Structure and Functions of the Dentin-Pulp Complex Husain Keylani R1 endo board

The transition to pulp occurs with the initiation of dentin formation. Dentin-pulp complex ? Embryologically, histologically and functionally; dentin and pulp should be considered the same. This entity is exemplified by the classic functions of the pulp. The transition to pulp occurs with the initiation of dentin formation.

The pulp The pulp incompressible, the total volume within the pulp chamber cannot be greatly increased. Thus Inflammatory reaction results in an increase in pulp tissue pressure instead of volume. (Heyeraas et al,1992)

Development The Primary oral cavity or stomodeum (lined with ectoderm )is a depression between the brain and the pericardium in an embryo, It is separated from the upper end of the foregut by (bucco-pharyngeal membrane ,27 days) Mid-brain bucco-pharyngeal membrane stomodeum pericardium

Development Most of the C.T. cells underlying the oral ectoderm are neural crest cells or ectomesenchyme in origin

Development Neural crest travel down the sides of the head into the maxilla and mandible to form the tooth germ

Development During sixth week ,tooth formation begin as localized proliferation of ectoderm to form two horseshoe-shaped structures called primary epithelial band or primary dental laminae which split into vestibular & dental lamina Oral vestibule Dental organ &

Stage of development Formation of the teeth is a continuous process has been divided in to three stages : bud stage Cap stage bell stage

Cont. 1-The bud stage: the initial stage , dental lamina proliferate to the adjacent ectomesenchyme

Cont. 2- Cap stage : the dental lamina cont. proliferate- aconcavity. The outer cells cuboidal and constitute the outer enamel epithelium . The inner cells elongated and represented the inner enamel epithelium . Between them is network of cells termed (the stellate reticulum)

Cont. 3-bell stage (18): The last period of growth is also known as histodifferentiation In the cervical loop where the outer and the inner enamel epithelia are joined continue to proliferate . The tooth development enters the bell stage During (BV) become established in the dental papilla

A tooth germ consists of 3 parts: form Origin tooth germ enamel ectoderm A-Enamel organ dentin and pulp. ectomesenchyme B- Dental papilla cementum, PDL, and alveolar bone. C-dental sac =tooth follicle

Cell differentiation mechanisms Embryonic development of any tissue is prompted by interaction with an adjacent tissue. Complex epithelial and mesenchymal interactions occur which direct the ameloblasts and odontoblasts diff. by changes in gene expression.

Cont. Epithelial- ectomesenchymal inductive interaction during normal odontogenesis lead to: 1- Cytodifferentiation of dentin and enamel forming cells. 2-dental hard tissue formation

Mechanisms of interaction A: cell-to-cell interaction 1-Direct cell-to-cell contact. 2-The transmission of molecules synthesized and secreted by one cell and then captured by surface receptors of another cells. CAMs(cell adhesion molecule )mediate morphogenesis. through contrall cell proliferation Cell contian membrane protein called (integrin)receptor for CAMs. integrin CAMs

Cont… B:Cell-to-ECM interaction. Carry by substrate adhesion molecule (SAMs) the best study of the ECM are fibronectins. G.factors are polypeptides produced by cells that initiate proliferation, migration and diff. of a variety of cells.

Cont… Dental basement membrane: It exists between IDE(inner dental epithelium and the underneath dental mesenchyme It consist of (thin basal lamina & layer of ECM)

Cont… Dental basement membrane: It exists between IDE(inner dental epithelium and the underneath dental mesenchyme It consist of (thin basal lamina & layer of ECM) BL is compsed of type IV collagen (as areceptors) which has binding sites for other BM consituents. (like laminin ,fibrinoctin ,proteoglycan) Laminin is the CAM in the basement membrane

Cont… Odontoblast cell surface proteoglycans act as receptors for matrix molecules .signals from matrix components influence migration and diff. of odontoblasts.

Differentiation of Odontoblasts occurs during the bell stage. Preameloblasts diff. at a faster rate than odontoblasts, but dentin matrix is formed before enamel matrix. There is still mitotic activity among the relatively immature cells of the inner enamel epithelium., mitotic activity ceases and the cells elongate.

Cont.Differentiation of Odontoblasts With the onset of differentiation a single layer of cell(preodontoblasts) align themselves along the basement membrane separating the inner enamel epithelium from the dental papilla. IEE PO BM DP

Cont.Differentiation of Odontoblasts These cells stop dividing and elongate into short columnar cells with basally situated nuclei Several cytoplasmic projections from each of these cells extend toward the basal lamina.

Cont.Differentiation of Odontoblasts As the odontoblasts continue to differentiate, they become progressively more elongated And cytoplasmic processes from these cells extend through the BM toward the basal lamina, and more and more collagen fibrils appear within the ECM.

Cont.Differentiation of Odontoblasts More odontoblastic diff elongation with characteristic of protein-secreting cells more collagen fibrils appear in the ECM and more defined large odontoblastic process toward BL.

Cont.Differentiation of Odontoblasts The odontoblasts reach full maturity and become tall columnar cells Production of the initial dentin matrix involves the formation, organization, and maturation of collagen fibrils and proteoglycans. As more collagen fibrils accumulate subjacent to the basal lamina,(The lamina becomes discontinuous and eventually disappears. )

Cont.Differentiation of Odontoblasts The odontoblasts reach full maturity and become tall columnar cells Production of the initial dentin matrix involves the formation, organization, and maturation of collagen fibrils and proteoglycans. As more collagen fibrils accumulate subjacent to the basal lamina,(The lamina becomes discontinuous and eventually disappears. ) Some of Odon. processes extend toward the ameloblasts Some of these become interposed between the processes of ameloblasts, resulting in the formation of enamel spindles

Cont.Differentiation of Odontoblasts At the onset of dentinogenesis the dental papilla becomes the dental pulp   As predentin matrix is formed, the odontoblasts commence to move toward the central pulp, depositing matrix. Within this matrix a process from each odontoblast becomes accentuated and remains to form the primary odontoblast process. It is around these processes that the dentinal tubules are formed.

Root Develop after completion of enamel formation. Proliferateion (inner and outer enamel epithelia), and form a structure known as the Hertwig epithelial root sheath (HERS) (HERS) determine the size and shape of root of the tooth .

Root The first layer of the dentin matrix mineralizes gap appear in the root sheath allowing mesenchymal cells from the dental sac to move into contact with the newly formed dentine . These cells then differntiation into cementoblast and deposit cementum matrix on the root dentine.

Epithelial Rests of Malassez Persistant of epithelial cells of the root sheath in the PDL after tooth development. Some of them retain & under go division Later produce periapical cyst. (Trowbridge,1967)

Accessory Canals During root formation : a break develops in the continuity of the sheath , producing a small gap ,dentinogenesis does not take place opposite the defect . The result is small “accessory “ canal between the dental sac and the pulp . If periodontal tissue lose their integrity , m/o go pulp

Cont.

DENTIN Composition of fully mature dentin : INORGANIC MATERIAL WATER ORGANIC MALTERIAL WATER 20% ~91%(collagen) I,V. ~9%(non-collagen) *phosphoproteins *proteoglycans *Gla proteins *acidic glycoproteins *Gr. Factors+lipids 70% Hydroxyapatite 10%

Types of the dentin 1-Developmental dentin : is forms during tooth developmet &classified as: A-orthodentin: - the tubular form of dentin

Cont. Types of the dentin B-mantle dentin -is the first formed dentin and is situated immediately subjacent to the enamel or cementum. -( 150μm, less mineralized and softer). (Herr P et al,1986)

Cont. Types of the dentin C-Circumpulpal dentin : - it constitutes the major part of developmental dentin. - oriented at right angles to the long axis of the dentinal tubules. -500nm in diameter

Cont. Types of the dentin 2-Secondary dentin: -Regular dentin which forms phisiologically after the root is fully developed. A-Primary physiological dentin B-Secondary physiological dentin

Cont. Types of the dentin 3-Tertiary dentin: -Irregular dentin forms in response to abnormal stimuli Reparative D filling Reactionary D irritant

Predentin *Is unmineralized organic matrix of dentin between the odontoblast layer and the mineralized dentin type I , II collagens. Noncollagenous elements (proteoglycans, Phosphophoryn) growth factors (Roberts-Clark D,2000) Dentin Predentin Odontoblasts Pulp cells

Mineralization Mineralization A B E C D Caph.accomu. In vesicle (prd) grow Rupsure  release mix  the mix adjoin to form advance crystl  merge to  form small globules  The globule expand  and fuse with other untill become mineraized Cont. in growing and increase mineral content. A B E C D Mineralization

Cont.Mineralization Mineralization front Mineralized dentin Predentin Odontoblasts

Dentinal tubules Dentinal tubules occupy from 1% (superficial dentin) to 30% (deep dentin) of the volume of intact dentin. (Garberoglio,Brannstrom 1976) It slightly tapered , wider portion toward the pulp.(no pretubular d)

Garberoglio R, Brännström M: 1976.   Number of Tubules (1000/mm2) Tubule Diameter (μm) DISTANCE FROM PULP (mm) MEAN RANGE Pulpal wall 45 30-52 2.5 2.0-3.2 0.1-0.5 43 22-59 1.9 1.0-2.3 0.6-1.0 38 16-47 1.6 1.0-1.6 1.1-1.5 35 21-47 1.2 0.9-1.5 1.6-2.0 30 12-47 1.1 0.8-1.6 2.1-2.5 23 11-36 0.9 0.6-1.3 2.6-3.0 20 7-40 0.8 0.5-1.4 3.1-3.5 19 10-25 0.5-1.2 . Mean Number and Diameter per Square Millimeter of Dentinal Tubules at Various Distances from the Pulp in Human Teeth

Cont.Dentinal tubules Coronal dentin S shape DEJ- pulp. b/c (crowding of odontoblasts) It converge ? the surface of the pulp chamber has a much smaller area than the surface of dentin along the DEJ. This results in a progressive increase in dentin permeability

Cont.Dentinal tubules Near the DEJ the dentinal tubules ramify into one or more terminal branches.

Peritubular and intertubular dentin Peritubular Dentin: is dentin lining the tubule , whereas that between the tubules is known as intertubular dentin minir+hard < collagn Presumably, precursors of the dentin matrix that is deposited around each odontoblast process are synthesized by the odontoblast, transported in secretory vesicles out into the process, and released by reverse pinocytosis. A corresponding reduction in the diameter of the process occurs with the formation of peritubular dentin.

Dentinal Sclerosis Partial or complete obturation of dentinal tubules. as result of aging or develop in response to stimuli such as attrition or caries It helps the pulp from irritation

Cont.Dentinal Sclerosis It is either:  Physiologic: acceleration of peritubular dentin formation in the apical third of the root.  Pathologic: Dentinal tubules are blocked by hydroxyapatite and whitlockite crystals (carious dentin, attrited dentin)

Cont.Dentinal Sclerosis If dentin is damaged the odontoblastic processes die leaving empty dentinal tubules which form areas of dead tracts (A). Dead tracts become filled with mineral and are called blind tracts (B). The dentin of blind tracts is known as sclerotic dentin.

Interglobular Dentin Refer to organic matrix that remains unmineralized. This occurs most often in the circumpulpal dentin just below the mantle dentin. Vit D-resistant rickets, hypophosphatasia Inter-globuler dentin

Dentinal Fluid volume : 1% of superficial dentin , about 22% of the total of deep dentin.

Pressure gradient exists between pulp Cont.Dentinal Fluid Outward movement of fluid is blocked peripherally by enamel or cementum. In case of d.tubules exposureoutward movements to the exposed area is in the form of tiny droplets. (Itthagarum,2000) Pressure gradient exists between pulp (14 cm H2O =10.3 mm Hg) and O. cavity that accounts for the slow outward flow of fluid.

Dehydrating ?the dentin can accelerate outward Cont.Dentinal Fluid Odontoblast process Dehydrating ?the dentin can accelerate outward Rapid flow stimulates pulpal nociceptors that innervate DT =dentin sensitivity= dentinal permeability (the hydrodynamic mechanism of dentin sensitivity) Ingress of irritants Dentin Outward fluid movement Predentin Desmosome Odontoblast Dental pulp (14 cm H2O / 10.3 mm Hg)

Dentin permeability Dentinal tubules are the major channels for fluid diffusion across dentin . Fluid permeation is proportion to tubule diameter and number The permeation of the radicular dentin <coronal dentin . Fogel HM et al,1988 deep cavity vs shallow

Cont.Dentin permeability The functional or physiologic diameter of the tubules is only about 5% to 10% of the anatomic diameter. bc(od process+collagen fiber ) (Michelich et al,1978) It is small enough to remove bacteria from dentinal fluid permitting sterile fluid to enter the pulp chamber (Michelich et al,1980)

Cont.Dentin permeability The smear layer is capable of physically preventing bacteria from penetrating dentin. (Michelich et al,1980) In nonvital teeth  bacterial invasion of dentinal tubules occurred more rapidly. ( Due to no permeability) (Nagaoka et al,1995) But in vital pulps.  increa .permeab +antibodies in dentinal fluid. (Hahn et al,1997) Dentin sclerosis beneath a carious lesion reduce the permeation by obstruction the tubules (Pashley,1990);(Tagami et al,1992)

smear layer The cutting during cavity preparation or root canal theory Cont.Dentin permeability by acid etching or EDTA smear layer The cutting during cavity preparation or root canal theory incidence of pulpal inflammation may be increased increases the permeability of the dentin

MECHANICAL PROPERTIES OF ROOT DENTIN Endodontically treated teeth showed only a 14% reduction in dentin toughness compared with vital dentin (Carter et al,1983) Endodontic therapy was shown not to change the Vickers hardness of human root dentin. (Lewinstein et al,1981)

MECHANICAL PROPERTIES OF ROOT DENTIN Much of the increased incidence of tooth fractures of endodontically treated teeth can be attributed to: 1 -The loss of tooth structure access opening (Howe et al,1990) 2-Physical weakening of roots by post spaces. (Isidor et al,1996)

MECHANICAL PROPERTIES OF ROOT DENTIN Age,dehydration and fatigue crack growth in dentin: old pts has a much shorter fatigue life than dentin from young teeth -it increase incidence of root fractures of RCT actually reflect reduction in the fracture toughness of old dentin. (Arola D,2004)

MECHANICAL PROPERTIES OF ROOT DENTIN Other factors Collagenolytic activity and gelatinolytic activity have measured in mineralized dentin powder . (Pashley et al,2004). These enzymes may slowly attack the collagenous matrix of dentin, thereby weakening it over many decades.

MECHANICAL PROPERTIES OF ROOT DENTIN Other factors Mineralized dentin surrounding post spaces that had been under function for more than 10 years , the functional stresses may cause microcracking of dentin ( Ferrari M et al,2004)