From Cardiovascular Stents to Endodontic Files and Orthodontic Retainers

1. Introduction

Nitinol (nickel-titanium alloy) has gained widespread use in the medical field due to its superior mechanical properties, including shape memory, flexibility, and biocompatibility. Initially utilized in cardiovascular stents and endodontic files, nitinol has also been adopted in orthodontic retainers. This article explores the reasons behind its selection in these applications and why its use in orthodontic retainers is highly beneficial.

2. Nitinol in Cardiovascular Stents

Cardiovascular stents are medical devices used to open narrowed arteries and maintain blood flow. Nitinol is the preferred material for these stents due to the following reasons:

• Shape Memory and Superelasticity: Nitinol can return to a predetermined shape when exposed to body temperature, allowing stents to be compressed into a catheter and then expand once placed in the artery.
• High Fatigue Resistance: Stents are subject to continuous mechanical stress due to the beating heart. Nitinol’s high fatigue resistance ensures long-term durability.
• Biocompatibility and Corrosion Resistance: Nitinol exhibits high resistance to corrosion in bodily fluids, making it a safe and long-lasting material for stents[1].

The Introduction and Widespread Adoption of Nitinol in Cardiovascular Stents

Nitinol was discovered in the 1960s, but its use in medical applications, particularly in cardiovascular stents, began in the late 1980s.

• 1989: The first self-expanding nitinol stents were introduced in clinical applications.
• Early 1990s: Nitinol stents started being widely used, especially for peripheral artery disease.
• Mid-1990s: The use of nitinol stents expanded into cardiovascular surgery, particularly in coronary artery interventions.
• 2000s: With the development of advanced coating technologies and drug-eluting stents, nitinol stents gained widespread acceptance and became a standard treatment option.

Today, nitinol stents are commonly used in peripheral artery disease and carotid arteries due to their superelastic properties and shape memory, making them ideal for areas with high movement and bending.

3. Nitinol in Endodontic Files

Endodontic files are used in root canal treatments to clean and shape the root canal. Nitinol is favored for this application due to:

• High Flexibility: Root canals have complex anatomy, requiring files that can navigate curved and narrow spaces without breaking. Nitinol files are significantly more flexible than stainless steel alternatives.
• Shape Memory Effect: Nitinol retains its shape during the procedure, minimizing deformation and ensuring consistent cleaning performance.
• Reduced Stress Accumulation: Unlike stainless steel files, nitinol files generate less stress on root canal walls, reducing the risk of instrument breakage[2].

The Introduction and Widespread Adoption of Nitinol in Endodontic Files

The use of nitinol in endodontic files was first proposed in 1988 by Walia and colleagues.

• 1988: Walia et al. published the first scientific study suggesting the use of nitinol in endodontic files, demonstrating its superior flexibility compared to stainless steel.
• 1990s: Nitinol files started being incorporated into mechanical endodontic systems and gained popularity.
• 2000s: With the advancement of rotary systems, nitinol files became a standard in endodontic treatments.
• 2010s and beyond: The development of heat-treated nitinol files provided even greater flexibility and resistance to fracture, further enhancing their clinical performance.

Today, nitinol endodontic files are essential in modern endodontics, particularly for shaping complex root canal systems, and they are a fundamental component of nearly all contemporary endodontic file systems.

4. Nitinol in Orthodontic Retainers

Orthodontic retainers are used to maintain teeth alignment after orthodontic treatment. The advantages of nitinol in retainers include:

• Low, Continuous Force Application: Nitinol wires apply a gentle but continuous force on teeth, preventing relapse without impeding natural physiological movement.
• High Durability and Fatigue Resistance: Fixed retainers must endure long-term intraoral conditions. Nitinol’s fatigue resistance prevents deformation and wire breakage over time.
• Shape Memory and Flexibility: Nitinol’s superelastic properties make it easy to bond to teeth while ensuring patient comfort. Additionally, surface treatments such as laser texturing and atmospheric plasma applications enhance its bonding strength.
• Biocompatibility and Corrosion Resistance: Since retainers remain in constant contact with saliva and food, nitinol’s biocompatibility reduces allergic reaction risks while its corrosion resistance ensures long-term reliability.

Historical Context & Adoption Trends:

• 1970s: The first fixed orthodontic retainers were introduced, but mainly using stainless steel.
• 1990s: Nickel-titanium (NiTi) began being tested for orthodontic applications.
• 2000s: The adoption of NiTi increased with the development of CAD/CAM and robotic wire bending.
• 2010s: More orthodontists started shifting to ribbon made retainers due to their flexibility.
• 2020s: More orthodontists started shifting to NiTi retainers due to their superior flexibility/durability/metal fatigue behaviours.

Why is there no hard data or graphics here for ortho-retainers?

• There is limited published data specifically on the market size of NiTi retainers.
• Most orthodontic industry reports focus on general retainer usage, not specifically NiTi.

We are at the very beginning of this journey, and we are probably 30 years behind heart stents and endodontic files in developing orthodontic retainer products.