O efeito do tratamento térmico regenerativo após desgaste da zircônia na resistência ao cisalhamento e na taxa de liberação de energia de fratura da união zircônia/porcelana de cobertura
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Data
2022-02-01
Autores
Rimachi Hidalgo, Karem Janeth
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O objetivo desse estudo foi avaliar a eficácia do tratamento térmico regenerativo (TTR) a 1000 °C por 30 min na melhoria da adesão entre cerâmicas bicamadas compostas de porcelana de cobertura (PC) e zircônia (Z), após desgaste prévio da zircônia. Para tanto, a resistência ao cisalhamento e a tenacidade da adesão foram determinadas experimentalmente. A tenacidade foi determinada pela taxa de liberação da energia elástica armazenada, ou energia de fratura (G), em corpos de prova bicamada entalhados e com tração na PC em flexão em quatro pontos. Diferentes geometrias de corpos de prova para testes de cisalhamento foram avaliadas pelo método dos elementos finitos, a partir de 10 modelos virtuais em 3D construídos com o software ANSYS® 19.1, variando-se a altura e a posição da PC na interface com a Z. Tais modelos foram organizados em blocos denominados REFERENCE (PC e Z com mesma altura), TOP (interface coincide no topo, e a altura da PC diminui da base em direção ao topo), MID (altura da PC diminui a partir do topo e da base em direção ao centro da interface com a Z) e DOWN (interface coincide na base, e a altura da PC diminui do topo em direção à base). Em todos os modelos, a Z foi engastada e uma carga de 150 N foi aplicada na PC a uma distância de 0,2 mm da interface. A partir da análise das tensões máximas resultantes, o modelo REFERENCE foi considerado mais adequado para os ensaios de cisalhamento, e essa geometria foi utilizada para confeccionar espécimes de zircônia 3Y-TZP (Lava Plus, 12,5 x 11 x 0,9 mm) distribuídos em 3 grupos (n=15): controle (C), desgastado (D) e desgastado com TTR à 1000 °C por 30 min (DT). O desgaste (0,3 mm) da Z foi realizado em dispositivo padronizador utilizando pedra diamantada MasterCeram® em baixa rotação sem irrigação. O TTR foi realizado em forno convencional de laboratório. A superfície da Z resultante dos tratamentos foi caracterizada por difração de raios X (DRX), microscopia eletrônica de varredura (MEV) e perfilometria óptica. As amostras foram recobertas com PC IPS e.max Ceram (2,5 x 11 x 0,9 mm). Os ensaios de cisalhamento foram realizados com velocidade de deslocamento do atuador de 0,5 mm/min. A taxa de liberação de energia elástica armazenada foi avaliada em espécimes de Z de 40 x 5 x 1,5 mm recobertos com 1,5 mm de espessura de PC, segundo a mesma metodologia utilizada nos espécimes de cisalhamento. Ensaios de flexão em 4 pontos foram realizados com limite de carga de 120 N e velocidade do atuador de 0,5 mm/min. DRX, MEV e perfilometria foram analisados descritivamente. Os resultados dos ensaios de cisalhamento e energia de fratura (G) foram avaliados de acordo com o teste estatístico t adotando-se ∝ = 0,05. O desgaste com pedra diamantada aumentou a rugosidade superficial da zircônia; o tratamento térmico por sua vez retornou os valores de rugosidade para os encontrados no grupo controle. Não houve diferença estatisticamente significante na resistência da união da interface entre procedimentos adotados (desgaste seguido ou não de tratamento térmico, p = 0,37). Também se observou que a taxa de liberação de energia de fratura não se alterou nos grupos desgastado e desgastado seguido de tratamento térmico regenerativo (p = 0,77), em comparação com o grupo controle (p = 0,12). Conclui-se que o tratamento térmico regenerativo a 1000 oC por 30 minutos não influenciou a resistência ao cisalhamento e a taxa de liberação de energia da união zircônia/porcelana de cobertura.
The aim of this study was to evaluate the effectiveness of regenerative heat treatment (HT) at 1000 °C for 30 min in improving the adhesion of bilayer ceramics composed by veneer porcelain (VP) and zirconia (Z), after previous Z grinding. The shear strength and the deformation energy release rate (�) were experimentally determined, this tenacity (�) was determined in bilayer notched specimens with traction on the VP in four-point flexion. Different geometries of specimens for shear tests were evaluated by the finite element method, from 10 virtual 3D models built with ANSYS® 19.1 software, varying the height and position of the VP at the interface with the Z. These models were organized in blocks called REFERENCE (VP and Z with the same height), TOP (interface coincides at the top, and the height of the VP decreases from the base towards the top), MID (height of the VP decreases from the top and from the top base towards the center of the interface with the Z) and DOWN (interface coincides at the base, and the height of the PC decreases from the top towards the base). In all models, the Z was crimped and a load of 150 N was applied to the PC at a distance of 0.2 mm from the interface. From the analysis of the resulting maximum stresses, the REFERENCE model was considered more suitable for the shear tests, and this geometry was used to fabricate specimens of 3Y-TZP zirconia (Lava Plus, 12.5 x 11 x 0.9 mm) divided into 3 groups (n=15): control (C), grinding (G) and G with HT at 1000 °C for 30 min (GHT). The grinding (0.3 mm) of the Z was performed in a standardizing device using MasterCeram® diamond stone at low-speed rotation without irrigation. HT was performed in a conventional laboratory oven. The surface of the Z resulting from the treatments was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical profilometry (OP). The samples were coated with VP IPS e.max Ceram (2.5 x 11 x 0.9 mm). The SBS test were performed with an actuator displacement speed of 0.5 mm/min. The (�) was evaluated in 40 x 5 x 1.5 mm Z specimens coated with 1.5 mm VP thickness, according to the same methodology used in the SBS specimens; 4-point bending tests were performed with a load limit of 120 N and actuator speed of 0.5 mm/min. XRD, SEM and OP were descriptively analyzed. The results of the SBS and (�) tests were evaluated according to the statistical t test, adopting ∝ = 0.05. The diamond stone grinding increased the surface roughness of the Z; HT, in turn, returned the roughness values to those found in the control group. There was no statistically significant difference in the SBS of the interface between the procedures adopted (G followed or not by HT, p = 0.37). It was also observed that (�) did not change in the groups G and GTH (p = 0.77) compared to the control group (p = 0.12). It is concluded that regenerative heat treatment at 1000 oC for 30 minutes does not influence the rate of energy release and shear in bilayer restorations.
The aim of this study was to evaluate the effectiveness of regenerative heat treatment (HT) at 1000 °C for 30 min in improving the adhesion of bilayer ceramics composed by veneer porcelain (VP) and zirconia (Z), after previous Z grinding. The shear strength and the deformation energy release rate (�) were experimentally determined, this tenacity (�) was determined in bilayer notched specimens with traction on the VP in four-point flexion. Different geometries of specimens for shear tests were evaluated by the finite element method, from 10 virtual 3D models built with ANSYS® 19.1 software, varying the height and position of the VP at the interface with the Z. These models were organized in blocks called REFERENCE (VP and Z with the same height), TOP (interface coincides at the top, and the height of the VP decreases from the base towards the top), MID (height of the VP decreases from the top and from the top base towards the center of the interface with the Z) and DOWN (interface coincides at the base, and the height of the PC decreases from the top towards the base). In all models, the Z was crimped and a load of 150 N was applied to the PC at a distance of 0.2 mm from the interface. From the analysis of the resulting maximum stresses, the REFERENCE model was considered more suitable for the shear tests, and this geometry was used to fabricate specimens of 3Y-TZP zirconia (Lava Plus, 12.5 x 11 x 0.9 mm) divided into 3 groups (n=15): control (C), grinding (G) and G with HT at 1000 °C for 30 min (GHT). The grinding (0.3 mm) of the Z was performed in a standardizing device using MasterCeram® diamond stone at low-speed rotation without irrigation. HT was performed in a conventional laboratory oven. The surface of the Z resulting from the treatments was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical profilometry (OP). The samples were coated with VP IPS e.max Ceram (2.5 x 11 x 0.9 mm). The SBS test were performed with an actuator displacement speed of 0.5 mm/min. The (�) was evaluated in 40 x 5 x 1.5 mm Z specimens coated with 1.5 mm VP thickness, according to the same methodology used in the SBS specimens; 4-point bending tests were performed with a load limit of 120 N and actuator speed of 0.5 mm/min. XRD, SEM and OP were descriptively analyzed. The results of the SBS and (�) tests were evaluated according to the statistical t test, adopting ∝ = 0.05. The diamond stone grinding increased the surface roughness of the Z; HT, in turn, returned the roughness values to those found in the control group. There was no statistically significant difference in the SBS of the interface between the procedures adopted (G followed or not by HT, p = 0.37). It was also observed that (�) did not change in the groups G and GTH (p = 0.77) compared to the control group (p = 0.12). It is concluded that regenerative heat treatment at 1000 oC for 30 minutes does not influence the rate of energy release and shear in bilayer restorations.
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Palavras-chave
Zircônio, Resistência ao cisalhamento, Tratamento térmico, Porcelana dentária, Testes mecânicos, Zirconium, Shear resistance, Thermic treatment, Dental porcelain, Mechanical tests