ABSTRACT
Statement of Problem: The application of nickel-titanium arch wires is very common in the first stage of orthodontic treatment
Purpose: The aim of this study was to evaluate the effect of activation value on load-deflection properties of two types of nickel-titanium archwires. The changes occurring in bending properties of these wires after recycling were also assessed
Materials and Method: In this in vitro study, 80 specimens from single-strand Ni-Ti [Rematitan "Lite"] and multistrand Ni-Ti [SPEED Supercable] wires were selected and subjected to a three point bending test in the "as-received condition" and "after 2 months immersion in a simulated oral environment and autoclave sterilization". The wires were activated up to 3 or 6 mm distances and unloading forces were recorded using Zwick testing machine. The data were analyzed using T-test
Results: Rematitan "Lite" showed significantly greater force than Supercable at both 3 and 6 mm activations [p <0.05]. The single-strand nickel titanium wire showed lower forces at 6 mm activation compared with 3 mm activation. In contrast, severe activation of multi-strand Ni-Ti wire caused a longer plateau range and, consequently, the unloading forces of this wire at 1.5, 1.0 and 0.5 mm deflections were higher in severe activation than in moderate activation. The effect of recycling on bending properties of Ni-Ti wires was not clinically considerable
Conclusion: Application of a multi-strand Ni-Ti wire is useful when a very light force is needed for tooth alignment. The magnitude of forces exerted in three point bending test depended on the amount of wire activation. The tested wires can be reused at least once
ABSTRACT
Statement of Problem: Understanding the effects of orthodontic force on the pulp is of particular interest, especially because altered pulpal respiration rate, secondary dentin formation, internal root resorption, and even pulpal necrosis have all been associated with orthodontic treatment
Purpose: The aim of this study was to evaluate and compare the effects of orthodontic extrusive and intrusive forces on the histologic changes of the human dental pulp after 3 days and 3 weeks
Materials and Method: In this study, 52 sound upper first premolars from 26 patients, scheduled for extraction for orthodontic reasons, were selected. The patients were divided randomly into 2 groups [3 days and 3 weeks]. In each group, 10 teeth received orthodontic extrusive forces, 10 teeth underwent intrusive forces and 6 teeth served as controls. Histologic changes were evaluated and the data were statistically evaluated by nonparametric tests
Results: Vacuolization and disruption of the odontoblastic layer showed statistically significant differences between the control and either of the experimental groups in each test period. Furthermore, fibrous tissue formation in the extrusive group was significantly higher than the control group in the 3-week period. There was no significant difference between 3-day and 3-week intervals in each experimental group, except that fibrosis in the extrusive group was significantly increased after 3 weeks of force application. Comparison between extrusive and intrusive groups revealed no statistical significance in each test period
Conclusion: The results indicate that if orthodontic forces are applied in the optimal range and are not more intense than the physiological limit of tissue tolerance, irreversible injuries to the pulp can be prevented