A cavity that forms at or below the gum line, often referred to as subgingival caries, presents a unique challenge in restorative dentistry. Unlike standard decay on the crown of the tooth, these lesions are partially or entirely hidden by soft tissue. The answer to whether they can be filled is a qualified yes, but the procedure requires specialized techniques to gain access and ensure the long-term success of the restoration. The complexity arises from the need to create a dry, clean field in an area naturally bathed in moisture and blood.
Causes and Characteristics of Below-the-Gumline Cavities
Cavities that develop below the gum line, known as root caries, typically begin when the gum tissue recedes, exposing the tooth’s root surface. The root is covered by cementum, a thin layer significantly softer than the hard enamel protecting the crown of the tooth. This softness makes the exposed root surface highly vulnerable to acid attack from plaque bacteria. The decay process can be accelerated by specific risk factors that change the environment in the mouth.
A diminished salivary flow, often caused by certain medications or medical conditions, reduces the mouth’s natural ability to neutralize acid and wash away food debris. This condition, known as xerostomia or dry mouth, allows plaque to become stickier and more damaging near the gum margin. Poor cleaning habits, especially failing to use interdental brushes or floss, also allow plaque to accumulate where the tooth meets the gum. The resulting root surface decay can quickly progress into the underlying dentin, spreading rapidly due to the tissue’s lower mineral content.
Locating and Assessing Subgingival Decay
Diagnosing a cavity beneath the gum tissue is often difficult because it cannot be seen during a standard visual examination. Dentists rely on a combination of clinical tools and imaging to accurately find and assess the extent of the lesion. A specialized, fine-tipped dental probe is used to gently explore the tooth surface just below the gum line, feeling for soft spots or irregularities that indicate decay.
Dental X-rays, particularly specialized digital images, are a necessary tool for revealing the internal depth and spread of the decay. However, X-rays may not always show the precise margin of the cavity, as soft tissues can sometimes obscure the lesion. Once decay is located, the dentist must assess its proximity to the dental pulp, the living tissue inside the tooth. If the decay has reached or is near the pulp, a standard filling may not be sufficient, and a root canal procedure may be required to save the tooth.
Surgical and Non-Surgical Access Techniques
The most significant technical hurdle in filling subgingival decay is gaining a clean, dry working field, which is necessary for the restorative material to bond correctly. For decay only slightly below the gum line, non-surgical techniques can provide temporary access. These methods involve placing gingival retraction cords—thin strings soaked in an astringent solution—into the space between the tooth and the gum. The cord gently pushes the tissue away and helps stem the flow of gingival fluid, creating a brief window for the dentist to work.
For deeper or more extensive lesions, a surgical approach is often unavoidable to achieve adequate visibility and isolation. A simple procedure called a gingivectomy may be performed, which involves removing a small amount of gum tissue to expose the cavity margin. If decay extends further down, approaching the bone level, a crown lengthening procedure is sometimes required. This involves reshaping both the gum tissue and the underlying bone to permanently reposition the gum margin lower on the root, ensuring the final filling is placed on visible tooth structure.
A less invasive non-surgical approach for certain deep defects is Deep Margin Elevation (DME), a two-step process. First, a small amount of restorative material is used to build up the subgingival margin, moving it above the gum line. This “elevated” margin can then be properly isolated with a rubber dam, a thin sheet used to keep the tooth completely dry. By creating a supra-gingival margin, the second step—placing the final filling—is made easier and more predictable, ensuring a strong, moisture-free bond.
The Filling Process and Material Requirements
Once access and isolation are achieved, the filling process begins with the careful removal of all decayed tooth structure. Preparation of the root surface is delicate because the remaining dentin is less dense and requires a gentle touch to avoid unnecessary removal of healthy tissue. Maintaining the dry field is the primary challenge, as the restorative material must adhere strongly to the tooth structure.
The selection of the filling material is driven by the unique requirements of root surface restorations. Resin-modified glass ionomer cements (RMGICs) are frequently preferred for their good moisture tolerance and ability to chemically bond to the tooth. Furthermore, RMGICs and traditional glass ionomers release fluoride over time, which helps prevent further decay at the filling margin.
Specialized composite resins, which are tooth-colored materials, may also be used, particularly where aesthetics are a primary concern. These materials require stricter moisture control during placement to ensure effective bonding. The placement technique involves layering the material in small increments to minimize shrinkage and ensure it completely fills the prepared cavity. After setting, the restoration is meticulously shaped and polished to create a smooth surface that will not irritate the surrounding gum tissue or promote plaque accumulation.
Post-Treatment Care and Prognosis
After a subgingival filling procedure, patients should expect some temporary sensitivity, particularly to hot and cold temperatures. Minor soreness or swelling in the gum tissue that was retracted or surgically altered is also normal and can usually be managed with over-the-counter pain medication. Patients should wait until the local anesthetic has completely worn off before attempting to eat to avoid accidentally biting the lip or cheek.
Long-term success depends heavily on the patient’s commitment to meticulous oral hygiene at home. Because the area is prone to plaque retention, diligent cleaning, including the use of interdental brushes or floss, is necessary to prevent the recurrence of decay at the filling margin. Regular dental check-ups and professional cleanings are important for monitoring the restoration’s integrity and the health of the surrounding gum tissue. While subgingival fillings have a good prognosis when properly placed, they remain susceptible to recurrent decay if underlying risk factors, such as dry mouth or poor hygiene, are not managed.