Planning and Care for Children and Adolescents with Dental Enamel Defects by Bernadette K. Drummond & Nicola Kilpatrick

Author:Bernadette K. Drummond & Nicola Kilpatrick
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

Composition

Enamel is made up of two phases: an inorganic (mineral) phase of hydroxyapatite crystals and an organic phase of mainly proteins and some lipids. The proteins are mainly intrinsic enamel proteins such as enamelin and amelogenin.

The inorganic component of MIH enamel has been studied extensively using a variety of methods. The conventional calcium hydroxyapatite crystals found in normal enamel is the only calcium phosphate phase present in MIH enamel [3]. The calcium and phosphate content is lower in MIH enamel than in sound enamel [23], but they have similar Ca/P ratios. However, MIH-affected enamel has increased carbon content which reflects an increase in both carbonate [2] and protein content [24]. The increase in carbonate makes the affected enamel more susceptible to dental caries because carbonated crystals dissolve more easily under caries acid attack. However, the increased protein content increases enamel resistance to acid attack, as the proteins are more resistant to acid dissolution. As a result the association between caries and MIH remains unclear.

As for other trace elements, there is probably a slightly higher amount of magnesium in MIH enamel than in sound enamel, which suggests some form of disruption to amelogenesis. However, concentrations of chlorine, strontium, sodium, and potassium in MIH enamel are comparable (or slightly higher) to those in sound enamel [9, 23].

As mentioned earlier there is an inverse relationship between the clinical appearance of the opacities seen in MIH and its mineral density, with darker lesions containing less mineral. Conversely, there is a positive correlation between the shade and the amount of protein contained in these lesions. Studies have shown that brown MIH enamel has a 15–21-fold higher protein content than sound enamel. The protein content of both white/opaque and yellow enamel is approximately eight times higher than sound enamel [21, 24]. Increases in protein content have also been reported in the hypomineralized enamel that characterizes both hypomaturation and hypocalcified amelogenesis imperfecta (AI) types (see Chap.​ 5) [25, 26]. However, while the proteins identified in AI enamel are mainly intrinsic enamel proteins (e.g., amelogenins, enamelins), those found in MIH enamel are mainly serum and blood proteins. Indeed MIH enamel has been reported to have essentially normal levels of amelogenins [27]. The main protein found in MIH enamel is albumin with other serum proteins, such as alpha-1-antitrypsin and antithrombin III also present. Hemoglobin and proteins involved in tissue injury and its repair, or in bleeding and coagulation, have also been detected, but with less abundance than serum proteins [24, 27].

The presence of serum proteins in MIH enamel is peculiar. While minute amounts of albumin and other serum proteins do enter enamel during development, they are degraded and removed during the maturation phase [28]. Only trace amounts are detected in mature sound enamel. It is unclear how such an abundance of serum proteins (and some hemoglobin) can gain access into MIH enamel. The most likely explanation is that there is “leakage” of serum (and perhaps blood) into MIH enamel during its formation. If this leakage occurs during the transition

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