**1.1 Definition**

Developmental defects of enamel were commonly defined as hypoplasia, but according to the FDI Commission on Oral Health, Research and Epidemiology (1992), these defects are best classified into two distinct categories: a) hypomineralized enamel or enamel opacities (Figures 1A and 1B) and enamel hypoplasia (Figures 1C and 1D). While opacity is defined as a qualitative defect of the enamel, hypoplasia is defined as a quantitative defect of the enamel. (Suckling, 1989) There are others differences between developmental defects of enamel that can be seen in Table 1.

In the dental literature a wide variety of terminology or definitions were used for developmental defects of enamel in molars, with or without association with post eruptive breakdown of enamel as non-fluoride enamel opacities, internal enamel hypoplasia, nonendemic mottling of enamel, opaque spots, idiopathic enamel opacities, enamel opacities or cheese molars. (Koch et al., 1987, van Amerongen & Kreulen, 1995) However, to better understand the occurrence of molar incisor hypomineralisation and its impact on the oral health, the use of a uniform terminology is strongly recommended. (Weerheijm, 2004, Weerheijm et al., 2003)

The term molar incisor hypomineralisation (MIH) was firstly cited by WEERHEIJM ET AL., 2001. (Weerheijm et al., 2001) and further, this terminology was definitively adopted by the international dental scientific community as a result of a consensus after innumerous discussions in relation to developmental defects of enamel (Weerheijm et al., 2003). Then, MIH was defined as the clinical appearance of morphological enamel defects involving the occlusal and/or incisal third of one or more permanent molars or incisors as result as "hypomineralisation of systemic origin." (Weerheijm, 2004) The first permanent molar enamel is affected to an extent ranging from mild to severe; in many cases the incisor enamel is affected, but often, minimally not necessarily involving a macroscopic defect of tooth. Furthermore, this specific form of developmental defects of enamel (Baroni & Marchionni, 2011) show opacities asymmetrically often distributed, with marked variation in severity within an individual and ranges from small demarcated white, yellow or brown

stainment of their affected incisor. (William et al., 2006a) In such circumstance, the esthetic complaint may also be considerable. Apart from the restorative difficulties faced by clinicians, children with MIH have dental fear and anxiety and these behaviour problems can be related to pain experienced by the patients during multiple treatment appointments, as many of them were either inadequately anesthetized or even had treatment without local analgesia (Jalevik & Klingberg, 2002). It has been shown that children with MIH receive much more dental treatment that unaffected children. (Jalevik & Klingberg, 2002, Kotsanos et al., 2005) Thus, treatment planning should also consider the long-term prognosis of teeth

Children during the period of eruption of their first permanent molars and/or incisors should be monitored very carefully in order to obtain an early diagnosis and immediate treatment for MIH. Considering all aspects mentioned above, MIH is one of the biggest challenges to great challenger of great clinical interest for dental practice because MIH has a great impact on the oral health as consequently, on the quality of life of children and adolescents. Thus, the objective of this chapter is to describe some epidemiological,

Developmental defects of enamel were commonly defined as hypoplasia, but according to the FDI Commission on Oral Health, Research and Epidemiology (1992), these defects are best classified into two distinct categories: a) hypomineralized enamel or enamel opacities (Figures 1A and 1B) and enamel hypoplasia (Figures 1C and 1D). While opacity is defined as a qualitative defect of the enamel, hypoplasia is defined as a quantitative defect of the enamel. (Suckling, 1989) There are others differences between developmental defects of

In the dental literature a wide variety of terminology or definitions were used for developmental defects of enamel in molars, with or without association with post eruptive breakdown of enamel as non-fluoride enamel opacities, internal enamel hypoplasia, nonendemic mottling of enamel, opaque spots, idiopathic enamel opacities, enamel opacities or cheese molars. (Koch et al., 1987, van Amerongen & Kreulen, 1995) However, to better understand the occurrence of molar incisor hypomineralisation and its impact on the oral health, the use of a uniform terminology is strongly recommended. (Weerheijm, 2004,

The term molar incisor hypomineralisation (MIH) was firstly cited by WEERHEIJM ET AL., 2001. (Weerheijm et al., 2001) and further, this terminology was definitively adopted by the international dental scientific community as a result of a consensus after innumerous discussions in relation to developmental defects of enamel (Weerheijm et al., 2003). Then, MIH was defined as the clinical appearance of morphological enamel defects involving the occlusal and/or incisal third of one or more permanent molars or incisors as result as "hypomineralisation of systemic origin." (Weerheijm, 2004) The first permanent molar enamel is affected to an extent ranging from mild to severe; in many cases the incisor enamel is affected, but often, minimally not necessarily involving a macroscopic defect of tooth. Furthermore, this specific form of developmental defects of enamel (Baroni & Marchionni, 2011) show opacities asymmetrically often distributed, with marked variation in severity within an individual and ranges from small demarcated white, yellow or brown

morphological and treatment management considerations about MIH.

suffering from this condition.

enamel that can be seen in Table 1.

Weerheijm et al., 2003)

**1.1 Definition** 

opacities (Figures 2A to 2F) to those covering much or the entire crown affecting cuspal areas and sparing the cervical areas. (Brook, 2009) CHAWLA ET AL. 2008 (Chawla et al., 2008) suggested that yellow–brown enamel defects are more severe than white–opaque ones it means that the stained degree of MIH enamel, may be used clinically to reflect the severity of the defect. (Farah et al., 2010a) In severe cases, the defective enamel is lost shortly after molar eruption, exposing underlying dentine favoring the tooth sensitivity and the dental carious lesion. (Kilpatrick, 2009)


Table 1. Differences between two developmental defects of enamel according to FDI Commission on Oral Health, Research and Epidemiology (FDI, 1982)

Molar Incisor Hypomineralization:

removed.

the enamel matrix are:

crystal growth;

**2. Morphological considerations about MIH** 

**2.1 Amelogenesis and developmental defects of enamel** 

(Smith , 1979). In other words, enamel formation occurs in three stages:

to promote mineralization and crystal elongation; and

regulation of crystal organization and growth of enamel.

1. matrix formation during which proteins involved in amelogenesis are produced; 2. calcification during which mineral content is acquired and the proteins are removed; 3. maturation during which the enamel is calcified and the remaining proteins are

The mineralization of the enamel matrix is described as a two-step process. Firstly, the ameloblasts secrete an organic matrix that is immediately mineralized to about 30% by weight. Secondly, when the full thickness of enamel has been secreted by an ameloblast, a progressive increases in mineral content begin. Smooth-ended ameloblasts remove of water and proteins from the enamel matrix, whereas ruffle-ended ameloblasts participate in the active transport of calcium and phosphate into the matrix. The principal proteins acted in

a. amelogenins (the major protein ~90% secreted into the enamel matrix) is a group of heterogeneous proteins (20-30 kDa) that are hydrophobic and rich in proline, histidine and glutamine and they are thought to play a role in the organization and regulation of

b. ameloblastins (Amelin, Sheathelin) constitutes 5-10% of the enamel matrix. It is thought

c. enamelins (60-80 kDa) are a heterogeneous group of proteins that may be involved in crystal nucleation. They are responsible for the progressive proteolytic cleavage of amelogenins. The processing of amelogenins to smaller peptides is necessary for the

According to BROOK, 2009 (Brook, 2009) in the secretory stage the enamel protein matrix deposited by the ameloblasts is predominantly formed of amelogenin (85%). At the midsecretory stage for appositional crystal growth and structural maintenance amelogenin is essential. However, while enamelin contributes less than 5% of the matrix it plays a major role in controlling the initiation of hydroxyapatite formation in early amelogenesis, being necessary for creating and maintaining enamel crystallite elongation at the mineralization front immediately adjacent to ameloblasts. The further enamel protein ameloblastin is a celladhesion molecule that maintains the differentiation stage of secreting ameloblasts and

Morphological, Aetiological, Epidemiological and Clinical Considerations 427

Tooth development is strictly genetically controlled but sensitive to environmental disturbances (Suckling et al., 1988) since teeth have been formed they do not undergo remodeling. (Brook, 2009) During dental development, a single layer of inner enamel epithelial cells undergoes a remarkable change in cell shape in preparation for the secretion of enamel extracellular matrix. These cells develop into tall ameloblasts with cellular extensions called Tomes' processes, which function during enamel matrix secretion. Following generation of the enamel layer, the ameloblasts shorten and reorganize during the transition stage; they then enter maturation, where they change histologically from ruffle-ended to smooth-ended at the location where Tomes' processes have retracted. These cells reduce the enamel protein content and increase the mineral content so that the enamel layer can develop into the hardest tissue in the body. Finally, the cells shorten further and adhere to the enamel surface until just before eruption of the tooth into the oral cavity

Fig. 2. A to F – In the same patient, note the presence of asymmetry and the different levels severity of lesions associated to the color opacities in molars and incisors.

Lately, MIH is understood as a hypocalcified subtype of enamel defect with reduced mineral content, low residual content of amelogenins and the presence of more than 16 types of proteins in affected teeth, thirteen of which are found in saliva and crevicular fluid (Kojima et al., 2000, Denny et al., 2008) and the three others (hemoglobin, albumin, complement C3) are major components of blood. Moreover, protein composition of MIH enamel varies with severity of enamel defect. (Mangum et al., 2010a)
