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

Crowns Flashcards

1
Q

The Principles of Crown prep

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

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.

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3
Q
  1. Retention and resistance definitions
A

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.

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4
Q

How can retention and resistance be achieved

A

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

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5
Q

How can structural durability be achieved.

A

Occlusal reduction, axial reduction, functional cusp bevel.

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6
Q

How can marginal integrity be achieved?

A

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

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7
Q

How can preservation of periodontium be achieved.

A

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

Be aware of BIOLOGICAL WIDTH (2mm)

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8
Q

Reduction values for metal (gold veneer) Crown

A

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

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9
Q

Reduction values for Traditional ceramic porcelain crowns

A

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

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10
Q

Reduction values for MCC

A

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.

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11
Q

Reduction values for Alumina, Zirconia crowns

A

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

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12
Q

Significance of buccal prep

A

2 PLANES - avoid pulp horn

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13
Q

What is kaolin

A

hydrated aluminosilicate

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14
Q

What do dental ceramics consit of

A
  • Little kaolin
  • feldspar
  • quartz
  • metal oxide
  • glass
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15
Q

What is feldspar and its purpose

A

Acts as a flux (binder)

- lowers the fusion and softening temperature of glass

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16
Q

Conventional dental ceramics - powder, how does this happen

A

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
Q

What is leucite and its purpose

A

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

18
Q

what happens during the fabrication of a crown

A

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
Q

Properties of conventional ceramics

A
  • aesthetics
  • abrasion resistance
  • chemically stable
  • biocompatible
  • thermal props
  • dimenionally stable
20
Q

Aesthetics of ceramics

A
  • best of any restorative material
  • stable colour, smooth surface
  • Optical properties - reflectance, translucency, opacity, transparency, opalescence
21
Q

Chemical stability

A
  • no reaction to other materials
  • not pick up stains
  • good biocompatibility
  • unaffected by pH
22
Q

Thermal properties

A

similar to tooth

  • TEC similar to dentine
  • LOW thermal diffusivity
23
Q

Dimensional stability

A

Very stable

-Fabrication shrinkage (20% during firing/sintering)

24
Q

Mechanical properties

A
  • 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
Q

Where should feldspathic crowns be used

A

LOW STRESS AREAS

- ANTERIOR

26
Q

Alumina core - use and 2 named examples

A

ANTERIOR

  • good aesthetics
  • > alumina means >strength (flex 120MPa)
  • INCERAM
  • PROCERA
27
Q

INCERAM - 85% Alumina

what technique is used to form this

A

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
Q

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

A

BETTER - >700Mpa

better translucency

29
Q

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

A

CAD-CAM.
>1600 degrees
- YTTRIA STABLISED ZIRCONIA

30
Q

How does Yttria stabilised zirconia stop crack propagation

What can they be used for
properties

A

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
31
Q

Fabrication steps of zirconia core

A
  • impression taken, scan cast digitally
  • create virtual bridge substructure, minimum thickness of connectors created.
  • raw zirconia milled
  • cut framework heated to 850 degrees, 20% shrinkage occurs
  • veneered with feldspathic porcelain prior to final restoration
32
Q

When would a crown be advised for a patient:

A
  • little tooth tissue - weakened tooth
  • fracture
  • cuspal coverage ie Endo
  • improve aesthetics
  • indicated by RPD design
33
Q

contraind to crown placement

A
  • active perio disease
  • active caries
  • lack of tooth for prep
  • destuctive prep
  • unable to provide post/core
  • unfavourable occlusion
34
Q

MCC measurements for anterior/posterior

  • labial
  • palatal
  • incisal
  • taper
A
  • labial: 1.4mm (0.9mm porcelain / 0.5mm metal) SHOULDER
  • palatal: 0.5mm CHAMFER / 1.5mm chamfer
  • incisal: 2-2.5mm
  • 2-7 degrees
35
Q

All-Ceramic measurements for anterior/posterior

  • labial
  • palatal
  • incisal/occlusal
  • taper
A
  • labial: 1.5-2mm SHOULDER
  • palatal:1.5-2mm CHAMFER
  • incisal/occlusal: 2.5mm
  • taper: 2-7 degrees

FRP - Crowns/Bridges/Wear/TMD/SDA/IMPLANTS (8 decks)

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