Orthodontic elastics, commonly known as rubber bands, are small, stretchable loops that play a significant role in orthodontic treatment. These bands are attached to brackets or specialized hooks on the upper and lower teeth, providing forces that braces alone cannot easily generate. Their purpose is to apply gentle, continuous pressure to achieve proper alignment of the bite and the upper and lower jaws. This force helps to move teeth into their ideal positions, ultimately contributing to a functional and aesthetically pleasing result.
The Underlying Mechanics of Tooth Movement
Orthodontic elastics work by introducing a controlled force vector between the upper and lower arches of the mouth. A force vector has both strength (magnitude) and direction, which dictates the path of movement. The constant pull creates stress on the periodontal ligament, the tissue that surrounds the tooth root. This stress triggers biological processes in the jawbone, leading to bone resorption on the pressure side and bone deposition on the tension side.
The elastics are designed to deliver a specific, gentle force over time, which is essential for healthy tooth movement. Orthodontists select elastics based on two primary characteristics: their diameter, which determines how far they must stretch, and their force rating (light, medium, or heavy). The specific size is chosen to ensure the force applied is optimal for the required distance and direction of movement.
The force exerted by the elastic bands is always decaying, which is why consistent replacement is necessary. Elastic bands can lose approximately 20–25% of their initial force within 24 hours. The direction of the elastic’s placement dictates the force vector, pulling the teeth in a specific, diagonal path that straight wires cannot duplicate. This mechanical principle allows for the comprehensive repositioning of teeth and the correction of jaw alignment issues.
Addressing Specific Alignment Issues
The primary clinical application of orthodontic elastics is the correction of discrepancies between the upper and lower jaws, known as malocclusions. One common issue is a Class II malocclusion, or overbite, where the upper teeth and jaw project too far forward relative to the lower jaw. To correct this, Class II elastics are stretched from an anchor point on the upper arch, such as the canine, to a posterior anchor on the lower arch, like a molar. This diagonal pull applies a force that simultaneously moves the upper teeth backward and the lower teeth forward.
Conversely, a Class III malocclusion, or underbite, occurs when the lower jaw protrudes past the upper jaw. Corrective Class III elastics are worn in the reverse configuration, running from a lower tooth forward to a corresponding upper tooth. This arrangement applies a force that pulls the lower teeth backward and the upper teeth forward, aiming to establish a balanced bite relationship. These inter-arch movements are essential for improving jaw function and facial symmetry.
Elastics are also used in other configurations, such as cross-elastics, to correct a crossbite, where the upper teeth fit inside the lower teeth. The elastic is stretched across the arch to move teeth into proper alignment. Vertical elastics, often forming a triangular or box shape, are used to close open bites, where the front or back teeth do not meet when the mouth is closed. These various patterns of wear allow for precise, three-dimensional control over the final dental alignment.
Practical Guidelines and Patient Responsibility
The success of treatment using orthodontic elastics depends heavily on patient adherence to the prescribed wearing schedule. Orthodontists instruct patients to wear the elastics for approximately 20 to 22 hours per day, removing them only for brushing, flossing, or eating. This near-constant wear is necessary because the tooth movement process requires a continuous application of light force. Wearing them only at night or for short, intermittent periods will not be effective and can cause the teeth to move back and forth, which slows or stops progress.
Patients should replace their elastics multiple times a day, often as frequently as after every meal or at least two to four times daily. This frequent replacement is crucial because the elasticity and force of the bands diminish rapidly over time due to wear and exposure to the environment of the mouth. Using worn-out elastics does not provide the required force for movement.
Non-compliance with the wearing schedule is the most common reason for extended treatment time. When elastics are not worn consistently, the teeth may revert to their previous positions, undoing days of progress. Patients may experience initial soreness for the first few days, which is a normal sign that the teeth are beginning to move. However, inconsistent wear causes this soreness to return repeatedly, as the teeth never fully adjust to the pressure.