Effect of oral exposure on chemical, physical, mechanical, and morphologic properties of clear orthodontic aligners

The dental industry is heavily committed to developing more esthetic solutions for orthodontic treatments. Invisalign is a system of transparent orthodontic aligners introduced as an alternative to conventional orthodontic fittings with brackets and metal wires. This study aimed to assess the chemical, physical, mechanical and morphologic changes in these polymeric aligners after exposure to the oral environment. Twenty-four Invisalign orthodontic aligners were equally divided into 2 groups: an in vivo aged group in which patients used aligners for 14 days and the reference group, unexposed to the oral environment. Different experimental techniques were used to study the chemical structure, the color changes and translucency, the density and subsequent volume of the aligners, mechanical properties, surface roughness, morphology and elemental composition. The data were subjected to several statistical analyses. Clear orthodontic aligners exhibit chemical stability but undergo a statistically significant optical change in color and translucency. There was a gradual increase in the water absorption rate and the dimensional variation of the polymer, indicating a strong correlation among these factors. The mechanical properties of the polymer showed a statistically significant decrease in its elastic modulus and hardness. There was a slight tendency toward increased surface roughness of the material, but no statistical differences were found between reference and aged groups. The surface morphology of the used aligners demonstrates microcracks, distortions and biofilm formation. Intraoral aging adversely affected the physical, mechanical, and morphologic properties of the Invisalign appliance.

Effect of oral exposure on chemical, physical, mechanical, and morphologic properties of clear orthodontic aligners.

INTRODUCTION: The dental industry is heavily committed to developing more esthetic solutions for orthodontic treatments. Invisalign is a system of transparent orthodontic aligners introduced as an alternative to conventional orthodontic fittings with brackets and metal wires. This study aimed to assess the chemical, physical, mechanical and morphologic changes in these polymeric aligners after exposure to the oral environment. METHODS: Twenty-four Invisalign orthodontic aligners were equally divided into 2 groups: an in vivo aged group in which patients used aligners for 14 days and the reference group, unexposed to the oral environment. Different experimental techniques were used to study the chemical structure, the color changes and translucency, the density and subsequent volume of the aligners, mechanical properties, surface roughness, morphology and elemental composition. The data were subjected to several statistical analyses. RESULTS: Clear orthodontic aligners exhibit chemical stability but undergo a statistically significant optical change in color and translucency. There was a gradual increase in the water absorption rate and the dimensional variation of the polymer, indicating a strong correlation among these factors. The mechanical properties of the polymer showed a statistically significant decrease in its elastic modulus and hardness. There was a slight tendency toward increased surface roughness of the material, but no statistical differences were found between reference and aged groups. The surface morphology of the used aligners demonstrates microcracks, distortions and biofilm formation. CONCLUSION: Intraoral aging adversely affected the physical, mechanical, and morphologic properties of the Invisalign appliance.

Surface morphology changes of acrylic resins during finishing and polishing phases.

INTRODUCTION: The finishing and polishing phases are essential to improve smoothness and shining on the surface of acrylic resins used to make removable orthodontic appliances. A good surface finishing reduces roughness, which facilitates hygiene, prevents staining and provides greater comfort to the patients. OBJECTIVE: The aim of this paper was to analyze the changes on surface morphology of acrylic resins during finishing and polishing phases. METHODS: Thirty discs (10 mm in diameter and 5 mm in length) were made with acrylic resin and randomly divided into ten groups. The control group did not receive any treatment while the other groups received gradual finishing and polishing. The last group received the entire finishing and polishing procedures. Surface morphology was qualitatively analyzed through scanning electron microscopy and quantitatively analyzed through a laser profilometer test. RESULTS: The acrylic resin surfaces without treatment showed bubbles which were not observed in the subsequent phases. Wearing out with multilaminated burs, finishing with wood sandpaper and finishing with water sandpaper resulted in surfaces with decreasing irregularities. The surfaces that were polished with pumice and with low abrasive liquids showed high superficial smoothness. CONCLUSIONS: Highly smooth acrylic resin surfaces can be obtained after mechanical finishing and polishing performed with multilaminated burs, wood sandpaper, water sandpaper, pumice and low abrasive liquids.

Surface morphology changes of acrylic resins during finishing and polishing phases

INTRODUCTION: The finishing and polishing phases are essential to improve smoothness and shining on the surface of acrylic resins used to make removable orthodontic appliances. A good surface finishing reduces roughness, which facilitates hygiene, prevents staining and provides greater comfort to the patients. OBJECTIVE: The aim of this paper was to analyze the changes on surface morphology of acrylic resins during finishing and polishing phases. METHODS: Thirty discs (10 mm in diameter and 5 mm in length) were made with acrylic resin and randomly divided into ten groups. The control group did not receive any treatment while the other groups received gradual finishing and polishing. The last group received the entire finishing and polishing procedures. Surface morphology was qualitatively analyzed through scanning electron microscopy and quantitatively analyzed through a laser profilometer test. RESULTS: The acrylic resin surfaces without treatment showed bubbles which were not observed in the subsequent phases. Wearing out with multilaminated burs, finishing with wood sandpaper and finishing with water sandpaper resulted in surfaces with decreasing irregularities. The surfaces that were polished with pumice and with low abrasive liquids showed high superficial smoothness. CONCLUSION: Highly smooth acrylic resin surfaces can be obtained after mechanical finishing and polishing performed with multilaminated burs, wood sandpaper, water sandpaper, pumice and low abrasive liquids.

INTRODUÇÃO: as etapas de acabamento e polimento são essenciais para a obtenção de lisura e brilho da superfície de resinas acrílicas utilizadas na confecção de aparelhos ortodônticos. O bom acabamento da resina facilita a higiene, previne o manchamento e propicia maior conforto ao paciente. OBJETIVO: o objetivo desse trabalho foi analisar as alterações na morfologia superficial de resinas acrílicas (Clássico, São Paulo) durante as etapas do acabamento e polimento mecânico. MÉTODOS: foram confeccionados 30 discos (10mm de diâmetro e 5mm de altura) de resina acrílica autopolimerizável, que foram divididos aleatoriamente em dez grupos. O grupo controle não recebeu nenhum tratamento. Os demais grupos receberam acabamento e polimento graduais. O último grupo recebeu todo o tratamento de acabamento e polimento. A morfologia superficial foi avaliada qualitativamente por microscopia eletrônica de varredura e quantitativamente pela análise da rugosidade superficial. RESULTADOS: as superfícies de resina acrílica sem tratamento apresentaram bolhas, as quais não foram observadas nas fases subsequentes. O desgaste com fresa multilaminada seguido de acabamento com lixa de madeira e lixa d'água produziram superfícies com irregularidades decrescentes. As superfícies polidas com branco de Espanha e líquido de baixa abrasividade (Kaol) apresentaram bom acabamento superficial. CONCLUSÃO: é possível obter resina acrílica com alta lisura superficial após acabamento e polimento mecânico com fresas, lixas de madeira, lixas d'água, branco de Espanha e líquidos de baixa abrasividade (Kaol).

Nanostructured severe plastic deformation processed titanium for orthodontic mini-implants.

Titanium mini-implants have been successfully used as anchorage devices in Orthodontics. Commercially pure titanium (cpTi) was recently replaced by Ti-6Al-4V alloy as the mini-implant material base due to the higher strength properties of the alloy. However, the lower corrosion resistance and the lower biocompatibility have been lowering the success rate of Ti-6Al-4V mini-implants. Nanostructured titanium (nTi) is commercially pure titanium that was nanostructured by a specific technique of severe plastic deformation. It is bioinert, does not contain potentially toxic or allergic additives, and has higher specific strength properties than any other titanium applied in medical implants. The higher strength properties associated to the higher biocompatibility make nTi potentially useful for orthodontic mini-implant applications, theoretically overcoming cpTi and Ti-6Al-4V mini-implants. The purposes of the this work were to process nTi, to mechanically compare cpTi, Ti-6Al-4V, and nTi mini-implants by torque test, and to evaluate both the surface morphology and the fracture surface characteristics of them by SEM. Torque test results showed significant increase in the maximum torque resistance of nTi mini-implants when compared to cpTi mini-implants, and no statistical difference between Ti-6Al-4V and nTi mini-implants. SEM analysis demonstrated smooth surface morphology and transgranular fracture aspect for nTi mini-implants. Since nanostructured titanium mini-implants have mechanical properties comparable to titanium alloy mini-implants, and biocompatibility comparable to commercially pure titanium mini-implants, it is suggestive that nanostructured titanium can replace Ti-6Al-4V alloy as the material base for mini-implants.

Sequential bone healing of immediately loaded mini-implants.

INTRODUCTION: The relatively small size and the ability to load mini-implants without delay are important changes in the simplification of bone rigid anchorage. The purpose of this study was to analyze interfacial healing 1, 4, and 12 weeks after the placment of titanium mini-implants in New Zealand rabbits by removal torque test (RTT) and scanning electron microscopy (SEM). METHODS: Eighteen animals were used in the experiment, in which 72 titanium grade 5 mini-implants 2.0 mm in diameter and 6.0 mm long, were placed. Each animal received 4 mini-implants; 2 were immediately loaded with 1 N. RESULTS: The RTT means for the unloaded mini-implants at 1, 4, and 12 weeks were 15.2 +/- 4.2 N mm (n = 5), 13.1 +/- 5.7 N mm (n = 5), and 54.4 +/- 12.8 N mm (n = 4), respectively. The loaded groups had means of 12.7 +/- 5.1 N mm (n = 4), 11.1 +/- 5.4 N mm (n = 4), and 32.9 +/- 12.8 N mm (n = 5) for the same healing periods, respectively. The statistical evaluation indicated significance in the comparison between loaded and unloaded 12-week groups (P <0.05). SEM analysis in the loaded group showed the formation of less fibrous interfacial tissue after 4 weeks and more lamellar appearance after 12 weeks. CONCLUSIONS: The immediate 1-N load did not cause significant changes in the fixation of the mini-implants after 1 and 4 weeks of bone healing. Nevertheless, after 12 weeks, the loaded group had significantly lower RTT values than the unloaded group without compromising the stability of the mini-implants (P <0.05).

Finalização ortodôntica: uma análise contemporânea / Orthodontic finishing: a contemporary view

O tratamento ortodôntico corretivo pode ser dividido em cinco fases: diagnóstico e planejamento, alinhamento e nivelamento, correção da relação molar e fechamento de espaços, finalização e contenção. A finalização ortodôntica é o estágio do tratameto no qual pequenas alterações são corrigidas, buscando aproximar-se o máximo possível da oclusão normal, possibilitando saúde, estética, função e estabilidade. Os procedimentos empregados nesta fase variam de acordo com a técnica empregada e com a maloclusão do paciente. Devido à grande variedade de técnicas presentes na Ortodontia contemporânea, várias correções são propostas durante a finalização. Recomenda-se que esta fase se inicie com a observação completa das arcadas dentárias e que em seguida seja escolhido o mecanismo da correção apropriado. O objetivo deste trabalho foi destacar aspectos importantes na finalização ortodôntica, propondo uma sequência de detalhes a serem observados, bem como algumas sugestões para solucionar pequenos problemas. Dentre as características que devem ser observadas, podem-se citar: rotações, intercuspidação dentária, linha média, trespasse horizontal, trespasse vertical, paralelismo radicular nos espaços das extrações, torque e as funções da ATM. Os dados devem ser anotados para traçar a estratégia necessária para a finalização do tratamento ortodôntico. Por fim, seleciona-se o fio que será utilizado para confecção dos arcos de finalização e adicionam-se os ajustes necessários. Alcançada a oclusão excelente, o aparelho é removido e a contenção é instalada.

Effect of argon laser curing on the shear bond strength of metal brackets bonded with light-cured glass ionomer cement.

INTRODUCTION: The purpose of this study was to evaluate the shear bond strength and debonding characteristics of glass ionomer cement cured with an argon laser. METHODS: Thirty extracted first premolars were divided into 2 groups of 15. The teeth were cleaned and mounted in resin, and metal brackets were bonded with glass ionomer cement. In the control group, the bond was cured with a halogen light for 40 seconds (20 seconds mesial and 20 seconds distal). In the test group, the specimens were cured with an argon laser for 5 seconds. Brackets were debonded in shear; bond strength was measured, and the adhesive remnant index was scored. RESULTS: The difference in mean shear bond strength was not statistically significant between groups when compared with a t test. More adhesive remained on the enamel surface in the laser group than in the control group. CONCLUSIONS: Argon laser curing produces bond strengths equivalent to those obtained with traditional light curing in much less time, but it leaves more adhesive on the tooth surface.