The field of restorative dentistry focuses on repairing and replacing damaged or missing tooth structure to restore function, health, and appearance. When a tooth has suffered significant damage from extensive decay, a large fracture, or the removal of an old, failed filling, the remaining structure may be too compromised for a simple restoration. In these situations, a foundational procedure is required to rebuild the tooth, creating a stable platform for a permanent covering. This foundational step, known as a core build-up, structurally prepares a severely weakened tooth for its final restoration.
Defining the Core Build-Up
A core build-up is a dental restoration that replaces missing coronal tooth structure, specifically the dentin and enamel layers above the gum line. Its primary objective is to create a sufficient volume of material that can be shaped to properly support a crown. The procedure ensures the tooth has the necessary bulk and stability to withstand chewing forces and the preparation process for the final restoration.
This procedure is indicated when a tooth has lost more than half of its natural structure, such as teeth with extensive decay or significant fractures due to trauma. Without a core build-up, the remaining tooth may lack the structural integrity or height required for a crown to be securely retained, potentially leading to restoration failure. The rebuilt core acts as a stable base, allowing the entire tooth-restoration complex to function successfully over time.
The Procedure and Materials Used
The core build-up procedure begins with the dentist removing all existing decay, old filling material, and any weakened tooth structure. The goal is to establish a clean, sound surface to which the new material can adhere. Isolation of the tooth, often using a matrix band or sectional matrix system, is necessary to contain the restorative material and mold it into the appropriate shape.
Modern dentistry primarily utilizes materials like composite resin or resin-modified glass ionomer cement. Composite resins are popular because they can be chemically bonded to the remaining tooth structure through an adhesive process, which helps conserve the natural tooth tissue. These materials also offer mechanical properties, such as compressive strength, that closely simulate natural dentin.
Dual-cure composite resins are frequently used, as they can be set quickly with a curing light while also having a self-curing mechanism for deeper areas. Glass ionomer materials are sometimes chosen for their ability to release fluoride and their strong adhesion to dentin. While amalgam was historically used, its use has declined because it requires more invasive tooth preparation for mechanical retention and does not bond adhesively like resin-based materials.
When a Post is Necessary
In cases where the tooth damage is severe, especially after root canal therapy, a standard core build-up may not provide adequate retention. A root canal procedure removes the tooth’s interior pulp, leaving the tooth hollowed out and often more brittle. When the remaining coronal structure is minimal, the core material needs additional support to prevent dislodgement under chewing forces.
This is when a post and core procedure is performed, which is a variation of the standard build-up. The dentist removes a small portion of the root canal filling material, creating a space to place a dental post. This post, often made of metal or fiber-reinforced composite, is cemented into the root canal space and extends above the gum line, functioning like rebar in concrete.
The core build-up material is then packed around the protruding post, anchoring the core deeply into the tooth’s root. The post itself does not strengthen the root against fracture; its sole purpose is to provide the retention needed to hold the core material in place. A post is reserved for situations where the tooth has lost a significant amount of structure, typically less than four millimeters of sound tooth tissue above the gum line.
Core Build-Up and Crown Placement
The core build-up is a preparatory step, not the final restoration, designed to facilitate the placement and longevity of a crown. Once the core material has been placed and cured, the dentist shapes this newly formed structure, along with the remaining natural tooth, into the specific geometry required to receive a crown. This shaping process is known as crown preparation.
This preparation must create a specific height and taper to provide the necessary retention and resistance form for the crown. Retention form refers to the features that prevent the crown from being pulled off the tooth, while resistance form prevents the crown from rotating or being dislodged by lateral forces. The built-up core ensures there is sufficient height for the crown to grip the tooth securely.
The core build-up also creates a stable, sealed margin where the edge of the crown will sit, protecting the underlying tooth structure from leakage and recurrent decay. After the core has been precisely prepared, an impression or digital scan is taken of the shaped tooth. This template is then sent to a dental laboratory, where the custom crown is fabricated, ready to be permanently cemented onto the stable foundation.