Oral Morphology Flashcards
What is cementum?
Covers root dentine
Made of collagen matrix and lamellar arrangement
Provides attachment for some periodontal fibres
What cell creates cementum?
Cementocytes
What are two types of cementum?
Cellular - contains cementocytes, later formed, present in apical part of root and in furcation regions
Acellular - adjacent to dentine, first formed
What is the alternative classification of cementum?
Acellular extrinsic fibre cementum - collagen fibres from PDL (sharpey’s fibres)
Cellular intrinsic fibre cementum - no sharpeys fibres, no role in tooth attachment
What are the 3 primary embryonic layers?
Ectoderm
Mesoderm
Endoderm
What is enamel derived from?
Ectoderm
All other parts of teeth and supporting structure derived from ectomesenchyme
What is the ectomesenchyme?
Part of the ‘neural crest’ that develops beside the primitive nervous system (ectoderm)
Besides enamel, what does the ectoderm differentiate into?
Nervous system (spine, peripheral nerves and brain) Epidermis
What do teeth develop from?
Tooth Germs
What is considered as the ‘fourth’ cell type?
Neural crest - forms between the ectoderm and the neural tube, the neural crest tissue is also called ectomesenchyme
What are the stages of tooth development?
Initiation Morphogenesis Cytodifferentiation Matrix Secretion Root formation
What is a stomodaeum?
Oral cavity of an embryo
When does tooth initation occur?
5-6 weeks in human embryo
Primary epithelial band develops at 6 weeks
Appears as thickening in epithelium of stomodaeum
What does the PEB split into?
Approx 7 weeks
Dental lamina - forms enamel
Vestibular lamina - forms buccal sulcus
When and where do tooth germs appear?
Approx 8 weeks,
Dental lamina
What are the two stages of morphogenesis?
Bud and Cap stages
What occurs in the bud stage of morphogenesis?
Approx 8-10 wks
Dental lamina thickens into a ‘bud’ enamel organ
Ectomesenchymal condensation appears - dental papilla
What occurs in the cap stage of morphogenesis?
Approx 11 wks Enamel organ forms a 'cap' over the papilla 'Cap stage' enamel organ made up of - external enamel epithelium - internal enamel epithelium These both meet at cervical loop
What occurs during cytodifferentiation?
‘bell’ stage
approx 14wks
More cell layers differentiated
Tooth shape is being defined
What are the 4 layers of the ‘bell stage’ enamel organ?
Stellate reticulum
Stratum intermedium
Internal enamel epithelium
External enamel epithelium
What occurs in the 12th week of tooth embryology?
An extension appears on the lingual side of the dental lamina
This is the dental lamina for the permanent successor
What occurs in the 16th week of tooth embryology?
1st permanent molar germ develops as a backwards extension of the dental lamina
What occurs in the late bell stage?
Approx 18 wks
Late bell stage enamel organ
Crown shape is well defined (crown stage EO)
Apposition of enamel and dentine begins
How does dentinogenesis occur?
IEE differentiates to odontoblasts
Deposition of dentine matrix by odontoblasts(mainly collagen)
This unmineralised dentine is predentine
Mineralisation of dentine (hydroxyapatite)
What are the two stages of enamel formation?
- Protein matrix deposition
- Organic component removal and mineralisation (‘maturation’)
What occurs during ameloblast differentiation of amelogenesis?
Dentine induces IEE cells to differentiate into ameloblasts
They elongate, becoming columnar and nucleus migrates to basal end
What occurs during secretory phase of amelogenesis?
Ameloblasts become secretory cells
They synthesise and secrete the enamel matrix proteins (amelogenins)
The matrix is then partially mineralised (30%)
What occurs during the maturation phase of amelogenesis?
Most of the matrix proteins are removed
Mineral content of enamel is increased
Mature enamel is 95% mineral
What occurs during the protection phase of amelogenesis?
Ameloblasts regress to form a protective layer - the reduced enamel epithelium
Involved in eruption
Formation of epithelial attachment
How is the root of a tooth formed?
HERS grows apically
HERS induces formation of root dentine
HERS then breaks up and persists as debris of Malassez
Mesenchymal cells from the follicle contact the dentine and differentiate into cementoblasts
These form cementum
Fibres from the developing PDL are embedded into the cementum (sharpeys fibres)
What is dentine?
Forms bulk of teeth
Harder than bone and cementum but not enamel
Greater compressive and tensile strength compared with enamel
Permeable; contains tubules
Contains cell processes
Yellowish in colour
What does dentine consist of?
Hydroxyapatite - 70% weight, 50% volume
Water - 10% weight, 20% volume
Organic matter - 20% weight, 30% volume
What are the contents of dentinal tubules?
Odontoblast process
Unmyelinated nerve terminals (sensory)
Dendritic cells
Dentinal fluid (ECF) from pulp
What does dental pulp contain?
- Connective tissue
- Cells - odontoblasts, fibroblasts, defence cells
- Extracellular components- fibres, matrix
- Nerves
- Blood vessels
- Lymphatics
What is the function of dental pulp?
- Nutritive
- Dentine growth
- Dentine repair
- Defence
- Neural - sensory, control of dentinogenesis
What is a morula?
4-6 days
Solid mass of cells
What is a blastocyst
6-10 days
A hollow ball of cells:
- Inner cell mass
- Trophoblast
What is a zygote?
Fertilised ovum - begins as single cell but rapidly divides into morula
What does the placenta do?
It is the embryo’s life support
Baby’s blood is replenished from the mother’s blood - circulations dont mix, seperated by a thin barrier
What is the bilaminar embryo?
At approx 10-12 days, the implanted trophoblast contains an embryo, which has 2 cell layers
- Epiblast - embryonic ectoderm, mesoderm and endoderm
- Hypoblast - endoderm and extraembryonic mesoderm
What is the difference between identica; and fraternal twins in the blastocyst?
Identical twins have a divided inner cell mass
Fraternal twins have two blastocysts
What occurs during gastrulation?
The embryo develops
- an axis
- formation of a groove - primitive streak
How are the mesoderm and endoderm formed?
Some ectodermal cells from the epiblast are induced to differentiate and migrate through the primitive streak, towards the hypoblast, these new cells are the mesoderm.
A ‘not so clear’ interaction between the newly formed mesoderm and hypoblast forms the endoderm.
How is the trilaminar embryo formed?
Mesodermal cells push through the primitive streak and spread out to form a third layer.
When does organogenesis occur?
Weeks 3-8, organs develop from the 3 basic germ cell layers
CNS one of first - formation of neural groove (approx 20 days)
What is spina bifida?
Persistance of the neural groove - neural groove should form the neural tube in production of the CNS
How does the trilaminar embryo begin to take shape?
Front and back ends begin to fold under the middle
The embryo folds round the yolk sac and some important organs appear - heart, liver, lungs
When is the embryo considered a foetus?
9 weeks
Where are embryonic stem cells found?
- Inner cell mass (‘totipotent’)
- Cells in 3 germ cell layers (‘pluripotent’)
Where are adult stem cells found?
Committed cell lines e.g. bone marrow stem cells
What does the ectoderm give rise to?
Skin
Mucous membranes of mouth and anus
Brain, spinal cord
Tooth enamel
What does the mesoderm give rise to?
Most connective tissues - dermis, tendons, cartilage, bone Muscle Blood vessels Kidney/Urinary system Reproductive system Serous membranes
What does the endoderm give rise to?
Alimentary canal (pharynx-rectum)
Respiratory system
Parts of urogenital system
What does ectomesenchyme give rise to?
Peripheral NS - sensory/autonomic Melanocytes in skin Adrenal medulla Mesenchyme in head Dentine, cementum, pulp, PDL, Jaw, bones
What is the periodontal ligament?
A connective tissue, containing:
- Cells
- ECM
- Fibres
- Nerves
- Blood vessels
What does the periodontal ligament matrix consist of?
- Hyaluronate glycosaminoglycans
- Proteoglycans
- Glycoproteins
Behaves as a viscous elastic gel
What are the cells of the PDL?
Fibroblasts Cementoblasts Osteoclasts and cementoclasts Epithelial cells Defence cells
What nerves/receptors do the PDL contain?
Sensory - mechanoreceptors, nociceptors
Autonomic (SNS) - blood vessel control, vasoconstriction
What are the periodontal fibres?
True periodontal ligament - fibres connecting tooth to alveolar bone
‘Gingival’ ligament - fibres mainly above the alveolar crest, including ‘free gingival’ fibres
What is the purpose of the PDL?
Attaches tooth to jaw
Transmits biting forces to alveolar bone
What are the alveolo-dental ligament fibres?
Alveolar crest Horizontal Oblique Apical Inter-radicular (multi-rooted teeth)
What are the interdental ligament fibres?
Trans-septal
What is the function of the oral mucosa?
Protection Sensation Secretion Absorption (Thermoregulation)
What are the types of oral mucosa in the mouth?
Gustatory - tongue
Masticatory - gingiva
Lining
What are the characteristics of masticatory mucosa?
(para) keratinised
Thick lamina propria (mucoperiosteum)
Subjected to friction, compression
What are the characteristics of lining mucosa?
Mobile and distensible
Non-keratinised
Loose lamina propria and wide submucosa
More rapid turnover than masticatory mucosa
What are the characteristics of gustatory mucosa?
Similar to masticatory
Keratinised
Present only on dorsum of tongue
Caracterised by papillae, some bearing taste buds
What is the structure on mucosa?
Epithelium
Lamina propria
Submucosa
Bone
What are the cell layers of the epithelium?
Stratum corneum
Stratum granulosum
Stratum spinosum
Stratum germinativum
What are examples of non-keratinocytes?
Melanocytes
Merkel cells
Langerhans cells - (dendritic cells)
What type of epithelium is in the oral cavity?
Stratified squamous
What are the 3 types of papillae present in gustatory mucosa?
Vallate
Filliform
Fungiform
Histologically how do you identify sebaceous or salivary glands?
Salivary gland subsections much larger
What is geographical tongue?
Irregular, smooth patches No FILIFORM papillae Red/white margins Asymptomatic - some ppl have discomfort No Tx usually required
What are the functions of oral fluids?
Protective
Digestive
What are the three major salivary glands?
Parotid - serous
Submandibular - mixed
Sublingual - mucous
What are the minor salivary glands?
Buccal (cheek) - mucous
Labial (lip) - mucous
Lingual (tongue) - mixed
Palatal (hard and soft palate) - mucous
What is the structure of a salivary gland?
Secretory units exist within the acinus
Secretory units supplied by ducts (intercalated, striated, collecting)
What is gingival crevicular fluid?
Fluid from epithelium lining the gingival crevice (sulcus), flow increases with inflammation
When is salivary flow rates the lowest and highest?
Lowest - sleeping
Highest - eating
What salivary gland contributes most when asleep?
Submandibular (70%)
No parotid
Equal sublingual (15%) and minor glands (15%)
What salivary gland contributes most when stimulated?
Parotid (50%)
Closely followed by submandibular (40%)
Minor glands 8%
Sublingual 2 %
What factors affect unstimulated salivary flow rate?
State of hydration Previous stimulation Circadian rhythm Circannual rhythms Medications Salivary gland disease
What is the composition of saliva?
Inorganic - water (99.5%), Ions (0.2%)
Organic - Mainly proteins (0.3%)
What is the function of fluoride in saliva?
Antibacterial
Forms fluoroapatite
Promotes remineralisation
What is the function of calcium and phosphate in saliva?
Remineralisation
What is the function of thiocyanate in saliva?
Antibacterial
What is the function of bicarbonate/phosphates in saliva?
Buffering - effective at high flow rates, when HCO3 is highest
Phosphates - important ‘at rest’
How is saliva secreted?
Through a chloride shift causing osmotic diffusion of water
What is the function of salivary amylase?
Hydrolyses 1-4 alpha starch glycosidic links to maltose, maltotriose and alpha limit dextrins
What is the function of salivary lysozymes?
Non-specific defence
Attacks bonds in bacterial cell walls causing lysis
What is the function of salivary lactoperoxidase?
Enzyme which allows oxidation of thiocyanate to hypothiocyanate which is antibacterial
What is the function of salivary cystatins?
Antimicrobial - Inhibits cysteine proteases
What is the function of salivary gustin?
Activates taste buds
Potent PDE 5 activator
What is the function of salivary histatins?
Histidine-rich proteins
Inhibit CaPO4 precipitiation - antimicrobial
Inhibits:
C. albicans
S. mutans
What is the function of salivary immunoglobulins?
Secretory IgA
Specific immunity against bacteria
Vaccine vs S.mutans
What is the function of salivary lacotferrin?
Iron-binding protein
Binds Fe3+
Antibacterial
What is the function of salivary lipase?
From von Ebner glands on tongue
Hydrolyses triglycerides
What is the function of salivary mucins?
Binds to tooth and epithelium for protective role, lubricant and component of primary pellicle
Affects bacterial adhesion
Promotes bacterial aggregation making it easier to clear from mouth
What is the function of salivary statherins?
Anticalculus action
What are examples of unconditioned salivary stimuli?
Mechanical - pressure on PDL/oral mucosa
Chemical - gustation, olfaction, common chemical sense
What is the most potent chemical type to receptors on taste buds?
Acid > umami = salt > sweet > bitter
What are examples of conditioned salivary stimuli?
Learned responses to
‘Psychic’ stimuli (thinking about food)
Visual stimuli
Auditory stimuli
How is saliva secretion controlled?
PNS - Increase secretion and increased blood flow
SNS - Increase secretion and decrease blood flow
What is the 2-stage mechanism of saliva secretion?
Primary secretion in acinus
Secondary modification in ducts
What occurs during ductal modification?
Primary saliva modified as it passes through striated ducts
Reabsorption of sodium and chloride
Secretion of potassium and bicarbonate
Final saliva is hypotonic to plasma
What is clearance?
Refers to the rate at which substances are removed from the mouth
What is the importance of clearance?
- Removal of harmful substances increased by high salivary flow rates (rapid clearance)
- Retention of ‘beneficial’ substances is improved by low salivary flow rates (slow clearance)
Thus topical F- preparations should be tasteless and tablets should be sucked, not chewed
What is the stephan curve?
A graph of plaque pH change over time
How does gum work to decrease plaque?
It increases salivary flow and will neutralise acid created from plaque by increased bicarbonate content of saliva
What are the categories of alternative ‘sugar-free’ sweeteners?
Bulk caloric (sucrose)/low caloric (mannitol) sweeteners
Non-calorie, high-intensity sweeteners (aspartamate)
What is xerostomia?
When salivary flow rates fall below 50% of normal levels
Such reductions require loss of function of more than one major salivary gland
What can cause decreased salivary flow?
Side effects of drugs - could effect ANS control of salivary glands
Radiotherapy
Diseases - Sjogrens syndrome
What are the consequences of reduced salivary flow?
Increased dental caries Increased oral disease Dysaesthesia (burning mouth) Impaired oral function Diminished taste perception
How do you manage xerostomia?
Depends on cause
If functioning tissue gland present - stimulate salivary flow by chewing or drugs
If not - saliva substitutes either mucin based or cellulose based can be used
