Crowns

Crowns

Posts
1. Indication
  1. Insufficient tooth tissue to retain a core
2. Method
  1. Remove GP
    1. Need 4-5mm of well-condensed GP left
    2. Gates glidden bur
    3. As soon as endo completed
3. Disadvantages
  1. need to remove dentine
    1. Weakens tooth
    2. Creates an area of stress
4. Best posts
  1. As long as possible
    1. 2/3rd of root length
  2. Serrated
    1. Threaded more retentive
      1. BUT create more internal stress
  3. Tapered
    1. but parallel are more retentive
  4. Leave 4-5mm of GP
5. Types
  1. Cast
    1. Less than 2mm supra gingival tissue
    2. Cementation
      1. Zinc phosphate
    3. Method
      1. 1a) Prepare canal
        1b) Take an imp using plastic post into prepare post hole
        1c) temp made with parapost (smooth metal)
        1d) post cast up in hard gold
        1e) cemented into tooth
        1f) impression for crown taken
    4. Types
      1. Parapost
        Parallel & serrated
      2. Radix
        Parallel & threaded
      3. Dentatus
        Tapered & threaded
    5. Dont get a crown on the post made because it will fracture
  2. Fibre
    1. 2 - 3mm of supragingival tissue
    2. Cementation
      1. Composite cements
        4-meta based
        scotch bond
      2. Core cem
    3. Made of quartz & glass fibres
    4. Properties
      1. Flexural strength & modulus of elasticity similar to dentine
    5. Failure reasons
      1. Technique sensitive
      2. Moisture control
      3. Debond
        Leads to micro leakage & secondary caries
Displaying predicted crown appearance
1. Diagnostic wax-up
2. Unbonded composite
3. Previous photos
4. Computer technology
Impressions
1. Problems
  1. Finish line not visible
  2. Air bubbles
    1. How to avoid
      1. Keep imp tip in during syringing
  3. Void/drag
    1. How to avoid
      1. Dry the prep before imp
      2. Gingival retraction and haemostats
  4. Unset
  5. Detachment from tray
Crown preparation
1. All Metal
  1. Occlusal : 1mm NF, 1.5mm F
  2. Margin (Axial) 0.5-1mm
  3. Chamfer
2. PJC
  1. Indication
    1. Limited to anterior but very weak and fracture
    2. not used anymore
    3. v good aesthetics so can be layered with other materials
  2. Incisal 2mm
  3. Margin (axial): 0.8-1mm
  4. Lingual: 1mm
  5. Shoulder
  6. composition
    1. feldspathic porcelain
3. PFMC
  1. Anterior
    1. 2mm incisal
    2. lingual: 0.5-1mm
    3. Margin: (axial)
      1. Porcelain: 1.2mm
      2. metal
        0.5mm
    4. Labial shoulder/heavy chamfer, lingual chamfer
  2. posterior
    1. occlusal
      1. Porcelain: 2mm NF, 2.5mm F  Metal: 1mm NF, 1 .5mm
    2. Axial
      1. Porcelain 1.2mm, Metal 0.5mm
    3. Labial shoulder/heavy chamfer, lingual chamfer
4. Aids
  1. Putty matrix
  2. Depth cuts
5. Margin
  1. Important for
    1. Perio health
    2. Aesthetics
    3. Marginal seal
      1. Microleakage
    4. Impression taking?
6. EMax
  1. Occlusal
    1. 2-2.5mm
  2. Margin (Axial): 0.8-1mm heavy chamfer/shoulder
7. Functional Cusp Bevel
  1. PUBL
  2. Makes sure its not high in occlusion or too bulky
Treatment planning
1. RCT through a crowned tooth
  1. Disadvantages
    1. Reduced strength of crown,
    2. Weaken porcelain bond,
    3. Predispose to fracture
    4. Loss of orientation
    5. Rubber dam can damage crown
2. Assessing restorability post-endo
  1. Any tooth with less than 3mm supra gingival tooth tissue is severely compromised
  2. RCT teeth are at risk of root fracture
  3. Is there a ferrule?
    1. If not there is a risk of root fracture
    2. 1.5-2mm ferrule needed
    3. Its a ring used to strengthen the end of a stick
Principles
1. Restore form & function
  1. Retention & resistance
    1. Retention
      1. Prevents removal of restoration along path of insertion
      2. Short over-tapered prep = poor retention
      3. Maximise
        Taper 6-12
        Grooves/boxes
        adhesive cements
        Consider surgical crown lengthening
    2. Resistance
      1. Prevents dislodgement by forces directed in apical / oblique direction
2. Aesthetics
3. Maintain structural integrity
  1. Protect weak teeth
4. Conservation of tooth tissue
  1. Over-prep
    1. Compromises pulp
    2. Weakens tooth
    3. To avoid
      1. Gauge depths
      2. use putty matrix
  2. Under-prep
    1. Bulbous crown
    2. Poor aesthetics
    3. Occlusal problems
    4. Periodontal problems
    5. Thin, weak crown
Types
1. Onlay
  1. Cuspal coverage
2. Inlay
  1. No cuspal coverage
3. Crowns
  1. PFM
  2. FMC
    1. Less destructive
    2. Easier to adjust
    3. More durable
    4. More reliable marginal seal
  3. High strength ceramic
  4. Cast ceramic
    1. Empress
  5. Milled ceramic
    1. Procera
      1. Strong
      2. Block out metal cores
  6. PJC

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	Created by Zainab Patel about 4 years ago

	Copied by sanna pathy about 4 years ago