Posts And Cores

Question 1

How to assess if RCT was successful?

Answer 1

Lacks of signs and symptoms clinically
No history or pain or discomfort
Not TTP
Not tender to buccal palpation
No sinus or swelling
Evidence of helping on radiographs
Functional and aesthetically good

Question 2

If the tooth is RCT-ed, and we are restoring it, do we re RCT?

Answer 2

If GP was exposed to saliva for longer period-yes
If post-treatment disease is diagnosed -yes

Question 3

Factors influencing if the tooth has good prosthodontic prognosis are:

Answer 3

Quantity and quality of remaining tooth tissue-most important factor

Question 4

Ferrule effect

Answer 4

Remaining coronal tooth substance offers retention and resistance to bond to

” A metal ring or cap intended to embrace the tooth structure cervically to achieve root strengthening and prevent shattering of the root
1 mm width between post hole and the edge of the substrate, 2 mm height of tooth substrate

Benefits offered by ferrule:
Longer ferrule- increases fracture resistance
It resists lateral forces from the post and leverage from the crown in function
Increases retention and resistance of the crown-harder to pull it out etc
Provides anti-rotational features
Increases longevity of the post and core restorations
Less likely of failure or if it happens more chance of repairing

Question 5

Crown and crown prep features needed for success

Answer 5

Ferrule (dentine axial wall height) of 2-3 mm
Parallel axial walls
Restoration must encircle the tooth
Margins on sound tooth tissue not restoration
Biological width not invaded

Question 6

Tooth restored with a post but no ferrule have what complications?

Answer 6

Increase risk of:
Root fracture
Coronal-apical leakage
Recurrent caries
Dislodgement of crown/core
Periodontal injury-LoA, bone loss.. from the invasion of biological width

Question 7

Is GP antimicrobial

Answer 7

No

Question 8

How to clean the pulp chamber?

Answer 8

With alcohol as it removes extra sealer from the pulp chamber
Vitrebond is placed so the pulpal floor is completely sealed.

Question 9

When do we place the post?

Answer 9

Immediately as we will be familiar with morphology and length of the roots( less chance of perforation or excessive GP removal). Apical seal won’t be disrupted. Decreases the chance of coronal leakage as there is no temporary crown or dressing though which leakage can happen

If delayed, the apical seal can be disturbed.

Question 10

Size of the post

Answer 10

Depends on materials
Metal or non metal, adhesive or non adhesive

The length is required- more important than width. Longer the post-better retention (especially if longer than crown length)
We need at least4-5 mm of GP apically- needed for the seal as many lateral canals in that apical region

Width-needed for resistance and strength of the post to fracture.
Ideally, at least 1 mm diameter as the tip (less than the third of the thickness of the diameter of the root at the corresponding depth)
Every tooth has a different morphology

Wider post risks:
Increased risk of perforation, increased cervical strength, decreased impact resistance, reduced resistance.to root fracture

Question 11

How to prepare post space

Answer 11

1. Remove GP by chemical (solvents, but avoid due to risk of apical leakage), mechanical (best option, burs with non cutting tips so lower risk of perforation, not so much heat generated) and thermal (ultrasonic, system B-avoid as can disturb apical GP)
2. Piezo reamer or parapost reamers used to complete the prep (gives parallel walls)- use after GP removed!

Question 12

Cements used to cement posts

Answer 12

Should be insoluble, prevent microleakage
Should stick to radicular dentine to reinforce the tooth
Withstand fatigue (as they can cause microcracks)

Question 13

Luting cements for posts

Answer 13

E.g. zinc phosphate or polycarboxylate:
No chemical bond, retention by mechanical means only

GIC
Depends on resin content (RMGIC)-not indicated for post cementation as exhibit hygroscopic expansion that can cause fracture of the roots
Conventional GIC- more resistant than zinc phosphate, and there is a degree of bonding to dentine

Resin based luting cements
Can reinforce the tooth, aid post retention, need conditioning of the dentine (etching) forming hybrid layer.
Use of sodium hypochlorite can affect this bond as is a strong oxidising agent, leaving oxygen rich layer on dentine that can inhibit polymerisation of the resin
If eugenol was used, also affects resin

Moisture sensitivity! - use self etch but can be less effective

Dual curing can be used

Self adhesive cement -
No pretreatment of root dentine- not so technically sensitive
Contain phosphoric acid that demineralises the dentine and infiltrates hard tissues

Question 14

Advantages of adhesive cementation

Answer 14

Improved marginal adaptation/better fit
Improved apical seal
Increased post retention
Relieves stress in root canals as it sticks and distributes stress
Optimizes fracture patterns-if fracture happens, still a chance to repair it

Question 15

Disadvantages of adhesive cementation

Answer 15

Difficult to access and see without magnification
Remnants of acid, debris from the prep may persis-bonding decreased by GP remnants, smear layer debris, sealer etc

Question 16

Treatment objectives of restoring RCTed teeth

Answer 16

1. Retain the tooth as a functional unit in the arch
2. Maintain the coronal seal of RCS
3. Protect and preserve remaining tooth structure

Question 17

Factors to consider when planning a final restoration

Answer 17

Amount of sound supra gingival remaining tooth structure

Position of the tooth in the arch (molars 6x more likely to fail if no cuspal coverage)

Opposing dentition

Length, width and curvature of the root

Question 18

Consequences of endo treatment upon a tooth

Answer 18

Brittleness
Proprioception ( reduced by 30%)
Fracture resistance

Question 19

What is a post

Answer 19

Peg/pin used for fastening of the artificial crown/core to a natural tooth root

Usually made of metal/fiber material that is filled into the prepared canal , when combined with a core it provides retention and resistance for the artificial crown

It’s function is to retain the core NOT to reinforce the root structure

Question 20

Restorative considerations for post retained restoration

Answer 20

If tooth has minimal access cavity and walls intact or has loss of one wall (MO, DO), loss of two walls (MOD)-no need for post

If tooth has lost 3 walls or has no walls at all- post IS required

Question 21

Ferrule

Answer 21

The remaining walls of dentine extending coronal to the shoulder of the preparation provide what is known as ferrule effect - a protective effect resisting root fracture

2-3mm of coronal dentine is considered an optimal height to produce a ferrule but NOT LESS than 1.5 mm
Restoration lacking resistance form (ferrule) will fail long term regardless of the retentiveness of the post

Ferrule offers retention, resistance, substrate to bond to and strengthening of the root

Ferrule resist lateral forces which means that it increases retention and resistance of the restoration

Importance of ferrule - functional lever forces, lateral forces exterted during post insertion, wedging effect of tapered posts
It resists stresses which otherwise cause root fracture

Question 22

Optimal post dimensions

Answer 22

Length - equal/ longer to the height of the crown, or 1/3-2/3 of the length of the root, more important than the width

Apical seal- 4-5 mm from the apex

Diameter/width - no more than 1/3 of the root diameter at that level, at least 1 mm at the tip

Curvature - only placed in the straight part of the canal

Retention increases with the width, but increasing the width does not improve retention (wider- increased risk of perforation, cervical stresses and decreased resistance to root fracture and impact resistance)

Question 23

Post types

Answer 23

Prefabricated a d custom made ( direct or indirect)

Metal ( SS, titanium) and non metal ( glass or ceramic fiber)

Parallel or tapered (geometry)

Serrated, smooth and threaded

Question 24

Metal vs fibre posts

Answer 24

Fiber- difficult to remove, tooth coloured- good aesthetics, compatible to adhesive systems, can be placed immediately, low elastic modulus/similar to dentine, can absorb/dissipate stress

Metal- useful in flared canal, custom made, if indirect - need impression, conserves tooth tissue which reduces risk of perforation compared to parallel-sided fibre post

Question 25

When fibre post cannot be used

Answer 25

If there is less than 2-3 mm of ferrule( supragingival tooth structure) or if there is parafunction or deep overbite -fiber post can debond at post cement interface and lead to recurrent caries

Question 26

Tapered Vs parallel

Answer 26

Tapered- follows root form ensuring maximum remaining root dentine apically, stress concentration coronally, wedging effect (bad side), retained by cement (bad side) Parallel- uniform stress distributing along length, increased pull-out strength, bad side - more tooth structure removed, stress concentration apically

Question 27

Surface design of posts

Answer 27

Smoother it is -less retention Increased retention comes from self-threading into the dentine But this sets up fracture lines as it cuts its way into the canal Installation pressure is subsequently relieved by root fracture

Question 28

Optimal post design

Answer 28

Non threaded - avoid installation pressure created by threading posts that will later be relieved by root fracture Parallel sided- avoids wedging forces Cement retained - cement tends to distribute masticatory forces evenly

Question 29

Types of cements for post

Answer 29

Adhesive resin cement- greater retention with adhesive resins, highest compressive strength, premature setting of the resin may not allow complete seating of post, bonding may be impaired by the presence of remnants of endodontic material Glass ionomer cement- provides a wear chemical bond to dentine, retrievability is easier, fluoride release and anti-cariogenic effect, requires several days/weeks to reach maximum strength RM GIC- fluoride release and anti-cariogenic effect, insoluble, provides good retention of prosthesis, imbibe water and expands with time

Question 30

MECHANICALLY, an endodontic post should not:

Answer 30

1. Break 2. Break the root 3. Distort or allow movement of the core and crown

Question 31

A post needs:

Answer 31

Retention Resistance Resilience Stiffness Strength

Question 32

The resistance of the post is influenced by:

Answer 32

Presence of ferrule Presence of antirotational features Post length and rigidity

Question 33

If the post has higher Modulus of elasticity than dentine, where is the stress concentration

Answer 33

At the bottom of the post Usually what happens in metal posts This kind of post is prone to fail due to tooth fracture

Question 34

If stiffness of a post is similar to the dentine, stress is?

Answer 34

Stress is dissipated by the coronal and the root dentine This happens in fibre-based posts This kind of post tends to fail due to debonding

Question 35

What are 3 clinical and 6 radiographic findings to say endo was successful?

Answer 35

Clinical: no swelling/sinus, no signs and symptoms, not ttp Radiographic: obturation to WL, reduction in periradicular radiolucency, bone healing, no coronal leakage, no secondary caries, narrower PDL space

Question 36

What is active post?

Answer 36

Primary retention from root dentine via threads screwed into the wall of the root canal Risk of vertical root fracture during placement as introduces great stress within the root during placement- wedging effect Is should be avoided

Question 37

What is passive post?

Answer 37

Passively placed in close contact to the dentine wall Retention relies on the luting cement (If adhesive cement improved retention) Can be parallel or tapered Parallel is more retentive that tapered but more constructive Parallel less likely to cause root fracture than tapered

Question 38

Luting cements for post

Answer 38

Should be insoluble and prevent microleakage Should adhere to dentine Should withstand fatigue forces E.g. zinc phosphate, GIC..

Question 39

Advantages and disadvantages of adhesive cementation

Answer 39

Advantages: improved marginal adaptation, improved apical seal, increased post retention, relives stress in root canal Disadvantages: difficult access and vision without magnification, can be compromised by acid and debris left in RCS..

Question 40

Desirable core properties

Answer 40

High compressive strength Flexural strength Dimensional stability Ease of manipulation Short setting time Ability to bond to tooth and post

Question 41

Where should margin of the core be?

Answer 41

At the sound tooth tissue Because: - fewer forces will be transmitted to the core restoration - if finishing on the core, more interfaces exposed in the oral cavity - if thin layer between restoration and tooth- can fracture and cause plaque retention, caries

Question 42

Five requirements needed for crown and crown prep to be successful

Answer 42

Ferrule much be 2-3 mm in height Parallel axial walls Restoration must completely encircle the tooth The margin must be on sound tooth tissue Crown and crown prep must not invade biological width

Question 43

Ferrule effect offers protection and what else

Answer 43

Provides anti rotational feature Increases longevity of post and core restoration When ferrule is present, failure of restoration can be retrievable Increases fracture resistance of root treated teeth

Question 44

Monoblock concept

Answer 44

A passive post system adhesively cemented and less rigid than metal post. This reduces incidence of root fracture. Bonding fibre post to root dentine can improve distribution of forces along the root and decrease the root fracture. A well adapted, adhesively cemented fibre post is considered the most retentive with the least stress generated on the canal walls. Adhesive cement acts as shock absorber. Modulus of elasticity is similar to dentine chemical homogenity among components Potentially can offer some reinforcement of remaining root structure. Biocompatible