[ effect of activation value on load-deflection properties of new and recycled nickel-titanium arch wires]

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

[Comparison of dental and chronological ages in early diagnosis of maxillary canine palatal impaction]

There are different views about the optimal time for detection and prevention of maxillary canine impaction. With respect to the large individual variation in the timing of eruption of the teeth, it seems reasonable not to consider chronological age as a valid criterion in this regard. The aim of this study was to compare dental and chronological ages in the diagnosis of potential maxillary canine impaction. This analytical cross-sectional study was done on 2704 students aged 10-11 year in Mashhad. In the first group [1232 children], all of the children whose maxillary canine bulges were not palpable were suspected with impaction and referred for radiographic examination. In the second group [1472 children], the children whose canine bulges were not palpable were referred for radiographic examination if only the first premolars had erupted or were erupting. The condition of the lateral incisor teeth was inspected in children suspected with impaction. The data were analyzed by comparing the proportion of success and Fisher's exact test. From the children examined in the first group, 9.3% and from those examined in the second group, 5.5% were suspected with impaction in the clinical examinations. The application of dental age reduced the number of referrals for radiographic examination significantly [p <0.05]. There was an association between palatal position of the maxillary canines and anomalous lateral incisors [p <0.05]. Consideration of chronological age in early diagnosis of maxillary canine impaction may result in unnecessary radiographic examination. The number of referrals for radiographic examination will be significantly reduced when the developmental stage of dentition is considered

[Comparative evaluation of elastic modulus of orthodontic elastomeric ligatures]

The application of elastomeric ligatures is one of the methods of archwires ligation to orthodontic brackets. Knowledge about modulus of elasticity of these ligatures is useful for selecting a specific brand of elastomeric ligature for a special condition. The purpose of this study was to compare elastic modulus of seven commercially available elastomeric ligatures in the initial condition and after 28 days immersion in a simulated oral environment. Changes in the modulus of elasticity were also surveyed for each brand of ligatures after 28 days. In this experimental laboratory-based study, elastomeric ligatures were obtained from different companies and their modulus of elasticity were measured in the initial condition and after 28 days immersion in a simulated oral environment using Zwick testing machine at 5mm/mm cross head speed. The data were analyzed using SPSS software and ANOVA, Duncan and student's t-test. Different brands of elastomeric ligatures showed significant differences in elastic modulus both in the as-received condition and after 28 days immersion in the simulated oral environment [p<0.05]. Ligatures from American Orthodontics and Ortho Technology showed the lowest and ligatures from Dentaurum revealed the highest elastic modulus in the as-received condition. Modulus of elasticity in the ligatures from American Orthodontics, Ortho Technology and ITO increased significantly while in ligatures from Dentaurum it was decreased significantly after 28 days immersion in the simulated oral environment [p<0.05]. Ligatures from American Orthodontics and Ortho Technology are suitable for immediate use after bonding and in sliding mechanics while ligatures from Dentaurum are not suitable to use immediately after bonding

Evaluation of tensile properties of several brands of elastomeric ligatures used in Iran

Elastomeric ligatures are used to secure archwires into orthodontic brackets. Unless the ligatures show adequate tensile properties, they may tear while inserting in the brackets or between patient's appointments. The latter may cause unwanted tooth movement and prolong orthodontic treatment. In this study the comparison of tensile properties [tensile strength, extension to tensile strength, and toughness] of seven commercially available molded clear elastomeric ligatures was performed. In this experimental laboratory-based study, eiastomeric ligatures were obtained from American Orthodontics, Ortho Technology, GAC, Techno Tak, All Star, Dentaurum and ITO companies and their tensile properties were measured using Zwick testing machine with 5mm/min cross head speed in the as-received condition and after 28 days immersion in a simulated oral environment. The data was analysed by SPSS software. All of the ligatures tested showed a significant decrease in tensile strength, extension to tensile strength and toughness excluding ITO's toughness after 28 days [P<0.001], Different brands of elastomeric ligatures showed significant differences in tensile properties both in the as-received condition and after 28 days immersion in the simulated oral environment [P<0.001]. Under the study conditions, ligatures from American Orthodontics and Techno Tak companies showed superior tensile properties and ligatures from Ortho Technology company exhibited weaker tensile features compared to other groups. There were significant differences in tensile properties of different brands of elastomeric ligatures in both the as-received condition and after 28 days immersion in the simulated oral environment. There was a significant reduction in strength properties of all types of elastomeric ligatures after 28 days immersion in a simulated oral environment. Thus, it is recommended that all ligatures should be replaced at each visit to reduce risk of tearing