ABSTRACT
<p><b>BACKGROUND</b>As the only active component in final treatment phase of Tip-Edge Plus technique, the activation of nickel-titanium orthodontic archwires is one of the factors that affect the torque expression. It is necessary to evaluate the mechanical properties of the nickel-titanium wire used in the final treatment phase in simulated oral environments to forecast the treatment outcomes.</p><p><b>METHODS</b>The mechanical properties of 171 thermal nickel-titanium wires of 0.35 mm (0.014-in) in diameters with different deflection of 40 mm in length were investigated with three-point bending test. The samples were divided into 2 groups: as-received and bended groups. In the bended group, samples were divided into 7 subgroups according to the amounts of deflection and named by the canine angulations (-25°, -19°, -13°, -7°, -1°, +5°, +11°). The deflection of wires was made by inserting the wires into the deep tunnel of Tip-Edge Plus brackets positioned in plaster casts with different canine angulations to mimic the use of nickel-titanium wires in the final treatment phase. Immersed the bended group in artificial saliva (pH 6.8) and preserved at 37.0°C. Eight durations of incubation were tested: 1 to 8 weeks. Three analogous samples of each group and subgroups were tested per week. Stiffness (YS:E) and the load-deflection characteristics of unloading plateau section were obtained.</p><p><b>RESULTS</b>Significant changes in specific mechanical properties were observed in long-term immersed and large deflected wires compared with as-received groups. Both immersion time and deflection affected the mechanical properties of wires in the simulated oral environment, and the two factors had synergistic effect. In groups -25°, -19° and -13°, stiffness (YS:E) increased then decreased and average plateau force and ratio of variance decreased then increased correspondingly at specific time.</p><p><b>CONCLUSIONS</b>In the final treatment phase of Tip-Edge Plus technique, the mechanical properties of nickel-titanium wire are associated with the using time and amounts of deflection and it may affect treatment outcomes. As the main reason for wire deflection, canine crown angulation plays an important role in the wire performance. It may be wise to focus on the canine crown angulations and using time in clinic with Tip-Edge Plus technique and make proper adjustment to help to make sure the treatment outcomes.</p>
Subject(s)
Humans , Mechanical Phenomena , Nickel , Orthodontic Wires , Titanium , Tooth Movement Techniques , MethodsABSTRACT
<p><b>OBJECTIVE</b>To evaluate casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and several fluoride products in inhibiting enamel demineralization.</p><p><b>METHODS</b>Seventy healthy premolars extracted before orthodontic treatment were divided into seven groups (A: CPP-ACP; B: CPP-ACP + fluoride mouth rinses; C: fluoride mouth rinses; D: fluoride glass ionomer protection; E: fluoride resin binder; F: fluoride varnish; G: control group). There were ten samples in each group. The teeth were dipped into an artificial caries solution ten minutes at a time, then applied separately with CPP-ACP, CPP-ACP + fluoride mouth rinses, fluoride mouth rinses, fluoride glass ionomer protection, fluoride resin binder and fluoride varnish on labial enamel. The samples were dipped into an artificial saliva solution (37°C). Then all samples were examined with atomic force microscope (AFM) at the end of first, second and third monthes.</p><p><b>RESULTS</b>At the end of the first month, surface roughness in group D [(114 ± 1) nm] was significantly lower than that in group G[(172 ± 9) nm]. At the end of the second month and the third month, significant difference was found in surface roughness between group G and the rest of groups (P < 0.05); between group B and the rest of groups; and between group C and groups (D, E and F).</p><p><b>CONCLUSIONS</b>CPP-ACP and fluoride could both inhibit enamel demineralization in vitro. Solid fluoride (groups D, E and F) had better results than liquid fluoride (group C).</p>