Week 10 - Eruption and Shedding Flashcards
How does primary and permenent dentition develop?
simultaneously as the jaws increase in size from infancy to adolescence. Upper and lower jaws grow at about the same rate
What does the jaw accommodate development of during infancy?
20 deciduous teeth
What does the jaw accommodate for at 4-5 years of age?
20 erupted teeth and 28 developing teeth
What does the jaw accommodate for at 8-12 years of age?
there is a mixed dentition stage that involves the concomitant exfoliation of deciduous teeth and eruption of permanent teeth
What is tooth eruption?
movement of a tooth from its site of development within the alveolar process to its functional position in the oral cavity
What three stages is tooth eruption divided into?
- Pre-eruptive stage
- Pre-functional eruptive stage/eruptive phase
- Functional phase/post-eruptive phase
What occurs during the pre-eruptive phase?
where there is growth of jaws, growth of tooth buds, along with remodeling of the body crypt
What direction do teeth have a tendency to grow? migrate?
grow distally and migrate mesially into their position
When does mesial migration occur?
when there is resorption of the mesial wall with concomitant apposition of bone on the distal wall
Over time, jaws increase in size to accommodate for teeth. They increase in:
- Length (anterior posterior) of jaw
- Width of jaw (coronal plate)
- Alveolar ridge height
- Buccal-lingual width of alveolus
Describe how deciduous teeth develop and how the tooth germs grow
the deciduous teeth develop within the jaw and have considerable room. However, the individual tooth germs grow rapidly and due to jaw length, they become crowded anteriorly
What happens to teeth as jaws increase in length?
the crowding is alleviated by migration of teeth distally which allows a more even distribution
What happens to teeth as jaws increase in size?
the developing teeth move outward (facially) and towards the oral cavity (upward or downward)
What happens to permanent developing molars because of jaw length?
Because of the jaw length, the permanent developing molars have angled inclination (mesially) prior to and during eruption and achieve vertical alignment only when jaw length is sufficient to allow it
Where do permanent teeth drift?
Permanent teeth drift mesially to take position in-between roots of primary teeth. Start distally and then drop down (??)
What are the theories of tooth eruption?
Most frequently cited theories are root growth, bone remodeling, and periodontal ligament formation
What are other factors that influence tooth eruption?
- Parathyroid hormone (influences mineralization and resorption of roots)
- MMPs produced by fibroblasts, osteoclasts, macrophages
What are root growth theories?
Elongation of the roots in relation to stability of the fundus of the socket allows tooth to erupt
What are vascular pressure theories?
Increase hydrostatic pressures in the apical dental sac or periodontal ligament
What are selective bone deposition and resorption theories?
- Coronal bone resorption concomitant with bone apposition in the fundus area
- Shifting of the tooth in an erupted path because you have bone being removed superiorly and bone being deposited inferiorly shifting things upwards into place
What is pulpal pressure theory?
- Tissue pressure differential in the pulp compared to the PDL
- As the tooth grows, you decrease pressure in pulp chamber (lower than PDL) causes PDL to increase pressure onto the tooth, pushing it upwards
What is the periodontal and gingival fiber ligament theory?
- Cells (myofibroblasts) exert traction on the tooth through the collagen network and cell-to-cell contacts
- Contraction of fibers push tooth up in a coronal direction
Describe the pre-functional eruptive stage/eruptive phase
due to pressure on fundus, root growth, and bone resorption/deposition
What happens in the pre-functional stage as the permanent tooth erupts?
causes resorption on deciduous tooth in front of it
What space does the pre-functional eruptive stage follow?
Follows its own canal space and remains a connection with the oral epithelium at the top (gubernacular canal)
What is the gubernacular canal?
eruptive pathway for succedaneous teeth. Is a strand of connective tissue that contains remnants of dental lamina epithelium (derived from successional lamina)
Describe the rate of eruption in the gubernacular canal
The rate of eruption is not constant but best described as a “burst of eruption” that averages about 3 mm every 3 months
Where is the gubernacular canal seen?
Intraorally
What are the parts of the functional phase/post-eruptive phase?
Occlusal surface wear
Proximal wear (mesial drift)
What occurs with the oblique fibers during the occlusal surface wear?
Oblique fibers of the PDL continually pull the tooth into occlusion as enamel is abraded
What does apical cementum deposition serve as during occlusal surface wear?
Serves as a compensatory eruptive mechanism to continual occlusal abrasion
What does mesial inclination of teeth in ful contact during interproximal wear yield?
an anterior force vector and when coupled with the pull of the transseptal fibers, resulted in mesial drift
What does wear between teeth cause?
Mesial drift so as we age this leads to more anterior crowding
What is exfoliation?
removal of primary/deciduous teeth
What is the stimulus for exfoliation?
Stimulus from dental follicle of adult tooth stimulates formation of odontoclasts and fibroclasts to degrade primary tooth structures to allow for eruption
Cell mediated tooth resorption involves the ________
Odontoclast
“multinucleated giant cell”
Describe the process of exfoliation
Odontoclasts and fibroclasts resorb the root from the apex up (**on lingual surfaces). Allows for tooth to start in mesial position and erupt
- It’s NOT the adult tooth that pushes against succedanous tooth and eating it away, but it is more like a front that clears away for tooth to have room to erupt
What are odontoblasts derived from?
monocytes that exit capillaries to become connective tissue macrophages
What are macrophages fused together to form?
form a syncytium (large multinucleated giant cell) that functions like an osteoclasts
What do odontoclasts degrade?
both the collagenous and non-collagenous matrix of cementum and dentin (lysosomal enzymes) and the hydroxyapatite mineral phase (acids)
- Odontoclasts degrade deciduous tooth materials to make room for succedanous tooth to come in
What are fibroclasts?
specialized fibroblast-like cells that destroy the collagen fibers of the PDL associated with the resorbing tooth root (primary)
What does the finding of apoptotic cell death in the resorbing PDL suggest?
that shedding of teeth is a programed event
Where is support for the apoptotic cell death theory found in?
tooth eruption in monozygotic twins, which indicates that tooth eruption and shedding is determined by genetic factors (approximately 80% genetic)
What teeth are most commonly involved in malocclusion? Why?
Canines
(due to erupting after incisors and premolars, having to squeeze in between)
What are examples of malocclusion?
- Excessive mesial drift
- Extra anterior teeth
- Impaction (can cause resorption of roots)
What is impaction common in?
3rd molars: can come with follicular cysts that contain activated odontoclasts and can eat away adjacent at 2nd molar
What can severe malocclusion lead to?
Arch defects, periodontal disease
