Dental Ceramics 2/28/2023

Question 1

Ceramic properties:

Answer 1

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.

Question 2

Metal ceramics (PFM):

How does ceramic bond to metal?

Answer 2

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.

Question 3

How does the coefficient of Thermal Expansion (CTE) work?

Answer 3

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.

Question 4

2 Different porcelain fractures

Answer 4

Adhesive porcelain fracture: Metal shown
Cohesive porcelain fracture: break through ceramic itself.

Question 5

Ceramic Alloys:
Composition

High noble metal:

Answer 5

High noble metal: Must contain > / = 60% noble metals (gold, platinum, palladium)

platinum, palladium -> increase strength / hardness, lower CTE

> / = 40% must be gold.

Question 6

Ceramic Alloys:
Composition:

Noble metal:

Answer 6

must contain > / = 25% noble metals

Question 7

Ceramic Alloys:
Composition:

Predominately base:

Answer 7

< 25% noble metals.

Question 8

Ceramic Alloys:
Composition:

Indium
Tin
Zinc
Silver
Copper

Answer 8

Indium - oxide formation
Tin - oxide formation
Zinc - scavenger (prevents oxidation of other metals)
Silver - fluidity - can cause discoloration
Copper - Hardness

Question 9

Feldspathic Porcelain
Composition:

Silica
Aluminum Oxide
Potassium & Sodium oxide:
Pigment Oxides

Answer 9

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.

Question 10

Sequence of Metal Ceramics (PFM)

Answer 10

Metal finishing
Air abrasion & heat treated
Add opaque layer
firing
Body porcelain addition
Firing
Incisal porcelain addition
Firing
Final

Question 11

All ceramics benefits / disadvantages:

Answer 11

“More” esthetic
new fabrication techniques

disadvantages: Requires adequate thickness, need more advanced equipment

Question 12

All ceramics

leucite glass-ceramic (empress)

Answer 12

very esthetic
high strength ~160 MPa flexural strength.

This one bonds to dentin and enamel.

can be pressed / milled

Question 13

All ceramics

Lithium disilicate (e. max)

Answer 13

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???)

Question 14

All ceramics

Zirconia

composition and phases:

Answer 14

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.

Question 15

All ceramics

zirconia

features:

Answer 15

> 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

Question 16

sintering:

Answer 16

heating ceramic particles to a temp just below melting point. it will then shrink after. Use this for zirconia fabrication.

Question 17

Zirconia vs lithium disilicate

Answer 17

Zirconia: generally for posterior, due to strength
Lithium disilicate: generally anterior due to esthetic.

Question 18

Why must everything be round for all ceramics when milling?

Answer 18

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.

Question 19

Provisional Cements:

Answer 19

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.

Question 20

Permanent Cements:

Hardening mechanisms of Dental Cements:

Answer 20

Acid-base reactions
Liquid: Usually acids
Powder: Usually basic

Question 21

3 liquids / 3 powders for different types of cements:

Answer 21

Liquids: Phosphoric acid, polyacrylic acid, water
Cements: Zinc Oxide powder, Alumino-silicate glass powder, calcium aluminate & GI Powder

Question 22

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:

Answer 22

1.) Zinc Phosphate Cement
2.) Polycarboxylate Cement
3.) Glass Ionomer Cement
4.) Calcium Aluminate Cement

Question 23

Zinc Phosphate Cement:

Answer 23

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

Question 24

Polycarboxylate cement:

Answer 24

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. *

Question 25

Glass Ionomer Cement:

Answer 25

Fluoride Release. Good for high caries risk patients.
adhesion to tooth structure

RMGIC = better adhesion to tooth. disadvantage: can absorb water and cause expansion.

Question 26

Resin cements:

Answer 26

Not soluble
adhesion
increased retention of crown

challenge: lot of blood / salivia makes it bad

Question 27

Light polymerization:

Dual polymerization

Answer 27

Can never be used with zirconia / metal
can only be used for thin porcelain veneers

Question 28

resin cement polymerization: Difference

Answer 28

Only light cure for 2 seconds in midstep.

Question 29

2 types of cementation:

Answer 29

Luting: fasten, attach or seal. not bonding. filling gap only. (polycarboxylate cements)
Bonding: join together, adhesively bond tooth to material. (Resin cements)

Question 30

When to do luted restoration or bonded restoration?

Answer 30

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.

Question 31

Lithium disilicate bonding protocol:

Answer 31

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.

Question 32

Zirconia bonding protocol:

Answer 32

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.