Influence of Cusp Inclination and Type of Retention on Fracture Load of Implant-Supported Crowns

Abstract There are few informations about the influence of cusp inclination on the fracture strength of implant-supported crowns. The study aimed to evaluate the influence of cusp inclination and retention type on fracture load in implant-supported metal-ceramic single crowns. Sixty crowns were made, classified as cemented and screw-retained with screw access hole (SAH) sealed or not. Standard (33°) and reduced (20°) cusp inclinations were tested for each group (n=10). To support crowns of a mandibular second molar, analogs of external hexagon implants 5.0 were used. The fracture load was measured in a universal testing machine EMIC DL2000 (10 kN load cell; 0.5 mm/min). Two-way ANOVA (retention and cusp inclination) followed by post hoc Tukey’s honest significant difference test was used for the statistical analyses (a=0.05). Crowns with reduced cusp inclination exhibited significantly higher fracture load (p<0.01) than crowns with standard cusp inclination. Cemented crowns showed significantly higher fracture load (p<0.01) than screw-retained crowns. The interaction among these factors was not significant (p>0.05) for the fracture load. The sealing of SAH did not influence the fracture load of screw-retained crowns (p>0.05). In conclusion, fracture load of implant-supported metal-ceramic crowns was influenced by retention and cusp inclination, and there was no influence of the sealing of SAH.

Resumo Existem poucas informações sobre a influência da inclinação de cúspide na resistência à fratura de coroas implantossuportadas. O objetivo do estudo foi avaliar a influência da inclinação de cúspide e do tipo de retenção na carga de fratura de coroas unitárias metalocerâmicas implantossuportadas. Sessenta coroas foram confeccionadas, classificadas como cimentadas e parafusadas com orifício de acesso ao parafuso selado ou não. Cúspides com inclinação padrão (33°) e reduzida (20°) foram testadas para cada grupo (n=10). Para suportar as coroas de um segundo molar inferior, análogos de implante hexágono externo 5.0 foram utilizados. A carga de fratura foi mensurada em máquina de ensaios universais EMIC DL2000 (célula de carga de 10 kN; 0,5 mm/min). ANOVA dois fatores (retenção e inclinação da cúspide) seguido do pós-teste de Tukey da diferença honestamente significativa foi utilizada para análise estatística (a=0,05). Coroas com inclinação de cúspide reduzida exibiram carga de fratura significativamente maior (p>0,05) que coroas com cúspides de inclinação padrão. Coroas cimentadas apresentaram carga de fratura significativamente maior (p<0,01) que coroas parafusadas. A interação entre os dois fatores não foi significante (p>0,05) para a carga de fratura. O selamento do orifício de acesso ao parafuso não influenciou a carga de fratura das coroas parafusadas (p>0,05). Concluindo, a carga de fratura de coroas metalocerâmicas implantossuportadas foi influenciada pelo tipo de retenção e inclinação da cúspide, e não houve influência do selamento do orifício de acesso ao parafuso

Effect of Glaze Cooling Rate on Mechanical Properties of Conventional and Pressed Porcelain on Zirconia

Abstract The aim of this study was to characterize a conventional and a pressed porcelain for zirconia core as to biaxial flexural strength (BFS), apparent fracture toughness (FT) and microstructure composition, and to investigate the effect of glaze cooling rate on the BFS of the zirconia/porcelain bilayers. Monolayers of conventional porcelain Vita VM9 and pressed porcelain Vita PM9 (n=15) (12 mm diameter x 1.2 mm thick) were prepared for the BFS test (MPa). Apparent fracture toughness (MPa.m1/2) was measured by indentation technique (n=15). t-Student test was performed for statistical analysis. Scanning electron microscopy and x-ray diffraction were used to analyze the porcelain's microstructure. For the BFS of bilayers, zirconia discs (12 mm diameter x 1 mm thick) (Vita In-Ceram YZ) were veneered with the two porcelains (1 mm thick). After the glaze firing simulation, the specimens were submitted to fast or slow cooling (n=15). Apparent fracture toughness (MPa.m1/2) was measured on the porcelain surface of bilayers (n=15) and residual stress was calculated. Two-way ANOVA (porcelain and cooling method) was used for the bilayer analysis (a=0.05). Vita PM9 monolayer exhibited significantly higher BFS (p<0.01), but there was no significant difference (p=0.41) in the FT between the porcelains. For bilayer specimens, the two-way ANOVA for BFS was significant for the porcelain variable only (p<0.01) better for Vita PM9/zirconia. Two-way ANOVA for the FT for the bilayers was not significant for any variable. All groups showed compressive residual stresses. The pressed porcelain seems to be mechanically more effective for zirconia veneering.

Resumo Este estudo teve como objetivo caracterizar uma porcelana convencional e uma prensada indicadas para infraestrutura de zircônia em termos de resistência à flexão biaxial (RFB), tenacidade à fratura aparente (TF) e composição microestrutural, e investigar o efeito da taxa de resfriamento do ciclo de glaze na RFB de espécimes bicamada de zircônia/porcelana. Espécimes monocamada de porcelana convencional Vita VM9 e porcelana prensada Vita PM9 (n=15) (12 mm de diâmetro x 1,2 mm de espessura) foram preparados para o ensaio de RFB (MPa). Tenacidade à fratura aparente (MPa.m1/2) foi mensurada pela técnica da indentação (n=15). O teste de t-Student foi aplicado para as análises estatísticas. Microscopia eletrônica de varredura e difração de raios-X foram utilizadas para análise microestrutural da porcelana. Para o ensaio de RFB nos bicamadas, discos de zircônia (12 mm de diâmetro x 1 mm de espessura) (Vita In-Ceram YZ) foram recobertos com as duas porcelanas (1 mm de espessura). Após a simulação da queima de glaze, os espécimes foram submetidos ao método de resfriamento rápido ou lento (n=15). A tenacidade à fratura aparente (MPa.m1/2) foi mensurado na superfície da porcelana dos bicamadas (n=15) e o estresse residual foi calculado. Foi utilizado ANOVA a dois fatores (porcelana e método de resfriamento) para análise estatística dos espécimes bicamada (a=0,05). Monocamadas de Vita PM9 exibiram valores de resistência à flexão biaxial significativamente maiores (p<0,01), mas não houve diferença estatística (p=0,41) em relação à TF entre as porcelanas. Para os espécimes bicamada, ANOVA a dois fatores para RFB foi significante apenas para a variável porcelana (p<0,01), com superioridade para Vita PM9/zircônia. ANOVA a dois fatores para TF dos espécimes bicamadas não apresentou significância para nenhuma variável. Todos os grupos apresentaram estresse residual de compressão. Porcelanas prensadas parecem ser mecanicamente mais efetivas para recobrimento de zircônia.

Comparison of the indentation strength and single-edge-v-notched beam methods for dental ceramic fracture toughness testing

Aim: To study influence of the cooling rate after sintering a veneering porcelain (Vita VM9) on fracture toughness by indentation strength (IS) and single-edge-v-notched beam (SEVNB) methods. Methods: Vita VM9 bars were sintered according to the manufacturer's recommendation and cooled under three conditions: Slow (inside the furnace from sintering temperature to room temperature); Normal (inside the furnace from sintering temperature to 500 ºC and outside the furnace from 500 ºC to room temperature); and Fast (outside the furnace from sintering temperature to room temperature). Fracture toughness was measured by IS (n=10) and SEVNB (n=10) methods. Data were analyzed by two-way ANOVA (α=0.05). Results: The fracture toughness obtained from SEVNB (slow - 1.02±0.10; normal - 1.09±0.13; and fast - 1,02±0.18 MPa.m1/2 cooling techniques) was significantly lower than IS (slow - 1.19±0.13; normal - 1.17±0.07; and fast - 1.16±0.06 MPa. m1/2 cooling techniques). There was no significant influence of the cooling technique (p=0.012). Conclusions: The measurement technique influenced the fracture toughness values . IS method overestimated the fracture toughness values. Irrespective of the measuring method, cooling rate did not influence the Vita VM9 veneering porcelain fracture toughness (Au)

Strength of 3Y-TZP and feldspathic porcelain subjected to different cooling methods

AIM: To investigate the effect of the cooling rate on flexural strength of monolayer and bilayer porcelain/zirconia (Y-TZP) bars. METHODS: Forty-five specimens were made for each design group: (PM) monolithic specimens of veneer porcelain Vita VM9 (Vita, Germany); (ZM) monolithic specimens of zirconia (ZiHP; ProtMat, Brazil); (PB) bilayer specimens zirconia/porcelain with porcelain on lower surface; and (ZB) bilayer specimens porcelain/zirconia with zirconia on lower surface. Each group was cooled by three different methods after porcelain sintering: slow specimens were cooled inside the turned-off furnace; normal specimens were removed from the furnace and cooled in air at room temperature; and fast specimens were removed from the furnace at 910°C and cooled by compressed air for 10 s. Specimens were polished and flexural strength was measured in water at 37 °C (n=15). Maximum load at fracture was recorded, and equations for simple (monolayer) and composite (bilayer) structures were used to calculate the flexural strength. RESULTS were analyzed using one-way ANOVA (p<0.05) and Tukey test separately for each design. RESULTS: The results of one-way ANOVA were statistically significant only for the PB group. The post-hoc Tukey test showed the highest flexural strength for fast cooling and the lowest for slow cooling; the normal cooling was statistically similar to both. CONCLUSIONS: Cooling methods affected only the flexural strength of bilayer specimens with porcelain on low surface (under tension) when the slow cooling method was used...

Caracterização mecânica de uma porcelana de aplicação convencional e uma prensada para recobrimento de infraestruturas de zircônia e o efeito do método de resfriamento na resistência à flexão biaxial do conjunto zircônia/porcelana / Mechanical characterization of a conventional porcelain and a pressable porcelain for zirconia core, and the effect of the cooling method on the biaxial flexural strength of bilayers zirconia/porcelain

Este estudo caracterizou mecanicamente uma porcelana feldspática de aplicação convencional e uma porcelana feldspática prensada, indicadas para infraestrutura em zircônia, quanto a resistência à flexão biaxial, dureza Vickers e tenacidade à fratura. Além disso, foi investigado o efeito da taxa de resfriamento após o ciclo de sinterização do glaze da porcelana na resistência à flexão biaxial de bicamadas zircônia/porcelana. Espécimes monocamada de VM9 (n=15) e Vita PM9 (n=15) (12,0 mm de diâmetro x 1.2 mm de espessura) foram confeccionados conforme as recomendações do fabricante e submetidos ao ensaio de resistência à flexão biaxial (MPa). Um fragmento de cada espécime fraturado foi aleatoriamente selecionado para a mensuração da dureza Vickers (n=15) (VHN). A tenacidade à fratura aparente(MPa.m½) foi determinada pela técnica da indentação Vickers (n=15). Para o ensaio de flexão biaxial dos bicamadas, discos de zircônia (Vita In-Ceram YZ) foram recobertos com porcelana convencional Vita VM9 (n=30) ou com porcelana prensada Vita PM9 (n=30). Após a simulação da queima de glaze, os espécimes foram submetidos a resfriamento rápido (n=15) ou lento (n=15). Após o ensaio de resistência à flexão, os espécimes foram analisados quanto ao tipo de fratura. Teste de T-Student para espécimes monocamada mostrou que Vita PM9 apresentou valores significantemente maiores de resistência à flexão biaxial (p<0,01) e dureza (p=0,017) em relação a Vita VM9, mas não quanto a tenacidade à fratura (p= 0.41). ANOVA a dois fatores (porcelana e método de resfriamento), utilizada para análise dos bicamadas indicou significância apenas para porcelanas, com superioridade para a combinação Vita PM9/zircônia (p<0,01). Porcelanas prensadas parecem ser uma alternativa mais efetiva para recobrimento de zircônia em relação as convencionais.

This study characterized mechanically a conventional and a pressed feldspathic porcelain indicated for zirconia core in terms of biaxial flexural strength, fracture toughness, Vickers hardness. In addition it was investigated the effect of the glaze cooling rate on the biaxial flexural strength of the zirconia/porcelain bilayer. Specimens monolayers of Vita VM9 (n=15) and Vita PM9 (n=15) (12.0 mm diameter x 1.2 mm thickness) were prepared according to manufacturer's recommendations for the biaxial flexural strength test (MPa). Afterwards, one fragment of each broken specimen was randomly selected for Vickers hardness measurements (n=15) (VHN). Apparent fracture toughness (MPa.m½) was determined by Vickers hardness indentation technique (n=15). For the biaxial flexural strength of bilayers, zirconia discs (Vita InCeram YZ) were veneered with the conventional porcelain Vita VM9 (n=30) or with the pressed porcelain Vita PM9 (n=30). After the glaze firing simulation, the specimens were submitted to fast (n=15) or slow cooling method (n=15). After the biaxial flexural test, the specimens were analyzed in relation to fracture pattern. T-Student tests were performed for the monolayer specimens, while two-way ANOVA (porcelain and cooling method) was used for the bilayer ones (α=.05). Vita PM9 exhibited significantly higher biaxial flexural strength (p<0.01) and hardness than VM9 (p=0.017). However, there was no significant difference (p= 0.41) in fracture toughness between the porcelains. The two-way ANOVA indicated significance only for the porcelain, with superiority for the combination Vita PM9/zirconia (p<0.01).The pressed porcelain seems to be a mechanically more effective alternative for zirconia veneering than the conventional one