Severely Decayed Teeth: Save, Crown or Extract

What a Rotten Tooth Is and How Decay Starts

A rotten tooth is a tooth that a bacterial infection has been dissolving from the outside in. Bacteria in dental plaque feed on sugary and starchy food and release acid, which draws minerals out of the enamel, the hard outer shell. When enamel has lost enough mineral it collapses into a cavity, and the softer dentin underneath dissolves faster still. Left alone, the lesion reaches the pulp, the nerve and blood supply at the centre of the tooth, and that is usually when pain begins.

Decay is therefore a process that unfolds over months, and the stage it has reached decides the treatment. Early mineral loss can still be reversed with fluoride. An established cavity cannot, because lost enamel and dentin do not grow back.

Rotten teeth are also more than an aesthetic problem. Dark spots and holes are the visible part, but the same lesion causes bad breath, pain on chewing and, in advanced cases, infection of the pulp and the surrounding bone. Inadequate brushing, frequent sugary snacks and a dry mouth, which removes the saliva that buffers acid, all make decay more likely. Some people also inherit a saliva composition or enamel structure that is less resistant, which makes regular care matter more for them.

How Common Untreated Decay Is Worldwide

Untreated decay is common enough that most families meet it. A global analysis built on 192 studies of children and 186 studies of people aged 5 and over found that in 2010, untreated caries in permanent teeth was the most prevalent condition worldwide, affecting 2.4 billion people (PubMed 25740856). Untreated caries in baby teeth ranked 10th among all conditions and affected 621 million children in the same year (PubMed 25740856).

The same analysis showed the burden shifting from children to adults, with three peaks in prevalence at ages 6, 25 and 70 (PubMed 25740856). Decay is often thought of as a childhood problem, yet adults in their twenties and people in later life carry a large share of untreated lesions, the latter often on root surfaces exposed by gum recession.

Among preschool children the picture is similar. A meta-analysis using the World Health Organization criteria pooled data on 59018 children from 29 countries and found a global prevalence of early childhood caries of 48 percent (PubMed 33735529). Almost half of the preschool children in those studies had decay in their baby teeth, and prevalence varied widely between countries, which suggests diet, fluoride exposure and access to care shape the risk alongside individual habits.

Symptoms and Why Pain Arrives Late

The first signs of a rotten tooth are small and easy to dismiss: sensitivity to hot and cold, a brief tingle with sugary food, black or brown spots on the surface, or bad breath that brushing does not fix. As the lesion grows, toothache appears, often worse at night, and chewing on that side becomes painful.

A common misconception is that a tooth without pain has no decay. Pain appears when the lesion approaches the pulp, so early and moderate decay can be completely silent. Home observation therefore has a limited role. Discolouration, small holes and bad breath are worth noticing, but a definitive diagnosis needs a dentist and often a radiograph, because lesions between teeth and under old fillings cannot be seen in a mirror.

Three other beliefs are worth correcting. Decay is driven by fermentable carbohydrates in general, so starchy snacks count along with sweets. Rinsing after eating helps but does not remove plaque, so it cannot replace brushing. And decay in baby teeth does need treatment, as a later section explains.

If decay keeps progressing, the pulp can die and infection can spread to the bone at the root tip, forming an abscess or cyst. At that stage the choices narrow to root canal treatment or extraction.

Grading Decay With the ICDAS Scale

Dentists grade decay with the International Caries Detection and Assessment System, known as ICDAS. It scores each tooth surface from 0 to 6, and the score points toward the treatment.

A score of 0 is a healthy surface. Scores 1 and 2 describe an early lesion, a chalky or discoloured area in the enamel without a hole. Scores 3 and 4 describe enamel breakdown and moderate decay. Scores 5 and 6 describe deep caries with a visible cavity and dentin damage.

The scale separates lesions that can still be stopped from those that need a restoration. Fluoride can remineralise an early lesion that has not yet collapsed, so grades 1 and 2 are handled with fluoride, diet change and monitoring. Once the surface has broken down into a cavity, the options become a filling, root canal treatment, a crown or extraction.

Decay is also described by the layer it has reached. Enamel decay stays in the outer shell and is often painless. Dentin decay has passed into the softer layer below and usually brings sensitivity. Pulp decay has reached the nerve and causes lingering or spontaneous pain. Root decay forms on root surfaces exposed by gum recession, where thin cementum takes the place of enamel.

Treatment From Filling to Extraction

Treatment follows the depth of the decay, and chair time grows with it.

Filling

For decay confined to enamel and the outer dentin, the dentist removes the softened tissue and seals the cavity with tooth-coloured aesthetic filling material. A simple filling takes 20 to 40 minutes in a single appointment.

Root canal treatment

When decay has reached the nerve tissue, a filling alone cannot solve the problem. In root canal treatment the infected pulp is removed and the canals are cleaned, shaped and sealed so the tooth can stay in the mouth. It usually takes one to two sessions.

Crown

When decay has destroyed a large part of the tooth, the remaining structure may be too weak to hold a filling under chewing forces. The tooth is then covered with a crown made of porcelain or zirconia. This takes a few days, because the crown is made outside the mouth.

Extraction

If the tooth cannot be saved, it is extracted, usually in one session. The gap can later be restored with an implant or a bridge.

A lesion caught at the filling stage leaves most of the tooth intact, while one found only after it aches often needs both root canal treatment and a crown.

Prevention With Fluoride, Diet and Check-Ups

Prevention works on the chain that causes decay: less acid, more mineral and earlier detection. Brushing twice a day with fluoride toothpaste is the foundation. A Cochrane review of 96 studies found that in children and adolescents, 1000 to 1250 ppm or 1450 to 1500 ppm fluoride toothpaste reduces caries increments compared with non-fluoride toothpaste (PubMed 30829399). In adults, 1000 or 1100 ppm fluoride toothpaste also reduced decay compared with non-fluoride toothpaste (PubMed 30829399). Professional fluoride applications add to what toothpaste provides, especially for people who develop new lesions often.

Brushing does not reach between the teeth, so dental floss or an interdental brush is needed once a day. Diet matters through frequency as much as amount. Carbohydrate-heavy, sugary and acidic foods feed the acid cycle, and each snack restarts it. Fibrous vegetables, water and sugar-free chewing gum, which stimulates saliva, help the mouth recover between meals.

The last step is detection. Because early decay can be silent, a check-up every 6 months finds lesions while fluoride or a small filling can still handle them. People with a dry mouth, many existing fillings or frequent new cavities may need closer follow-up, and the dentist sets that interval after the examination.

Decay in Children and During Pregnancy

Decay that starts in baby teeth progresses quickly, and baby teeth need treatment even though they will be replaced. With early childhood caries affecting 48 percent of preschool children across the pooled studies (PubMed 33735529), this is a common situation. A decayed baby tooth can cause pain and infection, and losing it early takes away the space holder for the permanent tooth beneath it. The standard responses are fluoride applications, fillings and brushing habits built at an early age, supported by regular check-ups so problems are found before the child complains.

Pregnancy changes the picture in a different way. Hormonal changes increase the risk of gum bleeding and decay, and morning sickness can expose enamel to stomach acid. Treatment should therefore not be postponed indefinitely. The second trimester is the preferred window for planned work, and local anaesthesia and radiographs can be used with the necessary precautions. Tell the dental team about the pregnancy and any medication before the appointment so the plan can be adjusted.

Signs That Call for an Examination

Some signs mean a tooth should be examined soon: sensitivity to hot, cold or sweets that keeps returning in the same tooth, a dark spot or small hole you can see or feel, food catching in one place, pain on chewing, and toothache that wakes you at night. Swelling of the gum or face, a bad taste near one tooth or fever point to infection and need prompt care.

At the examination the dentist checks each surface, grades any lesion on the ICDAS scale and takes radiographs where decay may be hidden between teeth or under old restorations. The findings map onto the options above: fluoride and monitoring for early lesions, a filling for a cavity, root canal treatment when the nerve is involved, a crown when little tooth structure remains and extraction when the tooth cannot be saved.

After treatment, some teeth are left discoloured or slightly misshapen, particularly front teeth that had large lesions. A natural appearance can be restored with teeth whitening, bonding or laminate veneers once the disease is under control, so the cosmetic work sits on healthy teeth.