The distribution of disease in those affected with MIH can vary greatly. It can be common for the enamel of one<unk>  to be affected while the enamel of the contralateral<unk>  is clinically unaffected, or with minor defects only. Lesions The lesions that appear in teeth affected with MIH can present as opacities that vary from white to yellow-brown. They are usually asymmetrical in appearance, with a sharp demarcation that distinguishes between normal and affected enamel. The lesions usually do not involve the cervical third of affected teeth. Post-eruptive breakdown Post-eruptive breakdown (PEB) is a clinical feature, often observed in the majority of severely affected cases. The rate of PEB may be increased by the loading of masticatory forces on enamel weakened by MIH. The lesions resulting from PEB are irregularly shaped, with rough margins from the shearing of the enamel. PEB is more likely to occur in MIH affected teeth with yellow or brown opacities rather than those with white opacities, as darker lesions reflect a greater deficit in mineral content. Atypical caries Teeth affected with MIH are at an increased risk of acquiring dental caries. This is because the properties of the enamel are altered by increased porosity and decreased hardness. Essentially, the balance between mineralisation and demineralisation shifts to favour demineralisation of enamel, giving the tooth less resilience in structure, thereby making it vulnerable to caries. The poor structural properties of the enamel in teeth with MIH also increase the likelihood of cavitation of any lesions, thereby causing the lesion to progress at a faster rate. Progression of the carious lesion is also more rapid in teeth with MIH as patients may experience tooth sensitivity while carrying out oral hygiene, causing them to avoid doing so and consequentially accelerating the decay. Hypersensitivity Teeth affected by MIH are often affected by hypersensitivity due to changes in temperature or toothbrushing. A study has suggested that a possible cause of hypersensitivity in MIH is the inflammatory reactions in the pulp due to oral bacteria penetrating through the hypomineralised enamel into the dentinal tubules. Difficult to anaesthetise It has been reported that MIH-affected teeth were more difficult to anaesthetise. Difficulty achieving anaesthesia in MIH-affected teeth may be caused by the chronic inflammation of the pulp due to the penetration of bacteria as the presence of inflammation can reduce the efficacy of local anaesthetics which may then result in more anaesthetic being given to achieve anaesthesia. Some dental treatment has been undertaken without local anaesthesia which could result in a child becoming more fearful and anxious when receiving dental treatment. This can be especially challenging in paediatric dentistry thus more specialised methods may be needed to increase the efficiency of anaesthetising teeth. Opacities due to MIH can be quite visible especially on anterior teeth which could present as a problem aesthetically. Patients frequently claim aesthetic discomfort when anterior teeth are involved. The discoloured appearance of the anterior teeth could also have negative effects on a child’s psychological development and self-esteem. Tooth breakdown and restoration problems MIH-affected teeth are more prone to breakdown as they are hypomineralised which weakens the enamel structure. Restorations placed on MIH-affected teeth were found to be more prone to failure due to both loss of tooth structure and material loss. The enamel can also fracture more easily due to chewing forces.
Molar incisor hypomineralisation
Maxillary lateral incisor agenesis
Chattering teeth
Shovel-shaped incisors
Cartilage–hair hypoplasia
Impacted wisdom teeth
Maxillary hypoplasia
Enamel hypoplasia