Clinical Trials in Zirconia: A Systematic Review

Department of Oral Rehabilitation, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
Journal of Oral Rehabilitation (Impact Factor: 1.68). 08/2010; 37(8):641-52. DOI: 10.1111/j.1365-2842.2010.02094.x
Source: PubMed


Zirconia is unique in its polymorphic crystalline makeup, reported to be sensitive to manufacturing and handling processes, and there is debate about which processing method is least harmful to the final product. Currently, zirconia restorations are manufactured by either soft or hard-milling processes, with the manufacturer of each claiming advantages over the other. Chipping of the veneering porcelain is reported as a common problem and has been labelled as its main clinical setback. The objective of this systematic review is to report on the clinical success of zirconia-based restorations fabricated by both milling processes, in regard to framework fractures and veneering porcelain chipping. A comprehensive review of the literature was completed for in vivo trials on zirconia restorations in MEDLINE and PubMed between 1950 and 2009. A manual hand search of relevant dental journals was also completed. Seventeen clinical trials involving zirconia-based restorations were found, 13 were conducted on fixed partial dentures, two on single crowns and two on zirconia implant abutments, of which 11 were based on soft-milled zirconia and six on hard-milled zirconia. Chipping of the veneering porcelain was a common occurrence, and framework fracture was only observed in soft-milled zirconia. Based on the limited number of short-term in vivo studies, zirconia appears to be suitable for the fabrication of single crowns, and fixed partial dentures and implant abutments providing strict protocols during the manufacturing and delivery process are adhered to. Further long-term prospective studies are necessary to establish the best manufacturing process for zirconia-based restorations.

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Available from: Basil Al-Amleh
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    • "In addition, the development of computer aided designing (CAD)/computer aided manufacturing (CAM) technology has increased the use. Thus, all-ceramic crowns and fixed dental prostheses (FDPs) utilizing zirconia as a framework have been provided to patients with sufficient strength and a good esthetic outcome [3] [4]. "
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    ABSTRACT: Objectives: The purpose of the present study was to analyze the relationship between fracture load of monolithic zirconia crowns and axial/occlusal thickness and to evaluate the fracture resistance of monolithic zirconia crowns with reduced thickness in comparison with that of monolithic lithium disilicate crowns with regular thickness. Materials and methods: Monolithic zirconia crowns (Lava Plus Zirconia, 3M/ESPE) with specified axial/occlusal thicknesses and lithium disilicate crowns (IPS e.max press, Ivoclar/Vivadent) with regular thickness were fabricated using a dental CAD/CAM system and a press technique, respectively. The crowns cemented onto dies were loaded until fracture. Based on measurements of the crown thickness made by micro-CT and the fracture load, multiple regression analysis was performed. Results: It was revealed that the occlusal thickness significantly affected the fracture load (p < 0.01), but the axial thickness did not (p = 0.2828). Although the reduction of the occlusal thickness decreased the fracture resistance of the monolithic zirconia crowns, the fracture load of the zirconia crowns with the occlusal thickness of 0.5 mm (5558 ± 522 N) was significantly higher than that of lithium disilicate crowns with an occlusal thickness of 1.5 mm (3147 ± 409 N). Conclusion: Within the limitations of the present study, it is suggested that monolithic zirconia crown with chamfer width of 0.5 mm and occlusal thickness of 0.5 mm can be used in the molar region in terms of fracture resistance.
    Full-text · Article · Jan 2015 · Acta Odontologica Scandinavica
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    • "Over the past ten years several in vitro [1] [2] [3] [4] [5] and clinical studies [6] [7] have attempted to document and understand the nature of porcelain veneer cohesive fractures in all-ceramic restorations, specially yttria-tetragonal zirconia polycrystals (Y-TZP) [6] [7]. Besides issues related to manufacturing process (i.e., porosities and micro-structural defects) [8], chipping has been suggested to be strongly related with; residual thermal stress [9] [10] [11] [12], coefficient of thermal expansion mismatches [1], poor framework design [3,4,13–15], and others [12]. "
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    ABSTRACT: To compare the fatigue life and damage modes of zirconia crowns fabricated with and without framework design modification when porcelain veneered using a fast or slow cooling protocol.Methods Composite resin replicas of a first molar full crown preparation were fabricated. Zirconia copings were milled as conventional (0.5 mm even thickness, Zr-C, n = 20,) or modified (lingual margin of 1.0 mm thickness, 2.0 mm height connected to two proximal struts of 3.5 mm height, Zr-M, n = 20). These groups were subdivided (n = 10 each) according to the veneer cooling protocol employed: fast cooling (Zr-CFast and Zr-MFast) and slow cooling (Zr-CSlow and Zr-MSlow). Crowns were cemented and fatigued for 106 cycles in water. The number of cycles to failure was recorded and used to determine the interval databased 2-parameter probability Weibull distribution parameter Beta (β) and characteristic life value Eta (η).Results2-parameter Weibull calculation presented β = 5.53 and β = 4.38 for Zr-MFast and Zr-CFast, respectively. Slow cooled crowns did not fail by completion of 106 cycles, thereby Weibayes calculation was applied. Increased fatigue life was observed for slow cooled crowns compared to fast cooled ones. Groups Zr-MFast and Zr-MSlow presented no statistical difference. Porcelain cohesive fractures were mainly observed in fast cooled groups. Slow cooled crowns presented in some instances inner cone cracks not reaching the zirconia/veneer interface.SignificanceImproved fatigue life in tandem with the absence of porcelain fractures were observed in slow cooled crowns, regardless of framework design. Crowns fast cooled chiefly failed by porcelain cohesive fractures.
    Full-text · Article · Nov 2014 · Dental Materials
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    • "Porcelain layered zirconia crowns were recently introduced and quickly become very popular in dentistry [1] [2] [3] [4]. Success may be defined as the achievement of treatment planning goals and expectations. "
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    ABSTRACT: Objectives: Chipping is the most frequent clinical failure of zirconia crowns. Causes of chipping have not been completely understood and different possible reasons have been considered. The study was aimed at evaluating the fracture resistance of 3 different CAD/CAM zirconia frame designs veneered with porcelain. Methods: Thirty extracted sound premolars were divided into 3 groups (n=10). Chamfer preparations were performed, impressions were taken. Three zirconia frame designs (Aadva, GC) were realized: reproduction of the abutment contour (flat design, FD); wax-up as for porcelain-fused-to-metal crowns (PFM); anatomically guided, designed to keep constant the thickness of the overlying porcelain veneering (AG). Porcelain veneering was made with pressure layering technique (Initial Zr, GC). Crowns were cemented utilizing a self-adhesive resin cement (G-Cem, GC). After a 24-h water storage at 37°C, using a universal testing machine (1 mm crosshead speed), crowned teeth were loaded in the central fossa in a direction parallel to the longitudinal axis of the tooth. Load at fracture was recorded in Newtons (N). Digital photographs of the specimens were taken in order to assess failure patterns. Between-group differences in fracture strength were statistically analyzed (One-Way Analysis of Variance, Tukey test, p<0.05). Result: Load at fractures differed significantly among the groups (p=0.004). AG exhibited significantly higher fracture resistance 1721.6 (488.1) N than PFM 1004.6 (321.3) N and FD 1179.5 (536.2) N, that were comparable. Repairable failures occurred in 80% of AG, 70% of PFM, and 50% of FD specimens. Significance: Anatomically guided zirconia frames resisted significantly higher loads than flat and PFM-like frame designs.
    Full-text · Article · Jul 2014 · Dental materials: official publication of the Academy of Dental Materials
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