Written by Dr. Tanya Prasad, BDS, MDS | Medically Reviewed by Dr. Shaista Salam, BDS; Dr. Zein El Hammouz, DDS, MFD/RCSI
Orthodontics involves the movement of teeth within the jaw. It allows clinicians to apply mechanical forces on the teeth and attain the desired teeth positions, functionality, and aesthetics for their patients.
It is important to understand the various methods through which orthodontic tooth movements occur since that can allow practitioners to design predictable treatment plans and better appliances, facilitating safe and accelerated tooth movements.
The primary motive of orthodontic treatment is to move teeth into more favorable and corrected positions for better aesthetics and functionality. This process can involve the movement of teeth in all three planes; sagittal, coronal, and transverse. These will correct both the A-P relationship and teeth alignment. Various types of tooth movements can occur during the process of orthodontic treatment, such as:
Tipping is the simplest type of tooth movement that occurs when a single force is applied to the crown of a tooth. Controlled tipping allows a unidirectional crown movement while the root moves minimally in the opposite direction. In contrast, uncontrolled tipping tips the crown in the direction of the force while the root moves in the opposing direction (1).
During the course of orthodontic treatment, the crowns of certain teeth may be tipped in a mesiodistal direction, with the roots tipped in the opposite direction. Tipping these roots back into a parallel orientation is accomplished by uprighting tooth movement (17).
Bodily movement or translation of teeth occurs when the crown with the root moves an equal distance in the same direction (1). This happens when the applied force passes through a tooth's center of resistance (COR). The COR of a single-rooted tooth lies between one-third and one-half of the root, while in a multi-rooted tooth, it lies between the roots.
Intrusion occurs when a tooth bodily moves along its long axis in an apical direction (towards the gingiva). In contrast, extrusion is the bodily movement of a tooth along its long axis towards the occlusal plane (17).
Orthodontic correction involves correcting rotated teeth and getting them into the correct alignment. This occurs through rotational tooth movement, allowing teeth to move labially or lingually/palatally around their long axis (17).
Torquing tooth movement allows orthodontists control over the axial inclinations of the teeth. It can also be considered reverse tipping, characterized by the lingual movement of the root (17).
The tooth is surrounded and held by periodontal fibers that hold the tooth within the bony socket. As a rule of thumb, it can be said that orthodontic tooth movement occurs due to compression of the periodontal ligament that undergoes resorption. At the same time, bone formation takes place under tensile force due to the stretching of the periodontal ligament.
Orthodontic tooth movement progresses through three stages:
The initial phase occurs immediately after the application of force onto the tooth. This results in rapid tooth movement over a short distance and then stops. This movement displaces the tooth within the periodontal membrane and bends the alveolar bone to a certain extent. The initial phase results in about 0.4 to 0.9 mm of tooth movement and usually occurs within a week after applying initial force (1,2).
The Lag phase sees little to no tooth movement and witnesses the formation of hyalinized tissue in the periodontal ligament. This hyalinized tissue must undergo resorption before further tooth movement can occur. The duration of the lag phase depends on the amount of force applied.
Supposedly a clinician applies lighter force, the amount of hyalinized tissue will be less; hence resorption of the same will occur faster. In contrast, a more prolonged lag phase is seen when heavier forces are applied orthodontically (2,3). The duration of the lag phase also depends on factors such as the patient's age and the density of the alveolar bone.
After the resorption of the hyalinized tissue or the lag phase, tooth movement progresses rapidly. This occurs in the post-lag phase, where bone undergoes resorption via the help of osteoclasts, resulting in direct resorption of the bone that faces the periodontal ligament (1,2).
Hormones such as estrogen, androgens, and thyroid can influence the rate of orthodontic tooth movement. A clinician should pay special attention to a patient's medical conditions that might cause fluctuations in their hormone levels (24).
Vitamin D influences the absorption of essential hormones such as calcitonin that influence the cells responsible for bone remodeling. Monitoring vitamin D levels under the supervision of a specialist can ensure an optimal rate of orthodontic tooth movement (4).
Non-steroidal anti-inflammatory drugs or NSAIDs are clinically used as anti-inflammatory medications. NSAIDs inhibit prostaglandin synthesis; hence, patients undergoing long-term acetylsalicylic acid therapy may show slow orthodontic tooth movement (7).
Bisphosphonates are potent inhibitors of bone resorption and are prescribed therapeutically during conditions such as osteoporosis and osteopenia. Bisphosphonates can inhibit tooth movement and impair bone healing (23).
Hence it is essential for patients to inform their doctors about any medications they might take. This will allow clinicians to optimize their orthodontic treatment plan accordingly (23).
Younger patients may experience faster orthodontic tooth movement during the first phase of the treatment than older age groups (8). However, it is still possible to have successful treatment outcomes as adults. The evolution of modern treatment modalities like aligners has led to hundreds of adults seeking out successful orthodontic treatments year after year.
In today's fast-paced world, orthodontic treatment aims not only to create a functionally harmonious occlusion but also to complete the treatment efficiently in minimal time. Over the years, several methods have been developed to accelerate tooth movement and reduce treatment duration.
Corticotomies involve placing intentional cuts on the cortical bone, allowing for increased bone remodeling. A corticotomy results in accelerated repair and recovery of the alveolar bone and can result in faster orthodontic tooth movement.
The Wilcko brothers introduced a method that combined corticotomies with alveolar bone grafting to effectively increase the orthodontic tooth movement rate.
PAOO has been shown to reduce treatment time, reduce root resorption, and increase bone support (9).
Micro-osteoperforations is a procedure that was developed to reduce the invasiveness of earlier surgeries. This procedure involves the creation of pinhole-sized perforations in the alveolar bone surrounding the teeth. As a result, the area witnesses increased osteoclast activity, subsequently leading to increased bone resorption. This resulted in accelerated tooth movement and reduce orthodontic treatment time by 62% (10).
A recent study reported that using CAD/CAM technology alone can significantly reduce treatment time from 543 days to 394 days when combined with piezocision (12). Auxiliaries like attachments, elastics, and TADS have also enabled the treatment of complicated cases and reduced treatment time (11).
The application of high-frequency vibration (at 120 Hz) during orthodontic treatments showed an increase in the rate of tooth movement. A study reports that high-frequency vibration, when used in adjunct to clear aligners, allowed shorter treatment time in minimum to moderate crowding cases (13).
Photobiomodulation is another non-invasive method to accelerate tooth movement in orthodontics (14).
In cases with challenging tooth movements, such as molar distalization or closing of extraction cases, acceleration with photobiomodulation can increase the predictability of the treatment and reduce post-adjustment pain (17).
According to some studies, electromagnetic fields increase the levels of enzymes that regulate intracellular metabolism and increase the rate of alveolar bone remodeling. This can potentially reduce orthodontic treatment time (15).
Direct electrical stimulation has been proven to increase the number of osteoclasts in the periodontal membrane, suggesting an acceleration of orthodontic tooth movement. Future research can help establish the potency of electrical stimulation on orthodontic tooth movements(15).
Fear of orthodontic pain has been one of the most common deterrents for patients seeking a beautiful smile. In addition, recent advancements such as aligners have allowed clinicians to apply light and continuous forces, resulting in quick tooth movement that also reduces the patient discomfort.
With the right treatment plan, the supervision of an experienced clinician, and a motivated patient, aligners cause minimal pain. In fact, evidence suggests that a proportion of patients undergoing clear aligner treatment have reported no pain during treatment (16).
During the course of orthodontic treatment, some cases report having cementum and dentine resorption, which has been termed "orthodontic-induced root resorption or (OIRR)." However, the development of aligners and co-axial wires is protective against OIRR(18). The occurrence of resorption can be easily minimized by implementing the right treatment plan and using modalities such as aligners that exert light forces on teeth.
Orthodontic appliances risk promoting plaque accumulation and the development of white spot lesions (19). However, modern modalities like aligners allow patients to maintain optimal oral hygiene throughout treatment. Aligners allow patients the ease of removing their trays during meals and ensure ease while brushing. Optimal cooperation by patients can ensure excellent oral hygiene during the course of orthodontic treatment.
Orthodontic tooth movement is a nuanced topic and requires a clinician to understand the biological changes that occur at the cellular level. With the application of gentle but continuous forces, clinicians can effectively change the position of teeth and bring them into harmonious occlusion.
Further, recent advancements in orthodontics, such as clear aligners, corticotomies, photobiomodulation, etc., not only bring about accelerated tooth movement but also act as effective time-saving techniques.
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