Development Of Tooth Part II PDF

Development of tooth Part II Basic and Preventive Sciences Department BMC Development of tooth/Oral Biology Learning objectives At the end of the lecture student should be able to Understand and be well versed with various stages tooth formation Know the significance of hist...

Development of tooth Part II Basic and Preventive Sciences Department BMC Development of tooth/Oral Biology Learning objectives At the end of the lecture student should be able to Understand and be well versed with various stages tooth formation Know the significance of histophysiology of tooth formation Applied aspects of tooth development Anodontia and Oligodontia Decreased activity of dental lamina Anodontia is the congenital absence of tooth germ of the entire dentition. Absence of single tooth germ or multiple tooth germs is termed oligodontia. Teeth commonly found missing are upper lateral incisors, third molars and lower second premolars. Applied aspects of tooth development Supernumerary Teeth Teeth which are present in addition to the normal number are called supernumerary teeth. This occurs due to hyperactivity of the dental lamina, leading to the initiation of additional tooth buds. The most common supernumerary teeth are the mesiodens (present between two upper central incisors) and paramolars (present by the side of the molars). Applied aspects of tooth development Macrodontia and Microdontia Macrodontia is an abnormally larger tooth and microdontia is an abnormally smaller tooth. This can occur because of abnormal proliferation of the tooth germ at the bud stage and can affect a single tooth or the complete dentition. Applied aspects of tooth development Gemination and Fusion Gemination is division of tooth germ Fusion is the union of the adjacent tooth germs Occur during the cap stage of tooth development. Dens Invaginatus Abnormal invagination of the enamel organ into the dental papilla Can cause an appearance of tooth within the tooth Called dens invaginatus or dens in dente. Applied aspects of tooth development Dens Evaginatus Occurs in bell stage It is cusp-like elevation seen in the occlusal surface of premolars or molars This aberrancy occurs due to the abnormal proliferation of inner enamel epithelium into the stellate reticulum Results in a core of dentin with intervening pulpal tissue covered by enamel. With occlusal wear or fracture of this cusp-like structure, pulp exposure and can occur Applied aspects of tooth development Tetracycline Staining Tetracycline is an antibiotic which has high affinity for calcified tissue. Ingestion of this antibiotic during the mineralization of enamel and dentin can lead to discoloration. This consequent discoloration of enamel and dentin occurring at the time of tooth development is called tetracycline staining. DEVELOPMENT OF A TOOTH: HISTOPHYSIOLOGICAL PROCESS On the basis of the histo-physiological process taking place, the development of a tooth can be studied under the following stages: Initiation Proliferation Histodifferentiation Morphodifferentiation Apposition Initiation Initiation of tooth development depends on the epithelial– ectomesenchymal interaction. The dental lamina formed due to such interaction has the ability to form enamel organs of both the dentitions Lack of initiation results in the absence of a tooth, a condition called anodontia. The tooth commonly absent are the upper lateral incisors, third molars and lower second premolars (missing teeth). Initiation An abnormal initiation can result in the formation of single or multiple supernumerary teeth (Extra teeth). The most common supernumerary teeth are The mesiodens (between two upper central incisors) The Para-molars (by the side of the molars) Similarly, aberration in initiation can result in the tooth developing at abnormal locations (ovary). Proliferation The enamel organ formed due to initiation undergoes proliferation to give the crown of the tooth its final size and shape. Any disturbance in proliferation will have effects on the developed tooth depending on the stage at which the disturbance occurs. Histodifferentiation As the cells continue to proliferate, they undergo Structural, biochemical changes Prepare themselves to carry out their function e.g. deposition of organic matrix (apposition) In this process, the cells may give up some of the properties they possessed earlier, like their ability to proliferate. Seen in the bell stage just before the formation and apposition of the enamel and dentin. Histodifferentiation In the bell stage, Inner enamel epithelium influences the adjacent cells of the dental papilla They differentiate into odontoblasts which form the dentin matrix. This constitutes the histodifferentiation of odontoblasts. Then, the inner enamel epithelial cells are differentiated into the ameloblasts That form the enamel matrix. This process is called as Reciprocal induction. Histodifferentiation When there is vitamin A deficiency, the ameloblasts fail to differentiate properly Their organizing influence on the adjacent cells of dental papilla is disturbed. As a result, odontoblasts fail to differentiate properly The dentin formed by these odontoblasts is known as osteodentin. Morphodifferentiation The morphological form and shape of the tooth are determined The dentinoenamel junction and the dentinocemental junction are characteristic for different teeth and determine the shape of the crown and root They are established before the formation of the hard tissue In accordance with their shape, the formative cells deposit enamel, dentin and cementum, to give the tooth its characteristic form and size. Morphodifferentiation Disturbances occurring during the morphodifferentiation can affect the morphology of the crown or root depending on the stage at which the disturbance occurs. E.g. In the crown - the formation of supernumerary cusp, loss of cusp and peg- shaped teeth. Formation of supernumerary root Dilaceration (abnormal curvature in the root caused due to trauma) Apposition Apposition is the deposition of the matrix of dental hard tissues, characterized by alternate periods of activity and rest. It is this regular and rhythmic appositional growth that gives the tooth its final shape. Apposition involves formation of the organic matrix and its subsequent calcification or mineralization. Hypoplasia is the term used to indicate disturbances involving the matrix formation Apposition Hypocalcification or hypomineralization indicates disturbances involving the calcification or mineralization of the matrix. Various genetic and environmental factors can cause disturbances in the formation of enamel matrix leading to enamel hypoplasia. Thank You