Avaliação do efeito de tratamentos superficiais sobre a força de adesão de braquetes em provisórios de resina acrílica Assessment of the effect of different surface treatments on the bond strength of brackets bonded to acrylic resin

OBJETIVO: avaliar a influência do tratamento de superfície de resinas acrílicas na resistência ao cisalhamento de braquetes colados com resina composta. MÉTODOS: foram confeccionados 140 discos de resina acrílica autopolimerizável (Duralay®), divididos aleatoriamente em 14 grupos (n=10). Em cada grupo, os corpos de prova receberam um tipo diferente de tratamento de superfície: grupo 1 = sem tratamento de superfície (controle); grupo 2 = silano; grupo 3 = jato de óxido de alumínio (JOA); grupo 4 = JOA + silano; grupo 5 = broca diamantada; grupo 6 = broca diamantada+ silano; grupo 7 = ácido fluorídrico; grupo 8 = ácido fluorídrico + silano; grupo 9 = ácido fosfórico; grupo 10 = ácido fosfórico + silano; grupo 11 = monômero de metilmetacrilato (MMA); grupo 12 = MMA + silano; grupo 13 = Plastic conditioner (Reliance®); grupo 14 = Plastic conditioner (Reliance®) + silano. Após o preparo de superfície, os corpos de prova foram analizados através da rugosimetria. Posteriormente, foram colados braquetes (Morelli®) de incisivo central "standard edgewise" com resina fotopolimerizável Transbond XT®; de acordo com as instruções do fabricante. RESULTADOS: o agente umectante à base de silano não teve um efeito estatisticamente significativo sobre os valores de força de adesão; os tratamentos com JOA e broca produziram maiores mudanças topográficas na superfície da resina acrílica, bem como os maiores valores de rugosidade; observou-se uma correlação não linear entre a força de adesão e a rugosidade de superfície; tratamentos com monômero e JOA resultaram nas maiores forças de adesão. CONCLUSÕES: o silano não foi capaz de aumentar a força de adesão entre braquete e resina acrílica. Sugere-se mais estudos sobre este tema, pois a força de adesão obtida foi muito baixa.<br>OBJECTIVE: To evaluate the influence of the surface treatment of acrylic resins on the shear bond strength of brackets bonded with composite resin. METHODS: Were fabricated 140 discs with autopolymerizing acrylic resin (Duralay™) and divided into 14 groups (n = 10). In each group, the specimens received a different type of surface treatment. Group 1= untreated surface (control), group 2= silane, group 3= aluminum oxide blasting (AOB), group 4= AOB + silane, group 5= diamond bur, group 6= diamond bur + silane, group 7= hydrofluoric acid, group 8= hydrofluoric acid + silane, group 9= phosphoric acid, group 10= phosphoric acid + silane, group 11= methylmethacrylate monomer (MMA), group 12= MMA + silane, group 13= plastic conditioner (Reliance®); group 14= plastic conditioner (Reliance™) + silane. After surface treatment the specimens were analyzed using a surface roughness tester. Subsequently, standard edgewise central incisor brackets (Morelli™) were bonded using Transbond XT™ light-cure adhesive system, according to the manufacturer's instructions. RESULTS: The silane-based wetting agent had no statistically significant effect on bond strength values. Treatments with AOB and bur generated the highest topographical changes on the surface of acrylic resin as well as the highest roughness values. A nonlinear correlation was found between bond strength and surface roughness. Monomer + AOB treatment yielded the highest bond strength values. CONCLUSIONS: Silane failed to increase the bond strength between brackets and acrylic resin. We encourage further studies on this subject since the bond strength achieved in our study was extremely low

Avaliação da superfície da porcelana após a descolagem de braquetes ortodônticos Porcelain surface evaluation after debonding of orthodontic brackets

OBJETIVO: o objetivo deste trabalho foi avaliar a influência do tempo de condicionamento ácido em superfície de porcelana e o estado desta após a descolagem de braquetes ortodônticos. METODOLOGIA: foram utilizadas 20 amostras de porcelana feldspática para esmalte (Duceram-LFC) divididas em 2 grupos de acordo com o tempo de condicionamento com ácido fluorídico 10% (15 segundos e 1 minuto). Após o ataque ácido, foi aplicado silano (3M Scotchbond), adesivo resinoso (Optibond Solo Plus) e resina (Fill Magic) nestas superfícies. A descolagem foi realizada através de força de cisalhamento numa máquina universal de ensaios (DL 500 - EMIC) calibrada com velocidade fixa de 0,5mm/minuto. O índice do adesivo remanescente (ARI) nas superfícies cerâmicas e o estado destas após a remoção dos braquetes foram avaliados através de fotos digitais. RESULTADOS: no grupo 15 segundos, a força de adesão média foi de 3,63MPa, significantemente inferior à do grupo 1 minuto, que foi de 7,18MPa (p<0,0001). Todos os modos de fratura durante a descolagem foram coesivos dentro da camada de resina composta (70%) ou adesivos entre o braquete e a resina (30%). Com relação à análise do ARI, o teste do Qui-quadrado não revelou diferença estatisticamente significante entre os grupos. CONCLUSÃO: o condicionamento com ácido fluorídrico a 10% por 1 minuto, seguido da aplicação de silano, adesivo e resina foi considerado o melhor método de preparo da porcelana previamente à colagem ortodôntica.<br>AIM: the aim of this study was to evaluate the influence of acid conditioning time in porcelain surface and its characteristics after debonding of orthodontic brackets. METHODS: twenty samples of feldspathic porcelain for enamel (Duceram-LFC) were divided in 2 groups according with the amount of time of acid conditioning with hydrofluoric acid 10% (15 seconds and 1 minute). After acid etching, it was applied silane (3M Scotchbond), adhesive (Optibond Solo Plus) and resin (Fill Magic) in these surfaces. The debonding was done with shear strength through a universal testing machine (DL 500 - EMIC) calibrated with a fixed speed of 0.5mm/minute. The adhesive remnant index (ARI) in the porcelain surfaces and their characteristics after removal of the brackets were evaluated through digital pictures. RESULTS: in the 15 seconds group, the mean bond strength was 3.63Mpa, significantly lower than the 1 minute group, that was 7.18Mpa (p<0.0001). All fractures during debonding were cohesive in the composite resin layer (70%) or bond between the bracket and the resin (30%). In relation to the ARI analysis, the Chi-square test showed no statistically significant difference between both groups. CONCLUSION: conditioning with hydrofluoric acid 10% for 1 minute, followed by the application of silane, adhesive and resin was considered the best porcelain preparation method before orthodontic bonding

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AimThe SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery.MethodsThis was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin.ResultsOverall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P ConclusionOne in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease