Resistencia adesiva a longo prazo entre zirconias odontologicas com diferentes niveis de translucidez e cimento resinoso / Long-term bond strength between dental zirconia of different translucency levels and resin cement

Este estudo avaliou a resistência e a confiabilidade adesiva entre zircônias com diferentes graus de translucidez com o cimento resinoso, sinterizadas de forma convencional e rápida, além de avaliar a susceptibilidade ao envelhecimento térmico dessas interfaces. Espécimes de quatro diferentes zircônias (3YTZP/Translúcida [T], 3Y-TZP/Alta Translucidez [HT], 4Y-PSZ/Super Translúcida [ST] e 5Y-PSZ/Extra Translúcida [XT]) foram obtidos a partir de blocos de CAD/CAM e polidos. Todas as zircônias foram sinterizadas de forma convencional (ciclo de ~12h), entretanto as zircônias T e HT foram subdivididas em grupos também sinterizados na forma rápida (~2h), seguindo o protocolo do fabricante. As superfícies adesivas foram jateadas com Al2O3 50 µm e silanizadas com primer contendo MDP, um cilindro de cimento resinoso foi construído na superfície cerâmica (Ø = 1 mm; h = 2 mm). Metade dos espécimes foram submetidos a termociclagem previamente ao ensaio (6000 ciclos; 5 ­ 55ºC); a outra metade das amostras foi submetida diretamente ao ensaio de microcisalhamento com fio em uma máquina de ensaios universal. Os dados de resistência adesiva foram submetidos a ANOVA 2-fatores e teste de Tukey (95%), bem como à análise de Weibull para determinação da confiabilidade adesiva. A média do valor da resistência adesiva foi estatisticamente diferente entre os materiais, apenas as zircônias HT e ST não foram afetadas negativamente pelo envelhecimento térmico. A forma de sinterização rápida foi estatisticamente semelhante à convencional para a zircônia T, entretanto a HT com sinterização rápida mostrou maior resistência adesiva imediata do que a convencional. O módulo de Weibull foi superior paras zircônias HT convencional e ST. O envelhecimento térmico causa uma degradação das interfaces adesivas das zircônias 3Y-TZP (T) e 5Y-PSZ (XT) com o cimento resinoso, entretanto não afeta as interfaces das zircônias 3Y-TZP (HT) e 4YPSZ (ST). O método de sinterização rápido não altera a resistência de união das zircônias estudadas com o cimento resinoso a longo prazo. A confiabilidade adesiva segundo o módulo de Weibull é superior para a 3Y-TZP (HT convencional) e 4Y-PSZ (ST). (AU)

This study evaluated the adhesive strength and reliability of zirconia with different degrees of translucency with resin cement, sintered in a conventional and speed mode, in addition to evaluating the susceptibility to thermal aging of these interfaces. Specimens of four different zirconia (3Y-TZP/Translucent [T], 3Y-TZP/High Translucent [HT], 4Y-PSZ/Super Translucent [ST] and 5YPSZ/Extra Translucent [XT]) were obtained from CAD/CAM blocks and polished. All zirconia were conventionally sintered (~12h cycle), however the T and HT zirconia were subdivided into groups also sintered in the speed mode (~2h), following the manufacturer's protocol. The adhesive surfaces were sandblasted with 50 µm Al2O3 and silanized with a primer containing MDP, a resin cement cylinder was built on the ceramic surface (Ø = 1 mm; h = 2 mm). Half of the specimens were submitted to thermocycling prior to the assay (6000 cycles; 5 ­ 55ºC); the other half of the samples were directly subjected to the wire microshear test in a universal testing machine. The bond strength data were submitted to 2-way ANOVA and Tukey's test (95%), as well as Weibull analysis to determine the adhesive reliability. The average value of bond strength was statistically different between materials, only HT and ST zirconia were not negatively affected by thermal aging. The speed sintering form was statistically similar to the conventional one for T zirconia, however the speed sintered HT showed higher immediate bond strength than the conventional one. The Weibull modulus was superior for conventional HT and ST zirconia. Thermal aging causes a degradation of the adhesive interfaces of 3Y-TZP (T) and 5Y-PSZ (XT) zirconia with the resin cement, however it does not affect the interfaces of 3Y-TZP (HT) and 4Y-PSZ (ST) zirconia. The speed sintering method does not change the bond strength of the zirconia studied with the resin cement in the long term. Adhesive reliability according to the Weibull module is superior for 3Y-TZP (conventional HT) and 4Y-PSZ (ST). (AU)

Computer Aided Design Modelling and Finite Element Analysis of Premolar Proximal Cavities Restored with Resin Composites.

This study evaluated the stress distribution in five different class II cavities of premolar models restored with conventional or bulk-fill flowable composite by means of finite element analysis (FEA) under shrinkage and occlusal loading. An upper validated premolar model was imported in the software, and five class II cavities with different occlusal extensions and dimensions were prepared: horizontal cavity on the mesial surface (horizontal slot), mesio-occlusal cavity, mesial cavity (vertical slot), tunnel type cavity and direct access cavity. The models were restored with conventional or bulk-fill flowable resin composite. The tested materials were considered as homogeneous, linear, and isotropic. The Maximum Principal Stress criteria was chosen to evaluate the tensile stress results. The lowest shrinkage stress value was observed in the direct access cavity restored with bulk-fill flowable resin composite (36.12 MPa). The same cavity, restored with conventional composite showed a score of 36.14 MPa. The horizontal slot cavity with bulk-fill flowable showed a score of 46.71 MPa. The mesio-occlusal cavity with bulk-fill flowable had a score of 53.10 MPa, while with conventional composite this was 55.35 MPa. Higher shrinkage stress was found in the vertical slot cavity with conventional resin 56.14 MPa, followed by the same cavity with bulk-fill flowable 56.08 MPa. Results indicated that the use of bulk-fill flowable composite resin more significantly decreased the polymerization shrinkage stress magnitude. The larger the cavity and the volume of material necessary to restore the tooth, the greater the residual stress on enamel and dentin tissue.

Influence of the dental implant number and load direction on stress distribution in a 3-unit implant-supported fixed dental prosthesis.

BACKGROUND: The choice between 2 or 3 implants to support a 3-unit implant-supported fixed dental prosthesis (FDP) still generates doubt in clinical practice. OBJECTIVES: The aim of this study was to evaluate stress distribution in 3-unit implant-supported FDPs according to the implant number and load direction. MATERIAL AND METHODS: A numerical simulation was performed to analyze stress and strain according to the implant number (2 or 3) and load direction (axial or oblique). A model of a jaw was created by means of the modeling software Rhinoceros, v. 5.0 SR8. External hexagon implants, micro-conical abutments and screws were also modeled. The final geometries were exported to the computer-aided engineering (CAE) software Ansys, v. 17.2, and all materials were considered homogeneous, isotropic and elastic. Different load directions were applied for each model (300 N) at the center of the prosthesis. RESULTS: The von Mises stress and strain values were obtained for the titanium structures and the bone, respectively. The implant number influenced the prosthesis biomechanics, with higher stress and strain concentrations when 2 implants were simulated. The oblique load also affected the mechanical response, showing higher stress and strain in comparison with the axial load, regardless of the implant number. CONCLUSIONS: It was concluded that for a 3-unit implant-supported FDP, a greater number of implants associated with axial loads can result in a better mechanical response during chewing.

Influence of Polymeric Restorative Materials on the Stress Distribution in Posterior Fixed Partial Dentures: 3D Finite Element Analysis.

BACKGROUND: This study evaluated the effect of interim restorative materials (acrylic resin (AR), resin composite (RC) or polyetheretherketone (PEEK) for dental computer-aided design/computer-aided manufacturing (CAD/CAM)) on the stress distribution of a posterior three-unit fixed partial denture. METHODS: The abutment teeth (first molar and first premolar) were modeled using the BioCAD protocol containing 1.5 mm of axial reduction and converging axial walls. A static structural analysis was performed in the computer-aided engineering software, and the Maximum Principal Stress criterion was used to analyze the prosthesis and the cement layers of both abutment teeth. The materials were considered isotropic, linearly elastic, homogeneous and with bonded contacts. An axial load (600 N) was applied to the occlusal surface of the second premolar. RESULTS: Regardless of the restorative material, the region of the prosthetic connectors showed the highest tensile stress magnitude. The highest stress peak was observed with the use of RC (129 MPa) compared to PEEK and AR. For the cement layers, RC showed the lowest values in the occlusal region (7 MPa) and the highest values for the cervical margin (14 MPa) compared to PEEK (21 and 12 MPa) and AR (21 and 13 MPa). CONCLUSIONS: Different interim restorative materials for posterior fixed partial dentures present different biomechanical behavior. The use of resin composite can attenuate the stress magnitude on the cement layer, and the use of acrylic resin can attenuate the stress magnitude on the connector region.

Study of the pterygoid canal (vidian canal) through images of cone beam computer tomography / Estudo do canal Pterigóideo (canal Vidiano) por meio de imagens de tomografia computadorizada de feixe cônico

Objective: The aim of this study was to evaluate the pterygoid canal (PC) by Cone Beam Computed Tomography (CBCT), establishing its configuration and proximity with anatomical structures. Material and Methods: We evaluated 398 CBCT exams, all from a public University radiology clinic archive. Four parameters were evaluated: single or double PC, distance between PC and the inferior part of the sphenoid sinus (SS), ratio of PC and SS and the distance between the PC and the foramen rotundum. Results: It was observed that most of the PC of the sample presented simple morphology, the most frequent type of relationship between the PC and the SS on both sides was the close contact with the wall. Among the cases that there were some distances between the PC and the inferior wall of the SS, the mean of this distance did not exceed 3.20 mm, being the left side (3.03 mm) slightly closer than the right (3.20 mm). Finally, the distances between the PC and the corresponding Foramen Rotundum are presented with mean values of 5.87 mm for the right side and 6.31 mm for the left side. Conclusion: CBCT examination is of paramount importance for PC identification; once in the studied sample, the mean values found evidence the close relation between the PC and the SS (AU)

Objetivo: O objetivo deste estudo foi avaliar o CP pela TCFC, estabelecendo sua configuração e proximidade com estruturas anatômicas. Material e Métodos: Foram avaliados 398 exames de TCFC, todos de um arquivo público da clínica de radiologia da Universidade. Foram avaliados quatro parâmetros: CP único ou duplo, distância entre PC e parte inferior do seio esfenoidal (SS), razão entre PC e SS e a distância entre o PC e o forame redondo. Resultados: Observou-se que a maioria dos CP da amostra apresentava morfologia simples, o tipo de relação mais frequente entre o CP e o SS de ambos os lados foi o contato próximo com a parede. Entre os casos em que houve algumas distâncias entre o CP e a parede inferior da ES, a média dessa distância não excedeu 3,20 mm, sendo o lado esquerdo (3,03 mm) um pouco mais próximo do que o direito (3,20 mm). Finalmente, as distâncias entre o PC e o forame redondo correspondente são apresentadas com valores médios de 5,87 mm para o lado direito e 6,31 mm para o lado esquerdo. Conclusão: O exame TCFC é de suma importância para a identificação do CP; uma vez na amostra estudada, os valores médios encontrados evidenciam a estreita relação entre o CP e o SS. (AU)