Design and Mechanical Evaluation of Sutureless Implants for the Surgery Treatment of Rotator Cuff Tears.

Rotator cuff (RC) tears cause pain and functional disability of the shoulder. Despite advances in suture anchors, there are still reports about the incidence of surgical-related injuries to RC mainly associated with sutures. The purpose of this study was to design and evaluate the mechanical behavior of sutureless implants to repair RC tears. We hypothesized that the implants present mechanical characteristics suitable for the surgical treatment of RC tears as suture anchors. Three different implants (T1, T2, T3) were designed and fabricated with titanium: T1 has two rods and rectangular head; T2 has two rods with a small opening and enlarged rectangular head; and T3 has three rods and a circular head. The implants were fixed in rigid polyurethane foam blocks by a series of blows, and the applied mechanical loads along with the number of blows were quantified. Pullout tests using tapes fixed between the implant head and testing machine grip were conducted until implant failure. The maximum pullout strength and displacement of the implant relative to the rigid foam block were computed. Statistical significance was set at p < 0.05. Owing to its geometric configuration, implant T2 presented the best characteristics related to stability, strength, and ease of insertion. Implant T2 confirms our hypothesis that its mechanical behavior is compatible with that of suture anchors, which could lead to the reduction of RC repair failures and simplify the arthroscopic procedure.

Biomechanical evaluation of acromioclavicular joint reconstructions using a 3-dimensional model based on the finite element method.

BACKGROUND: This study aims to evaluate the influence of stabilization of acromioclavicular (AC) joint dislocation through the modified Weaver-Dunn technique and coracoclavicular (CC) ligaments using the finite element method. The goal is to determine which surgical technique allows behavior that is most similar to the joint, guaranteeing the necessary stability without restricting joint movements for the considered conditions. METHODS: The analysis is based on the three-dimensional finite element models. The control group of this study is represented by a three-dimensional model of the whole structure based on finite element methods. FINDINGS: The finite element models showed the stress and displacement values found in the intact acromioclavicular joint and surgical procedures. It was concluded that transferring the coracoacromial ligament to stabilize the acromioclavicular joint did not have a positive impact on the outcome. INTERPRETATION: The finite element analysis on the treatment of acromioclavicular dislocation presented here provides medical teams with new parameters for choosing a suitable surgical procedure in the occurrence of acromioclavicular dislocation. The development and validation of the finite element models allow the variation of the conditions and enables different surgical configurations to be simulated.

Mechanical Study of the Properties of Sutures used in Orthopedics Surgeries.

Objective To evaluate the mechanical properties of sutures commonly used in orthopedic surgeries, characterizing their behavior through tensile tests and determining which one has greater mechanical strength. Method Tensile tests of different sutures were performed in a mechanical testing machine BME 10 kN, using a 50 kgf maximum capacity loading cell. Seven samples from each suture material were tested. Both ends of the sample material were fixed in the proper metal claw, maintaining an initial length of 5 cm. Tests were performed at a speed of 20 mm/minute and at room temperature, recording data for maximum displacement and maximum force at the rupture point. Results FiberWire® #2 (Artrhex, Naples, FL, USA) presented the highest mean strength of rupture (240.17 N), followed by HiFi® #2 (Conmed, Utica, NY, USA) (213.39N) and Ethibond® #5 (Ethicon Inc., Somerville, NJ, USA) (207.38 N). Ethibond® #2 (Ethicon Inc., Somerville, NJ, USA) had the lowest mean strength of rupture (97.8 N). Conclusion Non-absorbable braided polyblend sutures, more recently introduced, are superior to conventional, braided polyester sutures, and FiberWire® #2 is the most resistant suture evaluated in the present study.

Mechanical Study of the Properties of Sutures used in Orthopedics Surgeries / Estudo mecânico das propriedades dos fios de sutura usados em cirurgias ortopédicas

Abstract Objective To evaluate the mechanical properties of sutures commonly used in orthopedic surgeries, characterizing their behavior through tensile tests and determining which one has greater mechanical strength. Method Tensile tests of different sutures were performed in a mechanical testing machine BME 10 kN, using a 50 kgf maximum capacity loading cell. Seven samples from each suture material were tested. Both ends of the sample material were fixed in the proper metal claw, maintaining an initial length of 5 cm. Tests were performed at a speed of 20 mm/minute and at room temperature, recording data for maximum displacement and maximum force at the rupture point. Results FiberWire® #2 (Artrhex, Naples, FL, USA) presented the highest mean strength of rupture (240.17 N), followed by HiFi® #2 (Conmed, Utica, NY, USA) (213.39N) and Ethibond® #5 (Ethicon Inc., Somerville, NJ, USA) (207.38 N). Ethibond® #2 (Ethicon Inc., Somerville, NJ, USA) had the lowestmean strength of rupture (97.8 N). Conclusion Non-absorbable braided polyblend sutures, more recently introduced, are superior to conventional, braided polyester sutures, and FiberWire® #2 is the most resistant suture evaluated in the present study.

Resumo Objetivo Avaliar as propriedades mecânicas dos fios de sutura normalmente usados nas cirurgias ortopédicas e caracterizar seu comportamento por meio de ensaios de tração para verificar qual deles apresenta maior resistência mecânica. Método Os ensaios de tração dos diferentes tipos de fios de sutura foram feitos na máquina de ensaios mecânicos BME 10 kN, comcélula de carga de capacidademáxima de 50 kgf. Foram ensaiadas sete amostras de cada tipo de fio de sutura, foram fixadas cada uma das extremidades da amostra na garra metálica própria para o ensaio de fios e manteve-se o comprimento inicial de 5 cm. Os ensaios foram feitos com uma velocidade de 20 mm/minuto e à temperatura ambiente, registraram-se os dados de força máxima e o deslocamento máximo na ruptura dos fios. Resultados A força média de rupturamais elevada foi observada na sutura FiberWire® 2 (Artrhex, Naples, FL, EUA) (240,17 N), seguida pela HiFi® 2 (Conmed, Utica, NY, EUA) (213,39 N) e Ethibond® 5 (Ethicon Inc., Somerville, NJ, EUA) (207,38 N). A menor força média de ruptura foi obtida para o fio Ethibond® 2 (Ethicon Inc., Somerville, NJ, EUA) (97,8 N). Conclusão Os fios de sutura não absorvíveis de polimistura trançada, de surgimento mais recente, são superiores ao fio de sutura convencional de poliéster trançado. O FiberWire® 2 é o mais resistente dos fios avaliados no presente estudo.

Bioimpedance as an indicator in the distribution of interface pressure in vulnerable regions for pressure ulcers: A preliminary study.

AIM: To examine the influence of body mass index, bioimpedance, and skin folds on the distribution of body interface pressure in regions with the potential to develop pressure ulcers in contact with support surfaces. DESIGN: This was a descriptive and analytical study. METHODS: Twenty healthy volunteer adults were investigated in April 2017. Body mass index, skin folds, waist circumference, bioimpedance, and interface pressure on bony prominences were investigated. Descriptive statistics and correlations were analysed. RESULTS: Peak pressures in the subscapular region presented moderate and significant correlations with body mass index, waist circumference, total and extracellular body water, fat-free mass, and lean mass per body segment. The peak pressure on the right heel showed a moderate correlation with total and extracellular body water, fat-free mass, and lean mass per segment. CONCLUSION: The need for multicenter research was evident, focusing on bioimpedance assessment as a risk factor for the development of pressure ulcers.

Influence of support surfaces on the distribution of body interface pressure in surgical positioning.

OBJECTIVE: to evaluate the interface pressure (IP) of support surfaces (SSs) on bony prominences. METHOD: a quasi-experimental study with repeated measures on each SS. Twenty healthy adult volunteers participated in the study. The participants were placed in the supine position on a standard operating table for evaluation of IP on the bony prominences of the occipital, subscapular, sacral, and calcaneal regions using sensors. Seven evaluations were performed for each bony prominence: one on a standard operating table, and the others on tables containing SSs made of viscoelastic polymer, soft foam, or sealed foam. Descriptive statistics and analysis of variance were used to analyze the data. RESULTS: the mean IP was higher on the viscoelastic polymer-based SS compared to the other SSs (p<0.001). The mean IP was relatively lower on the density-33 sealed foam and density-18 soft foam. In addition, this variable was comparatively higher in the sacral region (42.90 mmHg) and the calcaneal region (15.35 mmHg). CONCLUSION: IP was relatively lower on foam-based SSs, especially on density-18 soft foam and density-33 sealed foam. Nonetheless, IP was not reduced on the viscoelastic polymer SS compared to the control SS.

Comparative analysis of stress distribution in different prosthetic solutions for Kennedy class I bilateral posterior edentulous arches / Análise comparativa da distribuição de tensão em diferentes soluções protéticas para desdentado posterior bilateral "classe I de Kennedy"

One of greatest challenges of dentists is the rehabilitation of free-end Kennedy class I and class II patients due to the improper occurrence of stress around the supporting structures of conventional removable dentures during mastication. This work aimed to compare the stress distribution in different prosthetic solutions. For this analysis, four photoelastic models (PM) were produced simulating a Kennedy class I arch with the remaining teeth 34 through 44. In all models, teeth 33, 34, 43, and 44 received metal crowns. In addition to the crowns, the A model (PMA) received a conventional removable partial denture (RPD), the B model (PMB) received a RPD associated with a semi-rigid attachment, the C model (PMC) received a RPD associated with a rigid attachment, and the D model (PMD) received a RPD associated with implant and rigid attachment. Evenly distributed loads were applied on the last artificial tooth of the prostheses. Based on the results of the distributed load, the conventional prosthesis presented the best results for all regions (averages ranging from 25.70 to 17.80), followed by the prosthesis associated with the implant, the prosthesis associated with the rigid attachment, and lastly, the prosthesis associated with the semi-rigid attachment. The same result can be observed in the localized load, where the conventional prosthesis presented superior results in all regions (averages ranging from 47.35 to 8.30), followed by the prosthesis associated with the implant, the prosthesis associated with the rigid attachment and, with the prosthesis associated with the semi-rigid attachment. Based on the data obtained, it may be concluded that the conventional RPD presented a balanced stress distribution in the three regions analyzed, and when associated with the semi-rigid attachment, it presented a more favorable behavior than that associated with the rigid attachment.

Um dos maiores desafios para os cirurgiões-dentistas consiste na reabilitação de pacientes com extremidade livre classe I e classe II de Kennedy, devido à ocorrência inadequada de tensão em torno das estruturas de suporte das próteses removíveis convencionais durante o processo da mastigação. O objetivo deste trabalho foi analisar comparativamente a distribuição de tensão em diferentes soluções protéticas. Para essa análise, foram confeccionados quatro Modelos Fotoelásticos (MF) simulando um arco classe I de Kennedy, e tendo como dentes remanescentes do dente 34 ao 44. Em todos os modelos, os dentes 33, 34, 43 e 44 receberam coroas metálicas. Além das coroas, o modelo A (MFA) recebeu uma Prótese Parcial Removível (PPR) convencional, o modelo B (MFB) recebeu uma PPR associada a encaixe semirrígido, o modelo C (MFC) recebeu uma PPR associada a encaixe rígido e o modelo D (MFD) recebeu uma PPR associada a implante e encaixe rígido. Foram aplicadas cargas uniformemente distribuídas e localizadas no último dente artificial das próteses. Baseado nos resultados da carga distribuída, a prótese convencional apresentou os melhores resultados para todas as regiões (médias variando entre 25,70 e 17,80), seguida da prótese associada ao implante, a prótese associada ao encaixe rígido e, finalmente, com a prótese associada ao encaixe semirrígido. O mesmo resultado pode ser observado na carga localizada, onde a prótese convencional apresentou resultados superiores em todas as regiões (médias variando entre 47,35 e 8,30), seguida da prótese associada ao implante, a prótese associada ao encaixe rígido e, finalmente, com a prótese associada ao encaixe semirrígido. Baseado nos dados obtidos pôde-se concluir que a PPR convencional apresentou uma distribuição equilibrada de tensões nas três regiões analisadas e, quando associado à fixação semi-rígida, apresentou um comportamento mais favorável do que aquele associado à fixação rígida.

Influence of support surfaces on the distribution of body interface pressure in surgical positioning / Influência das superfícies de apoio na distribuição da pressão de interface corporal durante o posicionamento cirúrgico / Influencia de las superficies de apoyo en la distribución de presión de la interfaz corporal durante el posicionamiento quirúrgico *

Abstract Objective: to evaluate the interface pressure (IP) of support surfaces (SSs) on bony prominences. Method: a quasi-experimental study with repeated measures on each SS. Twenty healthy adult volunteers participated in the study. The participants were placed in the supine position on a standard operating table for evaluation of IP on the bony prominences of the occipital, subscapular, sacral, and calcaneal regions using sensors. Seven evaluations were performed for each bony prominence: one on a standard operating table, and the others on tables containing SSs made of viscoelastic polymer, soft foam, or sealed foam. Descriptive statistics and analysis of variance were used to analyze the data. Results: the mean IP was higher on the viscoelastic polymer-based SS compared to the other SSs (p<0.001). The mean IP was relatively lower on the density-33 sealed foam and density-18 soft foam. In addition, this variable was comparatively higher in the sacral region (42.90 mmHg) and the calcaneal region (15.35 mmHg). Conclusion: IP was relatively lower on foam-based SSs, especially on density-18 soft foam and density-33 sealed foam. Nonetheless, IP was not reduced on the viscoelastic polymer SS compared to the control SS.

RESUMO Objetivo: valiar a pressão de interface (PI) das superfícies de apoio (SAs) em proeminências ósseas. Método: um estudo quase experimental com medidas repetidas em diferentes SAs. Vinte voluntários adultos saudáveis participaram do estudo. Os participantes foram colocados em decúbito dorsal em uma mesa cirúrgica para avaliação da PI nas proeminências ósseas das regiões occipital, subescapular, sacral e calcânea utilizando sensores. Sete avaliações foram realizadas para cada proeminência óssea: uma avaliação em uma mesa de operação padrão e as outras avaliações em mesas contendo SAs à base de polímero viscoelástico, espuma macia, ou espuma selada. Estatística descritiva e análise de variância foram utilizadas para analisar os dados. Resultados: a PI média foi maior na SA feita de polímero viscoelástico em comparação com as outras SAs (p<0,001). A PI média foi relativamente menor na espuma selada de densidade 33 e na espuma macia de densidade 18. Além disso, essa variável foi comparativamente maior na região sacral (42,90 mmHg) e na região calcânea (15,35 mmHg). Conclusão: a PI foi menor em SAs à base de espuma, especialmente espuma macia de densidade 18 e espuma selada de densidade 33. No entanto, a PI não foi reduzida na SA à base de polímero viscoelástico comparado com a SA controle.

RESUMEN Objetivo: evaluar la presión de interfaz (PI) de las superficies de apoyo (SAs) en prominencias óseas. Método: un estudio casi experimental con medidas repetidas en diferentes SAs. Veinte voluntarios adultos saludables participaron del estudio. Los participantes fueron colocados en decúbito dorsal en una mesa quirúrgica para evaluación de la PI en las prominencias óseas de las regiones occipital, subescapular, sacra y calcánea utilizando sensores. Siete evaluaciones fueron realizadas para cada prominencia ósea: una evaluación en una mesa de operación estándar y otras evaluaciones en mesas que contenían SAs a base de polímero viscoelástico, espuma blanda, o espuma sellada. Fueron utilizadas la estadística descriptiva y el análisis de la varianza para analizar los datos. Resultados: la PI media fue mayor en la SA hecha de polímero viscoelástico en comparación con las otras SAs (p<0,001). La PI media fue relativamente menor en la espuma sellada de densidad 33 y en la espuma blanda de densidad 18. Además, esa variable fue comparativamente mayor en la región sacra (42,90 mmHg) y en la región calcánea (15,35 mmHg). Conclusión: la PI fue menor en SAs a base de espuma, especialmente espuma blanda de densidad 18 y espuma sellada de densidad 33. Sin embargo, la PI no fue reducida en la SA a base de polímero viscoelástico comparado con la SA control.

Influence of Screw Surface Treatment on Retention of Implant-Supported Fixed Partial Dentures.

The aim of this study was to assess the effect of a diamond-like carbon (DLC) coating on the removal torque of prefabricated implant screws after cyclic loading. Four groups with two crowns supported by two implants (n = 5) were obtained according to splinted and nonsplinted prosthesis, using titanium or DLC screws (splinted crowns with titanium screw [STi], splinted crowns with DLC screw [SC], nonsplinted crowns and titanium screw [NSTi], and nonsplinted crowns and DLC screw [NSC]). The prosthetic screws were tightened at 32 Ncm and retightened, and the specimens were submitted to 106 mechanical cycles (4 Hz/98 N). After cyclic loading, loosening torque was evaluated, and the final measurements were performed. Data were analyzed by two-way analysis of variance and Tukey's test (α = .005). There was statistically significance in the interaction of screw × splinting (P = .003). For the group that used titanium screws, NSTi showed smaller removal torque compared with STi. It was concluded that the use of the DLC coating screws in nonsplinted prosthesis maintain the torque after cyclic loading.

Support surfaces in the prevention of pressure ulcers in surgical patients: An integrative review.

AIM: To assess the scientific evidence about the types of support surfaces used in intraoperative surgical practice in the prevention of pressure ulcers due to surgical positioning. METHOD: This is an integrative literature review. The electronic databases Cochrane, PubMed, Web of Science, Scopus, Lilacs, and CINAHL were used. The descriptors surgical patients, support surfaces, perioperative care, patient positioning, and pressure ulcer were used in the search strategy. Articles that addressed the use of support surfaces intraoperatively, published between 1990 and 2016, were selected. The PRISMA guidelines were used to structure the review. RESULTS: Of 18 evaluated studies, most were in English, followed by Portuguese and Spanish; most were performed by nurses. The most commonly cited support surfaces were viscoelastic polymer, micropulse mattresses, gel based mattresses, and foam devices. CONCLUSION: There are gaps in knowledge regarding the most efficient support surfaces and the specifications of the products used to prevent pressure ulcers due to surgical positioning.

Fracture Resistance of Internal Conical and External Hexagon: Regular and Narrow Implant-Abutment Assemblies.

PURPOSE: The aim of this study was to compare the maximum load on the elastic limit of internal conical (IC) implants with regular external hexagon (REH) and narrow external hexagon (NEH) implants. MATERIALS AND METHODS: Thirty cylindrical implants were divided in 3 groups (n = 10): REH (3.75 mm); NEH (3.3 mm); IC (3.5 mm). The implants were evaluated by means of cantilever bending loads using a mechanical testing machine. A strain qualitative analysis and the corresponding angles were analyzed. Using single factor analysis of variance with Tukey Test and Friedman Test (P < 0.05) the statistical analysis for data were performed. RESULTS: REH (294.37 N) and IC (294.37 N) groups presented statistically greater Fle than NEH (189.16 N). Regarding to the strain, there were no significant differences among groups. However, there were a greater number of fissures and more fractures present on NEH group. CONCLUSION: The IC implant with smaller diameter did not result in reduction of elastic limit when compared with the REH implants. Nevertheless, the reduction of 0.45 mm of the hexagonal connection implant's diameter has significantly diminished the elastic limit.

Stress distribution in implant-supported prostheses using different connection systems and cantilever lengths: digital photoelasticity.

Photoelastic analysis was used to evaluate the biomechanical behaviour of implant-supported, double-screwed crowns with different connection systems and cantilever lengths. Three models were made in PL-2 photoelastic resin and divided into six groups, on the basis of the implant connection system (external hexagon [EH] or Morse taper [MT]), type of abutment (Mini Pilar [Neodent, Curitiba, Paraná, Brazil] or "UCLA") and number of crowns in the cantilever (one or two). The implant-prosthesis unit was placed in a circular polariscope. Occlusal surfaces of the crowns were subjected to 100-N loads in the axial and oblique (45°) directions in a universal testing machine (EMIC). Generated stresses were recorded and analysed qualitatively in a graphics program (Adobe Photoshop). Under axial loading, all of the groups had similar numbers of fringes, which were increased when the crowns were subjected to oblique loading. The highest number of fringes was found during oblique loading in the EH + Mini Pilar group. In conclusion, although the type of implant connection system did not have a direct influence on the stress distribution for axial loading, the cantilever length did have a direct influence on stress distribution. Models with two crowns in the cantilever showed more stress, with a greater concentration of force on the cervical part of the implant.

The influence of interproximal contact on implant-supported fixed partial dentures in the posterior jaw: a photoelastic analysis.

The aim of this study was to analyze the effect of the separation of prosthetic crowns from fixed partial dentures by means of stress gradient evaluation. Three photoelastic models were created to examine contiguous implants with varying contact between the crowns (contact point [CP], contact surface [CS], splinted [SP]). The SP group presented the best results, followed by the CS group, indicating that the use of splinted prosthetic crowns and crowns with broad surface contacts is viable when considering the stress values.

Photoelastic stress analysis of mandibular fixed prostheses supported by 3 dental implants.

PURPOSE: To observe the photoelastic stress patterns generated around implants in relation to variations in the diameter and total number of implants supporting fixed complete-arch mandibular frameworks. MATERIALS AND METHODS: Three different implant configurations were analyzed (n = 3): 5 standard implants with diameters of 3.75 mm (C), 3 standard implants with diameters of 3.75 mm (3S), and 3 wide implants with diameters of 5.0 mm (3W). The samples were subjected to a vertical compressive load (1.33 kgf) applied at the end of the distal cantilever of the framework. The shear stresses were calculated around the implants, and the data were analyzed using one-way analysis of variance. RESULTS: The implants nearest to the loading showed higher stress values regardless of the group. The C group showed lower shear stress when compared with the other groups (P = 0.001). No significant difference was observed between the 3W and 3S groups (P = 0.785). CONCLUSION: A reduction in the number of implants, regardless of the implant diameter, showed higher stress concentration around the implants. Five-implant configuration showed lower stress concentration and seems to be more biomechanically predictable.

Analysis of stress induced by screws in the vertebral fixation system.

OBJECTIVE: To compare, using photoelasticity, internal stress produced by USS II type screw with 5.2 and 6.2 mm external diameters, when submitted to three different pullout strengths. METHODS: Two photoelastic models were especially made. The simulation was performed using loads of 1.8, 2.4 e 3.3 kgf.The fringe orders were evaluated around the screws. In all the models analyzed the shear stress were calculated. RESULTS: Independently of the applied load, the smaller screw showed higher values of shear stress. CONCLUSION: According to the analysis performed, we observed that the place of highest stress was in the first thread of the lead, close to the head of the screws. Experimental study.

Analysis of stress induced by screws in the vertebral fixation system

Objective: To compare, using photoelasticity, internal stress produced by USS II type screw with 5.2 and 6.2 mm external diameters, when submitted to three different pullout strengths. Methods: Two photoelastic models were especially made. The simulation was performed using loads of 1.8, 2.4 e 3.3 kgf.The fringe orders were evaluated around the screws. In all the models analyzed the shear stress were calculated. Results: Independently of the applied load, the smaller screw showed higher values of shear stress. Conclusion: According to the analysis performed, we observed that the place of highest stress was in the first thread of the lead, close to the head of the screws. Experimental study. .

Stress distribution in Co-Cr implant frameworks after laser or TIG welding.

Lack of passivity has been associated with biomechanical problems in implant-supported prosthesis. The aim of this study was to evaluate the passivity of three techniques to fabricate an implant framework from a Co-Cr alloy by photoelasticity. The model was obtained from a steel die simulating an edentulous mandible with 4 external hexagon analog implants with a standard platform. On this model, five frameworks were fabricated for each group: a monoblock framework (control), laser and TIG welding frameworks. The photoelastic model was made from a flexible epoxy resin. On the photoelastic analysis, the frameworks were bolted onto the model for the verification of maximum shear stress at 34 selected points around the implants and 5 points in the middle of the model. The stresses were compared all over the photoelastic model, between the right, left, and center regions and between the cervical and apical regions. The values were subjected to two-way ANOVA, and Tukey's test (α=0.05). There was no significant difference among the groups and studied areas (p>0.05). It was concluded that the stresses generated around the implants were similar for all techniques.

Stress Distribution in Co-Cr Implant Frameworks after Laser or TIG Welding

Lack of passivity has been associated with biomechanical problems in implant-supported prosthesis. The aim of this study was to evaluate the passivity of three techniques to fabricate an implant framework from a Co-Cr alloy by photoelasticity. The model was obtained from a steel die simulating an edentulous mandible with 4 external hexagon analog implants with a standard platform. On this model, five frameworks were fabricated for each group: a monoblock framework (control), laser and TIG welding frameworks. The photoelastic model was made from a flexible epoxy resin. On the photoelastic analysis, the frameworks were bolted onto the model for the verification of maximum shear stress at 34 selected points around the implants and 5 points in the middle of the model. The stresses were compared all over the photoelastic model, between the right, left, and center regions and between the cervical and apical regions. The values were subjected to two-way ANOVA, and Tukey's test (α=0.05). There was no significant difference among the groups and studied areas (p>0.05). It was concluded that the stresses generated around the implants were similar for all techniques.

Resumo A falta de passividade tem sido associada a problemas biomecânicos em próteses implantossuportadas. A proposta deste estudo foi avaliar, por meio da fotoelasticidade, a influência de três diferentes de fabricação de infraestrutura em liga de Co-Cr na passividade destas. O modelo foi obtido a partir de uma matriz de aço simulando uma mandíbula edêntula com 4 análogos de implantes de hexágono externo com plataforma padrão. Neste modelo, foram confeccionados cinco amostras para cada grupo: infraestruturas em monobloco, infraestruturas soldadas a laser e soldadas a TIG. O modelo fotoelástico foi feito com uma resina epóxi flexível (GIII, Polipox Industria e Comercio Ltda.). Na análise fotoelástica, as infraestruturas foram aparafusadas no modelo para a verificação da tensão de cisalhante máxima em 34 pontos selecionados ao redor dos implantes e 5 pontos na região média do modelo. Foram comparadas as tensões em todo o modelo fotoelástico, entre as regiões direita, esquerda e centro e também entre as regiões cervical e apical. Os valores foram submetidos à análise de variância a dois critérios, seguido pelo teste de Tukey (α=0,05). Os resultados não mostraram diferença significativa entre as tensões presentes nos grupos e nas áreas estudadas. Conclui-seque as tensões geradas ao redor dos implantes foram semelhantes entre as diferentes técnicas de confecção e entre todas as regiões analisadas. .

Distribution of peri-implant stresses with a countertorque device.

PURPOSE: To verify the effectiveness of a countertorque device in dental implants in redistributing stress to the bone-implant interface during tightening of the abutment screw. MATERIALS AND METHODS: Two prismatic photoelastic samples containing implants were made, one with a 3.75-mm-diameter implant and the other with a 5.0-mm-diameter implant (both implants had an external-hexagon interface) and the respective abutments were attached (CeraOne). The samples were placed in a support and submitted to torques of 10, 20, 32, and 45 Ncm with an electronic torque meter. The torque application was repeated 10 times on each sample (n = 10) with and without a countertorque device. Photoelastic patterns were detected; thus, a photographic register of each test was selected. The fringe patterns were analyzed at discrete points near the implants' external arch. RESULTS: In both implants analyzed, a stress gradient reduction was observed through the implant with the countertorque device. CONCLUSIONS: The countertorque device used in this study proved to be effective in reducing the stresses generated in the peri-implant bone tissue during torque application.

Photoelastic stress analysis of different wide implant/abutment interfaces under oblique loading.

PURPOSE: There is a variety of implant/abutment (I/A) junctions for the connection of implant-supported prostheses. The aim of this work was to compare the shear stress distribution in three types of I/A interfaces after application of oblique loading on the abutments, simulating loading on an anterior tooth. MATERIALS AND METHODS: Similar wide unthreaded and cylindric implants (13.0 mm in length and 5.0 mm in diameter) and abutments were fabricated and embedded in photoelastic acrylic resin. The I/A assemblies featured three different I/A interfaces: external hex, internal hex, and internal taper. The samples were submitted to a compressive load of 0.6 kgf, which was applied to the abutment at an angle of 135 degrees. The maximum shear stresses were determined and observed at 21 points around the implants in the photoelastic models (n = 4). Graphics describing the maximum shear stress (y-axis) and the analyzed points (x-axis) were created, and the curve areas were calculated. The Kruskal-Wallis test was applied to analyze the results (P < .05). RESULTS: There were no statistically significant differences between the groups (P = .058). CONCLUSION: All of the wide-diameter I/A junctions presented similar behavior under oblique loading and appeared to be suitable to support prostheses that could receive this type of loading.