How do dentists find cavities?

how do dentists find cavities

Dental cavities are widespread affecting 92% of the population worldwide. Due to their high rate of occurrence, it is essential to spot tooth decay as early as possible to prevent the teeth from further damage. If the cavities are left untreated, they may damage the tooth beyond repair. In this article, we will see how dentists find cavities in the teeth.

What is a cavity?

A cavity or dental decay is an irreversible bacterial infection of the tooth, characterized by the destruction of the tooth structure over time leading to a cavity or hole in the tooth. In dentistry, the cavity is also known as dental caries. 

How do dentists find cavities?

There are three standard steps to finding cavities in your teeth that nearly every dentist follows. 

  • Patient’s complaints or history
  • Oral examination
  • Dental x-rays 

In dental practice, most dental x-rays are taken ahead of oral examination, especially during a routine dental check-up or if you complain about a toothache.

Patient’s chief complaint

Your main complaint is the first step in diagnosing a cavity in the mouth.

When you walk into the dentist’s office, you will be given a form to fill. The first thing asked in the form is your chief complaint about visiting the office. Next, you will be asked about the history of any medical illnesses (diabetes, high blood pressure, or heart disease) and previous dental treatments (any fillings or root canals).  

This data provides valuable information to the dentist about your medical and dental health status. 

The following symptoms are tell-tale symptoms of a cavity in the mouth. 

  • Sharp pain in the tooth while eating or drinking something sweet, hot, or cold. 
  • Spontaneous severe pain in the tooth that lasts for hours.
  • Bad breath or foul smell from your mouth.
  • Fever, difficulty in opening mouth, and pus draining from the mouth.

Oral or mouth examination

The oral examination is a prerequisite for all patients who seek dental consultation. As mentioned earlier, your symptoms bring dentists one step closer to diagnosing a cavity. However, early and non-symptomatic cases of tooth decay are diagnosed during routine oral and radiographic examinations.

The dentist visually examines your mouth with a mirror and looks for any white, brown, or black spots on the teeth. Also, teeth with advanced cavities show up as a hole in a tooth. 

The dental instruments used to find cavities

A dental explorer, a blunt dental instrument with a long shaft, is used to find cavities by discerning a difference in the surface roughness of the teeth. The dental explorer is maneuvered over the teeth, and any alteration in the surface texture of the tooth raises suspicion for further evaluation. Some dental practices also use a blunt probe to spot cavities. 

The early carious process appears as a white spot on the tooth which is confirmed visually and with the dental tools.

Dental x-rays 

There are three primary dental x-rays used to detect cavities. 

  • Panoramic X-ray
  • Periapical x-ray
  • Bitewings radiographs 

A periapical x-ray shows the precise anatomy of three teeth and is taken when an x-ray of a single tooth is required. These small radiographs are most frequently used to detect a cavity in the tooth due to the low radiation exposure.

Panoramic x-rays (OPG) are full-mouth x-rays that capture all the teeth and their surrounding bone in the mouth. This x-ray is taken during the routine dental examination to see if there are any cavities in the teeth. Also, your dentist may request you to go for an OPG if a cavity is suspected in a wisdom tooth due to its complex and variable root anatomy.

A bitewing x-ray (red boxes show cavities between the teeth (Srivastava, Muktabh Mayank, et al. “Detection of tooth caries in bitewing radiographs using deep learning.” arXiv preprint arXiv:1711.07312 (2017).

Bitewings x-rays are small radiographs especially taken to reveal the caries status between the teeth. It displays the crowns (a portion of teeth visible in the mouth) of 6 teeth, three upper and three lower when they bite.  

How to find cavities on an x-ray?

X-rays are high-energy electromagnetic radiations that display images of hard structures such as bones and teeth or metal fillings. The rigid mineral-rich structures resist the passage of radiation through them and are seen white on the x-ray film. 

The more mineral or metal-rich the structure is, the whiter it appears on the film. However, the soft structures, such as gums or a cavity in the tooth, allow radiations to pass through and appear black on the radiograph. 

The cavities appear as black areas on the teeth on an x-ray and indicate the area of mineral loss. 

Additional methods to see the extent of infection in the tooth 

Once a cavity has been diagnosed, other techniques, such as cold, heat, or electric pulp tests, can be used to spot the extent of disease and the vitality of the tooth. 

In the cold method, an ice pick is placed on the teeth one by one, and the response of each tooth is noted. Healthy teeth feel no pain, but a sharp and lingering pain is felt on the teeth where the bacteria have penetrated the tooth’s nerves. The dead tooth shows no response to the ice picks. 

Similarly, an electric pulp tester probe in electric pulp test and a heated plastic material in heat test are placed on the teeth, and responses analogous to the cold test are noted. 

New ways to find cavities

Conventional x-rays provide a two-dimensional view of a three-dimensional object (tooth), making them 40-60% accurate in spotting cavities. Early decay is usually missed on these x-rays. The modern equipment available in some practices provides a more precise diagnosis of cavities.

Laser fluorescence : The laser device (DIAGNOdent) uses infrared radiation to detect tooth decay on any tooth surface. The tooth illuminated with the laser light gives readings from 0 to 99. The higher values show more profound damage to the tooth. Its results are up to 90% accurate.

Fiberoptic transillumination :  In this technique, a narrow beam of white light is directed across the dry tooth. The light brightens the tooth structure so that any color change or presence of cracks, fractures, or cavities can be seen. Also, some dentists use blue light to find cavities which is generally use to cure the white composite filling in the teeth. 

Electrical conductance : This device catches early decay in the teeth by sensing an increased influx of fluid from the healthy dentin to the diseased portion. During the initial stages of tooth decay, the fluid from the dentin flows into the cavity. The probe of the electric caries detector is run through the dry tooth, and the reading is recorded. The higher values signify a deeper cavity. Moreover, it gives 90% accurate results.

Frequently asked questions 

How do dentists find cavities where there aren’t any?

Most cavities between the teeth are hidden from the naked eye, especially when they are small. These small cavities are only visible on an x-ray. Therefore, the tooth that looks healthy may have a cavity. 

Also, in some cases, the bacteria enter the tooth through pits and grooves on the chewing surface of the back teeth (molars) and then spread to dentin. You may not realize anything except black discoloration in the pits and grooves of the tooth until the walls break down and form a cavity. 

Such cavities are diagnosed by dentists if there is no pain. It is, therefore, essential to get annual or biannual dental checkups for their early detection. 

How to find cavities at home?

Any pain or swelling in the tooth requires evaluation for a cavity. An individual may have more than one cavity at one time. Also, a black discoloration or hole in the tooth suggests a cavity. 

How can a dentist find cavities when no x-ray is taken?

Visual examination of the mouth and symptoms of the patients, such as pain or swelling in a particular tooth, helps the dentist to find cavities. X-rays are taken to confirm the decay and its spread in the tooth. 

Can dentists find cavities without a metal pick?

Yes, dentists can find cavities without a metal pick by using a mouth mirror. The mouth mirror is tapped it on the teeth to see any discomfort. A blunt probe can be used instead. 

Also, a cavity diagnosis can be done by relying entirely upon patients’ symptoms and x-rays without the metal pick examination. But for accuracy, these three steps are essential for the diagnosis.

Can cone beam CT scan find cavities?

Yes, cone beam CT can be used to find cavities in teeth. The three-dimensional scan gives a more accurate status of decay in the teeth. However, the increased cost, time, and effort required to carry out one scan make it impractical to use it for every case. 

Can you find cavities developing behind metal fillings?

Yes, dentists can find cavities developing cavities behind the metal fillings. On a radiograph, a black halo is seen under the filling on an x-ray. It is, however, difficult to find a developing cavity beneath a metal filling at home if you don’t have any pain or swelling in the tooth. 


Due to the high rate of cavities in this modern age, it is vital to detect cavities as soon as possible to prevent irreversible damage to the teeth. Dentists find cavities through three main steps, namely, symptoms of the patients and oral and x-ray evaluation. 

Once a cavity is spotted, other techniques like cold, hot, and electric pulp testing are used to see the vitality of the tooth and the extent of the decay. 

Modern and better techniques used to detect early decay includes laser fluorescence, Fiberoptic transillumination, and electrical caries detector.

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