|dc.description.abstract||Several studies have investigated possible aetiological factors for molar-incisor hypomineralisation (MIH). Despite that, the aetiology and the pathogenesis of MIH are still not understood. With knowledge gained from the previous investigations at the Faculty of Dentistry, University of Otago, the current study built on that knowledge and aimed to investigate the possible role of serum and blood proteins in the development of MIH. The hypothesis of this study was that MIH is of traumatic origin resulting in serum and blood to leak into developing enamel and interfere with its mineralisation.
The range of the proteins present in MIH and sound enamel was assessed biochemically. Small sections of MIH and sound enamel were dissolved in 20% trichloroacetic acid that dissolved the mineral phase and precipitated the proteins. After re-suspension in sodium dodecyl sulphate (SDS), the proteins were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Tryptic fingerprint tandem mass spectrometry (MS/MS) was performed on excised bands from the SDS-PAGE. Several new proteins were identified in sound enamel. Most of the proteins identified in MIH enamel were also present in sound enamel. The proteins unique to MIH enamel were known to play a role in tissue injury and repair, and in bleeding and coagulation. Due to high keratin and collagen contamination it was not possible to draw more conclusions.
Direct immunofluorescence (with quantum dots a fluorescent probe) on cut sections from MIH and sound enamel was used to map the distribution of serum albumin and haemoglobin in the cut sections. The albumin and haemoglobin were shown to be present in MIH enamel but not in sound enamel. A gradient of these proteins appeared to exist from deep enamel, close to the dentine-enamel junction, to outer enamel close to the surface. The source of albumin and haemoglobin is most likely from the serum/blood reaching enamel during its formation, and not from saliva after gaining access into MIH enamel after tooth eruption. This is because salivary α-amylase could not be detected in MIH or sound enamel, ruling out the possibility of saliva being the source of albumin and haemoglobin.
To understand the distribution of the proteins in the organic matrix of MIH enamel, histopathological investigation of decalcified cut sections from sound and MIH enamel demonstrated the presence of a very dense organic matrix in MIH enamel. The matrix constricted the enamel rods, and sometimes intervened between the rods as a thick sheath.
Based on the findings of this study it was not possible to accept or reject the study hypothesis that MIH is of traumatic origin. A model, developed based on the findings of this study, suggests that serum/blood proteins leak into MIH enamel during the maturation stage of enamel development in the occlusal part of the first permanent molar. Since the cervical part would still be passing through the less sensitive secretory stage, it remains unaffected.||