Navegando por Autor "Coelho, Paulo G."
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Artigo Biomechanical evaluation of internal and external hexagon platform switched implant-abutment connections: an in vitro laboratory and three-dimensional finite element analysis(ELSEVIER, 2012) Freitas Junior, Amilcar Chagas; Rocha, Eduardo P.; Bonfante, Estevam A.; Almeida, Erika Oliveira de; Anchieta, Rodolfo Bruniera; Martini, Ana P.; Assunção, Wirley G.; Silva, Nelson R. F. A.; Coelho, Paulo G.Objectives The aim of this study was to assess the effect of abutment's diameter shifting on reliability and stress distribution within the implant-abutment connection for internal and external hexagon implants. The postulated hypothesis was that platform-switched implants would result in increased stress concentration within the implant-abutment connection, leading to the systems’ lower reliability. Methods Eighty-four implants were divided in four groups (n = 21): REG-EH and SWT-EH (regular and switched-platform implants with external connection, respectively); REG-IH and SWT-IH (regular and switched-platform implants with internal connection, respectively). The corresponding abutments were screwed to the implants and standardized maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing. Use-level probability Weibull curves and reliability were calculated. Four finite element models reproducing the characteristics of specimens used in laboratory testing were created. The models were full constrained on the bottom and lateral surface of the cylinder of acrylic resin and one 30° off-axis load (300 N) was applied on the lingual side of the crown (close to the incisal edge) in order to evaluate the stress distribution (svM) within the implant-abutment complex. Results The Beta values for groups SWT-EH (1.31), REG-EH (1.55), SWT-IH (1.83) and REG-IH (1.82) indicated that fatigue accelerated the failure of all groups. The higher levels of σvM within the implant-abutment connection observed for platform-switched implants (groups SWT-EH and SWT-IH) were in agreement with the lower reliability observed for the external hex implants, but not for the internal hex implants. The reliability 90% confidence intervals (50,000 cycles at 300 N) were 0.53(0.33–0.70), 0.93(0.80–0.97), 0.99(0.93–0.99) and 0.99(0.99–1.00), for the SWT-EH, REG-EH, SWT-IH, and REH-IH, respectively. Significance The postulated hypothesis was partially accepted. The higher levels of stress observed within implant-abutment connection when reducing abutment diameter (cross-sectional area) resulted in lower reliability for external hex implants, but not for internal hex implants.Artigo Reliability evaluation of alumina-blasted/acid-etched versus laser-sintered dental implants(2013) Almeida, Erika Oliveira de; Freitas Junior, Amilcar Chagas; Bonfante, Estevam A.; Silva, Nelson R. F. A.; Coelho, Paulo G.Step-stress accelerated life testing (SSALT) and fractographic analysis were performed to evaluate the reliability and failure modes of dental implant fabricated by machining (surface treated with alumina blasting/acid etching) or laser sintering for anterior single-unit replacements. Forty-two dental implants (3.75 × 10 mm) were divided in two groups (n=21 each): laser sintered (LS) and alumina blasting/acid etching (AB/AE). The abutments were screwed to the implants and standardized maxillary central incisor metallic crowns were cemented and subjected to SSALT in water. Use-level probability Weibull curves and reliability for a mission of 50,000 cycles at 200 N were calculated. Polarized light and scanning electron microscopes were used for failure analyses. The Beta (β) value derived from use-level probability Weibull calculation of 1.48 for group AB/AE indicated that damage accumulation likely was an accelerating factor, whereas the β of 0.78 for group LS indicated that load alone likely dictated the failure mechanism for this group, and that fatigue damage did not appear to accumulate. The reliability was not significantly different (p>0.9) between AB/AE (61 %) and LS (62 %). Fracture of the abutment and fixation screw was the chief failure mode. No implant fractures were observed. No differences in reliability and fracture mode were observed between LS and AB/AE implants used for anterior single-unit crowns.