Lecture 10 Flashcards
tooth development and eruption
1
Q
List the chronology of teeth development
A
- W6-8: initiation of primary dentition
- W20-42: primordial of seccessional permanent teeth
- W20 - 5th year post natal - molars start to develop
2
Q
____________ - bands of thickened epithelial following the outlines of the future alveolar processes of maxilla & mandible. These bands divide into two thickenings.
A
Primary epithelial band
3
Q
Primary epithelial band rapidly divides into two thickenings:
A
- Dental lamina
- vestibular lamina
4
Q
The more superficial on labial/buccal side is the ___________.
A
Vestibular lamina
5
Q
Cells in the central part of the vestibular lamina degenerate & form a cleft which becomes the ____________.
A
oral vestibule
6
Q
The deeper part of the band on the oral side is the _________ from which the tooth buds develop.
A
Dental lamina
7
Q
Ten epithelial swellings grow down into the underlying __________ from each dental lamina. These are involved in the formation of the ___________ & also later the _________ apart from the molars which form from the tooth buds derived from the _______ parts of the dental laminae.
A
ectomesenchyme, deciduous teeth, permanent teeth, posterior
8
Q
T/F - As the tooth bud grows, ectomesenchymal cells accummulate around them.
A
True
9
Q
T/F - There is no basal lamina around the tooth bud, but it is present in cap & bell stages.
A
False, there is a basal lamina
10
Q
T/F - basal lamina temporarily breaks down during reciprocal induction
A
True
11
Q
T/F - connection of the tooth germ to the surface epithelium ends in late bell stage in humans.
A
False, it is still connected/persists until late bell stage
12
Q
_________ - the deep end of the tooth bud indents to form a cap shaped structure.
A
Cap stage
13
Q
At the cap stage, the deep end of the epithelial structure is often referred to as ________________ & the strand connecting the _______ to the surface ectoderm, the __________.
A
Enamel/dental organ, dental lamina
14
Q
Ectomesenchyme cells continue to accumulate around the dental organ to form the _________ (become cementoblasts & periodontal ligament).
A
dental sac
15
Q
The accumulated cells in the indentation of the cap are called __________ (become odontoblasts & pulp).
A
Dental papilla
16
Q
The cells on the outer/superficial part of the ‘cap’ are cuboidal & are the _________________.
A
External/outer enamel/dental epithelium (OEE).
17
Q
The cells facing the dental papilla are columnar & are the ___________________.
A
Inner/internal enamel/dental epithelium (IEE).
18
Q
the junction between outer and inner enamel epithelium is the ______________.
A
cervical loop
19
Q
The cells within the enamel organ are the _______________ because the cells are joined at intervals by desmosomes but elsewhere are forced apart by increased extracellular fluid.
A
Stellate reticulum.
20
Q
___________ is an accumulation of cells in the stellate reticulum adjacent to the central part of the inner enamel epithelium. These may extend across the full thickness of the cap to the outer enamel epithelium as the _____________.
A
enamel knot, enamel cord
21
Q
T/F - Enamel knot and enamel cord may be involved in determining the position of the first cusp of the tooth.
A
True
22
Q
The dental lamina is actually an indented sheet. The indentation is the _______, function unknown.
A
Enamel niche
23
Q
T/F - (Early bell stage) continued differential growth results in a deepening of the indentation on the overside of the cap
A
False, underside.
24
Q
A region of cells appear adjacent to the inner enamel epithelium in early bell stage - __________ - which play play a role in enamel formation
A
Stratum intermedium
25
T/F - (early bell stage), capillaries loop into the outer enamel epithelium (although endothelium & OEE both retain their basal laminae.
True
26
(Early bell stage) - a second tooth bud arises from the ______ side of the dental lamina of each of the deciduous tooth germs which is the germ of the permanent tooth (successional tooth).
Lingual
27
The connection of the permanent tooth germs with the deciduous dental lamina is called the ______________.
Lateral or successional lamina
28
T/F - in case of molars which have no deciduous precursor (accessional teeth) a strand of dental lamina grows anteriorly beneath the lining epithelium of the oral cavity from the posterior dental lamina.
False, it grows posteriorly.
29
T/F - Each posterior extension of the dental lamina gives rise to one tooth germ which along with the associated ectomesenchymal tissue will give rise to the first, second and third premolars.
False, each gives rise to three tooth germs, molars not premolars
30
T/F - (late bell stage) the dental & lateral laminae fragment so that the tooth germs are isolated from the oral epithelium.
True
31
( late bell stage) If the clusters of epithelial cells from the laminae persist these are called ___________ & may form cystic structures or even give rise to supernumerary teeth.
Epithelial pearls
32
T/F - reconnection of the enamel organ with the oral epithelium occurs just after tooth eruption
False, it occurs before
33
T/F - (late bell stage) the shape of the inner enamel epithelium folds into the shape of the crown of the developing tooth (due to different rates of cell division
True
34
T/F - dental hard tissues form in late bell stage by a process called apposition & reciprocal induction
True
35
T/F - the enamel organ is an epithelial structure that incorporates capillaries after formation of dentine & enamel
False, it incorporates capillaries around the same time as dentine and enamel formation.
36
T/F - enamel organ capillaries are derived from the dental sac & penetrate into the enamel organ complete with epithelium.
False, endothelium
37
T/F - most mammal species have capillaries from dental sac in enamel organ during crown formation
True
38
T/F - capillaries in enamel organ are present in reduced enamel epithelium
False, they are not present.
39
T/F - Mineralisation of enamel and dentine starts at the tips of developing cusps & is preceded by a cessation of mitosis in the cells of the IEE at these sites.
True
40
Ectomesenchymal cells adjacent to the IEE differentiate into ________ under the inductive influence of the ______ (these secrete several growth factors).
odontoblasts, IEE
41
Odontoblasts produce ______
predentine
42
Basal lamina separating ______ & _____ disintegrates called APPOSITION
Predentine, IEE
43
Once some dentine is present then _____________ follows (Amelogenesis) - process is called _____________
enamel formation, reciprocal induction
44
T/F - The differentiation of stratum intermedium & stellate reticulum is not lost as the enamel organ collapses due to an increase in extracellular fluid
False, differentiation is lost, due to decrease in ECF.
45
(Development of odontoblasts) - Describe Stage 1-4
- Shows dividing ectomesenchymal cells (lower row of cells) adjacent to the IEE (upper row of cells). Some differentiate into odontoblasts under the inductive influence of the IEE. Others remain as a reserve population of cells in the pulp. Basal lamina (solid line) is intact.
46
Describe stage 5 of development of odontoblasts
- shows odontoblasts producing predentine. Basal lamina (dotted line) separating predentine & IEE is disintegrating (APPOSITION)
47
Describe stages 6 & 7 of development of odontoblasts
- Odontoblast process developing & elongating & embedded in predentine & dentine. Note early enamel formation and in Stage 7, the beginning of Tomes process
48
Describe stages 1 & 2 (differentiation) of amelogenesis
ameloblasts differentiate from inner enamel epithelium cells
49
Describe Stage 3 of amelogenesis (Early secretory stage)
Ameloblasts elongate & secrete organic matrix which immediately undergoes some mineralization (about 30%) so that there is no pre-enamel. The first enamel lacks rods & interrods.
50
Describe Stages 4a & 4b of amelogenesis (Late secretory stage)
A single cytoplasmic process - Tomes processes - appears on the enamel side of each ameloblasts which continue to secrete. Tomes process result in the new enamel being laid down as rods & interrods.
51
Describe Stages 5a & 5b of amelogenesis (maturation stage)
After the entire volume of partly mineralized enamel is formed in a given region of the tooth, the ameloblasts undergo cytological differentiation & participate in both absorption of organic matrix components (& their intracellular breakdown) & in secretion of calcium ions (derived from plasma in capillaries) so that the final enamel is predominantly mineral (96%).
52
Describe Stage 6 of amelogenesis (protective stages)
Once enamel maturation is complete then a new basal lamina forms between the reduced enamel organ & the enamel. This is the protective stage of the ameloblast
53
T/F - Root & periodontal ligament formation only occur just before eruption
True
54
T/F - eruption involves complex movements of only deciduous teeth, not permanent teeth.
False, both teeth.
55
T/F - once crown has formed, internal & outer enamel epithelium grow upwards and then across the wide apical foramen.
False, they grow downwards.
56
T/F - There is no stellate reticulum & stratum intermedium between these two layers in part of the enamel organ which is involved in root formation.
True
57
The Inner & outer epithelium in root formation is called _____________________. The rim of the root sheath is the ___________________ & the space between the edges of the diaphragm is called the ______________________.
Hertwigs Epithelial root sheath, epithelial diaphraghm, primary apical foramen
58
Starting at the cervical region, odontoblasts differentiate & lay down ________ & _______ in a manner similar to that of the crown. Then the adjacent root sheath fragments, allowing cells of the ______ ______ to come into contact with the predentine & differentiate into ________. These then which secrete organic matrix of _______. This then calcifies
predentine, dentine, dental sac, cementoblasts, cementum
59
There is always a thin layer of unmineralised/partly mineralized cementum matrix on the developing cementum surface - ________________.
Precementum/cementoid
60
A very thin (10-20um thick) hyaline layer of enamel like material (______________________________) appears prior to cementum (may act as an attachment site for cementum.
hyaline layer of hopewell smith or intermediate cementum
61
(Crown part of enamel organ) - _________ covering of flattened cells over the enamel of the crown - was the coronal part of the enamel organ now called the ____________________.
Multilayered, reduced enamel epithelium
62
(Root Part) - Enamel organ is reduced to _____ layers IEE & OEE (Hertwigs Epithelial Root Sheath
Two
63
T/F - (root part of enamel organ) the epithelial root sheath rapidly loses connection with the reduced enamel epithelium as it fragments in a cervical (neck of tooth nearest CEJ) to apical direction (towards apex of root) as root dentine & cementum are formed.
True
64
What are epithelial rests/rests of malassez?
Remains of Hertwig's epithelial root sheath form clusters or networks of cells in the periodontal ligament.
65
What do rests of malassez secrete?
They secrete a new basal lamina & often persist the life of the tooth.
66
How are rests of malassez recognised?
They can be recognized as clusters of dark staining cells in healthy periodontium & appear to have no function.
67
T/F - if the periodontium becomes inflamed, rests of malassez may form epithelial lined cysts.
True
68
T/F - intermembranous bone is deposited around the developing tooth so that the inner wall of the alveolus comes to lie close to the tooth
False, intramembranous
69
T/F - blood vessels and nerves perforates the alveolar bone
True
70
T/F - initially the permanent tooth germ occupies the same bony compartment or crypt as the deciduous tooth.
True
71
T/F - Later, a partition develops so the permanent tooth germ still occupies same bony crypt on the buccal side of the root of the deciduous tooth.
False, it occupies a separate bony crypt, and it's on the lingual side.
72
this bony crypt has an opening on its lingual side, the ___________ _____.
Gubernacular canal
73
This gubernacular canal contains fine collagen & cords or clusters of cells derived from the dental lamina called the ______________.
Gubernacular cord.
74
T/F - gubernacular canals can be seen as openings on dry skulls of children on the lingual side of the deciduous teeth
True
75
T/F - (Tooth eruption) permanent tooth germs become positioned more apically (i.e. deeper in the alveolar bone)
True
76
T/F - (Tooth eruption) molars initially have their buccal surfaces directed posteriorly. These move into the buccal position as the jaws grow.
False, it's occlusal surfaces, and occlusal position.
77
T/F - Eruption of deciduous teeth is initiated with the formation of roots with accompanying remodelling of the periodontal ligament to accommodate eruptive movement.
True
78
T/F - prior to deciduous teeth eruption, the reduced enamel epithelium covering the crown of the tooth & the oral epithelium are not separated by connective tissue
False, they are separated
79
T/F - breakdown of this intervening connective tissue (in deciduous tooth) & proliferation in the two masses of cells results in fusion of the two epithelia.
True
80
T/F - following CT breakdown, it is followed by programmed cell death in the middle of the epithelia structure & the tooth erupts through this with haemorrhage.
False, no haemorrhage.
81
T/F - Reduced enamel epithelium remains attached to the gingival part of the enamel (in deciduous tooth) and becomes the junctional epithelium.
True
82
T/F - successional teeth includes permanent incisors, canines, molars
False, premolars not molars.
83
List mechanisms of successional teeth and shedding of deciduous teeth (6 parts):
- bone separating the crypts of deciduous & permanent teeth breakdown.
- root of deciduous tooth is resorbed
- the permanent tooth is repositioned (different growth & bone remodelling) to so that it lies beneath deciduous tooth rather than lingual to it.
- the gubernacular canal widens (osteoclastic activity).
- the remnant of the deciduous tooth is shed & permanent tooth erupts through widened gubernacular canal.
- post eruptive repositioning of the permanent tooth results from muscle movement of adjacent structures (tongue, cheeks etc) & occlusal forces. Post eruptive movements are ongoing throughout life - to accommodate occlusal changes including wear, tooth loss & mesial drift also orthodontic movements.
84
T/F - accessional teeth are those without deciduous precursors i.e. molars.
True
85
T/F - roots of deciduous teeth are kept and resorbed prior to the eruption of the permanent tooth by odontoclasts.
False, they are broken down and resorbed.
86
T/F - odontoclasts also break down periodontal ligament and some of the pulp and sometimes some of the enamel
True
87
T/F - odontoclasts lie in cavities in mineralized tissues
False, they lie in indentations called Howship's lacunae.
88
T/F - odontoclasts can be recognized because they are single nucleate.
False, they are multinucleate.
89
T/F - TEM studies have shown that the side of odontoclasts adjacent to the mineral has a small number of cytoplasmic processes (microvilli/brush border)
False, large number of cytoplasmic processes.
90
T/F - resorption is a smooth continuous process & may be accompanied by temporary formation of some reparative tissue.
False, it is not a smooth process
91
List mechanisms of tooth eruption (name 3)
- Root growth
- "cushion hammock ligament"
- periodontal ligament
92
T/F - Only teeth with roots can erupt.
False, teeth without roots can erupt too, and would require a fixed base for the roots to push against & it is known that pressure on the floor of the socket causes remodelling.
93
What is the "Cushion hammock ligament" referring to?
It refers to the connective tissue around the apex of the tooth - although this has no obvious attachment to the adjacent bone & cannot be a fixed base against the developing roots can push.
94
T/F - remodelling of the periodontal ligament during root growth may exert a force which results in tooth eruption.
True
95
T/F - teeth with periodontal ligaments may occasionally not erupt
True
96
T/F - teeth with gubernacular cord surgically removed cannot erupt.
False, they will still erupt.
