Molar incisor hypomineralisation (MIH) affects nearly 30% of Scandinavian children, according to researchers at the University of Copenhagen dental hospital. In the United Kingdom, the condition is also widespread: prevalence studies suggest it affects approximately one in eight children, with some estimates putting the figure as high as 20% — or one in five.
What is MIH?
MIH is a developmental defect of tooth enamel. The outer layer — the hardest material in the body — and sometimes the middle layer of the tooth do not form properly, leaving them softer and less mineralised than normal. The disruption occurs early in a child’s life, while the teeth are forming inside the jaw, typically from around birth until about the age of two.
The condition most often affects the first permanent molars — the so-called six-year molars — and the permanent incisors, although it can also affect the second primary molars (baby back teeth), which can be an early sign of future problems. The teeth can appear chalky white, yellow or brown, often with a clear border against healthy enamel. Because the enamel is fragile, the teeth can crumble or break easily and become sensitive to hot, cold or sweet foods and drinks. Some children avoid brushing because it hurts. At around six or seven years old, when the permanent molars and incisors first erupt, parents and dentists often notice the tell-tale discolouration and tenderness.
Causes of MIH: varied and not fully understood
Researchers emphasise that MIH is not caused by poor brushing, sugar intake or bad dental habits. Instead, it results from something that disrupts enamel formation before the teeth even appear. The exact triggers remain something of a puzzle, but current research points to several possible factors, often interacting with one another.
One leading candidate is prolonged illness in early life, such as high fevers, repeated infections (respiratory or urinary tract infections) or gastric disorders. Another is the long-term use of antibiotics, which may interfere with enamel development. Complications during pregnancy or birth are also suspected — these include oxygen deprivation, premature birth, and traumatic birth.
Environmental factors, including air pollution, have been proposed as contributors. Deficiencies, particularly of vitamin D, which is crucial for the body’s ability to form strong enamel, are also thought to play a role. In addition, a possible genetic vulnerability means some children may simply be more susceptible than others. A recent finding has linked MIH with an increased risk of hypodontia — congenitally missing teeth — which strengthens the case for a genetic component.
The wide variation in reported prevalence across the globe — MIH appears less common in Africa and Asia — is suspected to be largely due to differences in diagnosis and reporting, as well as genuine differences in early childhood illnesses and genetic factors.
What parents and dentists can do
With current knowledge, MIH itself cannot be prevented. However, parents can take steps to protect their child’s teeth. Twice-daily brushing with fluoride toothpaste is essential because the softer enamel is harder to keep clean and at greater risk of cavities. Dentists may recommend high-fluoride toothpaste, fluoride mouthwashes, or products containing CPP-ACP (Recaldent) to help with sensitivity. Limiting sugar intake is also important.
Parents are encouraged to help their child build a good relationship with the dentist by speaking positively about how dental treatment protects teeth and by asking the child to describe where and how a tooth hurts. The sensitivity and difficulty of treating MIH can contribute to dental anxiety, so early trust is valuable.
The dentist will assess the extent of the condition and classify affected teeth as mild, moderate or severe. For mild cases, concentrated fluoride gel or transparent fissure sealants are used. Moderate cases often require temporary or permanent fillings, and because the tooth is very sensitive, anaesthesia is needed. Severe cases may receive fillings and, in the most serious instances, a stainless steel crown — a foil cap that protects the tooth from breaking, cavities and pain. In rare cases where the long-term prognosis is poor, extraction may be recommended, typically between the ages of eight and ten.
Front teeth usually have only mild to moderate MIH and are often not treated initially. As children grow older, they may seek aesthetic treatment. Options include whitening combined with a newer technique in which a thin, fluid resin is infiltrated into the enamel, filling the empty spaces and making the discolouration disappear. In adulthood, severely affected molars may benefit from a crown or porcelain inlay.
Research needs
To tackle MIH effectively, researchers say the profession needs a clearer picture of how widespread it actually is. That requires stronger, more consistent studies and better agreement on how the condition is diagnosed and recorded. At the same time, basic questions remain: what are the key triggers, and why do some children develop MIH while others do not? UK centres are part of international research investigating associations between MIH and other dental anomalies, such as missing teeth. The European Association of Paediatric Dentistry has issued clinical guidelines for management, and studies are exploring the knowledge and attitudes of general dental practitioners in the UK to identify barriers to care.