NEET MDS Lessons
Dental Anatomy
Periodontal ligament
Composition
a. Consists mostly of collagenous (alveolodental) fibers.
Note: the portions of the fibers embedded in cementum and the alveolar bone proper are known as Sharpey’s fibers.
b. Oxytalan fibers (a type of elastic fiber) are also present. Although their function is unknown, they may play a role in the regulation of vascular flow.
c. Contains mostly type I collagen, although smaller amounts of type III and XII collagen are also present.
d. Has a rich vascular and nerve supply.
Both sensory and autonomic nerves are present.
(1) The sensory nerves in the PDL differ from pulpal nerves in that PDL nerve endings can detect both proprioception (via mechanoreceptors) and pain (via nociceptors).
(2) The autonomic nerve fibers are associated with the regulation of periodontal vascular flow.
(3) Nerve fibers may be myelinated (sensory) or unmyelinated (sensory or autonomic).
Cells
a. Cells present in the PDL include fibroblasts; epithelial cells; cementoblasts and cementoclasts; osteoblasts and osteoclasts; and immune cells such as macrophages, mast cells, or eosinophils.
b. These cells play a role in forming or destroying cementum, alveolar bone, or PDL.
c. Epithelial cells often appear in clusters, known as rests of Malassez.
Types of alveolodental fibers
a. Alveolar crest fibers—radiate downward from cementum, just below the cementoenamel junction (CEJ), to the crest of alveolar bone.
b. Horizontal fibers—radiate perpendicular to the tooth surface from cementum to alveolar bone, just below the alveolar crest.
c. Oblique fibers
(1) Radiate downward from the alveolar bone to cementum.
(2) The most numerous type of PDL fiber.
(3) Resist occlusal forces that occur along the long axis of the tooth.
d. Apical fibers
(1) Radiate from the cementum at the apex of the tooth into the alveolar bone.
(2) Resist forces that pull the tooth in an occlusal direction (i.e., forces that try to pull the tooth from its socket).
e. Interradicular fibers
(1) Only found in the furcal area of multi-rooted teeth.
(2) Resist forces that pull the tooth in an occlusal direction.
Gingival fibers
a. The fibers of the gingival ligament are not strictly part of the PDL, but they play a role in the maintainence of the periodontium.
b. Gingival fibers are packed in groups and are found in the lamina propria of gingiva
c. Gingival fiber groups:
(1) Transseptal (interdental) fibers
(a) Extend from the cementum of one tooth (just apical to the junctional epithelium), over the alveolar crest, to the corresponding area of the cementum of the adjacent tooth.
(b) Collectively, these fibers form the interdental ligament , which functions to resist rotational forces and retain adjacent teeth in interproximal contact.
(c) These fibers have been implicated as a major cause of postretention relapse of teeth that have undergone orthodontic treatment.
(2) Circular (circumferential) fibers
(a) Extend around tooth near the CEJ.
(b) Function in binding free gingiva to the tooth and resisting rotational forces.
(3) Alveologingival fibers—extend from the alveolar crest to lamina propria of free and attached gingiva.
(4) Dentogingival fibers—extend from cervical cementum to the lamina propria of free and attached gingiva.
(5) Dentoperiosteal fibers—extend from cervical cementum, over the alveolar crest, to the periosteum of the alveolar bone.
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Maxillary (upper) teeth |
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Primary teeth |
Central |
Lateral |
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First |
Second |
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Initial calcification |
14 wk |
16 wk |
17 wk |
15.5 wk |
19 wk |
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Crown completed |
1.5 mo |
2.5 mo |
9 mo |
6 mo |
11 mo |
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Root completed |
1.5 yr |
2 yr |
3.25 yr |
2.5 yr |
3 yr |
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Mandibular (lower) teeth |
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Initial calcification |
14 wk |
16 wk |
17 wk |
15.5 wk |
18 wk |
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Crown completed |
2.5 mo |
3 mo |
9 mo |
5.5 mo |
10 mo |
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Root completed |
1.5 yr |
1.5 yr |
3.25 yr |
2.5 yr |
3 yr |
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Histology of the Periodontal Ligament (PDL)
Embryogenesis of the periodontal ligament
The PDL forms from the dental follicle shortly after root development begins
The periodontal ligament is characterized by connective tissue. The thinnest portion is at the middle third of the root. Its width decreases with age. It is a tissue with a high turnover rate.
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)
The following cells can be identified in the periodontal ligament:
a) Osteoblasts and osteoclasts b) Fibroblasts, c) Epithelial cells
Rests of Malassez
d) Macrophages
e) Undifferentiated cells
f) Cementoblasts and cementoclasts (only in pathologic conditions)
The following types of fibers are found in the PDL
-Collagen fibers: groups of fibers
-Oxytalan fibers: variant of elastic fibers, perpendicular to teeth, adjacent to capillaries
-Eluanin: variant of elastic fibers
Ground substance
PERIODONTAL LIGAMENT FIBERS
Principal fibers
These fibers connect the cementum to the alveolar crest. These are:
a. Alveolar crest group: below CE junction, downward, outward
b. Horizontal group: apical to ACG, right angle
c. Oblique group: numerous, coronally to bone, oblique direction
d. Apical group: around the apex, base of socket
e. Interradicular group: multirooted teeth
Gingival ligament fibers
This group is not strictly related to periodontium. These fibers are:
a. Dentogingival: numerous, cervical cementum to f/a gingiva
b. Alveologingival: bone to f/a gingiva
c. Circular: around neck of teeth, free gingiva
d. Dentoperiosteal: cementum to alv. process or vestibule (muscle)
e. Transseptal: cementum between adjacent teeth, over the alveolar crest
Blood supply of the PDL
The PDL gets its blood supply from perforating arteries (from the cribriform plate of the bundle bone). The small capillaries derive from the superior & inferior alveolar arteries. The blood supply is rich because the PDL has a very high turnover as a tissue. The posterior supply is more prominent than the anterior. The mandibular is more prominent than the maxillary.
Nerve supply
The nerve supply originates from the inferior or the superior alveolar nerves. The fibers enter from the apical region and lateral socket walls. The apical region contains more nerve endings (except Upper Incisors)
Dentogingival junction
This area contains the gingival sulcus. The normal depth of the sulcus is 0.5 to 3.0 mm (mean: 1.8 mm). Depth > 3.0 mm is considered pathologic. The sulcus contains the crevicular fluid
The dentogingival junction is surfaced by:
1) Gingival epithelium: stratified squamous keratinized epithelium 2) Sulcular epithelium: stratified squamous non-keratinized epithelium The lack of keratinization is probably due to inflammation and due to high turnover of this epithelium.
3) Junctional epithelium: flattened epithelial cells with widened intercellular spaces. In the epithelium one identifies neutrophils and monocytes.
Connective tissue
The connective tissue of the dentogingival junction contains inflammatory cells, especially polymorphonuclear neutrophils. These cells migrate to the sulcular and junctional epithelium.
The connective tissue that supports the sulcular epithelium is also structurally and functionally different than the connective tissue that supports the junctional epithelium.
Histology of the Col (=depression)
The col is found in the interdental gingiva. It is surfaced by epithelium that is identical to junctional epithelium. It is an important area because of the accumulation of bacteria, food debris and plaque that can cause periodontal disease.
Blood supply: periosteal vessels
Nerve supply: periodontal nerve fibers, infraorbital, palatine, lingual, mental, buccal
HISTOLOGY OF SALIVARY GLANDS
Parotid: so-called watery serous saliva rich in amylase
Submandibular gland: more mucinous
Sublingual: viscous saliva
Parotid Gland: The parotid is a serous secreting gland.
There are also fat cells in the parotid.
Submandibular Gland
This gland is serous and mucous secreting.
There are serous demilunes
This gland is more serous than mucous
Also fat cells
Sublingual Gland
Serous and mucous secreting
Serous cells in the form of demilunes on the mucous acini.
more mucous than serous cells
Minor Salivary Glands
Minor salivary glands are not found within gingiva and anterior part of the hard palate
Serous minor glands=von Ebner below the sulci of the circumvallate and folliate papillae of the tongue; palatine, glossopalatine glands are pure mucus; some lingual glands are also pure mucus
Functions
Protection: lubricant (glycoprotein); barrier against noxious stimuli; microbial toxins and minor traumas; washing non-adherent and acellular debris; calcium-binding proteins: formation of salivary pellicle
Buffering: bacteria require specific pH conditions; plaque microorganisms produce acids from sugars; phosphate ions and bicarbonate
Digestion: neutralizes esophageal contents, dilutes gastric chyme; forms food bolus; brakes starch
Taste: permits recognition of noxious substances; protein gustin necessary for growth and maturation of taste buds
Antimicrobial: lysozyme hydrolyzes cell walls of some bacteria; lactoferrin binds free iron and deprives bacteria of this essential element; IgA agglutinates microorganisms
Maintenance of tooth integrity: calcium and phosphate ions; ionic exchange with tooth surface
Tissue repair: bleeding time of oral tissues shorter than other tissues; resulting clot less solid than normal; remineralization
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)
MAXILLARY FIRST MOLAR
The first molars are also known as 6-year molars, because they erupt when a child is about 6 years
Facial Surface:-The facial surface has a facial groove that continues over from the occlusal surface, and runs down to the middle third of the facial surface.
Lingual Surface:-In a great many instances, there is a cusp on the lingual surface of the mesiolingual cusp. This is a fifth cusp called the cusp of Carabelli, which is in addition to the four cusps on the occlusal surface.
Proximal: In mesial perspective the mesiolingual cusp, mesial marginal ridge, and mesiobuccal cusp comprise the occlusal outline. In its distal aspect, the two distal cusps are clearly seen; however, the distal marginal ridge is somewhat shorter than the mesial one.
Occlusal Surface:- The tooth outline is somewhat rhomboidal with four distinct cusps. The cusp order according to size is: mesiolingual, mesiobuccal, distobuccal, and distolingual. The tips of the mesiolingual, mesiobuccal, and distobuccal cusps form the trigon, Cusp of Carabelli located on the mesiolingual cusp.
Contact Points; The mesial contact is above, but close to, the mesial marginal ridge. It is somewhat buccal to the center of the crown mesiodistally. The distal contact is similarly above the distal marginal ridge but is centered buccolingually.
Roots:-The maxillary first molar has three roots, which are named according to their locations mesiofacial, distofacial, and lingual (or palatal root). The lingual root is the largest.
HISTOLOGY OF THE ODONTOBLAST
Formation of Dentin
Mantle dentin: First formed dentin
Type I collagen with ground substance
Formation of the odontoblast process
Matrix vesicles
Appearance of hydroxyapatite crystals
Predentin
Primary physiologic (circumpulpal) dentin
All organic matrix is formed from odontoblasts
Smaller collagen fibers
Presence of phosphophoryn
Mineralization
Globular calcification
Interglobular dentin: Areas of incomplete calcification
Incremental lines of von Ebner: Daily, 4mm of organic matrix is deposited. Also every 5 days the arrangement of collagen fibers changes. This creates the incremental lines of von Ebner.
Intratubular dentin
Dentin tubules
S-shaped in the coronal aspect, straight in root dentin
Von Korff fibers
They are an artifact