Orthodontic treatment is a common method for aligning teeth and correcting bite issues. A dental crown is a cap placed over a damaged or weakened tooth, restoring its shape, size, and strength. It is generally possible to undergo orthodontic treatment even with crowns, but the process requires specialized techniques and careful planning. The presence of a crown changes how brackets are attached and how the tooth responds to forces, necessitating a tailored approach.
How Brackets are Attached to Crowns
Attaching orthodontic brackets to a crown is technically more challenging than bonding them to natural enamel. Enamel’s natural, porous structure allows traditional bonding agents to create a strong mechanical lock after an acid-etching process. Crown materials, such as porcelain, metal, or zirconia, are much smoother and chemically inert, preventing the standard adhesive from achieving an adequate bond strength.
To successfully bond to a porcelain crown, the surface must be chemically and mechanically prepared. This often involves a process of micro-abrasion, followed by etching with hydrofluoric acid to create microscopic surface irregularities for retention. After etching, a specialized chemical agent known as a silane coupling agent is applied to create a chemical link between the porcelain surface and the adhesive resin.
For metal crowns, surface preparation may involve sandblasting or abrasion with a diamond bur, followed by the application of a metal primer before the bracket is placed. These specialized steps are necessary to achieve a bond strength that can withstand the continuous forces of orthodontic wires and chewing without the bracket constantly popping off.
Factors Affecting Tooth Movement with Crowns
The movement of a crowned tooth is governed by the health and structure of the underlying biological components, not the crown material itself. The crown acts only as a protective cap, while actual tooth movement occurs through the remodeling of the alveolar bone surrounding the root. The health of the remaining natural tooth structure, often called the core, is a primary factor in determining feasibility for movement. If the core is significantly compromised, it may not be able to withstand the forces required for movement.
The length and stability of the tooth’s root, along with the health of the surrounding bone and gum tissue, are also relevant. Orthodontic forces cause the bone to resorb on the pressure side and form on the tension side, a process that must occur gradually. Because crowned teeth often have a history of damage, the orthodontist must use lighter, gentler forces than those applied to healthy, natural teeth to prevent root damage or destabilization. Movement must be carefully controlled to ensure the root remains securely positioned within the bone socket throughout the treatment period.
Potential Risks and Complications
Patients with crowns undergoing orthodontic treatment face specific risks beyond those associated with treatment on natural teeth. The most common complication is a higher rate of bracket debonding, where the bracket repeatedly falls off the crown surface. Despite specialized bonding techniques, the bond strength to crown material is often less reliable than the bond to natural enamel, leading to frequent interruptions in treatment.
The specialized surface preparation, such as acid etching or sandblasting, can damage the crown’s outer glaze or finish. Furthermore, the process of removing the bracket at the end of treatment carries a risk of chipping, scratching, or pitting the crown’s surface. In rare cases, the orthodontic forces or the force of bracket removal can loosen the crown entirely, requiring it to be recemented or replaced.
Post-Treatment Crown Management
Once the orthodontic treatment is complete and the braces are removed, any residual bonding material left on the crown surface must be polished away. This step is important because the remaining adhesive can attract plaque and affect the crown’s appearance.
A more complex consideration is the crown’s margin, which is the edge where the crown meets the tooth and the gum line. When the tooth moves, the crown’s position shifts relative to the surrounding gum tissue. If this misalignment is significant, the crown may need to be replaced after the orthodontic treatment to prevent future decay or gum health issues.