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Module 6 - Fixed Pros > Crowns and Bridges - Core > Flashcards

Crowns and Bridges - Core Flashcards

1
Q

What is the core?

A

Restoration placed in teeth prior to preparation for an indirect restoration

  • Can be made of natural tooth, composite or a post-retained core.
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2
Q

What underpins the success of the indirect restoration?

A

The core.
Poor retention means the core will be lost and thus the indirect restoration will be lost.

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3
Q

6 materials direct cores can be made of?

A

Amalgam (posterior teeth), composite, glass ionomer, RMGI, compomer, metal alloy

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4
Q

Advantages of amalgam as core material (5)?

A
  • Not technique sensitive.
  • Strong if placed in sufficient bulk.
  • Can be used as a bonded amalgam (increase retention).
  • Easy to distinguish between amalgam and tooth structure.
  • Packable (pack well to avoid voids).
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5
Q

Disadvantages of amalgam as core material (6)?

A
  • Long setting time (adding extra visits).
  • Low initial tensile/ compressive strength.
  • Weak in thin section.
  • Mercury may be of concern for some patients (minimata treaty 2013 and EU regulation 2017 - breastfeeding and pregnancy).
  • Not adhesive (needs mechanical retention from the cavity).
  • Electrolytic galvanic action (between amalgam and other metals in crown).
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6
Q

Advantages of composite as core material (5)?

A
  • strong and can therefore be placed in thinner sections compared to amalgam.
  • immeditae setting (not complete) with light cure composites.
  • can be bonded to tooth structure
  • no mercury
  • tooth colored
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7
Q

Disdvantages of composite as core material (3)?

A
  • very technique sensitive (moisture contamination and polymerization shrinkage).
  • difficult to distinguish between tooth and composite.
  • Expand in water (compensated by die relief on the master die).
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8
Q

How are cores retained in vital teeth

A
  • Undercut preparation (especially for amalgam).
  • Dentine pins.
  • Adhesive materials (composites, GICs, bonded amalgam).
  • Elective endodontics (pulp chamber, posts).
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9
Q

When is amalgam used?

A

POSTERIOR TEETH.

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10
Q

Disadvantages of self threading pins (5).

A
  • Introduces stresses in dentine.
  • Dentinal crazing.
  • Perforation into periodontium.
  • self shearing pins often do not penetrate full depth of pin hole.
  • Fracture resistance of core material reduced (esp amalgam and more pins).
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11
Q

Amalgam bonding technique (7)

A
  • Complete cavity preparation
  • Place lining if necessary in extremely deep aspects ofcavity
  • Etch enamel 20 seconds, dentine 10s
  • Rinse and dry – good isolation
  • Dentine bonding agent (eg Panavia A&B, Scotch bond)on all aspects of cavity – light cure
  • Paint adhesive resin cement (dual cured, eg. Panavia orRelyX ARC) on base and walls of cavity
  • Pack amalgam onto unset cement – wipe away excess
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12
Q

Rention of cores in endodontically treated teeth?

A
  • Best achieved by removing all gutta percha from pulp chamber.
  • Place glass ionomer or resin modified glass ionomer over floor of pulp chamber and openings of the root canal.
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13
Q

Advantages of Nayyar core.

A

FRACTURE RESISTANCE.

  • no significant difference with amalgam, RMGI…
  • No significant different if GO removed from root canal (as long as pulp chamber is sufficiently undercut and of sufficient depth).
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14
Q
A
  • Thing root canals where placing cores can lead to perforations.
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15
Q

Disadvantages of posts in posterior teeth?

A
  • Posts do not reinforce roots
  • Roots often narrow/ Curved
  • Leading to: strip or lateral perforation, weakened tooth, root fracture.
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16
Q

What is used in posterior teeth for pulp chamber retention?

A

NAYYAR CORE NOT POSTS.

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17
Q

Removal of gutta percha for post space.

A
  • soften with heat or chemicals.
  • mechanical with rotating instrument (only cuts laterally and not at the tip).
  • no difference in disruption of the apical seal.
  • can be done immediately after obturation and may be better.
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18
Q

Advantages of mechanical removal of gutta percha

A
  • Most efficient.
  • Use burs with blunt non-cutting tips eg Gates-Gliddens.
  • Start with smaller size to reduce heat generated and preferential cutting to one side of post space.
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19
Q

Success of posts.

A
  • Leave 4mm GP apically.
  • Post as long as if not longer than crown.
  • diameter of post apically no greater than 1/3rd of root.
  • ferrule to crown or core.
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20
Q

Why are ferrules used?

A

Ferrule minimizes the chance of fracture of the root with movement (especially with canine guidance).

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21
Q

What post is best for retention

A

Threaded > serrated > smooth

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22
Q

What has the most important effect on the retention of a post?

A

the LENGTH.

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23
Q

Advantages of cast posts and cores (indirect)?

A
  • Unable to achieve parallel sided post.
  • Altering angle of core to post.
  • BUT Avoid integral cast postcrowns in tooth wear patients
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24
Q

Disadvantages of cast posts and cores (indirect)?

A
  • Poor fit - frequently shorter than length of impression post (due to cooling shrinkage).
  • Crown made on second impression?
  • May be unsuitable under all ceramic restorations (No bond, No translucency).
  • Frequent fracture (of the root by the post).
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25
Q

3 types of posts to avoid?

A
  • Tapered
  • Threaded
  • Preformed metal posts
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26
Q

advantages of pre formed serrated posts?

A
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27
Q

What does a core do? (2)

A
  • Replaces missing coronal tooth tissue.
  • Stablizes weakened parts of the tooth.
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28
Q

When is it generally recommended that a core is considered?

A

When MORE THAN 50% OF THE CORONAL PART OF THE TOOTH IS MISSING.

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29
Q

What material for cores is increasing in use?

A

COMPOSITE RESIN.

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30
Q

What do composites consist of?

A
  • Resin
  • Filler particles (silica, quartz, other types of glass).
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31
Q

What is the best composite for a core buildup?

A

HYBRID COMPOSITE (large filler + smaller coilloidal silica).

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32
Q

What is the core material of choice for an all ceramic crown?

A

COMPOSITE

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33
Q

3 properties of composite compared to dentine?

A
  • Similar compressive strength.
  • Higher flexural strength.
  • Higher tensile strength.
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34
Q

Can glass ionomer be used as a core buildup material?

A

Not sufficiently strong unless:
- Two intact walls remaining AND
- 1-2mm remaining tooth structure to prepare as a FERRULE.

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35
Q

What is GIC useful for (2)?

A
  1. As a filler to block out undercuts (when preparing for an inlay).
  2. To make good any defects/ irregularities in a tooth preparation for an indirect restoration.
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36
Q

How do RMGIC cure?

A
  1. Acid base reaction AND
  2. Resin polymerization (chemical or light cure or both).
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37
Q

What is a RMGIC advocated as a core material?

A

Vitremer.

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38
Q

Can you use RMGIC under all ceramic restorations?

A

AVOID as they undergo HYGROSCOPIC EXPANSION which could cause CERAMIC FRACTURE.

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39
Q

What cores is RMGIC good for?

A

Under all metal or metal ceramic onlays, inlays crowns or bridges.

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40
Q

What is a common limitation of GIC and RMGIC for core buildup?

A

Both need SIGNIFICANT REMAINING TOOTH STRUCTURE to be effective cores.

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41
Q

4 advantages of GIC and RMGIC as core materials?

A
  • Sets quickly, allowing immediate preparation.
  • Adhesive.
  • Fluoride release.
  • Low thermal expansion coefficient.
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42
Q

4 disadvantages of GIC and RMGIC as core materials?

A
  • Low compressive and tensile strengths.
  • WEAK material - only suitable when significant proportion of tooth is left.
  • Deterioration at low pH.
  • Sensitivity to moisture during setting.
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43
Q

What must be ensured prior to planning an indirect restoration (4)?

A

Tooth is:
- Symptom free.
- Ideally positive to sensibility testing.
- No periradicular pathology.
- No caries in tooth/ around any existing restoration.

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44
Q

How can retention for a core be achieved (2)?

A
  • Mechanical.
  • Chemical.
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45
Q

What is an advantage of a combined etch and prime?

A

Does not need to be washed off.

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46
Q

What is the hybrid layer?

A
  • Dentine surface is etched with an acid to allow MECHANICAL INTERLOCKING OF THE RESIN AROUND THE DENTINE COLLAGEN - produced the HYBRID LAYER.
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47
Q

What are 3 advantages of amalgam bonding (compared to normal amalgam)?

A
  • Improve restoration retention.
  • Reinforce remaining tooth tissue.
  • Enhance marginal seal against bacterial leakage.
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48
Q

What is used for amalgam bonding today? 6 named examples.

A
  • Self or dual curing metal adhesive resins.
  • GICs.
    ex. All Bond 2, Amalgambond Plus, Optibond 2, Rely X ARC, Panavia EX or Panavia F, Panavia 21.
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49
Q

7 steps for bonded amalgam preparation?

A
  1. Prepare cavity (gain max mechanical retention with undercuts, occlusal key ways and grooves).
  2. Place lining if needed in deep cavity (minimum - can affect bond).
  3. Etch enamel and dentine.
  4. Rinse, dry and isolate (place vaseline on inner aspect of matrix band).
  5. Apply DENTINE BONDING AGENT (Panavia AB, Scotchbond) on all aspects of cavity and LIGHT CURE.
  6. Paint ADHESIVE RESIN CEMENT (dual cured, ex. Rely X ARC or Panavia) on walls and base of cavity/.
  7. Pack amalgam onto unset cement and wipe away excess.
50
Q

What is a dentine bonding agent and resin system for bonded amalgam?

A

Scotchbond and RelyX ARC.

51
Q
A
  1. Pint hole cut into dentine which is slightly narrower in diameter than the thread on the corresponding pin.
  2. Pin cuts its own counter-threads.
52
Q

5 disadvantages of interdental pins for retention?

A
  1. Cause stresses in the dentine.
  2. Frictional forces often cause the pin to shear off and not penetrate the full depth of the pin hole (void beneath hole, unretentive, loose, can interfere with occlusion).
  3. Can perforate into the pulp or periodontal ligament.
  4. Dentine crazing (due to shearing forces).
  5. Reduce FRACTURE RESISTANCE of CORE MATERIAL (worse with amalgam and increased number of pins).
53
Q

If using dental pins, what rule must be followed?

A
  • Use the MINIMUM NUMBER OF PINS (one pin for every missing cusp).
54
Q

4 potential indications for elective root canal treatment?

A
  1. Teeth with doubtful pulpal status.
  2. Loss of substantial coronal tissue (ex. caries, wear, fracture, trauma) hence need a post to retain a core.
  3. Vital teeth that have overerupted into an edentulous space (decreasing height can expose a lot of dentine or pulp).
  4. Irreversible pulpitis from tooth preparation (history of repeated restorations, overzealous, not enough water irrigation).
55
Q

How can an amalgam core be retained in VITAL teeth where retention is limited (4)?

A
  • Intradental pins.
  • Slots and grooves.
  • Amalgam bond.
  • Elective RCT.
56
Q

What causes the increased incidence of fracture in endodontically treated teeth (2)?

A

Brittleness occurs due to:
- Loss of coronal tooth structure.
- Loss of structural integrity caused by the access preparation.

57
Q

What determines the type of definitive restoration placed on endodontically treated teeth (2)?

A
  1. The amount of remaining tooth structure.
  2. The position of the tooth (anterior teeth under less occlusal forces than posterior teeth).
58
Q

Is a crown needed for an endodontically treated anterior tooth?

A
  • If intact other than the access cavity, GENERALLY NO NEED.
  • If substantial tooth structure lost, LIKELY REQUIRES CROWN.
59
Q

Is a crown needed for an endodontically treated posterior tooth?

A

Posterior teeth subject to HIGHER OCCLUSAL LOADS and must therefore be protected against fracture.
- CUSPAL COVERAGE USUALLY INDICATED.

60
Q

When is a post indicated?

A

WHEN THERE IS INSUFFICIENT REMAINING TOOTH STRUCTURE TO RETAIN A CORE.

61
Q

Why is placement of posts in posterior teeth more challenging (2)?

A
  • More difficult access.
  • Narrower root canals.
62
Q

What can be used in posterior teeth instead of a post?

A

NAYYAR CORE

63
Q

What is a Nayyar core?

A
  • utilizes the shape of the access cavity to retain the restoration.
64
Q

When is a Nayyar core contraindicated? What can be used instead?

A
  • if there is little pulp chamber left as a result of extensive tooth tissue loss.
  • Posts can be used instead but POOR PROGNOSIS.
65
Q

What is the most important determinant to the successful restoration of a root filled tooth?

A

The FERRULE.

66
Q

What is a ferrule? What does it do?

A
  • A rim of supragingival tooth tissue.
  • Assists RETENTION.
67
Q

How much gutta percha must be left after post preparation to ensure an apical seal?

A

At least 4-5mm.

68
Q

What type of obturation technique must be avoided if it is suspected that a tooth may need a post?

A
  • Heated carrier technique.
  • Difficult to remove only coronal portion without disrupting the apical part.
69
Q

How can the root canal filling be removed prior to preparation of the post space (3)?

A
  1. Chemical (no control over depth of softening).
  2. Thermal (System B tip takes out gutta percha, plugger used to compact remaining gutta percha).
  3. Mechanical (Gates Glidden bur and plugger used to vertically compact GP).
70
Q

2 types of drills that can be used to remove gutta percha for post preparation?

A
  • Gates glidden burs.
  • Protaper D series.
71
Q

What is true about the relationship between post length and its properties?

A

THE LONGER THE POST, THE BETTER THE RETENTION.

72
Q

Why should a space between the end of the post and the GP be avoided?

A
  • Compromises SEAL.
  • Predisposes to LEAKAGE and thus FAILURE.
73
Q

What is true about the relationship between post width and its properties (2)?

A
  • Adequate width needed for STRENGTH and RESISTANCE TO POST FRACTURE.
74
Q

What is true about wide posts (2)?

A

AVOID as:
- Greater risk of lateral perforation.
- Greater risk of root fracture.

75
Q

What is the ideal post diameter?

A

At its apical end should be NO MORE THAN 1/3RD OF THE ROOT WIDTH AT THIS LEVEL.

76
Q

How should the twist drills be used when creating the post space? Why (2)?

A

Start with the SMALLEST size and gradually build up:
- Minimize heat buildup (prevent PDL cell damage).
- Reduce risk of lateral perforation/ keep dentine removal centered along the root canal.

77
Q

Posts can be parallel or tapered. What is important about this?

A

Although parallel posts more RETENTIVE, there is greater risk of PERFORATION OF THE APICAL ROOT DURING PREPARATION OF POST SPACE.

78
Q

Whats is a downside of stainless steel and brass posts?

A

Can corrode within the post space, causing DISCOLORATION.

79
Q

What is an advantage and 2 disadvantages of titanium posts?

A
  • Do not corrode.
  • Fracture more easily.
  • Similar radio-opacity to GP.
80
Q

What are active posts? What are the two types?

A
  • Cut threads into the root canal dentine prior to placement and are thus more RETENTIVE than passive posts.
  • Self threading or pre-tapped.
81
Q

What are self-threading posts? How must they be placed?

A

ACTIVE posts.
- Have a thread that is slightly wider than the prepared post space.
- Post cuts its own counter-thread into dentine when it is rotated in place.
- Try into post space WITHOUT luting cement, if retentive remove, add luting cement and re-place.

82
Q

What are the two types of self-threaded posts?

A
  • Parallel sided, ex. Radix anchor (threads only located at the coronal portion of the post).
  • Tapered, ex. Dentatus (high stresses into dentine, wedging effect and possible root fracture).
83
Q

Give a named example of a parallel sided, self-threading post? How is this inserted?

A
  • Radix anchor.
  • Threads only at the coronal portion of the post.
    1. Place without cement initially to cut the counter-thread.
    2. Reinsert to the full length of the post space with luting cement.
    3. DEROTATE by a QUARTER TURN to minimize stresses within the root dentine.
84
Q

What are pre-tapped posts?

A

Higher frequency of threads on a parallel sided shank.

85
Q

How are pre-tapped posts inserted?

A
  1. The post space is prepared.
  2. Root facer used to produce a flat surface to seat the post down to.
  3. The counter-thread is cut into the dentinal walls using a thread cutter/ pre-tapping device.
  4. Post is inserted.
86
Q

What is the downside of pre-tapped posts? Give a named example?

A
  • Designed to reduce stresses created compared to self threading.
  • Higher frequency of threads + lack of vent to allow escape of excess cement –> EXCESSIVE STRESSES WITHIN DENTINE.
  • Ex. K4 anchor system.
87
Q

Advantage and disadvantage of active posts?

A
  • Advantage: greater retention.
  • Disadvantage: stresses introduced into the dentine can cause ROOT FRACTURE.
88
Q

When should active posts be used?

A

Reserve for cases with COMPROMISED RETENTION:
- Short or curved roots.

89
Q

What are the 2 types of passive posts?

A
  1. Pre-fabricated
  2. Custom made.
90
Q

What can custom-made cast passive posts be made of (3)?

A
  • Type III, Type IV gold alloy.
  • Base metal alloys (harder and predispose to root fracture).
91
Q

What are the steps to the impression technique of post production (3)?

A
  1. Wash material syringed around the entrance of the post hole.
  2. Plastic impression post is pushed through the unset wash (drags it into post hole).
  3. Loaded impression tray is seated before wash sets.
92
Q

What type of post does the impression technique produce? When is it useful? Name 1 advantage and 1 disadvantage.

A
  • Smooth-sided, tapered post that matches the original taper of the root canal preparation.
  • Ideal for IRREGULAR CANALS (ex. upper second premolar).
  • Advantage: decrease the risk of root perforation apically.
  • Disadvantage: Compromised retention.
93
Q

What are serrated posts?

A

Have negative recesses that give more retention than smooth sided posts.

94
Q

What is an advantage of using Parapost XP by Coltene (3)?

A
  • Can make CUSTOM MADE, SERRATED, PARALLEL SIDED post.
95
Q

How does the Parapost XP system work?

A
  • For each size post there is a SMOOTH PLASTIC IMPRESSION POST.
  • Place a RETENTIVE MUSHROOM at the end of the impression post using a hot metal instrument (ex. flat plastic).
  • Serrated burn out post is sent to the lab with the impression.
  • Technician WAXES A CORE around it and CASTS using the LOST WAX TECHNIQUE.
96
Q

2 disadvantages of cast posts?

A
  • Time consuming.
  • Increased lab fees.
97
Q

Are prefabricated passive posts parallel sided or tapered?

A

Can be either.

98
Q

What is the design of prefabricated passive posts?

A
  • Have a VENT that allows escape of luting cement
  • Parapost (XT, XH) series have diamond-shaped serrations which act as a VENT for excess luting cement./
99
Q

How is the core build up for custom-made posts?

A

TECHNICIAN waxes a core around the die and CASTS it using the LOST WAX TECHNIQUE.

100
Q

How is the core build up for prefabricated posts?

A

Once the post is cemented, the core is built up directly in the mouth using the chosen material.

101
Q

What can non metal aesthetic posts be made of (3)?

A
  • These are PREFABRICATED, PASSIVE POSTS.
  • Zirconia, quartz fibre, ceramic.
102
Q

2 advantages and 1 disadvantage of pre-fabricated fibre posts?

A

Advantages:
- Have a SIMILAR STIFFNESS TO DENTINE, allowing for MICROFLEXURE which REDUCES THE RISK of VERTICAL ROOT FRACTURE.
- Better aesthetics (tooth coloured).

Disadvantages:
- Microflexure can lead to post fracture or delamination.

103
Q

What are fibre posts made of (3)?

A

Quartz, silica, glass fibre.

104
Q

When are fibre posts best indicated?

A
  • When a FERRULE can be achieved.
  • With no coronal tooth tissue, core can debond and microflexure can cause post fracture/ delamination.
105
Q

What must be ensured when preparing the post space for a quartz fibre post? Why?

A
  • CLEAN ALL TRACES OF GP AND SEALER (especially with EUGENOL).
  • Can interfere with the resin luting cements for cementing the post.
106
Q

What luting cement is ideal for quartz fibre posts? Why?

A

Self etching resin luting cement as post hole narrow.

107
Q

2 steps to removing a quartz fibre post?

A
  1. Pilot hole cut using a PIN DRILL.
  2. Use a NON END CUTTING bur like a Peeso drill.
108
Q

Name a self etching resin luting cement

A

Rely X unicem

109
Q

4 disadvantages of zirconia and ceramic posts?

A
  • Weaker than metal
  • Need to be made broader, thus wider post space and PERFORATION RISK
  • Zirconia cannot be etched (poor core retention).
  • Difficult to remove.
110
Q

Why do we restore endodontically treated posterior teeth (2)?

A

Restore with cuspal coverage restorations to:
1. Protect the remaining tooth structure.
2. Prevent failure due to FRACTURE or LEAKAGE.

111
Q

Why are posts not advantageous in molars and premolars (3).

A
  • Can cause STRIP or LATERAL PERFORATIONS.
  • Can WEAKEN THE ROOT and thus PREDISPOSE TO ROOT FRACTURE.
112
Q

How can core retention be gained in posterior teeth without posts (3)?

A
  • Undercut shape of pulp chamber.
  • Mechanical retention.
  • Adhesive retention.
113
Q

What is a Nayyar core?

A
  • Uses the PULP CHAMBER for retention.
  • (may remove 2-4mm of GP from root canals however research suggests this may not be necessary).
114
Q

What materials can be used for a Nayyar core (2)?

A
  • Composite (do not place in root canals as would be difficult to remove).
  • Amalgam (can be bonded to improve retention and seal - poor evidence).
115
Q

What influences the RETENTION of a post (5)?

A
  1. Length.
  2. Diameter.
  3. Taper.
  4. Active vs passive.
  5. Luting cement.
116
Q

Are parallel vs tapered posts more retentive?

A
  • PARALLEL more retentive yet have HIGHER RISK OF PERFORATION WITH INCREASING DIAMETER.
117
Q

Are active vs passive posts more retentive?

A
  • ACTIVE but if placed with too much torque can result in root fracture.
118
Q

How long should the post be?

A
  • As long as possible.
  • EQUAL TO IF NOT GREATER THAN THE CLINICAL CROWN HEIGHT.
119
Q

What determines a posts RESISTANCE (4)?

A
  1. Amount of remaining coronal tooth tissue.
  2. Length of the post.
  3. Presence of ferrule.
  4. Anti rotational key in the root surface.
120
Q

What is an ANTI ROTATIONAL KEY? When is it needed? How is it prepared?

A
  • Required for CYLINDRICAL posts.
  • When there is NO CORONAL TOOTH TISSUE FOR A FERRULE.
  • Cut on the PALATAL/LINGUAL aspect of the post hole to a depth of 2-3mm.
121
Q

What are the 2 most important determinants for a successful post crown?

A
  1. Presence of a ferrule.
  2. Length of post.
122
Q

What is a ferrule?

A
  • The band of EXTRACORONAL MATERIAL that encompasses coronal tooth structure that is at least 2mm in height.
  • usually provided by the CROWN.

Module 6 - Fixed Pros (8 decks)

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