What is a post and core, and why is a 'screw' put into a root-filled tooth?

Root canal treatment clears out the inflamed tissue inside the tooth, but it does not bring back the walls the tooth has lost. When decay, old large fillings and the access opening made to reach the canal all add up, sometimes only a few thin walls are left above the gum line. A crown cannot hold on to these walls alone; first, a core has to be built for it to sit on. According to a 2009 review by Slutzky-Goldberg and colleagues, a post is needed to hold the core if two or more walls are missing; if enough tissue remains to carry the final restoration, a post should not be used.

Contrary to popular belief, a post does not strengthen the tooth. The same review says so plainly, and adds that there are studies showing that teeth restored without a post and core are less prone to fracture. A systematic review published in Cureus in 2025 also defines the post's job as holding the core, not supporting the tooth; it notes that routine use of a post may bring no benefit when there is enough tooth structure, and that a post space widened more than necessary can weaken the root.

What really protects the tooth is called the ferrule, or the ferrule effect. When the crown wraps like a bracelet around the wall of sound tooth left above its finish line, chewing forces are spread through that wall. According to a 2012 literature review by Juloski and colleagues, a ferrule 1.5–2 mm high has a positive effect on the fracture resistance of a root-filled tooth, and when there is an adequate ferrule, the type of post system, cement and crown matters less. The Slutzky-Goldberg review reports that a ferrule reduces vertical root fractures by a third; in a 2024 meta-analysis of teeth restored with fibre posts, a ferrule running all the way around the tooth increased the success rate in a direct comparison based on two studies, while the broader indirect analysis found no difference, and the authors state that stronger studies are needed.

A ferrule cannot always go all the way around the tooth. The Juloski review draws three important conclusions here: if a full circumferential ferrule cannot be achieved, a partial ferrule is better than none; in a tooth with no crown left at all, pulling the root up orthodontically should be considered to gain a ferrule, rather than cutting back the gum and bone; and if none of these routes can be used, a poor clinical outcome is very likely. The heart of the choice between a post and core and an extraction lies in that last point.

There are two main types of post. For a cast post, an impression is taken, the post and core are made in one piece from a metal alloy in a laboratory, and the piece is then cemented into the canal; because there is a laboratory stage, at least two appointments are needed. A fibre post is a prefabricated rod made of glass or quartz fibres; it is bonded into the canal with resin cement, and the core is built up in composite at the same appointment. According to the Cureus review, the flexibility of a fibre post is closer to that of dentine, and this property is associated with fewer unrepairable fractures.

The difference in clinical outcomes is not as big as people think. A 2015 meta-analysis by Figueiredo and colleagues found no significant difference in the rate of root fractures between metal and fibre posts in studies with more than five years of follow-up; what is more, the included studies had a high risk of bias. In a 15-year randomised trial of 182 teeth in Belgium, the proportion of teeth still in the mouth was 53.6% with metal posts and 68.5% with prefabricated fibre posts. There was a trend in favour of fibre, and teeth with metal posts were lost to root fracture more often, but the effect of the material was not statistically significant.

These figures say two things. First, a tooth with a post and core does not last indefinitely, and over a fifteen-year horizon the losses are real. Second, the choice of material comes second to the amount of tooth structure left. Timing matters too: in a study cited by the Slutzky-Goldberg review, teeth that were not crowned after root filling were lost six times as often as those that were. Once root canal treatment is finished, do not put off the tooth's permanent restoration for months.

For the decision to become clear, the old filling and the decay have to be removed; the real amount of remaining tissue often only becomes visible then. Because this is a decision about a single tooth, the assessment is made by your own dentist, who will carry out your root canal treatment or make your crown. The lists below summarise which findings favour saving the tooth and which favour extraction.

The sequence below also shows the difference between a prefabricated fibre post and a cast post. The number of appointments depends most on the laboratory stage and on whether the root canal treatment needs to be redone.

1. 1

   Questions to ask your dentist before deciding

   How many millimetres of sound wall are left above the gum line, and does that wall go all the way around the tooth? How much root filling will be left at the root tip? Why has this type of post been chosen? If the root fractures, what option is left?

2. 2

   X-ray and assessment

   The dentist looks at the quality of the root filling, the bone at the root tip, and the length and thickness of the root. If the root canal treatment has failed, redoing it is planned first.

3. 3

   Removing the old filling and the decay

   Only after this step can the remaining sound walls be measured. This is where it becomes clear whether a ferrule can be created and whether a post is really needed.

4. 4

   Preparing the post space

   The upper part of the root filling is removed to make room for the post. At least 3 mm of filling is left at the root tip; not widening the space more than necessary protects the root.

5. 5

   With a fibre post: bonding and the core

   The prefabricated fibre post is bonded into the canal with resin cement, and the core is shaped in composite at the same appointment.

6. 6

   With a cast post: impression, laboratory and cementing

   An impression of the post space is taken and a temporary restoration is placed on the tooth; the post and core made in the laboratory are cemented at the next appointment. The Slutzky-Goldberg review points out that a temporary filling that leaks in the meantime can contaminate the post space with bacteria from saliva.

7. 7

   The crown

   The crown's finish line is placed on sound tooth structure, which creates the ferrule. Until the crown is fitted, you will be asked not to bite hard on that side.

The right order starts with the least invasive option.

A post and core is a common procedure, and usually a successful one. The following are its known limits, which you should discuss with your dentist when deciding.

Because a post and core is not a surgical procedure, there is no separate healing period. What matters is protecting the tooth until the crown is fitted, and keeping up with regular check-ups afterwards.

1. The same day

   If you had a local anaesthetic, do not eat until it has worn off. With a fibre post, the core is built the same day, so the tooth looks right again straight away.

2. Until the crown is fitted

   A temporary crown or temporary filling does not seal as well as a permanent restoration. Do not bite hard on that side, and do not put off your crown appointment.

3. After the crown is fitted

   The tooth is used and cared for as normal. Because a root-filled tooth has no nerve tissue, a problem can start without causing pain, which is why check-up X-rays matter.

4. Over the years

   If you grind your teeth, your dentist may recommend a night guard. If you notice decay at the edge of the crown or a change in the gum, show your dentist without waiting for your check-up.

A post and core is a single-tooth procedure, and your own dentist plans it; we do not give figures here. These are the main items that determine the scope and the number of appointments:

The state of the root canal treatment

If the existing root filling is adequate, the work moves straight on to the restoration on top; if not, it is redone first and the plan grows.

The type of post

A prefabricated fibre post is usually finished in a single appointment; a cast post needs a laboratory stage.

A preliminary procedure for the ferrule

If the root has to be pulled up orthodontically, or the gum and bone adjusted, a separate stage is added to the process.

The crown material

Porcelain fused to metal, zirconia and all-ceramic crowns each need different laboratory work.

Imaging

A dental X-ray is usually enough; if a crack in the root is suspected, the dentist may ask for a CBCT scan.