Clinical Success in Invisalign Orthodontic Treatment (eBook)

What Is Invisalign?

• Invisalign is a minimally visible method for moving teeth without band, wire, or bracket.

• Invisalign therapy consists of a series of clear aligners that are worn to gradually move teeth (Fig 1-1).

• An Invisalign aligner is a custom-made, removable, comfortable dental retainer made from thermoformed medical polycarbonate, which is inert and compatible with human saliva. (See following section for details on thermoforming.)

• Each aligner is worn approximately 22 hours a day over a 2-week period for a total of over 300 hours. This leaves 2 hours a day for eating and toothbrushing.

• Aligners are replaced every other week on average to allow for gentle tooth movement over time according to the clinician’s diagnosis and treatment plan.

• Treatment duration, which can range from 3 to 30 months, and cost depend on the extent of tooth malpositioning and malocclusion.

The Science of Invisalign Aligners: Thermoforming

Thermoforming is the art of shaping thermoplastic materials with heat. Chemically, plastics consist of polymers that are made up of numerous monomers, which are organic molecules with nuclei that contain one carbon atom. Examples of natural polymers include proteins, rubber, collagen, and cellulose. The behavior of plastics mostly depends on the type of structure developed by polymerization of constituent monomers. To optimize their behavior, additives can be used to modify physical and chemical properties, and reinforcements can be added to modify mechanical properties.

In orthodontics, plastic materials in the form of soft, resilient round or square sheets (Fig 1-2) possessing excellent modeling properties are often used. These materials are inert, unaltered by saliva, and resistant to daily cleaning detergents. In addition, they are transparent, nontoxic, odorless, and tasteless.

Scheu et al proposed the first thermoforming machine to synthesize orthodontic appliances in 1966. Currently, two types of thermoforming machines, the Ministar and Biostar (Scheu Dental) (Fig 1-3), are available. Based on the principles of Scheu et al, Align Technology developed a large-scale, custom-made thermoforming system, which continues to undergo development and improvement (Fig 1-4).

Development of Align Technology

Design for the thermoforming system began in April 1997 when two MBA students from Stanford University, Zia Chishti and Kelsey Wirth, with the aid of a computer specialist, founded Align Technology in a garage in Palo Alto, California.

Chishti, who had suffered a relapse of mandibular incisor crowding after undergoing fixed orthodontic treatment, was required to wear a retainer to realign his mandibular anterior teeth. Disappointed by the relative slowness and limited progress of the relapse correction, Chishti conceived a revolutionary treatment concept: moving teeth with multiple appliances, whereby each tooth movement would be progressively conceptualized in three dimensions and virtually simulated by computer-assisted design software.

Appliances would be mechanically fabricated under computer control through a stereolithographic process to create resin models for each stage of desired tooth movement. These models would then be combined with thermoformed polycarbonate sheets, which would allow for mass-produced, custom-made aligners for orthodontic treatment.

This new concept for orthodontic treatment combined orthodontic principles of tooth movement, 21st century three-dimensional (3D) computer-aided design/computer-assisted manufacture (CAD/CAM) technology, and computer-assisted, mass-prototyping industrial processes, ultimately leading to the development of the Align Technology company and the current Invisalign treatment concept and techniques.

This new system gained clearance from the Food and Drug Administration in 1998. It was presented at the American Association of Orthodontists conference in 1999 and arrived in Europe in 2001. By broadening the range of applications, Invisalign has introduced a new method of orthodontic therapy.

Advantages of the Invisalign System

Minimal visibility

The transparency of Invisalign is a key feature and responds to the increasing demand from adult and adolescent patients for discreet orthodontic devices that are more suitable to social and professional life. In this way, Invisalign provides access to new patients who would otherwise decline treatment. Even patients with complications such as a missing tooth can benefit from Invisalign therapy. A prosthetic replacement tooth, called a pontic, can be incorporated into the appliance to replace an extracted tooth for esthetic enhancement (Fig 1-5).

Removability

During treatment, the patient can remove the aligners to eat or drink or for an important meeting. A storage container is supplied with the first aligner in the Patient Starter Kit (Fig 1-6).

Versatility

Toothbrushing and periodontal maintenance are well facilitated. Aligners can be inserted on natural or prosthetic teeth, definitive or provisional fixed prostheses (implant-supported or not), and resin and metal removable prostheses. Aligners can also serve as drug or chemical diffusers during orthodontic treatment and can administer substances such as toothbleaching products (Fig 1-7). To reduce periodontal risk, some periodontists recommend adding a drop of chlorhexidine gel at the molar region of the aligner. When the aligner is inserted in the mouth, the gel will flow and spread over the inner surface.

Comfort

Custom-made aligners adapt to teeth so that the margin coincides precisely with the dentogingival junction. Lips, cheeks, and tongue naturally slide along aligners as they would teeth. Fabricated by a precise industrial and automated process, aligners do not produce the irritation usually caused by the defects and irregular borders of appliances made by traditional methods. Wounds in the mouth caused by brackets, bands, wire, and other accessories of fixed appliances are also eliminated. Emergency treatment visits for rebonding of accessories or repairs of material breakage are also avoided.

Ease

Simple

The computer-assisted design process provides clear images of the progressive tooth movements, allowing the patient to easily understand the treatment plan and immediately visualize the progression of treatment (Fig 1-8).

Understandable

The virtual treatment demo offered through the program ClinCheck is an excellent communication tool: It allows for informed consent regarding treatment duration, type of tooth movements, number of aligners, and any necessary attachments or interproximal enamel reductions necessary for the desired outcome. Note: All ClinCheck protocols and features mentioned refer to those associated with the current version, ClinCheck 2.9.

Practical

The treatment principle is simple and unvarying: Each aligner is worn an average of 300 hours—22 hours a day for 14 days. In-office replacement requires few instruments and little time per visit.

Efficiency

Precalculation of tooth movements can reduce the global treatment time by:

• Limiting the number of tooth movements to only those necessary by counteracting undesirable movements

• Eliminating dental arch leveling phases required in fixed orthodontic techniques

• Providing several treatment options via simulations that show methods with the shortest treatment time (Fig 1-9)

Disadvantages of the Invisalign System

Removability

The advantage of removability can become a disadvantage in the absence of patient compliance. Indeed, the patient must be vigilant in wearing an aligner every day for the requisite 22 hours a day and changing it every other week without fail. In addition, intra- or interarch traction elastics may be prescribed,...