Dental Development 1
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Why are the development of teeth important to LVTs?
- need to be able to advise clients about care of pregnancy animals and neonatal care (nutrition and baby teeth)
- general work with pregnant and neonatal animals (vaccines, what drugs to use)
- specific dental work on patients (deciduous tooth extraction, why not to perform endodontics on young animals)
What are the different layers of the teeth?
What is the ectoderm?
outside layer of early embryo - epithelial tissue - will form epidermis, nervous system, and enamel of teeth
What is the mesoderm?
middle layer of early embryo - mesenchyma
What does the mesoderm form?
- connective tissue (bones, cartilage, blood, bone marrow)
- lymphoid tissue
- dentin of teeth
What is the endoderm?
inner layer of early embryo - also epithelial tissue
What does endoerm form?
- inner lining of lungs
- inner lining of GI tract
What is the order of formation for the tooth?
- formation of the tooth bud
- formation of the root
- formation of enamel
- formation of dentin
What is the order of formation of the tooth bud?
- tooth bud
- dental papilla
- enamel organ
- growht of the tooth
What initiates the formation of a "tooth bud"?
How does the tooth bud form?
- epithelium invaginates into surrounding mesoderm
- this mesoderm will form the dental papilla and the bone of the jaw
- the invaginated epithelium flares out, its tip is pushed back in, and it assumes a double-walled "bell" shape
- the primary tooth bud develops (which will form the deciduous tooth)
- the secondary tooth bud develops at the same time as the primary tooth bud (it goes dormant until it is time for the permanent tooth to develop and replace the deciduous tooth)
The mesoderm inside this "future crown" is called ______.
the dental papilla
What do the cells within the dental papilla differentiate into?
What do odontoblasts make?
dentin (the bulk of the tooth)
What do the epithelial cells adjacent to odontoblasts differentiate into?
What are ameloblasts?
the cells which make enamel
What do the rest of the epithelial cells do after the ameloblasts are formed?
they become support cells for the ameloblasts
The ameloblasts and the epithelial support cells all together are called the _____ of the tooth.
Where does growth of the tooth begin?
begins at the tip of the crown and progresses toward the apex of the root
The enamel is fully formed before what?
the tooth erupts
What happens once the enamel is fully formed?
the tooth begins to erupt
What causes the tooth to erupt?
development of the root
What is the order of the formation of the root?
- formation of cementum
- formation of root dentin
What is the cementum?
the partially mineralized surface of the root
What is the Hertwig's epithelial root sheath?
is the structure that forms the cementum covering of the roots
What does the root sheath start as?
a band around the tooth at the base of the crown or more than one band if the tooth is multi-rooted
What do the epithelial cells in Hertwig's root sheath differentiate into?
What are cementocytes?
cells that produce cementum
How is the root dentin formed?
odontoblasts multiply at the inside edge of the root sheath and lengthen the root as they form dentin
How does the tooth erupt?
the formation of dentin pushes the crown to and throught the surface of the jaw
What is apexification?
- as the tooth root reaches its full length, the root sheath constricts forming the apex of the tooth
- small openings are left for blood vessels and nerves to enter then pulp cavity of the tooth
What are the small openings during apexification?
- apical foramen: one main hole, usually in humans
- apical delta: many tiny openings, most usual in dogs and cats
What can cause apexification to occur prematurely at an abnormally shortened length?
if something mechanical interferes with the eruption of the tooth (example...impacted tooth)
What is the hardest substance produced by living things?
What is the function of the enamel?
retards tooth wear and protects dentin
How does the enamel form?
- ameloblasts secrete enamel matrix towards the odontoblasts
- this pushes the ameloblasts away from the dentin
What is the enamel composed of?
mostly of mineral in crystallized prisms that are lined up at right angle to the surface of the tooth
What happens when enamel breaks?
it follows the prisms all the way to the surface of the dentin rather than across the enamel surface
Is enamel brittle and thin?
Is enamel live tissue?
no, since no part of a cell remains inside it
What produces dentin?
_____ secrete dentin toward the enamel-dentin junction.
What happens when more dentin is laid down?
the body of the odontoblast is pushed away from the enamel-dentin junction as it lays down more dentin. this leaves a thread-like cytoplasmic process inside the dentin as the odontoblast retreats
When the odontoblast retreats what does it form?
a tubule in the dentin - a dentinal tubule
What is the different between dentin and enamel?
- arrangement of mineral material
- amount of organic, or non-mineral, material
The dentin from adjacent odontoblasts joins...
- to form a solid wall of dentin
- perforated by dentinal tubules
Dentinal tubules exten almost all of the way to...
- the dentin-enamel junction in the crown
- the dentin-cementum junction
Is the dentin live tissue?
- yes since it is part of the odontoblasts stay inside it
- fluid from odontoblasts is able to circulate within the dentin
What are the different classifcation of dentin?
- primary dentin
- secondary dentin
- tertiary dentin
What is primary dentin?
the dentin laid down before the tooth erupts
What is secondary dentin?
the dentin laid down after the tooth erupts
What is tertiary dentin?
What continues to lay down dentin during the life of the tooth? What does this cause?
- this causes dentinal walls to thicken throughout life
- this causes narrowing of pulp cavity throughout life
Dentin laid down later in life tends to be what color? What is this due to?
- darker in color more tan or brownish
- arrangement and organic material
What is the arrangement of secondary dentin?
dentinal tubules are more closely packed
Why are dentinal tubules more closely packed in secondary dentin?
are more closely packed because odontoblasts converge together as the dentin thickens and pushes them all towards the tooth center
Why is the secondary dentin have more organic material?
- more closely packed dentinal tubules contain more organic material
- organic material tends to take up stain from the mouth
What happens if the tooth is worn or suffers a closed fracture?
Does infection occur during tertiary dentin?
no because the tubules are too small for bacterial to enter
What does the tooth with exposed dentin become sensitive to?
How does tertiary dentin fix the tooth?
odontoblasts are activated into laying down additional dentin into the exposed tubules
Describe the dentin in young teeth.
- when the tooth is young its walls are thin
- the young tooth is relatively resilient because the dentin walls are thin
- the young tooth is also relatively resilient because the tubules within the dentin are wide containing more dontoblast cytoplasm and fluid than in older tooth
- young animals tend to fracture their teeth more frequently
Describe the dentin of older teeth as they age.
- the dentin gets thicker
- the pulp cavity narrows - decreasing the blood supply
- the dentinal tubules become calcified
Where is the pulp cavity?
present inside the dentin of both crown and root and contains tooth pulp
What does the tooth pulp consist of?
blood vessels, lymph vessels, nerves, connective tissue and a layer of odontoblasts next to the dentin
What does the periodontium contain?
structures which support the tooth - periodontal ligament and alveolar bone
What is the periodontal ligament?
connective tissue fibers line up perpendicular to the root surface and suspend the tooth inside the alveolus or tooth socket
What do the spaces between fibers contain?
fibrocytes (fibroblasts), blood vessels, and nerves
Is the periodontal ligament always under repair? Why or why not?
yes because of constant wear
Does the periodontal ligament help cushion?
yes to prevent damage to bone during chewing and biting
Why does the periodontal ligament act as a physical barrier?
provides a physical barrier to osteoclasts present in alveolar bone that would tunnel into and damage dentin
What is alveolar bone?
is dense cortical type bone surrounded by less dense cancellous bone
What is the lamina dura?
the very white line of alveolar bone outside the dark periodontal ligament on a radiograph
How can the canine distemper virus affect dental development?
- attacks ameloblasts
- causes enamel hypoplasia if the pup is infected at the right stage of dental development
Why do we need to vaccinate for canine distemper virus?
prevents enamel hypoplasia
How can a severe fever affect tooth development?
can affect the enamel organ and cause the formation of abnormal enamel - enamel hypoplasia
Why do we need to remove retained deciduous teeth?
to provide room for permanent teeth to erupt properly
What do we need to be care we don't do when removing decidious teeth?
take care to not damage the emerging permanent tooth
Can we do root canals on young animals? Why or why not?
no becuase the pulp cavity is too wide
When we check a tooth fracture what do we need to check for?
open or closed
What is an open tooth fracture?
into the pulp
What is a closed tooth fracture?
not into the pulp
When we see a dark spot on a tooth we need to check it with a dental explorer. If the dental explorer slides over the dark area when what does that mean?
it is probably tertiary dentin and not a problem
If you can get the dental explorer to "catch" on a dark spot in the dentin then what does that mean?
it is a hole into the pulp and we need to bring it to the veterinarian's attention
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