Post and Core Fabrication Techniques

Question 1

What are the techniques used for fabrication of post and cores?

Answer 1

Direct: Pre-fabricated post + core (composite or amalgam)

Indirect (Impression technique)

Direct-indirect: Burnout resin technique

Question 2

How should coronal structure be prepared for post core and crown?

Answer 2

Removal of existing restorations.

Eliminate undesirable undercuts (cast post and core only)

Crown preparation to create ferrule

Question 3

What is the tradeoff that should be considered when choosing post length?

Answer 3

Retention vs seal of the root canal.

Question 4

What are the steps taken in the direct technique?

Answer 4

Select pre-fabricated post

Check if antirotational features are needed

Cement post

Core build up

Crown preparation

Temporary crown

Question 5

What are the steps taken in the impression technique?

Answer 5

Select impression post (plastic and smooth surface)

Impression using the impression post

Pour p

Burn-out post and core

Cast the post and core

Cast post and core cementation

Refinement of the crown preparation

Temporary crown

Question 6

What are the steps taken for the burn-out resin technique?

Answer 6

Select burn-out post (plastic and serrated surface)

Separator (canal and coronal surface)

Copy the shape of the canal using duralay resin (bead-brush technique)

Core build-up using duralay resin (bead-brush technique)

Crown preparation on the burn out post and core (rough prep)

Temp post-crown

Question 7

How is length of the post space determined?

Answer 7

At least 5mm apical seal

Very short roots and high crowns = 4mm apical seal.

Post length at least equal to the crown length (2/3rd of remaining tooth length, 1.2 of the clinical root, 3.4 of the root canal length)

Question 8

What steps should be taken for post space preparation?

Answer 8

Determine post length based on PA.

Rubber dam

Remove the GP

Take PA to verify if WL has been reached.

Post space preparation (using parapost system)

Question 9

Why is rubber dam used?

Answer 9

Avoid bacterial contamination (saliva/blood)

Avoid inhalation of instruments

Avoid contact of sodium hypochlorite with mucosa

Question 10

How is GP removed?

Answer 10

Start with heated plugger and use a rubber stop to mark the WL

Use a Gates Glidden bur to reach the WL

Question 11

How can perforation be avoided while removign GP with GG bur?

Answer 11

Use bur parallel with the path of insertion with light vertical forces.

Start with smaller bur and increase size.

Should see red GP coming out not white dentin.

Take PA if you aren’t sure if the bur is following the root canal.

Question 12

How is post space preparation done?

Answer 12

Use parapost drills

Create parallel walls (let the drill make the work do not tilt the drill)

Remove undercuts inside the canal

Establish the width and shape of the post

Take PA after all this to ensure there is no GP still in the walls prior to placing the post in

Question 13

How can width of the post be established?

Answer 13

1/3rd of the total width of the root.

Question 14

What factors should be considered when thinking about placing a post?

Answer 14

Increased post width = increased retention and resistance

Wide post weaken the root (removal of tooth structure)

No more than 1/3rd of the width of the root

Preserve buccal wall in upper incisors.

Question 15

What is the minimum size for a pre-fabricated post?

Answer 15

0.9mm

Question 16

1555

Answer 16

1555

Question 17

How can the post space be made anti-rotational?

Answer 17

The post space should have an elliptical shape to have an antirotational feature.

If the canal is circular, create a small groove in the root canal followign the path of insertion on the thickest wall

In multi-canal teeth, using more than one canal can provide the antirotational feature to improve retention.

Question 18

How is the small groove made in the post space to provide antirotational support?

Answer 18

It should be 3 - 4mm deep

Question 19

Should existing temporary restorations be removed and the crown prep done before or after the post space preparation?

Answer 19

Can be either:

If before you get better visualization of the canal, you know how much tooth structure remains so you can plan the post space preparation accordingly (length, shape, antirotational), but the issue is you can sometimes lose the reference point for the post space preparation meaning a new PA would be needed and a new reference point.

If done after, you can maintain the reference point that was established using the PA that was taken after the RCT which is easier to temporize using multi-appointment post space preparation

Question 20

How should the coronal tooth structure be prepared for the final restoration?

Answer 20

Remove all existing restorations

Eliminate undesirable undercuts

Make the full crown preparation

Eliminate unsupported tooth structure (<2mm)

Preparation of margins (create ferrule)

Positive horizontal stop

Question 21

How much width should be present when restoring tooth structure?

Answer 21

Minimum of 2mm of enamel width and 1.5 - 2mm of enamel height for ferrule.

Question 22

What are the indications for the impression technique?

Answer 22

Multiple post and cores

Abutments of bridges (easier to establish parallelism)

Posterior teeth with divergent canals

Question 23

What are the advantages of the impression technique?

Answer 23

Faster clinical procedure compared to burn-out resin

Lab will manufacture the post

Question 24

What are the disadvantages of the impression technique?

Answer 24

May introduce errors

May need more adjustments during the try in

Question 25

What should be done prior to the impression technique?

Answer 25

Use full arch stock tray or custom tray

Dry the canal (air and paper points)

Verify the impression post seating

Apply the light body PVS

Seat the impression post

Apply medium/heavy body on the tray

Insert the tray

Remove the tray with a snap movement

Question 26

Which post should be used for the impression technique?

Answer 26

Smooth surface round post.

Question 27

What are the indications and contraindications for the burn-out resin technique?

Answer 27

Indication: Uniradicular or multiradicular teeth without divergent root canals.

Contraindications:

Patients allergic to monomer

Patients who cannot stay with the mouth open for a long period of time.

Divergent roots

Question 28

What are the advantages and disadvantages of the burn-out resin technique?

Answer 28

Advantages:
You have control of the shape of the post and core

Less adjustment usually during try in

Disadvantages:

More difficult method

More clinical time is necessary.

Question 29

What is the technique for using burn-out resin technique?

Answer 29

Dry the canal (air and paper points)

Select the size of the burn-out post

Apply separator in the canal and coronal structure

Apply acrylic resin (Duralay or pattern resin) inside the canal and around the burn-out post (bead-brush technique) - PASSIVE FIT.

Insert the burnout post in the canal

Wait until the acrylic starts to set, then make in and out movements until the acrylic polymerize

Use water based lubricant in the canal and around the coronal tooth structure to avoid adherence between the resin and the tooth.

Build up the core after the modeling of the post

Apply duralay to reestablish missing coronal structure (do not overbuild)

Make the crown preparation

Remove the handle and check occlusal clearane (MIP and excursion)

Send acrylic post and core to the lab for cast

Question 30

What should be done in posterior teeth when there isn’t much coronal structure to support the core material?

Answer 30

Use more than one post

Question 31

What should be done if the roots are divergent?

Answer 31

Multipiece cast post and core

More retention

Impression technique

Question 32

Where should the main post be in upper molars?

Answer 32

Palatal root

Question 33

Where should the main post be in lower molars?

Answer 33

Distal root

Question 34

How is the burn-out resin technique done in teeth with divergent roots?

Answer 34

Copy with one post one of the canals (main canal)

Adjust first post with disc

Seat the second post in and when fully seated seat the first post (with vaseline)

Create the core attaching it to the second post but not the first.

Remove the first post while leaving the second post and the core intact.

Remove the second post and core.

Lab creates cast

Place the second post and core in followed by first post

Question 35

Which posts should be used for direct technique?

Answer 35

Stainless steel post or titanium post

Question 36

How can core retention be improved with the direct technique?

Answer 36

Leave undercuts

Add pins if necessary

Use amalgam tags in other canals (amalgam core in posterior teeth)

Question 37

How can core retention be improved with the direct technique?

Answer 37

Leave undercuts

Add pins if necessary

Use amalgam tags in other canals (amalgam core in posterior teeth)

Use pins if needed to retain the core.

Ensure that the canals are dried with paper points prior to placement of the core.

Question 38

What are the steps used in order to place the pre-fabricated posts in the canals?

Answer 38

Dry the canal (air + paper points) Important to prevent secondary infection

Select size of pre-fabricated post that fits tight in the post space (same as the last parapost drill used)

Check length of the post according to the interarch space (3 - 4 mm from the occlusal plane)

Adjust length by cutting apical end if needed (post completely embedded in the core material

Clean the post space and dry very well

Cement the post with resin (metal and fiber posts) or GIC and RMGIC (for metal posts)

Wait at least 10 minutes for complete setting

Place core and crown prep