NEET MDS Lessons
Dental Anatomy
Dentin
1. Composition
a. Inorganic (70%)—calcium hydroxyapatite crystals.
b. Organic (30%)—water and type I collagen.
2. Types of dentin
a. Primary dentin
(1) Dentin formed during tooth development, before completion of root formation.
It constitutes the majority of dentin found in a tooth.
(2) It consists of a normal organization of dentinal tubules.
(3) Circumpulpal dentin
(a) The layer of primary dentin that surrounds the pulp chamber. It is formed after the mantle dentin.
(b) Its collagen fibers are parallel to the DEJ.
b. Secondary dentin
(1) Dentin formed after root formation is complete.
(2) Is deposited unevenly around the pulp chamber, forming along the layer of dentin closest to the pulp.
It therefore contributes to the decrease in the size of the pulp chamber as one ages.
(3) It consists of a normal, or slightly less regular, organization of dentinal tubules. However,
as compared to primary dentin, it is deposited at a slower rate.
(4) Although the dentinal tubules in secondary dentin can be continuous with those in primary
dentin, there is usually a tubular angle change between the two layers.
c. Tertiary (reparative, reactive) dentin
(1) Dentin that is formed in localized areas in response to trauma or other stimuli such as caries, tooth wear, or dental work.
(2) Its consistency and organization vary. It has no defined dentinal tubule pattern
d. Mantle dentin
(1) The outermost layer of dentin
(2) Is the first layer of dentin laid down by odontoblasts adjacent to the DEJ.
(3) Is slightly less mineralized than primary dentin.
(4) Has collagen fibers that are perpendicular to the DEJ.
(5) Dentinal tubules branch abundantly in this area.
e. Sclerotic (transparent) dentin
(1) Describes dentinal tubules that have become occluded with calcified material .
(2) Occurs when the odontoblastic processes retreat, filling the dentinal tubule with calcium phosphate crystals.
(3) Occurs with aging.
f. Dead tracts
(1) When odontoblasts die, they leave behind empty dentinal tubules, or dead tracts.
(2) Occurs with aging or trauma.
(3) Empty tubules are potential paths for bacterial invasion.
3. Structural characteristics and microscopic features:
a. Dentinal tubules
(1) Tubules extend from the DEJ to the pulp chamber.
(2) The tubules taper peripherally (i.e., their diameters are wider as they get closer to the pulp). Since the tubules are distanced farther apart at the periphery, the density of tubules is greater closer to the pulp.
(3) Each tubule contains an odontoblastic process or Tomes’ fiber.
Odontoblastic processes are characterized by the presence of a network of microtubules, with
Occasional mitochondria and vesicles present.
Note: the odontoblast’s cell body remains in the pulp chamber.
(4) Coronal tubules follow an S-shaped path, which may result from the crowding of odontoblasts as they migrate toward the pulp during dentin formation.
b. Peritubular dentin (intratubular dentin)
(1) Is deposited on the walls of the dentinal tubule, which affects (i.e., narrows)the diameter of the tubule .
(2) It differs from intertubular dentin by lacking a collagenous fibrous matrix. It is also more mineralized than intertubular dentin.
c. Intertubular dentin
(1) The main part of dentin, which fills the space between dentinal tubules
(2) Is mineralized and contains a collagenous matrix.
d. Interglobular dentin
(1) Areas of hypomineralized or unmineralized dentin caused by the failure of globules or calcospherites to fuse uniformly with mature dentin.
(2) Dentinal tubules are left undisturbed as they pass through interglobular dentin; however,
No peritubular dentin is present.
(3) Interglobular dentin is found in the:
(a) Crown—just beneath the mantle dentin.
(b) Root—beneath the dentinocemental junction, giving the root the appearance of a granular
layer (of Tomes).
e. Incremental lines
(1) Dentin is deposited at a daily rate of approximately 4 microns.
(2) As dentin is laid down, small differences in collagen fiber orientation result in the formation of incremental lines.
(3) Called imbrication lines of von Ebner.
(a) Every 5 days, or about every 20 µm, the changes in collagen fiber orientation appear more
accentuated. This results in a darker staining line, known as the imbrication line of von
Ebner.
(b) These lines are similar to the lines of Retzius seen in enamel.
f. Contour lines of Owen
(1) An optical phenomenon that occurs when the secondary curvatures of adjacent dentinal tubules coincide, resulting in the appearance of lines known as contour lines of Owen.
(2) Contour lines of Owen may also refer to lines that appear similar to those just described; however, these lines result from disturbances in mineralization.
g. Granular layer of Tomes
(1) A granular or spotty-appearing band that can be observed on the root surface adjacent to the dentinocemental junction, just beneath the cementum.
Differences Between the Deciduous and Permanent Teeth
1. Deciduous teeth are fewer in number and smaller in size but the deciduous molars are wider mesiodistally than the premolars. The deciduous anteriors are narrower mesiodistally than their permanent successors. Remember the leeway space that we discussed in the unit on occlusion?
2. Their enamel is thinner and whiter in appearance. Side by side, this is obvious in most young patients.
3. The crowns are rounded. The deciduous teeth are constricted at the neck (cervix).
4. The roots of deciduous anterior teeth are longer and narrower than the roots of their permanent successors.
5. The roots of deciduous molars are longer and more slender than the roots of the permanent molars. Also, they flare greatly.
6. The cervical ridges of enamel seen on deciduous teeth are more prominent than on the permanent teeth. This 'bulge' is very pronounced at the mesiobuccal of deciduous first molars.
G. Deciduous cervical enamel rods incline incisally/occlusally.
Mandibular First Deciduous Molar
-This tooth doesn't resemble any other tooth. It is unique unto itself.
-There are two roots.
-There is a strong bulbous enamel bulge buccally at the mesial.
- the mesiolingual cusps on this tooth is the highest and largest of the cusps.
MAXILLARY LATERAL INCISORS
it is shorter, narrower, and thinner.
Facial: The maxillary lateral incisor resembles the central incisor, but is narrower mesio-distally. The mesial outline resembles the adjacent central incisor; the distal outline--and particularly the distal incisal angle is more rounded than the mesial incisal angle (which resembles that of the adjacent central incisor. The distal incisal angle resembling the mesial of the adjacent canine.
Lingual: On the lingual surface, the marginal ridges are usually prominent and terminate into a prominent cingulum. There is often a deep pit where the marginal ridges converge gingivally. A developmental groove often extends across the distal of the cingulum onto the root continuing for part or all of its length.
Proximal: In proximal view, the maxillary lateral incisor resembles the central except that the root appears longer--about 1 1/2 times longer than the crown. A line through the long axis of the tooth bisects the crown.
Incisal: In incisal view, this tooth can resemble either the central or the canine to varying degrees. The tooth is narrower mesiodistally than the upper central incisor; however, it is nearly as thick labiolingually.
Contact Points: The mesial contact is at the junction of the incisal third and the middle third. The distal contact is is located at the center of the middle third of the distal surface.
Root Surface:-The root is conical (cone-shaped) but somewhat flattened mesiodistally.
The pre-dentition period.
-This is from birth to six months.
-At this stage, there are no teeth. Clinically, the infant is edentulous
-Both jaws undergo rapid growth; the growth is in three planes of space: downward, forward, and laterally (to the side). Forward growth for the mandible is greater.
-The maxillary and mandibular alveolar processes are not well developed at birth.
-occasionally, there is a neonatal tooth present at birth. It is a supernumerary and is often lost soon after birth.
-At birth, bulges in the developing alveoli precede eruption of the deciduous teeth. At birth, the molar pads can touch.
Structure
There are 3 pairs
The functional unit is the adenomere.
The adenomere consists of secreting units and an intercalated duct, which opens, in a striated duct.
An secreting unit can be:
- mucous secreting
- serous secreting
THE SECRETING UNIT
THE CELLS
Serous cells
(seromucus cells=secrete also polysaccharides), They have all the features of a cell specialized for the synthesis, storage, and secretion of protein
Pyramidal, Nuclei are rounded and more centrally placed, In the basal 1/3 there is an accumulation of Granular EPR, In the apex there are proteinaceous secretory granules, Cells stain well with H & E (red), Between cells are intercellular secretory capillaries
Rough endoplasmic reticulum (ribosomal sites-->cisternae)
Prominent Golgi-->carbohydrate moieties are added
Secretory granules-->exocytosis
The secretory process is continuous but cyclic
There are complex foldings of cytoplasmic membrane
The junctional complex consists of: 1) tight junctions (zonula occludens)-->fusion of outer cell layer, 2) intermediate junction (zonula adherens)-->intercellular communication, 3)desmosomes-->firm adhesion
Mucus cells
Pyramidal, Nuclei are flattened and near the base, Have big clear secretory granules
Cells do not stain well with H & E (white)
Production, storage, and secretion of proteinaceous material; smaller enzymatic component
-more carbohydrates-->mucins=more prominent Golgi
-less prominent (conspicuous) rough endoplasmic reticulum, mitochondria
-less interdigitations
Myoepithelial cells
Star-shaped, Centrally located nucleus, Long cytoplasmic arms - bound to the secretory cells by desmosomes, Have fibrils like smooth muscle, Squeeze the secretory cell
One, two or even three myoepithelial cells in each salivary and piece body, four to eight processes
Desmosomes between myoepithelial cells and secretory cells myofilaments frequently aggregated to form dark bodies along the course of the process. The myoepithelial cells of the intercalated ducts are more spindled-shaped and fewer processes
Ultrastructure very similar to that of smooth muscle cells (myofilaments, desmosomal attachments)
Functions of myoepithelial cells
-Support secretory cells
-Contract and widen the diameter of the intercalated ducts
-Contraction may aid in the rupture of acinar cells of epithelial origin
Ductal system
Three classes of ducts:
Intercalated ducts
They have small diameter; lined by small cuboidal cells; nucleus located in the center. They have a well-developed RER, Golgi apparatus, occasionally secretory granules, few microvilli. Myoepithelial cells are also present. Intercalated ducts are prominent in salivary glands having a watery secretion (parotid).
Striated ducts
They have columnar cells, a centrally located nucleus, eosinophilic cytoplasm. Prominenty striations that refer to indentations of the cytoplasmic membrane with many mitochondria present between the folds. Some RER and some Golgi. The cells have short microvilli.
The cells of the striated ducts modify the secretion (hypotonic solution=low sodium and chloride and high potassium). There is also presence of few basal cells.
Terminal excretory ducts
Near the striated ducts they have the same histology as the striated ducts. As the duct reaches the oral mucosa the lining becomes stratified. In the terminal ducts one can find goblet cells, basal cells, clear cells. The terminal ducts alter the electrolyte concentration and add mucoid substance.
Connective tissue
Presence of fibroblasts, inflammatory cells, mast cells, adipose cells
Extracellular matrix (glycoproteins and proteoglycans)
Collagen and oxytalan fibers
Nerve supply
The innervation of salivary glands is very complicated. There is no direct inhibitory innervation. There are parasympathetic and sympathetic impulses, the parasympathetic are more prevalent.
The parasympathetic impulses may occur in isolation, evoke most of the fluid to be excreted, cause exocytosis, induce contraction of myoepithelial cells (sympathetic too) and cause vasodialtion. There are two types of innervation: epilemmal and hypolemmal. There are beta-adrenergic receptors that induce protein secretion and L-adrenergic and cholinergic receptors that induce water and electrolyte secretion.
Hormones can influence the function of the salivary glands. They modify the salivary content but cannot initiate salivary flow.
Age changes
Fibrosis and fatty degenerative changes
Presence of oncocytes (eosinophilic cells containing many mitochondria)
Clinical considerations
Role of drugs, systemic disorders, bacterial or viral infections, therapeutic radiation, obstruction, formation of plaque and calculus.
- Rich capillary networks surround the adenomeres.
Soft Oral Tissues
Oral Mucosa
The oral mucosa consists mainly of two types of tissues: the oral epithelium, which consists of stratified, squamous epithelium, and the underlying connective tissue layer, known as the lamina propria. There are three variations of oral mucosa.
A. Oral epithelium
1. Consists of stratified, squamous epithelium.
2. Four layers (Note: Cells mature as they progress from the deepest [basal] layer to the most superficial [cornified] layer) a. Basal layer (stratum germinativum or basale)
(1) A single layer of cuboidal or columnar cells overlying the lamina propria.
(2) Contains progenitor cells and thus provides cells to the epithelial layers above.
(3) Site of cell division (mitosis).
b. Prickle cell layer (stratum spinosum)
(1) Consists of several layers of larger, ovoid-shaped cells.
c. Granular layer (stratum granulosum)
(1) Cells appear larger and flattened.
(2) Granules (known as keratohyaline granules) are present in the cells.
(3) This layer is absent in nonkeratinized epithelium.
d. Cornified layer (stratum corneum, keratin, or horny layer)
(1) In keratinized epithelium:
(a) Orthokeratinized epithelium the squamous cells on the surface appear flat and contain keratin. They have no nuclei present.
(b) Parakeratinized epithelium the squamous cells appear flat and contain keratin; nuclei are present within the cells.
(2) In parakeratinized epithelium, both squamous cells without nuclei and cells with shriveled (pyknotic) nuclei are present.
(3) In nonkeratinized epithelium, the cells appear slightly flattened and contain nuclei.
B. Lamina propria
1. Consists of type I and III collagen, elastic fibers, and ground substance. It also contains many cell types, including fibroblasts, endothelial cells, immune cells, and a rich vascular and nerve supply.
2. Two layers:
a. Superficial, papillary layer
(1) Located around and between the epithelial ridges.
(2) Collagen fibers are thin and loosely arranged.
b. Reticular layer
(1) Located beneath the papillary layer.
(2) Collagen fibers are organized in thick, parallel bundles.
C. Types of oral mucosa
1. Masticatory mucosa
a. Found in areas that have to withstand compressive and shear forces.
b. Clinically, it has a rubbery, firm texture.
c. Regions: gingiva, hard palate.
2. Lining mucosa
a. Found in areas that are exposed to high levels of friction, but must also be mobile and distensible.
b. Clinically, it has a softer, more elastic texture.
c. Regions: alveolar mucosa, buccal mucosa, lips, floor of the mouth, ventral side of the tongue, and soft palate.
3. Specialized mucosa
a. Similar to masticatory mucosa, specialized mucosa is able to tolerate high compressive
and shear forces; however, it is unique in that it forms lingual papillae.
b. Region: dorsum of the tongue.
D. Submucosa
1. The connective tissue found beneath the mucosa . It contains blood vessels and nerves and may also contain fatty tissue and minor salivary glands.
2. Submucosa is not present in all regions of the oral cavity, such as attached gingiva, the tongue, and hard palate. Its presence tends to increase the mobility of the tissue overlying it.
E. Gingiva
1. The portion of oral mucosa that attaches to the teeth and alveolar bone.
2. There are two types of gingiva: attached and free gingiva. The boundary at which they meet is known as the free gingival groove .
a. Attached gingiva
(1) Directly binds to the alveolar bone and tooth.
(2) It extends from the free gingival groove to the mucogingival junction.
b. Free gingiva
(1) Coronal to the attached gingiva, it is not bound to any hard tissue.
(2) It extends from the gingival margin to the free gingival groove.
c. Together, the free and attached gingiva form the interdental papilla.
.F. Alveolar mucosa
1. The tissue just apical to the attached gingiva.
2. The alveolar mucosa and attached gingiva meet at the mucogingival junction .
G. Junctional epithelium
1. Area where the oral mucosa attaches to the tooth, forming the principal seal between the oral cavity and underlying tissues.
2. Is unique in that it consists of two basal lamina, an internal and external . The internal basal lamina, along with hemidesmosomes, comprises the attachment apparatus (the epithelial attachment). This serves to attach the epithelium directly to the tooth.
3. Histologically, it remains as immature, poorly differentiated tissue. This allows it to maintain its ability to develop hemidesmosomal attachments.
4. Has the highest rate of cell turnover of any oral mucosal tissue.
H. Interdental papilla (interdental gingiva)
1. Occupies the interproximal space between two teeth. It is formed by free and attached gingiva.
2. Functions to prevent food from entering the (interproximal) area beneath the contact point of two adjacent teeth. It therefore plays an important role in maintaining the health of the gingiva.
3. Col
a. If the interdental papilla is cross-sectioned in a buccolingual plane, it would show two peaks (buccal and lingual) with a dip between them, known as the col or interdental col. This depression occurs around the contact point of the two adjacent teeth.
b. Histologically, col epithelium is the same as junctional epithelium