Tooth development Flashcards
From which arch do the mandibular and maxillary arches develop?
The first brachial arch, by day 23
Which dental structures develop from the ectoderm or outer embryonic germ layer?
The oral epithelium, dental lamina and enamel organ
Which dental structures develop from the mesoderm?
The dental papilla and sac
Describe the bud stage of tooth development
An invagination of the dental lamina at the sites corresponding to the deciduous dentition.
Successional teeth develop as lingual extensions of the dental lamina buds. Where there are no deciduous teeth the permanent dentition develops directly from the dental lamina.
in late bud stage mesenchymal cells adjacent the IEE start to develop the dental papilla and sac.
Describe the cap stage of tooth development
The cap stage is defined by the formation of a concavity at the deepest portion of the bud.
The enamel organ becomes comprised of three parts the IEE- inner enamel epithelium, the SR stellate reticulum and the OEE outer enamel epithelium.
What structures arise from the dental sac
The cementum, the periodontal ligament and some alveolar bone.
What structure arises from the dental papilla?
The dentin and pulp
Which processes form the upper lip?
the two medial nasal processes and the two mxillary processes.
When does a cleft lip occur?
When migration fails and there is separation between the medial nasal and maxillary processes due to overstretching and tearing of the the connective tissue union between them
The incisive bone ( primary palate) is formed solely by which process?
the medial nasal process
What are the stages of enamel formation?
Mineralization - where all of the crystal within the rods is laid down at the same time
Maturation - when the crystals grow in size and become tightly packed. A failure at this point will result in poorly mineralised enamel ( less than 96% mineralisation)
The secondary palate is formed by which processes?
the left and right maxillary processes
How is the bell stage of development of the enamel organ defined?
The onset of the bell stage occurs when a fourth layer the SI stratum intermedium emerges between the IEE and the SR.
IEE cells become tall and form preameloblasts
The peripheral cells of the dental papilla become short and cuboidal and form odontoblasts.
At what point and due to what stimulation does mineralized tissue in the tooth begin to form?
At the end of the bell stage as the odontoblasts move away from the preameloblasts they cause a polarity shift and the PA’s become ameloblasts and begin secretion of the enamel matrix.
What final two functions of the ameloblasts occur after compression of the SR and SI by expansion of the rods during maturation causing the ameloblasts to make contact with the OEE.?
- a protective cuticle- Nasmyth’s membrane is laid down on top of the enamel ( lasts weeks to months following eruption).
- Once the cuticle is formed the ameloblasts merge with the OEE to form the reduced enamel epithelium. This forms the ginigval attachment at the bottom of the gingival sulcus.
What is amelogensis imperfecta?
Any genetic and/or developmental anomaly which causes abnormal enamel formation or maturation.
What is enamel hypoplasia?
Inadequate deposition of enamel matrix- the enamel is generally thinner than normal but is mineralised normally.
What is enamel hypomineralisation?
The enamel is poorly mineralised and is generally discoloured.
What constitutes the pulp?
nerves, blood vessels, lymphatics, fibroblasts, collagen fibres, undifferentiated mesenchymal cells. other connective tissue cells and odontoblasts.
NOTE: lymphatics is questionable based on Martin & Gasse.
What two layers become Hertwigs epithelial root sheath?
The inner enamel epithelium and the outer enamel epithelium where they meet at the cervical loop and the SI and SR are missing.
What determines the number of roots a tooth will have?
The growth pattern of the epithelial diaphragm. The point at which the diaphragm meets will be the apex of the tooth in a single rooted tooth and the furcation in a multi -rooted tooth
What stimulates odontoblasts to form?
The root sheath making contact with the dental papilla stimulates differentiation of cells into odontoblasts.
What are the rests of Malassez?
HERS cells which have moved away from the dentin and become trapped in the periodontal ligament
What is an enamel pearl and how is it formed?
An enamel pearl is formed when HERS cells fail to dissolve and remain in contact with dentin they can convert to ameloblasts secreting enamel onto the root forming small balls of enamel in the root known as enamel pearls.
