Histology Flashcards
1
Q
bud stage
A
- initiation
- 1st epithelial incursion into the ectomesenchyme of the jaw; the supporting ectomesencyhmal cells are closely packed beneath and around the epithelial bud
2
Q
cap stage
A
- proliferation
- bud proliferates more into ectomesenchyme
- epthithelial ingrowth looks like cap on ball of condensed ectomesenchyme
- ingrowth = dental organ — later forms enamel
- stage when blood vessels enter papilla (pulp)
3
Q
bell stage
A
- histodifferentiation and morphodifferentiation
- dental organ comes to resemble a bell as undersurface of the epithelial cap deepens
- phase when crown size/shape is determined
- phase when specific cell tissue types develop
4
Q
dental organ
A
forms enamel
5
Q
dental papilla
A
forms dentin and pulp
6
Q
dental follicle
A
- condensed ectomesenchyme that gives rise to supporting tooth structures – cementoblasts adn PDL
- limits dental papilla & encapsulates dental organ
7
Q
late bell stage
A
dental lamina disintegrates
tooth now develops divorced from epithelium
8
Q
enamel organ formation
A
occurs in cap to bell stages up til dentin formation
9
Q
crown stage
A
hard tissue is laid down
10
Q
changes from normal tooth devo??
A
cause extra or missing teeth
11
Q
ameloblasts from what germ layer
A
ectoderm. so enamel is from ectoderm (dentin is mesoderm)
12
Q
thickness of enamel
A
- thickest at incisal/occlusal surfaces and thinnest toward CEJ
- 2mm incisal edge incisors
- 2.3-2.5mm PM cusps
- 2.5-3.0mm molar cusps
13
Q
enamel thickness at jxn of devo features
A
decreases (at cuspal lobes) – non coalesced lobes have fissured jxn and zero enamel — PITS and FISSURES
14
Q
pits and fissures
A
pit – at deepest part of fossa
fissure – in grooves
15
Q
enamel hardess surface vs DEJ
A
hardest on surface, least hard at DEJ
16
Q
how hard is enamel
A
5x harder than dentin, like steel
17
Q
enamel high elastic modulus and low tensile strength
A
- stiff, does not deform under stress
- brittle, does not take much tensile strength to break
18
Q
enamel composition
A
by volume…. 90-92% HA; 1-2% organic matrix proteins; 4-12% H2O
19
Q
enamel structure
A
millions key hole shaped rods with HA crystals running at different angles; rods go from DEJ to surface and are densely packed and intertwined; rods are perpendicular to DEJ adn surface EXCEPT slightly apical at cervical region of tooth
20
Q
where are enamel rods not perpindicular
A
cervical region of tooth – slightly apical
21
Q
striae of retzius
A
growth rings, resulting variations in structure and mineralization due to rod formation process — rods are formed lineraly by successive apposition of enamel in discrete increments
22
Q
imbrication lines of pickerell
A
when straie of retzius circles (As viewed from horiz.section) are incomplete at enamel surface, these grooves form
23
Q
perikymata
A
elevation between the grooves called imbrication lines of pickerell that are due to incomplete circles of retizus striae; they are continuous around a tooth and parallel to CEJ and to each other
24
Q
rods and susceptibility to acid
A
rods are made of millions of small elongated apatite crystallites; the orientation of crystallites influences susceptibility to acid
- more dissolution in head region, where crystallites are almost parallel to rod long axis
- less in tail region where they incline with increasing angles to the prism axis
25
is the DEJ hypermineralized
yes.
26
enamel lamellae
thin, leaf like faults between enamel rod groups that extend from enamel surface to DEJ, sometimes into dentin
- -mostly organic material
- -WEAK area that predisposes tooth to entry of bacteria and caries
27
enamel tufts
hypOmineralized structures that project between adjacent groups of enamel rods from DEJ; arise in dentin and extend into enamel; can play role in caries spread
28
enamel spindles
odontoblastic processes whose ends are thickened; they cross DEJ into enamel; may serve as pain receptors, which explains enamel sensitivity experienced by some patients during tooth prep
29
what explains enamel sensitivity experienced by some patients during tooth prep
enamel spindles; odontoblast processes with thick ends that extend into enamel
30
histological structure of enamel rods --- acid etching
- mineral acids (phosphoric) selectively etch enamel rods
- 25-75micrometer holes surrounded by interprismatic substances, which increases surface area by 200x
- pores used to grip and retain composite resin tags
**acid opens spaces between rods, this allows resin monomers to permeate between crystals
31
where are fractures more likely in relation to enamel rods
in planes parallel to rods because bond btwn rods is weak; less likely in plane across rods
32
dentin support of enamel
prevents fractures, undermining is loss of dentinal support
rods are perpindicular to DEJ and surface
inner end of enamel rod must be on DEJ, not just air
33
enamel color
translucent, color comes from dentin
| localized discoloration from devo issues
34
enamel repair
--only self repair is partial remineralization by F- ions
35
enamel transport
- enamel is permeable to certain ions/molecules
- route of passage through HYPOmineralized structural units (which are rich in organic material) -- rod sheaths, enamel cracks and other defects
- H2O is transporting medium through small intercrystalline spaces
- H2O2 (bleaching agent) has low molecular weight, so it easily passes through enamel adn dentin
36
bleaching teeth
- lighten teeth by chemical agent that oxidizes the organic pigmentation of teeth
- H2O2 is a bleaching agent that easily passes through enamel adn dentin because low molec.wt
37
dentin origin
mesoderm
38
dentin composition by volume and weight
by volume: 45%mineral, 33%organic, 22%H2O
| by weight: 70%mineral, 20%organic, 10%H2O
39
dentin fxn
```
protect pulp (barrier to chemical/thermal insults)
support enamel
```
**thickness of the remaining dentin following a cavity prep is the MOST IMPORTANT factor in protection of pulp and contributes to success/failure of restoration
40
what is most important factor in protection of pulp following cavity prep
thickness of remaining dentin
41
characteristics of dentin -- thickness, compressibility, resiliency, etc
- elastic
- 1/5th as hard as enamel
- flexibility --- helps support more brittle/nonresilient enamel
- 3x harder at DEJ than pulp
- slight compressibility adn resiliency, counteracts brittle enamel
42
radiograph dentin vs enamel
dentin is more radiolucent (darker)
43
basic devo of dentin
- odontoblasts form dentin
- cell bodies are in pulp and the processes go up in dentin tubules
- dentin is series of S-shape tubules from pulp to DEJ
- predentin = unmineralized area lined by odontoblast cell bodies right agsint pulp
44
predentin
between pulp and dentin there is an unmineralized zone of dentin smack up against cell bodies of odontoblasts
45
where is dentin most dense adn tubules largest
- lumens are widest at PULP and most numerous adn dense at pulp
- closer to DEJ = smaller and more sparsely distributed tubules
- comparing similar depths btwn crown adn root dentin -- more tubules in coronal dentin
46
types of dentin
1. intertubular = primary product of odontoblasts, bwtn tubes
2. intratubular = lines the tubes, more mineralized
- -primary: forms initial shape of tooth
- -secondary: forms at reduced rate throughout life
- -tertiary = reparative: forms when stimulated to increase distance between pulp adn stimulus
47
intertubular dentin
- primary secretory product of odontoblasts
- type I collagen fibrils aligned at right angles to tubule
- apatite crystals oriented parallel to collagen fibrils
- crystals = .1 micrometer long
48
intratubular = peritubular dentin
lines tubules adn more mineralized than intertubular
49
reparative dentin
tertiary. formed in response to moderate level stimuli (attrition, caries, some op.procedures); structurally different from primary and secondary; increases distance between pulp and stimulus; some liners and pulp capping procedures used to stimulate tertiary dentin for protection
50
fluid movement adn dentin
fluid movement (such as cutting or air drying) distorts odontoblasts and afferent nerves adn causes pain
51
microscopic pulp exposures
- from any preps that have floor in dentin
- because dentinal tubules extend to pulp
- use cavity liners and bases to protect/seal cut dentinal tubules
52
smear layer
- thin layer of debris on surface when dentin is cut/abraded
| - composed of HA adn altered/denatured collagen
53
smear plug
when smear layer fills opening of dentin tubules
| smear plugs make dentin tubules 90% less permeable
54
micromechanical bonding to dentin
similar to enamel; adhesion relies primarily on penetration of adhesive monomers into the network of collagen fibers left exposed by acid etching
55
chemical bonding of dentin
important for adhesive materials that do not require etching; glass ionomer cements & phosphate based self etch adhesives
-- bonds between HA + either polycarboxylic monomers or phosphate monomers
56
3 step etch and rinse bonding
1. etchant: removes smear layer, exposes collagen, opens tubules, decreases surface free energy
2. primer: binfunctional molecules (h.phobic and h.philic); envelops external surface of collagen fibrils and increase surface free energy til compatible with h.phobic molecules
3. bonding agent: mainly h.phobic monomers; penetrate adn polymerize in interfibrillar spaces; structural backbone of hybrid layer
57
dentin etching -- role of acids
- partially or totally remove smear layer and demineralize dentin
- open tubules and expose dense filigree of collagen fibers
- increase microporosity of intertubular dentin
58
how much is dentin demineralized from etching
up to 7.5micrometers
| depends on type and concentration of acid and time it is applied
59
hybrid zone
primer and bonding agent appleid to etched dentin; they penetrate intertubular dentin and form HYBRID zone (resin-dentin interdiffusion zone)
60
dental pulp
- dentin all around it, immediatly lined by odontoblast cell bodies
- contains: nerves, arterioles, capillaries, lymph channels, conn.tissue cells, intercellular substance, odontoblasts, fibroblasts, macrophages, collagen and fine fibers
61
4 fxns of dental pulp
1. nutritive (supplies odontoblasts and processes)
2. formative/devo (primary dentin)
3. protective/sensory (pain sensation from nerves)
4. repair/defense (tertiary dentin)
62
pulp chamber size
decreases over life because secondary adn tertiary dentin make it smaller
63
cementum
- avascular, thin, bony tissue lining dentin of root
- fxn = attachment of supportive fibers of PDL
- cementoblasts (MESENCHYMAL CELL origin)
- 45-50% HA by weight, softer than dentin
- lighter yellow than dentin
- formed throughout life to replace itself as it wears so attachment is intact
64
sharpey's fibers
portions of pincipal collagenous fibers of PDL embedded in cementum and alveolar bone to attach tooth
65
2 types cementum
1. acellular: living tissue that does not incorporate cells into structure --- CORONAL
2. cellular: APICAL
66
cementum at apical part of root
surrounds apical foramen and can extend into inner pulp canal
67
cementum adn enamel meet, 3 ways
1. overlap
2. meet
3. space bewteen cementum and enamel -- SENSITIVE area
68
cementum composition by weight
45-50% inorganic HA and 50-55% organic adn water
69
resorption of cementum
not normal, but can happen if excessive ortho pressure
70
gingiva
- protective, easily damaged by operative instruments
- poor restoration contours and morphology --> long term perio issues
- incorporate the following into restoration design: embarsure form, contact area, contours, ht of contours
