Superelastic and shape memory equi-atomic nickel-titanium (Ni-Ti) alloy in dentistry: A systematic review

Abstract

According to the Global Burden of Disease (GBD) 2015, around 3.5 billion people suffer from dental diseases. The treatment of these disease requires either a specific dental device or a material which are usually subjected to stress and corrosion of the oral environment due to varying temperature, pH, occlusion, and masticatory forces. Various smart materials have emerged in the biomedical field because of their superior properties compared to conventional alloys. However, Nickel-Titanium (Ni-Ti) alloys with nearly equi-atomic composition have a long-standing history of successful use in dentistry because of their shape memory (SM) and superelastic (SE) properties with excellent cytocompatibility and corrosion resistance. The SM property offers preferable control of the transition temperature range (TTR) near the oral temperature providing multiple actuation. The SE property has revolutionized orthodontic treatment by delivering light and continuous physiological forces to the teeth, thereby improving patient comfort. The SE property of Ni-Ti alloy has been extensively used to produce orthodontic archwires and endodontic files as they exhibit higher flexibility compared to conventional stainless-steel alloy. However, the duration and type of heat treatment performed on these devices have been reported to modify their thermo-mechanical properties, producing adverse effects. Besides this, the devices are also subjected to short-term cooling or heating, sterilization, and disinfection protocols that creates a corrosive environment. Thus, thermo-mechanical properties and the influence of oral environment on various commercially available Ni-Ti alloy dental devices have been briefly explored and discussed. Besides orthodontic archwire and endodontic files, other Ni-Ti alloy-based dental devices are also reviewed, such as Shape memory Ni-Ti alloy sleeve for Abutment System, SM Ni-Ti alloy palatal expander, and SM Ni-Ti alloy porous dental implant. Thus, this manuscript aims to provide a concise assessment of the properties of SE and SM Ni-Ti alloys and their evolution in the field of dentistry. • Large population suffers from dental diseases. • Among the smart materials, Ni-Ti alloys have been successfully used in dentistry. • Shape memory offers control of transition temperatures near to oral temperature. • Superelasticity delivers light and continuous physiological forces to the teeth. • Thermomechanical treatment and oral environment create undesirable device behavior.