When a patient begins orthodontic treatment, the primary components are the brackets bonded to individual teeth and the archwire threaded through them. The archwire functions by storing and releasing energy to progressively move teeth into straight alignment. This system is highly effective at correcting crowded or crooked teeth within a single dental arch. However, achieving a beautiful smile requires the top and bottom teeth to fit together correctly, which is where orthodontic rubber bands, or elastics, become necessary.
Why Wires Alone Are Not Enough
The fundamental limitation of the bracket and archwire system is its focus on intra-arch movement, meaning movement within a single jaw. Wires use gentle, continuous force to remodel the bone supporting the tooth roots, guiding individual teeth into a level and aligned position. This system continually attempts to return to a smooth arch form, carrying the teeth along with them.
This system cannot, however, generate the necessary inter-arch force required to correct the relationship between the upper and lower jaws. When the upper and lower teeth do not meet properly—a condition called malocclusion or a bite problem—a direct force vector across the arches is needed. Elastics provide this specific, continuous force by connecting anchor points between the two dental arches. They are the mechanical means of moving entire groups of teeth or adjusting the skeletal relationship to ensure a healthy, functional bite.
This inter-arch force stimulates bone remodeling in both the upper and lower jaws simultaneously, guiding them into the correct three-dimensional relationship. Without this supplemental force, the teeth can be perfectly straight, yet the bite remains incorrect, leading to potential issues with chewing, jaw pain, or excessive wear on certain teeth. Elastics are introduced after initial alignment to fine-tune the final bite position, which is the ultimate goal of orthodontic treatment.
Applying Force Specific to Bite Correction
Orthodontic elastics are categorized by the specific bite correction they are designed to achieve, with their placement determining the direction of the force vector. The most common applications are classified by the direction of the front-to-back movement, referred to as sagittal correction. For patients with an overbite, where the upper teeth are too far forward relative to the lower teeth, Class II elastics are prescribed.
Class II elastics typically run from a hook near the upper canine or premolar back to a hook on a lower molar. This diagonal positioning creates a force that simultaneously pulls the upper teeth backward and the lower teeth forward. Conversely, to correct an underbite, where the lower jaw is too far forward, Class III elastics are used. These elastics are anchored from a hook on a lower canine or premolar and stretch forward to a hook on an upper molar.
This reverse placement of Class III elastics pulls the lower teeth backward while encouraging the upper teeth to move forward. The force applied by these elastics is typically a medium force, depending on the treatment stage. Beyond these sagittal movements, elastics can also be configured vertically to close a gap between the upper and lower front teeth, known as an open bite. Cross-elastics, which stretch across the mouth from the inside of a tooth on one arch to the outside of a tooth on the opposing arch, are used to correct crossbites.
The Role of Patient Adherence
Unlike brackets and wires, which are fixed appliances, elastics are removable, making their effectiveness entirely dependent on the patient’s discipline. The goal of elastics is to apply a light, continuous force to encourage biological changes in the bone and tooth position. This force must be sustained for the movement to be efficient and successful, which is why orthodontists typically instruct patients to wear the elastics for 20 to 24 hours per day. They should only be removed for eating, brushing, and flossing, and must be immediately replaced afterward.
Inconsistent wear, such as removing the elastics for several hours, can cause the progress made during wear time to be lost or even reversed. The most frequent consequence of poor adherence is a significantly extended treatment time, as the teeth and jaws cannot move as planned without the prescribed force. A lack of compliance can prevent the orthodontist from achieving the desired bite correction, potentially leading to a compromised final result. Patients must also change the elastics frequently, often several times a day, because the elastic material loses its tension and force over time.