Materials for crowns and bridgeworks Flashcards
🏗️ What is an indirect restoration?
It’s a restoration made outside the mouth and cemented in place to replace failed tooth structure.
❌ Why can’t direct materials be used for all restorations?
They often lack the physical properties required for strength, fit, and longevity.
🎯 What are the goals when choosing a material for indirect restorations?
Meet cosmetic expectations, preserve sound tooth tissue, and ensure optimum tissue response.
🧩 What should you consider when choosing a material?
Contact with opposing/adjacent teeth
Technical ease of use
Compliance with standards
What are the main material requirements?
Accurate fit
Strength against occlusal forces
Rigidity
Thermal expansion similar to teeth
Plaque resistance
Biocompatibility
🔧 What types of materials are used for crowns and bridges?
Metals
Ceramics
Metal-ceramics (PFM - Porcelain Fused to Metal)
🧠 Why is it important to know the properties of these materials?
For effective communication with patients and dental labs.
⚙️ What are noble metal options?
Type III Gold alloys
Silver-Palladium
Palladium-Silver-Gold
Gold-Silver-Copper-Palladium
🧪 What are base metal alloys?
Nickel-Chromium
Nickel-Chromium-Beryllium
Titanium
💸 How do we choose between metals?
Consider cost,
corrosion resistance,
strength,
stiffness
, ductility, and
clinical application (e.g. inlay vs. bridge).
🌟 What’s the composition of a gold crown from Leeds Dental Institute?
1-star medium gold casting alloy, extra hard, 60% gold.
🧬 What are the roles of alloy elements in gold crowns?
Gold: Tarnish resistance, malleability, density
Copper: Strength and reddish color
Silver: Balances copper’s red, can cause greenish tint
Palladium: Strengthens and stiffens alloy
🛡️ What is a key advantage of base metals?
Higher rigidity (modulus of elasticity) — ideal for long-span bridges.
⚠️ What are the risks of base metals?
Toxic casting fumes
Nickel can cause conjunctivitis, dermatitis, bronchitis
Nickel = carcinogenic & allergenic (contact dermatitis)
🔄 What is a PFM restoration?
A metal core with a ceramic outer layer, combining strength and aesthetics.
📏 What’s key to successful PFM bonding?
Mechanical retention (roughness)
Chemical bonding
Compatible thermal expansion (tangential compressive stress)
🧪 What does indium do in PFM alloys?
Strengthens and hardens, raises thermal expansion, lowers melting range, and forms bonding oxide.
🚫 What are aesthetic drawbacks of PFM restorations?
Lack of light transmission
Less translucency
Grey gingival margins
Allergy to metal
👑 What are the benefits of all-ceramic crowns?
No metal
Better aesthetics
Natural translucency and light transmission
🧱 Why are ceramics brittle?
No ability to bend
Governed by flaws (Griffith’s theory)
Catastrophic failure at a fixed strain point
🦾 What is aluminous porcelain?
Porcelain with 50% fused alumina crystals to stop crack propagation.
🧊 What are glass ceramics?
Heat-treated glass that forms fine crystals — this increases strength and crack resistance.
💎 What is IPS e.max made of?
60% lithium disilicate (framework)
Lithium orthophosphate
Fluorapatite (layering)
💅 What are indications for IPS e.max?
Posterior/anterior crowns
Inlays/onlays
Thin veneers
3-unit anterior bridges
Excellent aesthetics
What is the CAD/CAM process?
CCD camera captures images
Design on software
Milling machine creates crown
May be heat-treated before fitting
🧩 What is CEREC 3?
A CAD/CAM system with a wand for imaging and automated milling process.
🧨 What is transformation toughening in zirconia?
Stress-induced phase change from tetragonal to monoclinic, increasing volume and creating compressive stress to stop cracks.
⚙️ What core ceramics are commonly used?
Alumina, Zirconia, Lava, Cecon, IPS.
📈 How strong are lithium disilicate and zirconia?
Lithium disilicate: 360–400 MPa
Zirconia-veneered: 80–120 MPa
🔬 What’s the current status of research in digital workflows for fixed prosthodontics?
Promising but lacks high-quality RCTs; industrial progress is outpacing clinical research.
