Dentists use a combination of visual inspection, physical probing, X-rays, and sometimes advanced tools like laser devices to check for cavities. No single method catches everything, so most dental exams layer several techniques together to find decay at different stages and in different locations.
The Visual Exam Comes First
Your dentist starts by simply looking at your teeth under a bright light, often with magnification. They’re scanning for white spots on the enamel (an early sign that minerals are leaching out), brown or dark discoloration, visible holes or pitting, and any areas where the tooth surface looks chalky or rough. They’ll also check your gums for inflammation near specific teeth, which can hint at decay underneath the gumline.
This step sounds basic, but an experienced dentist can spot a surprising amount with sharp eyes and good lighting. Still, visual exams have a major limitation: they can’t see between teeth or beneath the surface, which is where many cavities start.
Probing With a Dental Explorer
After the visual scan, your dentist will use a thin metal instrument called an explorer to gently feel the surface of your teeth. The tool has a fine tip designed to pick up subtle texture changes. As the dentist runs it across your enamel, they rely on tactile feedback, feeling for soft spots, roughness, or slight catches that indicate the tooth structure has started to break down. Even decay too small to see can sometimes be felt as a change in resistance or a slight vibration through the instrument’s handle.
Interestingly, dental guidelines have shifted on how aggressively dentists should use this tool. Pressing a sharp explorer firmly into a suspicious pit or groove can actually puncture a weakened area that might have remineralized on its own. Current best practice calls for using a blunt probe or light pressure rather than poking hard into every crevice. The goal is to gather information without damaging enamel that still has a chance of repairing itself.
X-Rays Reveal What Eyes Can’t See
Bitewing X-rays are the gold standard for finding cavities between teeth. These are the small films or sensors you bite down on during a checkup. They capture the areas where your teeth press together, surfaces that are nearly impossible to examine visually or with an explorer. On the resulting image, healthy enamel appears as a bright white band. Decay shows up as a darker shadow where minerals have been lost.
X-rays also reveal how deep a cavity has progressed. A shadow confined to the outer enamel layer may be monitored rather than filled, while one that has reached the softer layer beneath (dentin) typically needs treatment. Decay hiding under an existing filling, which is invisible during a visual exam, also shows up clearly on radiographs.
How Often You Need X-Rays
The American Dental Association’s recommendations depend on your cavity risk. Adults with no active decay and no increased risk factors generally need bitewing X-rays every two to three years. If you have current cavities or are at higher risk (dry mouth, a history of frequent decay, heavy sugar intake), that window tightens to every six to eighteen months. Children and adolescents follow a similar pattern: every one to two years for low-risk kids, and every six to twelve months for those prone to cavities. Your dentist adjusts the schedule based on what they’re seeing at each visit.
Laser Fluorescence Detection
Some dental offices use a pen-shaped laser device that shines a specific wavelength of light onto the tooth. Healthy enamel and decayed enamel fluoresce differently when hit with this light. The device reads the fluorescence and gives a numerical score: a low number means the tooth is healthy, while a higher number suggests decay. It’s painless and takes seconds per tooth.
A large systematic review of this technology found it correctly identifies early enamel decay about 84% of the time and deeper decay about 81% of the time. Its specificity (correctly identifying healthy teeth as healthy) ranges from 77% for early lesions to 89% for deeper ones. These numbers make it a useful supplement to X-rays and visual exams, particularly for catching decay in the pits and grooves on the chewing surfaces of molars where cavities are easy to miss.
Fiber-Optic Transillumination
This technique involves shining a bright, focused light through the tooth. Healthy tooth structure transmits light relatively evenly, while areas of decay scatter the light differently, appearing as dark shadows or gray patches. It’s especially helpful for finding cracks and cavities between front teeth, where the thinner enamel lets light pass through more readily.
Digital versions of this tool capture the image on a screen, making it easier for your dentist to compare changes over time. Transillumination doesn’t use any radiation, which makes it a good option for monitoring borderline spots between X-ray appointments.
AI-Assisted X-Ray Analysis
A growing number of dental practices now run X-rays through artificial intelligence software before or alongside the dentist’s own review. These programs scan the image pixel by pixel, flagging areas that look like early decay. A meta-analysis of AI dental platforms found a mean sensitivity of 76% and specificity of 91%, meaning the software catches most cavities while rarely flagging healthy teeth as problems. Some individual platforms scored as high as 98.6% accuracy.
AI doesn’t replace your dentist’s judgment. It works more like a second set of eyes, highlighting subtle shadows that a human reviewer might scroll past, especially on a busy day. The dentist still makes the final call on whether something flagged actually needs treatment.
Why Cavities Between Teeth Get Missed
The surfaces where your teeth touch are the hardest place to detect decay early. You can’t see them, you can’t easily feel them with a probe, and the enamel in those contact areas is thin. This is exactly why bitewing X-rays exist, and why skipping them for several years can let a small cavity grow into one that needs a large filling or a crown.
Flossing pain or sensitivity in a specific spot, food constantly getting stuck between the same two teeth, or a visible dark line at the edge of a contact point are all clues worth mentioning to your dentist. Cavities in these areas don’t always hurt until they’re well into the dentin layer, so the absence of pain isn’t reassuring on its own.
What Happens When Something Looks Suspicious
Not every suspicious spot turns into a filling. If your dentist finds early enamel demineralization (a white spot or a very shallow shadow on an X-ray), they may recommend a watch-and-wait approach. Fluoride treatments, improved brushing and flossing, and dietary changes can sometimes reverse the earliest stage of decay before it becomes a true cavity. Your dentist will note the location, possibly photograph it or save the X-ray, and compare it at your next visit to see if the area has stabilized, improved, or worsened.
When decay has clearly broken through the enamel into dentin, or when a physical hole has formed, the standard next step is removing the damaged tooth structure and placing a filling. The size and location of the cavity determine what type of restoration makes sense, from a small composite filling to an inlay or crown for more extensive damage.