The field of orthodontics focuses on the repositioning of teeth within the jaw using light continuous mechanical forces. These forces are applied to enhance the function and improve the overall appearance of the teeth. An understanding of the different techniques used in orthodontic tooth movements allows the creation of treatment plans that are both predictable and efficient.
What is orthodontic tooth movement?
Orthodontics is a special discipline dedicated to the investigation and practice of moving teeth through the bone[1], it comprises tooth movement in the jaw from one position to another to attain function and esthetics[2]. The forces acting on the teeth, muscles, and bone stimulate a response within the periodontal ligament and alveolar bone resulting in tooth movement or alterations in the structure or growth of the bone. Orthodontic tooth movement relies on coordinated tissue resorption and formation in the surrounding bone and periodontal ligament[3].
What are the phases of the tooth movement?
The three phases of tooth movement are as follows:
1. The initial phase: It is characterized by the immediate and rapid movement, it occurs within 24 to 48 hours after the first application of force to the tooth[4]. The tooth undergoes rapid movement because of its displacement in the periodontal space. Due to the force applied to the tooth, there is a compression and stretching of the periodontal ligament[5]. In this stage, tooth movement ranges between 0.4 to 0.9mm and typically occurs within a week's duration.
2. The lag phase: In this phase, the movement is minimal or sometimes no movement at all; the reason for this phase is the hyalinization of compressed periodontal ligament, as the movement will not take place until the necrosed tissue is removed by the cells[6]. Depending on the degree of force applied, the lag phase usually lasts 20 to 30 days and shows relatively little to no tooth displacement[7]; however, sometimes it may at times extend to 10 weeks.
3. The post-lag phase: During the third phase, as the hyalinized zone is removed and the bone undergoes resorption, the movement of the tooth gradually or suddenly increases and is usually seen forty days after the initial force application[8].
What is the rate of predictability of the orthodontic tooth movement?
The predictability of orthodontic movement with aligners still has limitations related to the biomechanics of the system[9] . Aligners biomechanics knowledge plays a crucial role in defining the quality of the orthodontic treatment with aligners[10]. Furthermore, it is crucial to acknowledge that not all teeth exhibit the same response when undergoing orthodontic tooth movements with clear aligners, different teeth have different characteristics, which means that certain teeth may respond better to treatment than others. With that being said, there is no specific rate for tooth movement predictability.
What are the orthodontic tooth movement categories?
All the orthodontic tooth movements fall into two categories:
1. Translations: Bodily movement of teeth, implies an equal movement of crown and root in the same direction with no change or very little to their original inclination[11]. In this case, the force is distributed reasonably evenly along the root axis[12] and the center of rotation is effectively at an infinite distance away from the tooth because there is no rotation[13].
2. Rotations: Pure rotation occurs when a body rotates about the center of resistance[14]; In this case, the teeth undergo movement along a circular arc with the center of resistance being the center of rotation.
What are the orthodontic tooth movement types?
1. Tipping: There are two types of tipping that vary depending on the area on which the force is applied.
- Uncontrolled Tipping: This movement is indicated when we want to change the inclination of the tooth and this tooth may be tipped mesially, distally, buccally, or lingually[15]. Uncontrolled tipping is the simplest tooth movement to carry out and is achieved by the application of a force at one point on the crown of a tooth, such that the crown moves in the direction of the applied force and the apex in the opposite direction[16] . In this case, the center of rotation is near or apical to the center of resistance[17].
- Controlled Tipping: In this case, the center of rotation is at the apex of the tooth[18]. Here the crown moves in one direction but the root position remains the same or is minimally displaced[19].
2. Torquing: It is a differential tooth movement of one part of a tooth (root), physically restraining any other part movement (crown) in a labio-palatal direction[20]. In this case, the center of rotation is at the incisal edge of the crown
3. Rotation: Is a movement "circular" of the crown and the root around their long axis in its socket; this can be produced either by applying a force to one point of the crown and a "stop" to prevent movement of other parts of the crown, or more efficiently by opposite forces to different areas of a tooth[21]. In this case, the center of rotation is at the center of resistance[22].
4. Bodily movement: Whenever a force is applied to the surface of a tooth, the line of action will pass through the center of resistance. This will cause all the points on the tooth to move an equal distance in the same direction.
- Intrusion/Extrusion: It involves the movement along the long axis of the tooth where the center of rotation is at infinity[23]. This is considered a pure translation movement. Intrusion indicates the bodily movement of the tooth apically, whereas extrusion refers to the bodily movement of the tooth occlusally[24].
- Buccal/Palatal: The action of repositioning the teeth towards or away from the lingual side of the arch.
- Mesial/Distal: The act of relocating a tooth towards or away from the midline along the occlusal plane.
[1] Li et al., “Orthodontic Tooth Movement.”
[2] Asiry, “Biological Aspects of Orthodontic Tooth Movement.”
[3] Li et al., “Orthodontic Tooth Movement.”
[4] Zainal Ariffin et al., “Cellular and Molecular Changes in Orthodontic Tooth Movement.”
[5] Asiry, “Biological Aspects of Orthodontic Tooth Movement.”
[6] Adnan, “Biology of Tooth Movement.”
[7] Zainal Ariffin et al., “Cellular and Molecular Changes in Orthodontic Tooth Movement.”
[8] Asiry, “Biological Aspects of Orthodontic Tooth Movement.”
[9] Castroflorio et al., “Predictability of Orthodontic Tooth Movement with Aligners.”
[10] Castroflorio et al.
[11] “Types of Tooth Movements.”
[12] “Types of Tooth Movements.”
[13] McGill, “Physics in Orthodontics.”
[14] McGill.
[15] “Types of Tooth Movements.”
[16] “Types of Tooth Movements.”
[17] McGill, “Physics in Orthodontics.”
[18] McGill.
[19] “Types of Tooth Movements.”
[20] “Types of Tooth Movements.”
[21] “Types of Tooth Movements.”
[22] McGill, “Physics in Orthodontics.”
[23] McGill.
[24] “Biomechanics and Tooth Movement.Pdf.”