tooth eruption Flashcards
1
Q
What is tooth eruption?
A
axial or occlusal movements of the tooth from its developmental position within the jaw to its functional position in the occlusal plane
2
Q
When do movements of eruption start?
A
begin in the early bell stage and continue throughout the life span of the tooth
3
Q
What are the phases of eruption?
A
- pre-eruptive phase
- eruptive phase
- post-eruptive phase
4
Q
What is the pre-eruptive phase?
A
- starts in the early bell stage
- ends when the root formation begins
- in this phase the tooth germ grows to maintain its relation to the growing alveolar process by 2 movements
5
Q
What is drifting bodily movement?
A
osteoclastic activity in the crypt wall in advance of the moving tooth
and bone deposition on the crypt wall behind it
6
Q
What is eccentric growth?
A
one part of the developing tooth germ remain stationary while
the remainder part continue to grow so bone resorption is found on the surface of the crypt faces the growing part of the tooth germ (shift of the centre)
6
Q
What are the movements of deciduous teeth and when does it happen?
A
- deciduous tooth germs at first have good space between them
- because of their rapid growth they become crowded together especially in the anterior region
- when the infants jaw increase in length this crowding will be relieved by backward shift of the deciduous molars and forward drift of anterior tooth germs (bodily movements)
- also tooth germs move outwards as the jaw increase in width (bodily movements)
- the tooth germs move upward as the jaw increase in height (excentric growth)
7
Q
What are the movements of anteror permanent teeth and when does it occur?
A
- at first they develop lingual to the deciduous tooth germs at the same incisal plane and in the same bony crypts
- then because of the deciduous tooth germs movements, the
permanent germs will move more in apical position
8
Q
What are the movements of permanent premolars and when does it occur?
A
at first similar to anterior germs but they will be between the divergent roots of deciduous molars then become in apical position
9
Q
What are the movements of permanent molars and when does it occur?
A
- maxillary molars develop at maxillary tubrosity with occlusal
surfaces facing distally, then move round by the sufficient growth
of maxilla - mandibular molars develop with occlusal surfaces inclined
mesially and become upright by sufficient growth of mandible
10
Q
When does the eruptive phase start and end?
A
- starts at the time of root formation
- ends when the tooth has reached the occlusal plane
11
Q
What is formed during the eruptive phase?
A
- root
- attachment apparatus
- dento-gingival junction
12
Q
How is the root formed?
A
- by proliferation of epithelial root sheath of Hertwig at first apically leading to bone resorption in the floor of the bony crypt
- with the eruptive movement (coincide with PDL formation) space
will be created for the root and resorption will no longer occur
13
Q
How is the attachment apparatus formed?
A
- during root formation the dental sac will form the structures of attachment apparatus (PDL, cementum and bone on the crypt wall)
- it was thought that the readjustment of PDL during tooth eruption is via structure called intermediate plexus within the PDL
- by electron microscope such structure is not present and remodeling of periodontal ligament with fibroblasts occurs through the entire width of periodontal ligament
- fibroblast contains complex intracellular system of tubules and
filaments, some of them enable the cell to contract - this contractile ability has been shown in scar tissue
- the fibroblasts in PDL have numerous contacts with each other
through specialization of its cell membrane called fibronexus or adhesion plaque - this plaque is formed of a protein (integrin) which spans the cell
membrane and has receptors binding sites; - intracellular binds to the cytoskeleton
- extracellular binds to an adhesive glycoprotein called fibronectin, which in turn has the ability to bind strongly to extracellular collagen and hyaluronic acid
14
Q
How is the dento-gingival junction made?
A
- the crown is covered by R.E.E. which by its desmolytic enzymes
will cause degeneration of the overlying C. T., so the R.E.E. and
the basal layer of oral epithelium grows toward each other forming
epithelial plug from their union - the central cells of this plug will degenerate and form epithelial
lined canal through which the tooth erupt without hemorrhage - once the tooth erupts in the oral cavity the R.E.E. will form the
dento-gingival junction - the gradual appearance of the tooth in oral cavity due to occlusal
movement of the tooth called active eruption - where the gradual recession of D.G.J. from the tooth is called
passive eruption - sometimes when the tooth reach the occlusal plane, the root
continue to form; so again resorption of the socket floor will occur to accommodate to the forming root - all teeth have during this phase the previous structures but the
successional teeth have additional anatomical feature called gübernacular canal containing gübernacualar cord
15
Q
What is gübernacualar cord?
A
- formed of remnants of dental lamina and C. T, its function is guiding the permanent tooth as it erupts
- the cord present in Gübernacular canal
- the canal of anterior successors open lingual to the socket of
anterior deciduous teeth - the canals of premolars open in the socket of deciduous
molars (bi or trifurcated area)
16
Q
What are the movements that occur in eruptive phase?
A
- axial-occlusal movements: occurs in the direction of the long axis of the tooth
- drifting bodily movement: occurs in distal, mesial, lingual or buccal direction
- tilting or tipping movement: occurs around the transverse axis of the tooth
- rotating movement: occurs around the longitudinal axis of the tooth
17
Q
What happens in the post-eruptive phase?
A
- starts when the tooth reaches the occlusal plane
- ends at the end of the life span of the tooth
- the tooth movements in this phase occur to accommodate for;
- maintain the position of the tooth in the growing jaw: when the jaw increase in height the tooth will have axial movement with bone deposition on the floor and crest of the socket (this
will stop when jaw growth completed) - compensate for the occlusal and proximal wear
- this is done by axial and mesial movement of the tooth
- in mesial movement of the tooth, there is bone resorption mesially
and bone deposition distally of the socket wall - there was a thought that the axial movement is due to cementum formation apically but there is no evidence that cementum actually moves the tooth and it is probably an infilling phenomenon
18
Q
Why are the movements in post-eruptive phase done?
A
- close bite and injury to T.M.J.
- spaces between teeth (maintain the contact between teeth)
19
Q
What are the stages of mechanism of eruption?
A
- root growth
- vascular (hydrostatic) pressure
- bone remodelling
- periodontal ligament traction
20
Q
What happens during root growth?
A
- this theory based on root proliferation occur against fixed base (i.e. the bone) so the apical growth will be converted into axial-occlusal movements
- this is not true because root do not grow against fixed base, (pressure on bone will cause resorption)
- also if the root is the cause of eruption so the distances which will
the tooth move to reach the occlusal plane will be equal to root
length, but the tooth moves greater distance than the length of its root
length - previously there was a thought that the fixed base that the root grows against what is called cushioned-hammock ligament that inserted in the socket wall, but this structure is pulp delineating membrane and not inserted in socket wall so it can not act as fixed base
21
Q
What happens during vasculat (hydrostatic) pressure?
A
- the theory based on that the numerous b.v. apically maintain high extracellular fluid pressure that provides the eruptive force
- this is not necessary for tooth eruption because surgical excision of the growing root and associated tissues eliminates the periapical
vasculature, but it did not stop eruption
22
Q
What happens during bone remodelling?
A
- the theory based on that bone remodeling will bring about
eruption, but it is accepted that bone remodeling is the result and not the cause of eruption - the following experiments establish the absolute requirement for a dental follicle to achieve bony remolding and tooth eruption
- if the tooth germ is removed experimentally and the dental follicle is left intact, an eruptive pathway forms in the overlying bone
- also if a silicon replica is substituted for the tooth germ, it also erupt If the dental follicle is removed no emptive pathway forms.
- It is clear that the dental follicle seems to have some role in co-coordinating bony changes around the moving tooth since it provides the source for new bone forming and resorbing cells
23
Q
What happens during periodontal ligament traction?
A
- this theory suggests that the cells and fibers of the periodontal ligament pull the tooth into occlusion
- it is not known with certainty how this force is produced
- it has been suggested that the numerous cell to cell contacts
between fibroblasts could be involved in summating contractile
force - the fibronexus and associated fibronectin could transmit the force
to collagen fiber bundles. These bundles in turn are firmly attached to bone and tooth in the correct position to bring about tooth
movement - in summary the force moving the tooth is most likely generated by the contractile property of the ligament fibroblasts but a number of other conditions must exist to translate this contraction into tooth movement
- eruption must therefore be considered a multifactorial phenomenon
24
What are the local causes of disruption in eruption?
- premature loss of deciduous teeth
- fibromatosis gingiva
- ankylosis of bone and root
- successor of deciduous tooth is
missed
25
What are the systemic causes of disruption of eruption?
- endocrine disturbances (hypopitutarism and hypothyrodism)
- nutritional deficiency (protein, vit.D etc)
- the slight fever or general malaise which may accompany the eruption of deciduous teeth is due to a secondary infection via the soft tissue along the just emerging tooth
- the movements of the teeth during eruption are intricate and are
accomplished by minute coordination of growth of the jaws
- impacted tooth e.g. third molar may be due to uncoordination
between bone growth and tooth movements
- impacted tooth may lead to formation of dentigerous cysts
