Gabriel Schmidt Dolci

Biodegradação de braquetes ortodônticos: análise por microscopia eletrônica de varredura

OBJECTIVES: The purpose of this study was to analyze, with the aid of scanning electron microscopy (SEM), the chemical and structural changes in metal brackets subjected to an in vitro biodegradation process. METHODS: The sample was divided into three groups according to brackets commercial brand names, i.e., Group A = Dyna-Lock, 3M/Unitek (AISI 303) and Group B = LG standard edgewise, American Orthodontics (AISI 316L). The specimens were simulated orthodontic appliances, which remained immersed in saline solution (0.05%) for a period of 60 days at 37°C under agitation. The changes resulting from exposure of the brackets to the saline solution were investigated by microscopic observation (SEM) and chemical composition analysis (EDX), performed before and after the immersion period (T0 and T5, respectively). RESULTS: The results showed, at T5, the formation of products of corrosion on the surface of the brackets, especially in Group A. In addition, there were changes in the composition of the bracket alloy in both groups, whereas in group A there was a reduction in iron and chromium ions, and in Group B a reduction in chromium ions. CONCLUSIONS: The brackets in Group A were less resistant to in vitro biodegradation, which might be associated with the type of steel used by the manufacturer (AISI 303).

Assessment of the dimensions and surface characteristics of orthodontic wires and bracket slots

OBJECTIVE The purpose of this study was to evaluate the dimensions and surface characteristics of orthodontic wires and bracket slots of different commercial brands. METHODS Thirty metallic brackets (0.022 x 0.028-in and 0.022 x 0.030-in) were divided into three groups: DYN/3M group = Dyna-Lock, 3M/Unitek (stainless steel, or SS); STD/MO group = Slim Morelli (SS); and Ni-Free/MO group = Slim Morelli (Ni-Free). The stainless steel wires (0.019 x 0.025-in) were divided into two groups: MO group = Morelli; and 3M group = 3M/Unitek. The bracket and wire measurements were done by two methods: (a) Surface Electron Microscopy (SEM), and (b) Profile Projection. The surface analysis was done qualitatively, based on SEM images and/or by a rugosimeter. The quantitative results were analyzed by ANOVA with Tukeys test (p < 0.05) and Students t test. RESULTS A significant difference in the dimensions of slots was observed, and the NiFree/MO group showed the greatest changes when compared to the other groups. The analysis of surface topography of the brackets indicated greater homogeneity of the metallic matrix for DYN/3M and STD/MO groups. As for the dimensions of the wires, groups showed statistically different mean heights. CONCLUSIONS It was concluded that wires and brackets slots can present altered dimensions, which might directly and unintentionally affect the planned tooth movement.

A influência do jateamento na cimentação de bandas ortodônticas

AIM: to compare the shear-peel bond strength of five orthodontic cements: a conventional glass ionomer cement (Ketac Cem), two resin-modified glass ionomer cements (3M Multicure Glass Ionomer and Fuji Ortho LC) and two polyacid-modified composite resin cement (Ultra Band-Lok and Transbond Plus). METHODS: cements were placed in a 3mm diameter mold at bonding interface and bonded to 6 x 6mm standard and sandblasted stainless steel band specimens mounted to acrylic blocks. Specimens were stored at 37oC and 100% relative humidity for 24 hours and debonded in tension on a testing machine at 0.05cm/minutes. Data were analyzed by one-way analysis of variance (ANOVA) followed by a Tukey multiple comparison procedure in the same surface treatment groups (sandblasted or non-sandblasted) and by paired t-tests in different surface treatment groups (sandblasted and non-sandblasted) (p=0.01). RESULTS: Ultra Band-Lok demonstrated significant greater shear-peel bond strength (p<0.01) in the non-sandblasted groups, and no statistically significant differences were noted between others cements. In the sandblasted groups, resin-modified glass ionomer cements demonstrated the highest mean bond strength (p<0.01), and 3M Multicure Glass Ionomer showed a greater shear-peel bond strength (p<0.01) than Ketac Cem and Fuji Ortho LC. CONCLUSION: sandblasting increased shear-peel bond strength in all tested groups (p<0.01).