Embryology of the Crown PDF Revision

Embryology; Crown  Embryology of the crown = Formation of the tissues within Disruption can the tooth crown. affect quality or...

Embryology; Crown  Embryology of the crown = Formation of the tissues within Disruption can the tooth crown. affect quality or quantity of tooth tissues. Amelogenesis Dentinogenesis Pulp formation Enamel Dentine Coronal pulp Amelogenesis - (4 stages) Amelogenesis and Process of enamel formation. dentinogenesis Each stage is defined by the morphology (shape) and function of the continue in parallel ameloblasts. during crown Inner enamel epithelium cells differentiate into ameloblasts. embryology. 1. Pre-secretory stage Relates to dentinogenesis. Pre- Odontoblasts secrete pre-dentine matrix. ameloblast Ameloblast Pre-dentine matrix mineralises (goes hard). This causes basement membrane to break down. Dentine contacts pre-ameloblasts. Pre-ameloblasts differentiate into ameloblasts ready to start amelogenesis. 2. Secretory stage Ameloblast Ameloblasts develop a Tomes’ process (cone shaped structures). Tomes’ process secretes the enamel matrix. Tomes' process Enamel matrix is organic (proteins) and inorganic (crystal minerals) = soft. Ameloblasts travel outwards, away from forming dentine/odontoblasts Enamel matrix (towards outer edge of tooth). Pre-dentine matrix 3. Transition stage Once ameloblasts have reached full thickness of enamel they change. Change shape by retracting Tomes’ process. Retracted Tomes' Change function as can no longer secrete enamel matrix. process New function of ameloblasts - maturing enamel. 4. Maturation stage Ameloblasts mineralise/harden the enamel matrix to 96%. Organic proteins allow for inorganic crystals to grow, harden and solidify. Amelogenesis is complete - enamel formed. Enamel New function of ameloblasts - protective stage ready for eruption. Dentine Dentinogenesis Process of dentine formation. Starts before amelogenesis. Continues throughout life. Process Starts at basement membrane - future dento-enamel junction (DEJ). Odontoblasts secrete pre-dentine matrix. Pre-dentine matrix is mineralised/hardened in spheres - 70-75% organic. Odontoblasts travel inwards (towards border of the pulp). Cytoplasmic extension embedded into pre-dentine and dentine - Odontoblast process. Dentine can repair itself and form throughout life. Clinical significance Odontoblasts live for life of tooth, pick up stimuli and sensations and that trigger secondary and tertiary dentine formation. Coronal pulp formation During dentinogenesis, ectomesenchyme cells in centre of the dental papilla, form the pulp tissue in the crown (coronal pulp). Helps to provide nutritional source for the odontoblasts. Includes: blood vessels, lymph tissue, nerves, fibroblasts, stem cells and collagen. Pattern of formation = Amelogenesis and dentinogenesis start at the cusp tips and incisal edges of the future deno-enamel junction (DEJ). Incremental lines = Repeated cycles of matrix secretion and mineralisation (might be visible is there is disturbance). Before tooth eruption: After tooth eruption: Enamel complete. No more enamel forms. Ameloblasts adopt new function to protect. Ameloblasts lifecycle complete. Primary dentine complete. Secondary dentine forms slowly throughout life. Odontoblasts settle at periphery of pulp. Odontoblasts live at periphery of pulp. Disturbances in the processes Very complex processes. Disruption can affect quality or quantity of enamel - developmental anomalies. As enamel forms before tooth erupts, it is unable to repair or form new enamel - higher risk of oral diseases. Examples: Amelogenesis imperfecta Enamel hypo-mineralisation Enamel hypoplasia Fluorosis