Capítulo 5....................................................................................................................... 56
5.2 Desarrollo de las iteraciones
Cores:
- Used to replace coronal tooth structure to improve retention and resistance for the crown and/or provide coronal seal for endo.
- Ideal properties for cores: strength (compressive and flexural), LCTE similar to tooth (to reduce marginal leakage), ease of use, bonds to tooth, minimal absorption of water, inhibits caries - Types of core materials:
Pros Cons Examples
Gold - Good strength
- LCTE similar to dentin - No water absorption - Easy to distinguish from
tooth structure
- Requires post for retention - Requires 2 visits (impression
and cementation)
- Questionable esthetics with all ceramic crowns
Cast post and core
Amalgam - Good strength - Resists microleakage - Easy to distinguish from
tooth structure
- LCTE is 2x dentin - Can‘t prep on same day as
placement (2 visits)
- Questionable esthetics with all ceramic crowns
Tytin (Kerr)
Composite - Adequate strength - Bonds to dentin - Can prep same day as
placement (1 visit) - Good esthetics with all
ceramic crowns
- LCTE greater than dentin - Polymerization shrinkage - Absorbs water
- Requires controlled filling technique to control shrinkage/
prevent voids
- No published data on clinical performance
- LCTE greater than dentin - Polymerization shrinkage - Absorbs water
- Requires controlled filling technique to control shrinkage/
prevent voids does NOT strengthen the tooth
- General principles of post placement
Post width should not exceed 1/3rd width of root
Need >5mm of gutta percha remaining at apex
Post length should not be more than 2/3rd length of root or 1.5 times the length of the clinical crown
Coronal seal more important than apical seal
108 - Types of prefabricated passive posts:
Post Material
Pros Cons Examples
Metallic - Easy to use - Root fractures tend to be more apical – less favorable
- Questionable esthetics with all ceramic crowns
ParaPost
Carbon - LCTE similar to dentin - Questionable esthetics with all ceramic crowns
Composipost Fiber - Flexible
- Fractures tend to be coronal – can salvage - Esthetics
- Only short-term success proven Parapost
Zirconia - Good esthetics - Difficult retrieval after failure
When to Use a Post and Core
- A core is needed when the dimensions of the preparation will not provide adequate retention and resistance
- A post is needed when there is not enough remaining tooth (# of walls) to retain the core
- Wall: defined as the remaining dentin after crown preparation, needs to be >50% vertical height of preparation and >1mm in width
- Ferrule – crown margins should be placed in 2mm of sound tooth structure around the entire crown in order to guard against root fracture caused by the post. May need crown lengthening or
orthodontic extrusion to gain adequate Ferrule. Orthodontic extrusion retains better crown/root ratio.
Post Considerations All axial walls remaining No post needed
3 walls remain Usually no post needed 2 opposing walls remain Usually no post needed 2 adjacent walls remain Post required
1 wall remains Post required NO walls remain Post required
Recommended Acceptable Possible Anterior Cast post and core Composite core with
fiber post
--
Premolar Cast post and core Composite core with fiber post
Composite core with metallic post
Molar Amalgam or composite core with metallic or fiber post
-- Cast post and core
Post and Core Failures
- Most common reason for failure: de-cementation
- Type of failure with most clinical significance: root fracture
109 Post and Core Procedures
Set Up Procedure Prefab metal
post &
Amalgam or Fiber Core
(tooth already has endo)
- Hand piece - Composite
cassette - Diamond burs - Gates- Glidden
burs - Post drill - Prefab posts - Ketac Cem - Build-It - Etch
- Optibond Solo - Curing Light - Articulating
paper
- Review medical and dental history
- Get x-ray of tooth, and do quick exam of dentition, call instructor to begin - You can prepare the canal and remove access gutta-percha by using either a
―Touch and Heat‖ instrument (the safer way) or Gates-Gliddon drill.
- Select post size using the x-ray
- Decide how far you will extend the post (must be >5mm from apex) and prepare the canal with the instrument of your choice.
- Mark the instrument (use rubber stopper on drill to get proper depth).
- Remove all temporary and old restorative materials, isolate the tooth and if needed, place a matrix band around it.
- If you drill down the canal with the Gates-Gliddon, use VERY slow speed.
- Use post drill to the same length (can use post drill as hand file = safer) - Try in post and take a x-ray to confirm proper size and seat
- Trim the post - various opinions on how to do this: either from apical (best retention this way) end or coronal end – use diamonds and make the post 1mm below of the expected top of the core
- Dry the canal with paper points
For amalgam cores - use Ketac Cem to cement the post – apply cement on post tip, insert slowly, use pumping action to get voids out, and hold in place until set. Wait 15min and pack the amalgam.
For fiber composite cores: use Ketac Cem as described above OR etch, prime/bond, the tooth and the canal, making sure that there is no excess bonding agent in the canal. Fill the canal with very small amount of core material and place the post in all the way.
Add core material to fill the coronal aspect of the tooth. Cure and allow to set for 4 mins
- Call instructor to check
- Shape and smooth the margins of the core build up to eliminate ledges.
If amalgam core – wait at least 24 hours before prepping the tooth.
If composite – you can prep and temp the tooth at the same day, if you have the time to do it.
110 Set Up Procedure
Cast P/C Impression
(tooth already has endo) - Articulating
paper - Tempbond
- Review medical and dental history
- Get x-ray of tooth, and do quick exam of dentition, call instructor to begin - You can prepare the canal and remove access gutta-percha by using either a
―Touch and Heat‖ instrument (the safer way) or Gates-Gliddon drill.
- Decide how far you will extend the post (must be >5mm from apex) and prepare the canal with the instrument of your choice.
- Mark the instrument (use rubber stopper on drill to get proper depth).
- Remove all temporary and old restorative materials, isolate the tooth and if needed, place a matrix band around it
- If you drill down the canal with the Gates-Gliddon, use VERY slow speed.
- Use post drill to the same length (can use post drill as hand file = safer) - Try in preformed plastic post (burn out posts), make sure that it sits all the
way in to the prepared canal and doesn‘t bind
- Prep the coronal aspect of the tooth and make sure that you have NO UNDERCUTS in the canal and in the coronal aspect of the tooth , and then lubricate the canal (VERY IMPORTANT!) with Vaseline and perio probe - Apply Duralay pattern resin by first dipping the post in liquid monomer and
then using salt and pepper technique (dip a brush in liquid, then powder and dab it on to the post)
- Place post in the canal. Ensure that the pattern goes in and out of the canal easily (like a temp crown), otherwise it will get locked in there!
- Once the resin is set, remove the post and inspect for voids - if there are, add some material to that spot and reline margins
- Add pattern resin to form the core, then prep the core/ tooth for a crown - have instructor check impression!
- Remove cast post/core impression and save
- Place piece of paper clip in the canal to serve as a temp post, then fabricate a temp crown around it – then use Temp bond to cement the temp
- Adjust occlusion and have instructor check ALTERNATIVE TECHNIQUE:
Once the canal and the coronal aspects are prepped:
- If possible, place a matrix band around the tooth.
- Prepare 10 drops of liquid with adequate amount of powder
- Fill a single use syringe with the material and inject it slowly into the canal, without creating pressure.
- Place the plastic post into the canal and quickly fill up the whole coronal aspect with the material, making sure there are no voids.
After it gets to the ―doughy stage‖, take the pattern out of the tooth and place it back a few times to make sure it does not ―lock‖ in the canal.
Cast P/C Cementation
BEFORE THE PATIENT COMES
- Evaluate the casting, and make sure that there are no positive bubbles or areas that correspond to undercuts
- Remove such areas with a diamond bur WHEN THE PATIENT COMES
- Remove any temporary material and clean the canal and the coronal areas from any leftover materials.
- Try in the post by gently sliding it into position, NEVER PUT ANY PRESSURE ON IT!
- If the casting does not go in all the way, use fit-checker to evaluate which areas need to be adjusted.
- If you cannot get it in 3-5 minutes, as a faculty for help.
- Once the casting is in place – you are ready for cementation.
- Prepare the cement you decided to use (eg. Ketac Cem), dry the canal, place the cement on the post and gently tap it into place.
- Allow the cement to set and you are ready to go.
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