Orthodontic adhesive, the specialized material used to attach brackets to teeth, is a sophisticated dental composite resin, not common “super glue.” This material is engineered to create a temporary yet robust connection to the smooth surface of the tooth enamel. The adhesive must securely hold the bracket throughout treatment while also allowing for safe removal later without damaging the tooth structure. Its strength is carefully calibrated to resist the continuous forces of tooth movement and the intermittent, higher forces of chewing.
The Chemistry Behind the Bond
Orthodontic adhesive is primarily a composite resin, similar to the white fillings dentists use, consisting of a polymer matrix and filler particles. This material requires a specific curing process to harden, typically through light activation using a high-intensity blue light. The process begins by conditioning the enamel surface, usually with a mild acid like 37% orthophosphoric acid, to create a microscopic, porous texture.
This etching process facilitates micromechanical retention, which is the true source of the bond’s strength. The liquid adhesive and primer flow into these newly created pores on the enamel surface, forming thousands of microscopic anchors. When cured by light, these resin tags harden within the enamel structure, creating a physical interlock rather than a purely chemical connection. This mechanical anchoring ensures the bracket remains firmly attached, resisting forces that would shear it away from the enamel.
The Necessary Strength Balance
The strength of the braces glue is a precise engineering compromise: strong enough for treatment but weak enough for safe removal. Orthodontic adhesives must achieve a minimum shear bond strength (SBS), which is the force required to break the bond parallel to the tooth surface. Research suggests that a bond strength between 6 and 8 MegaPascals (MPa) is the ideal clinical range to withstand chewing forces and the continuous light forces used to move teeth.
If the bond strength is too low, the bracket will frequently detach, interrupting treatment and requiring re-bonding appointments. Conversely, if the adhesive is too strong, exceeding values like 13.5 MPa, there is a risk of damaging the underlying enamel upon intentional removal at the end of treatment. The bond is engineered to fail safely when a controlled, high force is applied by the orthodontist during debonding. The adhesive must resist three main types of force: tension (pulling away from the tooth), compression (pushing into the tooth), and, most importantly, shear, which occurs during chewing.
Protecting the Bond
While the adhesive is highly durable, its strength can be easily overwhelmed by patient behavior. The most frequent cause of bond failure is consuming certain foods, particularly those that are hard, sticky, or crunchy. Hard foods like nuts, ice, or hard candy apply excessive compression or tension forces that exceed the adhesive’s shear strength, fracturing the bond. Sticky foods, such as caramel or taffy, apply significant tensile forces as they are pulled away, stressing the adhesive-bracket interface.
Other habits, like chewing on pens, pencils, or fingernails, introduce intense shear forces that can lead to sudden bracket detachment. Trauma, such as a blow to the mouth, can also cause the bond to fail immediately, which is preferable to the tooth fracturing. Maintaining meticulous oral hygiene is important because plaque accumulation can lead to demineralization of the enamel, potentially weakening the micromechanical retention. Patient compliance with dietary and habit restrictions is a more significant factor in bond longevity than the inherent strength of the adhesive.
Safe Removal and Cleanup
At the conclusion of treatment, the intentional removal of the brackets, known as debonding, is performed using specialized instruments. The orthodontist uses debonding pliers designed to grip the bracket base and apply a controlled shearing force. This force deliberately fractures the adhesive layer, ideally without transferring stress to the underlying enamel. This controlled failure is precisely why the adhesive was engineered with a specific strength limitation.
After the bracket is removed, a small amount of composite resin, known as the “adhesive remnant,” typically remains attached to the tooth surface. This residual adhesive must be removed to restore the natural feel and appearance of the enamel, as leftover material can harbor plaque and cause discoloration. The clinician carefully removes this material using a low-speed handpiece with a multi-fluted tungsten carbide bur, which shaves away the composite. The process is finalized by polishing the tooth with rubber cups and polishing paste to ensure the enamel surface is smooth and healthy.