ABSTRACT
OBJECTIVE: The aim of this study was to evaluate the distribution of generated stress around implants and adjacent bone tissue using different implant-retained overdenture designs through photoelastic analysis. METHODS: Over an edentulous human mandible, achieved from a human model, 2 or 4 microunit analog abutments were embedded (Master; Conexao Systems Prosthodontics, São Paulo, Brazil), settled in the interforaminal region. Three models of photoelastic resin (Araltec Chemicals Ltda, Hunstman, Guarulhos, São Paulo, Brazil), with 2 or 4 incorporated implants and microunit abutments, were obtained from molds using silicone for duplication. Inclusion, finishing, and polishing procedures were applied on the frameworks. This study was based on 3 different mechanisms of implant-retained mandibular overdentures: O'ring (GI), bar-clip (GII) (both with 2 implants), and their association (GIII) (with 4 implants). After the adaptation of each overdenture system on the photoelastic models, 100-N alternate occlusal loads were applied on back-side and front-side regions. The photoelastic analysis was made with the aid of a plain polariscope linked to a digital camera, Sony Cybershot α100, which allowed visualization of the fringes and registration of images on digital photographs. RESULTS: The results demonstrated higher tension concentrated over the GIII, with a flat distribution of stress to the posterior ridge and overload on the posterior implants. GI showed the smaller stress level, and GII, intermediate level; there was distribution of stress to the posterior ridge in these 2 groups. CONCLUSION: The use of bar attachment proved to be a better alternative, because it showed a moderate level of tension with a more uniform stress distribution and possessed higher retention than did the ball system.
Subject(s)
Dental Implantation, Endosseous/methods , Dental Prosthesis, Implant-Supported , Dental Stress Analysis/methods , Denture Retention/methods , Denture, Overlay , Bite Force , Dental Abutments , Denture Design , Denture Retention/instrumentation , Epoxy Resins , Humans , Immediate Dental Implant Loading , Jaw, Edentulous/surgery , Mandible/surgery , Models, Dental , Phthalic AnhydridesABSTRACT
Objetivo: Avaliar a força de destorque de parafusos protéticos antes e após o procedimento de retificação da base de assentamento dos parafusos protéticos às infra-estruturas. Métodos: A partir de matriz metálica contendo três réplicas de pilares cônicos (Micro-Unit; Conexão) dispostos 10mm de centro a centro, foram confeccionadas dez estruturas múltiplas fundidas em monobloco de titânio. As estruturas múltiplas fundidas foram apertadas sobre os pilares da matriz metálica com torque de 10Ncm. A seqüência de parafusamento deu-se do pilar central para os distais. A força (Ncm) necessária para o destorque foi avaliada utilizando-se torquímetro digital (TQ3000; Lutron, Taipei, Taiwan). Esse procedimento foi conduzido antes e após a retificação da base de assentamento dos parafusos protéticos, por meio do uso de ponta retificadora manual (Conexão Sistemas de Prótese, São Paulo, Brasil). Foram calculados os valores médios de destorque para cada estrutura, antes e após a retificação. Teste t para amostras pareadas foi utilizado para comparação das situações avaliadas. Resultados: Observou-se diferença significativa entre o valor médio de força de destorque dos parafusos protéticos antes (5,78±1,03Ncm) e após (7,06±0,62Ncm) os procedimentos de retificação (p<0,01). Conclusão: O processo de retificação da base de assentamento aumentou significativamente os valores da força necessária para o destorque dos parafusos protéticos das estruturas múltiplas implanto-retidas fundidas.
Objective: To evaluate the counter-force of prosthetic screws before and after the rectification procedure of the seating base of prosthetic framework screws. Methods: With a metal matrix containing three replicas of conical abutments (Micro-Unit; Conexão) placed at 10 mm from center to center, ten multiple cast structures were made of a titanium monoblock. The multiple cast structures were fastened on to the metal matrix abutments with a torque of 10 NCm. The screwing sequence was performed from the central pillar towards the distal ones. The force (Ncm) necessary for counter-torque was evaluated using a digital torque meter (TQ3000; Lutron, Taipei, Taiwan). This procedure was carried out before and after rectification of the seating base of the prosthetic screws, by means of a manual rectifier tip (Conexão Sistemas de Prótese, São Paulo, Brazil). The mean counter-torque values were calculated for each structure before and after rectification. The t-Test for paired samples was used to compare the evaluated situations. Results: Significant difference was observed between the mean counter-torque force value of the prosthetic screws before (5.78±1.03Ncm) and after (7.06±0.62Ncm) the rectification procedures (p<0.01). Conclusion: The rectifying process of the seating base significantly increased the values of force required to counter-torque the prosthetic screws of cast implant-retained multiple frameworks.
