By definition, molar incisor hypomineralization (MIH) is a systemic hypomineralization of one to four permanent first molars with or without involvement of the incisors.¹ A major clinical challenge is the variability of hypomineralization and the different degrees of severity that result.

Therefore, in this chapter, the different clinical manifestations of MIH are described and explained.

2.1 Teeth

At least one 6-year molar is affected. The permanent incisors may or may not be involved (Figs 2-1 and 2-2). Clinically, the first molars are usually affected more frequently and more severely than the incisors. If the incisors are also involved in a patient, then those in the maxilla seem to be affected more often.²

Fig 2-1 MIH in a 7-year-old female patient with molars and incisors being involved. a) Frontal view: teeth 11, 21, and 31 show white opacities. The maxillary lateral incisors are not yet evaluable. b) Maxillary view: tooth 16 shows posteruptive enamel breakdowns, tooth 26 shows sharply defined opacities. c) Mandibular view: teeth 36 and 46 are also characterized by posteruptive enamel breakdowns.

Fig 2-2 MIH in an 8-year-old patient without incisors being affected. a) Frontal view: the permanent incisors are healthy. b) Maxillary view: tooth 16 and tooth 26 show hypomineralizations in the occlusal relief. c) Mandibular view: tooth 36 is healthy, tooth 46 has a small white opacity in the occlusal-mesial area.

2.2 Color

MIH teeth are clinically characterized by a change in the enamel translucency. The hypomineralized enamel can vary in shade from white to yellow to brown (Figs 2-3 and 2-4). The margins or borders are always clearly visible, well-defined, and can be clearly distinguished from healthy enamel.

Fig 2-3 Opacities on MIH molars of different colors. a) Tooth 46 with white discoloration in the buccal region at the mesiobuccal cusp in occlusal view. b) Tooth 46 from Figure 2-3a in buccal view. c) Tooth 26 with a yellow opacity. d) Tooth 26 with a brown opacity, which changes to white at the margins.

Fig 2-4 Opacities on MIH-affected incisors in different shades. a) Teeth 11, 21, and 22 with white opacities of varying degrees. b) Mid maxillary incisors with a white-yellow opacity on tooth 11 and a white opacity on tooth 21.

As a rule, the darker the color, the softer and more porous the enamel, and thus the higher the risk of posteruptive breakdown with dentin exposure.³ These enamel breakdowns are usually found at the tooth cusps, but can also be localized in other areas (Figs 2-5 and 2-6).

Fig 2-5 Posteruptive enamel breakdown of MIH-affected molars. a) Breakdown in the palatal area of tooth 26. b) Enamel breakdown in the occlusal and distopalatal areas of tooth 16. c) Occlusal substance loss in tooth 26. d) Breakdown of the complete occlusal surface including the cusps of tooth 46.

Fig 2-6 Posteruptive enamel breakdown of hypomineralized incisors. a) Substantial breakdown of tooth 11 in the distoincisal area. b) Enamel breakdown in the incisal area of tooth 42.

2.3 Localization

The mineralization disorder may be limited to a single cusp in the molar region or may extend over the entire smooth surface or fissure relief to the cervical area of the tooth⁴ (Fig 2-7). If multiple molars are affected in a patient, variations may also occur. Therefore, it is possible that in one patient, small, intact opacities are found in one molar, while large parts of enamel breakdown can be seen shortly after eruption in another molar⁵ (Fig 2-8).

Fig 2-7 Different localizations of hypomineralization. a) Tooth 36 with a white opacity in the buccal area of the mesiobuccal cusp. b) Opacity in the fissure relief of tooth 26 and in the palatal area of the distopalatal cusp. c) Hypomineralization (as far as can be assessed) of tooth 36 in the occlusal area and spreading to the cusps.

Fig 2-8 MIH molars with posteruptive breakdown shortly after eruption. a) A not yet completely erupted tooth 36 with small mucosa hood in the distal region, which already shows a loss of substance. b) Tooth 16 with enamel breakdown during eruption.

The incisors usually show hypomineralization in the buccal area. Here, many different manifestations are possible as well (Fig 2-9).

Fig 2-9

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