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Monolithic zirconia crowns may provide a valid treatment modality in the aesthetic zone in patients with severe tooth wear.

Zirconia‐based restorations are showing an increase as the clinicians’ preferred choice at posterior sites because of the strength and esthetic properties of such restorations. However, all‐ceramic restorations fracture at higher rates than do metal‐based restorations. Margin design is one of several factors that can affect the fracture strength of all‐ceramic restorations. The aim of this study was to assess the effect of preparation and crown margin design on fracture resistance. Four groups of bilayer zirconia crowns (with 10 crowns in each group) were produced by hard‐ or soft‐machining technique, with the following four different margin designs: chamfer preparation (control); slice preparation; slice preparation with an additional cervical collar of 0.7 mm thickness; and reduced occlusal thickness (to 0.4 mm) on slice preparation with an additional cervical collar of 0.7 mm thickness. Additionally, 10 hard‐machined crowns with slice preparation were veneered and glazed with feldspathic porcelain. In total, 90 crowns were loaded centrally in the occlusal fossa until fracture. The load at fracture was higher than clinically relevant mastication loads for all preparation and margin designs. The crowns on a chamfer preparation fractured at higher loads compared with crowns on a slice preparation. An additional cervical collar increased load at fracture for hard‐machined crowns.

Purpose: The aim of this study was to evaluate the effect of wall thickness on load at fracture of monolithic zirconia dental crowns after aging. Materials and Methods: Seventy translucent monolithic zirconia crowns (DD Bio ZX 2 , Dental Direkt GmbH) were produced to fit a second upper premolar preparation with a circumferential shallow chamfer. Thirty crowns had a minimum wall thickness of 0.4 mm and 40 had 0.8 mm. TwentyAQ4 of the thick-walled crowns were glazed. The remaining crowns were polished. Ten crowns from each group functioned as controls, while the remaining were subjected to an aging procedure of alternation between dynamic loading and autoclaving. The surviving crowns were assessed for margin damages and surface wear before beeing subjected to quasi-static loading until fracture. All fractures were analyzed by fractographic methods. Results: There were statistically significant differences among the test groups concerning the effects of aging and surface wear. All thick-walled and eight of the thin-walled crowns survived the aging procedure. All fracture origins both from dynamic and quasi-static loading were located in the cervical margin with crack propagation corresponding to cervical hoop stress as observed in clinical failures. Conclusions: Thin-walled translucent monolithic zirconia crowns were more affected by the aging procedure than thick-walled crowns.

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Background: This 10-year follow-up study reports denture satisfaction and oral health-related quality of life of edentulous patients treated with two-implant mandibular overdentures. Methods: This is a follow-up of a previous study carried out between 1997-2005. Originally, the patients were randomly divided into two groups: one receiving two-implant mandibular overdentures (IODs) and another, relined mandibular dentures (RCDs). The latter group were offered and accepted IODs at two years, which then became another IOD group. The main outcome variable of this study is patient opinion over time of the IODs. The participants completed a self-administered questionnaire containing demographics, 15 variables of denture satisfaction, and 20 questions of the Oral Health-Related Impact Pro le (OHIP-20). Comparison between groups were made with Mann-Whitney U-tests for denture variables and T-tests for OHIP-20 variables. Changes over time were analysed with multilevel linear models for denture variables and multilevel ordinal regression analyses for OHIP-20 variables. Results: Of the 54 original participants, 29 responded. Disregarding patients who had died at 10 years, this represented a response rate 76%. In the IOD group, the degree of denture satisfaction and OHIP-20 scores remained high and stable over the 10-years period for all but one variable. The RCD group showed a modest improvement of denture satisfaction and OHIP-20 scores for the rst two years. After treatment with IODs, these variables improved at 10 years to the same level as the original IOD group. Conclusions: The positive effect on denture satisfaction and oral health-related quality of life of edentulous patients treated with two-implant mandibular overdenture remains unchanged 10 years after treatment, con rming the advice that this should be the standard treatment for the edentulous mandible.

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Purpose: High-translucent dental zirconia has been introduced as a suitable material for anterior monolithic restorations. The material composition differs from traditional 3Y-TZP both with regard to yttria content and grain size. Little is known regarding how these alterations affect other properties than translucency and flexural strength. The aim of this study was to evaluate the crack propagation resistance and hardness of dental zirconias with different yttria content and different manufacturing methods. Materials and methods: Measurement of hardness (HV2/5) and crack propagation from the indents (damage tolerance) was performed using a hardness tester(Vicker) on a flat polished surface of five crowns from six different commercial dental zirconias; one hard-machined 3Y-TZP, three soft-machined 3-5% yttria-stabilized zirconias and two soft-machined zirconias with 5% yttria content. Results: Damage control varied greatly among dental zirconias with different compositions and fabrication methods. The hard-machined 3Y-TZP had better crack propagation resistance than soft-machined, 3-5% yttria-stabilized zirconias Conslusion: The ultra-translucent zirconias with 5% yttria content had the lowest crack propagation resistance. Hardness is not a suitable indicator for damage tolerance.