Evaluation of passive oxide layer formation–biocompatibility relationship in NiTi shape memory alloys: Geometry and body location dependency

Investigation of the Dissolution–Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires

“…The Nickel-Titanium (NiTi) shape memory alloys (SMAs) have been employed in biomedical applications at an increasing rate within the last decades owing to their superior thermo-mechanical properties [1][2][3][4][5][6][7][8][9][10]. Specifically, the NiTi alloys can assume two distinctly different shapes by means of solid-to-solid phase transformation between austenitic and martensitic phases upon temperature change or loading [2,5,[8][9][10][11], opening the venue for their utility in various dental, cardiovascular and orthopedic applications [2,7].…”

“…One of the well-known applications is the orthodontic archwire, which benefits from the pseudoelastic property of NiTi [2,5,7,9]: austenite-to-martensite phase transformation upon loading allows for attaining a state of constant stress for a relatively wide strain range [2,7,9,11], which eliminates the need for frequent readjustments of the orthodontic arch wire to keep the stress at an optimum level for simultaneous tooth movement and periodontal tissue regeneration despite the changing strain on the wires [9]. Shape memory gloves which are used for the physiotherapy of partially atrophied muscles benefit from another important property, namely the two-way shape memory effect, such that the natural motion of a hand is mimicked with the wires placed in the regions over the fingers which contract and stretch by heating and cooling [5,12].…”

“…. Even though the NiTi alloy has been employed as a material of choice in various biomedical applications, biocompatibility related issues have constituted a significant concern and continue to come under focus in various studies [1][2][3][4][5][6][7][8][9][10]13]. In particular, when NiTi alloys are implanted in the body they are attacked by the aggressive ions of the body fluids, such as chlorides, hydrocarbonates or sulfates [14].…”

“…In addition, stress corrosion cracking (SCC) constitutes another complication for the orthodontic treatments, such that when the archwires are loaded or archwire-bracket contact sites develop excessive stress along with the corrosivity of the saliva, the cracking of the archwires, and thereby the release of toxic Ni ions are enhanced [17,18]. When the amount of Ni ion release reaches a critical value of 0.12-0.5 mg/L, serious toxic, carcinogenic and allergic effects may prevail, necessitating additional treatment [2,8].…”

Microstructure-based modeling of the impact response of a biomedical niobium–zirconium alloy

“…[1][2][3][4] However, despite the utility of metallic materials of high strength in many implants, cases of implant failure due to metal fatigue and fracture have been reported. [4][5][6] In such an incident, not only the treatment is unsuccessful, but also infection and other severe consequences may prevail, making an urgent surgical intervention inevitable.…”