Orthodontic Tooth Movement: An Overview

Introduction:

The objective of orthodontics is to straighten the teeth in the jaw, aiming to improve aesthetics and function. Dentists focus on tooth movement to improve patient treatment. When pressure is applied to teeth, their position changes. Understanding the process of tooth movement is important for targeted interventions and improved results. This understanding can guide the design of safer treatment plans in order to achieve desired tooth movement and to improve patient outcomes. The orthodontic treatment plan is designed to be less damaging to the surrounding tissues, such as the gums, and more effective by comprehending these systems.

What Are the Phases of Tooth Movement?

The phases of tooth movement include:

Initial Phase:

• It is the initial phase right after force is applied to a tooth.

• The tooth moves quickly due to the jawbone pushing it.

• This phase lasts for one to two days.

• The ligament around the tooth gets compressed and stretched, leading to inflammation, blood vessel leakage, and the arrival of bone-forming cells.

Lag Period:

• Follows the initial movement and involves minimal to no tooth movement.

• In this phase, the compressed ligament undergoes hyalinization, making the tissue stiff like scar tissue.

• Over the next 20 to 30 days, the body eliminates dead tissue, including some bone.

After-Lag Phase:

• Begins approximately 40 days after force application, marking the third phase.

• The tooth starts moving again, either quickly or gradually.

• Ongoing development and tissue removal are thought to occur as the tooth continues its journey.

• This phase signifies the continuous adjustment of tooth positions.

What Are the Theories of Tooth Movement?

• Bone-Bending Theory: The orthodontic force has a profound impact on the surrounding tissues in the process of tooth movement. The stress generated by this force results in the bending of oral structures, including the periodontal ligament, teeth, and bone. Teeth exhibit faster movement in areas with less calcified (hardened) bone, such as extraction sites or in children, due to the greater elasticity of less rigid bones that bend more readily.

• Biological Electricity Theory: Introduced in 1962 by Becker and Bassett, the biological electricity theory suggests that electrical signals are released when the alveolar bone surrounding a tooth undergoes flexion or bending. These rapid signals, known as streaming potential, dissipate upon force application. The electric signals originating from the bone influence both bone activity and the periodontal ligament. There is a correlation between positively charged areas (indicating higher osteoblastic activity) and negatively charged areas (indicative of more osteoclastic activity). This theory suggests that external electric fields and piezoelectric reactions during bone bending can influence teeth movement.

• Pressure-Tension Theory: Dating back to early 1900s histology research, the pressure-tension theory revolves around the concept that moving the teeth induces tension and pressure zones within the periodontal space. On the pressure side, ligament compression leads to a decrease in blood flow and oxygen levels. On the contrary, the tension side experiences an increase in oxygen levels and blood flow. Variations in oxygen levels affect cellular differentiation and activity. The excessive force applied to the periodontium might result in tissue necrosis or cell death according to this theory.

What Is the Role of Chemical Mediators in Tooth Movement?

The role of chemical mediators is as follows:

Chemokines:

• Pressure-induced cell death in ligaments and bones triggers an inflammatory response.

• Chemokines, attract monocytes which are important for tooth movement.

• Initial hours of tooth movement release inflammatory mediators.

Cytokines:

• Short-range proteins (cytokines) control cell activity during tooth movement.

• Tumor necrosis factor (TNF) and interleukin-1 influence inflammation and bone remodeling.

• They are produced by macrophages, endothelial cells, fibroblasts, and osteoblasts.

Prostaglandins:

• Arachidonic acid breakdown produces prostaglandins, which contribute to inflammation.

• Prostaglandin release increases osteoclasts, which are responsible for bone breakdown.

• Mechanical stimulation during tooth movement triggers prostaglandin production.

Bone Resorption:

• Osteoclasts, derived from hematopoietic stem cells, play a key role in bone resorption.

• Cytokines like TNF-alpha and interleukin IL-1 stimulate osteoclast formation.

• Prostaglandins stimulate RANKL expression, promoting osteoclast development.

• Local cells regulate osteoclasts, and this activity can be viewed on an orthopantomogram (OPG).

What is the Role of Neurotransmitters in Tooth Movement?

Teeth and surrounding tissues receive input from nerves originating from the trigeminal ganglion. Neurons within these nerves contain specific chemicals, including substance P (SP), vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP).

Under typical circumstances, these nerves remain quiet and dormant during daily life.

During orthodontic treatment, such as the use of braces, the situation changes. The application of orthodontic force triggers the release of active proteins, which induces localized inflammation and activates previously dormant neurons. This altered neural activity contributes significantly to the dynamic process of tooth movement.

How Do Neuropeptides Work?

Neuropeptides work in the following ways:

• Capillary Interaction: Neuropeptides, upon release, interact initially with endothelial cells connected to the capillaries.

• Bone Effect: This interaction has a direct impact on bone by increasing blood artery permeability.

• Inflammation Process: The release of neuropeptides initiates acute inflammation as immune cells move out of capillaries. This leads to the release of signaling molecules such as growth factors and cytokines.

• Tissue Reorganization: Tissue remodeling is facilitated by chemicals, including cytokines released during this process.

• Inflammatory Cells: Various immune cells, such as mast cells, monocytes, and lymphocytes, contribute to the inflammatory process by producing cytokines.

• Effects of Substance P: Research indicates that substance P plays a role in tooth movement by increasing levels of collagenase and prostaglandin-E, which are the two inflammatory molecules.

• Role of Vasoactive Intestinal Polypeptide (VIP): Vasoactive intestinal polypeptide (VIP), a potent vasodilator, encourages bone resorption.

What Is the Effect of Medication in Orthodontic Tooth Movement?

• Leukotriene Impact: Leukotriene, a signaling molecule in inflammation, can influence tooth movement. Medications like Montelukast and Zafirlukast can minimize tooth movement by blocking leukotriene receptors.

• Non-steroidal Anti-inflammatory Drugs (NSAIDs) And Paracetamol: NSAIDs, commonly prescribed for various ailments, may affect tooth movement depending on the type, quantity, and duration of usage. Paracetamol (Acetaminophen), however, has little effect on tooth movement.

• Other Medications: Bisphosphonates, typically used for bone disorders, prevent tooth movement during orthodontic treatment. Additionally, the impact of corticosteroids on tooth mobility depends on when and how much of them are taken.

Conclusion:

Orthodontic tooth movement is a coordinated process that involves tissue resorption and formation in both the bone and periodontal ligament. This sequential process leads to osteoclast resorption in compressed areas and osteoblast deposition in tensioned regions, guided by specific signaling factors. A clear understanding of the biology of tooth movement is essential for determining the direction of force application and achieving desired outcomes in orthodontic procedures. Surgical, pharmacological, and physiological factors play significant roles, influencing the process and potentially affecting the final outcome.