Dental Pulp and Cementum Lecture 2024 PDF

Dental Pulp Karla Coburn, DDS, PhD [email protected] Learning Objectives 1. Describe the origin and distribution of the pulp tissue 2. Describe the composition of the pulp tissue 3. Describe the major cell types in the pulp 4. Describe the layers of the pulp tissue 5. Describe the nerve and b...

Dental Pulp Karla Coburn, DDS, PhD [email protected] Learning Objectives 1. Describe the origin and distribution of the pulp tissue 2. Describe the composition of the pulp tissue 3. Describe the major cell types in the pulp 4. Describe the layers of the pulp tissue 5. Describe the nerve and blood supply for the pulp tissue 6. Describe the major theories of dentin sensitivity 7. Describe how the pulp tissue respond to insults 8. Describe internal root resorption and how this relates to the pulp tissue 9. Describe the age-related changes in the dental pulp Dental Pulp - Origin ✓ Dental pulp develops from the dental papilla after being encased by dentin. ✓ It derives from the ectomesenchyme. Dental Pulp distribution ✓There are two forms of pulp: coronal radicular ✓Coronal pulp occupies the crown of the tooth and has pulp horns which extend up into the cusps. ✓Radicular pulp extends from the cervical region to the root apex. Accessory Root Canal ✓ An accessory canal is a branch of the main pulp canal that communicates with the external root surface. Composition ✓ Loose connective tissue ✓ 75% water ✓ 25% organic matrix ECM ✓ Collagen fibers (Type I, Type III) ✓ Ground substance: GAGs, proteoglycans and multi-adhesive glycoproteins Cell types ✓ Fibroblasts ✓ Mesenchymal cells ✓ Macrophages ✓ Mast cells ✓ Plasma cells ✓ Dendritic cells ✓ Neutrophils, eosinophils, ✓ Lymphocytes ✓ Odontoblasts Fibroblasts ✓Fibroblasts are the most abundant cell in the pulp. ✓They are spindle shaped and produce all the organic matrix of the pulp tissue. Lymphocytic infiltrate Odontoblasts ✓ The morphology of odontoblasts reflects their functional activity and ranges from an active synthetic phase to a quiescent phase. ✓ Active cell: elongated, polarized, with a well- developed RER (basophilia) and Golgi. ✓ Resting cell: stubby, with little cytoplasm, darker nucleus and autophagic vacuoles. Pre-odontoblast Secretory odontoblast Resting odontoblast Odontoblasts ✓ Odontoblasts synthesize dentin and respond to external stimuli. ✓ Their cell processes reside within the dentinal tubules Layers of Pulp 1. The odontoblasts 2. The cell free zone (zone of Weil) 3. The cell rich zone 4. The parietal layer of nerves 5. The bulk of pulp tissue: loose connective tissue with blood vessels and abundant nerve supply. Odontoblastic processes Predentin Odontoblastic layer Odontogenic Zone The cell free zone The cell rich zone The parietal layer of nerves  Dentin Odontoblastic zone Predentin Cell-rich zone Cell free zone Nerve Supply ✓ The dental pulp is heavily innervated (sensory and autonomic). ✓ Nerve supply reaches the pulp via the apical foramen and consists mostly of unmyelinated fibers. ✓ Nerve fibers come from the trigeminal nerve (sensory perception) and sympathetic nervous system (regulation of blood flow). Nerve Supply ✓ The nerve bundles reach the parietal layer of nerves and then form a plexus below the odontoblastic layer (subodontoblastic nerve plexus, AKA Plexus of Raschkow). ✓ Small nerve fibers pass between the odontoblast cell bodies to enter dentinal tubules. Subodontoblastic Nerve endings inside nerve plexus dentinal tubules Parietal layer of nerves  Dentin Sensitivity ✓The pulp is sensitive to temperature, pressure, electrical and chemical stimulation. ✓There are no specialized sensory receptors (Meissner, Pacinian and Ruffini Corpuscles), only free nerve endings. So, all these different stimuli are perceived as PAIN. Theories of Dentin Sensitivity ✓Direct Innervation theory: nerves Predentin extend all the way to the DE Intertubular Peritubular Odontoblast Nerve junction. dentin dentin ✓Transduction theory: the odontoblastic processes in the Direct Innervation dentinal tubules transduce the stimuli to the nerves in the pulp. Odontoblasts acting as receptors ✓Hydrodynamic theory: fluid in the dentinal tubules move within the tubules stimulating nerves in the To brain pulp Fluid in the dentinal tubules stimulates deep nerve endings Blood and Lymphatics Vessels Blood supply is essential for dentinogenesis! Odontoblastic process Predentin Odontoblast Blood vessels Pulp Response to Injury ✓Pulpitis is the inflammatory condition of the dental pulp. ✓ The increased vascular exudate can’t be alleviated by swelling, because the dental pulp is confined by hard tissue. This results in increased pressure within the pulp chamber, compressing nerve endings and causing extreme pain.  Pulp Necrosis: the death of the pulp tissue ✓ Most cases of necrosis develop when host defenses are unable to eliminate the irritant (usually pyogenic microorganisms, leading to liquefactive necrosis ). ✓ Severe trauma may also cut the blood supply to the tooth, causing pulp necrosis. ✓ Pulp necrosis and irreversible pulpitis are indications for endodontic therapy. Extricated pulp Pulp Response to Injury ✓ Dead tracts and sclerotic dentin are responses associated to the odontoblastic processes, which belong to the odontoblasts, cells of the pulp tissue. Therefore, these are also considered responses of the pulp tissue. ✓Tertiary dentin is laid down in response to a pulpal insult or injury. Osteodentin Dentin Pulp Response to Injury: Internal Root Resorption ✓ Internal resorption is a rare, insidious, resorptive pathological process, beginning in the pulpal space and extending into the surrounding dentin. It is characterized by the enlargement of the pulp chamber as a result of the ongoing resorptive process. ✓ In normal conditions, the inner surface of the dentin is protected by a thin layer of predentin and the odontoblasts. Damage to these layers triggers dentin resorption by odontoclasts. ✓ Resorption starts inside (within the pulp)! ✓ May occur as a result of chronic inflammation and bacterial invasion of the pulp tissue or trauma. Pink areas are suggestive of IR  Ballooning of the After endodontic Internal Resorption root canal therapy Age-Related Changes in the Dental Pulp ✓ The dental pulp gets smaller with age because secondary dentine deposition throughout life. Atretic canals can be challenging. Age-Related Changes in the Dental Pulp ✓ The older pulp is less vascular and, apparently, more fibrous than the young pulp. ✓ The innervation is reduced. ✓ The pulp often mineralizes in the form of pulp stones. Histologic preparation specially stained to reveal collagen. With age the collagen content becomes more abundant and aggregates to form larger fiber bundles  Pulpal Calcifications (Pulp Stones) ✓ The incidence of pulpal calcifications increases with age (age-related change rather than being pathological). ✓ Their presence can complicate root canal therapy when it is indicated for other reasons. ✓ According to their location, pulp stones may be free, Pulp stones can be detected attached to the dentine or embedded within dentin. on radiographs. ✓ According to their structure, pulp stones can be classified as: True Pulp Stones (or true denticles) False Pulp Stones (False Denticles)  False Pulp Stone True Pulp Stone Composed of Composed of dentin, exhibit a tubular concentric structure, predentin and a surrounding layers of layer of odontoblasts calcified material, but not dentin. Cementum Learning Objectives 1. Describe the origin of cementum 2. Describe the main features of cementum (contrasting from bone) 3. Describe the functions of cementum 4. Describe the composition of cementum 5. Describe the relationship between enamel and cementum at the C-E junction 6. Describe the cells of the cementum 7. Describe how cementum is distributed throughout the root 8. Describe the types of cementum, contrasting the morphologic and functional aspects of cellular and acellular cementum. 9. Identify the structures protecting the cementum surface and what may happen if they are lost – differentiate external and internal resorption 10. Identify cementicles and hypercementosis 11. Identify areas of cementum repair 12. Understand the consequences of cementum exposure  Cementum: Origin ✓ After the crown is formed, HERS induce the mesenchymal cells of the dental papilla to differentiate into odontoblasts. ✓ Odontoblasts make root dentin, leading to the fragmentation of the HERS. ✓ Mesenchymal cells of the dental sac approach the dentin surface and differentiate into cementoblasts. ✓ Cementoblasts make cementum to cover the root dentin. Cementum: Characteristics and Functions ✓ It is a responsive mineralized tissue, avascular and has no innervation. It is also less readily resorbed, compared to bone. ✓ Its prime function is to give attachment to collagen fibers of the periodontal ligament. It is slowly formed throughout life and this allows for continual reattachment of the periodontal ligament fibers. ✓ But also maintains the integrity of the root (seals the tubules of the dentin), helping to maintain the tooth in its functional position and being involved in the process of root repair. Cementum: Biochemical composition ✓ The composition of cementum is similar to that of bone: approximately 45% to 50% minerals (hydroxyapatite), and the remaining portion is collagen and noncollagenous matrix proteins. ✓ Type I collagen is the predominant collagen of cementum. Cementum: a component of the Periodontium ✓ The periodontium is defined as those tissues supporting and investing the tooth and consists of: Gingiva Cementum Periodontal ligament (PDL) Alveolar bone Cementum-Enamel Junction (CEJ) ✓ At the cervical area of the tooth, enamel and cementum form the cementum-enamel junction, which can exhibit three possible patterns: Enamel Enamel Enamel The order of frequency is known as OMG (Overlap, Meet, Gap). 60% 30% 10% Cementum overlaps Edge to edge Gap between enamel cementum and enamel Cementum-Enamel Junction (CEJ) Overlap Meet Gap Cell types of Cementum ✓ Cementoblasts ✓ Cementocytes Acellular cementum Cementocyte Cellular cementum Cell types of Cementum Cementocytes Cementum PL Dentin Lacunae Incremental lines Canaliculi Cementoblasts Lacunae Canaliculi Distribution of Cementum Enamel ✓ At the cervical margin, the cementum is very thin (approximately 50 µm thick) and increases in thickness as it progresses apically to approximately 200 µm. Dentin Cementum Types of Cementum ✓ Cementum is classified according to: - the presence or absence of cells within its matrix - the origin of the collagen fibers of the matrix. Type of cementum Origin of Fibers Location Function Acellular (primary) Extrinsic (some intrinsic From cervical margin to Anchorage fibers initially) the apical third Cellular (secondary) Intrinsic Middle to apical third Adaptation and repair and furcations Mixed (alternating Intrinsic and extrinsic Apical portion and Adaptation and repair layers of acellular and furcations cellular)  Types of Cementum ✓ Acellular cementum (Primary Cementum): provides attachment for the tooth ✓ Cellular cementum (Secondary Cementum): has an adaptive role in response to tooth wear/movement and is associated with repair of periodontal tissues. Acellular Cellular Acellular Extrinsic Fiber Cementum ✓ This cementum variety develops slowly as the tooth is erupting. Therefore, there is no incorporation of cementoblasts into the cementum matrix → acellular! ✓ Fibroblasts from the peridodontal ligament make the bulk of the collagen fibers that become embedded in the cementum matrix → extrinsic fibers! ✓ Cementoblasts secrete noncollagenous proteins that fill in the spaces between the collagen fibers. ✓ This is the principal tissue of attachment, extends from the cervical margin of the tooth and covers two thirds of the root and often more. Acellular Extrinsic Fiber Cementum ✓ The ends of the periodontal ligament fibers that are embedded in the cementum and alveolar bone are knows as Sharpey’s Fibers Sharpey’s Fibers of the PDL Thin collagen fibrils intermingled between dentin and cementum (that’s why CDJ looks poorly defined Acellular Extrinsic Cementum Periodontal Fiber Cementum Dentin ligament Bone Sharpey’s fibers Osteoblasts Osteocytes Cementoblasts Acellular Extrinsic Fiber Cementum Cementum Periodontal ligament Bone Sharpey’s fibers Sharpey’s fibers Osteoblasts Dentin Osteocytes Cementoblasts Acellular Extrinsic Fiber Cementum ✓ Perpendicular striations in the cementum layer correspond to the sites of insertion of collagen fiber bundles. ✓ Longitudinal lines (arrows) can appear as thin or thicker lines, and represent the interface between successive layers of cementum (Incremental Lines of Salter) Cellular Cementum (Secondary Cementum) ✓ Cellular cementum is confined to the apical third and interradicular regions of premolars and molars. Is often absent from single-rooted teeth, which indicates that its presence is not essential for tooth support. ✓ The type of cementum formed during periodontal wound healing appears to be cellular in origin. ✓ Cellular cementum can be made of intrinsic or mixed fibers (intrinsic and extrinsic)  Cellular Intrinsic Fiber Cementum ✓ In some teeth, after about 2/3 of the root is formed, the newly formed cementoblasts quickly form cementum over the unmineralized dentin. ✓ As cementum deposition progresses quickly, cementoblasts become entrapped in the extracellular matrix they secrete, becoming cementocytes within lacunae → cellular ✓ Mos of the collagen fibers are initially formed by the cementoblasts → intrinsic fiber  Cellular Mixed Fiber Cementum ✓ When the PDL becomes organized, however, fiber bundles become incorporated into the cellular cementum, which continues to be deposited around these fibers. ✓ The presence of intrinsic and extrinsic fibers creates the cellular mixed fiber cementum, which constitutes the bulk of secondary cementum. ✓ Cellular cementum may be layered with acellular cementum (as deposition slows down). Dentin Cellular Mixed Fiber Cementum The distinction between extrinsic and intrinsic fibers within cementum is readily apparent, the intrinsic fibers essentially surrounding the embedded portions of the extrinsic fibers, which constitute Sharpey's fibers. Cementoid ✓ Like dentin, cementum is first deposited as Cementoblast an organic material called cementoid, which calcifies gradually. ✓ Therefore, the cementum surface will always be covered be a layer of cementoid Cementoid and cementoblasts. Mineralized cementum Electron micrograph illustrating the insertion of periodontal ligament (PDL) fiber bundles into cellular cementum. Cementoid is seen at the surface of the mineralized cementum. Cellular Cementum Cellular Cementum Cellular cementum Periodontal ligament Bone Sharpey’s fibers Osteoblasts Cementocytes Cementoblasts Osteocytes Cellular Cementum versus Bone ✓ Areas of cellular cementum may look like bone, as both tissues contain cells (cementocytes and osteocytes) trapped in lacunae and surrounded by a mineralized matrix. ✓ However, cementum is different Alveolar bone Periodontal Cementum from bone in three important ligament ways: 1) Avascular → less metabolically active than bone → Cementocyte canaliculi are oriented toward PL 2) Not innervated 3) Doesn’t form Haversian systems Cellular Cementum versus Bone ✓ Cementocytes have processes that lodge in canaliculi that communicate but do not form a syncytium that extends all the way to the surface, as is the case within bone. Bone Osteocyte lacunae and canaliculi in ground section of Cementocyte lacunae and canaliculi in bone. ground section of tooth.  Cellular Cementum versus Bone ✓ Nourishment of the cells is believed to occur essentially by diffusion, from vessels of the periodontal ligament, therefore most of the canaliculi point toward the tooth surface. ✓ Nutrients may not reach cementocytes in deeper layers: may not be vital. ✓ Limited blood and oxygen supply affects the cementocytes’ metabolism, which is lower than bone’s. ✓ This lower metabolic activity affects cementum’s remodeling capacity: bone resorbs more readily than cementum. The practice of orthodontics is based upon this fact. Cementocyte lacunae in ground section. Other clinical correlations involving cementum… Cementicles ✓Round or ovoid calcified nodules found in the periodontal ligament, usually near the surface of the cementum. ✓May be free in the ligament or attached to the cementum surface. ✓More prevalent in older patients or in areas of trauma. Hypercementosis ✓ Excessive production of cellular cementum that generally involves the apical 1/3 of the root. ✓ Etiology: variable, involving such factors as compensation for occlusal trauma or overeruption, teeth clenching, periapical inflammation ✓ Can lead to bulbous roots forming at tip - makes extraction more difficult Mild Moderate Severe Normal Hypercementosis Hypercementosis Dentin Cementum Apical foramen Root Resorption ✓ Root resorption is a physiological process only in deciduous dentition, during the shedding process.  External Root Resorption ✓ The cementum surface is coated with a layer of cementoid and cementoblasts, that protect it from resorption. ✓Damage to these layers and the appearance of local inflammation predisposes to the occurrence of resorption. ✓Cementum resorption is usually associated with dentin resorption, changing the anatomy of the root surface. ✓Resorption starts on the outside (periodontium)! External Root Resorption ✓ This can be caused by local conditions (trauma, traumatic occlusion, excessive forces applied during orthodontic treatment, periapical and periodontal disease, pressure from misaligned erupting teeth, cysts, and tumors), systemic conditions (such as calcium deficiency) or may be idiopathic. Dentigerous cyst Impacted 3rd molar Cementum Repair Dentin PL ✓Removal of insult prevents further resorption, allowing cementum repair. ✓The newly formed cementum is cellular and can be distinguished from the resorbed surface by a deeply staining irregular line termed as reversal line. ✓In most cases of repair there is a tendency to re-establish the former outline of the root surface. This is called anatomic repair. Gingival recession: root exposure ✓Gingival recession leads to cementum exposure. Cementum has a rough surface compared to the smooth enamel, facilitating plaque retention and caries development. ✓ Cervical cementum is thin at the cervical area and susceptible to abrasion. Loss of cementum results in exposed dentinal surfaces: sensitivity ✓Pain and sensitivity decreases with time as sclerotic dentin and tertiary dentin forms.