BackgroundThis study aimed to assess the effect of surface preparation with sandblasting and diamond bur along with the use of three primers on shear bond strength (SBS) of metal brackets to aged composite.Material and MethodsIn this in vitro, experimental study, 60 Filtek Z250 composite discs were fabricated (10×2mm), immersed in distilled water for 24 hours and subjected to 5000 thermal cycles. They were randomly divided into two groups (n=30) of sandblasting with aluminum oxide particles for 10 seconds and surface roughening with bur. Each group was randomly divided into three subgroups (n=10) for use of Transbond XT, Assure Plus and Composite Primer. Metal brackets were bonded and the samples were stored in distilled water for 24 hours followed by 2000 thermal cycles. The SBS of brackets was measured and the adhesive remnant index (ARI) score was calculated. The data were analyzed by one-way ANOVA, t-test and Chi square test.ResultsThe difference in the mean SBS was not significant among the six subgroups. ConclusionsAll combinations of primers and surface preparation methods provided adequately high SBS between brackets and aged composite surfaces. Considering the ARI scores, surface roughening by bur is superior to sandblasting. Key words:Shear strength, composite resins, orthodontic brackets, aged composite, surface preparation.

Background: Stainless steel and Nickel Chromium alloys show special mechanical features, which has made them the most common materials for fabrication of orthodontic arch wires. Objectives: The aim of this study was to evaluate the effect of length of immersion and type of arch wire on release of nickel and chromium ions from fixed orthodontic appliances. Materials and Methods: 15 simulated half-arch maxillary fixed orthodontic appliances were divided into 3 groups according to the types of arch wires. Each sample was individually immersed in 50 ml of distilled water and incubated at 37ºC for 28 days. Afterwards, solutions were sent to laboratory for investigation of the released ions and the samples were incubated for another 28 days in new distilled water. After each 28-day time span, the concentrations of nickel and chromium were measured using an atomic absorption spectrophotometer. T-test was used for statistical analysis and P < 0.05 were considered statistically significant. Results: Stainless steel arch wires released the greatest amount of nickel and chromium ions at both 28 days periods. The lowest amount of nickel and chromium in both time spans was released from NiTi and HANT arch wires, respectively Nickel ion release decreased overtime while the chromium release increased. Conclusions:The amounts of released nickel and chromium ions from fixed orthodontic appliances from all three types of evaluated arch wires were below the daily dietary intake of these ions and do not bring about biological concerns.