C1 Oral Histo (An overview of oral tissues)

• The tooth is formed from the ectoderm and ectomesenchyme.
• Apart from light microscopy, tissues can be examined using electron microscope, fluorescent microscope, confocal laser scanning microscope, and autoradiography techniques for better recognition of cellular details, functions, and the series of events that take place within them.
• The enamel is derived from the enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum (primitive oral cavity).
• Epithelial mesenchymal interactions take place to determine the shape of the tooth and the differentiation of the formative cells of the tooth, and the timing of their secretion.
• The ectomesenchymal cells which are closer to the inner margins of the enamel organ differentiate into dental papilla and the ectomesenchymal cells closer to the outer margins of the enamel organ become dental follicles.
• Dentin and pulp are derivatives of dental papilla while cementum, periodontal ligament, and alveolar bone are all derivatives of dental follicle.
• The cells that form these tissues have their names ending with “blast.” Thus, ameloblast produces enamel, odontoblast produces dentin, cementoblast produces cementum, and osteoblast produces bone.
• These synthesizing cells have all the features of a protein-secreting cell —well-developed ribosomes and a rough endoplasmic reticulum (ER), Golgi apparatus, mitochondria, and a vesicular nucleus, which is often polarized.
• The cells that resorb the tissues have their names ending with “clast.” Thus, osteoclast resorbs bone, cementoclast resorbs cementum, and odontoclast resorbs all the dental tissues.
• The “clast” cells have a similar morphology in being multinucleated giant cells.
• Their ultrastructural features include numerous lysosomes and ingested vacuoles.
• Dentin is the first hard tissue of the tooth to form.
• Enamel starts its formation after the first layer of dentin has formed.
• The enamel formation is from its junction with dentin outward, first in the cuspal/incisal and later in the cervical regions.
• Dentin formation is similar, but from the dentinoenamel junction, the formation is toward the pulp.
• Cementum formation occurs after the form, size, shape and number of roots is outlined by the epithelial root sheath and dentin is laid down in these regions.
• Formation of enamel, dentin, and cementum takes place as a daily event in phases or in increments, and hence they show incremental lines.
• In dentin and cementum formation, a layer of uncalcified matrix forms first, followed by its mineralization.
• While in enamel formation, enamel matrix is calcified, its maturation or complete mineralization occurs as a secondary event.
• Mineralization occurs as a result of supersaturation of calcium and phosphorus in the tissue fluid.
• The formative cells concentrate the minerals from calcium phosphate (apatite) and secrete them into the organic matrix, in relation to specific substances like collagen, which act as attractants or nucleators for mineralization.
• The mechanism of mineralization is quite similar in all the hard tissues of tooth and in bone.
• Enamel is the hardest tissue in the human body.
• Enamel is the only ectodermal derivative of the tooth.
• Inorganic constituents account for 96% by weight and they are mainly calcium phosphate in the form of hydroxyapatite crystals.
• The integrity of the mucosa is interrupted by the teeth to which it is attached.
• The permanent successor teeth during the eruptive movement cause pressure on the roots of deciduous teeth and induce resorption of the roots.
• At the time of tooth eruption, the roots are about half to two-thirds complete.
• The odontoclast, which has a similar morphology to osteoclast and participates in this event, has the capacity to resorb all dental hard tissues.
• The ability of bone, but not cementum, to form under tension and resorb under pressure makes orthodontic treatment possible.
• The lymph node contains a variety of defense cells.
• The maxillary posterior teeth are related to the maxillary sinus in that they have a common nerve supply and that their roots are often separated by a thin plate of bone.
• The fibrous layer that lines the articular surface of the temporomandibular joint is continuous with the periosteum of the bones.
• The deciduous teeth are replaced by permanent successor teeth as an adaptation to the growth of jaws and due to the increased masticatory force of the masticatory muscles in the process of shedding.
• Just before the tooth makes its appearance in the oral cavity, the epithelium covering it fuses with the oral epithelium.
• Root growth, fluid pressure at the apex of the erupting teeth, and dental follicle cell contractile force are all shown to be involved in the eruption mechanism.
• The mucosa in these regions is a functional adaptation to mastication; hence, they are referred to as masticatory mucosa.
• The mucosa is firmly attached to the periosteum of hard palate and to the alveolar process (gingiva).
• The bony crypt forms and resorbs suitably to adjust to the growing tooth germ and later to its eruptive movements.
• The fibrous capsule, which covers the joint, is lined by the synovial membrane.