Starting From Scratch: Husbandry Techniques to Establish the First Population of 'Akikiki (Oreomystis bairdi) in Human Care Using Wild-Collected Eggs.

Conservation breeding programs can save species from extinction by establishing assurance populations that provide individuals for achieving species recovery goals in the wild. However, keeping animals in human care can result in the selection of phenotypes that may be suboptimal for post-release survival and reproduction. It is therefore essential that conservation breeding programs provide animals with naturalistic conditions that facilitate the performance of species-typical behaviors, an endeavor that is also a vital aspect of animal welfare. Here, we describe how we established a conservation breeding program for the 'Akikiki (Oreomystis bairdi), a Hawaiian honeycreeper that is facing imminent extinction in the wild. We share how we utilized the species' native habitat as a template for developing husbandry practices with a primary focus on how we simulate wild environmental conditions in enclosures, mimic naturalistic foraging experiences, and facilitate pair bonding and parental breeding behaviors.

Synthesis of Submicrometric Chitosan Particles Loaded with Calcium Phosphate for Biomedical Applications.

Chitosan particles loaded with dibasic calcium phosphate anhydrous (DCPA) is a promising strategy for combining antimicrobial and osteoconduction properties in regenerative medicine. However, mostly micrometer-sized particles have been reported in the literature, limiting their use and reducing their effect in the biomedical field. We have recently overcome this limitation by developing submicrometer-sized particles with electrospray technique. The objective of this study was to understand how the process parameters control the size and properties of submicrometer chitosan particles loaded with DCPA. Solutions of 10 mg/mL chitosan and 2.5 mg/mL DCPA in a 90% acetic acid were electrosprayed under three distinct flow rate conditions: 0.2, 0.5, and 1.0 mL/h. The particles were crosslinked in a glutaraldehyde atmosphere and characterized in terms of their morphology, inorganic content, zeta potential, and minimum inhibitory concentration (MIC) against S. mutans. All conditions showed particles with two similar morphologies: one small-sized with a spherical shape and another larger-sized with a bi-concave shape. All generated a broad particle size distribution, with a similar mean size of ~ 235 nm. The addition of DCPA decreased the zeta potential for all the samples, but it was above 30 mV, indicating a low aggregation potential. The lower flow rate showed the worst efficacy for DCPA incorporation. Antimicrobial activity was greater in chitosan/DCPA particles with flow rate of 0.5 mL/h. It can be concluded that the flow rate of 0.5 mL/h presents the best compromise solution in terms of morphology, zeta potential, MIC, and inorganic content.

Effect of processing methods on the chipping resistance of veneered zirconia.

OBJECTIVES: To evaluate the edge chipping resistance (ReA) and the fracture toughness (KC) of 3Y-TZP bilayers produced with the following materials/processing combinations: fluorapatite glass-ceramic applied on zirconia using the traditional layering and hot-pressing (press-on) techniques; feldspathic porcelain using rapid layer technology (RLT); and lithium disilicate glass-ceramic using CAD-on method. The influence of the cooling rate (slow and fast) was analyzed for layering and hot-pressing. METHODS: Bilayer bars (25x4x2 mm) were made following manufacturers' instructions. The edge chipping test was performed in an universal testing machine, using a coupled Vickers indenter. ReA was calculated dividing the critical load at fracture by the edge distance. Fracture toughness was calculated by a regression fit with a fixed slope of 1.5 correlating the critical chipping load regarding edge distance and also with indentation fracture (IF) method. Data were statistically analyzed using ANOVA and Tukey's test (α = 5%). RESULTS: ReA and KC was significantly higher for the CAD-on bilayers. RLT showed intermediate ReA means, and layering and hot-pressing techniques showed the lowest ReA values. For both processing methods there was no effect of the cooling protocol on the ReA and fracture toughness. CONCLUSIONS: There is a significant effect of the material/processing association on the edge chipping resistance and fracture toughness of the bilayers. There was no effect of the cooling protocol on the edge chipping resistance and fracture toughness for the specimens processed by both the layering and hot-pressing techniques.

Structural aspects controlling the mechanical and biological properties of tough, double network hydrogels.

Anticipating an increasing demand for hybrid double network (DN) hydrogels in biomedicine and biotechnology, this study evaluated the effects of each network on the mechanical and biological properties. Polyethylene glycol (PEG) (meth)acrylate hydrogels with varied monomer molecular weights and architectures (linear vs. 4-arm) were produced with and without an added ionically bonded alginate network and their mechanical properties were characterized using compression testing. The results showed that while some mechanical properties of PEG single network (SN) hydrogels decreased or changed negligibly with increasing molecular weight, the compressive modulus, strength, strain to failure, and toughness of DN hydrogels all significantly increased with increased PEG monomer molecular weight. At a fixed molecular weight (10 kDa), 4-arm PEG SN hydrogels exhibited better overall mechanical performance; however, this benefit was diminished for the corresponding DN hydrogels with comparable strength and toughness and lower strain to failure for the 4-arm case. Regardless of the PEG monomer structure, the alginate network made a relatively larger contribution to the overall DN mechanical properties when the covalent PEG network was looser with a larger mesh size (e.g., for larger monomer molecular weight and/or linear architecture) which presumably enabled more ionic crosslinking. Considering the biological performance, adipose derived stem cell cultures demonstrated monotonically increasing cell area and Yes-associated protein related mechanosensing with increasing amounts of alginate from 0 to 2 wt.%, demonstrating the possibility for using DN hydrogels in guiding musculoskeletal differentiation. These findings will be useful to design suitable hydrogels with controllable mechanical and biological properties for mechanically demanding applications. STATEMENT OF SIGNIFICANCE: Hydrogels are widely used in commercial applications, and recently developed hybrid double network hydrogels have enhanced strength and toughness that will enable further expansion into more mechanically demanding applications (e.g., medical implants, etc.). The significance of this work is that it uncovers some key principles regarding monomer molecular weight, architecture, and concentration for developing strong and tough hybrid double network hydrogels that would not be predicted from their single network counterparts or a linear combination of the two networks. Additionally, novel insight is given into the biological performance of hybrid double network hydrogels in the presence of adipose derived stem cell cultures which suggests new scope for using double network hydrogels in guiding musculoskeletal differentiation.

Fiber reinforcement of a resin modified glass ionomer cement.

OBJECTIVES: Understand how discontinuous short glass fibers and braided long fibers can be effectively used to reinforce a resin modified glass ionomer cement (RMGIC) for carious lesion restorations. METHODS: Two control groups (powder/liquid kit and capsule) were prepared from a light cured RMGIC. Either discontinuous short glass fibers or braided polyethylene fiber ribbons were used as a reinforcement both with and without pre-impregnation with resin. For the former case, the matrix was the powder/liquid kit RMGIC, and for the latter case the matrix was the capsule form. Flexural strength was evaluated by three-point beam bending and fracture toughness was evaluated by the single-edge V-notch beam method. Compressive strength tests were performed on cylindrical samples. Results were compared by analysis of variances and Tukey's post-hoc test. Flexural strength data were analyzed using Weibull statistical analysis. RESULTS: The short fiber reinforced RMGIC both with and without pre-impregnation showed a significant increase of ∼50% in the mean flexural strength and 160-220% higher fracture toughness compared with the powder/liquid RMGIC control. Reinforcement with continuous braided fibers gave more than a 150% increase in flexural strength, and pre-impregnation of the braided fibers with resin resulted in a significant flexural strength increase of more than 300% relative to the capsule control. However, for the short fiber reinforced RMGIC there was no significant benefit of resin pre-impregnation of the fibers. The Weibull modulus for the flexural strength approximately doubled for the fiber reinforced groups compared to the control groups. Finally, compressive strength was similar for all the groups tested. SIGNIFICANCE: By using a RMGIC as a matrix, higher flexural strength was achieved compared to reported values for short fiber reinforced GICs. Additionally, the short fibers provided effective toughening of the RMGIC matrix by a fiber bridging mechanism. Finally, continuous braided polyethylene fibers gave much higher flexural strength than discontinuous glass fibers, and their effectiveness was enhanced by pre-impregnation of the fibers with resin.

Anisotropic fracture resistance of avian eggshell.

In order to understand the fracture toughness anisotropy of avian eggshells, we have investigated eggshells of the emu (Dromaius novaehollandiae) whereby the large size (~13 cm × 9.5 cm) enabled the fabrication of beam samples in various orientations. The emu eggshell was found to have a hierarchical microstructure similar to chicken eggshell, with the only significant difference being the absence of a continuous cuticle layer. Emu eggshell was found to have significantly lower strength when samples were tested in the outwards direction (i.e., a crack initiates on the inside of the shell and propagates towards the outer surface) as compared to the inwards testing direction. Furthermore, samples that were oriented parallel to the egg axis (i.e., the longitudinal direction) and tested inwards showed higher strength, ~24 MPa, compared to the samples that were made from the latitudinal orientation, ~20 MPa. Independent of orientation, the outwards testing direction resulted in strength values of ~15 MPa. The fracture toughness of the emu eggshell for cracking in the circumferential direction was ~0.3 MPa√m, independent of sample orientation, and this value was comparable to the fracture toughness of chicken eggshell tested in the same orientation. In the radial outwards direction, however, the fracture toughness was ~80% lower (~0.06 MPa√m) than in the circumferential direction. The low fracture toughness for this orientation was associated with the separation of the highly oriented calcite crystals in the mammillary cone layer of the eggshell structure which is easier compared to calcite crystal fracture. The large anisotropy in fracture toughness is thought to allow for easy escape of the chick while simultaneously protecting the embryo during development.

Development of novel dental restorative composites with dibasic calcium phosphate loaded chitosan fillers.

The incorporation of antimicrobial agents in restorative dental composites has the potential to slow the development of carious lesions. OBJECTIVE: The objectives of the present study were to develop experimental composite resins with chitosan or chitosan loaded with dibasic calcium phosphate anhydrous (DCPA) particles and to demonstrate their antimicrobial potential without loss of mechanical properties or biocompatibility. METHODS: Chitosan and chitosan/DCPA particles were synthetized by the electrospray method. Experimental composites were formulated by adding 0, 0.5, or 1.0 wt% particles into a resin matrix along with 60 wt% barium glass. The degree of conversion and mechanical properties were measured after 1 and 90 days of aging in water after photoactivation. Cytotoxicity and genotoxicity were evaluated using fibroblasts from dental pulp in conditioned medium. The antimicrobial activity against Streptococcus mutans was assessed by crystal violet biofilm assay. RESULTS: The experimental restorative composites were not found to be cytotoxic or genotoxic, with cell viability of 93.1 ± 8.0% (p = 0.328) and 3.0 ± 0.8% micronucleus per group (p = 0.1078), respectively. The antimicrobial results showed that all composites with approximately 20% less biofilm (p < 0.001) relative to the control. No chitosan release was detected from the composites, suggesting direct contact of the bacteria with exposed chitosan particles on the surface was responsible for the observed antimicrobial effect. The addition of the chitosan and chitosan/DCPA submicrometer (<250 nm average diameter) particles to restorative composites did not change the degree of conversion, flexural strength, elastic modulus and fracture toughness compared to the control group after 90 days aging in water. SIGNIFICANCE: It can be concluded that the addition of chitosan or chitosan/DCPA particles in the restorative composites induced antimicrobial activity without compromising the mechanical properties or biocompatibility of the composites.

A diet high in fat and fructose adversely affects osseointegration of titanium implants in rats.

OBJECTIVES: Diet-induced metabolic dysfunction such as type 2 diabetes mellitus increases the risk of implant failure in both dental and orthopaedic settings. We hypothesised that a diet high in fat and fructose would adversely affect peri-implant bone structure and function including osseointegration. MATERIALS AND METHODS: Thirty female Sprague-Dawley rats were divided into three groups (n = 10), control group (normal chow) and two intervention groups on a high-fat (60%), high-fructose (20%; HFHF) diet. Titanium implants were placed in the proximal tibial metaphysis in all groups either before commencing the diet (dHFHF group) or 6 weeks after commencing the diet (HFHF group) and observed for an 8-week healing period. Fasting blood glucose levels (fBGLs) were measured weekly. Structural and functional features of the peri-implant bone, including bone-to-implant contact (BIC), were analysed post euthanasia using microcomputed tomography, pull-out tests, and dynamic histomorphometry. RESULTS: The fBGLs were unchanged across all groups. Peri-implant trabecular bone volume was reduced in the HFHF group compared with controls (p = .02). Percentage BIC was reduced in both HFHF group (25.42 ± 3.61) and dHFHF group (28.56 ± 4.07) compared with the control group (43.26 ± 3.58, p < .05) and reflected the lower pull-out loads required in those groups. Osteoblast activity was reduced in both intervention groups compared with the control group (p < .05). CONCLUSION: The HFHF diet compromised osseointegration regardless of whether the implant was placed before or after the onset of the diet and, despite the absence of elevated fBGLs, confirming that changes in bone cell function affected both the initiation and maintenance of osseointegration independent of blood glucose levels.

Effect of cooling protocol on mechanical properties and microstructure of dental veneering ceramics.

OBJECTIVES: Understand how cooling protocols control the microstructure and mechanical properties of veneering porcelains. METHODS: Two porcelain powders were selected, one used to veneer metallic frameworks (VM13) and one for zirconia frameworks (VM9). After the last firing cycle, the monolithic specimens were subjected to two cooling protocols: slow and fast. Flexural strength (FS) was evaluated by three-point beam bending and fracture toughness (KIC) was evaluated by the single-edge V-notch beam (SEVNB) method. Scanning electron microscopy (SEM) was performed to determine the leucite crystal volume fraction (%), particle size, and matrix microcrack density. The results were compared by analysis of variances (ANOVA) and Tukey's multiple comparison test. RESULTS: The mechanical properties were significantly (p<0.05) higher for the VM13 porcelain (FS=111.0MPa, KIC=1.01MPa.√m) compared to VM9 (FS=79.6MPa, KIC =0.87MPa.√m) regardless of cooling protocol due to ∼250% higher volume fraction of leucite crystals. The slow cooled VM13 and fast cooled VM9 resulted in the highest and lowest mechanical properties, respectively, while the VM9 slow cooled properties were similar to the VM13 fast cooled. The SEM revealed that the slow cooling significantly increased the volume fraction of leucite crystals by 33-41 %. Across both porcelains, a significant linear correlation between both mechanical properties (strength and toughness) and leucite crystal content was found. Slow cooling was also associated with increased crystal growth resulting in more matrix microcracking. SIGNIFICANCE: Controlled crystallization using slow cooling can be applied as a means of strengthening dental porcelains. However, the benefits of slow cooling may be partially offset by increasing the microcrack density in the glass matrix. To achieve the maximum benefit of slow cooling, it is recommending to develop heat treatments to produce porcelain with fine-grained and homogenously dispersed leucite crystals to achieve minimal glass matrix microcracking.

Why a zero CTE mismatch may be better for veneered Y-TZP structures.

OBJECTIVE: Compare residual stress distribution of bilayered structures with a mismatch between the coefficient of thermal expansion (CTE) of framework and veneering ceramic. A positive mismatch, which is recommended for metal-ceramic dental crowns, was hypothesized to contribute to a greater chipping frequency in veneered Y-TZP structures. In addition, the multidirectional nature of residual stresses in bars and crowns is presented to explore some apparent contradictions among different studies. METHODS: Planar bar and crown-shaped bilayered specimens with 0.7 mm framework thickness and 1.5 mm porcelain veneer thickness were investigated using finite element elastic analysis. Eight CTE mismatch conditions were simulated, representing two framework materials (zirconia and metal) and six veneering porcelains (distinguished by CTE values). Besides metal-ceramic and zirconia-ceramic combinations indicated by the manufacturer, models presenting similar mismatch values (1 ppm/°C) with different framework materials (metal or zirconia) and zirconia-based models with metal-compatible porcelain veneers were also tested. A slow cooling protocol from 600 °C to room temperature was simulated. The distributions of residual maximum and minimum principal stresses, as well as stress components parallel to the long axis of the specimens, were analysed. RESULTS: Planar and crown specimens generated different residual stress distributions. When manufacturer recommended combinations were analysed, residual stresses obtained for zirconia models were significantly higher than those for metal-based models. When zirconia frameworks were combined with metal-compatible porcelains, the residual stress values were even higher. Residual stresses were not different between metal-based and zirconia-based models if the CTE mismatch was similar. SIGNIFICANCE: Some conclusions obtained with planar specimens cannot be extrapolated to clinical situations because specimen shape strongly influences residual stress patterns. Since positive mismatch generates compressive hoop stresses and tensile radial stresses and since zirconia-based crowns tend to be more vulnerable to chipping, a tensile stress-free state generated with a zero CTE mismatch could be advantageous.

Influence of residual thermal stresses on the edge chipping resistance of PFM and veneered zirconia structures: Experimental and FEA study.

OBJECTIVE: Chipping fractures of the veneering porcelain are frequently reported for veneered all-ceramic crowns. In the present study, the edge chipping test is used to measure the toughness and the edge chipping resistance of veneered zirconia and porcelain-fused-to-metal (PFM). The aim is to describe an edge chipping method developed with the use of a universal testing machine and to verify the accuracy of this method to determine the influence of residual thermal stresses on the chipping fracture resistance of veneering porcelain. A finite element analysis (FEA) was used to study the residual stress profiles within the veneering porcelain. METHODS: Veneered zirconia and PFM bar specimens were subjected to either a fast or a slow cooling protocol. The chipping resistances were measured using the edge chipping method. The load was applied in two different directions, in which the Vickers indenter was placed in the veneering porcelain either parallel or perpendicular to the veneer/framework interface. The mean edge chipping resistance (ReA) and fracture toughness (KC) values were analysed. ReA was calculated by dividing the critical force to cause the chip by the edge distance. KC was given by a fracture analysis that correlates the critical chipping load (FC) regarding edge distance (d) and material toughness via KC=FC/(ßd1.5). RESULTS: The ReA revealed similar values (p>0.005) of chipping resistance for loads applied in the parallel direction regardless of framework material and cooling protocol. For loads applied in the perpendicular direction to the veneer/framework interface, the most chip resistant materials were slow cooled veneered zirconia (251.0N/mm) and the PFM fast cooled (190.1N/mm). KC values are similar to that for monolithic porcelain (0.9MPa.√m), with slightly higher values (1.2MPa.√m) for thermally stressed PFM fast cooled and veneered zirconia slow cooled groups. SIGNIFICANCE: The developed and reported edge chipping method allows for the precise alignment of the indenter in any predetermined distance from the edge. The edge chipping method could be useful in determining the different states of residual thermal stresses on the veneering porcelain.

Recent advances in understanding the fatigue and wear behavior of dental composites and ceramics.

Dental composite and ceramic restorative materials are designed to closely mimic the aesthetics and function of natural tooth tissue, and their longevity in the oral environment depends to a large degree on their fatigue and wear properties. The purpose of this review is to highlight some recent advances in our understanding of fatigue and wear mechanisms, and how they contribute to restoration failures in the complex oral environment. Overall, fatigue and wear processes are found to be closely related, with wear of dental ceramic occlusal surfaces providing initiation sites for fatigue failures, and subsurface fatigue crack propagation driving key wear mechanisms for composites, ceramics, and enamel. Furthermore, both fatigue and wear of composite restorations may be important in enabling secondary caries formation, which is the leading cause of composite restoration failures. Overall, developing a mechanistic description of fatigue, wear, and secondary caries formation, along with understanding the interconnectivity of all three processes, are together seen as essential keys to successfully using in vitro studies to predict in vivo outcomes and develop improved dental restorative materials.

Descriptions of crack growth behaviors in glass-ZrO2 bilayers under thermal residual stresses.

OBJECTIVES: This study was intended to separate residual stresses arising from the mismatch in coefficients of thermal expansion between glass and zirconia (ZrO2) from those stresses arising solely from the cooling process. Slow crack growth experimentes were undertaken to demonstrate how cracks grow in different residual stress fields. METHODS: Aluminosilicate glass discs were sintered onto ZrO2 to form glass-ZrO2 bilayers. Glass discs were allowed to bond to the ZrO2 substrate during sintering or prevented from bonding by means of coating the ZrO2 with a thin boron nitrade coating. Residual stress gradients on "bonded" and "unbonded" bilayers were assessed using birefringence measurements. Unbonded glass discs were further tested under biaxial flexure in dynamic fatigue conditions in order to evaluate the effect of residual stress on the slow crack growth behavior. RESULTS: When fast-ccoling was induced, residual tensile stresses on the glass increased significantly on the side toward the ZrO2 substrate. By allowing the bond between glass and ZrO2, those tensile stresses observed in unbonded specimens are overwhelmed by the contraction mismatch stresses between the ZrO2 substrate and the glassy overlayer. Specimens containing residual tensile stresses on the bending surface showed a time-dependent strength increase in relation to stress-free annealed samples in the dynamic biaxial bending test, with this effect being dependent on the magnitude of the residual tensile stress. The phenomenon observed is explained here on the basis of the water toughening effect, in which water diffuses into the glass promoting local swelling. An additional residual tensile stress at the crack tip adds an applied-stress-independent (Kres) term to the total tip stress intensity factor (Ktip), increasing the stress-enhanced diffusion and the shielding of the crack tip through swelling of the crack faces. SIGNIFICANCE: Residual stresses in the glass influence the crack growth behavior of veneered-ZrO2 bilayered dental prostheses. The role of water in crack growth might be of higher complexity when residual stresses are present in the glass layer.

Experimental and finite element study of residual thermal stresses in veneered Y-TZP structures.

The main complications of zirconia-based laminated systems are chipping and delamination of veneering porcelain, which has been found to be directly associated with the development of residual thermal stresses in the porcelain layer. This study investigates the effects of cooling rate and specimen geometry on the residual stress states in porcelain-veneered zirconia structures. Bilayers of three different shapes (bars, semi-cylindrical shells, and arch-cubic structures) with 1.5 mm and 0.7 mm thickness of dentin porcelain and zirconia framework, respectively, were subjected to two cooling protocols: slow cooling (SC) at 32 °C/min and extremely-slow cooling (XSC) at 2 °C/min. The residual thermal stresses were determined using the Vickers indentation method and validated by finite element analysis. The residual stress profiles were similar among geometries in the same cooling protocol. XSC groups presented significantly higher tensile stresses (p = 0.000), especially for curved interfaces. XSC is a time-consuming process that showed no beneficial effect regarding residual stresses compared to the manufacturer recommended slow cooling rate.

Characterization of three commercial Y-TZP ceramics produced for their high-translucency, high-strength and high-surface area.

Developing yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) with high strength and translucency could significantly widen the clinical indications of monolithic zirconia restorations. This study investigates the mechanical and optical properties of three Y-TZP ceramics: High-Translucency, High-Strength and High-Surface Area. The four-point bending strengths (mean ± standard error) for the three Y-TZP ceramics (n = 10) were 990 ± 39, 1416 ± 33 and 1076 ± 32 MPa for High-Translucency, High-Strength and High-Surface Area, respectively. The fracture toughness values (mean ± standard error) for the three zirconias (n = 10) were 3.24 ± 0.10, 3.63 ± 0.12 and 3.21 ± 0.14 MPa m1/2 for High-Translucency, High-Strength and High-Surface Area, respectively. Both strength and toughness values of High-Strength zirconia were significantly higher than High-Surface Area and High-Translucency zirconias. Translucency parameter values of High-Translucency zirconia were considerably higher than High-Strength and High-Surface Area zirconias. However, all three zirconias became essentially opaque when their thickness reached 1 mm or greater. Our findings suggest that there exists a delicate balance between mechanical and optical properties of the current commercial Y-TZP ceramics.

On the interfacial fracture resistance of resin-bonded zirconia and glass-infiltrated graded zirconia.

OBJECTIVE: A major limiting factor for the widespread use of zirconia in prosthetic dentistry is its poor resin-cement bonding capabilities. We show that this deficiency can be overcome by infiltrating the zirconia cementation surface with glass. Current methods for assessing the fracture resistance of resin-ceramic bonds are marred by uneven stress distribution at the interface, which may result in erroneous interfacial fracture resistance values. We have applied a wedge-loaded double-cantilever-beam testing approach to accurately measure the interfacial fracture resistance of adhesively bonded zirconia-based restorative materials. METHODS: The interfacial fracture energy GC was determined for adhesively bonded zirconia, graded zirconia and feldspathic ceramic bars. The bonding surfaces were subjected to sandblasting or acid etching treatments. Baseline GC was measured for bonded specimens subjected to 7 days hydration at 37°C. Long-term GC was determined for specimens exposed to 20,000 thermal cycles between 5 and 55°C followed by 2-month aging at 37°C in water. The test data were interpreted with the aid of a 2D finite element fracture analysis. RESULTS: The baseline and long-term GC for graded zirconia was 2-3 and 8 times greater than that for zirconia, respectively. More significantly, both the baseline and long-term GC of graded zirconia were similar to those for feldspathic ceramic. SIGNIFICANCE: The interfacial fracture energy of feldspathic ceramic and graded zirconia was controlled by the fracture energy of the resin cement while that of zirconia by the interface. GC for the graded zirconia was as large as for feldspathic ceramic, making it an attractive material for use in dentistry.

Teste de lascamento da aresta em barras e coroas como preditor do lascamento de porcelana sobre zircônia / Edge chipping test in bars and crowns to predict the chipping on veneered zirconia

Objetivos: aprofundar na interpretação dos dados obtidos pelo teste de lascamento da aresta, com espécime em formato de barra ou de coroa, para verificar se o ensaio é capaz de reproduzir o resultado já conhecido na clínica de que porcelana sobre zircônia apresenta maior facilidade de lascamento do que porcelana sobre metal, quando o resfriamento rápido é adotado. Material e método: o teste de lascamento da aresta foi aplicado em espécimes com dois formatos: barras (monolíticas: de VM13, VM9 ou zircônia; ou em duas camadas: de VM13-metal ou VM9-zircônia) e coroas (sempre com duas camadas). Nas barras monolíticas (5 mm x 32 mm x 2,5 mm) foi realizada uma análise da microestrutura para avaliar eventuais diferenças entre a VM13 e a VM9, que poderiam interferir na interpretação de diferenças encontradas nos espécimes de duas camadas. As barras com duas camadas (5 mm x 32 mm x 2,2 mm, com infraestrutura de 0,7 mm e porcelana de 1,5) receberam dois protocolos de resfriamento (lento e rápido) e foram testadas em duas direções de carregamento (paralela ou perpendicular à interface). Para estes espécimes foram avaliadas as tensões térmicas residuais por análise por elementos finitos. Para as coroas (correspondentes ao primeiro molar inferior, com infraestrutura de 0,7 mm de espessura), foram utilizados os mesmos protocolos de resfriamento das barras de duas camadas. As superfícies de fraturas de todos os espécimes foram analisadas em estereomicroscópio com um aumento de 20x a 50x. Os dados de lascamento foram analisados através de diferentes abordagens apresentadas na literatura, sendo o parâmetro ReA (resistência ao lascamento), correspondente à média de todas as razões de força necessária para criar a lasca pela distância da aresta (N/mm), o escolhido para comparar os vários grupos experimentais. Resultados: não foram encontradas diferenças estatisticamente significantes entre as resistências ao lascamento das porcelanas, apesar da VM13 apresentar maior fração de área de leucita. Nas barras de duas camadas resfriadas lentamente e carregadas na direção perpendicular à interface, a zircônia proporcionou resistência ao lascamento da porcelana estatisticamente superior à proporcionada pelo metal. Quando o resfriamento rápido foi utilizado ou quando o carregamento foi paralelo à interface, o teste não foi capaz de evidenciar diferenças entre os grupos. Nas coroas submetidas ao resfriamento rápido, o metal proporcionou resistência ao lascamento da porcelana estatisticamente superior à proporcionada pela zircônia. Quando o resfriamento lento foi utilizado, o teste não foi capaz de evidenciar diferenças entre grupos com materiais de infraestrutura distintos. Conclusão: O ensaio de lascamento em coroas reproduziu melhor que o ensaio de lascamento em barras a resistência ao lascamento relatada na clínica. Assim, esforços em aprimorar o teste utilizando espécimes com geometria mais semelhante à da coroa são importantes.

Aim: To deepen the investigation of the edge chipping method when using either bar or crown-shaped specimens, to verify whether the test is able to reproduce the well-known clinical outcome that veneered zirconia is more prone to chipping than porcelain-fused-to-metal when the fast cooling protocol is used. Materials and methods: edge chipping test was conducted with different shaped specimens: bars (monolithic: VM13, VM9 or zirconia; or bilayers: VM13-metal and VM9-zirconia) and bi-layer crowns. A microstructure analysis was performed on the monolithic bars (5 mm x 32 mm x 2.5 mm) to evaluate possible differences between VM13 and VM9, that could account for differences on bilayer specimens data. The bilayer bars (5 mm x 32 mm x 2.2 mm, 0.7 mm and 1.5 porcelain infrastructure) were subjected to two cooling protocols (slow and fast) and load was applied in two directions (parallel or perpendicular to the interface). For bilayer bars, residual thermal stresses were evaluated using finite element analysis. For crown-shaped specimens (corresponding to the first molar, with 0.7 mm framework thickness), the cooling protocol was the same employed for bilayer bars. The fractured surfaces of all specimens were examined utilizing a stereomicroscope at a magnification from 20x up to 50x. The edge chipping data were analyzed by several approaches presented in the literature, the ReA parameter (chipping resistance), corresponding to the average of force versus distance data collected over a broad range (N / mm), was chosen to compare the different experimental groups. Results: There was no significant difference between the veneers for chipping resistance, despite that VM13 presented the highest leucite content. On bilayer bars with slow cooling protocol and loading perpendicular to the interface, zirconia provided significantly higher chipping resistance than metal-based specimens. Edge chipping test was not able to detect differences between groups when fast cooling was used or loading was applied parallel to the interface. When crowns were subject to fast cooling, results revealed that metal framework has significantly higher veneer chipping resistance than zirconia. When the slow cooling protocol was used, differences between groups with different frameworks were not observed using edge chipping test. Conclusion: The chipping test on crowns reproduced the chipping resistance reported clinically better than bar-shaped specimens. Thus, efforts to improve the test using specimens more similar to the crown geometry are important.

Teste de lascamento da aresta em barras e coroas como preditor do lascamento de porcelana sobre zircônia / Edge chipping test in bars and crowns to predict the chipping on veneered zirconia

Objetivos: aprofundar na interpretação dos dados obtidos pelo teste de lascamento da aresta, com espécime em formato de barra ou de coroa, para verificar se o ensaio é capaz de reproduzir o resultado já conhecido na clínica de que porcelana sobre zircônia apresenta maior facilidade de lascamento do que porcelana sobre metal, quando o resfriamento rápido é adotado. Material e método: o teste de lascamento da aresta foi aplicado em espécimes com dois formatos: barras (monolíticas: de VM13, VM9 ou zircônia; ou em duas camadas: de VM13-metal ou VM9-zircônia) e coroas (sempre com duas camadas). Nas barras monolíticas (5 mm x 32 mm x 2,5 mm) foi realizada uma análise da microestrutura para avaliar eventuais diferenças entre a VM13 e a VM9, que poderiam interferir na interpretação de diferenças encontradas nos espécimes de duas camadas. As barras com duas camadas (5 mm x 32 mm x 2,2 mm, com infraestrutura de 0,7 mm e porcelana de 1,5) receberam dois protocolos de resfriamento (lento e rápido) e foram testadas em duas direções de carregamento (paralela ou perpendicular à interface). Para estes espécimes foram avaliadas as tensões térmicas residuais por análise por elementos finitos. Para as coroas (correspondentes ao primeiro molar inferior, com infraestrutura de 0,7 mm de espessura), foram utilizados os mesmos protocolos de resfriamento das barras de duas camadas. As superfícies de fraturas de todos os espécimes foram analisadas em estereomicroscópio com um aumento de 20x a 50x. Os dados de lascamento foram analisados através de diferentes abordagens apresentadas na literatura, sendo o parâmetro ReA (resistência ao lascamento), correspondente à média de todas as razões de força necessária para criar a lasca pela distância da aresta (N/mm), o escolhido para comparar os vários grupos experimentais. Resultados:

não foram encontradas diferenças estatisticamente significantes entre as resistências ao lascamento das porcelanas, apesar da VM13 apresentar maior fração de área de leucita. Nas barras de duas camadas resfriadas lentamente e carregadas na direção perpendicular à interface, a zircônia proporcionou resistência ao lascamento da porcelana estatisticamente superior à proporcionada pelo metal. Quando o resfriamento rápido foi utilizado ou quando o carregamento foi paralelo à interface, o teste não foi capaz de evidenciar diferenças entre os grupos. Nas coroas submetidas ao resfriamento rápido, o metal proporcionou resistência ao lascamento da porcelana estatisticamente superior à proporcionada pela zircônia. Quando o resfriamento lento foi utilizado, o teste não foi capaz de evidenciar diferenças entre grupos com materiais de infraestrutura distintos. Conclusão: O ensaio de lascamento em coroas reproduziu melhor que o ensaio de lascamento em barras a resistência ao lascamento relatada na clínica. Assim, esforços em aprimorar o teste utilizando espécimes com geometria mais semelhante à da coroa são importantes.

Aim: To deepen the investigation of the edge chipping method when using either bar or crown-shaped specimens, to verify whether the test is able to reproduce the well-known clinical outcome that veneered zirconia is more prone to chipping than porcelain-fused-to-metal when the fast cooling protocol is used. Materials and methods: edge chipping test was conducted with different shaped specimens: bars (monolithic: VM13, VM9 or zirconia; or bilayers: VM13-metal and VM9-zirconia) and bi-layer crowns. A microstructure analysis was performed on the monolithic bars (5 mm x 32 mm x 2.5 mm) to evaluate possible differences between VM13 and VM9, that could account for differences on bilayer specimens data. The bilayer bars (5 mm x 32 mm x 2.2 mm, 0.7 mm and 1.5 porcelain infrastructure) were subjected to two cooling protocols (slow and fast) and load was applied in two directions (parallel or perpendicular to the interface). For bilayer bars, residual thermal stresses were evaluated using finite element analysis. For crown-shaped specimens (corresponding to the first molar, with 0.7 mm framework thickness), the cooling protocol was the same employed for bilayer bars. The fractured surfaces of all specimens were examined utilizing a stereomicroscope at a magnification from 20x up to 50x. The edge chipping data were analyzed by several approaches presented in the literature, the ReA parameter (chipping resistance), corresponding to the average of force versus distance data collected over a broad range (N / mm), was chosen to compare the different experimental groups. Results: There was no significant difference between the veneers for chipping resistance, despite that VM13 presented the highest leucite content.

On bilayer bars with slow cooling protocol and loading perpendicular to the interface, zirconia provided significantly higher chipping resistance than metal-based specimens. Edge chipping test was not able to detect differences between groups when fast cooling was used or loading was applied parallel to the interface. When crowns were subject to fast cooling, results revealed that metal framework has significantly higher veneer chipping resistance than zirconia. When the slow cooling protocol was used, differences between groups with different frameworks were not observed using edge chipping test. Conclusion: The chipping test on crowns reproduced the chipping resistance reported clinically better than bar-shaped specimens. Thus, efforts to improve the test using specimens more similar to the crown geometry are important.