DOD - Departamento de Odontologia

URI Permanente desta comunidadehttps://repositorio.ufrn.br/handle/1/57

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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.
Influence of microthreads and platform switching on stress distribution in bone using angled abutments
(ELSEVIER, 2012) Ferraz, Cacilda Cunha; Anchieta, Rodolfo Bruniera; Almeida, Erika Oliveira de; Freitas Junior, Amilcar Chagas; Ferraz, Fábio Cunha; Machado, Lucas Silveira
To evaluate the stress distribution in peri-implant bone by simulating the effect of an implant with microthreads and platform switching on angled abutments through tridimensional finite element analysis. The postulated hypothesis was that the presence of microthreads and platform switching would reduce the stress concentration in the cortical bone. Methods Four mathematical models of a central incisor supported by an implant (5.0 mm × 13 mm) were created in which the type of thread surface in the neck portion (microthreaded or smooth) and the diameter of the angled abutment connection (5.0 and 4.1 mm) were varied. These models included the RM (regular platform and microthreads), the RS (regular platform and smooth neck surface), the SM (platform switching and microthreads), and the SS (platform switching and smooth neck). The analysis was performed using ANSYS Workbench 10.0 (Swanson Analysis System). An oblique load (100 N) was applied to the palatine surface of the central incisor. The bone/implant interface was considered to be perfectly integrated. Values for the maximum (σmax) and minimum (σmin) principal stress, the equivalent von Mises stress (σvM), and the maximum principal elastic strain (ɛmax) for cortical and trabecular bone were obtained. Results For the cortical bone, the highest σmax (MPa) were observed for the RM (55.1), the RS (51.0), the SM (49.5), and the SS (44.8) models. The highest σvM (MPa) were found for the RM (45.4), the SM (42.1), the RS (38.7), and the SS models (37). The highest values for σmin were found for the RM, SM, RS and SS models. For the trabecular bone, the highest σmax values (MPa) were observed in the RS model (6.55), followed by the RM (6.37), SS (5.6), and SM (5.2) models. Conclusion The hypothesis that the presence of microthreads and a switching platform would reduce the stress concentration in the cortical bone was partially rejected, mainly because the microthreads increased the stress concentration in cortical bone. Only platform switching reduced the stress in cortical bone.
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.
The use of a magnetic attachment in a removable partial denture of a patient with periodontal tissue loss
(2009) Carreiro, Adriana da Fonte Porto; Guerra, Cátia Maria Fonseca; Moraes, Sandra Lúcia Dantas de; Farias Neto, Arcelino; Torres, Érica Miranda de; Almeida, Erika Oliveira de
The use of magnets in removable partial dentures is a valid alternative for eliminating prosthetic structures that may interfere in esthetics without losing retention and stability. Magnets can also be recommended for patients with periodontal tissue loss, since they can decrease transmission of forces to remaining teeth. The aim of this clinical report was to present an alternative prosthetic rehabilitation treatment for periodontally-compromised abutment teeth, and to point out the advantages and disadvantages of using magnets in removable partial dentures (overdentures) from the functional, biological, and esthetic point of view.

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