The ideal age for examination is when the child is 8 years old - the age where all permanent first molars and most of the incisors are erupted. The permanent first molar will also still be in a comparatively sound condition without excessive post-eruption breakdown. Judgements of each individual teeth should be recorded, aiding the correct diagnosis of the condition. There is currently a lack of standardisation in the scoring system and severity indices used to record the diagnosis of MIH. Various systems commonly employed in studies include:

Modified Defect of Dental Enamel (DDE) Index: This set of criteria allows for enamel defects to be detected, enabling a distinction between demarcated and diffused opacities. European Academy of Paediatric Dentistry (EAPD) judgement criteria: This set of criteria was developed in 2003 to standardise classifications for use in epidemiological studies. However, while it allows the categorisation of the enamel condition, it does not address the severity of the enamel condition. Molar Hypomineralisation Severity Index (MHSI): This set of criteria has been developed to address deficiencies in indices concerning the severity of hypomineralisation. It is based on both the clinical characteristics of hypomineralised defects and the EAPD judgement criteria. It was found to be effective in guiding the clinical management of children by predicting treatment undertaken for affected permanent first molars. Ghanim et al index: The index combines principles of the EAPD judgement criteria and DDE index in order to grade the clinical status, amount of tooth surface area affected, and other enamel defects comparable to MIH.
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.