Differentiation of odontoblasts is mediated by expression of signaling molecules and growth factors in the inner dental epithelial cells
It is rich in endoplasmic reticulum and Golgi apparatus, especially during primary dentin formation, to give it a high secretory capacity (firstly collagenous matrix to form predentine, then mineral to form the complete dentine).
Calcium channels are localized to apical pole of preodontoblast.
Terminal web divide it into 2 part..cell body and odontoblastic process……this zone of attachment prevents the entrapment of odontoblast in the prsdenine matrix and ensures that the developing surface of the dentin remains relatively flat..
Golgi complex is subdivided into cis-golginetwork,golgi stacks, trans golgi network..cisgolgi acts as quality control—prevent the transfer of defective proteins.Retrograde traffic also return membranes lipids
GNRP – GUANINE NUCLEOTIDE RELEASING PROTEIN GTP-- GUANOSINE TRIPHOSPHATE..ARF– ADENOSINE DIPHOSPHATE RIBOSYLATION FACTORGDP—GUANOSINE DIPHOSPHATE BOUND STATE.SNAREs---N-ethylmaleimide-sensitive fusion attachment protein receptors
V-snare binding to appropriate t-snare..Arf-gtp is hydrolysed to arf- gdp …and dissociates from vessicles membrane..coatomer is also released..Attachment of v-snare to t-snare is monitered and stabilized by Rab-GTP molecule present in donor vesicle membraneNSF-P ---- N-ethylmaleimide sensitive fusion protein SNAPs---- soluble NSF attachment protiens
Dentin -kunal parekh..advancd oral biology
Dentinogenesis Dentin is formed by odontoblasts that differentiate from ectomesenchymal cells of dental papilla with influence from the inner dental epithelium
Differentiation of odontoblasts(withdrawal from the cell cycle, cytologicalpolarization, and secretion of predentin/dentin) Odontoblast precursor migrate from neural crest and become part of ectomesenchymal cell . During cap stage pre-odontoblast is concentrated adjacent to inner enamel epithelium and exit the cell cycle and differentiate befor pre-ameloblasts of IEE stop dividing.
REQUIREMENT OF INITIAL ODONTOBLASTICDIFFERENTIATION1. Fibronectin rich substratum.--- fibronectin receptors (165-kDa protein) – adherence appears to stabilize cytoskeletal elements , promotes preodontoblast polarization , and trigger other cytoplasmic process associated with differenciation . it also serve as reservoir for growth factors.2. Aperiodic fibrils for regulating differentiation.
2. Aperiodic fibrils for regulating differentiation.3. Transforming growth factor β 1 ( TGF - β 1 ) Bind to fibronectin , Inhibits cell proliferation ,promoter of odontoblast differenciation, Matrix synthesis.4.Calcium –calcium ions signals for mediating restructuring of cytoskeleton duringestalishment of of odontoblast shape ans polarity towards the IEE.5. Enamel matrix protein – are endocytosed in coated vesicle at odontoblast cell surface.
The intercellular spaces contain collagen fibres ,aperiodicmicrofibrils, proteoglycans and fibronectin.These intercellular fibres (von korff fibres) pass intopredentin between adjacent odontoblast at interruptions offascia occludens and fascia adherens junctions.The RER is the major cytoplasmic organelle within activeodontoblast ..the parallel cistern occupy the supranuclearcytoplasm.
Go l g i c o mp l e x …Display morphological ( forming face ) functional polarity ( mature face)Presecretory granules consisting of type 1procollagen , glycoproteins, and glycoaminoglycansdevelop from cisterns of mature face.
Ba s i c s c i e n c ec o r r e l a t i o n ..the complex cytoplasmic machinery operating in thegolgi complex for targeting secretory proteins to theirappropriate final destination.Proteins are synthesized in RER and futhertransported to golgi complex where it isposttranstionally modified ,sorted and packeged forfurther transport to either secretory granules, primarylysosome ,or cell membrane.
Un i d i r e c t i o n a la nt e r ogr a dev e s i c ul a r t r a ns por t
Glycosyltransferase and glycosidases contained in the golgicisternae sequentially decorate the peptide backbone of theprotein by addition of the carbohydrate side chain..1. Addtion of oligosaccharides by nitrogen linkage to asparagine..2. Oxygen linkage at serine and threonine residues ( 2 steps process…..1. addition of N-acetyl-galactosamine 2. addition of galactose and sialic acidThe budding process require recruitment and attachment of specific coat proteins on the parent cisternal membrane to form a mechanochemical “patch” capable of deforming the membrane into a seprate vesicle.Coatomer recruitment requires ATP, Ca2+ ,guanosine triphosphate (GTP) ANS SEVERAL cystolic proteins.
Sorting products to appropriate destinationsrequires specific signals to control thedocking of transport vesicles with thecorrect target compartment..This is accomplise by transmembraneprotein that act as surface markers.They are soluble N-ethylmaleimide-sensitive fusion attachment proteinreceptors (SNAREs)
F O R MA T I O N , D O C K I N GAND F US I ON OFT RANS P ORT VESI CL ES
Attachment of v-snare to t-snare is moniteredand stabilized by Rab-GTP molecule present indonor vesicle membrane.With the help of fusion protiensNSF-P ---- N-ethylmaleimide sensitive fusionproteinSNAPs---- soluble NSF attachment protiens
Od o n t o b l a s ts e c r e t or yp a t h wa yCtv-intermediate coated transport vesicle.CGN- cis golgi networkPsg-pre secretory granulesTgn– trans golgi network
Secretory granules formation involves of condensation ofsecretory product from larger condensing vacuoles(presecretory granules ) .Budding of membrane from the condensing vacuole continuesuntill a smaller and denser secretory granules is formed..intact microtubular system forms a radiating networkextending from the centrosome outward the cell periphery totranslocate granules to specific region of cell surface.Further transport toward plasma membrane is dependent onmyosinWhile in constitutive pathway products areimmediately exported..
S E CRE T I ON OF DE NT I NMA T R I XPreameloblast and preodontoblast express matrixmetalloproteinase 2 , an enzyme that degradecollagen and fibronectin ,coincident with theremoval of the basal lamina .After break up from basal lamima this newlydifferntiated odontoblasts adhere to adjacentodontoblast by stable gap junction and maculaadherens type .permitting ions and smallmetabolite to cross from odontoblast to
odontoblast grow in length and develop largeamount of rough endoplasmic reticulum (RER).A prominent golgi complex develops in thesupranuclear cytoplasm facin the IEE. in addition to increase expression of messengerRNA for collagen type 1,also express for osteocalcin, dentin phosphophoryn, and high level of alkaline phosphates.
As synthesis of type 1 collagen increasesexpression of type 3 decreases.Dental matrix contain type 1 collagen and varietyof glycoproteins and gylcosaminoglycans.
The matrix provides a framework for mineralization.Collagens comprise 90% of the dentin matrix, and areprincipally type ITy pe I c ol l a ge n iscomposed of two identical α1(I) chains and oneα2(I) chain, and a glycine in every third amino acidposition in an individual chain is needed for theformation of a triple helix structure.Proα2(I) mRNA has been shown to be expressedby mature human odontoblasts
Ty pe I c ol l a ge nis synthesised as a larger procollagen, whichcontains extensions at both the N- and C-terminalends, called the aminoterminal and carboxyterminalpropeptides,which prevent premature collagen aggregation intofibrils.After procollagen secretion from cells, extracellularmodification takes place, and propeptides areremoved by specific proteinases and maturecollagen molecules aggregate into a fibrous matrixwhich then serves as a support for mineraldeposition.
Ty pe I I I c ol l a ge n,a homopolymer of three α1(III) chains,In addition, there is strong evidence that calcified tissuesare also able to express type III collagen,Type III procollagen has been observed to be transientlylocated in human predentin during matrix formation, but notin mineralized dentin
some expression of type V has been observed in thepredentin of mature human teeth but not in dentin .Instead, type VI was detected both in predentin and dentinof intact teeth and it has also been found in the teeth ofdentinogenesis imperfecta patients.
No n c o l l a g e n o u sp r ophosphoprotein (DPP; phosphophoryn) dentin t e i nsdentin sialoprotein (DSP) represent the most abundant dentin-specific acid proteinsin the dental matrixOdontoblast secret proteoglycans, phosphophoryns andglycoproteins
Predentin protogylcan functions is to regulate the size and orientation ofcollagen fibril and also control the time and site ofmineralisation either by sequestering calcium or byshielding potential mineral nucleation sites in thematrix.Decorin – a chondroitin-dermatan sulfate proteogylcanwith binding affinity for type 1 collagen..
De n t i ns i a l ophos phopr ot e i n I s the only protein produced uniquely by odontoblasts, the cells thatproduce tooth dentin.DSPP protein is processed by proteases into several functional fragments;DSP, DPP and others.
These domains play unique biological functions duringdentinogenesis. Preliminary data showed that1). BMP2 induced DSPP expression.2). MMP-9 specially catalyzes DSP into the NH2-terminal andCOOH-terminal fragments. The NH2- and COOH-terminalfragments of DSP show a clear difference in tooth distributions. 3). The NH2-terminal and COOH-terminal domains bind to theirreceptors, integrin 26 and CD105, on cellular membrane.the transcriptional regulation, posttranslational modification andsignal transduction of DSPP are important for controlling theinitiation, rate and extent of dentin biomineralization.
Processing of dentin sialophosphoprotein (DSPP) (57). DSPP is the precursor ofdentin phosphoprotein (DPP), a phosphoprotein unique to dentin. DSPP isprocessed by proteases (BMP-1, MMP-20, MMP-2) into N-terminal dentinsialoprotein (DSP), intermediate dentin glycoprotein (DGP) and C-terminal DPP.DPP is adsorbed on hydroxyapatite crystals and is deposited in dentin matrix.
De n t i np h o p h o p r o t e i n , or p h o s phophor y n,is important in the regulation of mineralisation of dentinPhosphophoryn is the most acidic protein ever discoveredand has an isoelectric point of 1.This extreme acidity is achieved by its amino acid sequence.Many portions of its chain are repeating -D-S-S- (asparticacid-serine-serine) sequences. In protein chemistry, netacidity equates to negative charge. Being highlynegative, dentin phosphoprotein is able to attract largeamounts ofcalcium
Characteristic sequences in dentin phosphoprotein. Most of the DPP molecule iscomposed of repetitive sequences, DSS repeats (above). A unit of this sequenceconsists of 1 aspartic acid and 2 phosphoserines. The DSS repeat sequences are rich innegative charges and provide binding sites for many calcium ions (below) andfor hydroxyapatite crystals.
SIBLING-family genes. The SIBLING family is a family of acidic glycoproteinspresent in bone and dentin. The genes of this family are present as a genecluster at the 4q22 site of human chromosome 4. SPARCL1: SPARC-like protein1, DSPP: dentin sialophosphoprotein, DMP1: dentin matrix protein 1, BSP; bonesialoprotein, MEPE: matrix extracellular phosphoglycoprotein, OPN:osteopontin. Two genes of enamel matrix proteins are also present near thisgene cluster; AMBN: ameloblastin, ENAM: enamelin.
D e n t i n Ma t r i x P r o t e i DMP1 appears to belong to the family of dentin matrix proteins rich in serine and aspartic acid and has many potential phosphorylation sites, especially for messenger-independent kinases of the casein kinase II group.DMP1 could possibly regulate the expression ofosteocalcin and alkaline phosphatase.DMP1 is a calcium binding protein as demonstrated bycalcium binding assay
that DMP1 can nucleate the formation of hydroxyapatite invitro in a multi-step process that begins by DMP1 bindingcalcium ions and initiating mineral deposition.
P o r c i n e p r e d e n t i n e ma t r i x —Contains active neutral metalloproteinases (56 and 61 kDagelatinases ans 25 kDa proteoglycanase) capble of degradingproteoglycans at mineralisation site.Activity is clcium dependent..Proteoglycans, such a sd e c o r i n , b i g c l y c a n , f i b r o mod u l i n a n d l u m i c a n , which carryglycosaminoglycan (GAG) carbohydrate side chains within theirstructures, comprise another sizeable portion of thenoncollagenous proteins
Fi br one c t i nis re-distributed during odontoblast polarization andinteracts with cell-surface molecules.A nonintegrin 165-kDa fibronectin-bindingprotein, transiently expressed by odontoblasts, isinvolved in microfilament reorganization.
Growth factors (TGFβ1,2,3/B M P 2,4, a n d6),stimulates cytological but not functional differentiation of odontoblasts:The two events can thus be separated.Immobilized TGFβ1 (combined with heparin) induced odontoblastdifferentiation.Only immobilized TGFβ1 and 3 or a combination of FGF1 and TGFβ1stimulated the differentiation of functional odontoblasts over extendedareas and allowed for maintenance of gradients of differentiation. Presentation of active molecules in vitro appeared to be of majorimportance; the BM should fulfill this role in vivo by immobilizing andspatially presenting TGF(3s).
Mi n e r a l i z a t i o n1.) Matrix vesicles in mantle dentin..bud from tip of the odontoblastic cytoplasmic process.It initiate mineralization by concentrating calcium and phosphate ions.As ion increase hydroxyapatite crystallizes along the inner surface of matixvessicle surface..Calcium bonding phospholipids serves as templete for hydroxyapatiteprecipitation..Continue crystal growth ruptures the vesicle and release the hydroxyapatitecrystals into extracellular matrix..
2.) C o l l a g e n p h o s p h o p h o r y ncomplexes…Extracellular Kinases .phosphorylate dentin phosphophoryn which furtherlinked to collagen fibril,,This act as nucleators of hydroxyapatite crystal in late mantle dentin andcircumpulpal dentin.Zone of initial mineralization—• dot like mineral nuclei are aligned parallel to and superimposed oncollagen fibrils.• Mineral nuclei positioned over hole region of collagen fibrils, suggestingthat the DPPs are bound to collagen at those sites.• Dental sialoproteins and proteogylcans act as nucleating agents forperifibrillar hydroxyapatite crystals.
Nucleation of hydroxyapatite by acidic matrix proteins immobilized on insoluble collagenmatrix. Some acidic matrix proteins, e.g. dentin phosphoprotein, have an affinity tocollagen. The surface of the insoluble collagen matrix provides loci to reduce interfacialenergy for nucleation. Calcium ions are bound to the acidic groups of the acidicproteins, and inorganic phosphates are attracted by the calcium ions. The ionic complexthus formed may constitute a crystal nucleus.
Control of crystal shape by the acidic matrix proteins. Some acidic matrix proteins, e.g.dentin phosphoprotein, have affinity to a specific face (e.g. the (100) face) ofhydroxyapatite crystals. These proteins are potent inhibitors of crystal growth.Their specific adsorption results in the inhibition of growth perpendicular to the adsorbedface. For example, if the (100) face is covered by proteins, growth in the direction of the a-axis will be inhibited. As a result the crystal will preferentially grow in the direction of the c-axis.
S T R U C T U R E S ..1.DENTINAL TUBULES.. extend from mantle dentine to predentine.,across the thickness of circumpulpal dentin.. dentinal tubules contain serum proteins including fibrinogen ,albumin , and immunoglobins. this proteins are carried into the tubules in dentinal fuild ,where they may be come trapped in the lamina limiitans or bound to the mineral phase of dentin.
F O R MA T I O N O FI NT ERT UBUL AR1. Greatest bulk of mineralised circumpulal dentin.2. it is formed by the mineralisation of predentin.3. Matrix is rich in type 1 collagen fibrils
PERI T UBUL AR DENT I N.These inner organic lining is described as a thin organic lining high in GAG andrelatively free in collagen fibrils .Bone sialoprotein and osteonectin have been localized in peritubular dentin.Because of its small crystallites and non collagenous nature of its organicmaterial , it is more susceptible to demineralization and degradation duringthe caries process..
F o r ms o fde nt i n•Primary dentin, with straighttubules, is laid down before completionof the apical foramen.•Regular secondary dentin ischaracterized by a slower rate ofdeposition and an abrupt change in thedirection of the dentinal tubules.•Tertiary or irregular secondary (alsocalled irritation, reparative or reactive)dentin is laid down in response to anirritation or damage to the overlyingdentin and/or enamel.•This dentin has irregularly arranged A, Primary dentin; B, Secondary (regular) dentin;and few dentinal tubules. With aging or C, Reactive dentinsevere damage, tertiary dentin cantotally obliterate the pulp cavity.
Interglobulardentin in globularlayer -ground section•Between the mantle andcircumpulpallayers is a layer of dentinin which the calcified globules do notfuse evenly.•This is called the globular layer.•In a ground section of dentin, theless-calcified areas of dentin appearas irregularly shaped crescents calledinterglobulardentin.
AGE & F u n c t i o n a l Ch a n g e sThe main changes in dentin associated with aging are1. Increase in peritubular dentin.2. Increase in Dentinal sclerosis.3. Increase in the number of dead tracts.4. The dentinal permeability decreases with advancing age.5. The color of dentin becoming darker with age.6. Hardness of dentin increases with age, primarily due to increases in mineral content.
2. R e p a r a t i v e de nt i n If the provoking stimulus caused the destruction of the original odontoblasts, the new, less tubular, more irregular dentin formed by newly differentiated odontoblast like cells is called Reparative dentin. In such dentin the tubules are usually not continuous with those of secondary dentin. Unlike primary or secondary dentin, which forms along the entire pulp- dentin border, tertiary dentin is produced only by cells directly affected by the stimulus. The quality (or architecture) and the quantity or degree of tertiary dentin produced are related to the cellular response initiated, which depends on the intensity or duration of the stimulus. Tertiary dentin may have regular tubules continuous with those of secondary dentin, tubules sparse in number and irregularly arranged or no tubules at all.
The cells forming territory dentin either line its surface or are included in the dentin. In the latter case, this dentin is as referred to as Osteodentin. Various factors associated with cavity preparation and restoration can influence the tertiary dentinogenic response: The method of cavity preparation, the dimensions of the cavity, the residual dentin thickness (RDT) of the cavity, etching of the cavity, and the nature of the dental materials used and the method of their application for the restoration.
De a d t r a c t s In dried ground sections of normal dentin the odontoblast processes disintegrate, and the empty tubules are filled with air. These are called Dead tracts. They appear black in transmitted light and white in reflected light. Loss of odontoblast processes may also occur in teeth containing dental pulp as a result of caries, attrition, abrasion, cavity preparation, or erosion. Their degeneration is often observed in the area of narrow pulpal horns because of crowding of odontoblasts. Dentin areas characterized by degenerated odontoblast processes give rise to dead tracts.
These areas demonstrate decreased sensitivity and appear to a greater extent in older teeth. Dead tracts are probably the initial step in the formation of sclerotic dentin.
or , Tr a ns pa r e nt de nt i n: Sclerotic dentin results from aging or mild irritation such as slowly advancing caries and causes a change in the composition of the primary dentin. The peritubular dentin becomes wider, gradually filling the tubules with calcified material, progressing pulpally from the DEJ. These areas are harder, dense, less sensitive and more protective of the pulp against subsequent irritations. Sclerosis resulting from aging is physiologic dentin sclerosis. Sclerosis resulting from a mild irritation is Reactive dentin sclerosis.
It appears transparent or light in transmitted light and dark in reflected light. The amount of sclerotic dentin increased with age and is most common in the apical third of the root and in the crown midway between the DEJ and the surface of the pulp. Because sclerosis reduces the permeability of dentin, it may help to prolong pulp vitality. Eburnated dentin: Refers to the outward (exposed) portion of reactive sclerotic dentin, where slow caries has destroyed formerly overlying tooth structure, leaving a hard, darkened, cleanable
1. Hardness of sclerotic dentin is approximately 30% higher than normal dentin with equal depth, showing this to be a more mineralized tissue;2. The thickness of the hybrid layer formed on sclerotic dentin is less than normal dentin, thus, showing this tissue to be more resistant to demineralization caused by acid etching;3. Bond strength to sclerotic dentin is not as high as normal dentin;4. At the time of acid etching the sclerotic occlusal dentin, doubling the time of application of 35% phosphoric acid contributes to obtaining a bond strength similar to normal dentin; and5. For normal occlusal dentin, no difference exists in bond strength when 35% phosphoric acid etchant is applied following the manufacturer’s suggested time (15 seconds), or when the time is extended to 30 seconds.