Dental Materials in the Digital Age

Dental Materials in the Digital Age

• CAD-CAM technologies were introduced to dentistry about 50 years ago.
• Modern CAD-CAM systems can produce highly accurate dental prostheses at low cost.
• Materials used in CAD-CAM systems include ceramics, polymers, and metals.

Ceramics

• Ceramics are hard, stable, and strong but brittle under stress.
• Brittleness can be overcome by supporting the ceramic with a high-strength core material or using a ceramic with increased strength or bending resistance.
• Dental ceramics can be crystalline, non-crystalline, or a combination of both.
• Types of dental ceramics include glassy ceramics (like leucite and feldspathic), partially crystalline glass ceramics (like lithium disilicate), or polycrystalline ceramics (like zirconia and alumina).
• Ceramics with a mostly glassy microstructure (like leucite and feldspathic) are more aesthetic but have lower mechanical strength and are often used as veneers.
• Ceramics with more crystalline phases (like zirconia and alumina) are stronger but less aesthetically pleasing.
• Partially crystalline glassy ceramics (like lithium disilicate) have properties between glassy and polycrystalline ceramics.

Common Processing Methods

• Machinable and pressable CAD-CAM materials for ceramic restorations are almost defect-free before use, but the manufacturing process introduces various flaws.
• Pressing ceramic materials can lead to porosity, while grinding causes cracks and surface defects.
• Milling of fully sintered ceramics (which are very hard) often leads to cracks and chipping, reducing the quality of the restoration.
• Machining (milling) partially sintered or pre-crystalline ceramics (known as the "green phase") is preferred due to fewer problems.
• After milling, restorations in the green phase undergo crystallization or sintering heat treatment to complete sintering and improve mechanical properties.

Polymers

• Polymers are lightweight, ductile, and have lower strength compared to metals and ceramics.
• Aesthetics and ease of repair make them useful for dental applications.
• High functional loads in the oral environment require traditional polymers to be reinforced or supported by stronger materials.
• For full-mouth reconstructions, new, high-performance polymeric materials containing polyether ketones have been developed (e.g., polyether, ether ketone, poly-aryl-ether ketone).
• High-performance materials are often used as a supporting frame and require a covering material to mask the color.

Metal Alloys

• Metals used in dentistry are often alloys or combinations, improving material properties.
• Typical metal properties include high strength, polishability, and opacity.
• Dentistry's challenge with metals is hiding them from view by layering with polymers or ceramics.
• Historically, restorative metals were produced by casting, forging, or sintering, but most CAD-CAM workflows are now additive or subtractive.
• Common base metal alloys include cobalt-chromium and titanium.
• Scientific literature does not indicate that CAD-CAM milling technology significantly outperforms classical laboratory procedures for metal restorations. Both can produce clinically acceptable restorations.

Additive Manufacturing (AM)

• Innovations in AM (additive manufacturing) CAD-CAM workflows enable the production of complex shapes using selective laser melting and electron beam melting.
• The biggest disadvantage of AM may be the cost of initial equipment acquisition.

Case Selection

• Key factors for choosing materials in prosthetic reconstruction include:
  • Aesthetics
  • Expected forces
  • Mechanical properties
  • Available space
  • Wear resistance
  • Survival rate

Aesthetics

• Translucency is affected by light transmission, absorption, and reflectivity.
• Core materials affect translucency, especially in the gingival third of the restoration.
• Polycrystalline ceramics (e.g., alumina and zirconia) do not transmit light.
• Glass ceramics and zirconium partially stabilized with yttria (4 and 5 mol%) transmit light readily.

Anticipated Stress or Force

• Force magnitude on teeth and restorations is dependent on patient habits and the prosthetic design used,
• Conventional polymeric materials (like acrylics and urethanes) cannot withstand high functional forces without a high-strength framework.
• New high-performance polymers are often produced using high heat and pressure, with reliable industrial methods, to achieve high flexural strength suitable for milling machines to produce complex shapes.
• Precious metal-based alloys are often used, and may be 3D printed or milled.
• Glass ceramics have exceptional aesthetics and can be milled or pressed, resulting in moderate durability suitable for single-tooth restorations.
• Polycrystalline materials (alumina and zirconia) provide significant strength but are less aesthetic and require surface treatments for enhancements.

Soft Milling

• Diamond-coated milling tools with high RPM are used for milling hard materials like glass-ceramics to reduce stress.
• Soft milling strategy is used for high-strength ceramic restorations, and with lithium disilicate, pre-crystallized blocks are used instead of fully crystallized blocks.
• After milling, restorations are heat-treated.
• Zirconia restorations are pre-made larger size to compensate for shrinkage and shrinkage during the sintering process.

Composite Resin & Hybrid Resin Ceramic

• Mechanical properties (flexural resistance, resilience) of resin-infiltrated hybrid ceramic materials fall between those of composite resin and reinforced glass ceramic.
• The probability of marginal fractures occurring during milling is significantly lower compared to dental ceramic blocks of similar strength.
• Composite or hybrid resin ceramic blocks are mostly used for partial coverage restorations.

Explore the applications and advancements of CAD-CAM technologies in dentistry. This quiz will cover the various types of dental ceramics, their properties, and their uses in modern dental practices. Test your knowledge on the materials shaping the future of dental prostheses.