An indirect pulp cap (IPC) is a conservative dental procedure designed to save a tooth when deep decay (carious lesion) has approached the dental pulp, which contains the nerve and blood vessels. The goal is to protect the pulp from exposure while encouraging the tooth’s natural ability to repair itself. By placing a specialized material over the deepest decay, the dentist preserves the tooth’s vitality and stimulates the formation of new, protective dentin, avoiding a more invasive root canal treatment.
Rationale for Indirect Pulp Capping
The decision to perform an indirect pulp cap stems from the clinical recognition that complete removal of all decay from a deep lesion often risks accidentally exposing the pulp. Such iatrogenic exposure can introduce bacteria and lead to inflammation. Therefore, the strategy involves a selective removal of the decay, taking out the outer, heavily infected dentin but intentionally leaving a thin layer of affected dentin near the pulp.
This remaining dentin is less infected and is covered by a biocompatible material. The material acts as a barrier, sealing the dentin from the oral environment and the bacteria that drive decay. Sealing the area allows the pulp to calm down and begin self-healing. The ultimate purpose is to promote the formation of tertiary dentin, a reparative layer that walls off the pulp chamber and increases the distance between the pulp tissue and the remaining decay.
What Capping Materials Must Achieve
Any material used for indirect pulp capping must fulfill several specific biological and physical requirements. Foremost among these is providing an excellent marginal seal to prevent microleakage, which is the re-entry of bacteria and fluids from the mouth into the prepared cavity. Without a hermetic seal, the remaining bacteria can continue to irritate the pulp, leading to treatment failure.
The material must also demonstrate strong biocompatibility, meaning it is non-irritating or toxic to the underlying pulp tissue. It should be bioactive, actively stimulating the tooth’s defense mechanisms. This includes possessing inherent antibacterial properties and promoting the differentiation of stem cells into odontoblast-like cells, which create the reparative dentin layer. Finally, the material needs to be chemically stable and physically durable enough to withstand chewing forces while under the final restoration.
Comparing Specific Capping Materials
Historically, Calcium Hydroxide (\(\text{Ca(OH)}_2\)) has been the most widely used material for pulp capping. Its mechanism relies on its extremely high alkaline pH, which provides an antibacterial effect and causes a superficial, controlled necrosis of the pulp tissue, leading to a strong reparative response. This action potently stimulates the formation of tertiary dentin, which is its main biological advantage.
However, Calcium Hydroxide has significant drawbacks, including high solubility and disintegration over time, poor mechanical strength, and a lack of adhesion to dentin, which compromises the coronal seal. Furthermore, the reparative dentin it induces can be porous and contain “tunnel defects,” creating potential pathways for bacterial penetration.
Resin-Modified Glass Ionomers (RMGIs) are frequently used as cavity liners and protective bases in deep preparations. They are valued for their ability to bond chemically to the tooth structure, creating a superior marginal seal compared to Calcium Hydroxide. RMGIs also release fluoride ions, helping fight secondary decay at the restoration margins. While they provide excellent physical protection and sealing, they are generally less bioactive than other materials and do not stimulate dentin formation as robustly as bioceramics.
Bioceramics, primarily Mineral Trioxide Aggregate (MTA) and its derivative, Biodentine, are calcium silicate-based cements. These materials have overcome many of the deficiencies of Calcium Hydroxide by offering superior mechanical strength, lower solubility, and an excellent seal. They are highly biocompatible and induce a more regular and dense layer of reparative dentin compared to the porous layer formed by Calcium Hydroxide.
MTA is highly effective but has disadvantages such as a long setting time and the potential to cause dark discoloration of the tooth structure. Biodentine was developed to improve upon MTA, featuring a faster setting time, better handling characteristics, and mechanical properties similar to natural dentin, allowing it to function as a dentin substitute.
Crucially, Biodentine does not typically cause the tooth discoloration associated with MTA, making it a preferred choice in visible areas. Both MTA and Biodentine are highly tolerant of moisture, a common challenge in deep preparations. Their ability to release calcium ions and maintain a high pH makes them highly bioactive and antibacterial.
Determining Treatment Success and Material Selection
The success of an indirect pulp cap is determined by the long-term maintenance of pulp vitality. Successful outcomes are characterized by the tooth remaining asymptomatic, with no prolonged pain or swelling, and no signs of pathology like bone loss visible on radiographs.
The choice of material depends on several factors, including the depth of the lesion, the dentist’s experience, and the required timeline. A very deep lesion requiring a quick, robust biological response might favor a bioceramic like Biodentine due to its superior sealing and dentin-inducing properties. For less severe lesions, a highly sealing material like an RMGI may be prioritized as a reliable base.
Patient age is also a factor, as younger teeth with wider, healthier pulps respond more favorably than older teeth. Ultimately, while the capping material plays a significant role, the single most important factor for success is the quality of the final, overlying restoration, which must provide an impenetrable seal against bacteria.