Histology Exam 3 PDF

Chapter 12: Enamel **Enamel Properties** - Not a renewable tissue; nonvital; avascular - Hardest mineralized tissue in the body - Can endure crushing pressure about 100,00 lbs per sq in.! - When [healthy,] can be removed [only] by a rotary cutting instrument or files - By wei...

Chapter 12: Enamel **Enamel Properties** - Not a renewable tissue; nonvital; avascular - Hardest mineralized tissue in the body - Can endure crushing pressure about 100,00 lbs per sq in.! - When [healthy,] can be removed [only] by a rotary cutting instrument or files - By weight: 96% inorganic material or mineralized, 1% organic material, & 3% water - Consists mostly of [calcium hydroxyapatite] - Found less in dentin & cementum - Ribbon-like crystals of enamel are set at different angles throughout the crown, each 30% larger than dentin which is why enamel is harder than dentin - Covers anatomic crown (seen clinically) - Each tooth can withstand masticatory impact of 20-30 lbs of pressure - Thinner cervically, thicker at incisal edges & cusps to endure the masticatory forces - Protects the tooth from physical, thermal, & chemical forces **Clinical Considerations with Enamel Structure**  - **Attrition**- wearing of hard tissue from tooth-to-tooth contact - Increases with age - Parafunctional habits - Loss of vertical dimension - **Wear facets-** occlusal or incisal surfaces worn by attrition - Enamel rods are fractured & become highly reflective to light - **Abrasion-** loss of enamel from friction caused by excessive tooth brushing & abrasive toothpaste - **Erosion**- enamel loss through chemical means - Bulemia, gastric reflux, drug use - Lingual of maxillary anterior teeth & the occlusal surface of maxillary posterior teeth - If facial aspects are affected, the patient could be overusing carbonated drinks, sport drinks, citric acid diets Erosion: Bulemia Erosion: Gastric Reflux Erosion: Meth Mouth  - **Enamel caries-** loss of enamel mineralization due to acid produced by cariogenic bacteria & occurs when the [enamel pH is less than 5.5] - **Abfraction-** enamel loss by an increase in tensile & compressive forces during tooth flexure, which may occur during parafunctional habits with their occlusal loading - Found in cervical region - Enamel "pops off" from the dentin layers appearing as a notch in the tooth - May be sensitive - Typically covered with composite in severe cases **Enamel Matrix Formation** - **Amelogenesis-** formation of enamel matrix occurring in the [apposition stage] of tooth development - Enamel matrix produced by ameloblasts - Enamel matrix is secreted from each ameloblast from its own Tomes process (responsible for the way enamel is laid down) - Ameloblasts produce about 4 micrometers of enamel matrix daily during tooth development - Contains 2 classes of proteins: amelogenins & ameloblastin (as well as enamelins) - First formed in the [incisal or occlusal] part of future crown nearer to the forming DEJ & moves cervically toward CEJ **Clinical Considerations During Enamel Formation** - **Enamel pearl & enamel dysplasia:** deepened pit & groove patterns on [linguals of anteriors] & [occlusals of posteriors] - Created when ameloblasts back into one another during apposition stage, cutting off their source of nutrition which causes incomplete maturation of enamel matrix making it weak or absent in that area **Enamel Matrix Maturation** - Enamel mineralization occurs during the [apposition & maturation stages] and continues after tooth eruption - Ameloblasts are responsible for enamel matrix maturation into enamel - Forms first in incisal/occlusal followed by the cervical regions - After ameloblasts complete enamel apposition & maturation, they become part of the REE - The REE will later fuse with the oral mucosa, creating a protective tunnel to allow the cusp tip to erupt through the oral mucosa - This fused tissue disintegrates during eruption & ameloblasts are gone forever preventing further appositional growth of enamel - Enamel mineralization continues after eruption **Clinical Considerations with Enamel Pathology** - **Noncavitated lesion-** incipient caries lesion - Enamel is demineralized - Loss of color, glossiness, or surface structure - Can be reversed or remineralized (until it is cavitated into dentin) - First noted clinically as "white spot lesions" - With the cariogenic process, surface enamel stays intact while the subsurface demineralizes. Thus, enamel caries remains in the subsurface, enlarging the pathway to the connected dentin &/or pulp to form dentinal caries, or pulpitis if it continues. **Enamel Histology** - The **enamel rod (or enamel prism)** is the crystalline structural unit of enamel - Many variations in the structural arrangement of these cylindrical rods. Each ameloblast & Tomes process affects the crystalline pattern found within the rods - The crystals in the rods bend right or left at different angles than the adjacent groups which increases the enamel's strength - This is shown in the **Hunter-Schreger bands** alternating light to - Enamel rods are in rows along the long axis of the tooth, perpendicular to the dentin as well as the DEJ with a slight inclination toward the cusp as they pass outward, preventing enamel fracture - Near the cusp tip, they run more vertical - Cervical enamel runs mostly horizontal - Enamel rods interdigitate at each cusp tip to form a complex known as gnarled enamel. - This reduces occlusal stress on the enamel - Surrounding the outer part of each rod is the **interrod enamel,** creating an interprismatic region that has been secreted by surrounding ameloblasts - The **[Lines of Retzius]** are the incremental lines (or striae) that appear in a microscopic section of enamel - Associated with the lines of Retzius are the raised **imbrication lines** and grooves of **perikymata** on [non-masticatory] surfaces of teeth. - Lost through tooth wear - The **neonatal line** is a pronounced line of Retzius that marks the trauma experienced by ameloblasts during birth - Primary dentition [crowns & permanent 1^st^ molar cusps]  - **Enamel spindles** represent [short dentinal tubules] near the DEJ - Result from [odontoblasts] crossing the basement membrane before it mineralized into the DEJ - **Enamel tufts** appear as [small dark brushes] with their bases near the DEJ representing areas of less mineralization from an anomaly of crystallization - **Enamel lamellae** are partially mineralized vertical sheets of enamel matrix extending from the DEJ near the [tooth's cervix] to the outer occlusal surface - Anomaly of crystallization Figure 12-12. Transverse section of enamel showing enamel tufts (white arrow) and enamel lamella (black arrow). Chapter 13: Dentin & Pulp **Dentin- Pulp Complex** - In health, cannot be viewed clinically - Developed from the dental papilla **Dentin Properties** - Mature dentin is a [crystalline material] that is less hard than enamel but slightly harder than bone - By weight, 70% inorganic or mineralized material, 20% organic, & 10% water - Calcium phosphate is considered inorganic because it does not contain carbon - Organic materials consist of collagen, mucopolysaccharides, and other proteins - Consists mostly of calcium hydroxyapatite crystals that are 30% smaller in size than enamel - Covered by enamel in the crown, cementum in the root, as well as enclosing the pulp - Appears as an underlying yellow hue - If/when pulp undergoes infection or dies, there\'s a discoloration of the dentin causing darkening of the clinical crown - Appears radiolucent on radiographs compared to enamel due to being less dense and more radiopaque than pulp which has the least density **Clinical Considerations for Dentin Structure** - Coronal dentin can be exposed after attrition of enamel & also with certain enamel dysplasias - Coronal dentin can become exposed on the incisal ridge of anteriors when trauma causes it to become chipped or worn - Root dentin can be exposed when the thin layer of cementum is lost due to gingival recession with its lower margin of the free gingival crest - When using hand instruments to remove deposits along the root surface, dentin can be removed changing the overall shape & function of the root - **Dentinal caries**- demineralization resulting from cariogenic bacteria - [Demineralizes when pH is less than 6.8] - Cavity prep removes carious dentin - Dentinal hypersensitivity can occur when instruments expose dentin; can be prevented with certain mineralizing products or reduced with local anesthesia - If dentin is left exposed, it can become stained from beverages, food, or tobacco due to being more porous than enamel - Dentin is permeable due to [dentinal tubules acting as a sponge] - Whitening can be done, but can lead to dentinal hypersensitivity **Dentin Matrix Formation** - **Dentinogenesis** is the formation of dentin matrix or predentin during the [apposition stage] of tooth development - Predentin is a [mesenchymal] product consisting of nonmineralized collagen fibers produced by the [odontoblasts] - Newly formed odontoblasts are induced by the equally newly formed ameloblasts to produce predentin in layers, moving away from the DEJ. - Odontoblasts produce about 4 micrometers of dentin daily during tooth development - Appositional growth of dentin continues throughout the life of the tooth, filling the pulp chamber of both the crown & root - The wave pattern of dentin development is the same as enamel but on the opposite side of the DEJ- beginning at incisal/occlusal part spreading down the adjacent cervical loop of the enamel organ - Odontoblasts are retained allowing for the continuance of dentin production - Tall bowling pin-shaped cells lining up along outer pulpal wall - 2 phases: primary & secondary - [**Primary mineralization-**] calcium hydroxyapatite crystals form as globules in the collagen fibers of the predentin allowing both expansion & fusion - [**Secondary mineralization-**] new areas of mineralization occur as globules form in the [partially mineralized] predentin that expand and fuse incompletely resulting in differences noted in the microscopic appearance of the crystalline form of dentin - **[Globular dentin-]** dentin with [primary *&* secondary] mineralization - **[Interglobular dentin-]** dentin with [*only* primary] mineralization - less mineralized - Evident in coronal dentin, near DEJ, and certain dentin anomalies like dentin dysplasia **Mature Dentin Components** - **[Dentinal tubules-]** long tubes in dentin that extend from the DEJ in the crown area or dentinocemental junction (DCJ) in the root area to the outer wall of the pulp - Thinner at DEJ & wider near pulp - Contains dentinal fluid, an odontoblastic process, & afferent axon - **[Dentinal fluid-]** contains tissue fluid surrounding the cell membrane of the odontoblast - Avascular - Odontoblasts within the dentin receive nutrients by tissue fluid in the dentinal tubules that originally traveled from the pulpal blood vessels - Mature Dentin Components - 3 types of nerve fibers within dentin - [A (both delta & beta) fibers-] stimulated by an application of cold, producing a sharp pain - [C fibers-] produce dull aching pain; also responsible for referred pain **Dentin Types** - In relation to the dentinal tubules: - **[Peritubular (intratubular) dentin-]** creates the wall of the dentinal tubules; highly mineralized - **[Intertubular dentin-]** found between tubules; highly mineralized but less than peritubular dentin - In relation to enamel & pulp: - **[Mantle dentin-]** 1^st^ predentin that forms & [matures] within the tooth near the DEJ & under the enamel - Contains [Von Korff fibers-] large diameter collagen fibers - Contains more peritubular dentin resulting in higher levels of mineralization - Fibers run perpendicular to DEJ - **[Circumpulpal dentin-]** deep to mantle dentin surrounding the pulpal wall; makes up the [bulk] of the dentin within the tooth - Fibers run parallel to DEJ - In relation to the time it was formed within the tooth: - **[Primary dentin-]** formed *[before]* the completion of the apical foramen of the root; characterized by its regular pattern of dentinal tubules - **[Secondary dentin-]** formed *[after]* the completion of the apical foramen & continues to form throughout the life of the tooth; formed more slowly - **[Tertiary dentin-]** formed quickly in local regions in response to a localized [injury] to the exposed dentin such as caries, cavity prep, attrition, gingival recession **Clinical Considerations for Dentin Pathology** - Dentin can be resorbed in permanent dentition but the cause is unknown & can involve either an internal or external resorption process - When the process begins on the external surface of the root & then penetrates through the cementum into the dentin, it can lead to a pinkish crown color noted clinically as granulation tissue seen beneath the translucent enamel so it is now considered "pink tooth" - **[Dentinal caries-]** when the dentin tubules serve as an entry mechanism for cariogenic bacteria as the caries process extends from the enamel to dentin - Caries process moves more rapidly - [**Reparative dentin-**] a type of tertiary dentin in which odontoblasts in the area of the affected (injured) tubules die due to injury, but neighboring undifferentiated mesenchymal cells of the dental pulp move to the area & become odontoblasts - **[Sclerotic dentin-]** a type of tertiary dentin found in association with [chronic injury of caries], attrition, & abrasion, as well as in an aging tooth - Odontoblastic processes die & leave dentinal tubules vacant which is why its also referred to as transparent dentin - Tubules become retrofilled & occluded by mineralized substance similar to peritubular dentin - May be involved in prolonging pulp vitality due to reducing the permeability of the dentin - Clinically appears as a dark, smooth, and shiny region on the tooth surface - **[Smear layer-]** occurs when cutting dentin during cavity prep; composed of adherent biofilm debris - Function is to be protective as it decreases dentin permeability - **[Dentinal hypersensitivity-]** when dentin is exposed as a result of caries, cavity prep, gingival recession, or attrition, the tubules may be painful for a patient - Short, sharp pain can be triggered by thermal changes, mechanical irritation, dehydration, or chemical exposure - Caries, pulpal/gingival infections are dull and chronic pain - Treatments: desensitizing agents (fluoride), local anesthesia, restorations **Dentin Histology** - **[Imbrication lines of Von Ebner-]** microscopic [incremental lines] or bands of dentin that show the incremental nature of dentin during the apposition stage of tooth development & run 90˚ to the dentinal tubules - **[Contour lines of Owen-]** several adjoining parallel imbrication lines (seen microscopically) present in dentin that show a disturbance in body metabolism that affects the [odontoblast] by altering their formation efforts, [appearing as a series of dark bands] - The most pronounced is the neonatal line that occurs during the trauma of birth - **[Tomes granular layer-]** dentin beneath cementum & adjacent to DCJ that looks granular **Aging Dentin** - Dentinal tubule narrows in diameter with aging due to the deposition of peritubular dentin on the inner wall - May be related to decreased ability of pulp to respond to stimuli - Dentinal translucency is one of the best morphohistologic parameter to use for dental age estimation **Pulp Properties** - Innermost soft tissue of the tooth appearing radiolucent because it is less dense than the radiopaque hard tissue of the tooth - Connective tissue - Forms from the central cells of the dental papilla during tooth development - Pulp is involved in the support, maintenance, & continued formation of dentin because the cell bodies of the odontoblasts remain along the outer pulpal wall - Sensory function- pain - Serves as a nutritional function for itself as well as dentin because the dentin is avascular - Contains WBCs allowing for inflammatory & immune response - **[Pulp chamber-]** part of tooth containing pulp - The shape corresponds to each tooth shape - 2 main divisions: coronal pulp & radicular pulp - Pulp Anatomy - **[Coronal Pulp-]** located in the crown of the tooth - Smaller extensions of coronal pulp into the cusps of posterior teeth form the **[pulp horns]** - Pulp horns [not found on anterior teeth]; [recede with age] - **[Radicular pulp-]** located within the [root] of the tooth in the pulp canal ("root canal"); extends from cervical part of tooth to the apex - Contains openings from the pulp through the cementum into the surrounding PDL. These openings contain each apical foramen as well as accessory canals - Pulp Anatomy - **[Apical foramen-]** opening from the pulp into the surrounding PDL near each apex - Surrounded by layers of cementum but permits arteries, veins, lymphatics, & nerves to enter & exit the pulp from the PDL allowing the tooth to remain vital - Last part of tooth to form; after the crown erupts into the oral cavity - **[Accessory canals (lateral canals)-]** extra openings from the pulp to the PDL - Form when Herwig epithelial root sheath encounters a blood vessel during root formation **Pulp Histology** - Fibroblasts are the **largest** group of cells in the pulp - Odontoblasts are the **2^nd^ largest** group but only their cell bodies a located in the pulp; located only along the outer pulpal wall - **[Dental pulp stem cells-]** undifferentiated mesenchyme type of stem cells in pulp tissue - Can transform into fibroblasts or odontoblasts if either cell population is reduced after injury - Most viable in primary teeth; can be in wisdom teeth - WBCs, vascular supply, lymphatics - Pulp Histology - 2 types of nerves are associated with the pulp: myelinated & unmyelinated nerves - Mostly nocioreceptors- nerve cell endings that mostly relay the sensation of pain - [Myelinated nerves-] axons of sensory or afferent neurons that are located in the dentinal tubules - [Unmyelinated nerves-] associated with the blood vessels **Pulp Zones (4)** - **1. Odontoblastic layer-** closest to the dentin' lines the outer pulpal wall - Odontoblasts are capable of forming [secondary or tertiary dentin along outer wall] - **2. Cell free zone-** nearest to the odontoblastic zone and inward from dentin - Microscopically contains fewer cells than odontoblastic layer but not cell free - Contains a nerve & capillary plexus - No secondary or tertiary dentin is formed here initially, but newly formed dentin may trespass upon this zone - Pulp Zones (4) - 3\. **Cell-rich zone-** increased density of cells, but still not as many as the odontoblastic zone - Contains more extensive vascular supply - 4\. **Pulpal core-** center of pulp chamber - Consists of many cells & vascular supply **Aging Pulp** - Pulp horns recede during aging - Decrease in intercellular substance, water, & cells which are replaced with an increase \# of collagen fibers - Becomes more fibrotic leading to a reduction in the regeneration of pulp tissue due to loss of cells - Overall pulp cavity may be smaller due to the addition of secondary or tertiary dentin, clinically causing **[pulpal recession]** - Apical foramen may become obliterated with deposits of cementum over time leading to blockage of blood vessels - This can result in vascular congestion & then pulpal necrosis, resulting slowly in painless tooth death without any evidence of caries, periodontal disease, or endodontic infection **Clinical Considerations for Pulp Pathology & Repair** - **[Pulp stones (denticles)-]** mineralized masses of dentin complete with dentinal tubules and odontoblastic processes - [Formed during tooth development & also later as the pulp ages & they may be due to microtrauma ] - Appear as radiopaque masses radiographically - **[Pulpitis-]** inflammation of the pulp when it is injured; can be extremely painful - [Reversible pulpitis-] inflammation is localized to coronal portion of pulp - [Irreversible pulpitis-] can later cause pulpal infection in the form of a periapical abscess or cyst in the surrounding periodontium spreading through the apical foramen or accessory canal - Treatment: pulpectomy or root canal therapy - When pulp is removed, tooth is no longer vital; tooth may become dark & brittle  **Periodontium properties** - **[Periodontium]**- includes cementum, alveolar process, & PDL **Cementum properties** - Attaches the teeth to alveolar process by anchoring the PDL - Not clinically visible in a healthy mouth - Provides protective cover over open dentinal tubules within root dentin if exposure occurs - Thickest at tooth's apex & interradicular areas; thinnest at CEJ - No nerve supply, avascular; receives nutrition through own embedded cells from the surrounding vascular PDL - Can be deposited throughout the life of the tooth - By weight, 65% inorganic or mineralized material, 23% organic, & 12% water - Contains calcium hydroxyapetite **Clinical considerations with cementum structure** - When exposed through gingival recession, quickly undergoes abrasion, exposing the underlying dentin leading to dentinal hypersensitivity - **Cemental caries**- causes chronic infection in pulp **Cementum development** - Develops from dental sac & forms on the root dentin after the HERS disintegrates - Subdivided into prefunctional stage & functional stage - [Prefunctional stage-] occurs throughout root formation - [Functional stage-] starts when tooth comes into occlusion & continues throughout life - Many cementoblasts [become entrapped the cementum] they produce & become cementocytes - Cementocytes undergo cementogenesis, laying down cementoid. - When cementoid reaches necessary thickness, the cementoid surrounding the cementocytes become mineralized creating cementum - As a result of the appositional growth of cementum over the dentin, the dentinocemental junction (DCJ) is formed **Cementum histology** - Composed of a mineralized fibrous matrix of cells consisting of [Sharpey fibers & intrinsic nonperiodontal fibers] - **[Sharpey fibers]**-collagen fibers from PDL that are partially inserted into the outer surface of the cementum at 90˚ or perpendicular & inserted on the other end into the alveolar process at the same angulation - Organized to function as a ligament between the tooth & alveolar process - [Intrinsic non PDL fibers] are collagen fibers made by cementoblasts & laid down in a nonorganized pattern but still run parallel to DCJ - Cementocytes lie in lacunae that contain canals that are oriented toward PDL & contain cementocytic processes that diffuse nutrients from the vascularized PDL - Cementoblasts that do not become entrapped line up along the cemental surface for the entire length of the outer covering of the PDL & can form subsequent layers of cementum if the tooth is injured - **[3 transitional interfaces that may be present at the CEJ ]** - Cementum may overlap enamel at the CEJ (can be difficult determining if CEJ or calculus when scaling) - Cementum & enamel may meet end to end forming a butt-joint, presenting no problems for clinician or patient (most common interface) - Gap may exist between the cementum & enamel exposing dentin causing dentinal hypersensitivity **Cementum types (2)** - **[Acellular cementum (primary cementum)-]** consists of the 1^st^ layers deposited at the DCJ - Forms slower & does not contain cementocytes - Width never changes over time - 1 layer on entire surface of each root with several other layers covering cervical 1/3 near CEJ - **[Cellular Cementum (secondary cementum)-]** deposited over the acellular cementum mostly in apical 1/3 of root - Many embedded cementocytes - Cementoblasts in the PDL line up on its periphery allowing for the future productions of more cellular cementum in response to tooth wear & movement - Width can change during life of tooth **Cementum repair** - Can undergo removal within the tissue as a result of trauma including resorption by odontoclasts resulting in [reversal lines] - Can be repair of traumatic resorption area by involving appositional growth of cementum by cementoblasts in adjacent PDL - Appositional growth of this recently formed protective cementum is noted as [arrest lines] - Does not continually undergo remodeling or repair unless severely traumatized - Permeability may lessen with age **Clinical considerations for cementum pathology** - **[Cementicles-]** mineralized spherical bodies of cementum found either attached to the cemental root surface or lying free in PDL - Form from appositional growth of cementum around cellular debris in PDL, possibly a result of microtrauma to Sharpey fibers - May be seen radiographically - **[Cemental spurs-]** symmetrical spheres of cementum attached at cemental root surface similar to enamel pearls (found at or near CEJ) - Results from irregular deposition of cementum on root & may be noted radiographically - May interfered with perio therapy or homecare - Difficult to remove - Rapid ortho therapy can cause root apex resorption - Increased risk of tooth mobility - **[Hypercementosis]**- excessive productions of cellular cementum, which mostly occurs at the apex, but could occur anywhere on apical 1/3 of one or more teeth - May have resulted from occlusal trauma caused by excessive occlusal forces during certain pathologic conditions (chronic periapical inflammation), as well as systemic conditions (Paget disease) - Could result in pulpal necrosis if severe and blocking blood supply via apical foramen **Alveolar process properties** - **[Alveolar process]** supports & protects teeth as well as a part of the periodontium to which cementum is attached through PDL - By weight 60% inorganic or mineralized, 25% organic, 15% water - Contains calcium hydroxyapatite **Clinical considerations for Jaw development** - [Anodontia] may affect the development of the alveolar process of the associated jaw because the alveolar unit of each dental arch only forms in response to the tooth germs that will later erupt in that area (there are no tooth germs present with anodontia; no germ = no tooth) **Jaw anatomy & histology** - Each jaw is composed of 2 types of bone with different physiologic functioning - Part containing roots of the teeth is called **[alveolar process]** (alveolar bone or ridge) - The part apical to the roots of the teeth is **[basal bone]** which then forms the body of the maxilla or mandible & is not considered part of the periodontium - Both alveolar process & basal bone are covered by a periosteum - The alveolar process is divided into alveolar bone proper & supporting alveolar bone - **[Alveolar bone proper (ABP)-]** lines the tooth socket or alveolus - Composed of compact bone - May be referred to as the cribriform plate because it contains numerous holes where Volkmann canals with its nerves & blood vessels pass from the ABP to PDL - Also considered bundle bone because Sharpey fibers insert here - The attached gingiva along with the periosteum of the ABP serves as a mucoperiosteum - The part evident on radiographs is called the **[lamina dura]** - The **[alveolar crest]** is the most cervical rim of the ABP - In a healthy situation, it is slightly apical to CEJ - Can be used to educate patients on their bone loss/health on radiographs - **[Supporting alveolar bone]** consists of both cortical & trabecular bone - **[Cortical bone]** consists of a plate of compact bone on both facial & lingual surfaces of the alveolar process - Also referred to as cortical plate - Only visible on occlusal radiographs - **[Trabecular bone-]** consists of cancellous (spongy) bone located between ABP & cortical bone plates - **[Interdental septum (bone)-]** alveolar process separating 2 neighboring teeth - Visible on PAs & BWX - Consists of both compact bone of the ABP & cancellous bone of the trabecular bone - **[Interradicular septum (bone)-]** alveolar process found between the roots of the same tooth - Consists of both ABP & trabecular bone however only part of the interradicular septum is visible on PAs or BWX - Clinical considerations with dental procedures & pathology involving Alveolar process **Clinical considerations with dental procedures & pathology involving Alveolar process** - Bone remodeling can be forced with ortho to produce tooth movement for repositioning - The bands, wires, or ortho appliances put pressure on the side of the tooth & adjacent alveolar process creating a [compression zone] in the PDL leading to bone resorption - On the opposite side of the tooth & bone, the [tension zone] develops in the PDL causing deposition of new bone - **[Mesial drift-]** natural movement in which all teeth move slightly toward the midline over time which can cause crowding - When a patient becomes **[edentulous,]** bone resorption occurs - Bony trabeculae supporting the alveoli decreases, however the underlying basal bone does not as it does not need teeth to remain vital; the alveolar process depends on the functional simulation from retained teeth during mastication & speech for its preservation - Placement of a prosthetic appliance may provide some stimulation of the bone similar to having teeth - [**Overeruption (super-eruption)-**] physiologic movement of a tooth lacking an opposing tooth to occlude with - Root exposure may lead to dentinal hypersensitivity, root caries, & esthetic compromise as well as compromising the periodontal health of the affected tooth - The loss of alveolar process due to aging coupled with attrition causes a loss of height of the lower 1/3 of the vertical dimension - Alveolar process resorption can occur in higher levels in postmenopausal women who experience a shortage of estrogen or with onset of osteoporosis - Localized alveolar process is lost in varying degrees of chronic periodontal disease of periodontitis - Bone loss is 1^st^ evident in the most coronal part of the ABP, the alveolar crest & slowly progresses apically - Tooth becomes mobile & increased risk of tooth loss is possible - **[Mobility]**- tooth movement because of loss of support from the periodontium - Density of alveolar process in a given area also determines the route a dental infection will take with abscess formation - With occlusal trauma, the part of the ABP present on radiographs as the lamina dura may become thickened in response, along with widening of the PDL space - The PDL is the part of the periodontium that provides for the attachment of the teeth to the surrounding ABP by way of root cementum - Thinnest at middle 1/3 of tooth - Appears on radiographs as the **[periodontal ligament space]** that is radiolucent (darker) located between the lamina dura & cementum - Organized fibrous CT - Transmits occlusal forces from the teeth to bone, allowing for a small amount of movement & acting as a shock absorber for the soft tissue structures around the teeth - Periodontal ligament properties - Serves as periosteum for both cementum & alveolar process - Its blood vessels provide nutrients for the ligament's cells & surrounding cells of the cementum & alveolar process - The PDL & its nerve supply can transmit pain, pressure, touch, & temperature sensations - Develops from the dental sac - Decreases with age - Contains a vascular supply, lymphatics, & nerve supply that enters through the apical foramen **Periodontal ligament cells** - Fibroblast is the most common cell - Also contains cementoblasts along cemental surface of root, osteoblasts at periphery of ABP, as well as osteoclasts & odontoclasts, undifferentiated mesenchymal cells, & epithelial Rests of Malassez - These cells can either *form* cementum or bone or *resorb* either tissue **Periodontal ligament fiber groups** - PDL is wider near apex & cervix of tooth - All fibers are collagen in structure - **[Principal fibers-]** organized into groups on basis of orientation to tooth & related function (most fibers of PDL are principal fibers) - These fibers distribute the various mastication & speech forces (rotational, tilting, extrusive, or intrusive) - The ends of these fibers that are within either cementum or ABP are considered Sharpey fibers - **[Alveodental ligament-]** main principal fiber group that functions to resist rotational forces or twisting of the tooth in its alveolus - Periodontal ligament fiber groups - Alveodental ligament consists of 5 fiber subgroups classified into several groups based on their anatomic location: alveolar crest, horizontal, oblique, apical, interradicular - **[Alveolar crest group-]** attached at cementum just below CEJ inserting into the alveolar crest of the ABP - Functions to resist tilting, intrusive, extrusive, & rotational forces - **[Horizontal group-]** just apical to alveolar crest subgroup running 90° to the long axis of the tooth from cementum to the ABP - Functions to resist tilting forces, which work to force the tooth to tip mesially, distally, facially, or lingually & resist rotational forces - Periodontal ligament fiber groups - **[Oblique group-]** most numerous of the fiber subgroups & covers the apical 2/3 of root; runs from cementum in oblique direction to insert into ABP more coronally - Functions to resist intrusive forces which try to push the tooth inward as well as rotational forces - **[Apical group-]** radiates from cementum around apex to surrounding ABP forming the base of the alveolus - Functions to resist extrusive forces which try to pull the tooth in an outward manner & rotational forces - **[Interradicular group-]** found between roots of multirooted tooth; no bony attachment - Works together with the alveolar crest & apical subgroups to resist intrusive, extrusive, tilting, & rotational forces - **[Interdental ligament-]** principal fiber that inserts interdentally into cementum of neighboring toothcoronal to the crest of ABP & apical to base of junctional epithelium - Transverse from cementum to cementum without bony attachment - Functions to resist rotational forces holding the teeth in interproximal contact - **[Gingival fiber group-]** separate but adjacent group found within the lamina propria of the marginal gingiva; 2 types (circular & dentogingival) - Supports only marginal gingiva in an effort to maintain its relationship to the tooth - [Circular ligaments] encircle the tooth to maintain gingival integrity - [Dentogingival ligament] inserts into the root cementum extending into the lamina propria of marginal & attached gingiva; works with circular ligaments to maintain gingival integrity of mostly marginal gingiva **Clinical considerations for PDL pathology & repair** - During ortho, on the tension zone side the PDL becomes wider whereas the compression zone side becomes narrower - **[Occlusal trauma]** involves trauma to periodontium from occlusal disharmony - Does not cause periodontal disease but can accelerate the progression - PDL widens - Lamina dura thickens - Increased mobility when severe - Clinical considerations for PDL pathology & repair - PDL fibers become disorganized & attachments to the ABP or cementum through Sharpey fibers are lost because of resorption of these 2 tissues - 1^st^ fibers involved with periodontitis are the alveolar crest group of the alveolodental ligament and then progresses apically affecting (in order) the horizontal, then oblique, then apical fiber group, and lastly the interradicular if present - Interdental ligament remains the longest in the presence of active periodontitis