Adults seeking orthodontic treatment often have existing dental work, such as gold restorations like crowns, onlays, or inlays. Traditional braces can be applied to these gold surfaces. However, the process is more involved and requires specialized materials and techniques compared to bonding brackets directly to natural tooth enamel.
Why Gold Surfaces Resist Traditional Bonding
Traditional orthodontic bonding relies on conditioning the tooth’s enamel with an acid, typically phosphoric acid. This acid creates a rough, porous surface with microscopic irregularities, allowing the adhesive resin to mechanically lock onto the tooth surface. This process is known as mechanical retention.
Gold is a highly polished, non-porous metal that does not respond to acid etching. The surface remains smooth and chemically inert, preventing standard adhesive from forming a secure mechanical or chemical bond. Without specialized preparation, a bracket bonded to gold with conventional materials risks failure due to chewing and orthodontic movement. The gold’s metallic composition and smooth texture present a unique challenge that must be overcome.
Methods for Attaching Brackets to Gold
Achieving a successful bond on gold requires a two-pronged approach involving mechanical and chemical preparation. The first step is creating surface roughness, which is typically accomplished through micro-etching or sandblasting. This process often uses an intraoral air abrasion unit with fine aluminum oxide particles. This physically roughens the gold surface, creating micro-retentions for the adhesive to grip.
The second step is applying a specialized chemical agent known as a metal primer or coupling agent. These primers contain unique monomers, such as those in 4-META metal bonding resins, designed to chemically react and bond with the prepared metal surface. This chemical layer links the gold restoration to the conventional adhesive resin securing the bracket. Because the metal prevents the curing light from penetrating, a chemical-cure adhesive system or a pre-curing technique is often recommended to ensure complete polymerization and a strong bond.
Alternative Strategies for Orthodontic Movement
In certain clinical situations, the orthodontist may choose to avoid direct adhesive bonding to the gold surface entirely. This decision is often made when the gold restoration is very large, is subject to extreme biting forces, or if the practitioner desires the highest possible security of retention. A common alternative in these scenarios is the use of orthodontic bands, which are thin, pre-formed metal rings.
These bands are carefully fitted around the entire circumference of the gold-restored tooth, usually a molar, and are then cemented into place with a special, non-damaging cement. The orthodontic bracket or tube is already welded to the outside surface of the band. This allows the tooth to be incorporated into the treatment plan without relying on adhesive bonding to the gold itself. This method provides a secure form of mechanical retention that encircles the tooth.
Another strategy involves bypassing the gold-restored tooth if it is not necessary for the desired movement. Utilizing clear aligners is also an option, as they apply force to the tooth differently than traditional fixed braces and wires.