All Ceramics Quiz

Overview of All-Ceramic Systems

• Recent advancements in ceramic products have improved fracture resistance, aesthetic capability, and utilization due to CAD-CAM technology.
• Ceramic crowns and bridges have been widely adopted since the early 2000s.

Early Ceramic Materials

• IPS Empress was one of the first hot-isostatically pressed core ceramics; a leucite-based glass-ceramic.
• Initial ceramics were limited to anterior single-unit restorations due to lower flexural strengths and fracture toughness.
• Other early materials included Vitadur N, Cerestore, and Dicor, with Dicor being a castable glass containing tetrasilicic fluormica.

Glass-Ceramics

• Glass-ceramics are formed from glass that undergoes partial devitrification through heat treatment, which enhances strength and toughness.
• First suggested for dental use in 1968, MacCulloch pioneered continuous glass-molding for denture teeth and crowns.
• Dicor, developed for dental use, had a relatively low flexural strength (110-172 MPa) and low fracture toughness (1.6-2.1 MPa m1/2).

Hot-Isostatically Pressed (HIP) Glass-Ceramics

• Veneered restorations using leucite-based glass ceramics are suitable for anterior and premolar applications.
• Common leucite-based products include IPS Empress and IPS e.max CAD, generally containing around 35% leucite.
• Leucite-based glass-ceramics are not recommended for molar crowns due to low strength (≤112 MPa) and toughness (1.3 MPa m1/2).

Lithia Disilicate Products

• Lithia disilicate ceramics such as IPS Empress 2 and 3Y-TZP contain around 65-70% lithia disilicate, offering improved strength (mean flexural strength ~350 MPa).
• These glass-ceramics support anterior and posterior crowns but may chip upon impact.

Fluorapatite Glass-Ceramics

• Nano-fluorapatite glass-ceramics, like e.max Ceram, feature a low coefficient of thermal expansion (CTE) compatible with lithia disilicate and some alumina/zirconia ceramics.

Zirconia-Based Ceramics

• Zirconia (ZrO2) possesses low thermal conductivity and high corrosion resistance, making it useful since 2004 for crowns and bridges.
• Distinction exists between dental zirconia and gemstones (zircon and cubic zirconia).
• The crystal structure transformation occurs at high temperatures, impacting strength.

Stabilized Zirconia

• Oxide additives (e.g., yttria, magnesia) prevent phase transformations in zirconia at room temperature, preserving mechanical properties.
• Partially stabilized (PSZ) and fully stabilized (FSZ) demonstrate differing characteristics, with PSZ showing high fracture toughness (8-10.3 MPa m1/2).

Transformation Toughening

• Yttria stabilizes tetragonal zirconia, enabling a metastable state that enhances fracture resistance through transformation upon crack propagation.
• The phase transformation creates compressive stresses that hinder further crack expansion, increasing material durability.

Monolithic Zirconia

• Monolithic zirconia restorations reduce fracture susceptibility compared to layered ceramics, particularly valuable in high-stress areas.
• Advantages include high strength and wear compatibility with opposing enamel, though adjusting occlusion can be challenging.

Fracture Strength of Zirconia

• Fracture toughness in zirconia generally improves with larger grain sizes, contrasting with behaviors in other materials.
• Careful optimization of grain sizes is crucial to maintain strength while avoiding premature transformation leading to microcracking.

Hydrothermal Degradation

• Long-term performance of Y-TZP zirconia can be affected by hydrothermal degradation at oral temperatures, resulting in surface roughness and microcracking.
• The degradation initiates phase transformation, disseminating through neighboring grains, often related to temperature and moisture exposure.### Glass-Infiltrated Core Ceramics
• Three types developed to reduce sintering shrinkage: partially sintered alumina, magnesia-alumina spinel (MgAl2O4), and zirconia-alumina core.
• Partially sintered ceramics can be infiltrated with lanthanum glass without significant dimensional change.
• VITA In-Ceram Alumina consists of approximately 85% alumina, formed by slipcasting against a porous die.
• After firing at 1120 °C for 10 hours, the porous core framework is infused with molten lanthanum glass.
• In-Ceram Spinel is more translucent than In-Ceram Alumina or Zirconia but has lower mean strength (∼350 MPa vs. ∼600 MPa).
• Mean flexure strength of In-Ceram Zirconia (∼620 MPa) is slightly higher than that of In-Ceram Alumina.
• In-Ceram Zirconia is composed of 62% alumina, 20% zirconia, and ∼18% infiltrated glass, used for crowns and frameworks.
• Transformation toughening in ZTA occurs when stress induces conversion from tetragonal to monoclinic phases, doubling strength and increasing toughness by 2-4 times.

Alumina Core Ceramic

• Procera AllCeram (Nobel Biocare) is indicated for both anterior and posterior crowns.
• A digitalized die is produced from an impression, and an oversized die is created for pure alumina to be dry-pressed and sintered.
• Final size and shape are achieved post-sintering, allowing for feldspathic porcelain veneer application.
• Procera All-Ceram core exhibits greater translucency than In-Ceram Zirconia with comparable strength (620–700 MPa).
• Surface bonding requires silica-coated alumina particles via sandblasting, as alumina cannot be acid-etched for micromechanical retention.

Bonding of Resin to Dental Ceramics

• Resin-based composite cements improve retention, fracture resistance, and repair capacity of ceramic restorations.
• Silane-based coupling does not chemically bond to all ceramics; for example, the alumina framework can't be etched.
• Adequate bonding relies on macromechanical retention; large voids in the framework can lead to fracture.
• Silane primers bond through hydrolysis, creating siloxane bonds with silica-based ceramics.
• Hydrolysis, condensation, and hydrogen bonding lead to covalent link formation with ceramics.
• Monolayer silane primer is ideal, but multilayer adsorption may occur; thickness ranges from 3 to 8 molecular layers.
• Silane-based monomers based on phosphate ester or phosphonic acid yield better bonding to zirconia.
• Bonding mechanisms are essential in ensuring durability of ceramic prostheses and reducing crack formation.

Test your knowledge on recent advancements in dental ceramics and their applications in dentistry. This quiz covers various materials and processes, such as hot-isostatic pressing and devitrification in glass-ceramics. Dive into the specifics of core ceramics and their limitations within dental practices.