Tooth decay is one of the most common dental problems worldwide. It affects the vast majority of the population, both children and adults. According to the World Health Organization, 60% to 90% of schoolchildren worldwide and nearly 100% of adults have cavities. Cavities can appear very early: children can have cavities as soon as their first tooth appears.
But the good news is that tooth decay is largely preventable. With good oral hygiene, smart food choices, and regular dental care, you can protect your teeth and those of your children.
In this guide, we’ll walk you through what tooth decay is, how it forms, its symptoms and complications, and how to prevent and treat it.
What is tooth decay?
Tooth decay is an infectious disease that gradually destroys the hard tissues of your teeth. It begins when bacteria in the mouth produce acids that attack the enamel—the outer layer of the tooth. If left untreated, decay eventually affects the pulp, located in the center of the tooth, where the nerves and blood vessels are located. Decay can cause the pulp to die, leaving an empty space inside the tooth. Bacteria from the mouth can then enter this space and cause infection, pain, and even tooth loss.
How does tooth decay form?
Cavities are caused by sugars in food and the action of bacteria in the mouth. These bacteria are concentrated in dental plaque, a whitish substance that also contains saliva and food particles. Dental plaque is deposited on the surface of the teeth and is removed by brushing. When plaque remains on the teeth, the bacteria it contains convert the sugars in food into acids. These acids attack the tooth, forming a hole on its surface: this is tooth decay. If the cavity is not treated, the hole will enlarge and the cavity will become deeper.
The 4 stages of tooth decay
Tooth decay progresses through four main stages:
Stage 1: Enamel decay
- The cavity is limited to the outer enamel layer.
- Usually no symptoms or pain.
Stage 2: Dentin decay
- The decay reaches the softer dentin under the enamel.
- Teeth may become sensitive to hot, cold, or sweet foods.
Stage 3: Pulp involvement
- The infection reaches the dental pulp (where nerves and blood vessels are).
- Sharp, spontaneous, and constant pain may occur.
Stage 4: Dental abscess
- The pulp becomes infected, resulting in a buildup of pus.
- Symptoms may include severe pain, gum swelling, fever, and even facial swelling.
Symptoms of tooth decay
Symptoms vary depending on how advanced the decay is:
- No symptoms in the early stages
- Sensitivity to temperature or sweets
- Toothache or throbbing pain
- Pain when chewing
- Swollen or red gums
- Bad breath or a bad taste in the mouth
- Visible holes or dark spots on the tooth
- Fever or facial swelling in advanced cases
How is tooth decay treated?
1. Dental filling
A dental filling is used when a cavity has only affected the outer layers of the tooth, like the enamel or dentin. The dentist will remove the decayed part of the tooth, clean the area, and fill it with a tooth-colored material. This helps restore the tooth and stops the decay from spreading.
2. Root canal treatment
If the cavity has reached the inside of the tooth (called the pulp), a root canal treatment is needed. The dentist will remove the infected pulp, clean the root canals, and fill them to seal the space. Since a lot of the tooth is removed during this treatment, a crown is usually placed on top to protect and strengthen the tooth.
3. Tooth extraction
Sometimes, if the tooth is too badly damaged and cannot be fixed, it must be removed. This is called a tooth extraction. After the tooth is taken out, the dentist might suggest replacing it with a crown, bridge, or denture to fill the gap and help you chew and smile normally again.
Complications of untreated tooth decay
Ignoring tooth decay can have serious consequences for teeth and overall health.
It can cause:
- Persistent toothache and jaw pain
- Dental abscess and infection
- Tooth loss
- Difficulty chewing and eating
- Bad breath and poor appearance
- Speech and self-esteem issues
- Costly dental treatments
- School absenteeism and developmental problems in children
Tooth decay in children
Children are especially vulnerable to tooth decay. It can lead to:
- difficulty feeding, which can lead to growth retardation
- sleep problems
- growth and speech delays
- concentration problems
- anxiety, fatigue, and school issues
- early tooth loss affecting self-confidence and development
In some cases, dental procedures under general anesthesia may be necessary for young children.
Can tooth decay be transmitted?
Yes, tooth decay is caused by bacteria that can be transmitted through saliva:
- From adults to babies (e.g., kissing on the mouth, sharing utensils)
- Between children
At birth, a baby’s mouth does not contain bacteria that cause tooth decay. However, these bacteria can enter the baby’s mouth when the baby brings objects or food into the mouth that have been contaminated by another person’s saliva.
Adults can take certain precautions to avoid transmitting these bacteria. They should avoid:
- to kiss the baby on the mouth;
- to use the same spoon to taste the baby’s food and to make him eat;
- to put the baby’s pacifier in their own mouth to clean it.
Risk factors for tooth decay
The main risk factors for tooth decay are:
Having poor oral hygiene
- not brushing your teeth regularly;
- do not use fluoridated products, such as toothpaste and mouthwash, and do not drink fluoridated water when possible.
Having a diet high in sugars and often consuming sugary drinks and foods
- Frequently consuming sugary or acidic foods or drinks. This increases the contact time of sugar with teeth and increases the acidity in the mouth, which promotes the development of serious cavities.
- Consuming several small portions of sweets or sugary drinks throughout the day is more damaging to your teeth than consuming the same amount all at once.
- Eating sweets between meals or as a snack is more damaging to your teeth than eating them during a meal. The increased saliva production during a meal helps protect your teeth from cavities.
- Eating sweets in the evening without brushing your teeth before going to bed increases the risk of cavities because saliva production decreases at night, making teeth less protected.
- Give a child:
- a sugary drink in a baby bottle or sippy cup. These types of containers encourage frequent and prolonged contact between the teeth and the sugary liquid. This increases the risk of cavities developing quickly.
- a bottle of milk to put him to sleep. As saliva production decreases during sleep, teeth are less protected against the sugars in milk.
- a sugary or sticky snack. These types of foods can get stuck between teeth when they are already less protected by saliva, which is less abundant between meals. The risk of cavities is then higher.
For a parent, neglecting to have their cavities treated
- Parents can increase their baby’s risk of cavities by putting their baby’s utensils, food, or pacifier in their mouths. This can pass on cavity-causing bacteria. The younger a child is infected, the higher their risk of developing cavities. In babies, the risk of cavities is highest if parents have untreated cavities.
Suffering from dry mouth
Dry mouth can increase the risk of cavities. It can be caused by:
- Sjogren’s syndrome, a chronic disease characterized by insufficiency of the glands that produce saliva and tears;
- radiation therapy treatments to the head and neck;
- taking certain medications.
Being in loss of autonomy
- A loss of physical independence, caused for example by arthritis or Parkinson’s disease, can make it difficult to hold and use a toothbrush properly.
- A loss of cognitive autonomy, caused for example by Alzheimer’s disease, can prevent a person from ensuring their own oral hygiene.
How to prevent tooth decay
1. Practice good oral hygiene
- Brush twice daily with fluoride toothpaste
- Floss daily to clean between teeth
- Use fluoride mouthwash if recommended
2. Eat smart
- Limit sugary and acidic snacks
- Avoid frequent snacking between meals
- Rinse your mouth or brush after eating sweets
- Drink plenty of water—especially fluoridated water
3. Visit your dentist regularly
- Schedule dental checkups once or twice a year
- Get professional cleanings and fluoride treatments
- Ask about dental sealants for children
4. Avoid spreading bacteria to children
- Don’t kiss babies on the mouth
- Don’t share utensils or clean pacifiers with your mouth
- Treat your own dental problems to reduce bacteria transmission
Final thoughts
Tooth decay is common, but it’s not something you have to live with. With regular care, smart habits, and help from your dentist, you can prevent decay and maintain a healthy smile for life. If you or your child are showing signs of a cavity, don’t delay—early treatment can save the tooth and avoid pain and complications later.