A dental cavity represents the progressive destruction of tooth structure caused by acid-producing bacteria. The purpose of drilling is to meticulously remove this infected and softened material. This process is necessary to halt bacterial progression and create a clean, structurally sound space. Once the decay is removed, the tooth preparation is filled with a restorative material, sealing the tooth and preventing future infection.
Understanding the Tooth’s Layers
The sequential process of drilling is dictated by the tooth’s anatomy, which consists of three main layers moving from the exterior inward. The outermost layer is the enamel, the hardest substance in the human body, composed of mineralized calcium phosphate. Its primary function is to serve as a durable, protective shield against chewing forces and chemical attacks. Enamel contains no living cells and cannot regenerate.
Beneath the enamel lies dentin, which makes up the bulk of the tooth structure. Dentin is softer than enamel and contains microscopic channels called dentinal tubules. This tubular structure makes dentin highly sensitive when exposed, allowing stimuli like heat, cold, and pressure to transmit toward the nerve.
The innermost chamber holds the pulp, a soft tissue containing blood vessels, nerves, and connective tissue. The pulp supplies nutrients and hydration to the dentin and registers sensation, like pain. When decay reaches this layer, it can cause inflammation and severe pain, often necessitating a root canal treatment.
Drilling Through the Enamel and Dentin
The dental drilling procedure follows a precise sequence, beginning with the tooth’s hard outer shell. The dentist uses a high-speed handpiece, often with water spray for cooling, to penetrate the dense enamel. This initial entry requires significant force, but the patient feels minimal sensation due to the enamel’s lack of nerve fibers.
The feel and sound of the drilling change notably when the bur reaches the underlying dentin. Since dentin is significantly softer, the dentist often switches to a lower-speed handpiece or a specialized round bur for more control. This slower, careful excavation removes the infected dentin without sacrificing healthy tooth structure.
The removal of carious dentin is the most delicate part of the procedure. Dentin that is affected but not yet irreversibly infected is often left behind in the deepest parts to protect the pulp. The dentist relies on visual and tactile cues, such as the color and texture of the remaining dentin, to determine where to stop.
When Drilling Stops Short of the Pulp
The goal of a standard filling procedure is to remove all infected material while preserving the health and integrity of the pulp tissue. Dentists must differentiate between infected dentin (soft and mushy) and healthy or only affected dentin (firm and resistant to removal). If the cavity is exceptionally deep, the dentist may intentionally leave a thin layer of affected dentin over the pulp to avoid exposure.
Indirect Pulp Cap
This conservative approach is known as an indirect pulp cap, and it relies on the remaining dentin to heal and possibly generate new dentin over time. A pinkish hue, sometimes called “pulp blushing,” in the deepest part of the preparation can indicate very close proximity to the pulp. At this point, the drilling stops completely to prevent exposure.
A protective layer, such as a calcium silicate-based cement or glass ionomer liner, is then placed over the deepest part of the preparation. This material is biocompatible and serves to protect the pulp from the filling materials and the stresses of the restoration process. The liner also encourages the pulp to form reparative dentin, creating a thicker, natural barrier before the final filling is placed. This technique differentiates the procedure from a root canal, which involves intentionally accessing and removing the pulp tissue.