NEET MDS Lessons
Dental Anatomy
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.
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.
The periodontium consists of tissues supporting and investing the tooth and includes cementum, the periodontal ligament (PDL), and alveolar bone.
Parts of the gingiva adjacent to the tooth also give minor support, although the gingiva is Not considered to be part of the periodontium in many texts. For our purposes here, the groups Of gingival fibers related to tooth investment are discussed in this section.
Dentinogenesis
Dentin formation, known as dentinogenesis, is the first identifiable feature in the crown stage of tooth development. The formation of dentin must always occur before the formation of enamel. The different stages of dentin formation result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and tertiary dentin.
Odontoblasts, the dentin-forming cells, differentiate from cells of the dental papilla. They begin secreting an organic matrix around the area directly adjacent to the inner enamel epithelium, closest to the area of the future cusp of a tooth. The organic matrix contains collagen fibers with large diameters (0.1-0.2 μm in diameter). The odontoblasts begin to move toward the center of the tooth, forming an extension called the odontoblast process. Thus, dentin formation proceeds toward the inside of the tooth. The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix. This area of mineralization is known as mantle dentin and is a layer usually about 150 μm thick.
Whereas mantle dentin forms from the preexisting ground substance of the dental papilla, primary dentin forms through a different process. Odontoblasts increase in size, eliminating the availability of any extracellular resources to contribute to an organic matrix for mineralization. Additionally, the larger odontoblasts cause collagen to be secreted in smaller amounts, which results in more tightly arranged, heterogenous nucleation that is used for mineralization. Other materials (such as lipids, phosphoproteins, and phospholipids) are also secreted.
Secondary dentin is formed after root formation is finished and occurs at a much slower rate. It is not formed at a uniform rate along the tooth, but instead forms faster along sections closer to the crown of a tooth. This development continues throughout life and accounts for the smaller areas of pulp found in older individuals. Tertiary dentin, also known as reparative dentin, forms in reaction to stimuli, such as attrition or dental caries.
The dentin in the root of a tooth forms only after the presence of Hertwig's epithelial root sheath (HERS), near the cervical loop of the enamel organ. Root dentin is considered different than dentin found in the crown of the tooth (known as coronal dentin) because of the different orientation of collagen fibers, the decrease of phosphoryn levels, and the less amount of mineralization.
Disturbances to interarch alignment are
a. Excessive overbite where the incisal edge of the maxillary incisors extend to the cervical third of the mandibular incisors
b. Excessive overjet where the maxillary teeth overjet the mandibular teeth by more than 3mm
c. End-to-end relationship: edge-to edge bite where the anterior teeth meet at there incisal edge with no overjet or overbite; cusp-to bite where the posterior teeth meet cusp to cusp with no interdigitation
d. Crossbite where the normal faciolingual relationship of the maxillary to the mandibular teeth is altered for the anterior.teeth. the mandibular tooth or teeth are facial rather than lingual to the maxillary teeth for the posterior teeth, normal inercuspaton is not seen
Maxillary Second Deciduous Molar.
-The notation is A or J.
-It looks like a first permanent molar
-There are three roots.
-Usually it has four well developed cusps.
-It is somwhat rhomboidal in outline.
-They often have the Carabelli trait.
- the shape the maxillary first permanent molar strongly resembles that of the adjacent deciduous second molar.
Interarch relationship can be viewed from a stationary (fixed) and a dynamic (movable ) perspective
1.Stationary Relationship
a) .Centric Relation is the most superior relationship of the condyle of the mandible to the articular fossa of the temporal bone as determined by the bones ligaments. and muscles of the temporomandibular joint; in an ideal dentition it is the same as centric occlusion
Centric occlusion is habitual occlusion where maximum intercuspation occurs
The characteristics of centric occlusion are
(1) Overjet: or that characteristic of maxillary teeth to overlap the mandibular teeth in a horizontal direction by 1 to 2 mm the maxilla arch is slightly larger; functions to protect the narrow edge of the incisors and provide for an intercusping relation of posterior teeth
(2) Overbite or that characteristic of maxillary anterior teeth to overlap the mandibular anterior teeth in a vertical direction by a third of the lower crown height facilitates scissor like function of incisors
(3) Intercuspation. or that characteristic of posterior teeth to intermesh in a faciolingual direction The mandibular facial and maxillary lingual cusp are centric cusps yhat contact interocclusally in the opposing arch
(4) Interdigitation, or that characteristic_of that tooth to articulate with two opposing teeth (except for the mandibular central incisors and the maxillary last molars); a mandibular tooth occludes with the same tooth in the upper arch and the one mesial to it; a maxillary tooth occludes with the same tooth in the mandibular arch and the one distal to it.
2. Dynamic interarch relationshjps are result of functional mandibular movements that start and end with centric occlusion during mastication
a. Mandibular movements are
(1) Depression (opening)
(2) Elevation (closing)
(3) Protrusion (thrust forward)
(4) Retrusion (bring back)
(5) Lateral movements right and left; one side is always the working side and one the balancing or nonworking side
b. Mandibular movements from centric occlusion are guided by the maxillary teeth
(1) Protrusion is guided by the incisors called incisal guidence
(2) Lateral movments are guided by the Canines on the working side in young, unworn dentitions (cuspid rise or cuspid protected occlusion); guided by incisors and posterior teeth in older worn. dentition (incisal/group guidance)
c. As mandibular movements commence from centric occlusion, posterior teeth should disengage in protrusion the posterior teeth on the balancing side should disengage in lateral movement
d. If tooth contact occurs where teeth should be disengaged, occlusal interference or premature contacts exist.