Embryology and Dental Development Flashcards
What are syndromes?
They are systemic disorders – meaning that they show systemic manifestation.
What are the stages of pre-natal development?
- Zygote - single celled fertilised egg
- Embryo - 2-8 weeks
- Foetus - 9-birth
What is ontogeny?
It is stages of development of an individual.
What is teratology?
Study of what can go wrong during the developmental process
What are the 3 main phases in embryology?
- Phase 1 – fertilisation to 3 weeks in utero
- Phase 2 – 4-8 weeks in utero
- Phase 3 – 9 weeks to birth
What happens during phase 1 of embryonic development?
- Cell proliferation and migration, with small amount of differentiation
- Most perturbations in this phase result in embryo loss
- Fiest cell division (~24 hours) - initiation of cell-cell signalling; spatial orientation/axes of development
- Normally, cell division proceeds unchecked in the absence of external factors: exponential increase in cell number.
What is cleavage?
Cleavage – a rapid mitotic division with little net change in embryo size leading to morula then blastocyst
What is a blastocyst?
A blastocyst is a cell mass composed of external trophoblasts and embryoblasts
What is differentiation?
It is a process where cells must be competent to receive an external induction signal, competency is transient.
What happens on day 8 of embryological development?
Embryoblasts differentiates into bilaminar germ disk composed of ectodermal cells and endodermal cells
What happens on day 13 of embryological development?
Ectoderm contains amniotic cavity, mesoderm migration forms secondary yolk sac
What is gastrulation?
It is when the bilaminar disc in the embryo turns into a trilaminar disc during week 3
What happens in Phase 2 of embryotic development?
- Predominantly cellular differentiation and division, and organismal morphogenesis
- Histo-differentiation and organogenesis
- Pertubations in this phase can lead to significant congenital abnormalities
- Ectoderm give rise to neural crest tissues and nervous system, as well as external epithelium
- Mesoderm give rise to a range of internal tissues
- Endoderm forms the gut
- Embryo folding; rosto-caudal and lateral axes
What is the neural plate?
Neural plate it a thick plate of ectoderm along the dorsal midline of the early vertebrate embryo that gives rise to the neural tube and neural crest.
How does the neural plate develop?
Neural plate develops cranially
Where does the neural plate and neural crest forms?
The ectoderm
What happens on day 21 of the embryological develop?
- Embryo folding initiated
- Lateral folding results in ectoderm lining all outward-facing surface of the embryo – forms surface epithelium
- Rostro-caudal folding – head fold gives rise to primitive stomodeum
- Stomatodeum separated from gut by buccopharyngeal membrane
What gives rise to all components of the head and face?
The rostral head fold of the embryo
What is the rostral head fold composed of?
Frontal prominence within which the anterior neural tube forms the brain; and six branchial arches
What are branchial arches?
They are associated with formation of the face, palate, tongue, skull and dental arches. Branchial arches are formed in pharyngeal wall from proliferating lateral plate of mesoderm. They consist of the cartilage rod, muscular component, vascular component and neural component. First three are important in development of the face, mouth and tongue.
What does the first branchial arch give rise to?
- Meckel’s cartilage
- Muscles of mastication
- Maxillary artery and part of external carotid artery
- Trigeminal nerve
- Maxillary process
How does the maxilla form?
The maxilla forms in the embryo as a result of bulging of the first branchial arch
When does the face form?
The face forms during the 24-38 days post conception
What are the steps in formation of the palate?
- Common oronasal cavity – basically no maxilla
- Primary palate – the top bit of the palate
- Secondary palate – fusion of shelves from maxillary processes, directed downwards initially, tongue withdraws and shelves elevate, closure of secondary palate, loss of epithelium
What is the importance of Meckel’s cartilage?
It acts as a scaffold for the mandible development
What are some the triggers of congenital defects?
- Genetic factors
2. Environmental factors
What are the reasons to know the sequence of dental development?
- Understand the ‘normal’
- Age estimation
- Assess timing and duration of developmental disturbances on teeth
- Paedodontics/orthodontics
- Forensic odontology
What is the average timeline of dental development?
6 weeks in utero to late teenage years
How can we study timing/sequence of tooth calcification?
- Histologically
- Radiologically
- Clinically
What is the sequence of events in tooth development?
- Fomation of dental crypt
- Calcification of cusps
- Calcifiction of crown
- Calcification of roots
- Emergence
- Closure of the apical canal of roots
What is the sequence of primary tooth calcification?
- Central incisors
- First molars
- Second molars
- Canines
- Second molars
When does mineralisation begin?
3-6 months in utero
When does the calcification of permanent teeth occur?
All occurs post-natally
What is the sequence of initial calcification in permanent dentition?
- Sixes - at birth
- One’s – 3 months
- Mandibular Two’s + Canines – 5 months
- Maxillary Two’s – 1 year
- Four’s – 1.5-2.5 years
- Five’s + Seven’s – 2.5-3.5 years
- Eight’s – 7-12 years
What can create variability in tooth calcification?
- Individuals - agenesis
- Sex - females get their permanent dentition earlier
- Ethnicity
What is tooth eruption?
It is movement of a developing tooth initiated by initial formation of the root.
When does the shedding of primary teeth occur?
Between 5-12 years
What is usually the first permanent tooth to occur?
Usually the first molars erupt first
What are some general factors for eruption & emergence?
- Socio-economic status
2. Physical status
What are some general disturbances for eruption & emergence?
- Genetic conditions
2. Endocrine conditions
What are the local factors for eruption & emergence of teeth?
- Premature extraction of primary teeth
- Early extraction of 6 or 7 affects 8
- Amount of space – Ieeway space
- Crowding, inclination and obstacles
