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Trang 2 INTRODUCTIONDentin and dental pulp are differences in structure and composition:• Dentin is a hard tissue• Dental pulp is a soft tissueDentin and dental pulp have a common embryo
DENTIN-PULP COMPLEX: STRUCTURAL BIOLOGY AND ITS APPLICATION IN RESTORATIVE DENTISTRY People’s Teacher Prof Hoàng Tử Hùng, DDS, PhD E: tuhung.hoang@gmail.com Website: hoangtuhung.com INTRODUCTION Dentin and dental pulp are differences in structure and composition: • Dentin is a hard tissue • Dental pulp is a soft tissue Dentin and dental pulp have a common embryonic origin: ectomesenchyme They remain in intimate relationship throughout the life of the vital tooth Pulp and dentin are integrally connected in the sense that physiologic and pathologic reactions in one of the tissues will also affect the other Anything that affects dentin will affect the pulp and vice versa 🡪 The concept of a dentin-pulp complex [or organ] is, therefore, well founded and generally recognized HoangTuHung.com CHARACTERISTICS OF DENTAL-PULP TISSUE Most pulpal cells are considered to be of an undifferentiated or immature type They are abundant in newly erupted teeth and have the potential to differentiate into specialized cells, e.g., odontoblast-like cells Pulpal physiology under normal conditions, and especially during inflammatory responses, is dependent on interactions among cells, the blood and lymphatic vessels of the pulp, the interstitial fluid, and nerves Macrophages are seen in the normal pulp, and their numbers increase in association with pulpal injury The interstitial fluid surrounds the morphologic elements is an important intermediary link between cells, blood plasma, and lymph fluid The interstitial fluid of the pulp and the dentinal tubules form a continuum that extends from the dentinoenamel and cementodentinal junctions to the central parts of the soft connective tissue in the pulp HoangTuHung.com The structural characteristics of blood vessels in the pulp include: - thin walled, - discontinuities in the endothelial walls, and - fenestration of capillaries Characteristics of the blood vessels have a physiologic function: they facilitate the exchange of nutrients and waste products between the interstitial tissue fluid and the blood plasma This exchange is particularly important at the time of injury, including operative procedures, trauma, and caries lesions affecting the pulp Lymphatic vessels transport fluid out of the pulp and play a role in maintaining the fluid balance HoangTuHung.com DENTIN SENSITIVITY Dentin-pulp complex is a sensitive organ The exposed dentin is especially sensitive All stimuli: pressure, trauma, heat, cold and chemical irritation etc are perceived as some form of discomfort or “pain” Cold stimuli were found to be more painful than hot stimuli, probably because of the outward fluid flow that results from shrinkage of the contents of the tubules when cold is applied When heat is applied, the contents of the tubules expand and an inward flow occurs Typical dentin pain is short-lasting, sharp, and may be described as lancinating HoangTuHung.com Three mechanisms have been proposed to explain dentin sensitivity: 1- the direct innervation theory: dentin is innervated directly: dentin contains nerve endings that respond when it is stimulated 2- the transduction theory: odontoblast serve as receptors and are coupled to nerves in the pulp - The odontoblast receptor theory: intercellular odontoblast-neuron signal transduction 3- the hydrodynamic theory (by Brännström): the tubular nature of dentin permits dentin fluid movement to occur within the tubule when a stimulus is applied, a movement registered by pulpal free nerve endings close to the dentin HoangTuHung.com Any reduction in conductance will reduce the dentin sensitivity: - by occlusion of the tubules by mineral precipitation, adsorption of organic materials in the tubules, or - by hypermineralization of the surface dentin The formation of peritubular dentin at the interface between primary or secondary dentin and tertiary dentin will also reduce the conductivity of dentin fluid Agents that prevent the contents of the tubules flux across exposed dentin may eliminate or reduce dentin pain This is applied in treatment of dentinal hypersensitive products and the contemporary dentin adhesive techniques HoangTuHung.com Opened dentinal tubules (Dt) and naturally desensitized erea: the Dt are closed Interstitial fluid and Interstitial fluid pressure The interstitial fluid pressure in the pulp is relatively high, and it plays a role in the sudden pain experienced when a cavity preparation reaches unaffected dentin Chemically, pulp tissue: 25% organic and 75% water The pressure: – 15 mmHg With pulpal inflammation, the pressure can rise to 35 mmHg or higher, the pulp almost totally enclosed within a hard tissue chamber, can quickly suffer irreversible damage HoangTuHung.com AGING TOOTH AND DENTIN-PULP COMPLEX The dentin-pulp complex undergoes regressive change with time − Progressive narrowing of the pulp cavity [secondary & tertiary dentin] − Deposition of intratubular dentin continues, resulting in a gradual reduction of the tubule diameter and event complete closure The fiber-poor and cell-rich state is a characteristic feature of the young pulp, but it changes with age: Narowing of the pulp cavity, Translucent dentin, Depositon of cementum - Reduction in the number of blood vessels - Gradual decrease in the concentration of fibroblasts within the coronal pulp - Gradual increase of collagen fiber bundles within the root canals HoangTuHung.com Age-related changes in the pulp nerves and blood vessels accompany the cellular changes: In the pulp of older individuals, a large fibrous component is present and the number of cells is low Clinically, this change is important because progenitor cells are available to differentiate into other cell types or to take part in reparative processes in the pulps of young patients are less effective in the pulps of the elderly Tissue in the central part of the pulp in a newly erupted tooth: the large number of cells (left) and a 67-year-old individual: few cells are found BV = Blood vessel (x350 ) HoangTuHung.com An aging pulp tissue loses some of its functional capacity: • Degeneration of axons that correlated reduction sensitivity • Ability of the pulp-dentin complex to repair itself • Appearance of irregular areas of dystrophic calcification Formation of pulp stones (or denticles): discrete calcified masses of calcium –phosphorus They may be singular or multiple and found usually at orifice of the pulp cavity Physiologic aging changes of the dentin-pulp complex can be troubled or stopped by chronic pathological processes: caries, pulpitis, trauma, and especially pulpal necrosis Age changes in the pulp-dentin complex render it more resistant to environmental injury: - The spread of caries is slowed by tubule occlusion - Less sensibility in response to stimuli HoangTuHung.com DENTIN “WOULD” and PULPAL IRRITATION ≈ 30% volume of dentin is taken up by cytoplasm of the odontoblastic processes and their lateral branches ≈ 30 000 – 40 000 odontoblastic processes are cut for every mm² of dentin during classic box cavity preparation Crown preparation, which end in the peripheral zone of dentin, open ≈ 15 000 tubules/1 mm² The danger is reduced with aging tooth because of secondary dentin formation, reducing size of pulp chamber and sclerosis of the dentin This close association includes reactions to caries and common clinical procedures such as cavity or crown preparations and restorative procedures HoangTuHung.com DENTIN-PULP COMPLEX RESPONSE TO RESTORATIVE PROCEDURE A biologic approach to restorative dentistry requires knowledge of the normal structure and physiology of dentin and pulp, including age-related changes All components of the dental pulp, including the cells, blood and lymphatic vessels, nerves, and the interstitial fluid, are important in the response to restorative procedures Hydrodynamic effects and fluid shifts are, therefore, important under normal and pathologic conditions and they will affect the pulp-dentin organ The mere cutting of dentin, as it occurs during cavity and crown preparations, will result in several of reactions in the pulp and the dentin Pulpal pain is characteristically pulsating, long-lasting, and of variable severity, sometimes excruciating It is also affected by changes in blood pressure to the bead HoangTuHung.com PULPAL IRRITATIONS Protection of the vitality of the pulp is paramount goal of all restorative procedures Every dentin intervention that involves opening of dental tubules brings a reaction in the pulp tissue Tissue damage and reactions may be reversible or irreversible The type, duration, and severity of the pulp reaction will vary depending on the type of irritations produced by technical factors and: - cavity preparation, [physically, temperature and pressure reached during] - chemically, materials that use for dentin and enamel etching [acidic solutions] - bonding agent - filling material HoangTuHung.com Agents that prevent the dentin tubular contents flux across exposed dentin may eliminate or reduce dentin pain A smear layer is an adherent layer of debris on tooth surfaces when they are cut with rotary or hand instruments The orifices of the dentin tubules are obstructed by debris tags, called smear plugs, which may extend into the tubule to a depth of 1–10 mm These smear plugs are contiguous with the smear layer In dentin bonding procedures, a hybrid layer is created in which resin infiltrate into smear layer and smear plugs of dentin HoangTuHung.com MECHANISM OF DENTIN BONDING A smear layer of ≈ μm covers the entire dentin surface, and a smear plug, extending -10 μm into the dentin tubule, occludes the tubule’s orifice Dentin etched with 37.5% phosphoric acid At the dentin surface and tubule walls, the inorganic component of dentin smear and peritubular dentin has been dissolved, resulting in the typical funneling of the tubule orifice HoangTuHung.com With the infiltration of resin into smear layer, the hybrid layer is created on dentin surface and resin tags extend into the dentinal tubules, attaching the resin tags to tubules walls PULPAL IRRITATIONS (cont’d.) Temperature increases greater than 10ºC cause precipitation of protein and irreversible cell and tissue necrosis During cavity preparation with rotary instruments, the stream of coolant (spray) should be reaching the site Autopolymerization of acrylic resin in situ [temporary crown, anterior jig…] can rise the temperature in the pulp chamber to 75ºC In the worst case, the odontoblastic layer becomes devitalized over a large area HoangTuHung.com Summary From a functional point of view and especially in relation to restorative dentistry, dentin and pulp are integrated to an extent that they should be regarded as a complex A biologic approach to restorative dentistry requires knowledge of the normal structure and physiology of dentin and pulp, including age-related changes Protection of the vitality of the pulp is paramount goal of conservative dentistry All restorative procedures in a vital tooth should prevent the damage to the dentin-pulp complex HoangTuHung.com SUCGESTED READING - Shibukawa Y, Sato M, Kimura M, et al.: Odontoblast as sensory receptors: transient receptor potential channels, pannexin-1, and ionotropic ATP receptors mediate intercellular odontoblastneuron signal transduction, Pflugers Arch, 2014 - B.K.B Berkovitz, G.R Holland, B.J Moxham: Oral Anatomy, Histology and Embryology, Mosby, 2002 - A Nanci: Ten Cate’s Oral Histology, Mosby, 6th ed., 2003 HoangTuHung.com