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Objective: To evaluate the mechanical properties of different CAD/CAM ceramic systems and the post-fatigue fracture and stress distribution when used as cemented crowns. Materials and methods: Sixty (60) CAD/CAM monolithic crowns were milled using three different ceramic materials (FD - Feldspathic [Vita Mark II]), LE - Leucite-based ceramic [IPS Empress CAD] and LD - Lithium Disilicate [IPS e.max CAD]) and adhesively cemented on resin composite dyes. Specimens were stored in distillated water (37 °C) for 7 days. After, half of the crowns were submitted to immediate fracture load test while the other half was submitted to fatigue cycling. The average cement layer of approximately 80 µm was assessed using scanning electron microscopy (SEM). The average thickness was used in the three-dimensional (3D) Finite Element Analysis (FEA). For each ceramic material, the density, Poisson ratio, shear modulus, Young modulus, fracture toughness, and true hardness were assessed (n = 3). The data was used to assess the Maximum Principal Stress throughout 3D-FEA according to each material during load to fail and post-fatigue. Data were submitted to two-way ANOVA and Tukey test (α = 0.05). Results: LD showed the highest compression load, density, shear modulus, Young modulus, fracture toughness and true hardness values. While LE presented the lowest mechanical properties values. There is no difference in the Poisson ratio between the evaluated ceramics. Conclusion: LD was susceptible to aging process but presented stronger physicomechanical properties, showing the highest post-fatigue fracture load and highest stress magnitude.

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OBJECTIVES: To evaluate the marginal adaptation and internal space of crowns produced by 4 CAD/CAM systems using microcomputed tomography (µCT) and replica technique (RT). MATERIALS AND METHODS: Monolithic lithium disilicate crowns were milled (Ceramill, Cerec, EDG, and Zirkonzahn) (n = 10). The cement film obtained with low viscosity silicone was scanned by the µCT system and captured by a stereomicroscope, according to RT. Two-way ANOVA followed by Tukey's test were used for statistical analysis (α = 0.05). A uniformity index (UI) was idealized to describe the distribution of crowns' internal space and submitted to the Kruskal-Wallis and Tukey's test (α = 0.05). The correlation between µCT and RT was performed by Pearson's Correlation Coeficient (α = 0.05). RESULTS: Marginal adaptation and internal space were statistically significant different between the experimental groups for the µCT and RT (p < 0.05). The medians of the 4 systems tested were within clinically acceptable range and the mean (± SD) highest marginal discrepancy was recorded in the Ceramill group at 133.0 ± 71.5 µm (µCT) and 90.6 ± 38.5 µm (RT). For internal fit, the UI disclosed a better distribution of the internal space for the Zirkonzahn group (p < 0.001). There was a strong correlation between the methods (p = 0.01 and r = 0.69). CLINICAL RELEVANCE: Because of the variability of the CAD/CAM systems available, evaluating their accuracy is of clinical interest. The 4 systems are capable to produce restorations adaptated within clinically appropriate levels. The µCT and RT are efficient adaptation methodologies.

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PURPOSE: To evaluate the fatigue survival, fracture loads and failure modes of monolithic lithium disilicate screw-retained crowns, attached to titanium insert, and cement-retained crowns. MATERIALS AND METHODS: Internal tapered connection implants, embedded in acrylic resin at 30° inclination, were restored with lithium disilicate restorations, simulating a maxillary premolar (n = 20), with different designs: screw-retained titanium base abutment-crowns, and cement-retained crowns. The specimens were submitted to cyclic mechanical loading (1.2 × 106 cycles with a load of 0-250 N at 2 Hz). Surviving specimens were subjected to single load to fracture in a universal testing machine and failure modes were determined with the aid of an optical microscope. Maximum load values were analyzed statistically using the t-test and differences in failure modes were analyzed using the chi-squared test (α = 0.05). RESULTS: All specimens survived the cyclic mechanical loading. Fracture load was significantly higher for screw-retained crowns (821.69 ±196.71 N) than the cement-retained crowns (577.03 ± 137.75 N) (p = 0.005). Ceramic failure was the predominant mode, with no statistical difference between groups. CONCLUSIONS: Screw-retained and cement-retained lithium disilicate crowns survived the cyclic mechanical loading. The use of titanium inserts to support a monolithic restoration enhances the fracture strength of the crown/abutment system.

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INTRODUCTION: Polymer-based composite materials have been proposed as an alternative for single unit restorations, due to their resilient and shock absorbing behavior, in contrast to the brittleness of ceramic materials that could result in failure by fracture. OBJECTIVE: To evaluate the fatigue strength and damage modes of monolithic posterior resin nanoceramic and lithium disilicate glass ceramic crowns. METHODOLOGY: Twenty-six resin nanoceramic (RNC) and lithium disilicate glass ceramic (LD) 2 mm monolithic crowns (n=13) were cemented on composite resin replicas of a prepared tooth and subjected to cyclic load with lithium disilicate indenters for 2 million cycles. Specimens and indenters were inspected every 500,000 cycles and suspended when presenting fractures or debonding. Surviving specimens were embedded in epoxy resin, polished and subsurface damage was analyzed. Specimens presenting fractures or severe subsurface damage were considered as failures. Survival data was subjected to Fisher's exact test; damage modes were subjected to Mann-Whitney test (p<0.05). RESULTS: There were no debonding, cohesive or catastrophic failures. Considering subsurface damage, 53.8% of RNC and 46.2% of LD crowns survived the fatigue test, presenting no statistical difference. Chief damage modes were radial cracks for RNC and inner cone cracks for LD, presenting no statistical difference. CONCLUSIONS: The results suggest that if debonding issues can be resolved, resin nanoceramic figures can be an alternative to posterior crowns. Although distinct, damage modes revealed potential to cause bulk fracture in both glass ceramic and resin nanoceramic crowns.

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Abstract Polymer-based composite materials have been proposed as an alternative for single unit restorations, due to their resilient and shock absorbing behavior, in contrast to the brittleness of ceramic materials that could result in failure by fracture. Objective: To evaluate the fatigue strength and damage modes of monolithic posterior resin nanoceramic and lithium disilicate glass ceramic crowns. Methodology: Twenty-six resin nanoceramic (RNC) and lithium disilicate glass ceramic (LD) 2 mm monolithic crowns (n=13) were cemented on composite resin replicas of a prepared tooth and subjected to cyclic load with lithium disilicate indenters for 2 million cycles. Specimens and indenters were inspected every 500,000 cycles and suspended when presenting fractures or debonding. Surviving specimens were embedded in epoxy resin, polished and subsurface damage was analyzed. Specimens presenting fractures or severe subsurface damage were considered as failures. Survival data was subjected to Fisher's exact test; damage modes were subjected to Mann-Whitney test (p<0.05). Results: There were no debonding, cohesive or catastrophic failures. Considering subsurface damage, 53.8% of RNC and 46.2% of LD crowns survived the fatigue test, presenting no statistical difference. Chief damage modes were radial cracks for RNC and inner cone cracks for LD, presenting no statistical difference. Conclusions: The results suggest that if debonding issues can be resolved, resin nanoceramic figures can be an alternative to posterior crowns. Although distinct, damage modes revealed potential to cause bulk fracture in both glass ceramic and resin nanoceramic crowns.

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Among the ceramic materials used in dentistry, Zirconia presents the ideal opacity for cases where the clinical challenge is to neutralize the difference in the colors of the substrates. The "ceramic steel", so called by some authors, guarantees to Zirconia resistance and hardness similar to a metal, but with aesthetic advantages superior to the metal-ceramic restorations, which can exhibit exposure of the metal band over time. This article describes a complex rehabilitation treatment involving dental elements with different substrates: 11 - vital tooth with large crown damage; 21 ­ endodontically treated tooth and cast metal core; 22 - Morse taper implant. The selection of a completely zirconia-based ceramic system allowed masking the different conditions of substrates, so achieving the esthetic expectations. Moreover, considering the patient's high smile line, excellent gingival esthetics was obtained with an internal connection Morse taper implant associated with an individualized anatomic abutment.

Dentre os materiais cerâmicos utilizados na Odontologia, a Zircônia apresenta a opacidade ideal para os casos em que o desafio clinico é neutralizar a diferença nas cores dos substratos. O "aço cerâmico", assim chamado por alguns autores, garante à Zircônia resistência e dureza semelhantes a um metal, mas com vantagens estéticas superiores às restaurações metalocerâmicas, as quais podem apresentar exposição da cinta metálica ao longo do tempo. Este artigo descreve um tratamento reabilitador complexo, envolvendo elementos dentários com diferentes substratos: 11 - dente vital com ampla destruição coronária; 21 - dente com tratamento endodôntico e núcleo metálico fundido; 22 ­ ausente, reabilitado com implante do tipo cone morse. A seleção do sistema totalmente cerâmico à base de zircônia, permitiu mascarar as diferentes condições dos substratos atingindo as expectativas estéticas. Além disso, diante do sorriso alto gengivoso presente neste caso, a excelência na estética gengival foi obtida utilizando implante com conexão interna do tipo cone morse associado a um pilar anatômico individualizado.

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PURPOSE: To compare stresses in the peri-implant bone produced by fixed partial prostheses with mesial and distal cantilevers, when cemented or screwed onto implants. MATERIALS AND METHODS: The experimental design consisted of four 3D models obtained by volumetric computerized tomography and analyzed using finite element analysis (FEA). Stresses were simulated in two stages. Stage 1 consisted of application of the preload. A 288 N load was applied to pillar screws of the cemented prosthesis, resulting in 389 MPa peak; 257 N was applied to the intermediate screw (multi-unit) resulting in 390 MPa peak; and 111 N was applied to the prosthesis infrastructure screw in the screwed prostheses, resulting in 390 MPa peak. In stage 2, the axial and oblique loads were applied. The axial load consisted of 50 N for molar implants and 30 N for premolar implants. The oblique load (on the buccal slope of the buccal cusp of each crown) consisted of 30 N for premolar implants and 50 N for molar implants, with a buccolingual vector at a 45° angle with the occlusal plane. The response variables were the axial and oblique stresses on the peri-implant bone, according to the following groups: group 1-models of fixed partial prostheses cemented onto implants with mesial or distal cantilevers; group 2-models of fixed partial denture screwed onto implants with mesial or distal cantilevers. Data were recorded, evaluated, and compared. RESULTS: Oblique loads produced higher peak values than axial loads, and were located at the bone crest of the implant closest to the cantilever, regardless of the prosthesis type. In the cemented prosthesis models, oblique loads produced the highest peaks in the primary implant region when compared with the screwed prosthesis models. CONCLUSION: The screwed fixed prostheses caused less stress on peri-implant bone regardless of whether the cantilever was located mesially or distally.

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Because many mechanical variables are present in the oral cavity, the proper load transfer between the prosthesis and the bone is important for treatment planning and for the longevity of the implant-supported fixed partial denture. Objectives To verify the stress generated on the peri-implant area of cantilevered implant-supported fixed partial dentures and the potential effects of such variable. Material and Methods A U-shaped polyurethane model simulating the mandibular bone containing two implants (Ø 3.75 mm) was used. Six groups were formed according to the alloy's framework (CoCr or PdAg) and the point of load application (5 mm, 10 mm and 15 mm of cantilever arm). A 300 N load was applied in pre-determined reference points. The tension generated on the mesial, lingual, distal and buccal sides of the peri-implant regions was assessed using strain gauges. Results Two-way ANOVA and Tukey statistical tests were applied showing significant differences (p<0.05) between the groups. Pearson correlation test (p<0.05) was applied showing positive correlations between the increase of the cantilever arm and the deformation of the peri-implant area. Conclusions This report demonstrated the CoCr alloy shows larger compression values compared to the PdAg alloy for the same distances of cantilever. The point of load application influences the deformation on the peri-implant area, increasing in accordance with the increase of the lever arm.

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ABSTRACT Because many mechanical variables are present in the oral cavity, the proper load transfer between the prosthesis and the bone is important for treatment planning and for the longevity of the implant-supported fixed partial denture. Objectives To verify the stress generated on the peri-implant area of cantilevered implant-supported fixed partial dentures and the potential effects of such variable. Material and Methods A U-shaped polyurethane model simulating the mandibular bone containing two implants (Ø 3.75 mm) was used. Six groups were formed according to the alloy’s framework (CoCr or PdAg) and the point of load application (5 mm, 10 mm and 15 mm of cantilever arm). A 300 N load was applied in pre-determined reference points. The tension generated on the mesial, lingual, distal and buccal sides of the peri-implant regions was assessed using strain gauges. Results Two-way ANOVA and Tukey statistical tests were applied showing significant differences (p<0.05) between the groups. Pearson correlation test (p<0.05) was applied showing positive correlations between the increase of the cantilever arm and the deformation of the peri-implant area. Conclusions This report demonstrated the CoCr alloy shows larger compression values compared to the PdAg alloy for the same distances of cantilever. The point of load application influences the deformation on the peri-implant area, increasing in accordance with the increase of the lever arm.

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The purpose of this study was to evaluate the use of fractography principles to determine the fracture toughness of Y-TZP dental ceramic in which KIc was measured fractographically using controlled-flaw beam bending techniques and to correlate the flaw distribution with the mechanical properties. The Y-TZP blocks studied were: Zirconia Zirklein (ZZ); Zirconcad (ZCA); IPS e.max ZirCad (ZMAX); and In Ceram YZ (ZYZ). Samples were prepared (16mm×4mm×2mm) according to ISO 6872 specifications and subjected to three-point bending at a crosshead speed of 0.5mm/min. Weibull probability curves (95% confidence bounds) were calculated and a contour plot with the Weibull modulus (m) versus characteristic strength (σ0) was used to examine the differences among groups. The fractured surface of each specimen was inspected in a scanning electron microscope (SEM) for qualitative and quantitative fractographic analysis. The critical defect size (c) and fracture toughness (KIc) were estimated. The fractured surfaces of the samples from all groups showed similar fractographic characteristics, except ZCA showed pores and defects. Fracture toughness and the flexural strength values were not different among the groups except for ZCA. The characteristic strength (p<0.05) of ZZ (η=920.4) was higher than the ZCA (η=651.1) and similar to the ZMAX (η=983.6) and ZYZ (η=1054.8). By means of quantitative and qualitative fractographic analysis, this study showed fracture toughness and strength that could be correlated to the observable microstructural features of the evaluated zirconia polycrystalline ceramics.

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This study aimed to measure the preload in different implant platform geometries based on micro-CT images. External hexagon (EH) implants and Morse Tapered (MT) implants (n=5) were used for the preload measurement. The abutment screws were scanned in micro-CT to obtain their virtual models, which were used to record their initial length. The abutments were screwed on the implant with a 20 Ncm torque and the set composed by implant, abutment screw and abutment were taken to the micro-CT scanner to obtain virtual slices of the specimens. These slices allowed the measurement of screw lengths after torque application and based on the screw elongation. Preload values were calculated using the Hooke's Law. The preloads of both groups were compared by independent t-test. Removal torque of each specimen was recorded. To evaluate the accuracy of the micro-CT technique, three rods with known lengths were scanned and the length of their virtual model was measured and compared with the original length. One rod was scanned four times to evaluate the measuring method variation. There was no difference between groups for preload (EH = 461.6 N and MT = 477.4 N), but the EH group showed higher removal torque values (13.8±4.7 against 8.2±3.6 Ncm for MT group). The micro-CT technique showed a variability of 0.053% and repeatability showed an error of 0.23 to 0.28%. Within the limitations of this study, there was no difference between external hexagon and Morse taper for preload. The method using micro-CT may be considered for preload calculation.

Resumo Este estudo teve como objetivo medir a pré-carga em diferentes conexões implante/pilar baseado em imagens de micro-CT. Implantes de hexágono externo (EH) e Cone Morse (MT) (n = 5) foram utilizados para a medição de pré-carga. Os parafusos de pilares foram digitalizados em um micro-CT de alta resolução para obter seus modelos virtuais, que foram utilizados para registrar o comprimento inicial. Os pilares foram parafusados sobre o implante com um torque de 20 Ncm e, o conjunto composto por implante, parafuso do pilar e pilar foi levado para o micro-CT para obter cortes virtuais dos espécimes. Esses cortes permitiram a medida do comprimento dos parafusos após a aplicação do torque. Assim, com base no alongamento dos parafusos, os valores de pré-carga foram calculados usando a Lei de Hooke. A pré-carga de ambos os grupos foram comparados pelo Test-t independente. O torque de remoção de cada espécime foi registrado. Para avaliar a precisão da técnica de micro-CT, três bastões foram escaneados em micro-CT e o comprimento do seu modelo virtual foi comparado com o comprimento original dos bastões. Um bastão foi digitalizado e mensurado quatro vezes para avaliar a variação do método de medição e a sua repetitividade. Não houve diferença entre os grupos para a pré-carga (EH = 461,6 N e MT = 477,4 N), no entanto o grupo EH apresentou maiores valores de torque de afrouxamento do parafuso (13,8 ± 4,7 contra 8,2 ± 3,6 Ncm para o grupo MT). A técnica de micro-CT mostrou uma variabilidade de 0,053% e a repetitividade apresentou um erro de 0,23 a 0,28%. Dentro das limitações deste estudo, não houve diferença entre Hexágono Externo e Cone Morse para pré-carga. O método baseado em imagens de micro-CT pode ser considerado para mensuração da pré-carga.

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This study aimed to analyze the stress distribution in single implant system and to evaluate the compatibility of an in vitro model with finite element (FE) model. The in vitro model consisted of Brånemark implant; multiunit set abutment of 5 mm height; metal-ceramic screw-retained crown, and polyurethane simulating the bone. Deformations were recorded in the peri-implant region in the mesial and distal aspects, after an axial 300 N load application at the center of the occlusal aspect of the crown, using strain gauges. This in vitro model was scanned with micro CT to design a three-dimensional FE model and the strains in the peri-implant bone region were registered to check the compatibility between both models. The FE model was used to evaluate stress distribution in different parts of the system. The values obtained from the in vitro model (20-587 µÎµ) and the finite element analysis (81-588 µÎµ) showed agreement among them. The highest stresses because of axial and oblique load, respectively were 5.83 and 40 MPa for the cortical bone, 55 and 1200 MPa for the implant, and 80 and 470 MPa for the abutment screw. The FE method proved to be effective for evaluating the deformation around single implant. Oblique loads lead to higher stress concentrations.

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The aim of this study was to perform micro-Raman spectroscopy as an alternative and nondestructive method to identify the phase transformation of zirconia after mechanical stress. The groups evaluated were experimental zirconia, zirconcad, IPS e.max ZirCad, and In Ceram YZ. Ten specimens were constructed for each group (n = 30) and subjected to a three-point bending test with a crosshead speed of 0.5 mm/min. The fractured surfaces were analyzed by micro-Raman spectroscopy. The laser power was kept at 10 mW, and scanning was performed in three regions of the fractured surface: (i) near the source of the failure (region of tensile stress), (ii) central to the fractured surface, and (iii) far from the source of failure. All materials showed the characteristic bands of tetragonal and monoclinic phases of zirconia. All zirconia studied showed a monoclinic phase in the tensile stress region. Micro-Raman spectroscopy was effective in detecting the presence of crystalline phases in polycrystals ceramics.

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This study aimed to measure the preload in different implant platform geometries based on micro-CT images. External hexagon (EH) implants and Morse Tapered (MT) implants (n=5) were used for the preload measurement. The abutment screws were scanned in micro-CT to obtain their virtual models, which were used to record their initial length. The abutments were screwed on the implant with a 20 Ncm torque and the set composed by implant, abutment screw and abutment were taken to the micro-CT scanner to obtain virtual slices of the specimens. These slices allowed the measurement of screw lengths after torque application and based on the screw elongation. Preload values were calculated using the Hooke's Law. The preloads of both groups were compared by independent t-test. Removal torque of each specimen was recorded. To evaluate the accuracy of the micro-CT technique, three rods with known lengths were scanned and the length of their virtual model was measured and compared with the original length. One rod was scanned four times to evaluate the measuring method variation. There was no difference between groups for preload (EH = 461.6 N and MT = 477.4 N), but the EH group showed higher removal torque values (13.8 ± 4.7 against 8.2 ± 3.6 N cm for MT group). The micro-CT technique showed a variability of 0.053% and repeatability showed an error of 0.23 to 0.28%. Within the limitations of this study, there was no difference between external hexagon and Morse taper for preload. The method using micro-CT may be considered for preload calculation.

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UNLABELLED: Knowing how stresses are dissipated on the fixed implant-supported complex allows adequate treatment planning and better choice of the materials used for prosthesis fabrication. OBJECTIVES: The aim of this study was to evaluate the deformation suffered by cantilevered implant-supported fixed prostheses frameworks cast in silver-palladium alloy and coated with two occlusal veneering materials: acrylic resin or porcelain. MATERIAL AND METHODS: Two strain gauges were bonded to the inferior surface of the silver-palladium framework and two other were bonded to the occlusal surface of the prosthesis framework covered with ceramic and acrylic resin on each of its two halves. The framework was fixed to a metallic master model and a 35.2 N compression force was applied to the cantilever at 10, 15 and 20 mm from the most distal implant. The measurements of deformation by compression and tension were obtained. The statistical 2-way ANOVA test was used for individual analysis of the experiment variables and the Tukey test was used for the interrelation between all the variables (material and distance of force application). RESULTS: The results showed that both variables had influence on the studied factors (deformation by compression and tension). CONCLUSION: The ceramic coating provided greater rigidity to the assembly and therefore less distortion compared with the uncoated framework and with the resin-coated framework. The cantilever arm length also influenced the prosthesis rigidity, causing higher deformation the farther the load was applied from the last implant.

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Knowing how stresses are dissipated on the fixed implant-supported complex allows adequate treatment planning and better choice of the materials used for prosthesis fabrication. Objectives: The aim of this study was to evaluate the deformation suffered by cantilevered implant-supported fixed prostheses frameworks cast in silver-palladium alloy and coated with two occlusal veneering materials: acrylic resin or porcelain. Material and Methods: Two strain gauges were bonded to the inferior surface of the silver-palladium framework and two other were bonded to the occlusal surface of the prosthesis framework covered with ceramic and acrylic resin on each of its two halves. The framework was fixed to a metallic master model and a 35.2 N compression force was applied to the cantilever at 10, 15 and 20 mm from the most distal implant. The measurements of deformation by compression and tension were obtained. The statistical 2-way ANOVA test was used for individual analysis of the experiment variables and the Tukey test was used for the interrelation between all the variables (material and distance of force application). Results: The results showed that both variables had influence on the studied factors (deformation by compression and tension). Conclusion: The ceramic coating provided greater rigidity to the assembly and therefore less distortion compared with the uncoated framework and with the resin-coated framework. The cantilever arm length also influenced the prosthesis rigidity, causing higher deformation the farther the load was applied from the last implant. .

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STATEMENT OF PROBLEM: Endodontically treated teeth are known to have reduced structural strength. Glass fiber posts may influence fracture resistance and should be evaluated. PURPOSE: The purpose of this study was to evaluate the influence of glass fiber post length on the fracture resistance of endodontically treated teeth. MATERIAL AND METHODS: Forty intact human maxillary canines were selected and divided into 4 groups, the control group consisting of teeth restored with a custom gold cast post and core, with a length of two-thirds of the root. Other groups received prefabricated glass fiber posts in different lengths: group 1/3, removal of one-third of the sealing material (5 mm); group 1/2, removal of one-half of the sealing material (7.5 mm); and group 2/3, removal of two-thirds of the sealing material (10 mm). All the posts were cemented with resin cement, and the specimens with glass fiber posts received a composite resin core. All the specimens were restored with a metal crown and submitted to a compressive load until failure occurred. The results were evaluated by 1-way ANOVA, and the all pairwise multiple comparison procedures (Tukey honestly significantly difference test) (α=.05). RESULTS: The ANOVA showed significant differences among the groups (P<.002). The Tukey test showed that the control group presented significantly higher resistance to static load than the other groups (control group, 634.94 N; group 1/3, 200.01 N; group 1/2, 212.17 N; and group 2/3, 236.08 N). Although teeth restored with a cast post and core supported a higher compressive load, all of them fractured in a catastrophic manner. For teeth restored with glass fiber posts, the failure occurred at the junction between the composite resin core and the root. CONCLUSION: The length of glass fiber posts did not influence fracture load, but cast post and cores that extended two-thirds of the root length had significantly greater fracture resistance than glass fiber posts.

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Introdução: A estabilidade dimensional das resinas acrílicas influencia na adaptação das coroas provisórias e, consequentemente, no resultado do tratamento reabilitador. Objetivo: Avaliar a estabilidade dimensional, ao longo do tempo, de uma resina acrílica processada de diferentes maneiras. Material e Método: Cinco técnicas de polimerização da resina acrílica foram testadas: I - polimerização térmica utilizando líquido de polimerização rápida em mufla; II - autopolimerização sob pressão; III - autopolimerização utilizando pincel; IV - autopolimerização após mistura (pó + líquido) em pote Dappen e inserção em matriz de aço na fase arenosa; V - autopolimerização após mistura em pote Dappen com inserção na matriz metálica na fase plástica. Foram confeccionados dez corpos de prova para cada tipo de processamento. Avaliou-se a estabilidade dimensional por meio de matriz de aço inox confeccionada segundo a especificação nº19 da ADA. Os corpos de prova foram armazenados em água destilada a 37ºC e examinados nos períodos de 1 hora, 1, 7, 15, 10, 90 e 180 dias após a polimerização, com o auxílio de um microscópio óptico com aumento de 20×. Os resultados foram submetidos à análise de dupla variância (Teste de Tukey para Tempo e Técnica de processamento) em nível de 5% de significância. Resultado: Todos os grupos experimentais apresentaram alterações dimensionais entre o sétimo e o 15º dia; após esse período de tempo, houve alterações dimensionais estatisticamente significantes, para as diferentes técnicas estudadas. Conclusão: A estabilidade dimensional da resina acrílica não sofreu influência das diferentes técnicas de processamento avaliadas; entretanto, foi influenciada pelo tempo de armazenamento.

Introduction: The dimensional stability of acrylic resins influences the temporary crowns fitting and can affect the final restoration results. Objective: To evaluate the long-term dimensional stability of an acrylic resin used for fabrication of provisional crowns. Material and Method: Five types of processing techniques were evaluated: I - thermal polymerization using fast polymerization liquid and flask; II - auto-polimerization under pressure in a stainless steel matrix; III - auto-polimerization using the bead brush technique to build the sample; IV - auto-polimerization after mixture (powder + liquid) in a dappen dish and insertion in a stainless steel matrix at the sand stage; V - auto-polimerization after mixture in a dappen dish with insertion in a stainless steel matrix at the plastic stage. For each type of processing technique, 10 samples were made. Dimensional stability was evaluated by means of a steel matrix made following the ADA specification nº19. The samples were stored in distilled water at 37 ºC and examined at the periods of 1 hour, 1, 7, 15, 30, 90 and 180 days, with an optic microscope with 20× magnification. The results were subjected to the 2-way analysis of variance (Tukey Test) at the significance level of 5% for the variables Time and Processing Technique. Result: All samples had dimensional alterations from day 7 to the day 15, regardless of the technique used. From day 15 to 180, there were no statistically significant dimensional alterations. Conclusion: The dimensional stability of the acrylic resin was not influenced by the different processing techniques tested, however, it was influenced by the storage time.

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Objective: This study aimed at evaluating the micro-hardness of an acrylic resin used for provisional crowns. Materials and methods: Five different processing techniques (direct and indirect) were assessed: (I) auto polymerizing resin in sandy stage; (II) auto polymerizing resin in plastic stage; (III) bead-brush technique; (IV) auto polymerizing resin under pressure; (V) heatcured acrylic resin under pressure. Five specimens were made for each test group. For the initial micro-hardness test, the specimens were immersed in deionized water for 48 hours. For the analysis of the final micro-hardness, the specimens were subjected to pH-cycling to simulate the changes in the pH level which occur in the oral cavity. Results: Tests revealed that the micro-hardness was decreased after the pH-cycling. However, no statistical difference was found among the different types of acrylic resin polymerization techniques. Conclusion: It was concluded that the micro-hardness is not directly related to the polymerization technique for making provisional

Objetivo: Avaliou-se a dureza superficial de uma resina acrílica (PMMA) utilizada para a confecção de coroas provisórias. Material e Métodos: Cinco diferentes técnicas de processamento (Direta e Indireta) para polimerização da resina foram testadas: I - autopolimerização após mistura (pó + líquido) em pote dappen e inserção em matriz de silicona na fase arenosa; II - autopolimerização após mistura em pote dappen com inserção em matriz de silicona na fase plástica; III - autopolimerização utilizando a técnica do pincel; IV - autopolimerização sob pressão em matriz de silicona; V - polimerização térmica utilizando líquido de polimerização rápida em mufla. Foram confeccionados cinco corpos-de-prova para cada grupo. Para o teste de microdureza inicial os espécimes foram imersos em água deionizada por 48 horas. Para a análise da dureza final, os espécimes foram submetidos a ciclos dinâmicos de pH, para simular a variação de pH ocorrida na cavidade oral. Resultados: Os testes revelaram que houve diminuição da dureza do material após a ciclagem ácida, porém não foi verificada diferença estatística entre os diferentes tipos de processamento da resina acrílica. Conclusão: Concluiu-se que a microdureza não está relacionada diretamente com a técnica de confecção dos provisórios.

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RESUMO

When a cylinder is connected to an abutment it is expected that abutment and cylinder will be subjected to compression forces throughout their periphery because of the clamping force exerted by the screw. The deformation resultant of this compression should be measurable and uniform along the periphery of the abutment. Considering that multiple retainers connected to each other can affect the fit of a framework, as well as the use of different alloys, it is expected that the abutments will present different levels of deformation as a result of framework connection. The aim of this study was to evaluate the deformation of implant abutments after frameworks, cast either in cobalt-chromium (CoCr) or silver-palladium (AgPd) alloys, were connected. Samples (n  =  5) simulating a typical mandibular cantilevered implant-supported prosthesis framework were fabricated in cobalt-chromium and silver-palladium alloys and screwed onto standard abutments positioned on a master-cast containing 5 implant replicas. Two linear strain gauges were fixed on the mesial and distal aspects of each abutment to capture deformation as the retention screws were tightened. A combination of compressive and tensile forces was observed on the abutments for both CoCr and AgPd frameworks. There was no evidence of significant differences in median abutment deformation levels for 9 of the 10 abutment aspects. Visually well-fit frameworks do not necessarily transmit load uniformly to abutments. The use of CoCr alloy for implant-supported prostheses frameworks may be as clinically acceptable as AgPd alloy.

Assuntos