No abstract

Objective: To determine the mechanical properties of commercially available thermodynamic wires and to classify these wires mathematically into different groups. Materials and Methods:The samples examined were 48 nickel-titanium (NiTi) alloy orthodontic wires commercially available from five manufacturers. These samples included 0.016-inch, 0.016-ϫ 0.022-inch, 0.017-ϫ 0.025-inch, and 0.018-ϫ 0.025-inch wires. The superelastic properties of the NiTi wires were evaluated by conducting the three-point bending test under uniform testing conditions. The group classification was made under mathematically restricted parameters, and the final classification was according to their clinical plateau length.Results: The orthodontic wires tested are classified as follows: (1) true superelastic wires, which presented a clinical plateau length of Ն0.5 mm; (2) borderline superelastic with a clinical plateau length of Ͻ0.5 mm and Ͼ0.05 mm; and (3) nonsuperelastic, with a clinical plateau length of Յ0.05 mm. The results showed that the range of products displays big variations in quantitative and qualitative behavior. A fraction of the tested wires showed weak superelasticity, and others showed no superelasticity. Some of the products showed permanent deformation after the threepoint bending test. Conclusion: A significant fraction of the tested wires showed no or only weak superelasticity. The practitioner should be informed for the load-deflection characteristics of the NiTi orthodontic wires to choose the proper products for the given treatment needs.

A scanning electron microscopy study of possible root resorptions and their localization after application of continuous forces of different magnitudes was conducted. Twelve upper first premolars, indicated for extraction, were previously intruded with constant forces. The teeth were divided into 3 groups: 1. non-moved control teeth, 2. continuous force application of 50 cN for 4 weeks, 3. continuous force application of 100 cN for 4 weeks. Specially designed NiTi-SE-stainless steel springs were utilized to exert the actual forces. After experimental tooth movement, the extracted teeth were dehydrated, metal-coated and examined by scanning electron microscopy. The intruded teeth showed resorptive areas consisting of lacunae (concavities) in the mineralized root surface. The teeth moved with 50 cN showed in the apical third several, in the medial third few, and in the cervical third no resorptive areas. In the case of the teeth moved with 100 cN, we observed resorptive areas in most of the apical third--including the apex contour-, several in the medial third, and none in the cervical third. In the control group no resorptions were observed. Thus, our results suggest that intrusion of human teeth with continuous forces induces root resorption, depending on the magnitude of force applied.

The nature of the adhesive greatly influences the resultant bond strength, the risk of enamel damage, and the extent of residual composite on the teeth.

In the presence of a continuous cleft in the jaw and palate area, orthodontic forces (quadhelix) are apparently already sufficient to allow a skeletal expansion of the maxilla. Maxillary expansion using the quadhelix appliance represents a reasonable alternative to using conventional rapid maxillary expansion appliances among cleft patients.