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Intermediate restorative skills (Den 305) > Posterior full coverage crowns > Flashcards

Posterior full coverage crowns Flashcards

1
Q

Reasons for full coverage of compromised teeth

A
  1. Restores function and morphology (occlusion)
  2. Restoring and improving aesthetics
  3. Preserving remaining tooth tissues and
    increasing fracture resistance
  4. Integrating with other prosthesis
  5. Improves patient’s confidence & psychology
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2
Q

Structural integrity of endodontically treated teeth

A

Weakened?

1) Preparation of pulp access cavity
2) Loss of roof of the pulp chamber
3) Fragile due to loss of dentine elasticity

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3
Q

Structural integrity of posterior teeth

A 
Cuspal protection required?
1. Loss of marginal ridge
2. Loss of substantial tooth structure
3. Heavily restored tooth
Restored with?
1. Adhesive restorations (direct resin composite)
2. Cusp-coverage cast restorations (onlay, ¾ crown)
3. Full-coverage restorations (crowns)
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4
Q

Assessment/ design considerations

A
  1. Aesthetic considerations
  2. Adjacent/opposing Teeth
  3. Caries / restorations
  4. Periodontal Tissues
  5. Pulp, RCT and periapical tissue
  6. Is the tooth in function (occlusion)?
  7. Retention of the crown
  8. Materials
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5
Q

Assessment/ design considerations: aesthetic considerations

A
  1. Upper vs lower
  2. Premolars vs molars
  3. Smile line
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6
Q

Assessment/ design considerations: adjacent/ opposing teeth

A
  1. Orientation /Drifted teeth
  2. Contact points
  3. Diastema / Spaces between teeth
  4. Crowded teeth
  5. Length of tooth
  6. Insertion path (study model)
  7. positioning & supraeruption of opposing teeth
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7
Q

Assessment/ design considerations: caries/ restorations

A
  1. Location of caries, sub/supra gingival
  2. Quality of existing restorations
  3. Secondary caries
  4. Interproximal and root caries
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8
Q

Assessment / Design Considerations: periodontal tissues

A
  1. Good oral hygiene and plaque control
  2. Status of disease (active/stable)
  3. Periodontal attachment (no or min pockets)
  4. No or min mobility of tooth
  5. Alveolar bone level (radiograph)
  6. Crown / root ratio (radiograph)
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9
Q

Assessment / Design Considerations: occlusion

A
  1. Facet or wear on teeth (localised or
    generalised)
  2. Working or nonworking interferences
  3. Contact of teeth on both sides
  4. Canine or Group guided lateral movement
  5. The distance and deviation between CR/ICP
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10
Q

Assessment / Design Considerations: pulp, RCT and periapical lesions

A
  1. Periapical lesions
  2. Quality of root canal treatments
  3. Length, configuration and direction of roots
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11
Q

“Pulpal death” following crown preparation

A
  1. Average of 6 - 20% of prepared teeth
  2. Aggressive insult to the tooth, dentine and
    odontoblasts
  3. Thermal damage
  4. Local anaesthesia
    -due to adrenaline in LA reducing blood flow to pulp
  5. Desiccation
    -living tissues will die if dry
  6. Bacterial contamination
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12
Q

Crown preparation: shoulder

A

A 1.2mm shoulder crown preparation on a
posterior tooth leaves
≤ 0.7mm remaining dentine thickness
(0.7mm in 50 % of maxillary molars and < 0.7mm in all other premolars and molars)

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13
Q

Major risk of crown

A

Loss of vitality

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14
Q

Assessment/ design considerations: retention of the crown

A
  1. Shape of tooth (possible // axial walls)
  2. Occlusal morphology
  3. Tooth occ-ging length
  4. Path of insertion (inclined teeth)
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15
Q

design considerations: materials of the crown

A

Balancing function and aesthetics

  1. Full Metal (FGC)
    - minimal tooth reduction
    - least aesthetic
    - can be adjusted intra-orally
    - least abrasive to opposing teeth
    - high survival rate long term
  2. Metal-Ceramic (PFM)
    - metal core
    - extensive buccal tooth reduction
    - aesthetics at cost of tooth tissue
    - only metal component can be adjusted intra-orally
  3. All Ceramic
    - high strength ceramic core
    - most aesthetic
    - low edge strength
    - requires extensive reduction
    - intra-oral adjustment not possible
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16
Q

Principles of tooth preparation

A

Schillingburg

  1. Preservation of tooth structure
  2. Retention and resistance
  3. Structural durability
  4. Marginal integrity
  5. Preservation of periodontium
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17
Q
  1. Preservation of tooth structure
A

Partial coverage VS Full coverage
Supra-gingival VS Sub-gingival
FGC VS PFM/All ceramic

18
Q
  1. Retention and resistance
A

Retention prevents the removal of the restoration along the path of insertion or the long axis of the tooth
Resistance prevents dislodgement of the restoration by forces directed in apical or oblique direction and prevents any movement of the restoration under occlusal forces

19
Q

Retention

A

1.Create parallel axial walls
2.Increase occluso-gingival length
3.Add internal features
4. Limit the path of insertion
An imaginary line along which the restoration is placed onto or
removed / Parallel axial walls of preparation / Long access of tooth

20
Q
  1. Structural durability
A

Provide enough bulk of the restoration

  1. Occlusal Reduction
  2. Bevel of Functional Cusp
  3. Axial Reduction
21
Q

Inadequate occlusal reduction

A

Weaker restoration
Easily perforated restoration during finished or by wear
Insufficient functional morphology

22
Q

Gold alloy types

A

Type I (soft): very burnishable
-for inlays
Type II (medium): less burnishable
-multiple surface inlays
Type III (hard): most commonly used type of gold
-all-metal crowns and bridges
-gold 75%, silver 10%, copper 10%, palladium 3%, zinc 2%
Type IV (extra hard) used for partial denture frameworks

23
Q
  1. Structural durability: Occlusal Reduction
A
  • provide adequate bulk of material and strength to the restoration
  • follow morphology of occlusion (> retention, < vertical dislodging, adequate height)
24
Q
  1. Structural durability: bevel functional cusp
A

Functional cusps receive heavy occlusal load
Provides space for an adequate bulk of material
1. Insufficient thickness —> perforation
2. Poor occlusion & overcontouring
3. Overinclination of the buccal/lingual surface
 Excessive removal of sound tissues
 Reduced retention

25
Survival rates of full gold crown
97% survival at 9 years 90% survival at 20 years Extremely predictable, long term restorative service
26
3. Structural durability: axial reduction
``` 1. Provides space for an adequate thickness of the crown 2. Inadequate axial reduction: • Thin axial walls ---> distortion • Overcontouring ----> periodontal problems ```
27
4. Marginal integrity
Closely adapt the margins of restoration to the cavosurface finish line of the preparation -chamfer, radial shoulder, heavy chamfer, shoulder
28
5. Preservation of the periodontium
``` The placement of finish lines has a direct impact on 1. Ease of fabrication 2. Success of the restoration Margins  Smooth  Supragingival - (gingival) ```
29
PFM alloy types
High-noble alloys -60% noble metals (any combination of gold, palladium, silver) -min 40% of gold -chemical bond for pocelain Noble alloys -at least 25% by weight notble metal -relatively high strength, durability, hardness, ductility Base-metal alloys -less than 25% noble metal -much harder, stronger, 2x elasticity of high-noble and rigidity needed to support porcelain -contain nickel and beryllium (allergens)
30
5. Preservation of the periodontium: placement of margins
finish line/margins should be placed where margins can be:  Finished easily by the dentist  Duplicated by the impression without tearing or deformation  Kept clean by the patient Place finish line in ENAMEL wherever possible
31
PFM crowns survival
Meta-analysis, Pjetursson et al. 2007 5 year survival 93.9% all ceramic 95.6% for metal-ceramic crowns
32
Preparations should be
1. well-defined and finished 2. Has a clear finish line 3. Has Rounded internal line angles and point angles 4. Has min of 90° external line angles
33
Full crown and oral hygiene
• Full crown doesn’t protect against biological attacks such as caries although it covers tooth • OH improved and maintained prior to any fixed prosthodontic tx
34
Advantages of all ceramic crowns
Most aesthetic | High strength ceramic core
35
Disadvantages of all ceramic crowns
Х Brittleness Х Low tensile strength (low strength of edge) Х Less conservative (requires extensive prep) Х Not adjustable intra-oral Х Abrasive to opposing teeth (40X than gold to enamel)
36
All ceramic crowns fracture rates
5 year # rate 4.4% Molar crowns have higher # rate than premolar and anterior crowns Acceptable overall t-year fracture rate
37
Tooth prep for all ceramic crowns
``` Occlusal reduction reflects 1. Tooth morphology 2. Occlusion functional pathways -occlusal reduction >1.5mm Stress areas >2mm Shoulder margin Axial walls 5 degree tapered ```
38
Tooth prep for PFM crowns
Reduction -buccal (shoulder): 1.2-1.4mm - marginal integrity -lingual (chamfer): 0.5-0.7mm - marginal integrity and structural durability -proximal (chamfer) -occlusal: 2mm - structural durability Wing: preservation of tooth structure and retention and resistance Bevel of functional cusps - structural durability
39
Full metal crown
``` Planar occlusal reduction Axial reduction Chamfer -less stress to the luting cement Seating groove ```
40
Phase I: posterior crowns
1. Pre-op clinical and radiographic assessment (PA to assess bone levels and pulpal health/ vitality) 2. Further investigations, study models, diagnostic wax-up 3. Treatment Planning 4. Informed consent
41
Phase II: posterior crowns
1. Tooth build up (if necessary) and Preparation 2. Impression 3. Shade selection 4. Occlusal Record 5. Temporisation 6. Fabrication (Lab stage)
42
Phase III: posterior crowns
1. Removal of temporary crown 2. Try-in of definitive crown 3. Cementation of definitive crown 4. Occlusal check 5. Review

Intermediate restorative skills (Den 305) (16 decks)

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