• Phase transitions in coated nickel titanium arch wires: A differential scanning calorimetric and X-ray diffraction analysis

• # Fulltext

https://www.ias.ac.in/article/fulltext/boms/035/05/0905-0911

• # Keywords

Coated nickel titanium arch wire; austenitic–martensitic phase transition; differential scanning calorimetry; X-ray diffraction analysis.

• # Abstract

Shape memory and super-elastic properties of orthodontic nickel titanium wires, which are crucial for its clinical performance are dependent on the austenitic–martensitic phase transitions in its metallic microstructure that happen as a result of temperature or stress. The objective of this study was to compare the austenitic–martensitic phase transitions in new, black oxide coated nickel titanium (0.016 inch, Black Diamond, NiTi) arch wires in the as-received’ form, from the manufacturer and retrieved form’ after two months of intraoral use. This was done to analyse whether the new oxide coated nickel titanium wires suffered any significant loss in shape memory and super elasticity properties at the end of two months of intra oral use, findings of which could give valuable inferences prior to its widespread application in clinical practice.

Five arch wire samples in both groups were investigated for their austenitic–martensitic phase transitions in an in vitro set up, using differential scanning calorimetry (DSC), (−90° to 100°C at a rate of 10°C/min) and X-ray diffraction (XRD) analysis (10° to 90°), as a function of temperature. Martensitic–austenitic thermograms showed an intermediate rhombohedral phase in the heating cycle of both groups, but cooling cycles showed direct reversal from austenitic to martensitic phase. Lower austenitic start (𝐴s = 10.78 ± 0.46° C) and finish (𝐴f = 22.26 ± 0.24° C) temperatures of coated wires compared to the conventional wires showed

1. ability of the wire to remain in austenitic phase below oral temperature, that permits it to take up greater force during activation,

2. increased springiness and

3. consistent force delivery for an extended period of time.

Statistical analysis with paired Student’s `𝑡’ test did not show any significant difference in mean values of transition temperatures and enthalpies between the two groups which proved similar shape memory and super-elastic properties at the end of intra oral use. Black oxide coating of NiTi wires may, therefore, be effective in diversified oral conditions and may find acceptable for re-use after sterilization. Low enthalpy values (0.92–3.59 j/g) compared to conventional ones, implied complete phase transition at the atomic level that can improve performance of the material in activation and deactivation cycles of NiTi wires. X-ray diffraction analysis of the two groups demonstrated predominance of austenitic phases (A, 110, 220 and 211) with complete reversibility at the atomic level. Discrete crystallographic structure and absence of multiple phases showed complete martensitic–austenitic transition, which authenticated the differential scanning calorimetric findings. This can earn acceptance for the new product in contemporary orthodontic practice with adequate scope for indigenization.

• # Author Affiliations

1. Division of Orthodontics, Indian Army, 10 Corps Dental Unit, C/O 56 APO, Bathinda 151 001, India
2. Department of Biochemistry, Jigme Dorje Wangchuk National Referral Hospital (JDWNRH), Thimphu, Bhutan
3. Materials Division, National Institute of Inter Disciplinary Science and Technology (NIIST) (CSIR), Thiruvananthapuram 695 019, India
4. Commandant and Classified Specialist (Orthodontics), Army Dental Centre (Research and Referral), Delhi Cantt, Delhi 110 010, India

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020