patterns, and there was no noticeable difference in fractographic analysis. Lithium disilicates and zirconia-reinforced lithium silicates exhibited statistically high fracture resistance, indicating their suitability as restoration materials for natural teeth or implant abutments. There were no distinct differences in the fracture pattern based on the restoration and abutment materials showed that the fracture initiated at the groove where the ball indenter was toughed and propagated toward the axial wall.

Prospective study of monolithic zirconia crowns: clinical behavior and survival rate at a 5-year follow-up

Purpose To evaluate the clinical behavior and survival of full coverage monolithic zirconia crowns on posterior teeth over a 5-year follow-up.Methods Fifty patients were recruited and underwent restoration with a Lava Plus monolithic zirconia crown (Lava™ Frame Zirconia, 3M Espe, Germany) on premolars or molars. Patients were monitored over a 5-year follow-up (2014-19), recording any biological and/or mechanical complications; these data were used to estimate the crowns' success rate. Periodontal clinical parameters were recorded (pocket probing depth (PPD), plaque index (PLI), bleeding on probing (BOP), and gingival recession (GR)). Wear to the zirconia crowns and antagonist teeth were also evaluated with Geomagic software (3D Systems, U.S.A.). Patients' satisfaction with treatment was evaluated in a questionnaire.Results For the 50 monolithic zirconia crowns analyzed, the survival rate was 98% after 5 years. Only 6% of the crowns presented some type of complication (two debonding and one root fracture). No fracture or fissures were detected. GR and BOP were the only clinical parameters found to be significantly greater around teeth restored with crowns. The monolithic zirconia crowns suffered less wear than the enamel of antagonist teeth. Patient's general satisfaction with treatment was high.Conclusions Monolithic zirconia crowns on posterior teeth are a highly predictable treatment option, with a high survival rate. The single treatment failure was due to a biological complication arising from root fracture. This treatment may be recommended as a treatment that conserves dental structure, and requires minimal dental preparation.

Digital versus conventional impressions for full-coverage restorations: A systematic review and meta-analysis

BACKGROUND

The primary objective of this systematic review was to investigate the survival of full-coverage restorations fabricated by using digital impressions (DIs) versus that of those fabricated by using conventional impressions. The authors also compared secondary outcomes of marginal and internal fit and occlusal and interproximal contacts.

TYPES OF STUDIES REVIEWED

The authors conducted a systematic literature search in multiple databases to identify clinical trials with no restrictions by publication type, date, or language. The authors assessed study-level risk of bias and outcome-level strength of evidence. The authors performed a meta-analysis by using a random-effects model.

RESULTS

Ten studies met the inclusion criteria. The authors identified no studies in which the investigators compared the impression techniques with respect to survival of full-coverage restorations. Mean differences for marginal gap and internal gap were -9.0 micrometers (95% confidence interval, -18.9 to 0.9) and -15.6 μm (95% confidence interval, -42.6 to 11.4), respectively. Studies assessing internal gap were substantially heterogeneous (I² = 72%; P = .003).

CONCLUSIONS AND PRACTICAL IMPLICATIONS

Research is lacking to draw robust conclusions about the relative benefits of DIs in terms of restoration survival. Low-quality evidence for marginal fit and internal fit suggested similar performance for both techniques. Evidence quality for interproximal contact and occlusal contact was very low and insufficient to draw any conclusions regarding how the impression techniques compared. Given the uncertainty of the evidence, results should be interpreted with caution. With increasing popularity and adoption of digital scanners by dentists, pragmatic practice-based trials involving standardized, patient-centered outcomes may improve confidence in the comparative effectiveness of DIs.

Effect of Incisal Porcelain Veneering Thickness on the Fracture Resistance of CAD/CAM Zirconia All-Ceramic Anterior Crowns

Statement of Problem. In some clinical situations, the vertical length of either a prepared tooth or an implant abutment is short, while the occlusal clearance to be restored by a porcelain crown is large. Incisal thickness of the veneering porcelain should be considered to prevent mechanical failure of the crown. Purpose. The aim of this study is to evaluate the effect of two different incisal veneering porcelain thickness on the fracture resistance of the anterior all-ceramic CAD/CAM zirconia crown system as compared with the conventionally used metal ceramic crown system. Method. CAD/CAM zirconia all-ceramic and metal ceramic crowns were fabricated on the prepared dies with standardized dimensions and designs using standardized methods according to the manufacturer’s instructions. All crowns were then adhesively luted with resin-based cement (Multilink cement system), subjected to thermal cycling and cyclic loading, and were loaded until fracture using the universal testing machine to indicate the fracture resistance for each crown material in each veneering thickness. Results. Statistical analysis was carried out, and the results showed that the fracture resistance of the nickel-chromium metal ceramic group was significantly higher than that of the CAD/CAM zirconia all-ceramic group. Also, the fracture resistance of crowns with 1.5 mm incisal veneering thickness was significantly higher than those with 3 mm incisal veneering thickness in both groups. Furthermore, there was no significant difference in the fracture mode of the two groups where 50% of the total specimens demonstrated Mode II (veneer chipping), while 35% demonstrated Mode I (visible crack) and only 15% demonstrated Mode III (bulk fracture). Conclusion. High failure load values were demonstrated by the specimens in this study, which suggest sufficient strength of both incisal veneering thickness in both crown systems to withstand clinical applications; however, the fracture patterns still underline the requirement of a core design that support a consistent thickness of the veneering ceramic, and it is recommended to conduct long-term prospective clinical studies to confirm findings reported in the present study.

WITHDRAWN: Interventions for replacing missing teeth: partially absent dentition

BACKGROUND

Management of individuals presenting with partial loss of teeth is a common task for dentists. Outcomes important to the management of missing teeth in the partially absent dentition should be systematically summarized. This review recognizes both the challenges associated with such a summarization and the critical nature of the information for patients.

OBJECTIVES

To assess the effects of different prostheses for the treatment of partially absent dentition in terms of the following outcomes: long-term success, function, morbidity and patient satisfaction.

SEARCH METHODS

We searched the Cochrane Oral Health Group's Trials Register (to 21 March 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE via OVID (1950 to March 2011) and EMBASE via OVID (1980 to March 2011). There were no restrictions regarding language or date of publication. We contacted several authors to identify non-published trials.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing different methods (including the design and materials used) of treating partial edentulism, with clinically relevant outcomes, were included in this review. Trials reporting only surrogate outcomes, such as plaque accumulation or gingival volume, were excluded from this review.

DATA COLLECTION AND ANALYSIS

Two review authors independently carried out the screening of eligible studies, assessment of dimensions of quality of trials, and data extraction. Results were expressed as mean differences for continuous data, risk ratios for dichotomous outcomes, and hazard ratios with 95% confidence intervals for time-to-event data.

MAIN RESULTS

Twenty-one trials met the inclusion criteria for this review. Twenty-four per cent of these were assessed as being at high risk of bias and the remainder were at unclear risk of bias. The clinical heterogeneity among the included studies precluded any attempt at meta-analysis. There was insufficient evidence to determine whether one type of removable dental prosthesis (RDP) was better or worse than another. With fixed dental prostheses (FDPs), there was no evidence that high gold alloys are better or worse than other alloys, nor that gold alloys or frameworks are better or worse than titanium. There is insufficient evidence to determine whether zirconia is better or worse that other FDP materials, that ceramic abutments are better or worse than titanium, or that one cement was better or worse than another in retaining FDPs. There is insufficient evidence to determine the relative effectiveness of FDPs and RDPs in patients with shortened dental arch or to determine the relative advantages of implant supported FDPs versus tooth/implant supported FDPs.

AUTHORS' CONCLUSIONS

Based on trials meeting the inclusion criteria for this review, there is insufficient evidence to recommend a particular method of tooth replacement for partially edentulous patients.

Complications and survival rates of inlays and onlays vs complete coverage restorations: A systematic review and analysis of studies

OBJECTIVE

The aim of this study was to identify if different types of indirect restorations used for single teeth had different biological and technical complications, as well as survival rates.

METHOD

An electronic search was performed in various electronic databases to identify articles, published between 1980 and 2017. The search terms were categorised into 4 groups: inlay, onlay, inlay/onlay and crown. Manual searches of published full-text articles and related reviews were also performed.

RESULTS

A total number of 2849 papers were retrieved initially. After a detailed assessment for eligibility, 9 studies were selected for inclusion. The heterogeneity of the studies did allow neither a meta-analysis nor any meaningful comparison between types of restorations or materials. Only some pooling was performed for representative reasons. The mean survival rate of inlays was 90.89%, while for onlays and crowns it was 93.50% and 95.38%, respectively. For the fourth study group, consisting of both inlays and onlays, the survival rate was found to be 99.43%. Statistical analysis demonstrated caries to be the main biological complication for all types of restorations, followed by a root and/or tooth fracture incidence (11.34%) and endodontic incidence. Ceramic fractures represented the most common technical complication, followed by loss of retention and porcelain chipping.

CONCLUSION

The 5-year survival rate for crowns and inlays/onlays is very high, exceeding 90%. An association between the kind of complications and different types of restorations could not be established. Nevertheless, a relatively high failure rate due to caries and ceramic fractures was noted.

Metal-free materials for fixed prosthodontic restorations

BACKGROUND

Fixed prosthodontic treatment (crowns, fixed dental prostheses (FDPs), complete arch prostheses) involves the use of several different materials to replace missing tooth structure. Traditionally full metal or metal frameworks veneered with ceramic (metal-ceramic (MC)) have been used. In recent years several different metal-free systems have become available to clinicians and patients. In general, metal-free restorations should allow practitioners to better reproduce natural tooth colour, avoiding shortcomings of MC restorations. The comparative in service clinical performance of fixed prosthodontic treatments of different materials is unclear.

OBJECTIVES

To assess the effects of metal-free materials for prosthodontic restorations compared to metal-ceramic or other conventional all-metal materials.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (searched 3 May 2017), Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 4) in the Cochrane Library (searched 3 May 2017), MEDLINE Ovid (1946 to 3 May 2017), and Embase Ovid (1980 to 3 May 2017). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials (searched 3 May 2017). No restrictions were placed on the language or date of publication when searching the electronic databases.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in which the clinical performance of metal-free fixed prosthodontic restorations was compared with metal-ceramic (MC) or other conventional restorations in adult patients requiring prosthodontic treatment. RCTs in which the clinical performance of different kinds of metal-free systems were compared among themselves were also considered.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted independently and in duplicate. Trial authors were contacted for missing information. Available results for the outcomes of interest of the systematic review of the studies included were tabulated as they could not be included in a formal meta-analysis.

MAIN RESULTS

Nine trials involving a total of 448 participants were included. We judged two trials to be at unclear risk of bias and seven to be at high risk of bias. The majority of items of risk of bias were evaluated to be at unclear or high risk level in more than 50% of the included trials. Each trial except two was addressing a different type of intervention. All evidence was rated as being of very low quality due to problems with risk of bias and imprecision of results, the latter being due to very small sample sizes, low event rates, 95% confidence intervals including the possibility of benefit for both the test and control groups, or combinations of these problems. This means that we are very uncertain about all of the results presented in this review.One trial compared metal-free single crowns (full contour zirconia) to cast gold single crowns in 224 participants and found insufficient evidence of a difference in failure rate after one year, but after five years there was some evidence of a benefit for the gold crowns. There was insufficient evidence of a difference for crown complications at either time of assessment.One trial compared three-unit metal-free FDPs (lithium disilicate) to three-unit metal-ceramic FDPs in 37 participants. There was insufficient evidence of a difference in bridge failure at one and six years, but some evidence of a benefit for the lithium disilicate group in terms of bridge complications at six years. One trial compared zirconia-ceramic FDPs to metal-ceramic FDPs in 34 participants but found insufficient evidence of a difference in bridge failures (i.e. no failures in either treatment group), bridge complications or patients' aesthetic evaluation at any time of assessment up to three years.One trial compared metal-free cantilevered FDPs to metal-ceramic cantilevered FDPs in 21 participants. There was insufficient evidence of a difference for any primary outcome: bridge failures (i.e. no failures in either treatment group), bridge complications, or patients' aesthetic evaluation at any time of assessment up to three years.One trial compared metal-free implant-supported screw retained single crowns (zirconia veneered with feldspathic ceramic) to metal-ceramic implant-supported screw-retained single crowns in 20 participants. There was insufficient evidence of a difference for any primary outcome: crown failures (i.e. no failures in either treatment group), crown complications, or satisfaction/aesthetic evaluation at any time of assessment up to two years.Two trials compared metal-free implant abutments (zirconia) to metal implant abutments both supporting single crowns in 50 participants. There was insufficient evidence of a difference in abutment failure at one year.One trial compared metal-free implant-supported FDPs made of two different types of zirconia ceramic in 18 participants. There was insufficient evidence of a difference in failures at any time of assessment up to 10 years (i.e. no failures in either treatment group). There was some evidence of a benefit for the zirconia-toughened alumina group in terms of complications (chipping).One trial compared metal-free tooth-supported FDPs made with two different veneering techniques (pressed versus layered) in 40 participants. There was insufficient evidence of a difference for failures (i.e. no failures in either treatment group) or complications at any time of assessment up to three years.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or refute the effectiveness of metal-free materials for fixed prosthodontic treatment over metal-ceramic or other type of standard restorations. The overall quality of existing evidence was very low, therefore great caution should be exercised when generalising the results of the included trials. Until more evidence becomes available clinicians should continue to base decisions on which material to use for fixed prosthodontic treatment on their own clinical experience, whilst taking into consideration the individual circumstances and preferences of their patients. There is urgent need of properly designed RCTs.

Adhesive Cementation Promotes Higher Fatigue Resistance to Zirconia Crowns

Objective: The aim of this study was to investigate the influence of the cementation strategy on the fatigue resistance of zirconia crowns. The null hypothesis was that the cementation strategy would not affect the fatigue resistance of the crowns.

Methods and Materials: Seventy-five simplified molar tooth crown preparations were machined in glass fiber–filled epoxy resin. Zirconia crowns were designed (thickness=0.7 mm), milled by computer-aided design/computer-aided manufacturing, and sintered, as recommended. Crowns were cemented onto the resin preparations using five cementation strategies (n=15): ZP, luting with zinc phosphate cement; PN, luting with Panavia F resin cement; AL, air particle abrasion with alumina particles (125 μm) as the crown inner surface pretreatment + Panavia F; CJ, tribochemical silica coating as crown inner surface pretreatment + Panavia F; and GL, application of a thin layer of porcelain glaze followed by etching with hydrofluoric acid and silanization as crown inner surface pretreatment + Panavia F. Resin cement was activated for 30 seconds for each surface. Specimens were tested until fracture in a stepwise stress fatigue test (10,000 cycles in each step, 600 to 1400 N, frequency of 1.4 Hz). The mode of failure was analyzed by stereomicroscopy and scanning electron microscopy. Data were analyzed by Kaplan-Meier and Mantel-Cox (log rank) tests and a pairwise comparison (p&lt;0.05) and by Weibull analysis.

Results: The CJ group had the highest load mean value for failure (1200 N), followed by the PN (1026 N), AL (1026 N), and GL (1013 N) groups, while the ZP group had the lowest mean value (706 N). Adhesively cemented groups (CJ, AL, PN, and GL) needed a higher number of cycles for failure than the group ZP did. The groups' Weibull moduli (CJ=5.9; AL=4.4; GL=3.9; PN=3.7; ZP=2.1) were different, considering the number of cycles for failure data. The predominant mode of failure was a fracture that initiated in the cement/zirconia layer. Finite element analysis showed the different stress distribution for the two models.

Conclusion: Adhesive cementation of zirconia crowns improves fatigue resistance.

Zirconia Crown as Single Unit Tooth Restoration: A Literature Review

Ceramics has become increasingly popular as a dental restorative material because of its superior esthetics, as well as its inertness and biocompatibility. Among dental ceramics, zirconia is used as a dental biomaterial and it is the material of choice in contemporary restorative dentistry. Zirconia ceramics has both clinical popularity and success due to its outstanding mechanical properties and ease of machining in the green stage via computer-aided design and computer-aided manufacturing technology. Zirconia is one of the most promising restorative biomaterial because it has favorable mechanical and chemical properties suitable for medical application. Zirconia ceramics is becoming a prevalent biomaterial in dentistry. Clinical evaluations also indicate a good success rate for zirconia with minimal complications. This article reviews the current literature on dental zirconia with respect to basic properties, biocompatibility, and clinical applications in aesthetic dentistry as single unit crown.

Effect of sandblasting, silica coating, and laser treatment on the microtensile bond strength of a dental zirconia ceramic to resin cements

The purpose of this in vitro study was to evaluate the effect of laser irradiation as well as other surface treatment methods on the microtensile bond strength of a dental zirconia ceramic to the two types of resin cements. Zirconia ceramic blocks (ICE Zirkon) were sintered according to the manufacturer's instructions and duplicated in resin composites. The ceramic specimens were divided into four groups according to the following surface treatments: no surface treatment (control), sandblasting with alumina, silica coating plus silanization, and Nd:YAG laser irradiation. The specimens were divided equally and then bonded with Panavia F2.0 (self-etching resin cement) and Clearfil SA Luting (self-adhesive resin cement) to the composite blocks. The bonded ceramic-composite blocks were stored in distilled water at 37 °C for 72 h, cut to prepare bar-shaped specimens with a bonding area of approximately 1 mm(2), and thermocycled for 3000 cycles between 5 and 55 °C, and the microtensile bond strengths were measured using a universal testing machine. The data were analyzed by ANOVA and Tukey post hoc test. The results showed that the self-adhesive resin cement used in this study did not improve the microtensile bond strength when the zirconia surface was sandblasted by alumina. The use of the Nd:YAG laser did not enhance the bond strength between the zirconia and both types of resin cements. In addition, silica coating of the zirconia surfaces plus silane application significantly improved the bond strength regardless of the type of resin cement utilized.

Translucency of monolithic and core zirconia after hydrothermal aging

Objective: To evaluate the hydrothermal aging effect on the translucency of partially stabilized tetragonal zirconia with yttria (Y-TZP) used as monolithic or fully milled zirconia and of core type.

Methods: Twenty disc-shaped specimens (1 and 10 mm) for each type of monolithic and core Y-TZP materials were milled and sintered according to the manufacturer’s instruction. The final specimens were divided into two groups according to the type of Y-TZP used. Translucency parameter (TP) was measured over white and black backgrounds with the diffuse reflectance method; X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the microstructure of both Y-TZP types before and after aging. Data for TP values was statistically analyzed using Student’s t-test.

Results: Monolithic Y-TZP showed the highest TP mean value (16.4 ± 0.316) before aging while core Y-TZP showed the lowest TP mean value (7.05 ± 0.261) after aging. There was a significant difference between the two Y-TZP types before and after hydrothermal aging. XRD analysis showed increases in monoclinic content in both Y-TZP surfaces after aging.

Conclusion: Monolithic Y-TZP has a higher chance to low-temperature degradation than core type, which may significantly affect the esthetic appearance and translucency hence durability of translucent Y-TZP.

Fatigue Resistance of Y-TZP/Porcelain Crowns is Not Influenced by the Conditioning of the Intaglio Surface

OBJECTIVES

The objective of this study was to investigate the effects of treatments of the intaglio surface of Y-TZP frameworks and luting agents on the fatigue resistance of all-ceramic crowns.

METHODS

A research design was chosen that attempted to reduce the likelihood of Hertzian cracking and to increase the probability of fracture initiation at the intaglio surface of the framework. Ninety identical preparations were machined in a dentin-like epoxy composite. Each preparation was restored with a Y-TZP framework made by a CAD/CAM system and veneered using feldspathic ceramic. Prior to cementation the intaglio surface of the ceramic was treated using one of four treatments: 1) cleaning with isopropyl alcohol; 2) application of an overglaze; 3) sandblasting with 125 μm aluminum oxide powder; and 4) sandblasting with 30 μm silica powder (CJ). One of three luting cements were used: 1) zinc phosphate; 2) glass ionomer; and 3) adhesive resin cement (PN). All three cements were tested against frameworks that were alcohol cleaned. Only the PN cements were tested against frameworks that had been sandblasted or glazed. Altogether, six groups of 15 specimens each were tested. Fatigue resistance was evaluated using stepwise loads at 1.4 Hz until failure: 5000 cycles at maximum load of 200 N, followed by 10,000 cycles at maximum loads of 800, 1000, 1200, and 1400 N. The cement thickness and failure modes were analyzed using a stereomicroscope and scanning electron microscopy. The results were analyzed using the Kaplan-Meier and Mantel-Cox log rank tests (5%), a one-way analysis of variance, Tukey multiple comparison test, and Weibull nonparametric test.

RESULTS

The predominant failure mode was chipping of the veneer. The crowns cemented with the adhesive resin cement exhibited chipping failure at higher mean loads than did crowns cemented with cements that usually do not bond strongly with dentin. When the adhesive cement was used, glazing and sandblasting intaglio framework surface treatments exhibited lower mean loads at chipping than did crowns whose intaglio surface was only cleaned with alcohol. Weibull analysis indicated that all specimens had a high ratio of late-to-early failures.

CONCLUSIONS

The fatigue experiment produced a pattern of failures that is very similar to that observed in clinical trials of Y-TZP crowns that are veneered with feldspathic porcelain. Crowns cemented with an adhesive resin cement exhibited chipping at a significantly higher mean load than those cemented with luting cements that do not usually form strong bonds with dentin. When cemented with adhesive resin cement, glazing or sandblasting the intaglio surface of the framework significantly reduced the mean fatigue loads at which chipping of veneers occurred, as compared to crowns whose intaglio surface had only been cleaned with alcohol. For this cement glazing or sandblasting the intaglio surface of the crown is not recommended.

Clinical outcomes of zirconia-based implant- and tooth-supported single crowns

OBJECTIVES

Zirconia-based restorations have been increasingly used on implant and teeth abutments, but the evidence about clinical outcomes of these restorations is limited. The aim of this study was to assess up to 7-year clinical outcomes of implant- and tooth-supported zirconia-based single crowns.

MATERIALS AND METHODS

In this retrospective study, 261 patients with 556 single crowns supported by either teeth (324) or implants (232) were examined during 3- to 7-year follow-up (mean observation of 60.70 months for tooth and 59.20 months for implant-supported crowns). California Dental Association (CDA) quality evaluation system was used to evaluate the restorations. Soft tissue status was assessed using plaque and gingival index scores, bleeding on probing, and pocket depth. Patient and professional satisfaction were evaluated by visual analog scale (VAS).

RESULTS

The 5-year Kaplan-Meier survival probability was 98.3 and 97.3 for implant- and tooth-supported crowns, respectively. In regard to CDA rating, most of the crowns were ranked as either excellent or acceptable (99.5 %). The recorded failures were replacement of the crown due to porcelain chipping (3), implant failure (1), and teeth extraction (5). Soft tissue parameters were not affected by the restorations compare to control teeth. The VAS was high for both patients and clinicians.

CONCLUSIONS

Zirconia-based single crowns on both tooth and implant abutments showed promising clinical performance in this up to 7-year follow-up.

CLINICAL RELEVANCE

The zirconia-based single crowns can be used clinically for tooth- and implant-supported restorations.

Dual-scan technique for the customization of zirconia computer-aided design/computer-aided manufacturing frameworks

The use of bi-layered all-ceramic crowns has continuously grown since the introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia cores. Unfortunately, despite the outstanding mechanical properties of zirconia, problems related to porcelain cracking or chipping remain. One of the reasons for this is that ceramic copings are usually milled to uniform thicknesses of 0.3-0.6 mm around the whole tooth preparation. This may not provide uniform thickness or appropriate support for the veneering porcelain. To prevent these problems, the dual-scan technique demonstrates an alternative that allows the restorative team to customize zirconia CAD/CAM frameworks with adequate porcelain thickness and support in a simple manner.

The zirconia ceramic: strengths and weaknesses

Metal ceramic restorations were considered the gold standard as reliable materials. Increasing demand for esthetics supported the commercialization of new metal free restorations. A growing demand is rising for zirconia prostheses. Peer-reviewed articles published till July 2013 were identified through a Medline (Pubmed and Elsevier). Emphasizing was made on zirconia properties and applications. Zirconia materials are able to withstand posterior physiologic loads. Although zirconia cores are considered as reliable materials, these restorations are not problem free.

In vitro evaluation of the marginal and internal discrepancies of different esthetic restorations

Objective

This study examined the fit of two types of all-ceramic single crowns and indirect composite resin full coverage crowns.

Material and Methods

Thirty intact human mandibular first premolars were selected for this study and prepared using a machine to standardize the dimensions and randomly divided into 3 groups. Slip cast (IC) (In-Ceram Zirconia, Vita Zahnfabrik), copy-milled zirconia (CM) (ICE, Zirkonzahn) and indirect composite resin crowns (NECO, HeraeusKulzer, Hanau, Germany), (N=30, 10 per group) were fabricated according to each manufacturer's recommendations. Before cementation, discrepancies were measured at the marginal zone in each crown. Crowns were then cemented with G-Cem capsule self-adhesive luting cement (GC Corporation, Tokyo, Japan). Four positions were marked for each zone (mid-facial, mid-mesial, mid-distal, and mid-lingual) and three measurements were made at each of the four positions yielding to a total of 12 measurements per crown before and after cementation. The measurements were performed at a different magnification using a stereo microscope (SZ11, Olympus, Japan). Marginal, axial and occlusal zone discrepancies (µm) were evaluated after cementation. The data were statistically analyzed using two-way ANOVA and Tukey's test.

Results

Before cementation, significantly less marginal discrepancies were noted compared with after cementation in all groups (p<0.05). No significant differences were found within each zone (Marginal= IC: 84.2, NECO: 95.22, CM: 84.22; Axial= IC: 54.22, NECO: 64.2, CM: 55.22; Occlusal= IC: 119.97, NECO: 129.18, CM: 121.15) in the three crown systems (p>0.05). Occlusal zone discrepancies were significantly higher than those of the marginal and axial zones in all groups (p<0.05).

Conclusions

Slip cast and copy-milled zirconia crowns showed comparable fit to composite resin crowns in all marginal, axial and occlusal areas.

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.

A critical appraisal of evidence-based dentistry: the best available evidence

STATEMENT OF PROBLEM

The principle of evidence-based dentistry requires that relevant scientific literature be integrated into the dentist's practice and the patient's treatment needs and wishes. This approach involves critically appraising the scientific literature for the best available evidence in order to make clinical decisions.

PURPOSE

The purpose of the study was to critically appraise the process by which a practitioner attempts to make an evidenced-based clinical decision. This process is illustrated by evaluating the clinical literature pertaining to zirconia-based single crowns.

MATERIAL AND METHODS

An electronic search was performed in PubMed and the Cochrane Library by using Boolean operators for articles published in English between January 1950 and October 2012 to address the PICO (patients, intervention, comparison, outcome) question, "In adults, how does the long term prognosis of zirconia-based single crowns compare to conventional single crowns on natural teeth?" Comparisons were made across the publications to determine the quality of relevant information.

RESULTS

Three systematic reviews included 4 clinical trials. Two randomized clinical trials and 1 retrospective study met the search criteria but were not identified in the systematic reviews. The definitions of the outcomes and the presentation of the data varied among studies.

CONCLUSIONS

The lack of standardization of reporting data, the nonstandardized definitions of outcomes, and the impact of the length of the research study were identified as problems that need to be addressed to improve the quality of systematic reviews and other clinical trials.

A critical appraisal of the systematic review process: systematic reviews of zirconia single crowns

STATEMENT OF PROBLEM

Systematic reviews analyze the data of published research in an effort to assemble the scientific evidence to help clinicians apply evidence-based information in decision making. The quality of systematic reviews varies greatly.

PURPOSE

The purpose of this study was to critically appraise the current systematic review process by evaluating systematic reviews that pertain to zirconia-based single crowns.

MATERIALS AND METHODS

The following PICO (patients, intervention, comparison, outcome) question was formulated: "In adults, how does the long-term prognosis of zirconia-based single crowns compare with conventional single crowns on natural teeth?" An electronic search was performed in PubMed and the Cochran Library for articles published in English between 1950 and October 2012. Additional manual searches were completed. To be included in the analysis, the study must have been a systematic review, published in an English-speaking peer-reviewed journal, and evaluated zirconia crowns on teeth. Two examiners qualitatively evaluated the publications with an Assessment of Multiple Systematic Reviews checklist and the Oxford Systematic Review Appraisal form.

RESULTS

Three systematic reviews were identified that met the search criteria. Two studies met 5 of the 11 Assessment of Multiple Systematic Reviews criteria, whereas the third met only 1 criterion. The same 2 studies met 3 of the 5 Oxford Systematic Review Appraisal criteria and the third met only 2 criteria.

CONCLUSION

Because of the variation in methodologies, systematic reviews should be interpreted cautiously. The Assessment of Multiple Systematic Reviews Checklist and the Oxford Systematic Review Appraisal Sheet are practical tools for appraising and determining the quality of systematic reviews.

Clinical risk factors related to failures with zirconia-based restorations: an up to 9-year retrospective study

OBJECTIVES

The first objective of this study was to retrospectively evaluate zirconia-based restorations (ZBR). The second was to correlate failures with clinical parameters and to identify and to analyse chipping failures using fractographic analysis.

METHODS

147 ZBR (tooth- and implant-supported crowns and fixed partial dentures (FPDs)) were evaluated after a mean observation period of 41.5 ± 31.8 months. Accessorily, zirconia implant abutments (n=46) were also observed. The technical (USPHS criteria) and the biological outcomes of the ZBR were evaluated. Occlusal risk factors were examined: occlusal relationships, parafunctional habits, and the presence of occlusal nightguard. SEM fractographic analysis was performed using the intra-oral replica technique.

RESULTS

The survival rate of crowns and FPDs was 93.2%, the success rate was 81.63% and the 9-year Kaplan-Meier estimated success rate was 52.66%. The chipping rate was 15% and the framework fracture rate was 2.7%. Most fractographic analyses revealed that veneer fractures originated from occlusal surface roughness. Several parameters were shown to significantly influence veneer fracture: the absence of occlusal nightguard (p=0.0048), the presence of a ceramic restoration as an antagonist (p=0.013), the presence of parafunctional activity (p=0.018), and the presence of implants as support (p=0.026). The implant abutments success rate was 100%.

CONCLUSIONS

The results of the present study confirm that chipping is the first cause of ZBR failure. They also underline the importance of clinical parameters in regards to the explanation of this complex problem. This issue should be considered in future prospective clinical studies.

CLINICAL SIGNIFICANCE

Practitioners can reduce chipping failures by taking into account several risk parameters, such as the presence of a ceramic restoration as an antagonist, the presence of parafunctional activity and the presence of implants as support. The use of an occlusal nightguard can also decrease failure rate.

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.

How and when does fabrication damage adversely affect the clinical performance of ceramic restorations?

OBJECTIVES

As compared to factory-processed ceramic parts, one unique trait of all-ceramic dental restorations is that they are custom-fabricated, which implies a greater susceptibility to fabrication defects. A variety of processing techniques is now available for the custom fabrication of all-ceramic single and multi-unit restorations, these include sintering, heat-pressing, slip-casting, hard machining and soft machining, all in combination with a final staining or veneering step. All these fabrication techniques, from shaping to firing, are associated with the production of flaws of various shapes and sizes, in conjunction with thermal residual stresses, all of which are capable of inducing failure.

METHODS

This review will examine the various types of fabrication damage inherent to each technique and attempt to establish a relationship between fabrication defects and clinical performance of all-ceramic dental restorations with particular attention to their longevity in vivo.

RESULTS

Failure mechanisms in dental ceramics can be very complex and often involve the combination of physical factors, to which are added patient and clinician-related variables such as restoration design and in vivo conditions.

SIGNIFICANCE

Tremendous progress has been made in understanding the failure mechanisms of all-ceramic dental restorations over the past thirty years. It remains that there is still a need for laboratory tests that usefully simulate clinical conditions.

Clinical performance and failures of zirconia-based fixed partial dentures: a review literature

PURPOSE

Zirconia has been used in clinical dentistry for approximately a decade, and there have been several reports regarding the clinical performance and survival rates of zirconia-based restorations. The aim of this article was to review the literatures published from 2000 to 2010 regarding the clinical performance and the causes of failure of zirconia fixed partial dentures (FPDs).

MATERIALS AND METHODS

An electronic search of English peer-reviewed dental literatures was performed through PubMed to obtain all the clinical studies focused on the performance of the zirconia FPDs. The electronic search was supplemented by manual searching through the references of the selected articles for possible inclusion of some articles. Randomized controlled clinical trials, longitudinal prospective and retrospective cohort studies were the focuses of this review. Articles that did not focus on the restoration of teeth using zirconia-based restorations were excluded from this review.

RESULTS

There have been three studies for the study of zirconia single crowns. The clinical outcome was satisfactory (acceptable) according to the CDA evaluation. There have been 14 studies for the study of zirconia FPDs. The survival rates of zirconia anterior and posterior FPDs ranged between 73.9% - 100% after 2 - 5 years. The causes of failure were veneer fracture, ceramic core fracture, abutment tooth fracture, secondary caries, and restoration dislodgment.

CONCLUSION

The overall performance of zirconia FPDs was satisfactory according to either USPHS criteria or CDA evaluations. Fracture resistance of core and veneering ceramics, bonding between core and veneering materials, and marginal discrepancy of zirconia-based restorations were discussed as the causes of failure. Because of its repeated occurrence in many studies, future researches are essentially required to clarify this problem and to reduce the fracture incident.

A 5-year retrospective study of survival of zirconia single crowns fitted in a private clinical setting

OBJECTIVES

The aim of this report was to evaluate the 5-year clinical performance and survival of zirconia (NobelProcera™) single crowns.

METHODS

All patients treated with porcelain-veneered zirconia single crowns in a private practice during the period October 2004 to November 2005 were included. The records were scrutinized for clinical data. Information was available for 162 patients and 205 crowns.

RESULTS

Most crowns (78%) were placed on premolars and molars. Out of the 143 crowns that were followed for 5 years, 126 (88%) did not have any complications. Of those with complications, the most common were: extraction of abutment tooth (7; 3%), loss of retention (15; 7%), need of endodontic treatment (9; 4%) and porcelain veneer fracture (6; 3%). No zirconia cores fractured. In total 19 restorations (9%) were recorded as failures: abutment tooth extraction (7), remake of crown due to lost retention (6), veneer fracture (4), persistent pain (1) and caries (1). The 5-year cumulative survival rate (CSR) was 88.8%.

CONCLUSIONS

According to the present 5-year results zirconia crowns (NobelProcera™) are a promising prosthodontic alternative also in the premolar and molar regions. Out of the 143 crowns followed for 5 years, 126 (88%) did not have any complications. However, 9% of the restorations were judged as failures. Further studies are necessary to evaluate the long-term success.