Dental cement is a specialized adhesive material used by dental professionals to bond restorations, such as crowns, bridges, inlays, and onlays, to natural tooth structure. Its primary function is to secure the restoration firmly in place, creating a strong seal that prevents microleakage (the ingress of bacteria and fluids at the margin). While the process may seem straightforward, meticulous preparation and precise technique are required to ensure the restoration’s stability and long-term success. The longevity of a restoration relies heavily on the correct selection and application of this bonding agent.
The Different Types of Dental Cement
Dental cements are broadly categorized based on their function, primarily as luting agents or as bases and liners. Luting cements are the adhesives used to seat permanent restorations like crowns and bridges, providing the final, long-lasting bond. Base or liner cements are typically placed in a thin layer beneath a filling material to insulate the pulp from thermal changes or to promote the health of the dental pulp.
The material composition dictates the cement’s properties and how it is used clinically. Zinc phosphate cement, one of the oldest types, offers high compressive strength but relies solely on mechanical retention. Glass ionomer cements (GICs) and resin-modified glass ionomer cements (RMGICs) are popular choices because they chemically bond to the tooth structure and release fluoride, which helps prevent recurrent decay.
Resin-based cements offer the highest bond strength and superior aesthetics, making them the preferred choice for all-ceramic restorations and veneers. These materials require a more involved bonding process, including etching and priming steps to achieve maximum adhesion. Temporary cements, conversely, are designed for easy removal and are often zinc oxide-based, providing a moderate hold for provisional restorations.
Essential Preparation Before Application
Successful cementation depends on meticulous preparation of the tooth and the restoration before the cement is mixed. The first step involves thoroughly cleaning the prepared tooth surface to remove all traces of temporary cement, debris, and plaque. Professionals typically use a non-fluoridated pumice or a specialized cleaning agent, followed by a thorough rinse and air-drying.
Maintaining a dry field is essential for most cements, especially resin-based types, as moisture contamination can compromise the bond strength. Isolation is typically achieved using a rubber dam or strategic placement of cotton rolls and high-volume suction. For modern adhesive cements, the tooth structure is often treated with an etching gel (usually phosphoric acid) to microscopically roughen the enamel surface. This is followed by the application of a primer or bonding agent to enhance the chemical bond.
The internal surface of the restoration, particularly if ceramic or zirconia, requires decontamination after being tried in the mouth, as salivary phosphates can inhibit bonding. Specific cleaners or primers containing MDP (10-methacryloyloxydecyl dihydrogen phosphate) are applied to the restoration’s fitting surface to prepare it for the cement. Failure to prepare either the tooth or the restoration properly can lead to premature bond failure.
Step-by-Step Application and Curing
The application process begins with the precise preparation of the cement, involving mixing a powder and liquid or dispensing a paste from an auto-mix syringe. Manufacturer instructions must be followed exactly regarding the powder-to-liquid ratio and working time, as these factors affect the cement’s final strength and setting characteristics. A metal spatula is typically used to achieve a homogeneous, creamy consistency before the material begins to set.
Once mixed, the cement is immediately loaded into the internal surface of the restoration, ensuring all internal walls are thinly and evenly coated. Avoid overfilling, which can create hydraulic pressure and prevent the restoration from fully seating. The restoration is then carefully placed onto the prepared tooth, using firm, controlled pressure to ensure it is fully seated to the margin.
As the restoration seats, excess cement extrudes around the edges, which is typically removed after a brief period of initial setting, often called the gel phase. For light-cured or dual-cured resin cements, a brief exposure to a curing light—known as “tack-curing”—partially hardens the excess material, making it easier to peel away. After the bulk of the excess is removed with a dental explorer or scaler, the restoration is fully cured, either by chemical reaction or by final exposure to the curing light. Final cleanup involves using dental floss, carefully pulled through the contact points to ensure no cement remains between the teeth, preventing irritation and plaque traps.
Temporary vs. Permanent Use and Safety Precautions
Dental cement is formulated for either temporary or permanent use, a distinction based on the material’s intended bond strength and longevity. Temporary cements, such as those used for provisional crowns, are designed to be easily removed by a dental professional without damaging the underlying tooth structure. These materials offer enough retention to protect the tooth and minimize sensitivity while the final restoration is fabricated.
Permanent cements, conversely, form a tenacious, long-lasting bond intended to withstand years of chewing forces and exposure to the oral environment. Over-the-counter (OTC) products are available for emergency fixes, but these are solely for temporary reattachment of a dislodged crown and are not a substitute for professional care. The application of permanent dental cement should only be performed by a licensed dental professional.
Attempting to use permanent cement at home carries risks, including improper seating of the restoration, which can cause nerve damage, bite misalignment, or difficulty with future removal. If an OTC temporary fix is used, the individual must still schedule a follow-up appointment immediately, as the temporary material will dissolve over time, leaving the tooth vulnerable to decay and fracture. A temporary solution buys time, but only professional application ensures the restoration’s proper fit and durability.