Crowns and Conventional Bridges - The Core to Success

Question 1

What is the core?

Answer 1

a restoration placed in teeth prior to preparation for an indirect restoration
- build up of a core is indicated if the tooth doesn’t have adequate tooth tissue for crown preparation (e.g. if the tooth is heavily restored/broken down)

Question 2

what materials can be used for a direct core?

Answer 2

• amalgam
• composite
• glass ionomer
• resin modified glass ionomer
• compomer
• metal alloy

Question 3

what are the advantages of using amalgam as a core material?

Answer 3

• not particularly technique sensitive
• strong if placed in sufficient bulk
• can be used as a bonded amalgam
• easy to distinguish between amalgam and tooth structure (if needed to repair/take away)
• packable, if condensed well voids are avoided

Question 4

what are the disadvantages of using amalgam as a core material?

Answer 4

• long setting time
• low initial tensile/compressive strength
• weak in thin sections
• mercury may be a concern to some patients
• minamata treaty 2013 and EU regulation 2017
• amalgam and pregnancy/breastfeeding cooncerns
• potential for electrolytic action between amalgam and other metals in the crown
• not adhesive (unless using a bonding agent)

Question 6

advantages of composite resin as a core material

Answer 6

• stong and can therefore be placed in thinner sections (compared to amalgam)
• immediate setting (not complete) with light cured composite, therefore can cure and prepare on same day
• can be bonded to tooth strcuture
• no mercury
• tooth coloured hence ideal under all ceramic crowns

Question 7

what are the disadvantages of composite resin as a core material?

Answer 7

• very technique sensitive (moisture contamination and polymerisation shrinkage should be avoided)
• can be difficult to distinguish between composite and tooth structure when preparing crown margins
• composites are plastics

Question 8

what are the advantages of glass ionomer cements and resin modified glass ionomer cements?

Answer 8

• sets quickly allowing immediate preparation
• adhesive
• fluoride release - the clinical significance of this is controversial and there appears to be no conclusive evidence in the literature
• low thermal expansion coefficient

Question 9

what are the disadvantages of GIC and RMGIS as core materials?

Answer 9

• low compressive and tensile strengths
• deterioration at low pH
• sensitivity to moisture during setting
• can be difficult to distinguish between GIC and tooth structure when preparing crowns (can over come this by using fugi pink)
• not packable

Question 10

in vital teeth, where retention is limited for a crown, how can retention be improved?

Answer 10

• dentine pins
• adhesive materials
• elective RCT (placement of posts)
• undercut preparation (amalgam)

Question 11

what are the disadvantages of self threading pins?

Answer 11

• induce stresses
• dentinal crazing
• self shearing pins often do not penetrate full depth of pin hole
• fracture resistance of core material is reduced - worse with amalgam and increased number of pins
• perforation into periodontium

Question 12

what are some examples of amalgam bonding materials

Answer 12

panavia 21
panavia F
amalgam bond
rely x arc
glass ionomer

Question 13

what are the steps to amalgam bonding technique?

Answer 13

• complete cavity preparation
• place lining if necessary in extremely deep aspects of cavity
• etch enamel 20 seconds, dentine 10
• rinse and dry
• apply dentine bonding agent to all aspects of the cavity
• light cure
• paint adhesive resin cement on base and walls of cavity (dual cured)
• pack amalgam onto unset cement - wipe away excess

Question 14

what is a nayyar core

Answer 14

usually used in posterior root filled teeth
can be done with amalgam or composite
- 2-3mm of GP is removed from the canals and the pulp chamber is sufficiently undercut
- then filled to build a core

Question 15

what are the disadvantages of using posts in posterior teeth?

Answer 15

• posts do nto reinforce roots
• roots often narrow and curved
  leading to:
• perforation
• weakened tooth
• root fracture

Question 16

what is the most efficient technique for removing GP for post placement

Answer 16

• mechanical removal
  using burs with blunt non-cutting tips (e.g. gates-gliddens)

Question 17

how much GP should you leave apically when removing for a post placement

Answer 17

4mm ideally, 4-6 in certain circumstances

Question 18

how long should the post be?

Answer 18

at least as long as the crown height

Question 19

how wide should the post be?

Answer 19

no greater than 1/3rd of the root

Question 20

What are some factors which contribute to the success of a post

Answer 20

• leaving 4mm GP acpically
• careful post hole prep
• post as long as if not longer then the crown
• diameter of the post apically should be no greater than 1/3rd of the root
• ferrule to crown or core

Question 21

what is the ideal post shape for optimal retention and to minimize stress on the tooth?

Answer 21

For optimal retention and to minimize stress on the tooth, the ideal post shape for crown dentistry is parallel-sided, passive, and serrated and as long as possible

Question 22

what patients should you avoid cast post and cores in?

Answer 22

tooth wear patients - bruxist

Question 23

what is it called if a patient grinds/clenches their teeth involuntarily?

Answer 23

bruxist

Question 24

what are the disadvantages of cast post and cores?

Answer 24

poor fit - they are frequently shorter than length of impression post crown made of second impression may be unsuitable under all ceramic restorations - no bond, no translucency frequent fracture of root and post