A cavity, or dental caries, is a permanently damaged area of the tooth that results in a tiny opening or hole. This destruction occurs when acid, produced by oral bacteria as they consume sugars and starches, dissolves the mineral structure of the tooth’s hard outer layers. The process of decay is a continuous cycle of mineral loss and gain, but when demineralization outpaces remineralization, a lesion forms. Understanding the visual progression of this breakdown is the first step toward catching it early and maintaining oral health.
The Earliest Visual Signs
The first indication of decay is not a hole, but a subtle change in the enamel’s appearance called a white spot lesion. Minerals are lost from the subsurface enamel layer, causing these spots to appear opaque, chalky, or milky white. This occurs because the loss of minerals creates porous areas that scatter light differently than healthy, translucent enamel.
When the tooth surface is dried, this initial lesion becomes much more visible, often contrasting sharply with the surrounding shiny enamel. The surface is typically still intact, meaning no physical hole has formed. Because the damage is confined to the outer enamel, this stage is often reversible with professional care and improved hygiene.
Appearance of Developing and Advanced Cavities
If the mineral loss continues unchecked, the lesion progresses beyond the reversible stage and begins to break through the enamel surface. As the decay penetrates the enamel and reaches the underlying dentin, the appearance changes dramatically. The dentin layer is softer and less mineralized than enamel, allowing the decay to spread more rapidly.
Developing decay is commonly seen as a light brown stain that eventually darkens to dark brown or black as the organic material within the tooth structure is stained and destroyed. At this stage, a physical defect becomes visible as a rough pit, crater, or hole in the tooth surface. The texture of the affected area is often soft or leathery to the touch. Advanced cavities may appear as large, collapsed areas where a significant portion of the tooth structure is missing, sometimes exposing the inner layers entirely.
Where Cavities Form on the Tooth
The chewing surfaces of molars and premolars are prone to decay due to the deep pits and fissures that trap food and bacteria. Here, decay often first appears as a dark line or small spot within the grooves, which can hide the larger spread of decay underneath the surface.
Cavities forming on the smooth side surfaces of the teeth are harder to detect visually without an X-ray. When visible, smooth surface decay may present as a crescent or triangular shape near the gumline or as a gray shadow seen through the enamel. When gums recede, the softer root surface becomes exposed and highly susceptible to decay. Root surface caries typically appear yellow or light brown and have a softer, more rapid progression because they lack the protective enamel layer.
Visual Look-Alikes
Many common dental features can be mistaken for cavities. Extrinsic staining, which results from pigments in food, tea, coffee, or tobacco, often appears as brown or black discoloration, particularly in the fissures of back teeth. Unlike decay, these stains are superficial and feel smooth when the surface is gently examined.
Calculus (hardened plaque or tarter) is another common look-alike that can be yellow, brown, or white. Calculus forms on the tooth surface, typically near the gumline, and feels hard, but it does not represent a breakdown of the tooth structure itself. Old dental restorations, such as metal amalgam fillings, can cast a dark shadow through the remaining tooth structure, appearing as a dark spot beneath the enamel.