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Screw-retained implant-supported ceramic restorations have shown increased rates of technical complications compared with their cemented counterparts, including fracture and chipping of the ceramic structures. The present clinical report identified the causes leading to the catastrophic failure of a screw-retained lithium disilicate veneered crown cemented to a zirconia abutment with a titanium base by using a systematic fractographic approach. A combination of occlusal overloading, a deficient design and inadequate material selection was identified as being responsible for the fracture. These findings highlight the importance of a thorough analysis of the anatomic conditions and loading scenario of screw-retained implant-supported restorations.

Objective The aim of the present study was to assess the effect of water storage on the quasi-static properties and cyclic fatigue behavior of four contemporary CAD/CAM resin composite materials. Methods The CAD/CAM resin composites Grandio Blocs, LavaTM Ultimate, CerasmartTM and Brilliant Crios, as well as the direct resin composite Grandio SO, were evaluated. Rectangular plates were cut from the blocks or fabricated using a silicon mold to obtain specimens for fracture toughness (KIc, n = 10), biaxial strength (σ0, n = 30) and cyclic fatigue testing (n = 30). Half of the specimens was stored for 24 h in dry conditions and the other half was aged for 60 days in distilled water at 37 °C. KIc was determined using the Compact-Tension (C(T)) method and σ0 and cyclic fatigue were tested using the Ball-on-Three-Balls assembly. Additional disc-shaped specimens (n = 5) were produced to obtain water sorption curves of the materials. Weibull statistics and two-way ANOVA with Tukey’s post-hoc test were used for data assessment. Results The highest water sorption was observed for LavaTM Ultimate (42.6 μg/mm3), whereas Grandio SO displayed the lowest uptake (14 μg/mm3). A statistically significant drop in KIc and σ0 was measured for all materials after water storage, except for the σ0 of CerasmartTM. Water ageing had a dissimilar effect on the cyclic fatigue behavior, increasing the slow crack growth susceptibility of LavaTM Ultimate, but decreasing it for CerasmartTM and Brilliant Crios. Significance Contemporary CAD/CAM resin composites are susceptible to water driven degradative processes, although differences in filler content and resin matrix constitution play an important role in how it impacts their mechanical properties.

The testing of fracture toughness becomes problematic when only limited amount of material is available that hinders the production of typical beam specimens to be tested in bending. Here we explore fracture toughness testing methodologies that allow for small discs and plates having surface cracks to be tested in biaxial flexure using the Ball-on-3-balls (B3B) set-up, or sawed notches as in the Compact Tension geometry. The B3B-KIc test has shown to be versatile and account for a very small overestimation of the KIc-value in the order of 0.8–1.25% due to in-plane crack mispositioning, and a maximum of 4% if a worst-case scenario of additional out-of-plane mispositioning is assumed. The geometrical factor in the standard SCF method, derived by Newman and Raju, resulted in an overestimation of ∼8% of the KIc-value compared to the new calculation by Strobl et al. for materials with Poisson’s ratio

Lithium disilicate glass-ceramics show great potential in the fabrication of anisotropic structures due to their high-strength needle-form crystalline phase subjective to processing-induced alignment. Here we explore this strategy by focusing on the mechanistic aspects of fracture. Through different variations of the fracture toughness test we demonstrate the effect of bulk crystal orientation on fracture energy, toughening mechanisms, crystal size and aspect ratio. Using the anisotropic Poisson's ratio of the Li2Si2O5 crystal phase obtained by Resonant Ultrasound Spectroscopy, we apply the new geometry factor developed by Strobl et al. to provide a more accurate insight into the anisotropic crack propagation behavior in LS2 glass-ceramics. Raman spectra and X-Ray Diffraction patterns are resolved for the Li2Si2O5 phase aligned at plane parallel, anti-plane and random orientations. We show that Li2Si2O5 crystallites oriented perpendicular to the crack growth plane tended to induce large scale crack deflection unless the crack was forced into a straight path, thereby promoting crystallite fracture, increased KIc-values and accentuated R-curve behavior. Crystal aspect ratio and residual stresses in the glass have been identified as important influencing factors on crack growth behavior and toughening mechanisms.

Here we use the 3-point bending with eccentric notch test (3-PBEN) to investigate the fracture behavior of a pressable and a CAD/CAM lithium disilicate (LS2) glass-ceramics under combined mode-I and mode-II loading. The effect of the bulk texturization in the beams of the pressable LS2 is made visible through the fracture trajectory following the most energetically favorable path dictated by the crystallite alignment. The CAD/CAM LS2 shows an isotropic fracture mode but increasing fracture energy with mode-II contribution, similar to the pressable variant.

Objective Strength is one of the preferred parameters used in dentistry for determining clinical indication of dental restoratives. However, small dimensions of CAD/CAM blocks limit reliable measurements with standardized uniaxial bending tests. The objective of this study was to introduce the ball-on-three-ball (B3B) biaxial strength test for dental for small CAD/CAM block in the context of the size effect on strength predicted by the Weibull theory. Methods Eight representative chairside CAD/CAM materials ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Specimens were prepared with highly polished surfaces in rectangular plate (12 × 12 × 1.2 mm3) or round disc (O = 12 mm, thickness = 1.2 mm) geometries. Specimens were tested using the B3B assembly and the biaxial strength was determined using calculations derived from finite element analyses of the respective stress fields. Size effects on strength were determined based on results from 4-point-bending specimens. Results A good agreement was found between the biaxial strength results for the different geometries (plates vs. discs) using the B3B test. Strength values ranged from 110.9 MPa (Vitablocs Mark II) to 1303.21 MPa (e.max ZirCAD). The strength dependency on specimen size was demonstrated through the calculated effective volume/surface. Significance The B3B test has shown to be a reliable and simple method for determining the biaxial strength restorative materials supplied as small CAD/CAM blocks. A flexible solution was made available for the B3B test in the rectangular plate geometry.

Most dental ceramics are produced from partially crystallized glass. Even though these materials are hard, they are extremely susceptible to damage, especially due to the glass phase content. A strategy for strengthening these materials makes use of their microstructure to form reinforcing sites within the structural design. Such approach has potential for application with lithium disilicate (LS 2 ) glass–ceramics, which contain needle-form Li 2 Si 2 O 5 crystals that deflect oncoming cracks. By press injection of the glass melt through specifically oriented injection channels, crystals are aligned in patterns that lead to high mechanical anisotropy. Here we apply this approach in the context of monolithic dental bridges simulated by beams under 3-point bending. Notches at different distances from the midspan play the role of connectors, and the mixed-mode fracture toughness is measured at varying positions for a LS 2 and a 3Y-TZP material. A strong anisotropic fracture behavior is obtained with the LS 2 glass–ceramic through local crystal alignment, leading to fracture energies higher than for the isotropic 3Y-TZP ceramic. Further, the anisotropic nature of the LS 2 microstructure is successfully reproduced in dental bridge geometries, validating the use of bending beams for the study of the mechanical behavior of ceramic dental bridges.

Objectives The present study evaluated the effect of the coefficient of thermal expansion (CTE) mismatch and the cooling protocol on the distribution of residual stresses and crack propagation in veneered zirconia bilayers. Methods Ceramic discs with two different CTEs (Vita VM9 and Lava Ceram) were fired onto zirconia plates and cooled following a slow (0.5 °C/s) or a fast (45 °C/s) cooling protocol. The residual stress distribution throughout the veneer thickness was assessed by means of depth-wise Vickers indentation after sequentially sectioning the bilayers parallel compared to normal to the interface. A mathematical solution for the residual stress distribution was used as reference. Additionally, Hertzian cone crack propagation in the veneers was induced by cyclic contact loading and measured at different number of cycles to estimate the crack growth rate. Results The higher CTE mismatch of the VM9 group generated an important stress gradient with high compressive residual stresses near the interface, hindering the crack propagation. The low CTE mismatch group (Lava Ceram) developed only a slight stress gradient and higher cone crack growth rates. No differences were observed between the two cooling protocols applied regarding stress magnitude and crack propagation behavior. Significance The CTE mismatch has a predominant role in the generation of residual stress gradients within the veneer, which directly influences contact-induced crack propagation. Based on the results, the cooling protocol had no significant effect on the residual stress distribution in zirconia-veneer bilayers.

Objectives The aim of this study was to compare the microtensile bond strength (μTBS) and resin penetration into dentine of three universal adhesives (UAs) applied in two different etching modes (i.e. self-etch or etch-and-rinse). The effect of thermocycling on the μTBS was also evaluated. Methods The occlusal third of sound human molars was removed and the exposed surfaces were treated with three UAs (Futurabond Universal, Scotchbond Universal Adhesive and All-Bond Universal) in self-etch or etch-and-rinse mode. Two one-step self-etch adhesives (Futurabond DC and Futurabond M) were applied on additional teeth as reference. After composite build up, the specimens were stored for 24 h in distilled water at 37 °C or thermocycled for 5000 cycles. Composite/dentine beams were prepared (1 mm 2 ) and μTBS test was performed. Data was analyzed using three-way ANOVA and Tukey's test ( α = 0.05). One additional tooth was prepared for each group for evaluation of infiltration ability into dentine by dyeing the adhesives with a fluorochrome (Rhodamine B). After longitudinal sectioning, the generated interfaces were examined under confocal laser scanning microscopy. Results The addition of an etching step did not significantly affect the μTBS of none of the UAs, when compared to their self-etch application mode. All pre-etched specimens showed considerably longer resin tags and thicker hybrid layers. Thermocycling had no significant effect on the μTBS of the UAs. Conclusions Application of an etching step prior to UAs improves their dentine penetration, but does not affect their bond strength to dentine after 24 h or after thermocycling for 5000 cycles. Clinical significance Similar bond strength values were observed for the UAs regardless of application mode, which makes them reliable for working under different clinical conditions.

The aim of this study was to compare the effect of different mechanical surface treatments and chemical bonding protocols on the tensile bond strength (TBS) of aged composite. Bar specimens were produced using a nanohybrid resin composite and aged in distilled water for 30 days. Different surface treatments (diamond bur, phosphoric acid, silane, and sandblasting with Al₂O₃ or CoJet Sand), as well as bonding protocols (Primer/Adhesive) were used prior to application of the repair composite. TBS of the specimens was measured and the results were analyzed using analysis of variance (ANOVA) and the Student-Newman-Keuls test (α = 0.05). Mechanically treated surfaces were characterized under SEM and by profilometry. The effect of water aging on the degree of conversion was measured by means of FTIR-ATR spectroscopy. An important increase in the degree of conversion was observed after aging. No significant differences in TBS were observed among the mechanical surface treatments, despite variations in surface roughness profiles. Phosphoric acid etching significantly improved repair bond strength values. The cohesive TBS of the material was only reached using resin bonding agents. Application of an intermediate bonding system plays a key role in achieving reliable repair bond strengths, whereas the kind of mechanical surface treatment appears to play a secondary role.

In autumn 2007, the Medical University of Graz (MUG) upgraded the status of general practice in medical training by integrating a compulsory five-week clerkship in general practice surgeries in the sixth and last year of the curriculum. In cooperation with the Styrian Academy of General Practice (STAFAM), more than 200 general practitioners (GPs) had been accredited to introduce medical students to the specific tasks, problems and decision-making process in general practice. Between October 2007 and June 2009, more than 300 students completed the clerkship.To explore the perceptions of students and GPs towards this new approach to undergraduate teaching in Austrian general practice.Between March and June 2009, we conducted a cross-sectional survey by using a self-administered questionnaire with 14 items for students as well as GPs. To limit recall bias, we gave the questionnaire to all students (n = 146) and GPs (n = 146) immediately after the clerkship. The response rates were 146/146 (100%) and 114/146 (78%) for students and GPs, respectively.The study results show high satisfaction rates among students as well as GPs. Most of the students and GPs perceive the compulsory clerkship in general practice as an essential part of medical education. The organization of the clerkship had the least positive outcome.Our survey shows that the clerkship is well accepted among Austrian medical students and GPs.