Orthodontic elastics are small, medical-grade rubber bands used in conjunction with brackets and wires. They are not designed for maximum power but for delivering a specific, controlled force over time. Their primary function is to correct the relationship between the upper and lower dental arches, a process known as occlusion or bite correction.
The Purpose of Orthodontic Elastics
Orthodontic treatment requires consistent, light pressure to achieve biological movement. Applying excessive force can damage the root structures of the teeth and slow down the treatment process. Therefore, elastics are selected based on the precise force needed to guide teeth into a new position.
There are two types of elastics used in braces. Ligature elastics are small rings placed around each bracket to hold the archwire in place. Interarch elastics are the patient-worn bands that stretch between hooks on the upper and lower jaws. Interarch elastics are responsible for correcting bite alignment by applying force across the dental arches.
Measuring and Categorizing Force
The strength of an orthodontic elastic is a carefully calibrated measurement determined by two physical specifications. The first metric is the band’s diameter, measured in fractions of an inch (e.g., 1/8″, 1/4″). This size refers to the unstretched internal diameter of the elastic.
The second measure of strength is the force rating, listed on the packaging in ounces (oz) or grams (g). Ratings are categorized as light, medium, or heavy, corresponding to forces like 3.5 oz, 4.5 oz, or 6.0 oz. Manufacturers determine this rating by stretching the elastic to three times its internal diameter and measuring the static force it generates, an informal standard known as the “rule of 3.”
A higher ounce rating indicates a stronger elastic that produces a greater amount of force when stretched. Material also affects performance, with options including natural rubber (latex) and non-latex synthetic alternatives. The orthodontist selects the combination of size and force rating that generates the exact pressure required for the intended movement.
Classification of Elastic Wear
The necessary force depends entirely on the direction and distance of the required tooth or jaw movement. The two most common configurations are Class II and Class III elastics, which address discrepancies in the front-to-back relationship of the jaws.
Class II elastics correct an overbite (Class II malocclusion), where the upper jaw is positioned too far forward relative to the lower jaw. The bands stretch from a hook on the upper jaw to a hook further back on the lower molar. This configuration applies a rearward force to the upper teeth and a forward force to the lower teeth.
Conversely, Class III elastics correct an underbite (Class III malocclusion). This configuration is the opposite of Class II, running from a hook on the lower jaw to a hook on the upper molar. The resulting force pulls the lower teeth backward and the upper teeth forward.
Other patterns, such as vertical or crossbite elastics, are used for specific alignment issues. Vertical elastics, often configured as a box or triangle, help close an open bite by applying vertical force. The force level prescribed for these movements must be sufficient to move the entire dental arch, which is why forces in the range of 5 to 6 ounces are commonly used.
Maintenance and Compliance for Effective Treatment
Patient compliance is the single greatest factor in successful treatment, as even the technically strongest elastic is ineffective if not worn correctly. Elastics must be worn for approximately 22 to 23 hours a day to maintain the continuous pressure needed for biological tooth movement. Wearing them only at night, for example, is insufficient, as the intermittent force allows the teeth to drift back.
Elastics must be replaced multiple times throughout the day, often three to four times, because they quickly lose their elasticity and force capacity. They should only be removed for eating, brushing, and flossing, and a fresh set must be put in immediately afterward. The most effective rubber band is the specific one, with the precise force and size, prescribed by the orthodontist.