The bonding process in orthodontics is the method of securely attaching a bracket (the small metal or ceramic square) directly to the surface of a tooth. This procedure utilizes a specialized adhesive system to create a strong, reliable connection between the appliance and the enamel. This technique is a fundamental step in fixed orthodontic treatment, allowing forces to be transferred from the archwire to the teeth to guide them into new positions.
The Purpose of the Adhesive System
The specialized adhesive system is necessary to create a bond that is both mechanically and chemically sound. This bond must be secure enough to withstand the continuous forces applied by the archwire, as well as the significant stresses from chewing and biting throughout the treatment period. The adhesive acts as the interface, ensuring the bracket remains fixed despite the moist environment of the mouth and temperature fluctuations.
The design of the adhesive system is complex because the bond must be strong, yet also temporary. It needs to hold firm for the duration of the treatment, but also allow for safe, predictable removal without causing permanent damage to the tooth’s enamel. Manufacturers aim for a bond strength adequate for orthodontic function but low enough to permit safe debonding. This balance protects the integrity of the tooth surface from cracks, fractures, or excessive enamel loss.
Preparing the Tooth and Applying the Bracket
Attaching the brackets begins with a thorough cleaning and preparation of the tooth’s enamel surface. The teeth are polished with a pumice-based paste that does not contain oil to remove plaque, debris, or surface film that could interfere with bonding. The area is then isolated using cheek retractors and cotton rolls to ensure the teeth remain free of saliva and moisture contamination during subsequent steps.
The prepared enamel is then treated with an etching agent, typically 37% orthophosphoric acid gel, applied for about 30 seconds. This acidic material creates microscopic porosities, or channels, in the enamel surface, effectively roughening it. Rinsing the etchant off and thoroughly drying the tooth with oil-free air reveals a frosty, chalky-white appearance, confirming a receptive surface for the adhesive.
Following the etching and drying, a thin layer of primer or bonding agent is applied to the conditioned enamel. This liquid resin flows into the microscopic channels created by the etchant, beginning micromechanical retention. The bracket, which has adhesive resin on its base, is then carefully positioned onto the tooth surface by the orthodontist.
The final step involves curing the adhesive, which hardens the material and locks the bracket in place. Most modern adhesives are light-cured, meaning a specialized blue light is shone onto the bracket for 20 to 30 seconds per bracket. This light activates a photoinitiator, such as camphoroquinone, within the resin, causing it to rapidly polymerize and form a durable, secure bond.
Debonding and Post-Treatment Care
The debonding phase is the controlled removal of the brackets and adhesive upon completion of orthodontic treatment. Specialized debonding pliers apply a precise peeling or squeezing force to the bracket, designed to break the bond at the adhesive-bracket interface. The goal is to remove the bracket while leaving most of the adhesive on the tooth surface, minimizing the force applied directly to the enamel.
After the bracket is removed, residual adhesive material remains on the tooth and must be completely eliminated. This process, often called cleanup, is performed carefully using various rotary instruments, most commonly a slow-speed handpiece with a tungsten carbide bur. The material is gently shaved away until the natural enamel surface is reached, avoiding the removal of underlying tooth structure.
The final stage involves polishing the enamel to restore its smooth texture and shine. This step is accomplished using a sequence of finishing and polishing tools, such as fine-grit discs, rubber cups, and pumice slurry. Restoring the smooth surface is important because any remaining roughness could promote plaque accumulation, leading to staining or potential decalcification.