After a tooth undergoes root canal treatment, the remaining natural structure is often severely compromised by decay, trauma, or the necessary access preparation. Saving the tooth requires placing a final restoration, usually a crown, but a weak foundation cannot support this cap reliably. In these instances, an internal anchor known as a dental post is placed to provide the needed support for the subsequent restoration, ensuring the long-term survival and function of the tooth.
Defining the Post and Its Function
The dental post is a rod-like fixture cemented deep inside the cleaned and sealed root canal space of a tooth that has had its nerve and pulp removed. Its primary purpose is mechanical retention, acting as an anchor for the core material built up around it. The post itself does not directly strengthen the root, but it provides a foundation to replace the missing coronal tooth structure. Without this internal reinforcement, a tooth with extensive loss of its natural crown is at risk of fracture under normal biting forces.
The core is a buildup of restorative material, typically composite resin, that replaces the missing part of the tooth above the gum line. The post ensures this core material stays firmly attached to the root, which is then shaped to receive the final dental crown. Dentists generally recommend a post and core procedure when less than half of the tooth’s original coronal structure remains.
Materials and Design of Dental Posts
Posts are broadly categorized by their composition: metal or fiber-reinforced materials. Traditional metal posts are prefabricated from materials like stainless steel or titanium, or they can be custom-cast from gold alloys to match the internal root anatomy. Metal posts offer high rigidity and strength, which is advantageous in high-stress areas like back teeth. However, this rigidity can transfer stress unevenly to the root, increasing the risk of fracture.
Fiber posts are typically made of carbon, glass, or quartz fibers embedded in a resin matrix. They are popular because their modulus of elasticity is closer to that of natural dentin, meaning they flex more like the tooth itself. This property distributes stress more favorably and reduces the chance of catastrophic root fracture. Because they are tooth-colored, fiber posts also offer an aesthetic advantage, especially for front teeth where metal might show through a translucent crown.
The Placement Procedure
The placement of a post and core is performed after the root canal therapy is completed and sealed. The first step is to carefully remove a portion of the root canal filling material, known as gutta-percha, from the coronal part of the canal. A minimum of four to five millimeters of gutta-percha must remain at the root tip to maintain the apical seal and prevent re-infection. Specialized drills are used to prepare the resulting space, shaping the canal to match the post’s size and taper.
After the space is prepared, the post is tried in for fit and then cemented or bonded into place using a strong dental cement or adhesive. For fiber posts, a resin-based cement is often used to chemically bond the post to the dentin. Once the post is securely anchored, the core material is built up around it, replacing the lost tooth structure. This core is then shaped precisely to create the proper foundation, or abutment, for the final dental crown.
Post Failure and Long-Term Considerations
While a post and core restoration has a high success rate, various factors can lead to long-term failure. The most common issue is the loss of retention, where the post or core loosens and dislodges from the root, usually due to inadequate bonding or excessive force over time. Another concern is the development of recurrent decay at the margin where the crown meets the tooth structure, allowing bacteria to cause a new infection.
The most severe complication is a root fracture, which often makes saving the tooth impossible. Although fiber posts are designed to reduce this risk, any post placement inherently removes internal dentin, which can weaken the root structure. If a post and core restoration fails, the prognosis for saving the tooth becomes poorer, sometimes necessitating extraction and replacement with a dental implant. Regular dental check-ups and good oral hygiene are important for monitoring the restoration and ensuring its longevity.