Oral Biology - Exam 2

Periodontium

• Supporting structures of teeth

• Consists of:

  • Gingiva (gum)

  • PDL (ligament around cementum)

  • Cementum (root of tooth)

  • Alveolar Bone (bone where teeth rest in)

Cementum

• Calcified, avascular, and aneural (however, canaliculi do exist and may connect to dentinal tubule)

• Mesenchymal tissue (from dental sac) covering root from CEJ to apex

• Provides attachment site for PDL (anchors sharpey fibers)

• Protects root dentin and compensates for tooth loss with cementum deposition

• More resistant to resorption than bone (helpful for orthodontists)

• Can rearrange PDL fibers to repair PDL

• Two types: Acellular (primary) and cellular (secondary)

Cementum components

• Softer than bone and highest fluoride content

• 45% inorganic (HA) and 55% organic (collagen and non-collagen)

Extrinsic Fibers

• Sharpey fibers

• Made in ligament by fibroblasts and attach to cementum (type 1 coated by type 3)

Intrinsic Fibers

• Made by cementoblasts and in cementum matricx

Calcified interfibrillar matrix

• PGs, GP, and phosphoproteins

• Produced by cementoblasts

Cementum formation

• Dental papilla cells become odontoblasts that line the pulp and place predentin

• HERS is laid down to make root shape but will eventually start breaking down

• Surrounding dental follicle (sac) cells contact exposed forming dentin

• Cell signaling causes follicle cells to differentiate and become cementoblasts to make cementum until reaching apex

Primary/acellular cementum

• Found near CEJ

• Made before tooth reaches occlusal plane

• Sharpey’s fibers exist (no intrinsic fibers because of lack of cementoblasts)

• Incremental lines of Salter

Secondary/cellular dentin

• Cellular

• Has Sharpey and intrinsic fibers

• Found from middle to apex of root

• Forms throughout life (not so organized; if occlusal forces occur, it can develop to maintain occlusal height)

Intermediate cementum

• Poorly defined zone near CDJ

• Remnant of HERS

• Highly mineralized

• Seals dentinal tubules

Abnormal Cementum Levels

• Cemental aplasia or hypoplasia - Absence or decrease

• Cemental hyperplasia or hypercementosis - Excess cementum deposition (does not need treatment but extractions can be a bit more difficult)

Cementum Resporption

• Physiologic resporption - Done by cementoclasts

• Pathologic resorption

  • Local

    • Occlusal trauma

    • Orthodontic forces

    • Misaligned teeth

    • Cysts/tumors/pathologies

  • Systemic

    • Calcium deficiency

    • Hypothyroidism

    • Paget disease

  • Idiopathic

• Appears as resorption lacunae

• Reversal line is new cementum deposited in location of removed cementum

Ankylosis

• Fusion between cementum and alveolar bone (no ligament)

• No mobility

• Infraocclusion (below normal occlusal height)

• Common in primary teeth

• Radiographs may see resorption

CEJ

• 65% of cementum overlap enamel

• 30% of cementum meet at enamel

• 5% of cementum do not meet enamel (dangerous)

Alveolar Bone

• Part of maxilla and mandible that form tooth socket

• Forms during tooth eruption from dental follicle

• “Tooth dependent” (lack of tooth for 6 months includes loss of alveolar bone, trabeculae, and ligament)

Alveolar bone composition

• 2/3 inorganic (HA)

• 1/3 organic (90% type 1 collagen + non-collagen proteins)

• Harder than cementum, softer than dentin and enamel

• HA crystals are parallel to collagen to help reinforce bone strength

Alveolar and Basal Bone Components

• External cortical plate (compact bone)

• Alveolar Bone Proper (inner socket wall; also compact)

  • Bundle bone (histological name) - Where sharpey’s fiber inserts

  • Lamina dura (radiographic name)

• Cancellous Bone

  • Found between compact bone

  • Interdental septum

  • Has blood vessels and nerves

• Basal Bone

  • Below apex and not part of alveolar process

Bony Septum

• Interradicular septum (bone between roots)

• Interalveolar/interdental septum (bone between teeth)

  • If root of teeth contact one another, periodontium of one tooth contacts periodontium of another and you may lose septum forming a “boneless window”

  • Parallel line between adjacent CEJs and interdental crest indicates healthy bone

Periosteum

• Covers outer surface of bone

• Outer layer of bone has blood vessels, nerves, collagen, and fibroblasts

• Inner layer of osteoblasts

• Must be surgically maintained because of blood supply

Endosteum

• Internal surface of bone

• Active site of bone formation and remodeling

Osseous Topography

• Shape of alveolar bone depends on arrangement, alignment, position and flaring of tooth roots

Fenestration

• “Window” where exposed root is covered only by periosteum and gingiva, not bone

Dehiscence

• Root exposure as V or U shape

• From cervical region that extends inferiorly

• Anterior teeth, premolars, and mesiobuccal roots of first molars

Buttressing Bone

• Extra bone formation as a result of trauma

• Not organized bone

• Bulge or lip on facial or lingual surface

Exostoses

• Bony projections in mandible or maxilla

• Can affect dentures but are not symptomatic

Bone Remodeling

• Coordinated effort between osteoclasts (large and multi-nucleated cells that use acids and sequester ions) and osteoblasts (lay down osteoid)

Physiologic Tooth Migration

• Pressure side undergoes bone resorption (medial side during mesial drift)

• Tension side undergoes bone formation (distal side during mesial drift)

• Pressure and tension are acted on ligaments from normal and parafunction (tilting/rocking) forces

  • Interradicular bone is lost in furcation defect as a result of parafuncational forces

Tooth Hypofunction

• Occurs when a tooth does not have opposing tooth to antagonize with

• Causes PDL to narrow, bony trabeculae decreases, and tooth mobility occurs

Dental Pulp

• Derived from ectomesenchyme

• Soft connective tissue that functionally supports dentin

• Two parts - Coronal pulp (pulp chamber and horns) and radicular pulp (root canals)

Age Affects of Pulp

• Pulp gets smaller as you age (root canal becomes more difficult) because of secondary dentin formation

• Blood and nerve supply also decrease with age

• Number of dead dentinal tracts increase

• Reparative (tertiary) dentin is formed as well

Pulp Anatomical Features

• Apical foramen - Opening of pulp at root with neurovascular structures

• Accessory Canal - Formed from break in HERS that communicates with PDL

Histological Zones of Pulp

• Odontoblastic zone (line outer surface of pulp)

• Cell-free zone of Weil (cell-free zone inside pulp)

  • Subodontoblastic plexus of Raschkow (has nerve cells)

• Cell-rich zone

• Pulp core (has nerves)

Cells include odontoblasts, fibroblasts, mesenchymal cells, macrophages, and stem cells

Pulpal Matrix

• Fibers (Type 1 and 3 Collagen)

• Ground Substance

  • 90% water bound by PG

  • GP allow for movement, communication and proliferation of cells

Pulp innervation

• Sensory afferents of CN 5

• Post-ganglionic sympathetic branches from superior cervical ganglion

• Adelta fibers

  • Myelinated fibers with sharp localized pain when dentin is first exposed

• C fibers

  • Nonmyelinated fibers that are slow conducting, dull and diffuse

• Most nerves terminate at subodontoblastic plexus while others enter intratubular nerves and do not synapse

Sensory Perception in Pulp

• When you experience extremes of pressure or temperature, it is perceived as pain

• Odontoblasts have free nerve endings where pain originates from

• Three theories

  • Dentin directly innervated

  • Odontoblasts act as receptors

  • Hydrodynamic Theory - Tooth sensitivity arises from fluid movement within the dentinal tubules

• Ion channels are involved in pain perception

Pulp Stones

• False pulp stones (concentric) are circular and concentric

• True pulp stones (denticles) look like they have actual dentinal tubules

• They can be free floating or attached to pulp

• Only an issue when you do a root canal and it is in the way

Pulp Exposure

• Can happen naturally from caries or from caries excavation

• Can be saved or lost be necrosis

• Indirect pulp therapy:

  • Remove a large portion of deep caries but seal with biocompatible cement

  • After 6-8 weeks, reopen cavity and remove remaining caries. Sound dentin barrier protects the pulp and tooth is ready for restoration

• Direct pulp therapy:

  • Accidentally perforate pulp

  • Place medicated restoration over exposed pulp

  • Requirements:

    • Field needs to be sterile

    • Size of perforation must be minimal

    • No pain is felt

    • Clotting can occur

    • Calcium hydroxide or MTA stimulate “dentin bridge” formation

  • More successful in young teeth because apical foramen is larger, contains more cells, more vascular, more tissue fluid, and less collateral circulation

Infected vs Affected Dentin

• Infected Dentin

  • Soft

  • Must be fully removed

• Affected Dentin

  • Leatherlike

  • Can be partially removed

Periodontal Ligament

• Highly vascular connective tissue

• Develops from dental sac/follicle

• Connects tooth root to alveolar bone

• Radiolucent space between bone and cementum

• Portion of fibers that are inside cementum/bone and calcified is called Sharpey fibers

  • If Sharpey fibers are removed, the perforated bones are called bundle bone

• Has ground substance (GAGs, PGs like fibronectin and laminin, and 70% water)

PDL Fibers

• Periodontal fibers (Type 1 collagen)

  • Alveolar crest

    • Extend obliquely from crest to cervical part of root

    • Prevents extrusive lateral movement of teeth

  • Horizontal

    • At right angles to long axis of tooth

  • Oblique

    • Largest group

    • Extend from cementum obliquely to bone

    • Bear most vertical masticatory stress

  • Apical

    • Irregularly radiate at apical portion of socket

    • Only on teeth with complete root

  • Interradicular

    • Found in furcation areas of multi-rooted teeth

    • Resist non-axial occlusal forces

    • Inflammation from periodontal disease affects these fibers and causes bone loss between roots (called periodontal furcation involvement)

• Gingival fibers (not between alveolar bone and cementum)

  • Dentogingival (dentin and gingiva)

  • Alveologingival (alveolar bone and gingiva)

  • Dentoperiosteal

  • Circular (not connected)

  • Trans-septal (cementum to cementum of adjacent teeth)

PDL Fiber Composition and function

• 80% Type 1 collagen, 20% Type 3 collagen

• Collagen fiber proteins have high glycine, proline, hydroxyglycine, and hydroxyproline

• Fibronectin is needed for tooth structure attachment from collagen fibers to cementum/bone

• Elastic fibers have oxytalan which run parallel to root and attach to cementum in cervical 1/3rd. They regulate blood flow and support blood vessel

• PDL fibers have high turnover rate due to occlusion functional demands

PDL Cells

• Connective tissue cells

• Defense cells/Immune system cells

• Neurovascular cells

• Fibroblasts (principal cells of PDL, ovoid or spindle-shaped, synthesis of collagen)

• Cementoblasts

• Osteoblasts

• Osteoclasts

• Odontoclasts

• Epithelial Rests of Malassez

  • Remnant of HERS for periodontal tissue maintenance by acting as stem cells

  • Calcify to become cementicles (asymptomatic)

  • Can proliferate to form lateral or periapical cysts

PDL Functions

• Physical - Transmits and resists occlusal forces to bone (tipping/tilting, bodily, extrusive/pulling, intrusive/pushing, or rotational)

  • Different types of forces occur: axial, horizontal, shear, etc

  • Tensional theory - PDL fibers are normally relaxed, but presence of force tightens fibers and transmit force to bone

  • Viscoelastic theory - Tightening of fibers causes extracellular fluid movement from PDL to bone. Depletion from PDL causes tightening. Tightening causes blood vessel stenosis, ballooning and arterial back pressure, resulting in tissue fluid replenishing

• Formative and Remodeling

  • Factors affecting tooth movement include transduction (physical force to biologic response), time, and magnitude of force

  • Hyalinization happens from high force at high-speed resulting in loss of cell activity and vascularity

  • Undermining resorption happens with hyalinization; resorption happens on other side of bone without compensatory bone formation (BAD)

• Nutritional and Sensory

Oral mucosa

• Mucous membrane (stratified squamous epithelium)

  • Sublingual mucosa has thinnest epithelium for drug delivery

• May be orthokeratinized (full; cells with no nucleus), parakeratinized (partial; some cells with no nucleus) or non-keratinized

• Has underlying lamina propria to protect submucosa (basement lamina may exist separating epithelium and lamina propria)

  • Papillary layer - Under epithelium with loose CT

    Reticular layer - Under papillary layer with dense CT

• May have keratohyaline granules (deeply stained in cytoplasm)

• Lack of Langerhans cells make mucosa susceptible to allergens (tonsils in mouth compensate for this)

Oral Mucosa Function

• Mechanical protection from friction and abrasion

• Sensation as taste, touch or pain

• Secretion of saliva or sebum

Rete Pegs

• Folds of epithelium

• Prominent in papillary layer of keratinized epithelium

• Not as prominent in non-keratinized epithelium

Submucosa

• Submucosa may exist with blood vessels or nerves along with salivary glands and adipose tissue

• May have muscles and bone underneath submucosa

• When submucosa is absent, mucosa is tightly bound to bone (mucoperiosteum such as palatine raphe or attached gingiva) using its own rete pegs

Classification of Oral Mucosa

Based on functions:

• Resistance to abrasion of keratinized epithelia

• Flexibility of non-keratinized epithelium

Classification

• Specialized mucosa (dorsal side of tongue)

  • Papilla and taste buds, lamina propria, and tongue muscles

  • Can be keratinized or non-keratinized

  • Filiform is most numerous, covers entire dorsal tongue, but no taste buds

  • Fungiform is mushroom shaped on anterior tongue with taste buds

  • Circumvallate is largest in size and along sulcus terminalis surrounded with taste buds on lateral surface of trench (has serous von Ebner glands)

  • Foliate is at posterolateral border and has furrows

• Masticatory mucosa (gingiva and hard palate) is keratinized

  • Keratinized stratified squamous epithelium, lamina propria, and bone

  • Orthokeratinized to resist abrasion and heat

  • Has deep rete pegs for maximum adhesion and resisting movement

  • Free and marginal gingiva has sulcular epithelium

  • Attached gingiva has stippling and includes mucogingival junction

  • Interdental papilla

  • Col is valley-like depression between teeth where inflammation and periodontitis start

• Lining mucosa (lips, cheeks, floor of mouth, alveolar bone, soft palate, ventral surface of tongue) are non-keratinized

  • Non-keratinized stratified squamous epithelium, lamina propria, submucosa, and muscle

  • Highly flexible

  • Epithelium is thin

Mucocutaneous Junction

• Transition between skin and oral mucosa (Vermillion border)

• Vermillion zone which is thin keratinized epithelium, lacks salivary glands, and has capillary loops in papillae

• Intermediate zone is between vermillion zone and labial mucosa and has para-keratinized stratified squamous epithelium

Hard Palate

• Masticatory Mucosa

• Palatine or median raphe (mucoperiosteum)

• Anterior region (mucoperiosteum)

• Anterolateral (adipose tissue)

• Posterolateral (salivary glands)

• Should not do injections here because of lack of submucosa preventing spreading of fluid

Dentogingival Junction

• Has junctional epithelium at floor of gingival sulcus derived from REE and epithelial attachment (“glue”) consisting of basal lamina that have hemidesmosomes (to attach to enamel)

• Basal laminas are on either end of epithelial cells and meet at CEJ

• Extends apically along root to form seal

Gingival Sulcus

• Area between unattached gingiva and tooth and above junctional epithelium

• Healthy sulcus does not have rete pegs (it indicates inflammation)

Gingival, Sulcular, and Junctional Epithelium

• Gingival Epithelium and Sulcular Epithelium mature because they are superficial and receive instructive influences

• Junctional epithelium does not mature because it is lateral and has permissive influences. Hemidesmosomes can exist on both sides of epithelium. Also provides defense against periodontal bacterial infection

• Gingival epithelium is not supported by CT containing inflammatory cells. Has keratinization

• Sulcular and junctional epithelium is supported by CT containing inflammatory cells. Has no keratinization

• Junctional epithelium can only proliferate apically with help of inflammatory cells causing periodontal pocket and attachment recession

Fordyce’s spots

• Sebaceous glands

• Inner buccal and corners of mouth

Mucocoele

• Bubble in mucosa that is fluid filled caused by blockage of salivary glands or misalignment of gland and duct

Linea Alba

• Chronic irritation of teeth against buccal mucosa causes keratinization of lining mucosa

• Results in white line

Black Triangles

• “Open gingival embrasures” caused by interdental papillae not filling space between teeth

• Can be normal or sign of dental problems like veneers or implants

Age Changes to Mucosal Tissues

• Smoother and drier

• Thinner epithelium

• Losing filiform papillae and Langerhans cells

• Ventral side of tongue starts having varicose veins