Moving Teeth With Orthodontics

How and why teeth move — harnessing the forces of nature

Dear Doctor,
How and why do teeth move during orthodontic treatment, and what are the risks?

Dear Julia,
This question is far ranging, so here are some biology basics of the unique connection of teeth to bone that are key to what allows them to move and be moved. It is all about the connection, the periodontal ligament (“peri” – around, “odont” – tooth). The ligament consists of a group of fibers made of a protein called collagen. These fibers are what anchor and suspend the teeth in the bone. They join to the root surfaces by inserting into a substance appropriately called cementum that is deposited by living cells. On the other side of the ligament, the fibers insert into bone that is very much alive. The total ligament is like a hammock, allowing teeth some movement in their sockets, and through which they are able to respond to the stresses of biting (force).

Constant Change

The periodontal ligament is very dynamic and is constantly remodeling. This process of change is mediated through the cells of the ligament, cementum and bone. Together, they continually form and reform in response to the normal forces of the bite. Biting produces tension and compression transmitted through the fibers of the ligament. Tension causes the cells to respond by depositing bone and cementum, while compression causes resorption or melting away/dissolving of bone and cementum. As with most bodily systems, balance maintains the status quo, and as a consequence, it maintains teeth in their position and in health.

Harnessing The Forces Of Nature

What allows orthodontics to move teeth is the careful manipulation of force that is used to guide the teeth into a new, improved position and better equilibrium.

What allows orthodontics (“ortho” – to straighten; “dont” – teeth) to move teeth is the careful manipulation of force that is used to guide the teeth into a new, improved position and better equilibrium. Light, constant forces applied to the teeth allow them to move in a predictable manner and direction. The movement is preceded by resorption of bone on the compression side of the periodontal ligament and deposition of new bone on the tension side.

Orthodontic forces are applied to the teeth via small brackets rigidly attached to the crowns of the teeth, through which “arch wires” pass (so-called for their arched shape). The arch wires apply controlled forces and cause the teeth to move in a predictable manner and direction so that they can carefully modulate the process of deposition and resorption of bone. Alternatively, teeth can be moved using removable (non-rigidly attached) orthodontic appliances like clear aligners. The actual methods of tooth movement appliances are topics covered in other issues of Dear Doctor magazine.

Benefits and Risks

Clearly the benefits of orthodontic treatment are improved alignment of the teeth that can impact a person's self image. Other benefits include an enhanced and better functioning bite, improved long-term health as well as improved cosmetics (smile, speech and social acceptance). It also provides easier maintenance of periodontal (gum) tissue health.

There are, however, a few risks to orthodontic treatment. One of the risks is occasional root resorption — a blunting of the ends of the roots of the teeth that literally make the teeth shorter. No studies have isolated the cause of root resorption, but the risks are greater if too much force is applied to the teeth.

Resorption is not a deal breaker to going forward with treatment. Evidence of it can be watched for and monitored during the process of treatment. In suspect cases, radiographs (x-ray pictures) of the teeth can be taken during various stages of orthodontic treatment. They can be used to monitor the presence or absence of root resorption.

Another risk is “de-calcification” of the teeth surfaces, which is a loss of the mineral calcium due to acid attack. It is the beginning phase of tooth decay and is seen as white spots that form around the braces. It is imperative to clean the teeth as well as possible to effectively remove bacterial plaque biofilm, which can be challenging with braces on. It is also important to pay attention to proper diet, especially limiting sugar intake and acidic beverage intake.

Who Should Do Orthodontics

Orthodontists are dental specialists who have taken three or more year residencies in the study of growth and development of the face, jaws and teeth, and have specialized in how to move teeth safely and effectively. Some general dentists who have taken advanced training may also undertake orthodontic treatment; however, they must treat to the same standards as orthodontic specialists.

Be sure to have a candid discussion with an orthodontist or your dentist, about the risks, benefits and treatment alternatives for an improved bite and smile through orthodontic treatment.