Amelogenesis is the formation of tooth enamel, which is carried out in two phases by ameloblasts. A secreting phase is followed by a mineralizing phase that hardens the enamel. Enamel formation disorders make teeth more susceptible to decay and inflammation and are often treated with crowning.
What is amelogenesis?
Amelogenesis is the formation of tooth enamel, which is carried out in two stages by ameloblasts. Tooth enamel is the hardest tissue in the human body. It surrounds the dentine and performs a protective function. A large amount of enamel is located in the area of the tooth crowns in particular. Around 97 percent of the body’s own substance consists of inorganic materials such as calcium or phosphate. Only about three percent of tooth enamel is organic. Tooth enamel is therefore often referred to as dead tissue without the ability to regenerate. This is related to the way tooth enamel is formed, which is also known as amelogenesis. Amelogenesis is carried out in the crown stage of ontogenetic development by the ameloblasts. These are specialized cell types from the surface ectoderm that form the enamel and adhere to the formed layer from the outside after the work is completed. After the teeth have erupted, they are already chewed off. For this reason, enamel is a tissue without multiple regenerative capacity, such as in wound healing. However, remineralization is possible.
Function and task
Enameloblasts or ameloblasts correspond to cylindrically structured cells with a hexagonal cross-section. Their diameter is around four µm. They reach a length of up to 40 µm. They secrete two main proteins. In addition to enamelin, they produce amelogenin. In the course of ontogenetic development, these substances deposit salts and mineralize to form hydroxyapatite. In this way, they become tooth enamel. At the secretory end of each ameloblast sits a wedge-like process. This element of the cells is called the Tomes process and is responsible for the alignment of individual prisms in the enamel. Once enamel formation stops, all ameloblasts become squamous cells and form the marginal epithelium. From this point on, they no longer have the ability to divide, but lie statically on the outer layer of the enamel. After tooth eruption, they lose their authority and are therefore lost. During tooth eruption, they migrate piece by piece in the direction of the sulcus and eventually reach the furrow between the gum and the tooth, where they are rejected. Amelogenesis takes place in the so-called crown stage of ontogenetic development. The formation of dentin and the formation of enamel are subject to reciprocal induction. The dentin must always be formed before the enamel. The steps of amelogenesis just described are sometimes divided into two phases. During the secretory phase, the proteins including the organic matrix are formed, resulting in an incompletely mineralized enamel. Only after the subsequent maturation phase is mineralization considered complete. In the first phase, basic mineralization takes place by means of enzymes such as alkaline phosphatase. Usually, the first mineralization occurs by the fourth month of pregnancy. The enamel formed in this phase spreads outward bit by bit. The secreting phase is thus completed. In the mature phase, the ameloblasts take over transport tasks. They transport the enamel substances relevant for production to the outside. The transported substances are mainly proteins, which are used for the complete mineralization of the enamel at the end of the maturation phase. The most important of these proteins are considered to be the substances amelogenin, enamelin, tuftelin and ameloblastin.
Complications
Amelogenesis imperfecta is a congenital defect that destroys tooth enamel. It is a rarely occurring disease and has various manifestations. A detailed anamnesis helps to avoid serious complications. Already in the milk teeth there is a massive abrasion and tooth loss. The intake of food becomes increasingly difficult, painful inflammations and fever cause the child to suffer and the acquisition of speech can only be poorly developed.The teeth begin to chip, react hypersensitively to temperature differences and the symptom is often accompanied by growths on the gums and gingivitis. By means of differential diagnostics, the diagnosis is ensured and early therapeutic interventions are initiated. This method is especially important for young children, so that the dentition can develop in a functional way. The same applies to adults affected by tooth loss. Here, in addition to the loss of bite strength and bite height, the aesthetic aspect comes into play. The enamel density is measured on the basis of X-ray examination. Depending on the advanced stage, the teeth, and in children even the milk teeth, are fitted with strip or steel crowns or fillings made of plastic, all-ceramic or zirconium dioxide. In this way, they are preserved as long as possible. Amelogenesis imperfecta can present the patient with a great deal of psychological and physical stress, but complications can be avoided if diagnosed in time.
Diseases and medical conditions
Various complaints can occur during the formation of tooth enamel. Most often, these complaints are referred to as enamel formation disorders or amelogenesis imperfecta. The cause of such disorders is as yet largely unknown. The disorders usually manifest themselves in early childhood at the latest and are manifested by one or more teeth that, in extreme cases, have hardly any enamel or even none at all. The reason for this is the subject of speculation. Some scientists assume that disorders in enamel formation are predominantly related to external factors. For example, severe infections in infancy are speculated to contribute to enamel formation disorders. The same is possibly true for certain medications. On the other hand, internal factors have not yet been ruled out. These include, for example, genetic predispositions. Mutations in the coding genes of the ameloblasts or the amelogenetically relevant substances are also not excluded. Medical science has so far only agreed on causative malfunctions of the ameloblasts. Enamel hypoplasia makes the patient’s teeth more susceptible to caries and wear. In addition to caries, inflammations, such as root inflammation, are conceivable consequences. Damaged teeth are usually crowned therapeutically to produce a healthier appearance, chewing ability and artificial protection. In particularly severe cases, after hypoplasia of the enamel, a complete rehabilitation of the dentition is required, which may result in a complete crowning. The affected teeth can also be initially treated for secondary disease and then sealed. Under certain circumstances, severely affected teeth with too little enamel may also be extracted. If root inflammation has developed as a result of the formation disorder, root canal treatment is performed first. The tooth must be opened for this so that the affected tissue can be removed. During a detailed cleaning of any root canals, the bacteria causing the inflammation are removed. Usually, an antibiotic medication is introduced into the affected tooth. Only if there is a recurrence should removal of the affected tooth be considered. If the enamel formation disorder is detected early enough and crowned, often no subsequent tooth disease occurs.
