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
What initiates odontogenesis and when does it occur?
Odontogenesis is initiated in the 6th week of development with the formation of primary epithelial bands, which divide into dental lamina (for teeth) and the vestibular lamina (for the vestibule)
What happens in the 7th and 8th weeks of development regarding tooth formation?
In the 7th week, the epithelial band divides into the vestibular lamina (buccally) and the dental lamina (lingually). By the 8th week, swellings called tooth germs develop at the end of the dental lamina, surrounded by condensed ectomesenchyme.
How do deciduous and permanent teeth develop from the dental lamina?
Deciduous teeth develop directly from the dental lamina. Permanent incisors, canines, and premolars develop from a successional dental lamina on the lingual aspect of the deciduous tooth germ. Permanent molars develop from an accessional dental lamina, which extends posteriorly.
What are the five histological identifiable stages of odontogenesis?
The five stages are: bud stage, cap stage, bell stage, apposition, and maturation.
What occurs during the bud stage of odontogenesis?
During the bud stage, the dental lamina forms a bud that penetrates the ectomesenchyme. The epithelial cells show little change, and the ectomesenchyme condenses around the bud.
Describe the cap stage of odontogenesis.
In the cap stage, the epithelial bud invaginates to form a cap shape, surrounding the dental papilla. The enamel organ, dental papilla, and dental follicle begin to differentiate, marking the start of morphogenesis and histogenesis.
What are the main cellular processes involved in odontogenesis?
The main cellular processes are: initiation, proliferation, differentiation, morphogenesis, and maturation.
What happens during the apposition and maturation stages?
During apposition, the dental hard tissues (enamel and dentine) are secreted. In maturation, these tissues undergo mineralization to reach their final form.
What are the key features of the bell stage in odontogenesis?
The bell stage is characterized by the enamel organ taking a bell shape with distinct layers: inner enamel epithelium, stratum intermedium, stellate reticulum, and outer enamel epithelium. The dental papilla and follicle continue to develop, and the dental lamina disintegrates. Transitory structures such as the enamel knot, cord, and niche may be present.
What is the role of initiation in odontogenesis?
Initiation involves reciprocal induction between the oral epithelium and ectomesenchyme, setting off the tooth development process through various signaling mechanisms.
How does proliferation contribute to tooth development?
Proliferation involves controlled cell growth that helps in shaping the tooth through differential rates of cell division in specific areas.
What is differentiation in the context of odontogenesis?
Differentiation is the process where cells become specialized, altering their shape and organelle composition to perform specific functions in tooth development.
Explain morphogenesis in odontogenesis.
Morphogenesis is the process by which the tooth attains its specific shape, facilitated by differential cell proliferation and inhibition in various regions.
What does maturation entail in odontogenesis?
Maturation involves the final mineralization of dental hard tissues, allowing the tooth to achieve its adult function and size.
What controls tooth development during the cap stage?
The dental papilla (ectomesenchyme) appears to control tooth development during the cap stage, as evidenced by experimental recombinations where the type of tooth formed depends on the origin of the dental papilla.
What are the field model and clone model in tooth patterning?
The field model suggests that factors for tooth shape reside in the ectomesenchyme in graded fields for each tooth type. The clone model proposes that each tooth class derives from a clone of ectomesenchymal cells programmed by the epithelium to produce specific tooth patterns.
How does the clone model explain tooth type determination?
The clone model suggests that each tooth type is derived from a clone of ectomesenchymal cells that are programmed early by the epithelium. Experimental evidence shows that the ectomesenchyme dictates the tooth type.
What is the role of pre-migratory neural crest cells in odontogenesis?
Pre-migratory neural crest cells give rise to the ectomesenchyme, which is crucial for tooth development and is influenced by the overlying epithelium.
What is amelogenesis?
Amelogenesis is the complex process of enamel formation, involving the secretion and maturation of an enamel matrix by specialized cells called ameloblasts.
It begins with the secretion of an organic matrix that mineralizes up to 30% during initial stages, followed by a maturation phase where the matrix is broken down and replaced with minerals, reaching up to 96% mineralization.
What are the main stages of the ameloblast lifecycle?
The ameloblast lifecycle consists of three primary stages: Presecretory, Secretory, and Maturation, with a subsequent Protective Stage.
Each stage is marked by distinct cellular activities and protein expressions critical to enamel development.
What happens during the Morphogenetic Phase of the Presecretory Stage?
The Morphogenetic Phase occurs during the bell stage of tooth development, determining the tooth’s shape.
Inner Enamel Epithelium (IEE) cells are cuboidal with poorly developed organelles, and a basal lamina separates them from the Dental Papilla (DP).
What cellular changes occur in the Histodifferentiation Phase?
In the Histodifferentiation Phase, IEE cells differentiate into preameloblasts, transitioning from a cuboidal to a columnar shape.
The basal lamina disintegrates, enabling direct contact between predentine and preameloblasts, triggering their full differentiation into secretory ameloblasts.
What occurs in the Initial Secretory Stage without Tome’s Process?
In the Initial Secretory Stage, ameloblasts begin secreting enamel proteins before developing a Tome’s process.
These proteins form a layer of rodless (aprismatic) enamel that mineralizes almost immediately up to 30%.
How does the Main Secretory Stage with Tome’s Process work?
During the Main Secretory Stage, ameloblasts develop a Tome’s process, enabling the secretion of enamel rods and interrod enamel.
A narrow rod sheath, rich in organic material, separates the rods from interrod enamel.
What are the key proteins in the Secretory Stage and their roles?
Three key proteins dominate the Secretory Stage:
* Amelogenin (AMELX, AMELY)
* Ameloblastin (AMBN)
* Enamelin (ENAM)
Amelogenin is the main enamel protein, Ameloblastin is prominent in newly formed enamel, and Enamelin is critical for enamel structure.
What happens during the Transitional Phase of the Maturation Stage?
The Transitional Phase marks the shift from secretion to maturation, with ameloblasts undergoing significant morphologic changes.
Approximately 25% of ameloblasts die during this phase, reflecting the intense cellular turnover.
What is modulation, and how does it contribute to enamel maturation?
Modulation involves cyclic changes in ameloblast apical surfaces every 8 hours, alternating between ruffle-ended and smooth-ended states.
Ruffle-ended ameloblasts introduce inorganic material to promote crystal growth, while smooth-ended ameloblasts remove water and organic material.
What are the key proteins in the Maturation Stage and their significance?
Two key proteins emerge in the Maturation Stage:
* Amelotin (AMTN)
* Odontogenic Ameloblast-Associated (ODAM)
Amelotin’s function is unclear, while ODAM is linked to periodontal integrity.
What is the role of the Protective Stage?
In the Protective Stage, ameloblasts form the reduced enamel epithelium to shield the fully mineralized enamel until tooth eruption.
This stage ensures the enamel remains intact and protected post-mineralization.
How do ameloblasts change across their lifecycle?
Ameloblasts undergo distinct changes throughout their lifecycle, from cuboidal IEE cells to columnar preameloblasts, to secretory ameloblasts, and finally to the protective state.
Each phase is characterized by specific cellular and morphological changes.
Which genes and proteins are critical in amelogenesis?
Key genes and proteins in amelogenesis include:
* Amelogenin (AMELX, AMELY)
* Ameloblastin (AMBN)
* Enamelin (ENAM)
* Amelotin (AMTN)
* Odontogenic Ameloblast-Associated (ODAM)
Each plays a significant role in enamel formation and structural integrity.
What begins after crown formation and coincides with tooth eruption?
Root Development
Root development is essential for the proper positioning and stability of teeth.
Which tissue gives rise to cementum, periodontal ligament, and alveolar bone?
Dental Follicle
The dental follicle plays a critical role in the formation of supporting structures around the tooth.
What guides root formation during tooth development?
Epithelial Root Sheath (Hertwig’s)
Hertwig’s Epithelial Root Sheath is crucial for the correct morphology of the tooth root.
What is the process of cementum formation called?
Cementogenesis
Cementogenesis is key for anchoring teeth to the jaw via the periodontal ligament.
What forms the cervical loop during root formation initiation?
The junction of outer enamel epithelium (OEE) and inner enamel epithelium (IEE)
This structure is essential for the subsequent development of the root.
What induces dental papillae cells to differentiate into odontoblasts?
Hertwig’s Epithelial Root Sheath (HERS)
This process is vital for the production of root dentine.
What occurs after dentinogenesis begins in root formation?
Root Sheath Fragmentation
This process allows for interaction between dental follicle cells and the dentin surface.
What do dental follicle mesenchymal cells differentiate into during cementum formation?
Cementoblasts
Cementoblasts are responsible for laying down cementum, which is crucial for tooth stability.
What are the three layers of the dental follicle?
Inner layer, Outer layer, Intermediate layer
Each layer has distinct roles in tooth development and support.
What are the Epithelial Rests of Malassez (ERM)?
Fragments of HERS that persist in the periodontal ligament
ERM are involved in periodontal repair and can potentially form odontogenic cysts.
True or False: Multi-rooted teeth have root division occurring at sites of high vascularity.
False
Root division occurs at sites of low vascularity, leading to the formation of multiple roots.
What growth factor promotes cell differentiation and cementogenesis?
Transforming Growth Factor beta Superfamily (e.g., BMPs)
BMPs are crucial for various developmental processes, including those in the periodontium.
Which adhesion molecule promotes mineralisation?
Bone Sialoproteins
These molecules are essential for the proper mineralization of bone and cementum.
What role do collagens play in periodontal tissues?
Structural roles
Collagens provide the framework necessary for the integrity and function of periodontal tissues.
Fill in the blank: _______ prevents ectopic calcification.
Matrix Gla Protein
This protein plays a significant role in regulating mineralization processes.
Which transcription factors drive cementoblast differentiation?
Runx-2 & Osterix
These factors are also involved in osteoblast differentiation, highlighting the similarities between these cell types.
What are the processes involved in tooth eruption?
- Enamel covered by reduced enamel epithelium
- Overlying bone resorbs
- Outer cells of reduced enamel epithelium proliferate
- Fusion with oral epithelium
These processes are crucial for the proper emergence of teeth into the oral cavity.
What are the clinical and radiographic features of abnormalities of tooth development?
Outline and recognize the features
Clinical features can include tooth discolouration and sensitivity, while radiographic features may show abnormal root shapes or pulp chamber sizes.
What is the pathogenesis of abnormalities of tooth development?
Describe the process of tooth development
Involves stages from primary epithelial band to tooth eruption.
List the stages of odontogenesis.
- Formation of primary epithelial band
- Down growth of dental lamina
- Development, differentiation, and morphogenesis of tooth bud
- Bud stage
- Cap stage
- Bell stage
- Crown formation
- Dentinogenesis
- Amelogenesis
- Root formation
- Tooth eruption
What disturbances can occur during the initiation stage of odontogenesis?
- Andontia
- Supernumerary teeth
What disturbances can occur during the bud stage of odontogenesis?
- Microdontia
- Macrodontia
What types of abnormalities can occur during the cap stage of odontogenesis?
- Dens in dente
- Gemination
- Fusion
- Rubercle
What conditions are associated with the apposition and maturation stages of odontogenesis?
- Amelogenesis imperfecta
- Dentinogenesis imperfecta
- Concrescence
- Enamel pearl
What are the categories of defects in tooth development?
- Localised Developmental Defects of Teeth
- Acquired Defects
- Morphological Abnormalities
- Multisystem Genetic Disorders
Define Amelogenesis Imperfecta.
Genetic condition affecting enamel matrix proteins
Involves genes like Ameloblastin and Enamelin.
What is the prevalence of Amelogenesis Imperfecta?
1:700 to 1:14,000
What are the characteristics of enamel in Amelogenesis Imperfecta?
- Hypoplastic
- Hypomineralised
- Combination of both
What are the types of Amelogenesis Imperfecta?
- Hypoplastic Amelogenesis Imperfecta
- Hypomaturation Amelogenesis Imperfecta
- Hypocalcified Amelogenesis Imperfecta
What are the clinical features of Hypoplastic Amelogenesis Imperfecta?
Inadequate matrix formation, pitted or thin enamel
Enamel is hard and translucent.
What are the clinical features of Hypomaturation Amelogenesis Imperfecta?
Normal enamel on eruption, opaque appearance, soft and vulnerable
Colors can include white and brown-yellow.
What are the clinical features of Hypocalcified Amelogenesis Imperfecta?
Normal enamel matrix quantity, poor calcification, opaque and chalky appearance
Stains and wears rapidly.
What is Dentinogenesis Imperfecta?
Uncommon defect of dentine formation due to mutations in dentine sialoprotein (DSPP)
Inheritance is autosomal dominant.
What are the clinical features of Dentinogenesis Imperfecta?
- Normal contour at eruption
- Translucent or amber-like hue
- Enamel weakly attached
What are the radiographic features of Dentinogenesis Imperfecta?
- Short, blunt roots
- Partial or total obliteration of pulp chambers
What is Dentinal Dysplasia?
Rare autosomal dominant disease affecting dentine
Types include Type I (Rootless Teeth) and Type II (Coronal Dentine Dysplasia).
What is Regional Odontodysplasia?
Localized disorder affecting a group of teeth
Most often affects maxillary teeth.
What are the disturbances in tooth number?
- Anodontia
- Hypodontia
- Supernumerary teeth
What are common teeth affected by isolated hypodontia?
- 3rd molars
- 2nd premolars
- Maxillary lateral incisors
Define Fusion in dental abnormalities.
Union between dentine and/or enamel of two or more separate developing teeth
Define Gemination in dental abnormalities.
Partial development of two teeth from a single tooth bud following incomplete division
Define Concrescence in dental abnormalities.
Roots of one or more teeth united by cementum after crown formation
Define Dilaceration.
Acquired developmental anomaly caused by trauma resulting in angulated root
What is Dens in Dente?
Inward folding of the enamel organ into the dental papilla
Forms an enamel-lined opening from pulp to tooth surface.
What are the steps in the diagnostic process for dental abnormalities?
- History
- Examination
- Investigations
- Diagnosis
What techniques are used in dental examination?
- Inspection
- Palpation
- Percussion
What should be included in the dental history questions?
- Dental and systemic medical history
- Teeth
- Bones
- General health
- Febrile disease
- Fluoride intake
What is the focus of examination in dental abnormalities?
Understand normal tooth structure and pattern of tooth structure loss
What type of investigations may be necessary for diagnosing dental abnormalities?
Genetic testing for dentinogenesis imperfecta and dentine abnormalities
Histology may also play a role.
What is the importance of differential diagnosis in dental abnormalities?
Based on clinical, radiographic, and histologic information
Information collection includes lesion characteristics and history.
