Oral histology

The periodontal Ligament

PERIODONTIUM
Cementum PDL Alveolar bone Sharpey's fibers Attachment organ
Cementum
Periodontal ligament
Alveolar bone
Apical foramen
Pulp cavity
Enamel
Dentin
Gingiva
Root canal
Alveolar vessels & nerves


The periodontal ligament is the dense fibrous connective tissue that occupies the periodontal space between the root of the tooth and the alveolus.

cells

Histological structureThe periodontal ligament is formed of :
Fibers,

Intercellular substances

Synthetic
Resorptive
Progenitor
Defensive
ground substances
blood vessels, nerves & lymphatics.

Epithelial cells remnants of the epithelial root sheath of Hertwig

The cells
Synthetic cells
Resorptive cells
Progenitor cells
Defensive cells
fibroblasts, osteoblasts and cementoblasts.
cementoclasts , osteoclasts and fibroclasts. Note that fibroblasts perform both synthetic and resorptive activities.
undifferentiated mesenchymal cells
macrophage, lymphocytes and mast cells



A- The principal fibers: They are formed of collagen bundles, which are wavy in course and are arranged in three groups.
a) Gingival fibers. b) Transseptal or interdental ligament. c) Alveolodental ligament

A- The principal fibers:a- The gingival fibers:

1- Dento-gingival fibers: extend from the cervical cementum into the gingiva. 2- Alveolo-gingival group: extends from the alveolar crest into the gingiva. 3- Circular group: a small group of fibers that encircles the tooth and interlaces with the outer fibers. 4- Dento-periosteal fibers: they extend from the cementum directed over the bone crest and then incline apically between the periosteum of the alveolar bone and the gingiva.


Function of gingival fibers:They form a rigid cuff around the tooth that can add stability and resist gingival displacement.

b- The transseptal ligament:

*It connects two adjacent teeth. *The ligament runs from the cementum of one tooth over the crest of the alveolus to the cementum of the adjacent tooth. *Function: Resists mesial and distal tooth separation.


Dentoalveolar group Alveolar crest group (ACG): below CE junction, downward, outward b. Horizontal group: apical to ACG, right angle to the root surface c. Oblique group: most numerous, oblique direction and attaches coronally to bone d. Apical group: around the apex, base of socket e. Interradicular group: multirooted teeth Runs from cementum and bone , forming the crest of the interradicular septum

B- Accessory fibers:

They are collagenous in nature and run from bone to cementum in different planes, more tangentially to prevent rotation of the tooth and found in the region of the horizontal group.

Oxytalan fibers

These are immature elastic (pre- elastic) fibers. They need special stains to be demonstrated. They tend to run in an axial direction, one end being embedded in bone or cementum and the other in the wall of blood vessels. At the apical region they form a complex network.

The functions of oxytalan fibers: 1-Support nerves. 2- Support blood vessels. 3- Help fibroblasts migration.

Classification of oral mucosa

Based upon primary function served Masticatory Mucosa (25%) Lining Mucosa (Covers 60% of total area) Specialised Mucosa (15%) Based upon keratinisation Keratinised 2. Non-keratinised.

Structure of Oral Mucosa

Epithelium Lamina Propria. Submucosa

Epithelium

Epithelium of the oral mucosa is stratified squamous epithelium. It may be 1.Keratinized 2.Non keratinized

Keratinized oral epithelium Most of the oral mucosal surface is lined by nonkeratinized stratified squamous epithelium except gingiva, hard palate and dorsal surface of the tongue where the epithelium is keratinized The keratinized cells have no nuclei and the cytoplasm is displaced by large numbers of keratin filaments Keratinized epithelium is associated with masticatory function and have four layers of cells

The four layers are: Stratum Basale Stratum Spinosum Stratum Granulosum Stratum Corneum

Cellular layers of oral epithelium - Keratinized

Nonkeratinized oral epithelium Nonkeratinized epithelial cells in the superfecial layers do not have keratin filaments in the cytoplasm The surface cells also have nuclei The stratum corneum and stratum granulosum layers are absent This epithelium is associated with lining of the oral cavity

Connective tissue

Connective tissue can be differentiated as Lamina Propria and Submucosa Lamina Propria Two Layers Papillary layer Close to epithelial ridges. Arranged loosely. Reticular layer Parallel to epithelium. Fibers are very thick. Consists of cells , blood vessels, neural elements & fibers embedded in amorphous ground substance.

Submucosa Submucosa lies below the lamina propria and serves as an attachment between lamina propria and bone or skeletal muscle It is found in the cheeks, lips and parts of the palate It consists of large blood vessels, nerves and lymphatics and its functions are nutrition and defense

Gingiva

Covers the alveolar process of jaws and surrounds the cervical portion of teeth. It develops from the union of oral epithelium and reduced enamel epithelium Gingiva can be classified as Free gingiva, Attached gingiva and Interdental papilla

Free gingiva Attached gingiva Interdentalpapilla

The gingival epithelium can be studied under three headings :
GINGIVAL EPITHELIUM
Oral epithelium
Sulcular epithelium
Junctional epithelium
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