Dental Ceramics 2/28/2023 Flashcards
Ceramic properties:
High compressive strength, low tensile strength.
Can deal with a lot of stress. If it starts to flex too much, it then breaks.
Do not tolerate flexure. Must be supported.
Harder than enamel, meaning they wear out enamel.
Metal ceramics (PFM):
How does ceramic bond to metal?
1.) chemical bonding. Molecular bond between oxides in dental ceramic and the oxides on the metal surface.
2.) Mechanical Retention (metal roughness, air particle abrasion {sand blasting it})
3.) Van Der Walls forces
4.) Compression Bonding (coefficient of Thermal Expansion (CTE)) - material expands from heat. As it cools, the metal will shrink a little bit more than the ceramic.
How does the coefficient of Thermal Expansion (CTE) work?
material expands from heat. As it cools, the metal will shrink a little bit more than the ceramic.
Metal has slightly higher CTE than ceramic so it shrinks more. but because they are bonded together, it will pull more towards the center which gives it more strength.
2 Different porcelain fractures
Adhesive porcelain fracture: Metal shown
Cohesive porcelain fracture: break through ceramic itself.
Ceramic Alloys:
Composition
High noble metal:
High noble metal: Must contain > / = 60% noble metals (gold, platinum, palladium)
platinum, palladium -> increase strength / hardness, lower CTE
> / = 40% must be gold.
Ceramic Alloys:
Composition:
Noble metal:
must contain > / = 25% noble metals
Ceramic Alloys:
Composition:
Predominately base:
< 25% noble metals.
Ceramic Alloys:
Composition:
Indium
Tin
Zinc
Silver
Copper
Indium - oxide formation
Tin - oxide formation
Zinc - scavenger (prevents oxidation of other metals)
Silver - fluidity - can cause discoloration
Copper - Hardness
Feldspathic Porcelain
Composition:
Silica
Aluminum Oxide
Potassium & Sodium oxide:
Pigment Oxides
Silica (SiO2) - ~60% - Framework
Aluminum Oxide - Increase strength
Potassium and Sodium Oxide - increase CTE to better match CTE of the metal
Pigment oxides: Iron = brown, copper = green.
Sequence of Metal Ceramics (PFM)
Metal finishing
Air abrasion & heat treated
Add opaque layer
firing
Body porcelain addition
Firing
Incisal porcelain addition
Firing
Final
All ceramics benefits / disadvantages:
“More” esthetic
new fabrication techniques
disadvantages: Requires adequate thickness, need more advanced equipment
All ceramics
leucite glass-ceramic (empress)
very esthetic
high strength ~160 MPa flexural strength.
This one bonds to dentin and enamel.
can be pressed / milled
All ceramics
Lithium disilicate (e. max)
made of Lithium Disilicate (LiS2) - 70%.
esthetic
360-400 MPa flexural strength
bonds to dentin and enamel
can be pressed / milled
(might delete - typically for veneers???)
All ceramics
Zirconia
composition and phases:
composition: zirconia dioxide (ZrO2)
phases: Monoclinic, Tetragonal, Cubic - strongest
additional composition: 3% yttrium oxide: used to stabilize zirconia and keep it in tetragonal state at room temperature.
All ceramics
zirconia
features:
> 900 MPa flexural strength
as you go more translucent (more esthetic), you lose some of the strength.
not as strong bonding to dentin and enamel as lithium disilicate.
fabrication: milled - in partially sintered state 20-25% larger to compensate for shrinkage.
It literally is 1/4 bigger to compensate
can only mill. no press
sintering:
heating ceramic particles to a temp just below melting point. it will then shrink after. Use this for zirconia fabrication.
Zirconia vs lithium disilicate
Zirconia: generally for posterior, due to strength
Lithium disilicate: generally anterior due to esthetic.
Why must everything be round for all ceramics when milling?
If it is sharp edges, bur will over mill and make it round
note. if you are pressing and not milling, you can have sharp edges. Zirconia cannot be pressed.
Provisional Cements:
Typically zinc oxide powder / zinc oxide paste mixed with eugenol liquid
Important: Eugenol can actually disrupt composite bonds. Dont want eugenol if ur doing some type of bonding with resin cement.
Permanent Cements:
Hardening mechanisms of Dental Cements:
Acid-base reactions
Liquid: Usually acids
Powder: Usually basic
3 liquids / 3 powders for different types of cements:
Liquids: Phosphoric acid, polyacrylic acid, water
Cements: Zinc Oxide powder, Alumino-silicate glass powder, calcium aluminate & GI Powder
1.) phosphoric acid + Zinc oxide powder:
2.) Polyacrylic acid + zinc oxide powder:
3.) Polyacrylic Acid + Alumino-silicate glass powder:
4.) Water + Calcium Aluminate & GI Powder:
1.) Zinc Phosphate Cement
2.) Polycarboxylate Cement
3.) Glass Ionomer Cement
4.) Calcium Aluminate Cement
Zinc Phosphate Cement:
Higher solubility than other cements
good marginal fit minimizes exposure of cement to oral fluids
acid penetrates dentin tubules
no fluoride release
no adhesion, retention mechanically
uses cool glass slab
add powder, add liquid on cool glass slab, keep adding powder to liquid until u get right consistency
Polycarboxylate cement:
good for sensitive teeth
good as a base
uses adhesion, bonds to calcium in tooth.
add set amount of powder / liquid and just mix
*IF It comes in contact with titanium, will corrode surface. *
Glass Ionomer Cement:
Fluoride Release. Good for high caries risk patients.
adhesion to tooth structure
RMGIC = better adhesion to tooth. disadvantage: can absorb water and cause expansion.
Resin cements:
Not soluble
adhesion
increased retention of crown
challenge: lot of blood / salivia makes it bad
Light polymerization:
Dual polymerization
Can never be used with zirconia / metal
can only be used for thin porcelain veneers
resin cement polymerization: Difference
Only light cure for 2 seconds in midstep.
2 types of cementation:
Luting: fasten, attach or seal. not bonding. filling gap only. (polycarboxylate cements)
Bonding: join together, adhesively bond tooth to material. (Resin cements)
When to do luted restoration or bonded restoration?
how high or tall? how parallel? Resistance/retention of prep? What is the material that the crown is made of?
Lithium disilicate: must be bonded to get max strength
Metal / Zirconia: can be luted / bonded.
Lithium disilicate bonding protocol:
1.) Lab conditions crown. Etch it. OH groups stick out of lithium disilicate.
2.) then fit in mouth to make sure it fits, but by doing this u contaminate it with saliva / blood.
3.) Clean surface via ivoclean. Cleans surface and OH groups back up.
4.) Monobond plus scrub inside crown. Air dry. Gives CH group to OH.
5.) Apply resin cement now. Ready to go.
Zirconia bonding protocol:
Cant etch bc harder material. U sandblast it, roughens surface.
NEver use phosphoric acid to clean zirconia. Use Ivoclean.
Zirconia has same steps as lithium disilicate, but after ivoclean cleaning, its more of a positive / negative bond than an OH bond. Weaker bond.
