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The increase in the use of energy from forest biomass has increased the demand for knowledge about tree-chipping operations. Therefore, this study aimed to evaluate the effect of different drying times of wood logs and various combinations of knife and anvil configurations in the horizontal chipper on the quality of Eucalyptus dunnii chips produced for energy purposes. The study was conducted in a seven-year-old stand of E. dunnii. A horizontal chipper was used to chip whole trees and obtain nine types of chips, resulting from the interaction between the three drying times of the trees and three configurations of the horizontal chipper. The chips were characterized, followed by an evaluation of energy quality for comparison between the treatments. Among the outcomes discerned, it became evident that the employed wood exhibited a Basic Density (0.506 g.cm-³). The chip dimensions and bulk density presented notable disparities owing to the distinct chipper configurations and tree drying time. The extended drying period (150 days) conferred a lower average moisture content (34.20%) to the study materials. Moreover, the ash content was lower in the treatment with 150 drying days (0.52%). Both the useful calorific value and the Fuel Value Index were also greater in the treatment (150 drying days), measuring 2600.00 kcal kg-1 and 128.06 cal cm-3, respectively. In the analysis of the Fuel Value Index concerning chipper configurations, it was observed that for chips featuring a granulometry of 25 mm, the treatment involving 150 days of drying, four knives, and one shim proved the most efficient (Q = 0.979). Conversely, for chips with a granulometry of 16 mm, the treatment involving 150 days of drying, eight knives, and one shim emerged as the most efficient (Q = 0.970). Consequently, the proposed index is efficacious and underscores the necessity of adapting knife settings in response to moisture content changes to maintain the desired granulometry and apparent density standards.
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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.
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Porcelana Dentária , Resistência à Flexão , Reprodutibilidade dos Testes , Teste de Materiais , Análise do Estresse Dentário , Zircônio , Propriedades de Superfície , Cerâmica , ÍtrioRESUMO
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.
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Cerâmica , Zircônio , Porcelana Dentária , Análise do Estresse Dentário , Facetas Dentárias , Teste de Materiais , Transição de FaseRESUMO
OBJECTIVE: To evaluate edge chip resistance (ReA) and fractographic features of ceramic systems submitted to edge chipping. METHODS: Samples were fabricated using the following materials: YZ-yttria-stabilized tetragonal zirconia ceramic (IPS e.max® Zir-CAD); LG-leucite-reinforced glass-ceramic (IPS Empress® CAD); LD-lithium-disilicate glass-ceramic (IPS e.max® CAD); ZF- YZ veneered by a pressable fluorapatite glass-ceramic (IPS e.max® Zir-CAD + IPS e.max® Zir-Press); ZD- YZ-LD fused together by a glass-ceramic (IPS e.max® Zir-CAD + IPS e.max® crystall./connect + IPS e.max® CAD). Half of the sample size was bonded (B) to a dentine analogue substrate (NEMA G10) and the remaining samples were kept non-bonded (NB). Structures were indented (n = 25) at different edge distances (d = 0.3, 0.4, 0.5, 0.6, 0.7 mm) using a universal testing machine to produce chips. Force (F) and d values were recorded and ReA was calculated. Data were statistically analyzed using ANOVA, Student t and Tukey tests (α = 0.05). Chipping was evaluated visually and under optical and scanning electron microscopy based on fractography principles. RESULTS: Data (F vs d) showed a positive linear trend for all groups. There was no significant difference in ReA values at d = 0.5 mm (SE0.5) between NB and B for same ceramic system. Fracture pattern was similar between NB and B for same ceramic system at d = 0.5 mm. CONCLUSIONS: Bonding neither influenced ReA values nor the fracture pattern that were similar between NB and B structures from same ceramic system. The greater the distance from structure edge, the lesser the chance of chipping occurred.
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Cerâmica , Desenho Assistido por Computador , Porcelana Dentária , Análise do Estresse Dentário , Humanos , Teste de Materiais , Fenômenos Mecânicos , Microscopia Eletrônica de Varredura , ProibitinasRESUMO
OBJECTIVE: Literature on edge chipping test applied to dental materials and structures has been systematically reviewed with regard to the evaluation methods and parameters used. DATA: A systematic search of the literature retrieved 3484 relevant studies. After removing duplicates, 1848 records were screened by titles and abstracts and 1797 were excluded; 51 papers were assessed full text for eligibility. Twenty papers were included in this study and they were organized according to the dental materials and structures tested as follows: 2 studies on human tooth, 9 on dental ceramics, 5 on polymer-based composites, and 4 studies evaluated both ceramic and polymer-based materials. SOURCES: MEDLINE/PubMed, Scopus and Web of Science databases were searched up to June 2019 without restriction on date and language. STUDY SELECTION: In vitro studies using edge chipping test on dental materials and structures were included. CONCLUSIONS: Different methods have been used for edge chipping test, regardless of reported parameters. There is significant evidence that edge chipping test is a relevant approach to predict chipping behavior of dental materials and tooth tissues because chips produced from most edge chipping studies are similar to clinically reported chipping failures.
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Cerâmica , Materiais Dentários , Planejamento de Prótese Dentária , Falha de Restauração Dentária , Análise do Estresse Dentário , Odontologia , HumanosRESUMO
Objective: To evaluate the wear behavior of human enamel and chipping of veneered and monolithic zirconia for posterior full coverage restorations. Material and methods: Thirty-four zirconia full coverage restorations (seventeen in each group) were fabricated. The patients were divided into two groups according to the type of zirconia used; group 1 (comparator group) veneered zirconia crowns and group 2 (intervention group) monolithic zirconia single crowns. All crowns were lab fabricated and polished. For opposing teeth wear measurements 3D non-contact profilometer was used where epoxy resin replicas were constructed for opposing arch immediately after crowns cementation, three, six and twelve months. Restoration chipping was measured using modified United States Public Health Services (USPHS) criteria. Results: All restorations were reported as alpha with no chipping. There was no statistically significant difference between (Group 1) and (Group 2) for wear test. Conclusion: Both monolithic and veneered restorations revealed satisfactory mechanical properties with no chipping after one year of clinical use. Wear of opposing enamel was clinically acceptable for both materials. (AU)
Objetivo: Avaliar o comportamento ao desgaste do esmalte humano e lascamento de zircônia estratificada e monolítica para coroas totais posteriores. Material e métodos: Trinta e quatro coroas totais de zircônia (dezessete em cada grupo) foram fabricadas. Os pacientes foram divididos em dois grupos de acordo com o tipo de zircônia utilizada; grupo 1 (grupo controle) coroas de zircônia estratificada e grupo 2 (grupo de intervenção) coroas de zircônia monolítica. Todas as coroas foram fabricadas e polidas em laboratório. Para medidas de desgaste de dentes opostos, foi utilizado um perfilômetro 3D sem contato, onde réplicas de resina epóxi foram construídas para o arco oposto imediatamente após a cimentação das coroas, três, seis e doze meses após. O lascamento da restauração foi medido usando critérios modificados dos Serviços de Saúde Pública dos Estados Unidos (USPHS). Resultados: Todas as restaurações foram relatadas como alfa sem lascamento. Não houve diferença estatisticamente significativa entre (Grupo 1) e (Grupo 2) para o teste de desgaste. Conclusão: Ambas as coroas monolíticas e estratificadas revelaram propriedades mecânicas satisfatórias sem lascamento após um ano de uso clínico. O desgaste do esmalte oposto foi clinicamente aceitável para ambos os materiais. (AU)
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Humanos , Ligas Metalo-Cerâmicas , Esmalte Dentário , Desgaste dos DentesRESUMO
OBJECTIVE: This article presents a retrospective analysis of an anterior single crown that showed chipping of the veneering ceramic, the clinical stages of intraoral repair made in composite resin, and fractographic analysis of the causes of failure. CLINICAL CONSIDERATIONS: The ceramic chipping occurred in the incisal and labial surfaces of the crown, 1 year after installation. Clinical examination revealed the presence of occlusal interference, which was probably responsible for chipping. Vinyl-polysiloxane impression was made from the patient, and epoxy replica was produced. The replica was gold coated and inspected under the optical microscopy and scanning electron microscope (SEM) for descriptive fractography. Optical microscopy and SEM images showed that chipping initiated at the incisal edge, where it is possible to note an area of damage accumulation. At the labial surface, multiple arrest lines with their convex sides facing the incisal edge were observed. The fractured area was repaired intraorally with composite resin, and the patient's occlusion was checked and monitored. CONCLUSION: According to the fractographic analysis, occlusal interference was related to ceramic chipping in the incisal edge. Intraoral repair technique with composite resin was indicated for this moderate chipping. CLINICAL SIGNIFICANCE: Retrieval analysis of chipping ceramic delivers better understanding of the failure origin and could prevent future failures. Intraoral repair is a practical and conservative technique and may be performed in a single clinical session without requiring the removal of prosthesis.
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Falha de Restauração Dentária , Facetas Dentárias , Cerâmica , Coroas , Porcelana Dentária , Humanos , Teste de Materiais , Estudos Retrospectivos , Propriedades de SuperfícieRESUMO
OBJECTIVE: To evaluate the edge chip resistance (ReA) of two CAD/CAM monolithic ceramics (GC- IPS e.max CAD and YZ- Zenostar Zr Translucent) bonded to a dentine analogue substrate (G10- NEMA G10). METHODS: Plate-shaped specimens were prepared from GC and YZ ceramics and were either bonded (B) to G10 or attached (NB) to a universal testing machine for edge chipping test. Samples from all groups (GC-B, GC-NB, YZ-B and YZ-NB) were indented (n = 25) at different edge distances (d = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mm) to produce chips. Force (F, in N) and d values were recorded and ReA (in N/mm) were calculated. Data were statistically analyzed using Pearson´s correlation, Student t, ANOVA and Tukey tests (α = 0.05). RESULTS: A strong correlation (R ≥ 0.98) was found between F and d values for all groups. ReA values increased with increasing d, irrespective of ceramic type (GC and YZ) or fixation method (B and NB). Significant differences (p < 0.05) in mean ReA values were found between B and NB ceramics at lower d (0.1-0.3 mm) that did not persist (p > 0.05) at greater d (0.5 and 0.6 mm), meaning, bonding (B) to G10 protected both materials against chipping close to the edge. CONCLUSIONS: The larger the distance from the occlusal contact to the restoration edge, the greater the chance to avoid ceramic chipping in monolithic restorations. For d ≤ 0.3 mm, such F vs d relation is less critical for edge resistance of YZ and for resin bonded monolithic ceramics.
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Cerâmica/química , Dentina/química , Fenômenos Mecânicos , Desenho Assistido por Computador , Teste de MateriaisRESUMO
OBJECTIVES: The residual stress profile developed within the veneering ceramic during the manufacturing process is an important predicting factor in chipping failures, which constitute a well-known problem with yttria-tetragonal-zirconia polycrystal (Y-TZP) based restorations. The objectives of this study are to measure and to compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic framework materials: Y-TZP, alumina polycrystal (AL) and zirconia toughened alumina (ZTA). METHODS: The stress profile was measured with the hole-drilling method in bilayered disk samples of 19 mm diameter with a 0.7 mm thick Y-TZP, AL or ZTA framework and a 1.5mm thick layer of the corresponding veneering ceramic. RESULTS: The AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6mm from the surface, and then becoming compressive again near the framework. SIGNIFICANCE: Y-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Results support the hypothesis of the occurrence of structural changes within the Y-TZP surface in contact with the veneering ceramic to explain the presence of tensile stresses. Even if the presence of Y-TZP in the alumina matrix seems to negatively affect the residual stress profiles in ZTA samples in comparison with AL samples, the registered profiles remain positive in terms of veneer fracture resistance.
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Óxido de Alumínio/química , Cerâmica , Facetas Dentárias , Estresse Mecânico , Ítrio/química , Zircônio/química , Microscopia Eletrônica de VarreduraRESUMO
El chipping es una problema que se presenta en las restauraciones de cerámica sobre zirconio. el objetivo de este trabajo es revisar las causas de esta falla. a tal fin, se seleccionaronpublicaciones en Pub Med y revistas científicas de alto impacto desde el año 2007 a 2010, incluyendo estudios in vitro e in vivo. Mediante lectura y análisis exhaustivo de los artículos, se planteó a manera de resultados, la frecuencia del problema y los factores que predisponen al chipping de la cerámica sobre el zirconio. Se discute acerca de los hallazgos en pruebas in vitro y con elementos finitos de las propiedades y comportamiento de dichos materiales, tanto como su correlación con el desempeño clínico de las restauraciones. tras esta revisión, se intenta evaluar el impacto del problema en la situación clínica y aclarar los factores que predisponen, odirectamente provocan, la falla cohesiva de las restauraciones cerámica sobre zirconio.