Evaluation of physical-mechanical properties of self-adhesive versus conventional resin cements

Aim: The purpose of this study was to compare the microhardness, diametral tensile strength, compressive strength and the rheological properties of self-adhesive versus conventional resin cements. Methods: Specimens of a conventional (RelyX ARC) and 3 self-adhesive (RelyX U200, Maxcem Elite, Bifix SE) types of resin cements were prepared. The Knoop test was used to assess the microhardness, using a Microhardness Tester FM 700. For the diametral tensile strength test, a tensile strength was applied at a speed of 0.6 mm/minute. A universal testing machine was used for the analysis of compressive strength and a thermo-controlled oscillating rheometer was used for the Rheology test. One-way ANOVA and Tukey's test (α=0.05) were used for data analysis. Results:According to microhardness analysis, all the cements were statistically similar (p>0.05), except for Maxcem that presented lower hardness compared with the other cements in relation to the top surface (p<0.05). In the diametral tensile strength test, Relyx U200 and RelyX ARC cements were statistically similar (p>0.05), presented higher value when compared to the Maxcem and Bifix cements (p<0.05). The compressive strength of RelyX ARC and Maxcem Elite cements was statistically higher than RelyX U200 and Bifix cements (p<0.05). Regarding the rheology test, Maxcem Elite and RelyX ARC cements showed a high modulus of elasticity. Conclusions: The self-adhesive cements presented poorer mechanical properties than conventional resin cement. Chemical structure and types of monomers employed interfere directly in the mechanical properties of resin cements

Cleansing orthodontic brackets with air-powder polishing: effects on frictional force and degree of debris

ABSTRACT Introduction: Debris buildup on the bracket-wire interface can influence friction. Cleansing brackets with air-powder polishing can affect this process. Objective: The aim of this study was to evaluate the frictional force and amount of debris remaining on orthodontic brackets subjected to prophylaxis with air-powder polishing. Methods: Frictional force and debris buildup on the surface of 28 premolar brackets were evaluated after orthodontic treatment. In one hemiarch, each bracket was subjected to air-powder polishing (n = 14) for five seconds, while the contralateral hemiarch (n = 14) served as control. Mechanical friction tests were performed and images of the polished bracket surfaces and control surfaces were examined. Wilcoxon test was applied for comparative analysis between hemiarches at p < 0.05. Results: Brackets that had been cleaned with air-powder polishing showed lower friction (median = 1.27 N) when compared to the control surfaces (median = 4.52 N) (p < 0.01). Image analysis showed that the control group exhibited greater debris buildup (median = 2.0) compared with the group that received prophylaxis with air-powder polishing (median = 0.5) (p < 0.05). Conclusion: Cleansing orthodontic brackets with air-powder polishing significantly reduces debris buildup on the bracket surface while decreasing friction levels observed during sliding mechanics.

RESUMO Introdução: o acúmulo de detritos na interface braquete-arco pode influenciar no atrito, mas a limpeza dos braquetes usando jatos de bicarbonato de sódio pode interferir nesse processo. Objetivo: o objetivo desse estudo foi avaliar a força de atrito e a quantidade de detritos remanescentes em braquetes ortodônticos submetidos à profilaxia com jatos de bicarbonato de sódio. Material e Métodos: avaliou-se, ao final do tratamento ortodôntico, a força de atrito e o acúmulo de detritos na superfície de 28 braquetes de pré-molares. Em uma hemiarcada, os braquetes foram jateados com bicarbonato de sódio (n = 14) por 5 segundos, enquanto a hemiarcada contralateral serviu de controle (n = 14). Foram realizados ensaios mecânicos de atrito e análise imagiológica dos braquetes de ambas as hemiarcadas, a jateada e a controle. O teste de Wilcoxon foi utilizado para a análise comparativa entre as hemiarcadas, com p < 0,05. Resultados: os braquetes submetidos à limpeza com jatos de bicarbonato de sódio apresentaram menor atrito (mediana = 1,27N), quando comparados aos do lado controle (mediana = 4,52N) (p < 0,01). A análise imagiológica demonstrou que o grupo controle apresentou maior acúmulo de detritos (mediana = 2,0), em comparação ao grupo que recebeu profilaxia com jatos de bicarbonato (mediana = 0,5) (p < 0,05). Conclusão: a limpeza dos braquetes ortodônticos por meio do jateamento com bicarbonato de sódio reduz significativamente o acúmulo de detritos na superfície deles, bem como os níveis de atrito observados durante a mecânica de deslizamento.