Microscopic Anatomy of the Periodontium (CH 2)

Microscopic Anatomy of ​Sulcular Epithelium​

• The epithelial lining of the gingival sulcus is thin and nonkeratinized​

• Continuous with oral epithelium extending from crest of gingival margin to coronal edge of junctional epithelium​

• Permeable, allowing fluid to flow from gingival connective tissue into sulcus---gingival crevicular fluid​

• Three cellular layers:​

  • Basal cell layer​

  • Prickle cell layer​

  • Superficial cell layer​

• Joins connective tissue with a smooth interface and no epithelial ridges in health​

Sulcular Epithelium

• In a healthy state the epithelium is smooth and intact​

• In health the sulcus is generally 1-3mm deep​

• Probe measurements are subject to variation for several reasons​

  • Probe insertion pressure​

  • The ability of the probe tip to penetrate tissue​

  • The accuracy of the clinician reading the measurement​

Microscopic Anatomy of Junctional Epithelium

• Forms the base of the sulcus and joins gingiva to the tooth​

• The base of the sulcus is made up of the coronal-most cells

• In health, attaches to the tooth slightly coronal to the cementoenamel junction​

• Thin and nonkeratinized, easily penetrable​

• Easiest entry point for bacteria to invade into connective tissue​

• Comprised layers of closely packed epithelial cells​

• Has a sparse extracellular matrix with a thin basal lamina between JE and the tooth surface and JE and gingival connective tissue​

• Two cell layers:​

  • Basal cell layer​

  • Prickle cell layer​

• 15 to 30 cells thick at coronal zone(the zone that attaches highest on the tooth) and tapers to 4 to 5 cells thick at the apical zone​

• Cells next to tooth form hemidesmosomes that attach the internal basal lamina with the tooth surface​

  • ​The attachment of the hemidesmosomes and internal basal lamina to the tooth surface is not static​

    • Cells of the JE can move along the tooth surface​

• Cells next to gingiva form hemidesmosomes that attach the external basal lamina with gingival connective tissue​

• Has a smooth tissue interface with connective tissue in health​

Why the Teeth Need a Junctional Epithelium​

• Teeth create break in epithelial protective covering​

  • Protective epithelial sheet covers body​

  • Teeth erupt and puncture protective epithelial sheet​

• Body attempts to seal opening by attaching epithelium to tooth​

Gingival Fibers (Supragingival Fiber Bundles)

• A network of rope-like collagen fiber bundles in the gingival connective tissue​

• Located coronal to the crest of the alveolar bone​

• Embedded in the gel-like extracellular matrix of the gingival connective tissue​

• Strengthen attachment of JE to tooth by bracing the gingival margin against the tooth​

• JE and gingival fibers are known collectively as dentogingival unit​

Function of Supragingival Fibers

• Reinforce​

  • Reinforce attachment of JE to tooth​

• Provide​

  • Provide rigidity to free gingiva so it can withstand chewing forces​

• Connect​

  • Connect free gingiva with root cementum and alveolar bone​

• Connect​

  • Connect adjacent teeth to one another​

Classification of Gingival Fiber Groups​

• Classified based on:​

  • Their orientation​

  • Sites of insertion​

  • Structures that they connect​

Alveologingival Fibers

• Extend from the periosteum of the alveolar crest into the gingival connective tissue of the attached gingiva​

• Attach gingiva to the underlying bone​

Circular Fibers

• Encircle the tooth in a ring-like manner​

• Coronal to the alveolar crest​

• Not attached to the cementum of the tooth​

• Support the free gingiva​

Dentogingival Fibers

• Attached in cementum near the CEJ and fan into the gingival connective tissue of the free and attached gingiva​

• Support the gingiva​

• Attach gingiva to the teeth​

Periosteogingival Fibers

• Extend laterally from the periosteum to the alveolar bone​

• Attach the gingiva to the bone

Intergingival Fibers​

• Extend in a mesiodistal direction along the entire dental arch and around the last molars in the arch​

• Link adjacent teeth into a dental arch unit​

Intercircular Fibers

• Encircle several teeth​

Interpapillary Fibers​

• Located in the papilla coronal to the Transseptal fiber bundles​

• Connect the oral and vestibular interdental papillae of the posterior teeth​

Transgingival Fibers​

• Extend from the cementum near the CEJ and run horizontally between adjacent teeth​​

• Link adjacent teeth

Transseptal Group

• Cementum to cementum of adjacent teeth​

• Maintain relationship between teeth​

Supragingival Fiber Groups​
(looking down on occlusal)​

Periodontal Ligament Fibers​

• Rope-like collagen fibers that stretch across space between cementum and alveolar bone of tooth socket​

• Have a rich supply of nerves and blood vessels​

Composition of the Periodontal Ligament​

• Components ​

  • Cells​

  • Mainly fibroblasts​

  • Some cementoblasts​

  • Some osteoblasts​​

• Extracellular Matrix​

  • A rich gel-like substance with specialized connective fibers​​

• Fiber Bundles​

  • A specialized connective tissue the surrounds the root of the tooth and connects it to the alveolar bone​

Origin of the Periodontal Ligament​

• The PDL is derived embryologically from the ectomesenchymal tissue of the dental follicle that surrounds the developing tooth in its bony crypt​

• At the time of tooth eruption the cells and collagen fibers in the dental follicle, i.e. the future PDL, are orientated primarily with their long axis parallel to the root surface.​

• Remodeling of the follicle into a PDL begins at the CEJ and proceeds in an apical direction.​

Functions of the Periodontal Ligament​

• Supportive​

  • Anchor the tooth to the bony socket​

  • Separate the tooth from the socket wall so the root does not traumatize the bone during mastication​

• Sensory​

  • The PDL is supplied with nerve fibers that transmit tactile pressure and pain sensations​

• Nutritive​

  • The PDL is supplied with blood vessels that provide nutrients to the cementum and bone​

• Formative​

  • The PDL contains cementoblasts that produce cementum throughout the life of the tooth​

    • Osteoblasts maintain the bone of the tooth socket​

• Resorptive​

  • In response to severe pressure, osteoclasts in the PDL can induce rapid bone resorption and sometimes resorption of cementum​

Periodontal Ligament Fibers – Five Principal Fiber Groups​

• Alveolar crest​

• Horizontal​

• Oblique​

• Apical​

• Interradicular ​

Alveolar Crest Fiber Group​

• Extend from the cervical cementum running downward in a diagonal direction to the alveolar crest​

• Resists horizontal movements of the tooth​

• Prevents tooth extrusion

Horizontal Fiber Group

• Located apical to the alveolar crest fibers ​

• Extend from the cementum to the bone at right angles to the long axis of the tooth​

• Resists horizontal pressure against the crown of the tooth​

Oblique Fiber Group

• Located apical to the horizontal group​

• Extend from the cementum to the bone in a diagonal direction​

• Resist vertical pressures that threaten to drive the root into the socket

Apical Fiber Group

• Extend from the apex of the tooth to the bone​

• Secures the tooth in the socket​

• Resists forces that might lift the tooth out of the socket​

Interradicular Fiber Group

• In the furcation of multi-rooted teeth​

• Extend from the cementum in the furcation to the interradicular septum of the alveolar bone​

• Helps stabilize the tooth in its socket​

Sharpey Fibers

• The ends of the PDL fibers that are embedded in the cementum and alveolar bone​

• As cementum forms, the tissue calcifies around the ends of the periodontal ligament fibers surrounding them with cementum ​

• As the walls of the tooth socket calcify, it surrounds the ends of the periodontal ligament fibers with bone​

Microscopic Anatomy of Cementum​

• Is a mineralized tissue that covers roots of the teeth and serves to attach the tooth to alveolar bone via collagen fibers of the PDL​

• Anatomically it is part of the tooth​

• Functionally it is part of the periodontium​

Functions of Root Cementum ​

• Primary function is for periodontal ligament attachment​

• Sharpey fibers are the terminal endings of periodontal ligaments attached to cementum​

• Seals ends of open dentinal tubules​

• Compensates for occlusal attrition to maintain tooth length​

• Excess deposit in apical third of root is called hypercementosis which appears radiopaque on an x-ray​

Composition of Cementum​

• Comprised of:​

  • Organic substances​

    • 50-55% - Primarily Type I collagen and non-collagenous matrix proteins​​

• Inorganic substances​

  • 45% - ​

    • Hydroxyapatite (calcium and phosphate)​

    • Trace elements​

• Contains no blood vessel or nerves​

• Has been shown to contain biologically active mediators​

  • It is believed that growth factor molecules are produced during cementum formation and then stored in the cementum matrix to induce PDL regeneration when needed.​

Thickness of Cementum

• 20 to 50 microns - coronal half​

• 50 to 200 microns - apical region​

• Cementum deposition continues after eruption​

  • As teeth wear down on the occlusal or incisal surface there is compensatory deposition of cementum in the apical area​

Conservation of Cementum During Periodontal Instrumentation​

• Historically it was accepted that bacterial products penetrate the cementum of periodontally diseased root surfaces​

  • This concept resulted in intentional, aggressive removal of all or most cementum during instrumentation​

• Current research​

  • Bacterial products are not located within cementum and removal of cementum is not necessary for successful periodontal treatment​

Cementoenamel Junction​

• Relationship of the Cementum to Enamel at the CEJ​

  • Overlap​

    • 60% of time​

    • Cementum overlaps the enamel for a short distance

  • Meet​

    • 30% of time​

    • Cementum meets the enamel​​

  • Gap​

    • 10% of time​

    • There is a small gap between the cementum and enamel​

    • Exposes dentin​

Microscopic Anatomy of Alveolar Bone​

• Part of maxilla and mandible that forms and supports sockets​

• Anatomy​

  • Alveolar bone proper​

  • Trabecular bone​

  • Cortical (compact) bone​

Functions of Alveolar Bone​

• Protects roots of teeth​

• Changes in response to mechanical forces and inflammation​

  • Constantly undergoes periods of bone formation and resorption in response to mechanical forces on he tooth and inflammation of the periodontium​

  • The process of bone formation and resorption is called bone remodeling

Components of the Alveolar Bone​

• Major cell types​

  • Osteoblasts: ​

    • deposit, synthesize/secrete ​

• Osteoclasts:​

  • destroy or resorb​

• Extracellular matrix​

  • Collagen fibers​

  • Gel-like substance

• Matrix deposited by osteoblasts is not mineralized and is termed osteoid. ​

  • As new osteoid is deposited the old osteoid mineralizes. ​

• Bone matrix undergoes mineralization by the deposition of minerals such as calcium and phosphate, which are subsequently transformed into hydroxyapatite​

• Alveolar bone has blood vessels and innervation