Resumo O objetivo neste estudo foi avaliar o efeito de diferentes números de ciclos térmicos na resistência da união de braquetes metálicos à cerâmica feldspática usando resina composta. Vinte e cinco cilindros de cerâmica foram condicionados com ácido fluorídrico a 10% por 60 s e duas camadas de silano. Braquetes foram fixados nos cilindros usando Transbond XT e depois separados em 5 grupos (n=5): Grupo 1 - Grupo Controle (sem ciclagem térmica); Grupo 2 - 500 ciclos térmicos; Grupo 3 - 5.000 ciclos térmicos; Grupo 4 - 7.000 ciclos térmicos e Grupo 5 - 10.000 ciclos térmicos. A fotoativação foi realizada com aparelho LED Radii Plus. O ensaio de resistência de união ao cisalhamento foi realizado após armazenagem por 24 h em água deionizada ou após a ciclagem térmica (5º/55 ºC, com banhos de 30 s cada). Cinco braquetes foram fixados em cada cilindro, totalizando 25 bráquetes por grupo. Os dados foram submetidos à análise de variância de um fator e ao teste de Tukey (α=0,05). O Índice de Remanescente Adesivo (IRA) foi avaliado com aumento de 8x. Os valores de resistência (MPa) dos grupos controle (9,3±0,8), 500 (9,0±0,7) e 5.000 (8,4±0,9) ciclos térmicos foram significantemente maiores do que os grupos submetidos à 7.000 (6,8±0,6) e 10.000 (4,9±1,0) ciclos térmicos (p<0,05). O IRA mostrou predominância do escore 0 para todos os grupos, com aumento de escores 1 e 2 para os grupos controle e submetidos a 500 ciclos térmicos. Em conclusão, a fadiga térmica pode comprometer a união entre os braquetes metálicos e as restaurações cerâmicas. Para testes in vitro, o uso de pelo menos 7.000 ciclos é recomendado para determinar fadiga significante na interface de união.

Abstract The aim of this study was to evaluate the effect of different number of thermal cycles on the shear bond strength (SBS) of metallic orthodontic brackets bonded to feldspathic ceramic by a composite resin. Twenty-five ceramic cylinders were etched with 10% hydrofluoric acid for 60 s and received two layers of silane. Brackets were bonded to the cylinders using Transbond XT and assigned to 5 groups (n=5): Group 1 - Control group (without thermal cycling); Group 2 - 500 thermal cycles; Group 3 - 5,000 thermal cycles; Group 4 - 7,000 thermal cycles and Group 5 - 10,000 thermal cycles. Light-activation was carried out by Radii Plus LED. SBS testing was carried out after 24 h of storage in deionized water and thermal cycling (5/55 oC and 30 s dwell time). Five brackets were bonded to each cylinder, totalizing 25 brackets for each group. Data were submitted to one-way ANOVA and Tukey’s test (α=0.05). The Adhesive Remnant Index (ARI) was evaluated at 8× magnification. The SBS (MPa) of control group (9.3±0.8), 500 (9.0±0.7) and 5,000 (8.4±0.9) thermal cycles were significantly higher than those after 7,000 (6.8±0.6) and 10,000 (4.9±1.0) thermal cycles (p<0.05). The ARI showed a predominance of Scores 0 (adhesive failure) prevailed in all groups, as shown by the ARI, with increased scores 1 and 2 (mixed failures) for control group and 500 thermal cycles. In conclusion, thermal fatigue may compromise the bonding integration between metallic brackets and ceramic restorations. For in vitro testing, use of at least 7,000 cycles is advised to result in significant fatigue on the bonding interface.

Aim: To evaluate the force decay of orthodontic elastomeric chains after immersion in disinfecting solutions. Methods: One-hundred and fifty segments of elastomeric chains were divided in 3 groups: Control group - no disinfection; Chlorhexidine group - disinfection in 0.12% chlorhexidine digluconate solution; and Peracetic acid group - disinfection in 0.2% peracetic acid solution. Elastomeric chains of 14 mm were stretched up to 20 mm and the given force (kgf) was evaluated in an Instron universal testing machine at the following intervals: 1 h, 1 day, 7, 14, 21 and 28 days after the immersion in the disinfecting solutions. Data (kgf) were analyzed statistically by Analysis of Variance and Tukey's test at a 5% significance level. Results: Both groups presented similar force decay along 7 days and remained stable up to 28 days. Force degradation was observed in the first hours of activation (~50%). Conclusions: It may be concluded that there were no significant differences among the investigated groups, in most interval times, indicating that both chemical solutions can be used for previous disinfection of orthodontic elastomeric chains.

AIM: To evaluate the frictional force between the archwire and orthodontic bracket generated by elastomeric ligatures with polymer coating (Super slick, TP Orthodontics) and conventional ligatures (Morelli) using two types of insertion techniques. METHODS: Forty elastomeric ligatures, 20 with polymer coating and 20 conventional, were evaluated. Each type of ligature was separated into two groups (n=10), according to the insertion mode: conventional or crossed (from mesial to distal region crossed in front). To analyze friction, 40 5-cm-long segments of stainless steel orthodontic archwire 0.019" x 0.025" (Morelli) and Edgewise brackets (slot 0.022" x 0.028"; Morelli) were used. Each set (bracket, wire and elastic) was submitted to frictional testing in a universal test machine (Instron 4411) at a crosshead speed of 5 mm/min. Each bracket was moved 5 mm on the wire, with maximum friction and mean friction being recorded by software. Three readouts were taken for each bracket. Data were submitted to two-way ANOVA and Tukey's test (p<0.05). RESULTS: It was shown that for maximum and mean friction, the polymer-coated ligature did not differ statistically from the conventional type in a dry environment condition. Ligatures placed in crossed mode promoted significantly greater friction than those placed in conventional mode, irrespective of the type of elastomeric ligature. CONCLUSIONS: Friction depended on the insertion mode, but not on the type of elastomeric ligature.