Dental caries, commonly known as a cavity, is a prevalent health condition resulting in the breakdown of tooth structure. This localized damage occurs over time, creating tiny openings or holes in the teeth. The physical texture of the lesion changes dramatically depending on its stage of progression. Understanding the nature of a cavity requires examining the underlying chemical and physical processes that determine its state.
The Chemistry of Tooth Decay
The formation of a cavity is fundamentally a chemical process driven by an imbalance in the mouth’s natural environment. It begins with specific oral bacteria, such as Streptococcus mutans, living in dental plaque. These bacteria consume carbohydrates and produce organic acids, which rapidly lower the pH level within the biofilm.
This acidic environment attacks the tooth’s mineral structure, primarily composed of crystalline hydroxyapatite. When the pH drops below a critical level (around 5.5 for enamel), the acid dissolves the calcium and phosphate ions. This process, called demineralization, leads to a net loss of mineral content. The mouth is constantly engaged in a demineralization-remineralization cycle. If acid attacks are frequent, saliva cannot restore the minerals quickly enough, and demineralization dominates.
Physical Properties of Cavities
Early Stage Decay (Hard)
The physical state of a carious lesion directly correlates with how far the chemical process has advanced. In the earliest stage, decay presents as an initial white spot lesion on the enamel surface. This lesion is hard to the touch because the surface layer of the enamel remains intact despite subsurface demineralization. These initial lesions are often reversible if the chemical environment is corrected and remineralization occurs.
Active Decay (Soft)
As the decay progresses and breaks through the enamel, it enters the underlying dentin, which is softer and more porous. This stage acquires the physical texture most associated with active decay, often feeling soft or sticky upon gentle probing. The softened dentin contains destroyed, porous tissue that feels mushy or leathery when assessed clinically. This soft texture indicates that the mineral structure has been significantly compromised and the decay is actively progressing.
Arrested Decay (Hard)
A third manifestation is arrested decay, which has stopped progressing and become inactive. These lesions are characterized by a dark brown or black color due to mineral changes and staining. Unlike active decay, an arrested lesion feels smooth and hard when evaluated because demineralization has ceased. This physical firmness signals that the tooth has successfully stabilized the lesion.
Diagnosing and Treating Cavities
Dental professionals assess the physical state of a potential cavity using visual inspection, specialized instruments, and diagnostic imaging. Dentists look for visible chalky spots or use X-rays to detect decay, and gently probe the surface to check for soft areas. If the lesion is detected in the early, hard stage of demineralization, treatment focuses on non-invasive intervention. The dentist may apply professional-strength fluoride treatments, which promote the reincorporation of minerals to harden the weakened area.
If the lesion has progressed to the established, soft stage and formed a cavitation, restorative treatment is necessary. This involves the physical removal of the soft, infected, and compromised tooth material using a drill. Once the decay is cleared, the resulting space is filled with a durable material to restore the tooth’s shape and function. Advanced decay that reaches the inner pulp tissue may require procedures such as a root canal or the placement of a crown.