Quintessence of Dental Technology 2017

Fixed Appliances

Clear Aligners

Future Directions

FIXED APPLIANCES

The history of orthodontics dates back more than 2,000 years, making it the oldest specialty in the field of dentistry. Around 300 to 500 BC, Hippocrates and Aristotle reflected on different ways to straighten teeth and address various other dental conditions. Excavations from the Etruscan period revealed human mandibles with wire ligatures and bands splinting teeth together (Fig 1-1). In 1728, Pierre Fauchard, also known as the "father of modern dentistry," published a book called The Surgeon Dentist. In the chapter on orthodontics, he proposed a horseshoe-shaped piece of precious metal that helped to expand the dental arch, known as Fauchard's bandeau (Fig 1-2). It was ligated to the teeth with wire ligatures and expanded the dental arches to move the teeth into alignment.

Fig 1-1 (a and b) Excavations from the Etruscan period showing metal bands and gold wire ligatures splinting teeth together.

Fig 1-2 Fauchard's bandeau.

In 1901, Edward Angle founded the first school of orthodontics in St Louis, Missouri. Angle devised a simple classification for malocclusion that is commonly used today. In the early 1900s, fixed appliances were known as the "ribbon arch" appliance and consisted of gold bands formed around individual teeth with brackets soldered onto the band (Fig 1-3). Wire ligatures and pins were used to secure the archwire to the bracket. Precious metals that were soft and malleable such as gold and silver-nickel alloy were used.

Fig 1-3 Pin and tube design of the "ribbon arch" appliance.

By the 1950s and 1960s, these once relatively expensive bands were being made out of stainless steel (Fig 1-4). Full-arch banded appliances remained the norm until the innovation of direct bonding allowed orthodontists to directly bond a bracket onto enamel. At that time, the fixed edgewise appliance was known as a "zero-degree" appliance. The orthodontist had to make first-order (in-and-out), second-order (tip), and third-order (torque) bends in the archwire to finish the occlusion.

Fig 1-4 Full-banded stainless steel appliances.

In 1970, Dr Lawrence Andrews proposed building the in-and-out, tip, and torque into the appliance itself, either into the bracket base or the bracket slot. This eliminated the need to make bends in the archwire. This became known as the "straight-wire" appliance and remains the standard of fixed appliances used today (Fig 1-5). There are now many different bracket prescriptions with varying degrees of tip and torque available. Clinicians may choose the bracket prescription of their preference depending on their orthodontic philosophy and the treatment mechanics employed to move teeth.

Fig 1-5 Andrews's straight-wire appliance with brackets directly bonded onto teeth. (Reprinted with permission from Alexander RG. The Alexander Discipline, vol 3: Unusual and Difficult Cases. Chicago: Quintessence, 2016.)

In 1975, two orthodontists, one American and the other Japanese, independently developed a bracket and wire system that could be placed on the lingual surfaces of teeth. "Lingual braces," as they were known, became an esthetic alternative for patients who did not want the brackets to be visible. Lingual bracket systems have also evolved over time to include digital computer imaging to assist with custom-fabricated bracket bases and archwires (Fig 1-6).

Fig 1-6 Lingual bracket system.

As the quest for a more esthetic orthodontic appliance progressed, sapphire and ceramic brackets became available in the early 1980s (Fig 1-7). Around the same time, new archwires with elastic and thermal properties such as nitinol, titanium molybdenum alloy (TMA), and heat-activated nickel-titanium eliminated the need to make complex loops and bends in the archwire. Today, there is a plethora of variations of the standard twin bracket available in different prescriptions, as self-ligating or nonself-ligating, and made of metal, plastic, ceramic, or sapphire.

Fig 1-7 Ceramic brackets. (Reprinted with permission from Alexander RG. The Alexander Discipline, vol 2: Long-Term Stability. Chicago: Quintessence, 2011.)

As we trace the evolution of the orthodontic appliance over the last 100 years, we can see a distinct shift toward an orthodontic appliance that is more esthetic, is more hygienic, occupies less surface area on the teeth, and is able to accurately move teeth into the final occlusion with compatible biologic forces.

CLEAR ALIGNERS

The history of clear aligners may be traced back to 1945, when Dr H. D. Kesling first proposed a clear, vacuum-formed tooth-positioning appliance for minor tooth movement. It was a labor-intensive process that required manually repositioning teeth reset in wax, and a clear vacuum-formed retainer was made for every tooth movement in a series of stages until the teeth were aligned. This technique was capable of minor tooth alignment. However, the amount of labor required for the task precluded its use on a wide scale, particularly for correction of more complex malocclusions.

Another half-century went by until two graduate students at Stanford University in 1997 applied three-dimensional (3D) computer imaging graphics to the field of orthodontics and created the world's first mass-produced, customized clear aligner system. This new technology revolutionized the world of dentistry and orthodontics, launching it into the 21st century.

There is a distinct difference between evolutionary change and revolutionary change. Evolutionary change comprises incremental changes that take place gradually over time. The evolution of fixed appliances represents variations and incremental improvements on a bracket and wire system that has taken place over the last 100 years. Revolutionary change, in contrast, is transformational change. Revolutionary change is profound, dramatic, and disruptive. Revolutionary change challenges conventional thinking and requires a radical paradigm shift in our mindset. Clear aligner technology represents a revolutionary, transformational change in orthodontics that challenges the conventional thinking of how orthodontists move teeth. However, the advent of clear aligner technology does not mean that 150 years of orthodontic principles are no longer valid. The time-tested principles and concepts of bone biology, biomechanics, anchorage, and occlusion still apply. However, in this 21st century of digital technology, the clinician must now learn to apply those principles of orthodontics to the field of clear aligner technique.

Clear aligners have already evolved since they were released to the market in 1999. In the early days of clear aligners, most clinicians understood them to be an orthodontic appliance that was suitable for the treatment of Class I cases with minor crowding, resolved primarily with interproximal reduction. Today, clear aligners from Align Technology are made of a new tripolymer plastic and make use of optimized attachments (Fig 1-8). The teeth are moved according to sophisticated computer algorithms developed in the software program. There are many clear aligner systems being developed all over the world, and it is evident that this will be the future of orthodontics.

Fig 1-8 Clear aligners.

It is important to understand that clear aligner treatment is a technique, not a product. There is a common misconception that clear aligners are a "compromise" orthodontic appliance that is only capable of minor tooth movement. However, the clear aligner system of today is a comprehensive orthodontic appliance, capable of treating a wide range of malocclusions. The remaining chapters of this text discuss the principles of clear aligner technique and lead the clinician through a process of learning how to apply the principles of orthodontics to clear aligner technique.

FUTURE DIRECTIONS

As we look toward the future evolution of orthodontics, the ideal orthodontic appliance could be conceived as a custom-made orthodontic appliance, made to adapt to individual tooth morphology and anatomy. It would be customized to move each individual tooth with exactly the amount of force required to move it based on the tooth morphology and root surface area. It would have customized biomechanics and would be able to adjust the rate of tooth movement according to the individual's bone physiology. The final occlusal outcome would be customized according to the individual's dental arch form, smile esthetics, and soft tissue lip support. The tip, torque, in-and-outs, and occlusal contacts could be designed uniquely for each individual. This ideal appliance would be esthetic, hygienic, and comfortable and would accomplish correction of the malocclusion in the shortest time frame possible.

In reality, the future evolution of orthodontics has already arrived in the present, as clear aligners utilize digital technology for diagnosis, treatment planning, and designing the final occlusal outcome. To a certain degree, it is possible to customize the biomechanics by staging tooth movements...