The dental post and core procedure. -

How a dentist places a post and core. | How just a core alone is placed. | What is the procedure like for the patient? | Kinds of posts - prefabricated, cast, ceramic, metal, fiber.

Post
placement.

Link to post and core placement animation.

Core
placement.

Link to core placement animation.

Post and core placement.

Once it's been decided that your tooth requires a core, or a post and core, this page explains how your dentist then performs the procedure.

It outlines the basic steps of the process. Discusses the types of decisions your dentist will need to make along the way, such as if added retention is needed for the core (e.g. pin placement), and what kind of post will be used (metal, ceramic, prefabricated, cast, flexible).

It also explains how these factors may affect your case. And what it's like to experience this procedure.

As shortcuts for accessing the information found on this and associated pages, use the following links:


The post and core placement procedure.

Background.

Post and cores are only placed in teeth that have already had root canal treatment. And then, only for those that have large portions of natural tooth structure missing. (Indications for a post and core.)

The initial frame of our animation below illustrates this type of situation. 1) It shows a tooth that has been endodontically treated. (The red in our illustration represents the gutta percha that is placed during this procedure.) 2) And its crown portion has broken off, almost flat with the gum line.

Creating the post space.

Post placement may be required before a dental crown can be placed.

Step #1 - Creating the post space.

As an initial step, your dentist will need to create the space inside your tooth in which the post will be cemented.

This space will lie within one of the tooth's root canals, which during its endodontic treatment was sealed by filling it in with the rubber-like compound gutta percha (see link above).

How this step is performed.

1) Using a drill.

Many dentists use a (slow speed) dental drill to create the needed channel for the post.

Since gutta percha has the consistency of a soft pencil eraser, the dentist's drill will usually burrow through it, along the path of the root's canal, without much resistance or heading off course.

As an aid, sometimes a dentist will touch a heated instrument to the gutta percha to soften it up, so the drilling process proceeds more easily and predictably.

2) Working by hand.

A more cautious approach involves the dentist heating the canal's gutta percha to soften it up, and then scraping/scooping it out using hand tools. The shape of the empty canal is then refined via the use of root canal files or a dental drill.

This is a safer approach because when a drill is used by itself to create the post space, there's always a chance it will go off course. As a worst case scenario, a perforation (a hole out the side of the root) may be created.

Issues your dentist will consider as they work.

A dentist's main objective is simply placing an adequate post, without damaging or unduly weakening the tooth's root.

  • The size of the post that's placed isn't as much of a concern as the goal of minimizing the amount of internal tooth structure that must be removed to place it.

    Placing a comparatively smaller diameter post, and therefore leaving a greater thickness of root structure, places the tooth at less risk for fracture. As a general rule, a post shouldn't be more than about 1/3 the diameter of the root that it's placed in.

  • The post's retention (resistance to being dislodged) generally correlates with the length it extends into the tooth's root.

    At a bare minimum, the post should extend at least a distance equal to the height of the crown being placed. Most ideally, it will extend around 2/3rds the length of the root. However, 3/16ths of an inch or so of gutta percha needs to be left undisturbed at the root's tip to maintain an adequate endodontic seal.

  • Juggling all of the above issues (post diameter, post length) with the concern of not causing any procedural harm (root perforation, loss of seal integrity) can be challenging for the dentist. Especially in cases where the root being treated is small, curved or has a non-conical shape.

Evaluating the post fit.

Post placement may be required before a dental crown can be placed.

Step #2 - Fitting the post.

Once the space inside the tooth has been created, the dentist must evaluate the fit of the post they plan to place.

It's easy enough for them to know which one from their assortment to choose. Posts typically come in sizes (diameter, taper) that matches drill and root canal file sizes (the instruments that have been used to create the post space).

What they'll do.
  • The dentist will measure the length of the channel they've created, and trim the post they've selected to match.
  • As an evaluation, they'll slip the post into place. If it's too long, they'll remove it and trim it some more. If it's fit is slack, wobbly or exceedingly tight, the dentist might select a different post size, or re-prepare/further refine the post space.
Posts typically have a passive fit.

When being evaluated, most types of posts can be slipped in and out of their tooth fairly easily because they've been designed to have a passive (non-engaging) fit.

  • The biting threads of screw-like posts tend to create tension and stress points within a tooth's root, thus leaving it at greater risk for fracture.

    While just backing a screw-style post off a partial turn will typically relieve most of this stress, non-threaded designs are more frequently used. But in cases where extra retention is needed, like with short roots, your dentist may decide that the use of a screw design makes the right choice.

  • With a passive-fit post, factors such as its snug fit in its channel, its shape (straight rod vs. tapered), its surface texture, its length, and the type of cement used are all collectively relied upon to provide it with the retention required.

(Rosenstiel - linked above.)

Step #3 - Cementing the post.

Once the fit of the post has been checked, it's ready to be cemented in its tooth.

Cement options.

You may be surprised to learn that historically the types of cements dentists have had available to use contributed little to post retention. (The cement filled in space around the post but created no bond with it or the tooth.)

Nowadays, a dentist has a number of different types of adhesive cements to choose from. Even so, the physical characteristics of a post listed above still all play important roles in creating post retention. (The use of an adhesive cement is unlikely to overcome the deficiencies associated with a poorly designed post system.)

Cementing the post.

This is a simple step. The chosen cement is prepared and slathered onto all sides of the post. Your dentist may coat the sides of its channel inside the tooth with cement too.

The post is then teased into the tooth until that point where it's fully seated. (Pushing the post in place too quickly can create excessive pressure within the tooth.)

Any excess cement (that which squishes out of the tooth) needs to be removed. But when this step is taken (before, after or during its setting period) depends on the type used.

(Rosenstiel - linked above.)

Placing the core ...

Placement of a crown on a tooth that has a dental post and core.

... and shaping the tooth for its crown.

Step #4 - Placing the core.

Once the post's cement has set, the tooth's core can be added.

The material most frequently used is routine dental restorative, with the most common ones being dental amalgam (silver filling material) or composite (dental bonding).

  • The restorative is packed over and around the post's exposed end. And is typically added until the dimensions of the tooth approach those that it had originally.

    (The actual dimensions needed can vary, depending on the plans and timeline associated with the tooth's future dental work. The main goal is simply one where the size of the rebuilt tooth will provide the dentist with the ideal amount of tooth structure for the crown that will be placed.)

  • In some cases, little natural tooth structure may remain that can be used to help secure the core. And while the only reason to place a post is to anchor the tooth's core buildup, relying on it alone for retention may not be enough to prevent case failure.

    In these types of situations, a dentist may create additional retention for the core by placing pins (screws) in the tooth, around which the restorative can then be packed and anchored (we discuss the use of pins below).

(Rosenstiel - linked above.)

X-ray of tooth that has a completed post & core and dental crown.

An x-ray image of a dental post and core.

Step #5 - Completing the tooth's reconstruction.

Once the process of placing the post and core has been completed, the tooth's dental crown can be fabricated, just like for any tooth. We outline the steps of this process here: How dental crowns are made.

  • Depending on the materials that have been selected for the post and core buildup, it may be possible for the dentist to begin the tooth's crowning process during the same office visit.
  • In cases where this won't be done, a dentist will frequently rely on the completed post and core to serve as the tooth's interim (temporary) restoration.

    (Your dentist will have to inform you as to what precautions might be indicated [like avoiding heavy biting forces and generally favoring the tooth], and the time frame that would be considered acceptable before your new crown is made.)

Is anesthetic required for the post and core procedure?

Since posts are only placed in teeth that have already had root canal treatment (hence their nerve has been removed), in theory there is no requirement for anesthesia (getting a dental "shot"). But exceptions do exist and you'll simply have to ask your dentist what will be needed.

  • A common exception would be the case where the tooth has broken off at a level at or below the gum line, and this tissue will need to be manipulated (touched, prodded, poked) during the placement procedure.
  • Another is that your dentist may want to perform this procedure under the protection of a rubber dam. (So the interior of the tooth isn't exposed to saliva and contaminants. And as protection for you from swallowing items.)

    Because the placement of a clamp is involved (to hold the dam on its tooth), when one is used an anesthetic may be needed.

What will you feel during the post and core placement procedure?

Whether anesthetic is used with your procedure or not, you will feel the gentle vibrations of the drilling process, or the use of hand instruments as your dentist creates the space for the post inside your tooth.

The same goes for core placement, which may involve tooth trimming, pin placement and restoration contouring/buffing.

Types of dental posts.

Traditionally, the posts dentists have placed in teeth have been made out of metal (stainless steel, titanium, cast metal). Today, dentists have an ever increasing range of materials to choose from, like ceramics (zirconia), or ceramic or carbon-fiber.

Flexible vs. Rigid

The flexible nature of a fiber post offers the advantage that as a tooth's root flexes under load, it will too. That little bit of give transfers less stress to the root, and therefore may help to prevent its fracture.

Considering that studies have shown that case failures involving posts may result in tooth extraction (because of damage to the tooth), your dentist may feel that placing a flexible post is important.

White vs. Metallic

Some kinds of dental crowns, especially those placed on front teeth, have an all-ceramic construction. And as such, they may be relatively translucent. (Porcelain translucency tends to give a crown a more lifelike appearance.)

The color of a metallic post and core may darken the appearance of the all-ceramic crown that covers over it. As a solution, your dentist may opt for placing one that's tooth-colored. Ceramic (zirconia) and some types of fiber posts are white.

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Cast vs. Prefabricated post and cores.

A cast post and core is a single-unit object (post and core combined) that is specially made for your tooth in a dental laboratory. As disadvantages, placing one is a two-appointment procedure, and typically involves a higher fee.

The main advantage of placing a cast post and core is that it's custom made for your tooth. That could be important in cases where the root it's placed in has unique anatomical characteristics (noncircular cross section, extreme canal taper) that would be difficult to manage with a standardized post.

Studies have shown that both types of post and cores generally offer the same expected survival rates. That suggests that placing a prefabricated post (the quicker, cheaper procedure we describe and illustrate above on this page) can make a good choice in most situations.

(Rosensteil - linked above.)


The dental core placement procedure.

When placing just a core alone (no post), a dentist simply applies the dental restorative (usually dental amalgam or bonding) to fill in the missing portions of the tooth, not unlike when a regular filling is placed.

In fact, the only real differences between placing a dental filling and a core are that:

  • The final contours of a dental core aren't as critical as with a filling, since it will ultimately be trimmed down for crown placement anyway.
  • And the dentist must envision in advance how the retention of the core might be compromised when it's trimmed down, and insure that this does not become an issue.

When creating adequate retention for the core is expected to be difficult.

Many teeth that have been damaged will still retain enough natural tooth structure to provide a number of substantial anchor points to solidly secure the core that's placed.

In situations where this isn't the case, additional retention points will need to be created.

  • Dentists routinely screw tiny "pins" into a tooth, around which the dental restorative is then packed.

    (These little screws are around 1/4 inch in length and about 1/2 the diameter of the usual straight pin. The procedure is quick and simple. It literally takes a dentist 60 seconds or less to place one.)

  • As an alternative, a dentist might cut grooves or "post holes" in the tooth and pack the restorative into them to gain the extra retention that's needed.

    (This is an even simpler, and just as quick, solution as placing a pin.)

  • If the tooth has had root canal treatment (but a post isn't required), the dentist has the option of extending the dental restorative down into the tooth's root canal system as a way of obtaining added retention.

 Reference: 

Shillingburg HT, et al. Fundamentals of fixed prosthodontics. Chapter: Preparations for Severely Debilitated Teeth.

Rosensteil SF, et al. - linked above.

Will you need an anesthetic for your core placement procedure?

In cases involving vital teeth (the situation where the tooth has a live nerve in it), then the answer is yes (getting a "shot" will be required).

As mentioned above, placing a core isn't substantially different than placing a filling, a procedure that typically does require anesthetic to maintain patient comfort.

 

Last revision/review: 12/11/2018 - Page created.

 
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