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Module 6 - Fixed Pros > Basics of Tooth Preparation for Fixed Prosthodontics > Flashcards

Basics of Tooth Preparation for Fixed Prosthodontics Flashcards

1
Q

Is crown direct or indirect?

A

Indirect (made in the lab)

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2
Q

What is a crown?

A

A FULL COVERAGE, EXTRACORONAL restoration

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3
Q

5 materials that can be used to make crowns?

A
  1. Metal (gold, silver palladium, non-precious metals).
  2. Ceramic bonded to metal.
  3. All ceramic.
  4. Composite.
  5. Acrylic (provisional)
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4
Q

What space does an extra coronal restoration occupy in 3D? What is it bounded by?

A
  • The proximal surfaces of adjacent teeth.
  • The occlusal surfaces of the opposing tooth/ teeth.
  • The soft tissues buccally and lingually/ palatally.
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5
Q

What space does an intra coronal restoration occupy in 3D? What is it bounded by?

A
  • the proximal surfaces of adjacent teeth.
  • The occlusal surface of the opposing tooth/ teeth.
  • The tooth preparation buccally and lingually/ palatally.
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6
Q

6 principles of preparation

A
  1. Conservation of tooth tissue.
  2. Resistance form.
  3. Retention form.
  4. Structural durability.
  5. Marginal integrity.
  6. Preservation of the periodontium.
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7
Q

Name 3 metal types a fixed prosthesis can be made of?

A
  • Gold (precious metal).
  • Silver palladium
  • Nickel chrome (non precious metal)
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8
Q

2 reasons to conserve tooth tissue?

A
  1. Protect the pulp.
  2. Maintain strength in tooth.
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9
Q

3 downsides to preparing teeth too much?

A
  1. Risk of PULPAL DAMAGE (direct exposure or indirect damage).
  2. Risk of losing retention and resistance form.
  3. Compromised strength of tooth.
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10
Q

What % of vital teeth lose vitality when prepared for crowns?

A

Up to 20% of vital teeth prepared for crowns get pulp necrosis and need RCT.

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11
Q

What happens if we do not prepare a tooth enough for a crown (2)?

A
  • Thin material for crown (inadequate strength, poor aesthetics).
    OR
  • Overbuilt crown (plaque trap, poor aesthetics).
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12
Q

2 downsides of a thin crown?

A
  • Poor aesthetics.
  • Inadequate strength.
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13
Q

2 downsides of an overbuilt crown?

A
  • Poor aesthetics.
  • Plaque trap.
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14
Q

Define retention form?

A

Ability of the preparation to retain a restoration in an OCCLUSAL DIRECTION.

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15
Q

Define resistance form?

A

Ability of the preparation to prevent dislodgment of a restoration to LATERAL AND OBLIQUE FORCES.

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16
Q

When is chemical retention (of the cement/ lute) GOOD?

A

Good when loaded in COMPRESSION, achieved when there is a HIGH preparation.
- Rotational forces on one side of the tooth will intersect with the other site –> equal force on both sides and thus COMPRESSION OF CEMENT.

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17
Q

When is chemical retention (of the cement/lute) BAD?

A

Bad under SHEARING FORCES (sliding), caused when there is a SHORT preparation.
- Rotational forces NOT intersected by the opposing surface, causing SHEARING forces and SLIDING.

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18
Q

What is the degree of taper?

A

The angle of the restoration is relation to the long axis of the tooth.

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19
Q

What is the ideal preparation? What is a downside to this?

A

Ideal preparation taper should be NEAR PARALLEL for maximum retention and resistance.
- Too parallel –> risk of UNDERCUTS.

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20
Q

What is the taper AIM? What is the more common taper clinically?

A
  • Aim for a taper of 6 degrees.
  • Clinically taper of 10-20 more often achieved.
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21
Q

What is the total occlusal convergence angle?

A

Taper of one axial wall in relation to the taper of an opposing axial wall. (TWO OPPOSING WALLS).

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22
Q

What is the degree of taper vs the total occlusal convergence angle?

A
  • Degree of taper: angle of restoration in relation to long axis of tooth.
  • Total convergence angle: Taper of one axial wall in relation to the taper of an opposing axial wall. (TWO OPPOSING WALLS).
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23
Q

What is a the benefit of a good occlusal convergence angle?

A
  • Reduces ROTATION of crown and increases COMPRESSION forces (rather than shearing).
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24
Q

2 preparations/ restorations where grooves may be indicated.

A
  1. ROUND preparations: in almost circular preparations, nothing is stopping crown from twisting/rotating.
  2. NON FULL COVERAGE RESTORATIONS: Grooves help stop crown from dislodging in all different directions - add RETENTION and RESISTANCE.
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25
Q

What is the effect of adding grooves to preparations for non-full coverage restorations?

A

Add RETENTION and RESISTANCE.

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26
Q

What is the minimum clearance for metal?

A
  • 0.5mm minimum clearance.
  • at least 1mm occlusal clearance.
27
Q

What type of finishing margin should be used with metal?

A

ANY TYPE OF FINISHING MARGIN.
- Chamfer margin: more conservative thus preferred.
- Shoulder margin: less conservative.

28
Q

What reduction is needed for a metal-ceramic crown?

A

AXIAL REDUCTION:
- Total:1.5mm,
- 0.5mm for metal, 1mm for ceramic.
OCCLUSAL REDUCTION:
- 1-2mm reduction (2mm if ceramic extended onto occlusal).

29
Q

What reduction is needed for ceramic?

30
Q

What margin is needed for ceramic?

31
Q

What reduction is needed for a ceramic composite crown?

A
  • AXIAL REDUCTION: 0.6-1mm.
  • OCCLUSAL REDUCTION: 1-1.5mm.

EXACT VALUES DEPEND ON MANUFACTURER INSTRUCTIONS

32
Q

What finishing margin is needed for a ceramic composite crown?

A

CHAMFER margin

33
Q

What is the long fissure bur used for when doing a crown prep (2)?

A
  • Shoulder preparation.
  • Depth grooves.
34
Q

What is a flat ended, tapered bur used for when doing a crown prep (2)?

A
  • Groove/box preparation.
  • Shoulder preparation.
35
Q

What is a chamfer bur used for when doing a crown prep (4)?

A
  • Occlusal reduction.
  • Axial reduction.
  • Proximal reduction.
  • Chamfer preparation.
36
Q

What is a long needle bur used for when doing a crown prep (1)?

A
  • Initial proximal reduction.
37
Q

What is a rugby ball bur used for when doing a crown prep (1)?

A
  • Lingual/ palatal reduction.
38
Q

What is a red band chamfer bur used for?

A
  • Refinement of preparation.
39
Q

Why are tapered burs used?

A

To ensure the preparation is not TOO PARALLEL.

40
Q

How must the chamfer bur be held to achieve ideal preparation (2)?

A
  1. Parallel to the LONG AXIS of the tooth to achieve the ideal TAPER.
  2. Chamfer bur sitting halfway into the tooth (half of the tip in the tooth).
41
Q

What is a knife/ leather edge margin?

A

Very thin margin, difficult to tell lab where the restoration ends.

42
Q

Why do we only want half of the chamfer bur sitting in the tooth?

A

As if full bur is in tooth, the slither of enamel will be very thin and will break off.

43
Q

Where should the ideal preparation margin be (4)?

A
  • On sound tooth structure (not caries or restoration).
  • Not subgingival.
  • Below the contact point.
  • Allow enough preparation height.
44
Q

Why do we want the margin of the crown preparation to end below the contact point?

A

As more likely to get secondary caries in the contact point.

45
Q

Why do we not want the margin of the crown preparation to be subgingival (3)?

A
  • More difficult to clean.
  • More difficult to take impression of.
  • more difficult to make in the lab.
46
Q

How do we check the margins of the restoration? What must the margin be when looking like this (2)?

A

Check if you are able to see them from the top/ bird’s eye view.
- EVEN, clear around the WHOLE CIRCUMFERENCE of the tooth.

47
Q

What does it mean if we are unable to see the margin from a bird’s eye view (2)?

A
  • Tooth not prepared enough.
  • Tooth has an undercut.
48
Q

What is an undercut?

A

Top part of the tooth is covering the bottom part.

49
Q

How is occlusal reduction carried out?

A

Make DEPTH GROOVES:
- at the HIGHEST PARTS (cusp tips) and the LOWEST PARTS (fissures).

50
Q

What is the functional cusp bevel? Why is it done?

A
  • Increased occlusal reduction in the FUNCTIONING CUSP.
  • To accommodate a THICKER AMOUNT OF MATERIAL to reduce the chance of damage to the crown when the tooth is in function.
51
Q

What is the functional cusp?

A
  • The cusp of one tooth which touches the cusp of the tooth on the opposing arch in function.
  • Maxillary teeth: palatal cusp.
  • Mandibular teeth: buccal cusp.
    BUT DEPENDS ON OCCLUSAL RELATIONSHIP!!
52
Q

How is buccal reduction carried out?

A

Done in 2 PLANES:
- 1st plane: held parallel to the long axis of the tooth.
- 2nd plane: Reduce the incisal third of the tooth.

53
Q

How is lingual/ palatal reduction of POSTERIORS carried out?

A

Generally straighter so can be done in ONE PLANE OF REDUCTION.

54
Q

How interproximal reduction carried out?

A

Done in 2 STAGES:
- Cut an INTERPROXIMAL SLICE below the contact point using a LONG THIN NEEDLE BUR.
- Use chamfer bur to continue reduction.

55
Q

What is a red banded chamfer bur used for (3)?

A
  • Define margins.
  • Smooth.
  • Round.
56
Q

How is palatal reductions of ANTERIORS done?

A

2 STAGES:
1. Cingulum part/ gingival third: HOLD CHAMFER BUR PARALLEL TO BUCCAL SIDE OF PREPARATION.
2. Above the cingulum: USE RUGBY BALL BUR to reduce ABOVE THE CINGULUM.

57
Q

What will happen if you do not use a rugby ball bur to reduce the palatal side of the anteriors (2)?

A
  • Will get MUCH CLOSER TO THE PULP.
  • Much more TAPERED restoration, thus LESS RETENTIVE.
58
Q

How can we assess if we have prepared the tooth enough? (5)

A
  1. Pre-operative silicone index.
  2. Wax.
  3. Temporary restoration.
  4. Depth cuts.
  5. Eyes.
59
Q

How can a silicone index be used to assess if we have done enough reduction?

A
  1. Take a pre-operative impression.
  2. Cut it in half and set it onto the preparation. You see where the preparation made is relative to the pre-operative tooth.

CHECKS FOR REDUCTION AROUND THE WHOLE TOOTH.

60
Q

What can help check for reduction around the WHOLE TOOTH (2)?

A
  • Preoperative putty index.
  • Temporary crown.
61
Q

How can wax be used to assess if we have done enough reduction?

A
  • Get patient to bite on a bit of wax.
  • Any very thin areas may indicate underprepared areas.

CHECKS FOR OCCLUSAL REDUCTION.

62
Q

What can help check for occlusal reduction?

A

Wax (+ putty, temporary crown).

63
Q

How can a temporary crown be used to assess if we have done enough reduction?

A
  • See if there are any very thin areas/ holes in the temporary crown.

CHECKS FOR REDUCTION AROUND THE WHOLE TOOTH.

Module 6 - Fixed Pros (8 decks)

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