Zirconia crowns are durable, tooth-colored restorations favored in modern dentistry for their strength and natural appearance. Although this ceramic material is robust, its surface must be carefully smoothed and polished by a dental professional. This process ensures the crown’s longevity and protects the surrounding oral environment. Polishing involves a series of precise steps, starting with gross adjustments and finishing with a high-luster shine, designed to maintain the crown’s integrity and biocompatibility.
The Necessity of a Smooth Zirconia Surface
Polishing the surface of a zirconia crown is a safeguard against several potential oral health issues. Zirconia is an extremely hard material, and if its surface is left rough after adjustments, it can cause significant wear on the opposing natural tooth enamel during chewing and grinding. Research indicates that a rough zirconia surface is the primary cause of wear on opposing dentition, not the material’s inherent hardness.
A rough surface provides an ideal environment for bacteria, leading to increased plaque accumulation. A smooth, high-luster finish reduces the surface energy of the crown, making it more resistant to the adherence of plaque and debris. This lack of roughness minimizes the risk of gum irritation and secondary decay at the margins of the restoration. A polished surface also retains its luster indefinitely, unlike a glazed surface, which can wear off and expose the underlying abrasive ceramic.
Professional Preparation and Contouring
The process begins if the crown requires adjustment after being seated, often to refine the bite or occlusion. Because zirconia is so hard, specialized, fine-grit diamond burs are necessary for this initial material removal. Using standard burs or applying excessive pressure can generate heat, which risks microscopic flaws or microfractures within the zirconia structure.
A light touch and continuous water or air-water spray are used to dissipate heat and prevent damage to the crown. An electric handpiece is typically used at a lower speed, generally between 6,000 and 20,000 revolutions per minute. This speed provides sufficient torque while minimizing the risk of overheating. The goal of this phase is to remove deep scratches and shape the restoration, maintaining a convex contour.
Achieving the High-Gloss Finish
Once the gross adjustments and contouring are complete, the surface must be mechanically polished in a sequential, multi-step process to achieve a mirror-like luster. This phase transitions from removing the fine scratches left by the diamond burs to creating a smooth finish. It involves using a series of specialized rubber wheels, points, and cups that are often impregnated with diamond particles.
The sequence typically starts with a medium-grit polisher to smooth the area, followed by a fine-grit polisher to remove the marks left by the previous step. The final step involves the use of ultra-fine polishers and a high-quality diamond polishing paste. The paste is applied with a soft felt wheel or brush to restore the surface to a mirror-like shine. Maintaining low pressure and low speed throughout this process is important to avoid generating frictional heat, which could diminish the final surface quality.
Maintaining the Polish at Home
Patients can take specific, daily steps to preserve the professional polish and ensure the longevity of their zirconia crown. Use a soft-bristled toothbrush and a non-abrasive, fluoride toothpaste to clean the crown gently. Highly abrasive pastes can scratch the polished surface, reducing its shine and increasing plaque retention. Regular flossing or using a water flosser is necessary to clean the margins of the crown, preventing plaque accumulation at the gum line.
Routine professional dental cleanings and check-ups are required. Dental professionals use instruments and polishing pastes formulated specifically for zirconia. Avoiding excessively hard or sticky foods also helps prevent physical damage to the crown.