Dental Ceramics In-Depth Notes

Dental Ceramics Overview

  • Attributes and Shortcomings:

    • Highly aesthetic but brittle and weak in high-function areas.
    • Indirect restorative materials made in dental labs.

  • Categories:

    • Glass-based ceramics: Silica as a main component, has a glassy matrix.
    • Non-glass-based ceramics: Made of simple or complex oxides, no glassy matrix.

Advantages and Disadvantages

  • Advantages:

    • Excellent esthetics and biocompatibility.
    • Good wear resistance and stain resistance under function.
    • Ability to achieve precise contacts and contours.

  • Disadvantages:

    • Prone to brittleness and wear of opposing enamel.
    • Difficult to repair and requires two appointments.
    • Challenging to polish properly.

Types of Glass-based Ceramics

  • Porcelain:

    • High glass content, very aesthetic, mostly used for anterior teeth.
    • Brittle and prone to fractures compared to newer options.

  • Feldspathic porcelain:

    • Older, most aesthetic but weakest ceramic, used in veneers and PFM crowns.

  • Alumina porcelain:

    • Double the fracture resistance of feldspathic porcelain.

  • Reinforced Glass-based Ceramics:

    • Developed to tackle porcelain’s fracture issues.
    • Leucite-reinforced ceramics: Enhanced by leucite crystals for waveform resistance.
    • Lithium disilicate: High strength and biocompatibility, used for anterior and posterior applications.

Porcelain Failures

  • Common causes include:
    • Small cracks due to force.
    • Rough surfaces from acid etchants.
    • Chipping at margins, often from scaling.
    • Resin cement should be used for all glass-based ceramics.

Non-Glass-Based Ceramics

  • Composed mainly of alumina and/or zirconia:
    • Zirconia: Strongest material with highest flexural strength.
    • Ideal cementation with resin or conventional cements; allows for esthetic porcelain veneering.

Properties of Ceramic Materials

  • Physical: Stiff and brittle – contributes to fractures.
  • Thermal: Insulating properties, expands/contracts with temperature changes.
  • Biocompatibility: Highly biocompatible with no adverse tissue response.

Optical Properties

  • Translucency: Allows light passage; glass-based ceramics are more translucent.
  • Opacity: Non-glass ceramics are usually more opaque (less aesthetic).
  • Vitality: Glass-based ceramics offer a more lifelike appearance.

Processing Techniques

  • Sintering: Heating ceramic particles.
  • Slip-casting: Firing ceramic mixtures.
  • Heat-pressing: Utilizes lost wax technique.
  • CAD/CAM Technology::
    • Optical scanning and milling to produce restorations.

CAD/CAM Technology Advantages and Disadvantages

  • Advantages:

    • 3D imaging and modification capability before processing.
    • Simplifies impression procedures and reduces errors.
    • Improved convenience, needing only one visit.

  • Disadvantages:

    • High initial costs and significant learning curve.
    • Possible need for custom staining.

Clinical Applications and Selection Rationale

  • Porcelain primarily for anterior teeth and low-stress areas.
  • Veneers used for aesthetic improvements on anterior teeth and premolars.
  • Porcelain-metal restorations once common, now largely replaced by newer ceramics.

New Ceramic Materials

  • Stronger, suitable for posterior regions with resin bonding.
  • Excellent aesthetics, biocompatibility, low wear, and stain resistance.
  • Applications: inlays, onlays, crowns, veneers; main drawback is susceptibility to fracture.

Finishing and Polishing Techniques

  • Use low-speed handpieces and progressively finer abrasives for polishing.

Cementation Protocol

  • All-glass-based ceramics should bond with resin cement; acid etching and silane coupling agent necessary for preparation.

Shade Taking Techniques

  • Consider hue, chroma, and value; use natural lighting and neutral backgrounds to ensure accurate shade matching.

Summary Points

  • Two categories: glass-based (more esthetic) and non-glass-based.
  • Key strengths: newer ceramics developed for durability.
  • Understanding CAD/CAM processes is essential for modern clinical applications.
  • Benefits of modern ceramics include improved aesthetic qualities and biocompatibility while addressing previous weaknesses of older materials.