L6 Flashcards
Osteogenesis Imperfecta
(Type I Collagen)
Dentinogenesis Imperfecta
(Dentin Sialophosphoprotein)
Dentin is
~ 50% mineral (by volume).
Dentin is ~ 30% organic matrix (by volume)
~ 90% collagen-I (by weight)
~ 90% of the non-collagenous protein is derived from DSPP (dentin sialophosphoprotein).
Other components: dentin matrix protein (DMP1), osteonectin (SPARC); bone sialoprotein (BSP); osteopontin (OPN); proteoglycans etc.
Odontoblasts differentiate from
dental papilla cells
Odontoblastic process:
A long cytoplasmic extension encased in dentin
Rate of deposition:
~4 µm/day
Cell free area
why it might be there (no one really knows): odontoblasts are moving away, so there is an area that is kind of empty so that there is room (kind of like an elastic slinky).
Odontoblastic layer
Cell-free zone:
nerve and capillary plexus
Cell-rich zone:
extensive vascular system
Pulpal core
odontoblastic layer
The lines of von Ebner,
~1 day growth (or Owen, accentuated lines due to disturbances in mineralization) are oriented in the horizontal axis at approximately right angles to the dentinal tubules which run in the vertical axis. Unstained, 40x
With age your pulp chambers get smaller T o F
T
90% of the non-collagenous proten in dentin is:
Dentin SPP (DSPP)
T o F: Approx every day a line of ebner forms in dentin
T
Dentin sensitivity is mediated by
Odontoblast processes. Dentists take care not to overheat or dessicate dentin during restorative procedures
More terminal branching of dentinal tubules occurs in
root dentin compared to coronal dentin
Coronal Tubules have an
S-Shaped Curvature
Ground section showing the S-shaped primary curvature of the dentinal tubules in the crown and their straight course in the root.
Why? There could be more elasticity here, but we don’t really know.
radicular dentin =
root dentin
Dentinal tubules are
1 to 3 µm in diameter.
More dentin tubules are in the crown relative to the
root.
More dentin tubules are near the
pulp than the surface.
Predentin
The fibrillar organic matrix before its calcification.
Odontoblasts exhibit a tall columnar shape, with their nucleus located at their basal region. Whereas at early stages the forming matrix is unmineralized (asterisk), when it becomes mineralized (arrows), a layer of newly formed matrix (the predentine, Pd) is always interposed between the odontoblasts and the mineralizing front. A, differentiating ameloblasts. Hematoxylin-eosin staining (900×)
Primary (1˚) Dentin
Dentin made during
tooth formation
Most of the tooth is 1˚ dentin
Also called circumpulpal dentin
Its outer layer is mantle dentin
Secondary (2˚) Dentin
Secondary dentin forms by the slower, continuing deposition of dentin by odontoblasts following completion of the root.
The junction between primary and secondary dentin is characterized by a
change in the direction of dentinal tubules, but the tubular structure is continuous with 1˚ dentin
Secondary dentin: It is not made at the
same rate everywhere. Deposition is fastest on the roof & floor of the pulp chamber, leading to pulp recession.
A demarcation line (arrowheads) delineates the primary dentin from the
more irregular secondary dentin. Unstained, 40x.
Tertiary (3˚) Dentin: Tertiary dentin formation is a local reaction to
attrition, caries, or dental restoration.
Tertiary (3˚) Dentin
The “quality” (architecture) and quantity of 3˚ dentin depends upon the
intensity and duration of the stimulus.
Tertiary (3˚) Dentin
Tubules can be
continuous, sparse, irregular, or absent.
Tertiary (3˚) Dentin
The dentin in this illustration was deposited slowly in response to a
mild stimulus. The tubular pattern is regular with no cellular inclusions.
Tertiary (Reparative) Dentin
Subtypes of tertiary dentin:
Reactionary dentin is formed by preexisting odontoblasts. Reparative dentin is formed by newly differentiated odontoblast-like cells. These cells can be included in the hard tissue, which is called osteodentin.
Sclerotic Dentin
Dentin that has become translucent due to calcification of the dentinal tubules as a result of injury or normal aging. Also called transparent dentin.
Globular mineralization occurs at
high rates of dentin deposition (best seen in mantel dentin)
while Linear Mineralization occurs at
slower rates where the mineralization front appears more uniform.
Globular Dentin
Globular mineralization results in an irregular mineralization front (arrows) at the predentin-dentin interface.
Interglobular Dentin
There are localized areas of hypomineralized dentin, often just beneath the mantle dentin, where globular zones of mineral fail to fuse into a homogeneous mass. This is called interglobular dentin.
Interglobular Dentin is a
mineralization defect (failure of calcospherite fusion). Dentinal tubules pass through the interglobular dentin, but peritubular dentin is not present in these areas.
Peritubular dentin (PTD) surrounds the
dentinal tubules. It is lower in collagen, higher in dentin sialophosphoprotein (DSPP) & more highly mineralized than intertubular dentin (ITD)
Absence of Collagen in
Peritubular Dentin
Etched Dentin
Dentin surface after etching for 15 secs.
Inherited Defects of Dentin
Etiology: Genetic Mutations
Clinical Classification (Shields 1973)
Dentinogenesis Imperfecta (Types I-III)
Dentin Dysplasia (Type I-II)
Genes encoding dentin matrix proteins
Type I Collagen
Dentin Sialophosphoprotein (DSPP)
DGI type I: This is the dental phenotype in persons afflicted with
osteogenesis imperfecta.
DGI type I:
The teeth show marked
discoloration and attrition in both the deciduous and permanent dentition.
DGI type I:
Pulpal obliteration occurs soon after
eruption and sometimes even prior to tooth eruption.
DGI type I:
The degree of expressivity is
variable, even within a single individual patient, ranging from total pulpal obliteration to normal dentin.
Mutations in the COL1A1 (17q21.31-q22) and COL1A2 (7q22.1) genes cause
osteogenesis imperfecta.
COL1A1 and COL1A2 mutations can:
reduce the amount of collagen (less severe phenotype) or
produce defective collagen molecules (more severe phenotype).
Two type I collagen alpha 1 chains fold with one
alpha 2 chain to form a triple helix.
Peritubular dentin is harder than
intertubular dentin. - higher level of DSPP
Dentinogenesis Imperfecta
Mutations in the Dentin Sialophosphoprotein Gene (DSPP)
Expression of DSPP in teeth
preameloblasts, preodontoblasts, and odontoblasts
2 main structural domains:DSPP:
DSP & DPP
Dentin Sialoprotein (DSP) is a
proteoglycan
Dentin Phosphoprotein (DPP) is the most
acidic protein
Highly repetitive sequence DSS
Hundreds of phosphoserines
Isoelectric point: 1.0
Intertubular dentin is harder away from the
pulp.
Dspp is expressed by
odontoblasts and pre-ameloblasts (at DEJ)
Molars of Dspp-/- mice show
discoloration and severe attrition, leading to the complete disappearance of tooth crown (dotted circle)
These features are similar to human DGI-III
1 yr Dspp(-/-) Mice
enlarged pulp cavity (*)
decreased mineral density
globular mineralized zones
Dentinogenesis Imperfecta type II
is distinct from OI as only the teeth are affected.
has an incidence of 1 in 6000 to 8000.
is caused by mutations in DSPP (4q21.3).
teeth are blue-gray or amber brown and opalescent.
On dental radiographs, the teeth have bulbous crowns, narrow roots, and pulp chambers and root canals that are small or completely obliterated.
Enamel may split from dentin when subjected to occlusal stress (suffer extreme abrasion).
Secondary dentin
mature teeth
Tertiary dentin
reactionary and reparative dentin, osteodentin
Dentinogenesis Imperfecta Type III:
This was first found in the Brandywine isolate from southern Maryland and Washington D.C.
In coloration and shape, the teeth appear somewhat variable as in either DGI type I and DGI type II, but unlike the latter two traits, multiple pulp exposures are observed in the deciduous teeth.
Radiographically the deciduous teeth show considerable variation in appearance, ranging from pulpal obliteration, to normal, even to shell teeth
Dentin Dysplasia type I: incidence ~1:100.000.
Clinically both permanent and deciduous teeth are of normal shape, form, and color in most cases.
Radiologically the teeth have short roots with unusual mobility and early exfoliation.
Crescent-shaped pulpal remnants parallel to the CEJ in the permanent dentition and total pulpal obliteration in the deciduous dentition.
There are usually numerous periapical radiolucencies in non-carious teeth.
Dentin Dysplasia type II:
The deciduous teeth have features of DGI type II.
The permanent teeth are of normal shape, form, and color in most cases.
The pulp cavities show a thistle-tube deformity and commonly contain pulp stones.
The root length is normal and frequent periapical radiolucencies are not observed.
DGI-II, DGI-III and DD-II are likely to be the
same disease. All cases appear to be caused by dominant-negative effects (not haploinsufficiency).
The effect of DSPP mutations on the protein may determine the
severity of the clinical phenotypes.
Osteogenesis imperfecta (OI, AD) In ~
95% of cases, OI is caused by COL1A1 or COL1A2.
Ehlers-Danlos syndrome
In rare cases, a qualitative defect of
type I collagen can also be caused by recessive mutations in ADAMTS2 encoding the extracellular protease cleaves procollagen, resulting in Ehlers-Danlos syndrome (EDS) type VIIC (human dermatosparaxis)
Odontochondrodysplasia (ODCD, AR)
Etiology unknown
Spondylometaphyseal dysplasia, joint lexity, DGI
Schimke immunoosseous dysplasia (SIOD, AR)
Swi/snf–related,
matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1 (SMARCAL1
T o F Linear dentin is deposited at a faster rate than globular dentin.
F: Because linear requires more organization (?)
