A cavity, or dental caries, is a hole in the tooth structure caused by the decay process. This begins when bacteria in the mouth produce acids that erode the tooth’s hard outer enamel layer. While some advanced signs of damage can be visible, relying only on self-examination is risky for detecting tooth decay in its early stages. The nature of how and where cavities form means that most decay is entirely hidden from a quick visual check.
Early Signs and What You Might See
In the later stages of decay, a cavity can sometimes be visible to the naked eye. One of the most obvious signs is the presence of dark staining, which appears as brown or black spots on the chewing surfaces or along the sides of the tooth. This discoloration usually indicates that the decay has progressed beyond the enamel and into the underlying dentin.
Before reaching the stage of visible discoloration, the earliest sign of decay can be a chalky white spot on the enamel. This white patch, known as an early lesion, signals demineralization where the tooth has lost minerals. In this initial state, the decay is often reversible with proper care and fluoride treatment. If decay is advanced, a patient might see or feel a visible pit, hole, or crater in the tooth surface. The edges of the tooth may also feel rough or jagged if a piece has broken away due to the structural compromise caused by the internal decay.
Why Most Cavities Are Hidden From View
The majority of tooth decay is not visible in a mirror because of the specific locations where bacteria and acid thrive undisturbed. A common hiding spot is between the teeth, known as the interproximal surface, where toothbrush bristles cannot reach and flossing is required to remove plaque. Decay in these areas can progress significantly without causing any visible change to the front or back of the tooth.
Sub-surface decay occurs when bacteria penetrate the enamel through microscopic defects, but the surrounding surface remains intact. This process can create a large cavity inside the tooth while leaving only a small, nearly invisible opening on the outer shell. Cavities frequently develop in the deep grooves, pits, and fissures on the chewing surfaces of the back molars, which are difficult to see even with a mirror and are prone to trapping food and plaque. Decay can also hide along the gum line or on the root surface, particularly in people with receding gums.
How Dentists Find What You Cannot
Dental professionals rely on a combination of technology and physical examination to detect cavities that are invisible to the patient. The most reliable method for finding hidden decay, especially between teeth, is the use of dental radiographs, commonly known as X-rays. Bitewing X-rays are designed to capture clear images of the crowns of the back teeth, revealing decay between them and under existing fillings.
During the physical examination, dentists use a small, pointed instrument called an explorer to gently check the tooth surface for subtle changes in texture. They look for softened enamel, sticky grooves, or rough patches that indicate a loss of mineral structure. More advanced tools, such as laser fluorescence devices, are also utilized to detect early decay by measuring how the tooth reflects light. Decayed areas reflect light differently than healthy enamel, helping to identify demineralization that is still too small to be seen on an X-ray or felt with an explorer.