Lithium disilicate is a glass-ceramic material used to create high-quality, durable dental restorations, including crowns, veneers, inlays, and onlays. It offers a balance between longevity and natural appearance, replacing older materials that often sacrificed aesthetics for strength or vice versa. This modern solution in restorative dentistry mimics the properties of natural tooth structure, allowing for conservative and visually appealing treatments.
Understanding the Material’s Foundation
Lithium disilicate is classified as a glass-ceramic, composed of a glass matrix reinforced by a crystalline phase. The composition includes quartz, lithium dioxide, and phosphorus oxide, which are melted and processed to form the final material. Its superior mechanical properties come from its microstructure, where interlocking, needle-like lithium disilicate crystals are densely dispersed within the glassy phase.
These crystals make up approximately 70% of the material’s volume in the final, fully crystallized state. This high concentration differentiates it from traditional feldspathic porcelain, which has far fewer reinforcing crystals. The interlocking crystal network acts to deflect and blunt tiny cracks, significantly increasing the material’s resistance to fracture and ensuring high mechanical performance.
Primary Advantages in Dental Restorations
The primary benefit of lithium disilicate is its outstanding aesthetic quality, which is crucial for visible restorations. The material exhibits high translucency and opalescence, allowing light to pass through and scatter like natural tooth enamel. This enables the restoration to blend seamlessly with surrounding teeth, avoiding the flat or opaque look of other dental materials.
Dentists can select blocks of varying opacity and shades to precisely match the patient’s existing dentition, ensuring a lifelike result. This ability makes it an ideal choice for anterior (front) crowns and veneers. Its strength and beauty allow it to be used as a monolithic restoration, where the entire crown is made from this single ceramic material.
Beyond aesthetics, the material offers high flexural strength, typically ranging from 360 to 400 Megapascals (MPa). This strength profile allows for conservative dentistry, as less healthy tooth structure needs to be removed during preparation. Its durability and fracture resistance make it suitable for single crowns, inlays, and onlays, even in moderate-load posterior (back) areas. The material’s resilience ensures it can withstand chewing forces over a long period, with studies indicating a high survival rate.
Fabrication Methods for Creating Restorations
Lithium disilicate restorations are created using two primary, distinct manufacturing techniques, each relying on the material’s unique properties at different stages.
Hot-Pressing Technique
The first method is the hot-pressing technique, which involves melting an ingot of the ceramic and pressing it into a mold created from a wax pattern of the desired restoration. This technique uses high pressure and heat to ensure a dense, highly accurate fit. Hot-pressing is often favored for producing restorations with the most nuanced and complex aesthetic characteristics.
CAD/CAM Milling
The second common method utilizes modern digital technology through Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) milling. In this process, the restoration is designed digitally from a 3D scan of the prepared tooth. A milling machine then cuts the final shape from a pre-manufactured block of lithium disilicate. These blocks are often in a pre-crystallized state, sometimes referred to as the “blue stage,” which is softer and easier for the milling machine to cut.
After milling, the restoration must undergo a heat treatment process called crystallization. This process transforms the material into its final, hard, and high-strength form. Both the hot-pressing and CAD/CAM techniques produce restorations with clinically acceptable marginal fit, ensuring a tight seal between the restoration and the tooth. The choice between the two methods often depends on the specific clinical situation, the equipment available, and the desired balance between speed and precision.
Comparison to Common Dental Alternatives
Lithium disilicate is often compared to zirconia, another popular all-ceramic restorative material. Lithium disilicate is generally considered the more aesthetic option, offering superior light-transmitting properties due to its lower crystalline content. Zirconia, while less translucent and more opaque, boasts a significantly higher flexural strength, often exceeding 1000 MPa. Zirconia is the preferred choice for high-stress posterior bridges and molar crowns, while lithium disilicate is typically selected for high-aesthetic zones like the front teeth.
Another common alternative is the traditional Porcelain-Fused-to-Metal (PFM) crown, which has a metal substructure covered by a layer of porcelain. Lithium disilicate restorations offer a substantial aesthetic improvement over PFM because they eliminate the risk of a visible dark or gray line at the gum line, which can occur as gum tissue recedes from the underlying metal. Lithium disilicate’s high strength and all-ceramic composition provide a more biocompatible and visually appealing outcome than PFM crowns.
Lithium disilicate restorations demonstrate excellent longevity, with survival rates comparable to those of metal-ceramic crowns. Proper care, including regular professional polishing and maintenance, is necessary to prevent excessive wear on opposing teeth, a consideration for all ceramic materials. With appropriate patient selection and adherence to bonding protocols, these modern restorations are an excellent long-term investment.