agent. however, more evidence is needed from clinical based studies. cavity design there is still much debate of whether margin extension should include removal of all defective enamel or only the porous enamel. the former provides sound enamel for bonding but leads to excessive tooth tissue loss. the latter is less invasive, but the margins may have a high risk of breakdown due to defective bonding. yet, it is agreed that adhesive restorations should be used as opposed to those reliant upon mechanical retention (such as amalgam). composite resin restorations composite resin material has been shown to have longer-term stability in mih teeth, with a median survival rate of 5.2 years and a success rate of 74%-100% during a 4-year follow-up period. self-etching adhesive was found to have better bond strength to enamel affected by mih compared to total etch single-bottle adhesive. the use of composite should be considered both for permanent molars affected by mih, as well as incisors. furthermore, composite veneers may achieve a better aesthetic result where deep lesions are seen in incisors. glass ionomer cement (gic) restorations gic materials have adhesive capabilities with both enamel and dentine, long-term fluoride release and hydrophilicity when there is inadequate moisture control intra-orally, during early post-eruptive stages. however, gic’s poorer mechanical properties suggest avoidance in stress-bearing areas. in later post-eruptive stages gic may be valuable as sub-layer beneath composite restorations. preformed metal crowns pre-formed metal crowns (pmc), also known as stainless steel crowns, can be used to reduce the risk of marginal breakdown, coronal leakage and has a good longevity. the use of preformed metal crowns on mih-affected molars can prevent further tooth loss, control hypersensitivity and aim to establish correct interproximal and occlusal contact. they are relatively inexpensive and require little preparation. to prevent further tooth preparation and tissue loss, use of the hall technique should also be considered. there advantage is use during any stage of post-eruptive breakdown, but evidence of their efficacy is limited. although the pmc has evidence to show that it is well accepted, a few of the children and their carers expressed their concerns about the metallic appearances of the restoration. cast restorations cast restorations may include full coverage crowns for mih-affected permanent teeth. generally cast restorations requiring tooth preparation are not recommended in young children due to large pulp size, short crown height and potential difficulties in obtaining a good impression for subgingival crown margins. extractions tooth extraction is one of the treatment options for mih, especially for symptomatic cases. a list of considerations can affect the final decision on whether extraction of the affected teeth should be carried out or should it be retained such as: severity of mih; patient’s aesthetic expectations; whether the patient is suitable to undergo orthodontic treatment; orthodontic concerns (e.g. crowding, facial profile, missing or supernumerary teeth, presence of third molars). timely extractions are often the preferred treatment plan for first permanent molars that are severely affected and symptomatic. the facilitation of eruption of the second permanent molars to the space of the first permanent molar removes the burden of continuous restorative treatment. a favourable occlusion may be acquired following a well-planned treatment and this eliminates the need for fixed orthodontic appliances therapy. however, a comprehensive discussion of the possible need of orthodontic sequelae and treatment is important. favorable eruption position of the second permanent molar may result if the first permanent molar is extracted when the child is at the age of between 8–10 years old. this is when the crown formation of the second permanent molar is complete and the mineralization of the bifurcation is commenced. extraction of first permanent molars before 8 years old increases the chances of the unerupted second permanent premolar drifting distally. extraction after the age of 10 years reduces the likelihood of the mesial movement of the second permanent molar in to the first permanent molar space and may result in tilting of the second permanent molar. epidemiology since first recognised in the late 1970s, the condition has puzzled many people. it is thought to be a unique defect unlike other enamel disturbances e.g. fluorosis or amelogenesis imperfecta. many prevalence studies have now been published from findings across the globe. however, there is a large amount of variation across the results of these studies. it is reported that the prevalence of mih ranges from 3.6% to 40.2% with an estimate of 14.2% of the global population suffering. worldwide there is much variation between continents with south america having the highest prevalence (18%), closely followed by oceania (16.3%). the continent found to have least sufferers was africa (10.9%). multiple studies have provided evidence that there is no gender difference. however, a study by kathmandu university reports that post eruptive breakdown occurs more frequently in boys than it does in girls. a different study found that children under the age of 10 are more highly affected by the disease (15.1%) compared to older children (12.1%).