MOLAR-INCISOR HYPOMINERALISATION (MIH)
Nicola Clooney | MChD BChD BSc
Dentist, Community Dental Service, Salford Royal NHS Foundation Trust
What is it?
MIH has been defined as "hypomineralisation of systemic origin, affecting one to four first permanent molars, frequently associated with incisors" .
It is understood that MIH occurs during the maturation stage of enamel formation, when the ameloblasts, the cells which form enamel, are disturbed.
The aetiology is complex and unclear, although a number of theories have been proposed. It is likely due to an assortment of systemic factors, present pre-natally, peri-natally, or post-natally, which can act alone or in combination.
These may include: exposure to environmental contaminants; a number of common childhood illnesses including asthma, ear infections, fevers, chicken pox and tonsillitis; antibiotic use; being born prematurely; and maternal illnesses during pregnancy and while breast-feeding. Currently, the factor with the strongest evidence appears to be childhood illnesses, particularly fever .
The prevalence of MIH can vary greatly depending on the exact population studied. The current literature suggests a figure between 2.8% and 25%, with no significant difference between males and females .
MIH primarily presents as opacities or discolourations that can vary between white, cream, yellow or brown4. The lesions are usually asymmetrical, with clear margins between normal and affected enamel1. They do not normally involve the cervical third of the tooth5. It is not uncommon for molars to be affected unilaterally only . Crucially, the affected enamel should only be more translucent; the thickness should not be altered.
The ideal age for examination is 8, by which time all potentially-affected teeth should have erupted. When performing the examination the teeth should be clean but wet, with good lighting available .
Conditions with Similar Clinical Presentation
Unlikely to affect previously sound teeth, and white spot lesions are unusual on anterior teeth.
Will normally affect multiple teeth, with the opacities being more irregular and diffuse than those in MIH.
A defect affecting the quantity of enamel, not the quality, which manifests as a localised reduction in enamel thickness.
Manifests mainly as ‘bands’ of dark brown-grey discolouration.
A genetic condition affecting all the teeth, both primary and permanent. Depending on the sub-type, the enamel can be pitted, grooved, have a roughened surface, or flake away easily.
Consequences of Trauma
Likely to be localised to one tooth, usually incisors. A history of trauma is normally present. The discolouration normally affects the incisal edge.
Implications for the Patient
Children with MIH have a higher caries rate  and more rapid progression of caries4, because the affected enamel is weaker and more porous . Masticatory loading on the weakened enamel, primarily on FPMs, leads to rapid post-eruptive breakdown. Darker lesions have a lower mineral content; therefore post-eruptive breakdown is more likely to occur .
A common complaint in children is hypersensitivity, as the hypomineralised enamel allows increased fluid flow through the dentinal tubules to the pulp. This sensitivity can be problematic, as it can mean that patients avoid brushing the affected teeth, thus further accelerating the caries progression.
MIH-affected teeth can be notoriously difficult to anaesthetise. One theory proposed is that as bacteria penetrate the tubules more easily, the pulp becomes chronically inflamed and more resistant to anaesthesia10. Adjunctive techniques, such as PDL or intra-osseous injections, may need to be considered. Nitrous oxide sedation is also useful in reducing pain perception in children .
When affecting the incisors, the cosmetic implications of MIH can cause distress to both children and their parents. This needs to be managed carefully, particularly if associated with other issues, such as bullying at school.
Prevention of caries and tooth wear is essential from an early age to prevent post-eruptive breakdown. Appropriate dietary advice, and toothpaste with at least 1000ppm of Fluoride, should be recommended. For children over 6 years of age, prescribing toothpaste with 2800ppm Fluoride should be considered . To reduce hypersensitivity and prevent caries, professional applications of Fluoride varnish (e.g. Duraphat 22,600ppm F) up to four times a year are also advised.
GC ‘Tooth Mousse’, containing Casein Phosphopepetide-Amorphus Calcium Phosphate can be applied topically to the affected teeth, in an attempt to relieve symptoms of sensitivity. CPP-ACP provides a supersaturated environment of calcium and phosphate, which has the potential to enhance remineralisation of the enamel surface . The evidence supporting its clinical effectiveness has, however, proved mixed. It should be noted that CPP-ACP is derived from milk protein and is therefore contraindicated in children with milk allergies.
FPMs should be fissure sealed with resin sealant as soon as they erupt if there is a cause for concern.
The choice of treatment will be determined by the clinical presentation and the cooperation of the child, particularly if the child is young.
Lesions, particularly if cream or yellow in colour, may respond favourably to microabrasion with 18% hydrochloric acid or 37.5% phosphoric acid and abrasive paste . Care should be taken to avoid overtreatment, which can cause hypersensitivity, mucosal irritation or damage to the enamel.
Composite veneers can be an effective option for improving the appearance of teeth with minimal tooth tissue removal. Whilst porcelain veneers are a better long term option, they should be delayed as long as possible as tooth tissue removal can cause irritation to immature pulps, and the gingival margin can be unstable while teeth are erupting.
Resin Composite is the preferred restorative material due to its adhesive properties. Studies have shown it to have favourable survival rates15. There is some discussion as to how far the margins should be extended. Some authors advocate removing all the defective enamel, ensuring minimal marginal leakage. Others suggest removing only the very porous enamel until good resistance to the bur is felt, thereby minimising the extent of the restoration and so ensuring more structural stability for the tooth.
Glass Ionomer Cements have adhesive properties, release fluoride and can be used where moisture control is compromised. They should, however, be avoided in load-bearing areas16.
Pre-Formed Metal Crowns are indicated when there is moderate post-eruptive breakdown, as they help prevent further deterioration and control sensitivity. They can be placed relatively quickly, which is useful in young children, but care should be taken as poorly-adapted margins can lead to gingivitis. They should only be used to preserve teeth until cast restorations are possible .
Cast Restorations have the added advantages of good long term survival and supra-gingival margins, as well as preventing further deterioration and controlling sensitivity. However, a good degree of cooperation is required during the preparation, and tooth tissue removal has the potential to cause pulpal irritation. As such, cast restorations are not a first-line option .
Extractions may be the treatment of choice for severely-affected FPMs with large multi-surface lesions, severe sensitivity, inability to achieve adequate anaesthesia and children with poor cooperation.
In line with the RCS Guidelines , and depending on orthodontic considerations, extraction of FPMs and allowing the second molars to erupt in their place may provide the best long term outcome for the child, by reducing the restorative burden.
Ideally, FPMs should be extracted between the ages of 8-9, or when the mineralisation of the bifurcation of the second molar has commenced and is visible radiographically .
Regular recalls are important, particularly to monitor restoration margins for any further post-eruptive breakdown.
Early diagnosis, consistent follow up and careful treatment planning are essential. The aim of any treatment should be to provide a long-lasting outcome in a pain-free environment.
It is important to take into account the patient’s cooperation and anxiety level, and to involve the patient and parents in all treatment planning decisions, making sure they have realistic expectations which are maintained throughout.
Weerheijm, et al. 2003. "Judgement criteria for molar incisor hypomineralisation (MIH) in epidemiologic studies: a summary of the European meeting on MIH held in Athens, 2003". European Journal of Paediatric Dentistry: Official Journal of European Academy of Paediatric Dentistry. 4 (3): 110–113.
Taylor, and Greig, D. 2017. "Molar incisor hypomineralisation". Evidence-Based Dentistry. 18 (1): 15–16. doi:10.1038/sj.ebd.6401219.
Gotler M, Ratson T. 2010. Molar incisor hypomineralization (MIH) – a literature review. Refuat Hapeh Vehashinayim. 27(2):10-18
Garg et al. 2012. Essentiality of Early Diagnosis of Molar Incisor Hypomineralization in Children and Review of its Clinical Presentation, Etiology and Management". International Journal of Clinical Pediatric Dentistry. 5 (3): 190–196. doi:10.5005/jp-journals-10005-1164.
Jälevik, B.; Norén, J. G. 2000. Enamel hypomineralization of permanent first molars: a morphological study and survey of possible aetiological factors. International Journal of Paediatric Dentistry. 10 (4): 278–289.
Restrepo, M. et al. 2016. Effect of Fluoride Varnish on Enamel Remineralization in Anterior Teeth with Molar Incisor Hypomineralization. The Journal of Clinical Pediatric Dentistry. 40 (3): 207–210. doi:10.17796/1053-4628-40.3.207.
Leal, SC et al. 2017. Do parents and children perceive molar-incisor hypomineralization as an oral health problem?. International Journal of Paediatric Dentistry. 27 (5): 372–379. doi:10.1111/ipd.12271.
Silva, MJ et al. 2017. What's new in molar incisor hypomineralization?. Dental Update. 44 (2): 100–106. doi:10.12968/denu.2017.44.2.100.
Da Costa-Silva, CM. et al. 2011. Increase in severity of molar-incisor hypomineralization and its relationship with the colour of enamel opacity: a prospective cohort study. International Journal of Paediatric Dentistry. 21(5): 333–341. doi:10.1111/j.1365-263X.2011.01128.x.
Ueno, T. 2008. Local anesthetic failure associated with inflammation: verification of the acidosis mechanism and the hypothetic participation of inflammatory peroxynitrite. Journal of Inflammation Research. 1: 41–48.
Discepolo, Keri & Baker, Suher. (2011). Adjuncts to traditional local anesthesia techniques in instance of hypomineralized teeth. The New York state dental journal. 77. 22-7.
Department of Health, 2017. Delivering better oral health: an evidence-based toolkit for prevention. 3rd Edition.
Azarpazhooh, A. et al. 2008. Clinical efficacy of casein derivatives: a systematic review of the literature". Journal of the American Dental Association. 139 (7): 915–924.
Wong, FS. 2002. Effectiveness of microabrasion technique for improvement of dental aesthetics. British Dental Journal. 193 (3): 155–158. doi:10.1038/sj.bdj.4801511a.
Lygidakis, NA et al. 2003. Evaluation of composite restorations in hypomineralised permanent molars: a four year clinical study. European Journal of Paediatric Dentistry: Official Journal of European Academy of Paediatric Dentistry. 4 (3): 143–148.
Fayle SA, (Molar incisor hypomineralisation: Restorative management. Eur J Paediatr Dent. 2003 Sep;4(3):121–126.
Cobourne MT et al, 2014. A Guideline for the Extraction of First Permanent Molars in Children. Royal College of Surgeons.