Dental Ceramics: Key Concepts and Applications

Dental Ceramics Selection Principles

• Dental ceramics are crucial materials in modern dentistry
• They are used in various restorations, including crowns, bridges, veneers, and inlays
• Ceramics provide high-quality aesthetics, mimicking the natural appearance of teeth

Advantages of Ceramics

• Compressive Strength: Withstands intense chewing forces, especially in posterior teeth where pressure is higher
• Biocompatibility: Does not contain toxic substances or allergens, reducing side effects. Chemically inert; doesn't react with oral cavity substances
• Color Stability: Maintains consistent color over time

Review of Terms

• All-ceramic: Dental restorations entirely made of ceramic material
• Monolithic/Uni-layer: Restorations formed from a single ceramic material
• Bilayered Restorations: Consist of a ceramic core covered by a ceramic veneer, with the core supporting the restoration, and the veneer providing the final appearance

Types of Ceramic Restorations (Porcelain)

• High-temperature porcelain: Mixture of quartz, clay, and feldspar powders; used for prosthetic teeth
• Feldspathic porcelain: Contains potassium feldspar and glass powders; used in ceramometallic restorations and porcelain inlays/veneers
• Aluminous porcelain: Similar composition to feldspathic porcelain, but with aluminum oxide fillers

Alumina

• Also known as aluminum oxide, used as an implant material since 1964
• Early clinical use showed high fracture rates (13%) due to material failure when sintering wasn't to full density
• Improvements in mechanical properties and manufacturing methods have been made with third-generation alumina

Zirconium Dioxide

• Advantages: Excellent biocompatibility, superior toughness, fatigue resistance, and strength
• Monolithic Zirconia: Commonly used for less aesthetic areas (posterior teeth) due to opacity, lack of translucency, and fluorescence. Used to mask discolored preparations.
• High-translucency Zirconia: More aesthetically pleasing, with a higher translucency and opalescent characteristics. Suitable for anterior teeth. It's slightly weaker than the monolithic counterpart, but still has a high biaxial flexural strength (590-720 MPa)
• Porcelain-layered Zirconia: Designed to have the appearance of porcelain and the structural strength of zirconium dioxide, using a porcelain veneer over a ceramic coping. Aesthetic quality similar to high-translucency zirconia

Lithium Disilicate

• Lithium oxide crystals dispersed in a silica matrix. Provides high flexural strength (up to 440 MPa), inhibiting crack propagation through interlocking orientation.
• Failure rate of 3.3% and may experience ceramic fracturing, chipping, or core rupturing
• Mainly used to repair anterior teeth due to excellent aesthetic properties

Methods for Fabrication of All-Ceramic Restorations

• Conventional Technique: Common method for veneer ceramic in ceramometallic restorations
• Hot Pressing Technique: Uses stone model and putty matrix from diagnostic wax-up, involving steps of wax-up, sprueing, investing, pressing, divesting, removing the reacting layer, staining, firing, and glazing
  • Materials: leucite, lithium disilicate, spinel, and related ceramics
  • Disadvantage: High equipment cost due to specialized automated pressing furnaces.
• Dry Pressing Method: Creates polycrystalline restorations (alumina or zirconium dioxide) by scanning a life-sized natural model, expanding it to fabricate a mold, and pressing/sintering a ceramic powder into the oversized mold, compensating for shrinkage.
• Slip-casting and Glass Infiltration: Offers high strength but has high opacity and long processing times.
• CAD/CAM: Advantages include reduced clinical time, fewer cross-infections, and decreased patient discomfort when using intraoral scanning. Disadvantages include the high cost and maintenance of the equipment

Ceramics Rationale for Material Selection

• Treatment planning with ceramic follows a systemic process, with specific guidelines.
• Important to consider, conservatively remove tooth structure, and maintain long-term oral health.
• Four broad ceramic categories:
• Category 1: Powder/Liquid Feldspathic
• Category 2: Pressed/Machinable Glass-ceramics
• Category 3: High-Strength Crystalline Ceramics (Zirconia, Alumina)
• Category 4: Metal-Ceramics

Five Clinical Parameters to Evaluate for Choosing a Material

• Space Required and Color Change for Esthetics: Varying thickness and space requirements for various shades and materials.
• Substrate: Bond strength depends on enamel quality and thickness. Less predictable on dentin.
• Flexure Risk Assessment: Assessing for signs of past tooth flexure (cracking, wear, fracture). Different risk levels.
• Excessive Shear and Tensile Stress Risk Assessment: Identifying areas with anticipated large tensile and shear stress that dictates stronger materials.
• Risk of Bond Failure: Moisture control, variable bonding interfaces, and operator experience are also crucial factors