Dental Ceramics Basics

Introduction

• Presenter: Dr. Suresh Shenvi
• Topic: Dental Ceramics
• Suggested by: Gagan Yadhav
• Difficulty: Noted as challenging for undergraduates

Evolution of Dental Crowns

1. Types:
   • Metal Crowns
   • Metal Ceramic Crowns
   • All Ceramic
2. Key Objective: Achieve both strength and aesthetics

Composition and Methods

• Ceramics/Porcelain
  • Used widely in many fields
  • Dental ceramics have additional components

Silica

Forms of Silica

1. Crystalline Form
   • Used in: investment materials, dental cements, composites
   • Example: Quartz
   • Advantage: Low melting temperature
   • Disadvantage: Low strength
2. Non-Crystalline Form
   • Used in dental ceramics
   • Example: Fused Silica
   • Advantage: High strength

Structure of Silica

• Silica Tetrahydrate
  • Silica ion surrounded by oxygen
  • Strength from bonds between ions

Challenges with Fused Silica

• High Fusion Temperature: Not feasible for dental labs
• Solution: Adding Glass Modifiers (Carbonates of sodium, potassium, calcium)

Glass Modifiers

• Function: Reduce fusion temperature and viscosity
• Limitations: Can reduce strength and increase susceptibility to oral fluids
• Effect: Leads to devitrification (increased opacity)

Classification of Ceramics by Fusion Temperature

1. High Fusing: > 1300°C
2. Medium Fusing
3. Low Fusing
4. Ultra Low Fusing: < 850°C

Key Considerations

• Use low fusing ceramics for high-force areas like bridges

Feldspar

• Composition: Potassium aluminum silicate
• Functions:
  1. Forms a glass phase to allow silica particles to fuse
  2. Undergoes incongruent melting (creates liquid and crystalline lucite)

Components Added to Ceramics

• Boric oxide: Acts as a glass modifier, facilitates silica movement
• Pigments: Provide different shades
• Category: Feldspathic ceramics

Challenges with Feldspathic Ceramics

Strength Issues

• Good compressive strength
• Low tensile strength (brittle)

SEM Image Observation

• Presence of microscopic cracks
• Bending forces propagate cracks leading to fractures

Metal-Ceramic Crowns

Benefits

• Aesthetics from ceramic layer
• Strength from metal core

Disadvantages

1. Requires more tooth reduction
2. Lacks translucency (opaque appearance)

Bonding

• Chemical bonding: Between metal oxides and ceramic
• Essential metals: Iron, indium, tin

Research Advances

Strengthening Techniques

1. Glazing
   • Types: Self-glaze vs. Over-glaze
   • Preferred: Self-glaze (longer-lasting)
2. Residual Compressive Stress
   • Generated by: Ion exchange, thermal tempering, thermal expansion coefficient mismatch
   • Methods:
     1. Ion Exchange: Sodium replaced by larger potassium
     2. Thermal Tempering: Differential cooling rates
     3. Thermal Expansion Coefficient Mismatch: Different shrink rates in core and surface materials
3. Interruption of Crack Propagation
   • Methods: Dispersion of crystalline phase, transformation toughening
   • Alumina and Zirconia: Interrupt crack propagation
4. Design Modifications
   • Avoid sharp margins and sudden thickness changes

Zirconia-based Ceramics

Advantages

• Strong, allows metal-free crowns

Disadvantages

• Opaque nature
• High abrasion resistance

Summary

• Evolution from metal to aesthetic ceramics
• Various modifications to improve ceramic strength

Conclusion

• Collaboration for more informative videos
• Encouragement for feedback and shares