Orthodontic elastics, often called rubber bands, are used with braces or clear aligners to achieve proper alignment of the teeth and jaws. Interarch elastics, like the Class III type, create a continuous, gentle force between the upper and lower arches to correct a specific alignment issue, known as a malocclusion. They apply directed pressure across the bite that the fixed wires and brackets alone cannot produce. Class III elastics are prescribed to address a jaw relationship that requires coordinated movement of both the upper and lower dental arches.
Defining the Class III Malocclusion
The Class III malocclusion is commonly referred to as an underbite. It occurs when the lower jaw or lower teeth are positioned forward relative to the upper jaw and teeth. The lower front teeth sit in front of the upper front teeth when the mouth is closed, reversing the typical bite. This misalignment is often apparent in the patient’s profile, leading to a more prominent chin appearance.
The protrusion of the lower dental arch impairs normal mouth function. The misalignment interferes with chewing efficiency, as the teeth do not meet correctly. The incorrect bite relationship can also impact speech patterns, particularly the pronunciation of certain sounds. Addressing this condition is important for facial aesthetics and for the long-term health and stability of the jaw joints and teeth.
The Biomechanical Function of Class III Elastics
Class III elastics generate a reciprocal force vector to reposition the dental arches. The rubber band runs diagonally from a hook on the upper arch (often near the molar) to a hook on the lower arch (closer to the front teeth). This diagonal placement creates a continuous tension that acts in opposite directions on the two jaws. The force simultaneously pulls the upper arch forward and the lower arch backward.
On the upper arch, the force pulls the teeth forward (mesial direction). Conversely, the tension pulls the lower teeth backward (distal direction). This coordinated movement shifts the lower dental arch backward and the upper dental arch forward until the teeth meet in a balanced Class I bite relationship. The sustained, light force encourages the slow remodeling of the bone surrounding the tooth roots, allowing for the necessary repositioning of the teeth.
Proper Usage and Patient Compliance
The effectiveness of Class III elastics depends entirely on consistent patient wear. To produce reliable tooth movement, the elastics must be worn nearly 24 hours a day. They should only be removed briefly for eating and thorough brushing and flossing. Wearing the elastics for fewer than 20 to 22 hours per day significantly reduces the treatment’s efficiency.
Elastics must be changed frequently, typically at least once or twice daily, even if they have not broken. Over several hours of use, the rubber band loses its elasticity, meaning the force decreases below the optimal therapeutic level. Using a fresh elastic ensures that the force remains consistent, which is necessary for continuous tooth movement. Failing to maintain this consistent wear pattern leads to significant setbacks, causing teeth to drift back and stalling the entire treatment process.
Inconsistent wear prolongs the overall time spent in orthodontic treatment and makes achieving the final correction difficult. Patients may experience some initial tenderness in the teeth and jaw muscles due to the new pressure. This soreness is temporary and usually resolves within the first week as the mouth adjusts to the force. Continuing to wear the elastics through this initial period manages the discomfort and ensures the treatment progresses as planned.