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Teeth move through the use of force. The force applied by the archwire pushes the tooth in a particular direction and a stress is created within the periodontal ligament. The modification of the periodontal blood supply^[2] determines a biological response which leads to bone remodeling, where bone is created on one side by osteoblast cells and resorbed on the other side by osteoclasts.

Two different kinds of bone resorption are possible. Direct resorption, starting from the lining cells of the alveolar bone, and indirect or retrograde resorption, where osteoclasts start their activity in the neighbour bone marrow. Indirect resorption takes place when the periodontal ligament has become(necrosis or hyalinization), for an excessive amount and duration of compressive stress. In this case the quantity of bone resorbed is larger than the quantity of newly formed bone (negative balance). Bone resorption only occurs in the compressed periodontal ligament. Another important phenomenon associated with tooth movement is bone deposition. Bone deposition occurs in the distracted periodontal ligament. Without bone deposition, the tooth will loosen and voids will occur distal to the direction of tooth movement.

A tooth will usually move about a millimeter per month during orthodontic movement, but there is high individual variability. Orthodontic mechanics can vary in efficiency, thus explaining a wide range of response to orthodontic treatment.

Types of braces

Modern orthodontists can offer many types and varieties of braces:

• Traditional braces are stainless steel, sometimes in combination with nickel titanium, and are the most widely used. Many stainless steel brackets are offered by various orthodontic supply companies. These include coventional braces that require ties and newer self-tying (or Self-Ligating Braces) brackets, like Time brackets by American Orthodontics, SmartClip Brackets by 3M Unitek, In-Ovation R by Dentsply GAC, SPEED, or Damon brackets. Self ligating brackets, in some conditions, determine a reduction of friction between the wire and the slot of the bracket.
• Clear braces serve as a cosmetic alternative to traditional metal braces by blending in more with the natural color of the teeth. Typically, these brackets are made of ceramic or plastic alloys, but function in a similar manner to traditional metal brackets. Clear elastic ties and white metal ties are available to be used with these clear braces to help keep the appliances less noticeable. Clear braces have the highest component of friction, and tend to be more brittle than the metal braces, causing them to fracture easily. This can make removing the appliances at the end of treatment more difficult and time consuming.
• Gold-plated stainless steel braces are for people allergic to nickel (a component of stainless steel), but may be chosen because they blend better with teeth, and some people simply prefer the look of gold over the traditional silver-colored braces.
• Lingual braces are fitted behind the teeth, and are not visible with casual interaction. Lingual braces can be more difficult to adjust to, since they can hinder tongue movement. Only dentists and orthodontists who have been trained in Lingual technique can offer Lingual braces.
• Progressive clear retainers, marketed under the tradename Invisalign, may be used to gradually move teeth into their final position. These have the same effect as braces but can be removed easily for eating. These type of braces are generally not used for complex orthodontic cases, such as when extractions, jaw surgery, or palate expansion are necessary.
• Like Lingual braces, Ceramic braces, and clear retainers; shaped braces are also available as an aesthetic option. These shaped braces, developed and marketed by WildSmiles Brackets, work like any normal non-shaped bracket. On normal non-shaped brackets the pad (the part of the bracket that attaches to the tooth) is a square shape. For the shaped braces the pad is not square but heart, star, round, diamond, and even flower shaped.
• A new concept under development are braces using so-called smart brackets. The smart bracket concept consists of a bracket containing a microchip capable of measuring the forces applied to the bracket/tooth interface. The goal of this successfully demonstrated concept is to significantly reduce the duration of orthodontic therapy and to set the applied forces in non-harmful, optimal ranges.

Post-treatment

In order to avoid the teeth moving back to their original position, retainers may be worn once the treatment with braces is complete.

Patients may need post-orthodontic surgery, such as a fiberotomy or alternatively a gum lift, to prepare their teeth for retainer use and improve the gumline contours after the braces come off.

Pre-finisher

If a person's teeth are not ready for a proper retainer, the orthodontist may prescribe the use of a pre-finisher. This rubber appliance similar to a mouthguard fixes gaps between the teeth, small spaces between the upper and lower jaw, and other minor problems that could worsen. These problems are small matters that dental braces cannot fix.

The pre-finisher is molded to the patient's teeth by use of severe pressure to the appliance by the person's jaw. The pre-finisher is then worn for the prescribed time, with the user applying force to the pre-finisher in their mouth for ten to fifteen seconds at a time. The goal is increasing the "exercise" time, time spent applying force to the appliance. Like the retainer, the pre-finisher is not a permanent addition to one's mouth, and can be moved in and out of the mouth.

Treatment time and cost

Typical treatment time is from six months to six years, depending on the severity of the case, location, age, etc., although research has shown that the average duration is 28.6 months.^{[citation needed]} Treatment can be accelerated using novel planning and positioning techniques.

The typical cost of braces ranges widely in various regions. The cost depends on whether both arches are being treated and the length of treatment. Typical orthodontic treatment comprises metal braces on both arches for 12 to 24 months. The 2007 orthodontic practice study done by the Journal of Clinical Orthodontics showed the national average cost of braces for comprehensive orthodontic treatment to be $4,941 for children and $5,354 for adults.^{[citation needed]} Some cases in the United Kingdom cost £3,500, although they can much of the time be provided free on the NHS, providing the patient is under 18, a student up to to 19, a pregnant woman, a nursing mother or living on a low income.

In some European countries (e.g. Finland, Sweden, Slovenia, Germany, Croatia or Denmark) orthodontic treatment is available without charge to patients under 18 (or for treatment to start at 16, such as Ireland and the UK) as benefits for orthodontic treatment are provided under government-run health care systems. In some countries (e.g. Ireland), adults can also get treatment at a discounted rate, or claim tax relief after paying a full cost with a private practitioner.

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