OPG, Odontogenesis, Embryo Flashcards
(295 cards)
1
Q
What are syndromes?
A
They are systemic disorders – meaning that they show systemic manifestation.
2
Q
What are the stages of pre-natal development?
A
- Zygote - single celled fertilised egg
- Embryo - 2-8 weeks
- Foetus - 9-birth
3
Q
What is ontogeny?
A
It is stages of development of an individual.
4
Q
What is teratology?
A
Study of what can go wrong during the developmental process
5
Q
What are the 3 main phases in embryology?
A
- Phase 1 – fertilisation to 3 weeks in utero
- Phase 2 – 4-8 weeks in utero
- Phase 3 – 9 weeks to birth
6
Q
What happens during phase 1 of embryonic development?
A
- 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.
7
Q
What is cleavage?
A
Cleavage – a rapid mitotic division with little net change in embryo size leading to morula then blastocyst
8
Q
What is a blastocyst?
A
A blastocyst is a cell mass composed of external trophoblasts and embryoblasts
9
Q
What is differentiation?
A
It is a process where cells must be competent to receive an external induction signal, competency is transient.
10
Q
What happens on day 8 of embryological development?
A
Embryoblasts differentiates into bilaminar germ disk composed of ectodermal cells and endodermal cells
11
Q
What happens on day 13 of embryological development?
A
Ectoderm contains amniotic cavity, mesoderm migration forms secondary yolk sac
12
Q
What is gastrulation?
A
It is when the bilaminar disc in the embryo turns into a trilaminar disc during week 3
13
Q
What happens in Phase 2 of embryotic development?
A
- 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
14
Q
What is the neural plate?
A
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.
15
Q
How does the neural plate develop?
A
Neural plate develops cranially
16
Q
Where does the neural plate and neural crest forms?
A
The ectoderm
17
Q
What happens on day 21 of the embryological develop?
A
- 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
18
Q
What gives rise to all components of the head and face?
A
The rostral head fold of the embryo
19
Q
What is the rostral head fold composed of?
A
Frontal prominence within which the anterior neural tube forms the brain; and six branchial arches
20
Q
What are branchial arches?
A
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.
21
Q
What does the first branchial arch give rise to?
A
- Meckel’s cartilage
- Muscles of mastication
- Maxillary artery and part of external carotid artery
- Trigeminal nerve
- Maxillary process
22
Q
How does the maxilla form?
A
The maxilla forms in the embryo as a result of bulging of the first branchial arch
23
Q
When does the face form?
A
The face forms during the 24-38 days post conception
24
Q
What are the steps in formation of the palate?
A
- 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
25
What is the importance of Meckel's cartilage?
It acts as a scaffold for the mandible development
26
What are some the triggers of congenital defects?
1. Genetic factors
| 2. Environmental factors
27
What are the reasons to know the sequence of dental development?
1. Understand the 'normal'
2. Age estimation
3. Assess timing and duration of developmental disturbances on teeth
4. Paedodontics/orthodontics
5. Forensic odontology
28
What is the average timeline of dental development?
6 weeks in utero to late teenage years
29
How can we study timing/sequence of tooth calcification?
1. Histologically
2. Radiologically
3. Clinically
30
What is the sequence of events in tooth development?
1. Fomation of dental crypt
2. Calcification of cusps
3. Calcifiction of crown
4. Calcification of roots
5. Emergence
6. Closure of the apical canal of roots
31
What is the sequence of primary tooth calcification?
1. Central incisors
2. Lateral Incisors
3. First molars
4. Canines
5. Second molars
32
When does mineralisation begin?
3-6 months in utero
33
When does the calcification of permanent teeth occur?
All occurs post-natally
34
What is the sequence of initial calcification in permanent dentition?
1. Sixes - at birth
2. One's – 3 months
3. Mandibular Two's + Canines – 5 months
4. Maxillary Two's – 1 year
5. Four's – 1.5-2.5 years
6. Five's + Seven's – 2.5-3.5 years
7. Eight's – 7-12 years
35
What can create variability in tooth calcification?
1. Individuals - agenesis
2. Sex - females get their permanent dentition earlier
3. Ethnicity
36
What is tooth eruption?
It is movement of a developing tooth initiated by initial formation of the root.
37
When does the shedding of primary teeth occur?
Between 5-12 years
38
What is usually the first permanent tooth to occur?
Usually the first molars erupt first
39
What are some general factors for eruption & emergence?
1. Socio-economic status
| 2. Physical status
40
What are some general disturbances for eruption & emergence?
1. Genetic conditions
| 2. Endocrine conditions
41
What are the local factors for eruption & emergence of teeth?
1. Premature extraction of primary teeth
2. Early extraction of 6 or 7 affects 8
3. Amount of space – Ieeway space
4. Crowding, inclination and obstacles
42
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)
43
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.
44
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.
45
What are the five histological identifiable stages of odontogenesis?
The five stages are: bud stage, cap stage, bell stage, apposition, and maturation.
46
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.
47
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.
48
What are the main cellular processes involved in odontogenesis?
The main cellular processes are: initiation, proliferation, differentiation, morphogenesis, and maturation.
49
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.
50
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.
51
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.
52
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.
53
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.
54
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.
55
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.
56
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.
57
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.
58
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.
59
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.
60
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.
## Footnote
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.
61
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.
## Footnote
Each stage is marked by distinct cellular activities and protein expressions critical to enamel development.
62
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.
## Footnote
Inner Enamel Epithelium (IEE) cells are cuboidal with poorly developed organelles, and a basal lamina separates them from the Dental Papilla (DP).
63
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.
## Footnote
The basal lamina disintegrates, enabling direct contact between predentine and preameloblasts, triggering their full differentiation into secretory ameloblasts.
64
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.
## Footnote
These proteins form a layer of rodless (aprismatic) enamel that mineralizes almost immediately up to 30%.
65
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.
## Footnote
A narrow rod sheath, rich in organic material, separates the rods from interrod enamel.
66
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)
## Footnote
Amelogenin is the main enamel protein, Ameloblastin is prominent in newly formed enamel, and Enamelin is critical for enamel structure.
67
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.
## Footnote
Approximately 25% of ameloblasts die during this phase, reflecting the intense cellular turnover.
68
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.
## Footnote
Ruffle-ended ameloblasts introduce inorganic material to promote crystal growth, while smooth-ended ameloblasts remove water and organic material.
69
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)
## Footnote
Amelotin's function is unclear, while ODAM is linked to periodontal integrity.
70
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.
## Footnote
This stage ensures the enamel remains intact and protected post-mineralization.
71
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.
## Footnote
Each phase is characterized by specific cellular and morphological changes.
72
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)
## Footnote
Each plays a significant role in enamel formation and structural integrity.
73
What begins after crown formation and coincides with tooth eruption?
Root Development
## Footnote
Root development is essential for the proper positioning and stability of teeth.
74
Which tissue gives rise to cementum, periodontal ligament, and alveolar bone?
Dental Follicle
## Footnote
The dental follicle plays a critical role in the formation of supporting structures around the tooth.
75
What guides root formation during tooth development?
Epithelial Root Sheath (Hertwig’s)
## Footnote
Hertwig's Epithelial Root Sheath is crucial for the correct morphology of the tooth root.
76
What is the process of cementum formation called?
Cementogenesis
## Footnote
Cementogenesis is key for anchoring teeth to the jaw via the periodontal ligament.
77
What forms the cervical loop during root formation initiation?
The junction of outer enamel epithelium (OEE) and inner enamel epithelium (IEE)
## Footnote
This structure is essential for the subsequent development of the root.
78
What induces dental papillae cells to differentiate into odontoblasts?
Hertwig’s Epithelial Root Sheath (HERS)
## Footnote
This process is vital for the production of root dentine.
79
What occurs after dentinogenesis begins in root formation?
Root Sheath Fragmentation
## Footnote
This process allows for interaction between dental follicle cells and the dentin surface.
80
What do dental follicle mesenchymal cells differentiate into during cementum formation?
Cementoblasts
## Footnote
Cementoblasts are responsible for laying down cementum, which is crucial for tooth stability.
81
What are the three layers of the dental follicle?
Inner layer, Outer layer, Intermediate layer
## Footnote
Each layer has distinct roles in tooth development and support.
82
What are the Epithelial Rests of Malassez (ERM)?
Fragments of HERS that persist in the periodontal ligament
## Footnote
ERM are involved in periodontal repair and can potentially form odontogenic cysts.
83
True or False: Multi-rooted teeth have root division occurring at sites of high vascularity.
False
## Footnote
Root division occurs at sites of low vascularity, leading to the formation of multiple roots.
84
What growth factor promotes cell differentiation and cementogenesis?
Transforming Growth Factor beta Superfamily (e.g., BMPs)
## Footnote
BMPs are crucial for various developmental processes, including those in the periodontium.
85
Which adhesion molecule promotes mineralisation?
Bone Sialoproteins
## Footnote
These molecules are essential for the proper mineralization of bone and cementum.
86
What role do collagens play in periodontal tissues?
Structural roles
## Footnote
Collagens provide the framework necessary for the integrity and function of periodontal tissues.
87
Fill in the blank: _______ prevents ectopic calcification.
Matrix Gla Protein
## Footnote
This protein plays a significant role in regulating mineralization processes.
88
Which transcription factors drive cementoblast differentiation?
Runx-2 & Osterix
## Footnote
These factors are also involved in osteoblast differentiation, highlighting the similarities between these cell types.
89
What are the processes involved in tooth eruption?
1. Enamel covered by reduced enamel epithelium
2. Overlying bone resorbs
3. Outer cells of reduced enamel epithelium proliferate
4. Fusion with oral epithelium
## Footnote
These processes are crucial for the proper emergence of teeth into the oral cavity.
90
What are the clinical and radiographic features of abnormalities of tooth development?
Outline and recognize the features
## Footnote
Clinical features can include tooth discolouration and sensitivity, while radiographic features may show abnormal root shapes or pulp chamber sizes.
91
What is the pathogenesis of abnormalities of tooth development?
Describe the process of tooth development
## Footnote
Involves stages from primary epithelial band to tooth eruption.
92
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
93
What disturbances can occur during the initiation stage of odontogenesis?
* Andontia
* Supernumerary teeth
94
What disturbances can occur during the bud stage of odontogenesis?
* Microdontia
* Macrodontia
95
What types of abnormalities can occur during the cap stage of odontogenesis?
* Dens in dente
* Gemination
* Fusion
* Rubercle
96
What conditions are associated with the apposition and maturation stages of odontogenesis?
* Amelogenesis imperfecta
* Dentinogenesis imperfecta
* Concrescence
* Enamel pearl
97
What are the categories of defects in tooth development?
* Localised Developmental Defects of Teeth
* Acquired Defects
* Morphological Abnormalities
* Multisystem Genetic Disorders
98
Define Amelogenesis Imperfecta.
Genetic condition affecting enamel matrix proteins
## Footnote
Involves genes like Ameloblastin and Enamelin.
99
What is the prevalence of Amelogenesis Imperfecta?
1:700 to 1:14,000
100
What are the characteristics of enamel in Amelogenesis Imperfecta?
* Hypoplastic
* Hypomineralised
* Combination of both
101
What are the types of Amelogenesis Imperfecta?
* Hypoplastic Amelogenesis Imperfecta
* Hypomaturation Amelogenesis Imperfecta
* Hypocalcified Amelogenesis Imperfecta
102
What are the clinical features of Hypoplastic Amelogenesis Imperfecta?
Inadequate matrix formation, pitted or thin enamel
## Footnote
Enamel is hard and translucent.
103
What are the clinical features of Hypomaturation Amelogenesis Imperfecta?
Normal enamel on eruption, opaque appearance, soft and vulnerable
## Footnote
Colors can include white and brown-yellow.
104
What are the clinical features of Hypocalcified Amelogenesis Imperfecta?
Normal enamel matrix quantity, poor calcification, opaque and chalky appearance
## Footnote
Stains and wears rapidly.
105
What is Dentinogenesis Imperfecta?
Uncommon defect of dentine formation due to mutations in dentine sialoprotein (DSPP)
## Footnote
Inheritance is autosomal dominant.
106
What are the clinical features of Dentinogenesis Imperfecta?
* Normal contour at eruption
* Translucent or amber-like hue
* Enamel weakly attached
107
What are the radiographic features of Dentinogenesis Imperfecta?
* Short, blunt roots
* Partial or total obliteration of pulp chambers
108
What is Dentinal Dysplasia?
Rare autosomal dominant disease affecting dentine
## Footnote
Types include Type I (Rootless Teeth) and Type II (Coronal Dentine Dysplasia).
109
What is Regional Odontodysplasia?
Localized disorder affecting a group of teeth
## Footnote
Most often affects maxillary teeth.
110
What are the disturbances in tooth number?
* Anodontia
* Hypodontia
* Supernumerary teeth
111
What are common teeth affected by isolated hypodontia?
* 3rd molars
* 2nd premolars
* Maxillary lateral incisors
112
Define Fusion in dental abnormalities.
Union between dentine and/or enamel of two or more separate developing teeth
113
Define Gemination in dental abnormalities.
Partial development of two teeth from a single tooth bud following incomplete division
114
Define Concrescence in dental abnormalities.
Roots of one or more teeth united by cementum after crown formation
115
Define Dilaceration.
Acquired developmental anomaly caused by trauma resulting in angulated root
116
What is Dens in Dente?
Inward folding of the enamel organ into the dental papilla
## Footnote
Forms an enamel-lined opening from pulp to tooth surface.
117
What are the steps in the diagnostic process for dental abnormalities?
* History
* Examination
* Investigations
* Diagnosis
118
What techniques are used in dental examination?
* Inspection
* Palpation
* Percussion
119
What should be included in the dental history questions?
* Dental and systemic medical history
* Teeth
* Bones
* General health
* Febrile disease
* Fluoride intake
120
What is the focus of examination in dental abnormalities?
Understand normal tooth structure and pattern of tooth structure loss
121
What type of investigations may be necessary for diagnosing dental abnormalities?
Genetic testing for dentinogenesis imperfecta and dentine abnormalities
## Footnote
Histology may also play a role.
122
What is the importance of differential diagnosis in dental abnormalities?
Based on clinical, radiographic, and histologic information
## Footnote
Information collection includes lesion characteristics and history.
123
Label the areas and which stage of odontogenesis is it in?
Black arrow = Meckel's Cartilage
Black dashed circle = tooth germ
Pink dashed circle = dental papilla
Red arrow = dental follicle
Blue arrow = enamel organ
This photomicrograph shows the cap stage of odontogenesis
124
What stage is this in?
Bell stage
125
Identify and labeled the tissues in the photograph
Black arrow = Dental lamina
Red arrow = Oral epithelium
Black dashed circle = Successional dental lamina
Orange dashed circle = Stellate reticulum
Red dashed circle = Alveolar bone
Pink dashed circle = Dental papilla
126
Identify the labeled tissues in the photomicrograph
Green dashed circle = stellate reticulum
Orange dotted rectangle = outer enamel epithelium
Purple dotted rectangle = inner enamel epithelium
Red dashed circle = cervical loop
Pink dashed circle = dental papilla
127
Red dashed circle = stellate reticulum
Purple dotted circle = stratum intermedium
Green dotted rectangle = inner enamel epithelium
Blue star = acellular zone
Black dashed circle = dental papilla
128
The photomicrograph depicts a section of a tooth in what stage of development?
Late bell stage
129
Identify the labeled tissues in the photomicrograph
Red arrow = stratum intermedium
Black arrow = ameloblasts
Blue star = predentine
Yellow arrow = odontoblasts
Red dashed circle = stellate reticulum
130
What stage is this?
Late bell stage
131
Identify the labelled tissues in the photomicrograph
Red arrow = enamel matrix
Black arrow = dentine
Blue star = enamel space
Yellow arrows = cervical loop
Red dashed circle = dental pulp
132
Identify the labeled tissues in the photomicrograph
Red arrow = stratum intermedium
Black arrow = ameloblasts
Red dashed circle = enamel matrix
Blue star = enamel space
Yellow arrow = dentine
133
134
Drag the steps of reciprocal interaction
135
136
Which one of the following genes encodes for the protein that makes up the bulk of enamel?
AMELX (amelogenin)
137
Which one of the following molecules is involved in the differentiation of cementoblasts?
Osterix
138
Which one of the following Homeobox genes is associated with the development of molar teeth?
Barx-1
139
140
What is a phenotype?
It is our genotype + environment
141
What is the main difference between somatic cells and gametes?
Somatic cells have a diploid number of chromosomes. Gametes have a haploid number of chromosomes
142
What is dominance/recessiveness?
Differences in the DNA code between alleles at the same locus may give rise to dominance or recessivness which couple with sex linkage, may give rise to simple modes of inheritance.
143
What is the law of segregation?
The two alleles for a heritable character segregate during gamete formation and end up in different gametes
144
What is the law of independent assortment?
Each pair alleles segregates independently of each other pair of alleles during gamete formation
145
What are the phases of mitotic divisions?
Growth 1 phase
S phase – genetical replication phase
Growth 2 pahse
Mitotic phase – PMAT
Cytokinesis
146
What is the process of meiosis?
Meiosis is a process which reduces the chromosome number so that each daughter cell has only one of each kind of chromosome. The process of meiosis ensures that the next generation will have:
1. A diploid number of chromosomes
2. A combination of traits that differs from that of either parent
147
What are the steps of meiosis?
1. A cell exist with no DNA replication
2. DNA replication occurs – sister chromatids are connected by the centromere
3. Non-sister chromatids may exchange genetic material – this is called synapsis – or crossing-over
4. Meiosis I occurs – the homologous pairs are separated
5. Meiosis 2 occurs – sister chromatids are separated
6. Result - 4 different cells with haploid number of chromosomes now exists
148
What is the key mechanistic difference between mitosis and meiosis?
Mitosis has 1 round of division, while meiosis has 2 rounds of division.
149
How does meiosis create genetic variation?
At meiosis I the separation of homologous pairs creates a segregation of different locuses into different gametes. The random assortment also occurs, as pairs may line up in different assortments thus creating different pattern of creating gametes. Both Mendel's laws are dependent on the separation of homologous pairs during meiosis I.
150
Where does variation come from?
1. Alteration, disruption or damage to the genetic material
2. Ttanscription + alternative splicing
3. Recombination during meiosis
4. Fertilisation
5. Epigenetic factors regulating gene expression
151
What are the 2 types of alterations?
1. Somatic – only affects the host.
2. Germline - may affect the offspring.
152
What causes of point mutations?
Causative agents – internal during process of replication and repair, chemical, ionizing radiation, viral.
153
What does the accumulation of point mutation cause?
The accumulation of point mutation may cause an alteration in protein structure.
154
What are some of the sources of chromosomal variation?
1. Deletions/Insertions
2. Amplification
3. Translocation
4. Aneuploidy
155
What are the three checkpoint in cell cycle?
1. G1 prior to S
2. During G2 prior to M phase
3. At the end of M phase
156
Where does the exchange of genetic material occur during synapsis?
It occurs on non-sister chromatids.
157
What are the genetic and phenotypic outcomes from single gene segregation in pure breeding parents?
The potential traits of the offspring can be predicted.
158
What is the mendell's law of segregation?
In a heterozygous organism the two different alleles will be separated during meiosis.
159
What happens to two different genes on the same chromosome?
If no crossover changes, the F2 progeny may have a very limited coupling and repulsion.
160
How do we overcome the issue of genes being on the same chromosome?
Crossing over or synapses – this resolves the independent assortment of genes on the same chromosome by inducing an exchange in genes from two non-sister chromatids.
161
What is the main difference between assorting independently and complete linkage of genes?
When assorting independently, the genetic variation is considerably greater than when there is crossing over occurring
162
What is the difference between coupling and repulsion?
Coupling reference to inheritance of two dominant or two recessive genes. Repulsion is an inheritance of one dominant and one recessive gene.
163
What can we say about the events of synapsis of two genes that are not close to each other?
They are more likely to undergo synapses, if 2 genes are not next to each other thus undergo recombination e.g. polar ends of the chromosome.
164
What is the recombination frequency?
It is the proportion of recombinant phenotypes to the total phenotypes is called recombination frequency. It is calculated by combining all instance of the phenotype and dividing by all sample taken. This can also be used to calculate the genetic map distance, just multiply the recombination frequency by 100.
165
What are homeobox genes?
A homeobox gene is a type of gene containing a DNA sequence called a homeobox that encodes a homeodomain protein, which acts as a transcription factor to regulate the expression of other genes during development, particularly in establishing body plans and segmentation in organisms.
166
What are transcription factors?
They are molecules that upregulate or downregulate the activity of certain genes
167
What is development?
It is a combination of proliferation, migration and differentiation
168
What are morphogen gradients?
They are positional cues for cells during development; this establishes cell signalling networks to control gene expression
169
What are the steps of embryogenesis?
1. Fetilisation
2. Induction, competence, differentiation
3. Formation of the three layered embryo
4. Formation of neural crest cells
5. Folding of the embryo
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What are growth factors?
They are inter-cellular signalling mechanism. They promote cell growth, differentiation and maturation. Produced at 2 cell stage. They also control gene expression.
171
What are homeobox genes?
They are key genes, that are usually the first genes to cause differentiation. They actually DNA sequences found within genes that are involved n the regulation of patterns of anatomical development. These transcription factors typically switch on cascades of other genes.
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What are hox genes?
It is a group related genes that determine the basic structure and orientation of an organism. They are critical for proper placement of segment structures. Most are linked together in sequential clusters. This means that there is not much synapsis occurs relating homeobox genes.
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What is the objective of homeobox genes?
Create a transcription factor and start a transcription cascade
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What are morphogenetic field?
It is a protein concentration that drives morphological change.
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How many homeobox clusters are there?
4 – C-7,-17,-12 and -2.
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With current technologies, how long and how much does it cost to sequence a single human genome?
It costs under $1000 and takes under 8 hours.
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What are some of the potential treatments we might have available soon in the field of genetics?
1. Genetic engineering
2. Gene therapy
3. Genetic testing and counselling
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What are the potential use of genetic engineering in dentistry?
1. Growing new teeth in vitro/in vivo
2. Stem cell therapy for periodontitis
3. Changing the oral ecology
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What can genetic testing reveal?
1. DNA sequence information
2. Specific genes present in the individual
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What is a gene pool?
It is a set of genetic information (all alleles) carried by the members of a sexually reproducing population.
181
What can you comment on the variation in regards to population genetics?
Variation is even more important in population genetics, as it allows for a larger number of individuals to be adapted to certain events thus making them more likely to survive and reproduce.
182
What is monomorphic?
When there is 1 gene in a allele
183
What is dimorphic?
When there are 2 genes in an allele
184
What is a polymorphic gene?
It is 1 allele that is present in at least 1% of the population
185
How do you calculate genotype frequencies?
Occurrence divided by total number
186
How do you calculate allele frequencies?
Times the occurrences by 2 and remember that heterozygous individuals need to be separated into 2 different alleles
187
What is a Hardy-Weinberg equilibrium law?
It is a law that is used to calculate allele frequencies in non-evolving populations, with assumption that shuffling of alleles has no effect on the overall gene pool. Deviations from this law result in evolution. Due to limitations above this law cannot be used in natural populations but it help us to understand how the evolution occurs.
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What are the necessary conditions for Hardy-Weinberg equilibrium?
1. No new mutations
2. No migration in or out of the population
3. No selection
4. Random mating
5. Very large population
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What are the key steps ocurring during Meiosis?
Meiosis involves the same four phases seen in mitosis. They occur during both meiosis I and meiosis II. The period of time between meisosis I and meiosis II is called inter-kinesis. No replication of DNA occurs during inter-kinesis because the DNA is already duplicated.
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Compare and contrast mitosis and meiosis
Mitosis produces two identical diploid cells for growth, repair, and asexual reproduction, maintaining chromosome number and genetic consistency in somatic cells, while meiosis generates four diverse haploid gametes for sexual reproduction, halving chromosomes and introducing variation through crossing over and independent assortment in germ cells. Both share stages like prophase and metaphase but differ in division number (one for mitosis, two for meiosis), chromosome dynamics, and outcomes, with mitosis ensuring uniformity and meiosis driving evolutionary diversity.
Mitosis and meiosis, both preceded by a single DNA replication in interphase, are cell division processes with distinct roles: mitosis, requiring one division, produces two genetically identical diploid daughter cells in somatic cells for growth and repair, while meiosis, involving two divisions, generates four genetically diverse haploid gametes in reproductive organs for sexual reproduction, halving chromosomes and introducing variation through crossing over and independent assortment
191
Describe the relationship between Mendel's Law and Meiosis.
Mendel's observations ( and his law) are a consequence of events that occur during gamete formation - meiosis.
192
Describe how meiosis supports new genetic variations
There are two sources of genetic recombinations during meiosis:
1. crossing-over: non-sister chromatids of a chromosome pair exchange their genetic material
2. Independent assortment: homologous chromosomes are distributed to daughter cells randomly
Both events assure new genetic combinations in the offspring. Fertilisation between haploid gametes result in a third source of genetic recombination because there is the combining chromosomes from different individuals.
193
Determine a cell's position in the meiotic cycle from its chromosomes and gene copy number
194
What determines phenotype?
Genotype and environment
195
What is the purpose of genetics?
High fidelity information transfer
196
What is the basic unit of inheritance?
Gene
197
What are genes arranged on?
Chromosomes (circular or linear)
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What is DNA and what's its significance?
Genes / chromosomes are made of DNA
DNA is sugar-phosphate backbone + nucleic acid 'code' (A, G, C, T)
DNA is is a linear macromolecule with 3 main functions:
- Protein synthesis (transcription & translation)
- Self-replication (cellular / organism)
- Inter-generational information transfer
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Describe the relationship between Dominance/Recessiveness and Sex Linkage
Differences in the DNA code between alleles at the same locus give rise to Dominance / Recessiveness and this, sometimes coupled with sex linkage, may give rise to simple modes of inheritance.
200
Describe the key concepts of Mendel's Law
- Alternative versions of genes account for variations in inherited characters
- For each character, an organism inherits two alleles, one from each parent (ONLY TRUE FOR DIPLOID ORGANISMS REPRODUCING SEXUALLY)
- If two alleles at a locus differ, then one, the dominant allele, determines the organisms' appearance; the other, the recessive allele, has no noticeable effect on the organims's appearance.
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What are the two fundamental laws of Mendel's Law?
1. The law of segregation -> The two alleles for a heritable character segregate during gamete formation and end up in different gametes.
2. The law of independent assortment -> Each pair of alleles segregates independently of each other pair of alleles during gamete formation.
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Why is cell division necessary?
- Reproduction (prokaryotes) -> meiosis
- Growth (eukaryotes) -> mitosis
- Maintenance and repair (eukaryotes) -> mitosis
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What is Gametogenesis?
It is required for sexual reproduction in eukaryotes
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Describe Meiosis (gametogenesis)
Meiosis reduces the chromosome number so that each daughter cell (gamete) has only one of each kind of chromosome.
The process of meiosis ensures that the next generation will have:
1. a diploid (2n) number of chromosomes
2. a combination of traits that differs from that of either parents
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What happens during Meiosis I?
Separates the homologous pairs of chromosomes.
- Daughter cells are haploid, but chromosomes are still in duplicated condition.
- Synapsis occurs during meiosis I
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What happens during Meiosis II?
Separates sister chromatids
- The completely haploid daughter cells mature into gametes
- Fertilisation restores the diploid number of chromosomes during sexual reproduction
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What is n and c?
"n" represents the number of chromosome sets (haploid number, e.g., n=23 in humans), while "c" denotes the DNA content, which doubles after replication (e.g., 2c in G2 phase).
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What is a chromatid?
A chromatid is one of the two identical copies of a replicated chromosome, joined at the centromere, that separate during cell division to become individual chromosomes in daughter cells.
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What are the major differences between mitosis and meiosis, both mechanically and functionally?
Mitosis and meiosis differ mechanically and functionally in key ways. Mechanically, mitosis involves one division, producing two diploid cells, with chromosomes aligning as single chromatids in metaphase and sister chromatids separating in anaphase, while meiosis requires two divisions (meiosis I and II), yielding four haploid cells, with homologous chromosomes pairing and crossing over in prophase I, aligning as pairs in metaphase I, and separating in anaphase I, followed by sister chromatid separation in meiosis II. Functionally, mitosis occurs in somatic cells to produce genetically identical cells for growth, repair, and asexual reproduction, maintaining the chromosome number (2n) and DNA content (2c post-replication), whereas meiosis occurs in germ cells to form gametes for sexual reproduction, halving the chromosome number (n) and DNA content (c) per cell, and introducing genetic diversity through crossing over and independent assortment.
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What is Mendel's second law and where does it occur in meiosis?
Mendel's Second Law, the Law of Independent Assortment, states that alleles for different traits segregate independently during gamete formation, provided the genes are on different chromosomes. This occurs during meiosis I, specifically in metaphase I, when homologous chromosome pairs align randomly at the metaphase plate, allowing each pair to assort independently of others, leading to genetic variation in the resulting gametes.
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What is Mendel's First Law and where does it occur in meiosis
Mendel's First Law, the Law of Segregation, states that each individual has two alleles for a given trait, and these alleles segregate (separate) during gamete formation, so each gamete carries only one allele. This occurs during meiosis I, specifically in anaphase I, when homologous chromosomes (each with two sister chromatids) are pulled apart to opposite poles, ensuring that each resulting gamete receives only one chromosome—and thus one allele—of each homologous pair.
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How is Mendel's Law derived experimentally?
Mendel's Laws were derived experimentally by cross-breeding pea plants with distinct traits, observing inheritance patterns in offspring over generations, and analyzing ratios of phenotypes to formulate the principles of segregation and independent assortment.
213
Define P, F1 and F2
P is the parental generation, F1 is the first filial generation (offspring of P), and F2 is the second filial generation (offspring of F1 crosses) in genetic breeding experiments.
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Use Punnet squares to exmaine allele transmission for biallelic phenotypes
215
Describe the concepts of coupling and repulsion
Coupling refers to linked genes on the same chromosome inherited together (e.g., AABB producing AB gametes), while repulsion describes opposite allele combinations on the same chromosome (e.g., AAbb producing Ab gametes), affecting inheritance patterns in progeny.
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Describe how genes on the same chromosomes are physically linked
Genes on the same chromosome are physically linked because they reside on the same DNA molecule, tending to be inherited together unless separated by crossing over during meiosis, with closer genes having lower recombination rates.
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Explain that synapsis / crossing over can resolve Mendel's Laws for genes on the same chromosome
Synapsis and crossing over during meiosis I shuffle linked alleles via genetic exchange, enabling independent assortment and creating new allele combinations for genes on the same chromosome.
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Explain why the closer two genes are on a chromosome, the lower the chance of crossover event recombining gene/allele combinations during meiosis
Closer genes on a chromosome have a lower chance of crossover because the physical distance between them reduces the likelihood of a recombination event occurring during meiosis, keeping their allele combinations intact.
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Explain the expected frequencies for a biallelic cross assorting independently or under complete linkage
For a biallelic cross assorting independently (e.g., AaBb x AaBb), phenotypic frequencies are 9:3:3:1 (dihybrid) or 3:1 (monohybrid), while under complete linkage, only parental phenotypes (e.g., AB/ab or Ab/aB) appear in F2, with frequencies reflecting parental combinations (e.g., 3:1 for coupling, 1:1 for repulsion in test-cross).
220
Explain the concept of a test-cross/back-cross
In a test-cross or back-cross, an organism displaying a dominant phenotype but with an unknown genotype is mated with a homozygous recessive individual, allowing the offspring's phenotypic ratios—either all dominant (indicating homozygous dominant) or a 1:1 dominant-to-recessive ratio (indicating heterozygous)—to reveal the unknown genotype, providing a critical tool in Mendelian genetics for mapping inheritance patterns and studying gene linkage.
221
Explain the idea of parental and recombinant phenotypes
Parental phenotypes are traits in offspring that precisely match those of the parents due to inheriting identical allele combinations without recombination, whereas recombinant phenotypes are novel trait combinations arising from crossing over during meiosis, which shuffles alleles between homologous chromosomes to produce new genetic configurations distinct from the parental types.
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Explain the simple rules that enable us to apply this to simple breeding experiment
To apply a test-cross or back-cross in a simple breeding experiment, select an individual expressing a dominant phenotype but with an unknown genotype (homozygous dominant AA or heterozygous Aa), mate it with a homozygous recessive individual (aa), and observe the offspring's phenotypes: if all offspring display the dominant trait, the tested individual is homozygous dominant (AA); if the offspring show a 1:1 ratio of dominant to recessive traits, the tested individual is heterozygous (Aa), leveraging Mendel's laws of segregation and the predictable inheritance patterns of single-gene traits.
223
What are the different types of point mutations in the genetic code, their causes and their outcomes in terms of protein structure?
Point mutations include silent, missense, and nonsense mutations, caused by internal replication errors, chemicals, ionizing radiation, or viruses, resulting in no change, altered amino acid sequences, or truncated proteins, respectively, affecting protein structure and function.
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What are the internal regulators of DNA replication in the cel cycle?
Internal regulators of DNA replication in the cell cycle include cyclins and cyclin-dependent kinases, which control progression through G1, G2, and M phase checkpoints to ensure accurate DNA synthesis and repair.
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What are the external regulators of DNA replication in the cell cycle?
External regulators of DNA replication include environmental factors like cell size and DNA damage signals, which influence checkpoint activation during G1, G2, and M phases to prevent replication errors.
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What can happen if internal and external regulators of DNA replication in the cell cycle fail?
Failure of internal and external regulators can lead to unrepaired DNA damage, replication errors, or improper chromosome segregation, resulting in mutations, chromosomal instability, or cell cycle dysregulation, potentially causing diseases like cancer.
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How does mutation contribute to generating new phenotypic variation?
Mutations, such as point mutations or chromosomal rearrangements, introduce genetic variation by altering DNA sequences or gene arrangements, which can lead to new protein functions or structures, thereby generating novel phenotypic traits subject to natural selection.
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What are the different sorts of chromosomal rearrangements that can occur (structure/number)?
Chromosomal rearrangements include structural changes like deletions, insertions, amplifications, and translocations, and numerical changes like aneuploidy due to non-disjunction, altering chromosome structure or number.
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What are the regulation of the cell cycle and how defective checkpoints can give rise to chromosomal errors?
The cell cycle is regulated by checkpoints in G1, G2, and M phases, controlled by cyclins and kinases, but defective checkpoints can allow unrepaired DNA damage or improper chromosome segregation, leading to chromosomal errors like aneuploidy or translocations.
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What are the differences between germline and somatic changes in genes / chromosomes, expecially in the context of disease?
Germline changes in genes or chromosomes occur in reproductive cells, are heritable, and can predispose offspring to diseases like cancer, while somatic changes occur in non-reproductive cells, are not inherited, and may cause diseases like tumors in the affected individual.
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Triplets encode specific amino acids with a degree of redundancy - why is this important?
it minimizes the harmful effects that incorrectly placed nucleotides can have on protein synthesis.
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Humans have 23 pairs of chromosomes and ~20,000 genes. Where might this macro genetic variation have originated?
Macro genetic variation, such as humans having 23 pairs of chromosomes and ~20,000 genes, likely originated from chromosomal rearrangements, gene duplications, and mutations accumulated over evolutionary time, contributing to speciation and genetic diversity.
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Some genes/loci are invariant in the population, some are bi-allelic and some are poly-allelic ... sequence differences in DNA. Where does this 'micro' sequence variation come from?
Micro sequence variation in genes/loci, leading to invariant, bi-allelic, or poly-allelic states, originates from point mutations (SNPs, duplications, indels) caused by internal replication errors, chemical agents, ionizing radiation, or viral influences.
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What are the possible causes of alteration, disruption or damage to the genetic material?
- Genetic codes (A, C, G, T), allelic variation
- Gene copy number; chromosomal rearrangement
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Where do alleles come from?
- Point mutations (SNPs, duplications, indels)
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What are the checkpoints of the cell cyle?
The cell cycle checkpoints occur during G1 (assessing cell size and DNA damage), G2 (checking DNA damage and replication completeness), and M phase (verifying chromosome attachment to the spindle), ensuring proper progression and genome stability.
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238
Compare and contrast the advantages and disadvantages of direct and indrect digital imaging systems in dental radiography.
Advantages of DDI: highlight the immediate image acquisition with solid-state sensors (e.g., CCD/CMOS), reduced radiation dose compare to indirect system, superior resolution with 256 shades of gray, and elimination of processing error due to real-timie capture.
Disadvantages of DDI: discuss the high cost and fragility of solid-state sensors, patient discomfort due to rigid and bulky sensors, smaller viewable surface area, and inability to withstand heat sterilisation, requiring disposable sleeves.
Advantages of IDI: Note the lower initial cost of the PSP plates, flexibility with various plate sizes (0~4), compatibility with existing X-ray units, and ease of positioning in complex anatomical areas.
Disadvantages of IDI: Explain the slower processing time due to laser scanning, potential for lower resolution compared to direct systems, shorter lifespan of PSP plates, and risk of incorrect plate orientation (E.g., blue active surface errors)
239
Explain the role of position indicating device (PIDs) and film holders in achieving accurate periapical radiographs using the paralleling technique.
PIDs for beam alignment, Film holder for stability, Reduction of errors (minimises retakes by maintaining angulation, and minimises exposure), system-specific design (holders are tailored for solid-state sensors or PSP plate, accomodating different detector types while ensuring precise positioning in the oral cavity.
240
Discuss the technical challenges of using solid-state sensors in direct digital imaging and propose solutions to mitigate these issues.
Challenge: Patient Discomfort: Solid-state sensors are rigid, bulky, and can cause gagging or discomfort, particularly in patients with small mouths or sensitive gag reflexes.
Solution: Sensor Design: Use smaller sensor sizes or wireless sensors to reduce bulk, and employ specialized holders to improve intraoral positioning and patient comfort.
Challenge: Fragility and Cost: Sensors are expensive and easily damaged if dropped or mishandled, increasing replacement costs.
Solution: Handling Protocols: Implement strict handling and storage protocols, use protective covers, and train staff to minimize careless damage, extending sensor lifespan.
241
Evaluate the impact of incorrect PSP plate placement in indirect digital imaging and its consequences for diagnostic quality.
horizontal&vertical detector positioning
horizontal&vertical beam angulation
central beam positioning
collimator rotational angulation
impact on workflow
242
Describe the process of image acquisition in indirect digital imaging using PSP plates and identify potential sources of error in this workflow.
Process Overview: X-rays strike the PSP plate, exciting phosphor crystals to store a latent image; the plate is scanned by a laser, emitting light that is converted into a digital signal, after which the plate is erased for reuse.
Error: Plate Misplacement: Incorrect orientation (e.g., blue active surface visible or “P” misaligned) results in no image capture, requiring re-exposure.
Error: Scanner Issues: Dust or scratches on the plate or scanner can introduce artifacts, degrading image quality and affecting diagnostic accuracy.
Error: Plate Wear: Over time, PSP plates degrade, reducing their ability to store latent images, leading to lower resolution or incomplete images if not replaced timely.
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Explain how anatomical restrictions can complicate the paralleling technique in periapical radiography and suggest modifications to address these challenges.
Restriction: Shallow Palatal Vault: A shallow palate makes it difficult to position the detector parallel to the tooth, potentially causing patient discomfort or image distortion.
Restriction: Large Tori: Mandibular or palatal tori obstruct detector placement, preventing proper alignment with the tooth’s long axis.
Modification: Smaller Detectors: Use smaller film sizes (e.g., size 0 or 1) or pediatric sensors to fit constrained spaces while maintaining parallelism.
Modification: Alternative Technique: If paralleling is infeasible, switch to the bisected angle technique (taught in BDS3) for patients with severe anatomical limitations, though this may compromise image accuracy.
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What are the two types of digital imaging?
1. Solid state (detector) detector
2. Photostimulable phosphor plate (indirect) detector
-> both utilise same X-ray source
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What are the equipment required for a PA?
- Standard dental X-ray tube
- Detector: solid-state sensor / storage plate
- Computer with large hard drive, high resolution monitor, software, storage and external drive / offsite back-up
- printer
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What are the advantages of Digital Radiography?
- Reduced patient radiation dose: -> analogue (chemical processed, most radiation) > indirect (PSP) plate > direct (solid state sensor, least radiation)
- No ongoing purchase / storage of films, processing solution
- Workplace Health Safety (WHS) issues reduced: chemical hazards
- large dynamic range -> less sensitive to exposure settings
- darkroom not needed
- decreased processing time: film (longest processing time taken) > indirect > direct (fasted)
- Elimination of processing errors
- Electronic storage & transmission of images
- linkage of images to patient electronic files
- Superior resolution: 256 shades of gray
- Software allows image enhancement
- Inversion is possible
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What is inversion and what does it do?
Inversion in radiographs refers to a digital image processing technique where the grayscale values of the image are reversed, transforming light areas to dark and vice versa, to enhance diagnostic visualization.
Allowing you to observe additional detail
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What are the disadvantages of digital radiography of direct (solid state) sensors?
- Expensive, easily damaged if careless
- Require specialised holders
- Rigid & bulky
- Patient discomfort and/or gagging
- Viewable surface area is smaller than size of the sensor
- Not universal & not interchangeable between different systems
- Can't withstand heat sterialisation -> require coverage with disposable plastic sleeves
- Initial purchase cost and set up
- possible medical-legal issues from image enhancement
250
What are PIDs?
Position Indicating Device
251
What are the different types of Direct Digital Imaging?
- Cabled / wired or cordless / wireless sensor
- acquisition with minimal delay or in real time
252
Wireless Vs Wired sensors
Wireless:
- Thicker and requires a battery
- Image quality not affected
- roughly 1.5 X more expensive
- easier to lose or drop the sensor
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What are the characteristics of Indirect Digital Imaging?
- Detector needs to be read by laser scanner
- Plates of various size: 0, 1, 2, 3, 4
- Less expensive than solid-state sensors
- Possible shorter life than solid-state sensors
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Does digital technology compensate for poor radiographic technique?
If information isn't recorded correctly, no amount of manipulation can produce a good image on the monitor
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What is a P.A. radiograph & How to explain to a patient?
- An intra-oral radiograph used to show individual teeth and the structures around their apices.
- Paralleling technique requires use of a dedicated detector holder.
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What are the indications for P.A.?
- Detection of apical pathology
- Periodontal assessment
- Endodontics
- Assessment of tooth and alveolar bone following trauma
- Pre/post extraction assessment
- Pre/post implant evaluation
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What are the advantages of paralleling technique?
- Relatively simple
- Minimal elongation / shortening of image
- Bone levels well presented
- film holders (e.g., Rinn) used
- use of long cone
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What does the Rinn System ensure?
- image fairly reproducible at different appointments and with different operators
- Stable: film holders secured by bite force, steady position
- Reduced cone cutting
- Correct vertical and horizontal positioning and angulation
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What does long cone ensure?
- Minimal magnification
- Minimises exposure
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What are the advantages of using film holders?
- Improves diagnostic quality of intra-oral radiographs
- reduced number of retakes
- assist us to position film
- allows us to align the beam correctly horizontally and vertically
- essential for accurate, reproducable alignment with the intra-oral film, especailly when using rectangular collimation
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263
Describe the detailed process of P.A.
1. Set exposure factors
2. Seat patient upright
3. Establish rapport, show patient detector / holder etc
4. Remove jewellery, dentures, glasses as required
5. Occlusal plane of interest horizontal - not strictly necessary
6. Mid-sagittal plane vertical - not strictly necessary
7. Head support (important)
8. Position detector in the mouth
9. Stabilise detector (bite gently onto bite plane of detector holder)
10. Align the beam
11. Rotate collimator to correct position
12. Advise patient to remain still
13. Expose film
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How to assess the placement of the detector?
film placement viewed from proximal aspect
- film parallel to long axis of tooth
- film as close to tooth as possible
- vertical beam alignment at 90 degrees to film & tooth
film placement viewed from occlusal aspect
- film parallel to line fo the arch
- film as close to tooth of interest as possible
- horizontal beam alignment at 90 degrees to film and at tangent to contact points
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What are some anatomical restriction to paralleling technique?
- Shallow palatal vault
- Large tori
- Shallow floor of mouth
- Short lingual frenum
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What are the requirements for Hardy Weinberg Equilibrium?
- No new mutation
- No migration in or out of the population
- No selection
- Random mating
- Very large population
267
What happens on W1 of Embryological Development?
Fertilisation occurs in felopian tube and implantation of embryo in the uterus.
- After egg combined with sperm, zygote -> morula -> blastocyst via mitosis
- Blastocyst is composed of trophoblast (the cells lining the primary yolk sac) and embryoblast (the cells in the primary yolk sac)
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What happens on W2 of embryological development?
bilaminar embryonic disc forms
- Cells in embryoblast differentiate into bilmainar disk, cells differentiate into epiblast or hypoblast
- 2 cavities, the amniotic cavity and secondary yolk sac are formed with a disc suspended between them.
- Prochordal plate which is thickened area where epiblast & hypoblast meet also forms.
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What happens on W3 of Embryological Development?
- Gastrulation -> formation of trilaminar disk with neurulation and NCC (Neural Crest Cells) migration and mesoderm differentiation
- Cells of amniotic cavity differenitate & burrow forming the primitive streak.
- Epiblast cells (soon to be ectoderm) move towards the hypoblast (soon to be endoderm) to form the mesoderm
- Neurulation: ectoderm cells -> neural plate -> invaginates inwards to form neural groove & folds -> neural folds undergo fusion to become neural tube -> neural tube later becomes brain & spinal cord
- NCC: develop from neuroectoderm -> epithelial-mesenchymal transformation; migrates from the crests of neural folds to join the mesoderm --> mesenchyme --> ectomesenchyme
- Mesoderm cells differentiate form somites
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What happens on W4 of Embryological Development?
formation of stomodeum, forebrain, tongue
- Rostrocaudal axis folding -> primitive stomodeum
- Neural tube expansion at head end -> primitive forebrain and produces a bulge called the frontal prominence
- 6 thickenings of mesoderm sprout from primitive pharynx to become branchial arches on each side on the lateral aspect of the embryo going from the head to tail
- neural crest cells migrate to the branchial arches to support development of ectomesenchyme which are required for cranial facial development
- first branchial arch develops to form maxillary process and mandibular process. Mandibular process grows towards each other and fuse very early on.
- Development of face begins in week 4, nasal placodes form on frontonasal prominence
- Tongue: from local proliferation of mesenchyme in the floor of the mouth (tuberculum impar & lingual swellings at 1st branchial arch, fuse with hypobranchial eminence)
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What happens on W5 of Embryological Development?
- Mesodermal cells surrounding the nasal placodes rapidly proliferate to form a horseshoe shape swelling
- Inner and outer half are the medial and lateral nasal process
- Apparent fusion of mandibular processes to form lower lip
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What happens on W6 of Embryological Development?
Rudimentary Mandible formation
- Meckel’s cartilage acts as a scaffold for intramembranous ossification; it is then resorbed
- Ossification occurs where IAN divides into incisive & mental branch
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What happens on W7~9 of Embryological Development
- Upper lip formed -> fusion of medial nasal process and maxillary process
- 2 medial nasal processes and frontonasal process fuse together to form intermaxillary segment -> develops into the philtrum, bridge of nose, primary palate and anterior maxilla
Secondary palate formation
- Nasal septum grows downwards from frontonasal process
Palatal shelves (from Mx processes): grow downwards following curvature of tongue, tongue then descends, allowing the palatal shelves to grow towards each other and undergo true fusion
- Palatal shelves stick to one another via glycoprotein coat and desmosomal junctions on the medial edge epithelia. This forms the midline seam (MES)
- MES disintegrates by week 12, allowing formation of 1 palate
274
What happens on W12 of Embryological Development?
final palate is formed
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What is Odentogenesis?
Formation of primary epithelial band -> dental and vestibular laminar
Including:
- amelogenesis
- dentinogenesis
- root formation and cementogenesis
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Early Tooth Development
At 6 weeks of development -> Appearance of primary epithelial band at the future Mx and Md arches
- Primary epithelial band divides into dental and vestibular laminae at 7th week
- Dental lamina -> gives rise to teeth, forms tooth germs surrounded by ectomesenchyme.
- Cap stage -> enamel organ, dental papilla, dental follicle
- Bell stage -> enamel organ has IEE, stratum intermedium, stellate reticulum, OEE
- Apposition
- Maturation
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What does amelogenesis involve?
It is the enamel matrix formation and enamel maturation.
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What happens in pre-secretory phase?
● The pre-ameloblasts induce dental papilla cells → differentiate into odontoblasts
● Odontoblasts secretes predentine (unmineralised dentine matrix)
● The basal lamina between two cell layers disintegrates (when the odontoblasts secrete predentine)
● Contact between predentine and preameloblasts leads to the complete differentiation of preameloblasts to secretory ameloblasts
● Preameloblasts → Secretory ameloblasts → secretion of enamel matrix
279
What happens during morphogenetic phase?
Morphogenetic phase - Inner enamel epithelium is still cuboidal, with poorly developed or scattered
cytoplasmic organelles necessary for enamel secretion.
280
Differentiation phase
Inner enamel epithelium is now columnar (now pre-ameloblasts), nuclei shift proximally towards the stratum intermedium, golgi complex increases in volume and migrates distally, Rough ER increases significantly (for protein synthesis to be carried out)
281
What happens in initial secretory stage?
● Ribosomes translate mRNA for enamel proteins
● Proteins produced progress to Golgi complex → Packaged into granules and migrate into Tome’s process
● The granule contents released against newly formed mantle dentine → formation of aprismatic (rodless) enamel
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What happens in secretory stage?
● Deposition of enamel matrix from the Tome’s process
● Deposition from the distal - Rod enamel
● Deposition from the proximal - Interrod enamel
● Between the rod and interrod - Rod sheath which is filled with organic material
● At the end of the process - ameloblasts shorten
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What happens during maturation phase?
● Transitional Phase - The ameloblasts reduce in height and volume
Modulation
● creation, loss and re-creation of invaginate ruffle-ended apical surface
● Smooth ended cells - removal of water and organic material from enamel (proteins and organic materials must be replaced by the inorganic crystals for enamel to reach its mineralised state).
● Ruffle-ended cells - Introduction of inorganic material
284
What happens during dentinogenesis?
● Undifferentiated dental papilla cells become differentiated odontoblasts when induced by signalling molecules expressed by IEE.
● Each dental papilla cell divides into two cells → Terminally differentiated odontoblast and the other remains undifferentiated (stem cell reservoir)
● The undifferentiated cells - reservoir for differentiation into odontoblast-like cells in case the odontoblasts are lost (e.g., due to trauma or caries)
● Formation of more RER and golgi apparatus, becomes more elongated and fully functional secretory odontoblasts with odontoblastic processes.
285
What happens during root formation / cementogenesis
● The junction of OEE and IEE undergoes proliferation to form a cervical loop called Hertwig’s root sheath.
● The cells on the internal layer of the root sheath induce the dental papilla cells to differentiate into odontoblasts.
● Upon onset of root dentinogenesis, root sheath fragment occurs.
● Dental follicle cells differentiate into cementoblasts → start laying down cementum.
● Some fragments of the Hertzwig epithelium → survive in the PDL space → called epithelial cell rests of Malassez (ERM)
286
What are the genetic factors that can cause CLP?
- Homeobox gene mutations that
- Regulate genes that regulate other genes
- Regulate effectors genes that form the tissues, structures and organs
- Regulate cell division & adhesion, apoptosis & cell migration
- Msx-1 gene -> needed for expression of BMP2 and BMP4 in palatal mesenchyme, disruption in cell signalling
- FGF9 gene -> responsible for palatal growth and fusion
Other causes of CLP (environmental factors)
- Folic acid: lack of folic acid is associated with neural tube defects
- Rubella virus
- Heavy alcohol use during pregnancy
287
What are teh physiological reasons for occurrence of CLP?
288
What are the consequences of CLP?
- Speech
- Suckling/swallowing/mastication -> nutritional problems
- Hearing problems
- Dental defects
- Psychosocial impacts
- Increased risks for upper respiratory tract infection
- Will have to undergo many surgeries and procedures
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How does CLP cause Trouble Suckling
- Usually soft palate elevates -> blocks off nasopharynx (protect airways), muscles of lips contract around nipple -> form seal -> unable to do so due to gap in palate and lips
- Tongue presses against source to express liquid -> soft palate remains raised blocking nasopharynx
- Vocal folds close, pharynx elevates and move anteriorly > Liquid pushed towards UES
- UES opens -> liquid enters oesophagus -> UES closes and LES opens -> Liquid enters stomach
290
Age of eruption
291
Calcification sequence of teeth.
292
Crown and root formations
293
Dental Growth and Development
294
OPG and Age Estimation
295
Defect onset and duration estimation
Onset: 5 months + ¼ x 4 years = 1 y 5 mths
Duration: around 10% thickness (0.1) x 4 years = 0.4 years = 5 mths
DDX:
Most likely: Accident/trauma to 61 at 1 y 5 mths old
Probable: PA inflammation/infection
Unlikely: deep caries on 61 (unlikely, as this will usually spread to 51 as well)
The trauma likely persisted around 5 mths, and significant enough to affect 21 crown calcifying
