Cavities (Tooth Decay or Caries)

How a Cavity Forms

Cavities do not appear overnight. The process moves through distinct stages, and the earlier it is caught, the simpler the treatment.

Stage 1 – Demineralization: Bacteria in the mouth feed on sugars and carbohydrates and produce acid as a byproduct. That acid begins dissolving the minerals in the outer enamel layer. The tooth surface is still intact at this point, but a white or chalky spot may appear.

Stage 2 – Enamel Decay: If acid attacks continue, the enamel weakens further and begins to break down. The surface becomes increasingly vulnerable. This stage is still within the enamel and has not yet broken through.

Stage 3 – Dentine Decay: Once decay breaks through the enamel, it reaches dentine — the softer layer beneath. Dentine breaks down faster than enamel, and patients often begin to notice sensitivity to sweet, cold, or hot stimuli at this stage.

Stage 4 – Pulp Involvement: Decay reaches the pulp — the living tissue at the center of the tooth containing the nerve and blood supply. This is typically when pain becomes significant. Root canal treatment is usually required to save the tooth at this stage.

Stage 5 – Abscess: If pulp infection is left untreated, bacteria spread to the surrounding tissue and bone, forming a dental abscess. This is a serious condition that requires prompt treatment.

Stages 1 and 2 can be arrested or reversed with fluoride and improved oral hygiene — no drilling required. From Stage 3 onward, restorative treatment is needed. The further decay progresses, the more complex and involved the treatment becomes.

Types of Cavities

Cavities are classified by where on the tooth they develop, which affects how quickly they progress and how they are managed.

• Pit and Fissure Cavities

  These form in the grooves, pits, and fissures on the chewing surfaces of the back teeth — molars and premolars. The anatomy of these surfaces makes them natural traps for food and bacteria, and the enamel here is relatively thin. Pit and fissure cavities are the most common type and tend to progress quickly. They often begin in childhood and adolescence, when the permanent back teeth first erupt.

• Smooth Surface Cavities

  These develop on the flat enamel surfaces between teeth (interproximal surfaces) or along the gumline. Because these areas depend on flossing and correct brushing technique to stay clean, smooth surface cavities are strongly linked to inadequate oral hygiene. They progress more slowly than pit and fissure cavities and, when caught very early, can sometimes be arrested with fluoride before a cavity fully forms.

• Root Cavities

  Root cavities form on the root surfaces of teeth — areas that are normally protected by the gum. When gum recession occurs, the root is exposed. Unlike enamel, root surfaces are covered by cementum, a much softer tissue that is far more vulnerable to acid attack. Root cavities are more common in older adults and patients with gum disease, and they progress more rapidly than cavities on the crown of the tooth.

• Recurrent Cavities

  These develop at the edges of existing fillings, crowns, or other restorations, where a microscopic gap or worn seal allows bacteria to enter. Recurrent cavities are a key reason why existing dental work needs to be monitored and replaced as it ages.

What Causes Cavities

Cavities result from an imbalance between the forces that break down tooth mineral and the forces that rebuild it. Several factors shift this balance toward decay.

• Bacterial Plaque

  The mouth is home to hundreds of species of bacteria. Certain strains — particularly Streptococcus mutans — metabolize sugars and produce acid as a waste product. These bacteria live in dental plaque, the sticky film that builds up on teeth throughout the day. The more plaque is left undisturbed on the tooth surface, the more sustained the acid attack becomes.

• Dietary Sugar and Carbohydrates

  Every time you eat or drink something containing fermentable carbohydrates — sugar, starch, fruit juice, soft drinks — the bacteria in plaque have a meal. They produce acid within minutes, dropping the pH at the tooth surface and triggering demineralization. Frequent snacking or sipping keeps the mouth in an acidic state for longer periods, giving the tooth less time to recover between acid attacks.

• Dry Mouth

  Saliva is the mouth's natural defense against caries. It neutralizes acids, washes away food debris, delivers calcium and phosphate to help remineralize enamel, and contains antibacterial proteins. When saliva flow is reduced — due to certain medications, medical conditions like Sjögren's syndrome, or mouth breathing — caries risk rises significantly.

• Inadequate Oral Hygiene

  Brushing twice daily and flossing daily removes plaque before it can produce sustained acid attack on the tooth surface. Skipping flossing in particular leaves interproximal surfaces — the spaces between teeth — largely unprotected.

• Fluoride Deficiency

  Fluoride strengthens enamel and inhibits the bacteria that cause cavities. Populations with access to fluoridated water and fluoride toothpaste have significantly lower rates of decay. Insufficient fluoride exposure — whether from diet, water supply, or oral hygiene products — reduces enamel's resistance to acid.

• Age and Tooth Anatomy

  Children are at high risk when the primary and permanent teeth first erupt, before the enamel has fully matured and before good hygiene habits are established. Older adults face a different risk profile: gum recession, dry mouth from medications, and aging restorations all increase vulnerability. Teeth with deep natural grooves are inherently more difficult to clean and more susceptible to pit and fissure decay.

Symptoms and Signs to Watch For

Early-stage cavities — where demineralization is present but no hole has formed — typically produce no symptoms at all. The absence of pain is not a sign that teeth are healthy.

As a cavity progresses, the following signs may develop:

• A white, chalky spot on the enamel surface. This is one of the earliest visible indicators of demineralization. At this stage, the process may still be reversible with fluoride.
• Visible discoloration. The affected area may appear brown or black as the decay advances and the tooth structure begins to break down.
• A visible hole or pit in the tooth. Once a cavity has fully cavitated, it may be visible to the naked eye or felt with the tongue.
• Tooth sensitivity. As decay reaches dentine, the layer beneath enamel, patients often notice sharp sensitivity to sweet, cold, or hot stimuli. Dentine is far more porous than enamel and contains microscopic channels that lead toward the nerve.
• Toothache or spontaneous pain. Pain that occurs without an obvious trigger — or that lingers after the trigger is removed — suggests the decay may be reaching the pulp (the innermost part of the tooth containing nerves and blood vessels).
• Pain on biting. Discomfort when chewing can indicate a cavity on a chewing surface or a tooth that is structurally compromised.

Because early cavities are often painless, routine dental examinations — including X-rays to detect decay between teeth or beneath the surface — are the most reliable way to catch them before symptoms develop.

How Cavities Are Treated

The right treatment depends on how far the decay has progressed. The guiding principle of modern dentistry is to be as conservative as possible — preserving healthy tooth structure at every stage.

Fluoride Remineralization

For very early-stage lesions where demineralization has begun but the enamel surface is still intact, professionally applied fluoride can support remineralization and arrest the caries process without any drilling. This may involve fluoride varnish, fluoride gel, or a high-concentration fluoride toothpaste prescribed for home use. The ADA's 2018 clinical guidelines confirm the effectiveness of fluoride-based non-restorative approaches for early, non-cavitated lesions.

Dental Sealants

Sealants are thin protective coatings applied to the pits and fissures of back teeth to seal out bacteria and food. They are most commonly placed on children's permanent molars when they first erupt, before decay has a chance to begin. Sealants are also effective in arresting early non-cavitated lesions in these surfaces.

Dental Fillings

For cavities that have broken through the enamel surface, a dental filling is the standard treatment. The decayed tissue is removed, the cavity is cleaned, and the space is filled with a restorative material — most commonly tooth-colored composite resin, which bonds to the tooth and blends naturally with the surrounding enamel. Glass ionomer cement is another option, particularly for cavities near the gumline or in primary teeth, as it releases fluoride to help protect the remaining tooth structure.

Dental Crown

When decay is extensive and has removed a significant portion of the tooth's structure, a filling alone may not provide sufficient strength. A dental crown — a custom-fitted cap that covers the entire visible tooth — protects what remains, restores function, and prevents fracture. Crowns are also used when decay recurs repeatedly around existing fillings or when the tooth has been weakened by previous treatment.

Root Canal Treatment

When decay reaches the pulp of the tooth, root canal treatment becomes necessary to save the tooth. The infected pulp tissue is removed, the canals inside the root are cleaned and shaped, and the tooth is sealed. A crown is typically placed afterward to protect the treated tooth. Root canal treatment is performed by general dentists and Specialist Endodontists, depending on the complexity of the case.

Tooth Extraction

When a tooth has been destroyed by decay beyond the point where it can be saved, extraction may be the only remaining option. Missing teeth can then be replaced with an implant, bridge, or denture to restore function and prevent the surrounding teeth from shifting.

Can Cavities Be Prevented

The good news is that most cavities are preventable — not through anything complicated, but through consistent daily habits and regular professional care. Small things, done reliably, make a real difference.

Brush twice daily with fluoride toothpaste. Use a soft-bristled toothbrush and brush for two minutes, covering all surfaces. The fluoride in toothpaste is one of the most effective caries-prevention tools available — it strengthens enamel and disrupts bacterial acid production.

Floss daily. Brushing cleans the outer and chewing surfaces of teeth, but it cannot reach the spaces between teeth. These interproximal areas are a primary site for smooth surface cavities. Flossing once a day removes the plaque that brushing misses.

Reduce the frequency of sugary and acidic foods and drinks. Every exposure to sugar or fermentable carbohydrates triggers an acid attack on enamel. It is not just the amount of sugar consumed but how often — three sugary snacks spread throughout the day are more damaging than the same amount consumed in one sitting, because they create three separate acid attacks with less time for recovery in between.

Drink water, especially fluoridated water. Water rinses away food and acid, and in regions where the public water supply is fluoridated, drinking water contributes meaningfully to enamel protection.

Attend regular dental checkups. Early-stage cavities are detectable through clinical examination and X-rays long before they become symptomatic. Treating a small cavity costs far less — in time, money, and tooth structure — than treating a cavity that has reached dentine or pulp.

Consider dental sealants for children. Sealants on newly erupted permanent molars provide highly effective protection during the years when children are most vulnerable to pit and fissure decay.