Post Crowns
Why does a tooth need a post or core?
If your patient has had a root filling previously, and now requires a crown, a post will be needed to give support and strength – retention - to the crown and tooth as root filled teeth are a weaker than healthy teeth. If a tooth is very badly broken down and can no longer be filled, a post crown is an alternative to having a tooth extracted. Due to the state the tooth will be in to require a post crown, the dentist will build up a core inside the tooth to make it solid and stronger to support the post and crown.
How is it carried out?
With a root filled tooth, the dentist will need to remove most of the gutta percha from inside the tooth; bit will leave around 5mm at the apex as to keep it sealed. The dentist may chose to use a prefabricated post and core method which can take less time to prepare and fit than if the post and core was to be constructed by a laboratory. If they choose this method, the dentist will as before, remove some of the gutta percha and will choose the correctly sized post for the tooth. One brand of posts that some dentists choose to use is Parapost XT (www.coltene.com) Once happy with the size, width and fit of the post, the dentist will require some cement to hold the post inside the tooth. This will be mixed by the nurse and can be something like Fuji Plus or a Zinc Oxide Phosphate mix. Once this has set the dentist will build up a core around the post. Some dentists will use a Compomer material – a mix of Composite and Glass Ionomer, such as Dyract. This gives more strength than regular composite. Others will choose to use a core build up material such as Paracore (www.coltene.com). This is specifically designed for core build-ups and comes in a Dentine or a white shade. It seals to prevent marginal microleakage which can compromise the Root Filling and then in turn the Post Crown. It is Radiopaque and releases Fluoride. The dentist will acid etch the area to make the area rough and therefore more retentive. The nurse will be required to aspirate the area to remove it form the patients’ mouth as the dentist washes it off. The dentist will then require a bonding agent such as Prime and Bond or the bonding agents found within the dentists chosen core kit, such as Paracore, and will light cure this for approximately 30 seconds depending on the manufacturers’ instructions. Once this has been cured the dentist will begin to place the core material to the area and will cure it intermittently.
Once the dentist as achieved the required build up they will begin to shape it down into the required dimensions for the crown to sit upon. This is just like the procedure the dentist would do when shaping a vital tooth for a crown and the impression stages will take place just like they would in a regular crown preparation.
If the dentist decides that the tooth requires more strength and support they may opt for a cast post and core. This is where the dentist sends impressions to the lab for them to construct the core and post in a metal alloy. This will usually require an extra visit for the patient as the dentist may choose to have this post and core sent for a try in before the porcelain is bonded on.
When it comes to choosing which size post to use, the dentist will factor in some points. The general consensus is to use the longest and narrowest post that will fit down inside the tooth canal. To use the longest length possible means that the pressure that is put on the tooth when the patient is biting down is distributed through and around more of the tooth structure instead of putting too much pressure too far up the tooth which in turn will fracture the tooth eventually. To use the narrowest means that there is more of the natural tooth remaining. Using a threaded post design will engage the walls of the tooth as they are screwed in making them more retentive but can put on a lot of force to the already brittle walls of the tooth. A smooth or serrated post which literally sits inside the tooth isn’t as retentive but is more passive in that there is less pressure put upon it and the tooth.
Within the ParaPost kit, each drill bit and corresponding post is colour coded in size order:
Brown – size 3 0.036in, 0.90mm
Yellow – size 4 0.040in, 1.00mm
Blue – size 4.5 0.045in, 1.14mm
Red – size 5 0.050in, 1.25mm
Purple – size 5.5 0.055in, 1.40mm
Black - size 6 0.060in, 1.50mm
The size numbers are what fraction of an inch they are – i.e. – 4.5 = 0.045in,
Each kit will have one drill bit per size and will contain 2 hand wrenches – ‘A’ for sizes 3, 4, 4.5 and ‘B’ for sizes 5, 5.5, 6
The patient will need to be made aware that if the tooth is in need of a post crown, that there is a risk of it failing as the tooth is already compromised due to the weakness. If it does fail, the only option is extraction. If this happens the patient has the option of leaving the gap, having a partial denture constructed, bridging the gap providing there is a suitable tooth to either side of the gap, or getting an implant.
Why does a tooth need a post or core?
If your patient has had a root filling previously, and now requires a crown, a post will be needed to give support and strength – retention - to the crown and tooth as root filled teeth are a weaker than healthy teeth. If a tooth is very badly broken down and can no longer be filled, a post crown is an alternative to having a tooth extracted. Due to the state the tooth will be in to require a post crown, the dentist will build up a core inside the tooth to make it solid and stronger to support the post and crown.
How is it carried out?
With a root filled tooth, the dentist will need to remove most of the gutta percha from inside the tooth; bit will leave around 5mm at the apex as to keep it sealed. The dentist may chose to use a prefabricated post and core method which can take less time to prepare and fit than if the post and core was to be constructed by a laboratory. If they choose this method, the dentist will as before, remove some of the gutta percha and will choose the correctly sized post for the tooth. One brand of posts that some dentists choose to use is Parapost XT (www.coltene.com) Once happy with the size, width and fit of the post, the dentist will require some cement to hold the post inside the tooth. This will be mixed by the nurse and can be something like Fuji Plus or a Zinc Oxide Phosphate mix. Once this has set the dentist will build up a core around the post. Some dentists will use a Compomer material – a mix of Composite and Glass Ionomer, such as Dyract. This gives more strength than regular composite. Others will choose to use a core build up material such as Paracore (www.coltene.com). This is specifically designed for core build-ups and comes in a Dentine or a white shade. It seals to prevent marginal microleakage which can compromise the Root Filling and then in turn the Post Crown. It is Radiopaque and releases Fluoride. The dentist will acid etch the area to make the area rough and therefore more retentive. The nurse will be required to aspirate the area to remove it form the patients’ mouth as the dentist washes it off. The dentist will then require a bonding agent such as Prime and Bond or the bonding agents found within the dentists chosen core kit, such as Paracore, and will light cure this for approximately 30 seconds depending on the manufacturers’ instructions. Once this has been cured the dentist will begin to place the core material to the area and will cure it intermittently.
Once the dentist as achieved the required build up they will begin to shape it down into the required dimensions for the crown to sit upon. This is just like the procedure the dentist would do when shaping a vital tooth for a crown and the impression stages will take place just like they would in a regular crown preparation.
If the dentist decides that the tooth requires more strength and support they may opt for a cast post and core. This is where the dentist sends impressions to the lab for them to construct the core and post in a metal alloy. This will usually require an extra visit for the patient as the dentist may choose to have this post and core sent for a try in before the porcelain is bonded on.
When it comes to choosing which size post to use, the dentist will factor in some points. The general consensus is to use the longest and narrowest post that will fit down inside the tooth canal. To use the longest length possible means that the pressure that is put on the tooth when the patient is biting down is distributed through and around more of the tooth structure instead of putting too much pressure too far up the tooth which in turn will fracture the tooth eventually. To use the narrowest means that there is more of the natural tooth remaining. Using a threaded post design will engage the walls of the tooth as they are screwed in making them more retentive but can put on a lot of force to the already brittle walls of the tooth. A smooth or serrated post which literally sits inside the tooth isn’t as retentive but is more passive in that there is less pressure put upon it and the tooth.
Within the ParaPost kit, each drill bit and corresponding post is colour coded in size order:
Brown – size 3 0.036in, 0.90mm
Yellow – size 4 0.040in, 1.00mm
Blue – size 4.5 0.045in, 1.14mm
Red – size 5 0.050in, 1.25mm
Purple – size 5.5 0.055in, 1.40mm
Black - size 6 0.060in, 1.50mm
The size numbers are what fraction of an inch they are – i.e. – 4.5 = 0.045in,
Each kit will have one drill bit per size and will contain 2 hand wrenches – ‘A’ for sizes 3, 4, 4.5 and ‘B’ for sizes 5, 5.5, 6
The patient will need to be made aware that if the tooth is in need of a post crown, that there is a risk of it failing as the tooth is already compromised due to the weakness. If it does fail, the only option is extraction. If this happens the patient has the option of leaving the gap, having a partial denture constructed, bridging the gap providing there is a suitable tooth to either side of the gap, or getting an implant.
