Validation of an experimental polyurethane model for biomechanical studies on implant-supported prosthesis: compression tests

OBJECTIVES: The complexity and heterogeneity of human bone, as well as ethical issues, most always hinder the performance of clinical trials. Thus, in vitro studies become an important source of information for the understanding of biomechanical events on implant-supported prostheses, although study results cannot be considered reliable unless validation studies are conducted. The purpose of this work was to validate an artificial experimental model based on its modulus of elasticity, to simulate the performance of human bone in vivo in biomechanical studies of implant-supported prostheses. MATERIAL AND METHODS: In this study, fast-curing polyurethane (F16 polyurethane, Axson) was used to build 40 specimens that were divided into five groups. The following reagent ratios (part A/part B) were used: Group A (0.5/1.0), Group B (0.8/1.0), Group C (1.0/1.0), Group D (1.2/1.0), and Group E (1.5/1.0). A universal testing machine (Kratos model K - 2000 MP) was used to measure modulus of elasticity values by compression. RESULTS: Mean modulus of elasticity values were: Group A - 389.72 MPa, Group B - 529.19 MPa, Group C - 571.11 MPa, Group D - 470.35 MPa, Group E - 437.36 MPa. CONCLUSION: The best mechanical characteristics and modulus of elasticity value comparable to that of human trabecular bone were obtained when A/B ratio was 1:1.(FAPESP) São Paulo Research Foundatio

Comparison between calcium hydroxide mixtures and mineral trioxide aggregate in primary teeth pulpotomy: a randomized controlled trial

Objectives: To evaluate the effect of calcium hydroxide (CH) associated with two different vehicles as a capping material for pulp tissue in primary molars, compared with mineral trioxide aggregate (MTA). Methodology: Forty-five primary mandibular molars with dental caries were treated by conventional pulpotomy using one of the following materials: MTA only (MTA group), CH with saline (CH+saline group) and CH with polyethylene glycol (CH+PEG group) (15 teeth/group). Clinical and periapical radiographic examinations of the pulpotomized teeth were performed 3, 6, and 12 months after treatment. Data were tested by chi-squared analysis and a multiple comparison post-test. Results: The MTA group showed both clinical and radiographic treatment success in 14/14 teeth (100%), at all followup appointments. By clinical evaluation, no teeth in the CH+saline and CH+PEG groups had signs of mobility, fistula, swelling or inflammation of the surrounding gingival tissue. However, in the CH+saline group, radiographic analysis detected internal resorption in up to 9/15 teeth (67%), and interradicular bone resorption and furcation radiolucency in up to 5/15 teeth (36%), from 3 to 12 months of follow-up. In the CH+PEG group, 2/11 teeth (18%) had internal resorption and 1/11 teeth (9%) presented bone resorption and furcation radiolucency at all follow-up appointments. Conclusion: CH with PEG performed better than CH with saline as capping material for pulpotomy of primary teeth. However, both combinations yielded clinical and radiographic results inferior to those of MTA alone

Optimum passivity levels of implant prosthesis according to abutment deformation

O assentamento passivo tem sido considerado um dos mais importantes requisitos para o sucesso de próteses implanto-suportada. Este estudo in vitro investigou a deformação do intermediário de prótese implantosuportada após o aperto do parafuso tanto do cilindro de Paládio-Prata como de Cobalto-Cromo. Um modelo mestre foi usado para simular uma mandíbula humana com cinco implantes. Extensômetros foram colados nas faces mesial e distal de cada intermediário para registrar as deformações causadas pelos cilindros após o aperto dos parafusos. Os intermediários foram montados sobre as réplicas dos implantes e os parafusos foram apertados com um torque de 20 Ncm e as leituras foram gravadas. Após este passo, os parafusos tanto dos cilindros de Paládio-Prata como de Cobalto-Cromo foram apertados com um torque de 10 Ncm e as leituras também foram gravadas. Estas medições foram repetidas por cinco vezes. O teste estatístico de Mann-Whitney foi aplicado aos resultados. Nenhuma diferença estatística foi encontrada entre as tensões geradas tanto pelos cilindros de Paládio-Prata como os de Cobalto-Cromo. No entanto, existiram diferenças com relação à qualidade da tensão. A deformação gerada pelo aperto dos parafusos dos cilindros de Cobalto-Cromo foi de compressão e o aperto dos parafusos dos cilindros de Paládio-Prata gerou forças de compressão e tração.Passive fit has been considered one of the most important requirements for the success of implant supported prostheses. This in vitro study investigated the abutment deformation of an implant-supported prosthesis after screw tightening of palladium-silver and cobalt-chromium prosthetic cylinder. A master model was used to simulate a human mandible with five implants. The Strain gauges were attached on the sides of each abutment to capture deformations because of the cylinders screws after was tightened. The abutments were mounted onto implant replicas and the screws were tightened to a 20 Ncm torque, and the readings were recorded. After this step, palladiumsilver and cobalt-chromium prosthetic cylinders were tightened to a 10 Ncm torque and the readings were recorded. The measurements were repeated five times. Mann-Whitney statistical test was applied to the results. No statistical differences were found between the deformation generated by palladium-silver and cobalt-chromium prosthetic cylinders. However, there were differences relative to the quality of the strain. The deformation generated by screw tightness of the cobalt-chromium prosthetic cylinders was compressive while palladium-silver prosthetic cylinders generated compressive and tensile strain

Evaluation of abutment and perimplantar region deformation of implant-supported screwed prostheses: an study using strain gauges

O implante dental depende do osso de suporte para sua estabilidade e ongevidade funcional. O comportamento mecânico e a estrutura trabecular do osso afetam a interface com o implante. Tal conhecimento pode fornecer uma base para melhoramentos na função e desenho dos implantes atuais minimizando a reabsorção da crista óssea e falha na junção osso-implante. Desta forma a correta quantificação das forças que atuam sobre o sistema de implante e principalmente no osso de suporte ao qual ele está inserido é importante para o entendimento da biomecânica possibilitando que intervenções possam ser realizadas pelos profissionais visando assim à longevidade das próteses implanto-suportadas bem como dos implantes que as sustentam. Por essa razão, a proposta deste trabalho foi avaliar, com auxílio de extensômetros elétricos, se o processo laboratorial de confecção de coroas metalocerâmicas resulta em alterações das tensões no osso ao redor dos implantes. Para isto foi utilizado um modelo de poliuretano em forma de U simulando o osso mandibular com dois implantes de hexágono externo de 3,75mm de diâmetro por 13 mm de comprimento, nos quais foram fixados intermediários multi-unit. Os corpos de prova foram confeccionados com dois tipos de ligas odontológicas - Cobalto-Cromo e Paládio-Prata - e três tipos de cilindros protéticos calcinável, usinado de Cobalto-Cromo e usinado de Ouro. As leituras de deformação foram realizadas em dois momentos: 1- após a fundição das infra-estruturas e 2 após estas infra-estruturas terem recebido cobertura cerâmica. Os testes foram realizados parafusando os corpos de prova sobre os intermediários utilizando-se para isto um dispositivo eletrônico de torque com força máxima de 10 Ncm. Os resultados mostraram que, após a aplicação da cobertura cerâmica, ocorreu piora da condição de assentamento aos intermediários. O mesmo não foi detectado quando se avaliou a deformação do osso simulado, já que os valores de deformação não ndicaram diferenças antes e após a aplicação da cerâmica.The dental implant depends on the supporting bone for its stability and functional longevity. Mechanical behavior and trabecular bone structure affect the interface with the implant. Such knowledge may provide a basis for improvements in the current implant function and design, decreasing bone crest resorption and failure at bone-implant junction. Adequate quantification of forces that act upon the implant system and mainly on the supporting bone is important for understanding the biomechanics, allowing the intervention by professionals with the purpose of achieving the longevity of implant-supported prostheses. Therefore, this work aims at evaluating, with the aid of strain gauges, whether the laboratorial process of metal ceramic crown fabrication results in changes of the tensions around the implants. A U-shaped polyurethane model simulating the mandibular bone with two 3.75-mm diameter and 13-mm length external hexagon implants were used with fixed multi-unit abutments. Specimens were prepared with two types of dental alloys - cobalt-chromium and silver-palladium - and three types of prosthetic cylinder castable plastic, prefabricated in cobalt-chromium or gold. The deformation readings were performed in two moments: 1- after framework casting and 2- after ceramic layering of the framework. The tests were performed with the framework screwed onto the abutments at 10Ncm using an electronic torque device. The results showed that the ceramic layering worsened the fit between the crowns and the abutments. The same was not detected when bone deformation was evaluated since the values were not statistically different

Rely XTM U200 versus Rely XTM ARC: uma comparação da resistência à microtração

Resumo Introdução Os cimentos resinosos são extensivamente utilizados na fixação de restaurações indiretas de cerâmica e cerômero, sendo classificados em duas categorias: os cimentos resinosos convencionais, que não apresentam uma adesão inerente à estrutura dental e requerem o uso de um sistema adesivo e os cimentos resinosos autoadesivos, que não requerem um tratamento adesivo prévio do substrato dentário. Objetivo Avaliar a resistência de união de dois cimentos resinosos, convencional e autoadesivo, quando utilizados na cimentação de restaurações cerâmicas e ceroméricas, trazendo elementos para propiciar melhor compreensão da interação adesiva em procedimentos de cimentação com as referidas categorias de cimentos resinosos. Material e método Dentes humanos (n=20), cedidos pelo banco de dentes da Universidade Federal de Alfenas (UNIFAL), foram preparados para que cilindros de cerâmica ou de cerômero fossem cimentados utilizando-se dois tipos de cimentos resinosos (autoadesivo e convencional). Após a cimentação, 20 palitos foram obtidos e submetidos ao teste de tração, avaliando-se a força necessária para a fratura. Os valores obtidos foram submetidos à análise estatística empregando-se a análise de variância (ANOVA) e o teste de Tukey. Resultado As forças mínimas e máximas necessárias ao rompimento do cimento convencional foram superiores às mesmas requeridas para o rompimento da união promovida pelo cimento autoadesivo, bem como as medianas e as médias aritméticas, independentemente do material restaurador empregado. O teste de Tukey demonstrou que as diferenças entre os cimentos empregados são estatisticamente significantes, independentemente do material restaurador. Conclusão Os resultados deste trabalho sugerem que o material utilizado para a confecção dos corpos de prova (cerâmica ou cerômero) não influenciou na resistência à tração, sendo que o cimento convencional apresentou valores superiores de resistência

Effect of cantilever length and alloy framework on the stress distribution in peri-implant area of cantilevered implant-supported fixed partial dentures

Because many mechanical variables are present in the oral cavity, the proper load transfer between the prosthesis and the bone is important for treatment planning and for the longevity of the implant-supported fixed partial denture. Objectives To verify the stress generated on the peri-implant area of cantilevered implant-supported fixed partial dentures and the potential effects of such variable. Material and Methods A U-shaped polyurethane model simulating the mandibular bone containing two implants (Ø 3.75 mm) was used. Six groups were formed according to the alloy’s framework (CoCr or PdAg) and the point of load application (5 mm, 10 mm and 15 mm of cantilever arm). A 300 N load was applied in pre-determined reference points. The tension generated on the mesial, lingual, distal and buccal sides of the peri-implant regions was assessed using strain gauges. Results Two-way ANOVA and Tukey statistical tests were applied showing significant differences (

Effect of cantilever length and alloy framework on the stress distribution in peri-implant area of cantilevered implant-supported fixed partial dentures

ABSTRACT Because many mechanical variables are present in the oral cavity, the proper load transfer between the prosthesis and the bone is important for treatment planning and for the longevity of the implant-supported fixed partial denture. Objectives To verify the stress generated on the peri-implant area of cantilevered implant-supported fixed partial dentures and the potential effects of such variable. Material and Methods A U-shaped polyurethane model simulating the mandibular bone containing two implants (Ø 3.75 mm) was used. Six groups were formed according to the alloy’s framework (CoCr or PdAg) and the point of load application (5 mm, 10 mm and 15 mm of cantilever arm). A 300 N load was applied in pre-determined reference points. The tension generated on the mesial, lingual, distal and buccal sides of the peri-implant regions was assessed using strain gauges. Results Two-way ANOVA and Tukey statistical tests were applied showing significant differences (p<0.05) between the groups. Pearson correlation test (p<0.05) was applied showing positive correlations between the increase of the cantilever arm and the deformation of the peri-implant area. Conclusions This report demonstrated the CoCr alloy shows larger compression values compared to the PdAg alloy for the same distances of cantilever. The point of load application influences the deformation on the peri-implant area, increasing in accordance with the increase of the lever arm

Implant Abutment Deformation During Prosthetic Cylinder Screw Tightening: An In Vitro Study

Purpose: Nonpassive fit frameworks are believed to lead to implant overload and consequently loss of osseointegration. This is one of the most commonly reported failures of implant prostheses. In an ideal situation of passive fit, when torque is applied to bring the abutment-cylinder interface together some amount of deformation can be expected, and it should be homogeneous along the periphery of the abutment. The aim of this study was to verify the amount of abutment deformation that can be expected when a free-standing cylinder is screwed into place. This could give insight into what should be accepted as passive fit. Materials and Methods: Strain gauges were bonded to the sides of five standard abutments that had machined palladium-silver cylinders or cobalt-chromium cast cylinders screwed into place. Measurements were taken to verify the deformation at each site. Results: Values of abutment deformation after abutment screw tightening ranged from -127.70 to -590.27 mu epsilon. The deformation recorded for palladium-silver prosthetic cylinder tightening ranged from 56.905 to -381.50 mu epsilon (mean: 173.298 mu epsilon) and from -5.62638 to -383.86 mu epsilon ( mean: 200.474 mu epsilon) for cobalt-chromium cylinders. There was no statistically significant difference among the two groups. Conclusion: Both abutment screw tightening and prosthetic cylinder screw tightening result in abutment deformation, which is compressive most of the time. Int J Prosthodont 2009; 22: 391-395

In vivo qualitative analysis of the biocompatibility of different cyanoacrylate-based adhesives

Cyanocrylates have been widely used in the medical and dental fields for several years. In Dentistry, cyanoacrylates have been used for suturing, pulp capping, as retrofilling material in endodontic surgeries, and as cervical plug for pulpless teeth bleaching. The biocompatibility of these adhesives has been the topic of many researches and subcutaneous implantation is an effective methodology for these studies. The present study evaluated the biocompatibility of three different cyanoacrylate-based adhesives. Thirty-six Wistar rats were used, divided into four groups of 9 animals each: A (control) - distilled water, B - cyanoacrylate ester (Super Bonder), C - n-butyl-cyanoacrylate (Histoacryl) and D - alpha-cyanoacrylate (Three Bond). The materials were dispensed in sponges of polyvinyl chloride, the animals were incised and the sponges were inserted in the subcutaneous tissue and sutured. Each group was sub-divided according to the time of sacrifice of the animals: 7, 21 and 45 days. Subjective analysis of the histologic material showed that all groups presented some degree of irritability, but the inflammatory reaction decreased with the experimental time in all groups. Group D showed an inflammatory reaction which was closer to that of the control group and was considered to have good biocompatibility. Groups B and C were similar and presented more aggressive inflammatory reactions when compared to the control group. Based on the results, it was concluded that alpha-cyanoacrylate (Three Bond) was the most biocompatible adhesive because it caused the lowest levels of inflammation

Dental bleaching gels do not alter the surface roughness and microhardness of feldspathic porcelain

ABSTRACT Objective: To evaluate whether two different bleaching gels affect the microhardness and surface roughness of feldspathic ceramic specimens, in vitro. Methods: A total of 48 feldspathic porcelain IPS In Line (Ivoclar-Vivadent) discs (16/treatment group) were immersed in distilled water (Group I, Untreated control, UN), or treated with the bleaching gels: Opalescence (15% carbamide peroxide; OPA) and Opalescence Xtra Boost (38%hydrogen peroxide; OPAXB), for 1h or 6h daily for 14 days. Surface roughness (Ra) and microhardness (Knoop, or KNP) measurements were made before and after treatment, and data were subjected to statistical analysis by paired Student’s t-test (p < 0.05). Results: Treatments using Opalescence and Opalescence Xtra Boost did not altered surface roughness (p=0.6199861) or microhardness (p=0.14286744) of the feldspathic porcelain tested in this study. Conclusion: Bleaching treatments using Opalescence and Opalescence Xtra Boost may be suitable for treatment in patients having ceramic prosthodontic treatment. Conclusion: Bleaching treatments using Opalescence and Opalescence Xtra Boost may be suitable for treatment in patients having ceramic prosthodontic treatment