What is a Single Unit Posterior?
A **single unit posterior** crown is a dental restoration designed for the molars and premolars located in the back of the mouth. Unlike anterior crowns that are primarily judged on aesthetics, posterior crowns are engineered to withstand the immense forces of chewing and grinding, also known as mastication. The functional demands placed on these teeth require a restoration that is exceptionally strong, durable, and resistant to wear. While they are not as visible as front teeth, posterior crowns must still have a natural appearance to blend seamlessly with the patient's dentition.
Materials of Choice
The selection of material for a posterior crown is critical and is heavily influenced by the need for strength. While traditional materials like **porcelain-fused-to-metal (PFM)** are still an option, they are often overshadowed by modern materials that offer superior durability and biocompatibility. The most common material today for posterior crowns is **zirconia**. This all-ceramic material is known for its incredible fracture toughness and resistance to chipping, making it ideal for the high-stress environment of the back of the mouth.
Other materials, such as **e.max** (lithium disilicate), are sometimes used for premolars where aesthetics are a higher priority, but zirconia's strength profile often makes it the preferred choice for molars. For patients with parafunctional habits like bruxism (teeth grinding), gold alloys may also be considered due to their gentle wear characteristics on opposing teeth. These crowns are typically fabricated using **CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing)** technology, ensuring a precise and accurate fit that is essential for a long-lasting restoration.
Clinical Procedure
The clinical procedure for a single unit posterior crown is similar to an anterior crown but with an added focus on structural integrity. The dentist begins by meticulously preparing the tooth, ensuring there is a sufficient amount of space for the crown material without compromising the pulp. This preparation is essential to prevent future crown fracture. Following the preparation, an impression is taken, which can be done digitally or with traditional materials. This impression serves as the blueprint for the dental lab to fabricate the final crown.
A temporary crown is placed to protect the tooth and maintain proper spacing while the permanent crown is being made. Once the final crown is delivered, the dentist carefully checks the fit, occlusion (the way the teeth bite together), and contact points with adjacent teeth. Proper occlusion is vital to prevent future jaw problems and excessive wear. The crown is then bonded to the tooth using a durable cement. The success of a posterior crown is measured by its longevity and ability to withstand the extreme forces of daily function.