Abstract
Aims: To study the effect of artificial saliva and time interval on the amount of force values of nitinol and superelastic NiTi wires. Materials and Methods: Two types of orthodontic wires chosen for the study nitinol and superelastic NiTi wires of a guage of 0.016 inch in diameter (Dentaurum, Germany). Specimens of the wires were divided in to two groups ;the control group(dry condition) contained the wires as - received condition and experimental groups for the study of the force value of wires which subjected to artificial saliva for three time incubation periods (3 days, 7 days, 28 days) . At end of each incubation periods ,the wire specimens were tested for the effect of artificial saliva on force values of the wire. The measurement of force values of arch wires done with a universal tensile testing ma-chine ,the force values of specimens were evaluated with the help of three point bending test. The re-sults were subjected to the descriptive statistics and to the ANOVA and Duncan’s Multiple Range Analysis Tests to detect the amount of changes among these groups . Result: The findings of the present study showed that the control group of nitinol wires had the highest rate of force value with significant difference (P≤ 0.05) with experimental groups, while the experimental group after 28 days gave rise to the lowest one with significant difference (P≤ 0.05) from other groups. For the superelastic nickel titanium the result showed that the control group had the highest rate of force value while the experimental group after 28 days gave rise to the lowest one with significant difference (P≤ 0.05) from control and non significant difference (P> 0.05) with the experimental groups after 3 days and 7 days. Conclusion: The nitinol wires showed a continuous change in force values with increase time in ar-tificial saliva, so this required reactivating or changing the wire at a certain interval of use. While force values of the superelastic nickel titanium wires decreased after 3 days interval and remained constant after that .
Highlights
A vital component of the fixed orthodontic appliance is the orthodontic arch wire.[1,2] Recent advances in orthodontic wire alloys have resulted in a varied array of wires and these include stainless steel, cobalt chromium, nickel – titanium, beta – titanium and multistranded stainless steel wires.[3]
While force values of the superelastic nickel titanium wires decreased after 3 days interval and remained constant after that
The Effect of Artificial Saliva on force value on nitinol wire: The results of the present study showed that the control group displayed a significantly higher force value during loading than the experimental groups and this finding is similar to the result obtained by Harris et al[24] who attributed this finding to corrosive attack in chloride environment, this attack was a pitting type of corrosion that affect the surface of the wires and result in degradation of their mechanical properties, so the long term use of nitinol wire would appear to be associated with decreased performance of the wire the elasticity of the wire
Summary
A vital component of the fixed orthodontic appliance is the orthodontic arch wire.[1,2] Recent advances in orthodontic wire alloys have resulted in a varied array of wires and these include stainless steel, cobalt chromium, nickel – titanium, beta – titanium and multistranded stainless steel wires.[3]. [7,8] These environmental conditions of the oral cavity might alter the morphological, structural and compositional characteristics, force delivery of archwires, superelasticity and fracture of orthodontic alloy.[9] These oral environments include saliva, acids arising from degradation and decomposition of food (PH), oral flora and its by products, temperature change and stress.[10, 12] The quantity and quality of saliva may influence corrosion.[13, 14] The anticorrosion properties of nickel – titanium arch wires are due to the formation of oxide layers on the surface of alloys, which inhibit further corrosion. The general mechanism for the corrosion and subsequent release of metal ion involve the loss of passivated layer (oxide layer) so when the oxide layer dissolve, the onset of surface corrosion begins.[17]
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