Tooth Decay

What Is Tooth Decay?

Every time you eat or drink, bacteria in your mouth feed on sugars and starches, producing acids as a byproduct. These acids attack the hard outer layer of the tooth — the enamel — in a process called demineralisation. Saliva naturally helps neutralise these acids and replenish lost minerals (remineralisation), but when acid attacks occur too frequently or oral hygiene is insufficient, the balance tips in favour of enamel breakdown.

Bacterial plaque is a sticky, colourless film that continuously forms on tooth surfaces. When plaque is not removed through regular brushing and cleaning between the teeth, it provides a concentrated environment for oral bacteria to thrive and produce sustained acid attacks. Over time, the enamel weakens, develops white spots, and eventually breaks down to form a tooth cavity — a hole in the tooth surface.

Once a cavity penetrates through the enamel, it reaches the softer dentine layer beneath. Dentine is less resistant to acid, so decay progresses more rapidly at this stage. If left untreated, the decay continues inward toward the pulp — the living tissue at the centre of the tooth containing nerves and blood vessels — leading to infection, pain, and abscess formation.

Tooth decay is one of the most common chronic diseases worldwide and affects people of all ages. In the UK, it remains a significant oral health concern despite being almost entirely preventable with good oral hygiene, a balanced diet, and regular dental care.

Stages of Tooth Decay

Tooth decay develops in a predictable progression. Recognising the stage helps determine the most appropriate treatment and whether the damage can still be reversed.

Early Tooth Decay

In its earliest stage, tooth decay appears as small white or chalky spots on the enamel surface. These areas indicate enamel demineralisation — the mineral structure of the enamel has started to weaken, but no physical cavity has formed yet. At this point, the enamel surface remains intact.

This is the only stage at which tooth decay can potentially be reversed. With improved brushing, fluoride application, and dietary adjustments, the enamel can remineralise and regain strength. Your dental team can identify these early changes during routine examinations and recommend targeted preventive measures before a cavity develops.

Moderate Tooth Decay

When demineralisation progresses beyond the point of reversal, the enamel surface breaks down and a cavity forms. At this stage, bacteria have penetrated through the enamel layer and reached the dentine beneath. Because dentine is softer and more porous than enamel, the decay typically spreads more quickly once it reaches this layer.

Patients may begin to notice sensitivity to sweet, hot, or cold foods and drinks as the cavity exposes the dentine. The tooth may also develop visible dark spots or discolouration. At this stage, the decay requires professional treatment — typically a dental filling to remove the damaged tissue and restore the tooth's structure and function.

Severe Tooth Decay

When decay extends deep into the tooth, it reaches the dental pulp — the soft tissue containing the tooth's nerve and blood supply. Infection of the pulp causes significant pain, often described as a persistent throbbing toothache that may wake you at night. The tooth may also become tender to bite on.

At this advanced stage, a simple filling is no longer sufficient. Treatment typically involves root canal therapy to remove the infected tissue and save the tooth, followed by a crown to protect the weakened structure. In cases where the tooth is too badly damaged to restore, extraction may be the only remaining option.

Common Causes of Tooth Decay

Understanding what causes dental caries helps you take targeted preventive action. Tooth decay develops when several risk factors work together over time.

• Inadequate oral hygiene — insufficient brushing and failure to clean between teeth allows bacterial plaque to accumulate on tooth surfaces, particularly along the gumline and between teeth where cavities most commonly develop
• Frequent sugar consumption — every time you consume sugary food or drink, oral bacteria produce acids for approximately 20–30 minutes. Frequent snacking or sipping maintains a prolonged acid environment that overwhelms the mouth's natural repair processes
• Plaque bacteria — specific strains of oral bacteria, particularly Streptococcus mutans, are especially efficient at converting dietary sugars into enamel-damaging acids. These bacteria colonise plaque and thrive when oral hygiene is inconsistent
• Dry mouth — saliva is essential for neutralising acids, washing away food debris, and delivering minerals back to enamel surfaces. Reduced saliva flow — whether from medications, medical conditions, or dehydration — significantly increases decay risk
• Acidic drinks — fizzy drinks, fruit juices, energy drinks, and wine are acidic and contribute directly to tooth enamel erosion, weakening the surface and making it more susceptible to bacterial decay
• Tooth shape and position — back teeth (molars) have deep grooves and fissures that trap food and plaque. Crowded or overlapping teeth create additional areas that are difficult to clean effectively
• Receding gums — when gum tissue pulls back from the tooth, the root surface becomes exposed. Root surfaces lack the protective enamel coating and are softer, making them particularly vulnerable to rapid decay

Symptoms of Tooth Decay

Tooth decay symptoms vary depending on the stage and location of the cavity. In its earliest stages, decay often produces no noticeable symptoms at all — which is why regular dental examinations are essential for early detection.

• Tooth sensitivity — a sharp or lingering sensation when consuming hot, cold, sweet, or acidic foods and drinks, caused by exposed dentine beneath thinning enamel
• Visible holes or pits — as decay progresses, you may notice a hole or rough area on the tooth surface, particularly on biting surfaces or between teeth
• Toothache — persistent or spontaneous pain that can range from a dull ache to sharp, throbbing discomfort, often indicating deeper decay
• Dark spots or discolouration — brown, black, or grey patches on the tooth surface that indicate areas of enamel breakdown and mineral loss
• Pain when chewing — discomfort or sharp pain when biting down, particularly if the cavity has weakened the tooth structure or reached the dentine
• Bad breath or unpleasant taste — bacteria within a cavity produce waste products that can cause persistent bad breath or an unpleasant taste in the mouth
• Food catching — food regularly getting stuck in the same area can indicate a cavity or rough surface where tooth structure has broken down

Diagnosis and Assessment

Detecting tooth decay early — before symptoms develop — gives you the best chance of simple, effective treatment. A thorough dental examination is designed to identify cavities and enamel changes at the earliest possible stage.

• Visual examination — your dental team carefully inspects each tooth surface, checking for discolouration, white spots, visible cavities, and areas of enamel damage
• Tactile assessment — using a fine dental probe to check for soft or rough areas on tooth surfaces that indicate enamel breakdown
• Checking gum health — assessing the gums around each tooth, as gum recession can expose vulnerable root surfaces to decay
• Evaluating existing restorations — checking the margins of existing fillings and crowns where secondary decay can sometimes develop
• Risk assessment — discussing your diet, oral hygiene habits, medical history, and medications to identify factors that may increase your decay risk

Tooth Decay Treatment Options

The right tooth decay treatment depends entirely on how far the decay has progressed and how much tooth structure remains. Early intervention with a straightforward filling is far simpler than treating advanced decay that has reached the nerve. Your dental team will recommend the most appropriate approach based on your individual assessment.

Dental Fillings for Tooth Decay

For small to moderate cavities, a dental filling is the standard treatment. Your dental team carefully removes all decayed tissue from the cavity under local anaesthetic, cleans the prepared area, and restores the tooth with a filling material that bonds to the remaining structure.

Modern white fillings (composite resin) are colour-matched to your natural teeth, providing a discreet and durable restoration. The material bonds directly to the tooth, sealing the cavity and restoring the tooth's shape and function. A tooth decay filling is typically completed in a single appointment and is one of the most common dental procedures.

Root Canal Treatment for Severe Decay

When severe tooth decay reaches the dental pulp, infection sets in and the tooth becomes painful. At this stage, a simple filling cannot resolve the problem because the infected tissue inside the tooth must be addressed.

Root canal treatment involves removing the infected pulp tissue from the tooth's root canals, cleaning and disinfecting the internal chambers, and sealing the space to prevent reinfection. Despite its reputation, root canal treatment is a comfortable procedure performed under local anaesthetic and allows you to keep a tooth that would otherwise require extraction.

Tooth Restoration After Decay

Teeth that have lost significant structure to decay — particularly after root canal treatment — are weakened and more vulnerable to fracture. Protecting these teeth with a full-coverage restoration is essential for their long-term survival.

Dental crowns encase the entire visible portion of the tooth, restoring its original shape, strength, and function. Custom-made from durable materials, a crown distributes chewing forces evenly across the tooth, protecting the underlying structure from further damage. For teeth with moderate damage, an inlay or onlay may provide a more conservative alternative.

Preventing Tooth Decay

Tooth decay is one of the most preventable dental conditions. Consistent daily habits combined with professional care can dramatically reduce your risk, even if you have a history of cavities.

• Brush twice daily with fluoride toothpaste — use a soft-bristled toothbrush and fluoride toothpaste (1350–1500 ppm) for two minutes each time. Brush last thing at night and at least one other time during the day
• Spit, don't rinse — after brushing, spit out the excess toothpaste without rinsing with water. This allows the fluoride to remain on the teeth and continue strengthening the enamel
• Clean between teeth daily — use interdental brushes or floss to remove plaque from between teeth where your toothbrush cannot reach. These contact areas are common sites for hidden cavities
• Reduce sugar frequency — limit sugary snacks and drinks to mealtimes rather than grazing throughout the day. Each sugar exposure triggers approximately 30 minutes of acid attack on the enamel
• Choose water as your main drink — water does not contribute to decay and helps rinse food particles from the mouth. Tap water in many UK areas also contains fluoride
• Regular dental hygiene visits — professional cleaning by a dental hygienist removes hardened plaque (tartar) that brushing cannot shift, and provides personalised guidance on keeping your teeth clean
• Regular dental check-ups — routine examinations detect early enamel changes and small cavities before they become larger problems requiring more complex treatment

Tooth Decay in Children

Tooth decay remains the most common chronic disease affecting children in the UK. Children's teeth have thinner enamel than adult teeth, making them more susceptible to acid attack and faster decay progression. Combined with a natural preference for sweet foods and still-developing brushing skills, the risk is significant.

Early dental visits are essential. Introducing your child to the dental team from a young age establishes positive habits and allows monitoring of tooth development. Children's dentistry focuses on prevention, education, and creating a comfortable experience that encourages lifelong dental attendance.

Preventive measures for children include supervised brushing until the age of seven, age-appropriate fluoride toothpaste, fissure sealants to protect the grooves of back teeth, and dietary guidance to reduce sugar exposure. Even baby teeth deserve protection — premature loss of primary teeth can affect spacing and alignment of the permanent teeth that follow.

Parents play a crucial role in preventing childhood decay. Supervising brushing, limiting sugary snacks and drinks (including fruit juices and smoothies), avoiding sugar-containing drinks at bedtime, and maintaining regular dental appointments all contribute to keeping children's teeth healthy.

When to See a Dentist About Tooth Decay

Because early decay often causes no symptoms, regular check-ups remain the most reliable way to detect cavities before they require complex treatment. However, the following signs should prompt you to arrange a dental appointment.

• New or increasing sensitivity to hot, cold, sweet, or acidic foods and drinks
• Persistent or spontaneous toothache that does not settle
• A visible hole, pit, or dark spot on any tooth
• Pain when biting down or chewing
• Food regularly catching in the same area
• Swelling in the gum near a specific tooth
• A broken or crumbling tooth

At St Paul's Medical & Dental in the City of London, our experienced team provides thorough dental assessments, early detection of decay, and a full range of restorative treatments to protect your teeth. Book a consultation to have your teeth checked and receive a clear, personalised treatment plan.

Frequently Asked Questions About Tooth Decay