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FRP - Crowns/Bridges/Wear/TMD/SDA/IMPLANTS > Crowns > Flashcards

Flashcards in Crowns Deck (35)
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1

The Principles of Crown prep

1. Preservation of tooth tissue
2. Retention and Resistance
3. Stuctural Durability
4. Marginal Integrity
5. Preservation of periodontium
6. Aesthetics

2

1. Preservation of tooth tissue - how

Avoid weakening tooth structure and damage to the pulp.
Under prep - Poor aesthetics and occlusal and periodontal consequences
Over prep - Tooth strength and pulp comprimised.

3

2. Retention and resistance definitions

Retention - prevents removal of restoration along PoI or long axis of tooth prep

Resistance - prevents dislodgement of restoration in apical of oblique direction. Prevents movement of restoration under occlusal forces.

4

How can retention and resistance be achieved

Taper - 6 degrees for opposing walls
length of walls - longer means < tipping displacement
grooves and slots
Improve retention by reducing numbers of PoI's

5

How can structural durability be achieved.

Occlusal reduction, axial reduction, functional cusp bevel.

6

How can marginal integrity be achieved?

Finish line configuration - knife edge, bevel, chamfer, shoulder and bevelled shoulder.

7

How can preservation of periodontium be achieved.

margins: smooth and fully exposed - cleaning
Placed where dentist can finish and patient clean
Placed at gingival margin

Be aware of BIOLOGICAL WIDTH (2mm)

8

Reduction values for metal (gold veneer) Crown

Axial - 0.5mm,
Occlusal F cusp - 1.5mm, NF cusp - 0.5mm
Finish line - CHAMFER 0.5mm

9

Reduction values for Traditional ceramic porcelain crowns

Axial - 1mm
Occlusal - F cusp - 1.5mm, NF cusp - 1mm
Finish line - SHOULDER 1mm

10

Reduction values for MCC

Axial -1.3mm
Occlusal - F cusp - 1.8mm NF Cusp - 1.3mm
Finish line CHAMFER 0.5MM IF METAL
SHOULDER - 0.9MM PORCELAIN, 0.4MM METAL.

11

Reduction values for Alumina, Zirconia crowns

Axial -1.5mm
Occlusal - F cusp - 2mm NF cusp - 1.5mm
Finish line - CHAMFER 1-1.5mm

12

Significance of buccal prep

2 PLANES - avoid pulp horn

13

What is kaolin

hydrated aluminosilicate

14

What do dental ceramics consit of

-Little kaolin
-feldspar
-quartz
-metal oxide
-glass

15

What is feldspar and its purpose

Acts as a flux (binder)
- lowers the fusion and softening temperature of glass

16

Conventional dental ceramics - powder, how does this happen

Powder made by heating to >1000 degrees then:

-RAPIDLY COOLING, create crazing/cracks.
thiis frit is then milled, a binder added then mixed with distilled water to form restoration

17

What is leucite and its purpose

Potassium Aluminium silicate
-forms glass phase of ceramic,
Gives thermal and physical properties.

18

what happens during the fabrication of a crown

Heating -> sintering
occurs just above glass transistion temperature.
-this is when glass becomes single mass (coalesce)

-during this material shinks by 20% (need to allow for this during construction)

19

Properties of conventional ceramics

-aesthetics
-abrasion resistance
-chemically stable
-biocompatible
-thermal props
-dimenionally stable

20

Aesthetics of ceramics

- best of any restorative material
-stable colour, smooth surface
*Optical properties - reflectance, translucency, opacity, transparency, opalescence

21

Chemical stability

-no reaction to other materials
-not pick up stains
-good biocompatibility
-unaffected by pH

22

Thermal properties

similar to tooth
-TEC similar to dentine
-LOW thermal diffusivity

23

Dimensional stability

Very stable
-Fabrication shrinkage (20% during firing/sintering)

24

Mechanical properties

-high compressive strength
-high hardness
-tensile strength = LOW
-flexural strength = LOW
-# toughness = LOW
-Static fatigue - gradual decrease in strength over time (Si-O hydrolysis)
-surface microcracks ->slow crack growth

25

Where should feldspathic crowns be used

LOW STRESS AREAS
- ANTERIOR

26

Alumina core - use and 2 named examples

ANTERIOR
-good aesthetics
->alumina means >strength (flex 120MPa)

-INCERAM
-PROCERA

27

INCERAM - 85% Alumina
what technique is used to form this

SLIP CASTING
-ceramic core formed on refractory model, alumina slurry applied.
-heated to 1120 degrees for 20 hrs (below glass transition temp)
-PARTIAL SINTERING OCCURS
-porous core produced, infiltrate with lanthanum glass

HIGH strength - >400MPa

28

PROCERA -99% core - better/worse strength, what other property is better in this type of ceramic

BETTER - >700Mpa
better translucency

29

ZIRCONIA CORE - purpose/how can it be produced.
What temperature can it be sintered at?
-What other material is used with it in dentistry

CAD-CAM.
>1600 degrees
- YTTRIA STABLISED ZIRCONIA

30

How does Yttria stabilised zirconia stop crack propagation

What can they be used for
(properties)

Yttria is a tetragonal crystal structure
-if a crack begins when the stress at a crack tip reaches critical level, the crystal structure transforms into a monoclinic structure.
- this causes expansion and closes up crack tip

- used for bridge framework
strong/hard/tough