 Hello everyone, welcome back to another session in dentistry and more today's topic is enamel so enamel as you all know it is a Hardest biological tissue So this session is about the beginning part of enamel. So we'll be covering the enamel under a few sessions So let's see the details of enamel and its structures Enamel it is an epithelially derived protective covering of variable thickness over the entire surface of crown. Okay, it is above the crown So hope you remember the stages of tooth development the cap stage but stage and It starts from but stage then cap stage and then Bell stage so hope you remember all the stages because the enamel or genesis the ameloblast and its Conversion to enamel it's all Interconnected so hope you remember all those concepts well and clear So let's start enamel it is a epithelial covering which is maybe in variable thickness over the entire surface of Crown and it is as I thought it is the hardest biological tissue and It attains maximum thickness around two to two point five millimeter on the cusp of molars and primolars so at cuspal regions of molars and primolars it has a maximum thickness and Minimum thickness that is Near the neck of the tooth. So this part Neck of the tooth it has a Thinness with that is like a knife. So knife edge around the neck of the tooth and maximum Cuspal thickness is seen at the cusp of molars and primolars So let's see some of the physical properties the thickness I mentioned 2.5 mm thickness Around the cusp of molars and primolars and 2 mm at the incisal edge and knife edge thickness at cervical region So thick at maxillary lingual surface of molars and mandibular buckle surfaces So colors it depends on thickness and translucent of enamel It changes from grayish white to yellowish white So yellowish at thin areas with underlying enamel and grayish at thick opaque enamel Hardness it is 296 noob hardness number So as I mentioned it is a hardest biological tissue and peripheral regions are more harder and Solubility it dissolves in acidic media. That is why KDs is happening because when sucrose is acting Sucrose is converted to lactic acid by the presence of bacteria There will be solubility of enamel it leads to cavitation, which is known as dental caries Regarding the permeability the enamel is selectively permeable The root of passage occurs via road sheath enamel lamella enamel tufts, which are rich in organic content those things we will be dealing in detail Specific gravity is around 2.8 and Translucency it is semi-translucent Regarding the chemical properties that is it has the highest inorganic content in dental tissues coming regarding Cementum and dentin it has highest inorganic content that is 96 percentage organic content is 4 percentage in the inorganic content It has basically the hydroxyapatite that is calcium phosphate and Ion such as strontium magnesium lead fluoride and the Organic portion basically the proteins such as amylogenins amylogenins and non amylogenins 90 percentage of the total protein belong to amylogenin which is low molecular weight Which is rich in proline histidine amino acids also glutamine and leucine But as non amylogen which is around only just 10 percentage which has high molecular weight proteins are amyloblastin Teflin enamel in proteins and they have amylo acid such as Glycine serine aspartic acid So we have various structures to learn in enamel these are very important because it is a short on questions Sometimes this will be asked as long essay So we have various structures in an animal such as roads road sheath in deprismatic substance The striations are important direction of enamel roads are important Hunder sugar bands incremental lines of red CS Surface structures of enamel enamel cuticle enamel lamella enamel tufts dentino enamel junction Hunderblast process and enamel spindles So these all can be asked as short notes. So all are very very important So there might be a question like hypo calcified structures So all are not hypo calcified structures Some are hypo calcified structures because they are not properly mineralized. Okay So if not properly mineralized that become hypo and if it is over mineralized that becomes hyper So hypo means it is not up to the normality Hyper means it is above the normality. Whatever it is hypo please here Hyper please here we know so it depends on the normal up to the normality. So normally it is Reaching it is fine. If it is not reaching its maturation its function its work Then we call it as hypo and the remaining part will Give the idea of that sentence hypo calcified. So the calcification is not proper It is less than normal. So among these the hypo calcified structures are road treat incremental line of red CS enamel lamella enamel tufts enamel cracks enamel spindle and neonatal lines So these might be asked as a separate question. What are the hypo calcified structures of enamel? So that time you need to write all these structures not the entire structures So we'll start one by one first. We have enamel roads, which is cylindrical in shape It starts from D easier to the towards the outer enamel surface So this blue line the second blue line inside is a dentino enamel junction. Okay, so the pink the ground Lines are enamel and the pink lines are dentine. So this is a dentino enamel junction So it starts from dentino enamel junction towards the outer surface. So the number is 5 million in left lateral incisor Lower lateral incisor it is around 5 million and upper first smaller It is around 12 million in number that is enamel roads and its course is torches So it is torches starting from DJ to outer surface. It is not going in a straight line It is having a torches course So it starts from DJ to outer surface of enamel and length Regarding the length it is greater than the thickness of enamel because since it is a torches course So it is not going straight line. Okay So if it is going straight line The length might be lesser since it is going torches. So this is the thickness of enamel Since it is in a torches way if we straighten this line, it will be more than this Total thickness. Okay, so that is why I'm saying the thickness is greater than Sorry, the length is greater than the thickness of enamel. So this is a thickness between two lines This is thickness. So since it is the torches way if we straighten up this torches enamel This will be definitely greater than the thickness of enamel So the length is greater than thickness And diameter is 4 micrometer. It increases from the DJ to outer enamel surface by a ratio of 1 is to 2 So at DJ it is 1 and outer enamel it is 2 that is Diameter usually it is 4 micrometer at DJ it is 1 means at outer surface It will be 8. Okay, so at DJ if it is 2 outer surface, it will be 4 so it appears as very clear crystalline nature in light microscopy We have these roads shape as Hexagonal. Okay, so this is the basic picture of an enamel. It will be hexagonal or fish scale appearance so in light microscopy this roads that is enamel roads appear as Hexagonal shape. So this is hexagonal. That means hexam in six. So six sides one two three four five six so basically this enamel roads are hexagonal in shape because it looks like a Asymmetrical with asymmetrical structures with six sides. Okay, so that is why it is Hexagonal in shape whereas in cross section. Okay, when we do cross section So cross section it looks like fish scale appearance. Okay, fish scale appearance in cross section and in light microscopy it is Hexagonal in shape then arcade outline pattern near DJ and Keyhole outline at enamel surface. So in our surface, it looks like a keyhole appearance. Okay, so all these are very very important Keyhole appearance fish scale appearance Hexagonal in shape arcade outline pattern. So arcade outline pattern near Dentino enamel junction. Okay, so why it is important because of inter woven network of roads Teeth can resist mastic air free forces up to 20 to 30 pounds per tooth That is why it is clinically Significant because of it's inter woven network of roads. So fish scale appearance. It is not really Plainly arranged. There is inter woven arrangement. So it can resist up to 20 to 30 pounds of force per tooth So, don't forget fish scale appearance keyhole appearance Hexagonal appearance and arcade outline near Tentino enamel junction. Okay So this ultra structural or electromicroscopic view gives the keyhole also known as paddle paddle shaped prisms which has mine micrometer in length and five micrometer in breadth So we are talking about enamel rods. Okay, so the first structure in enamel enamel rods So bodies of these roads always seen near the occlusal or incisal Surface so occlusal or incisal surface the enamel rod bodies will be seen and the tails Okay, so the tails will be at the Servical area, so if this is particularly a tooth Okay, so at this area occlusal surface, there will be body of Enamel rod and the cervical area there will be tail of Enamel rod So that is about enamel rod now. We have hydroxyl appetite crystals So they are arranged parallel to the long axis of rod which has 0.05 to 1 micrometer with 90 micrometer which has pyramidal shape and the hydroxyl appetite crystals are Placed within this hexagonal shape, so that is about Enamel rods and hydroxyl appetite crystals now. Let's see about road sheath So the next structure is road sheath which is a thin peripheral layer which is more darker than the Enamel roads and which is less calcified more organic content So because of this reason it is more acid resistant than the enamel roads because it has less calcification or more organic content than the roads The decalcification or acid is acting on the minerals, so there will be demineralization So less calcification means less demineralization more calcification more demineralization Since it has less mineral content than the roads The acid resistance will be more because there will be less calcification and It is basically incomplete structure. It looks like incomplete structure in electron microscopic examination The next thing how we have inter prismatic substance So inter prismatic substance is the substance which is present between the enamel prisms So they are the cementing Enamel rods together the structures which cement enamel rods together Which is more calcified than the road sheath, okay So this is more calcified than the road sheath, but less calcified than the roads and It appears to be minimum in human teeth So that is about inter prismatic substance next we have striations Striations enamel rods is built up of segments of uniform length about four micrometer Okay, and these are separated by dark lines that gives it a striated appearance So there will be a striated appearance due to the dark lines and they are more visible by the action of mild acids The appearance is because of the formation of enamel matrix in a rhythmic manner So always the deposition of minerals or enamel formation or the matrix formation in a rhythmic manner So it will be layer by layer it will be added So there will be presence of striations between these layers and they are more pronounced in hypocalcified areas, okay And what are the directions of these roads? So the directions of roads are different in different region So the next thing is direction of roads So these roads are oriented at right angles to the dental surface So the inner blue line is the dental surface So always it starts at right angle to the dental surface in the cervical and And central portion of the crown of deciduous teeth. They are approximately horizontal So at the cervical portion and central portion it is almost horizontal direction Whereas at the incisal edge and tip of the cusp they change gradually to an increasingly oblique direction So you can see the change of this roads to a oblique ankle Until they are almost vertical in the region of Edge or tip of the cusp so almost vertical, okay almost vertical at incisal edge or cusp tip So it is horizontal at cervical and middle portion of deciduous teeth So in permanent teeth the arrangement of roads is similar to deciduous teeth in occlusal 2-3rd so occlusal 2-3rd it will be almost same in the cervical region what happens is It deviates from horizontal to more apical direction. So its cervical portion It is more apically inclined in the permanent teeth, okay so The alternative clockwise and counterclockwise Deviation of roads from radial direction can be observed at all level. So there will be Clockwise and counterclockwise because it has both right and left side So clockwise and counterclockwise deviations will be there So in deciduous teeth as I mentioned the roads are horizontal in cervical and central Part of the crown near the incisal edge or this cusp tip They gradually increase in oblique direction and almost vertical at incisal Tip or cusp region incisal tip or cusp Tip region in permanent teeth what happens is at the cervical portion the occlusal 2-3rd is almost same but in cervical region it deviates from horizontal to more apical Direction, okay, so that is about the direction of roads now. We have null enamel. It is also a Change in directional pattern because null enamel is a very important shock node So null enamel is the near the dentine in The region of cusp or incisal edge. What happens is this is incisal tip, okay incisal tip or cusp tip So what happens is the bundles of roads seem to intertwine more irregular and especially in Section which is cut obliquely. So this optical appearance of enamel is called as null enamel So you can see this is almost horizontal the pattern is more rhythmic and Regular fashion but at incisal edge or cusp tip this Roads what happens to the roads these bundles of roads which seem to Interwind interwind more so intervining of roads will be there at incisal edge or cusp tip So this particular intervining of bundles of road that is known as small enamel And this is a optical appearance at the incisal tip or cusp edges So in addition the enamel rods they converge in outward course in pits and fissure occlusal surface of mollusks and primolus, okay So in occlusal surface of mollusks and primolus what happens to these enamel roads? They converge in outward course, okay when it is going outward they converge Next we have enamel spindle. So enamel spindle is end of odendoblastic Processes which is penetrating the enamel and Passing the dentino enamel junction, okay, so odendoblastic processes Which penetrates so odendoblastic processes from the dentino side which penetrates? enamel and dj, okay, which is known as enamel spindle, okay, that is enamel spindle, okay, so This all comes under directions of rods, now enamel and enamel spindle. Now we have very important structure which is known as Hunder-Schrieger bands, which is a very common question So that's about the beginning part of enamel that is we have covered the basic Properties of enamel then the structures like roads, road-treat, inteprismatic substances and Variations in striations and variations in directions of roads So now we'll move to the next part of enamel where we'll be dealing with the very important Hunder-Schrieger bands, incremental lines of red CS and Various surface structures such as perichemata prismless structure Enamel cups, enamel broaches that comes under enamel rodents neonatal line Enamel cuticle that is nasmith's membrane Then enamel spindle So all this will be dealt in next session as it is going very lengthier video So we are stopping this session here Till directions of roads, so we'll be coming with These topics that is incremental lines of red CS, Hunder-Schrieger bands and various surface structures in my next video. Thank you So this video is basically about the surface structures such as Hunder-Schrieger bands Incremental lines of red CS and various surface structures such as perichemata, prismless enamel Nasmith's membrane which is enamel cuticle enamel lamella enamel teffs, dentino enamel junction enamel spindle and enamel road ends so these are the structures which is seen in Surface, DEGES another type which is the junction of dentine and enamel which is a scallop structure and enamel spindle and argentoblastic process So let's see the surface structures and DEGES in detail Hunder-Schrieger bands Hunder-Schrieger bands it is a regular change in direction of roads responsible for the appearance of alternating dark and light strips of varying width So there will be dark and light This is not possible to show it here So there will be black and white appearance When we take sections of teeth we can see the dark and light lines So these changes is due to the change in direction of enamel roads So this alternating dark and light strips of varying width is known as Hunder-Schrieger bands So this is most commonly seen in longitudinal ground section So when we take longitudinal ground section we can see Hunder-Schrieger bands So they originate from DEGES and which pass outwards ending in some distance from outer enamel surface So it originates from DEGES and it ends from little distance from outer enamel surface So this could be due to, there are many things, it could be due to the change in calcification process Calcification will not happen very regularly So sometimes the change in will be rhythmic matter but in various frequency So that change in calcification process could be the reason for Hunder-Schrieger bands And they may not be an optical phenomena but they are composed of alternate zones having slightly different permeability and different content of organic material Nulled enamel is an optical appearance of interwind bundles of roads at incisal edge and cuspel tape Whereas Hunder-Schrieger bands, it is alternate white and dark bands or strips at various width Which could be, which is not an optical phenomena but they are composed of alternate zones having slightly different permeability So slight different permeability with different content of organic matter So that is why it is seen as white and black alternating bands So that is Hunder-Schrieger bands which is very important Now we have incremental line of red sea ice Next we have incremental lines of red sea ice So these are brownish bands which is seen in ground sections of enamel That illustrate successive opposition of layers of enamel during formation of the crown Which are known as incremental lines of red sea ice It is nothing but enamel mineralization will happen layer by layer the minerals will be deposited So this particular rhythmic pattern of opposition, this mineral deposition by layer by layer So in the crown section it is reflected in ground section as particular lines So these lines are nothing but indicative of mineralization, rhythmic mineralization pattern So that is known as incremental lines of red sea ice So Hunder-Schrieger bands is another type of reflection and oblique light That is also another pattern of optical appearance That is white alternative white and black bands in oblique light when we take a longitudinal section So similarly incremental lines of red sea ice is also a brownish band And which is seen in ground sections of enamel which is indicative of mineral opposition So these longitudinal sections which surround the tip of tentane from DEJ in cervical parts Which from oblique deviates to occlusion side So we can see at the tip of tentane which surrounds the tip of tentane which surrounds the tip It is not easy to show in this type of board So in transfer section they appear as concentric circle It has been attributed to the periodic bending of enamel roots So it is due to the periodic bending of enamel roots And there will be physiologic calcification happening So why it is important? Because this broadening of incremental lines may reflect the metabolic disturbance at the time of matrix formation So if something happens so if it is broader then there will be some disturbances happened in matrix formation So the metabolic disturbances is causing this change So we can make out that something happened during the matrix formation So that is the importance of this incremental lines of red sea ice So that is about incremental lines of red sea ice Now we have surface structures, various surface structures such as enamel, cuticle, enamel, enamel types We have cracks, road and peri-chaimata We have also peri-chaimata Peri-chaimata also is a surface structure So we are going in detail about the surface structure So we have various surface structures The first one is prismless enamel So we have prismless enamel, peri-chaimata, road ends, enamel cracks, enamel cuticle, enamel lamella, enamel tufts So let's see what is prismless enamel Which is present in 70% of permanent teeth and all deciduous teeth Which found least over the cusp tip and commonly in the cervical area Which is least in cusp tip and commonly in cervical areas Which will not be visible And all the epithelial crystals are parallel to one another And they are perpendicular to stria of red sea ice So they are more mineralized than the bulk of enamel Which is present beneath that So that is structure less or prism less enamel So that is about prismless enamel Now we have peri-chaimata These are the transverse wave like grooves believed to be the external manifestation of stria of red sea ice So stria of red sea ice Which is externally manifested as peri-chaimata So there will be 30 peri-chaimata per millimetre in the region of cemento enamel junction And their concentration gradually decreases near occlusal or incisal surface at 10 So here it will be 30 per mm and at the occlusal or incisal edge it will be 10 per mm So this is the external manifestation of incremental line of red sea ice So stria of red sea ice And enamel road ends So we have enamel road So we have another structure which is a surface structure which is enamel road ends So these are concave and very in depth they are shallow, cervical and deep occlusally And widths of about 1 to 1.5 micrometre in diameter and small elevations Which are known as enamel caps So we are talking about enamel road ends Enamel road ends Enamel road ends If it is between 10 to 15 micrometre Which is known as enamel caps Enamel caps And if it is very larger enamel elevations Which is known as enamel broach Enamel broach and enamel caps That is enamel road ends Okay now we have enamel cracks They are actually outer edges of lamellae They originate from incisal edge and extend to varying distance in enamel In perpendicular direction towards dentino enamel direction So if any crack is present here it will be Starts from here towards DEJ So mostly it will be 1 mm in length So these are known as enamel cracks Neonatal line We have neonatal line in surface structure of enamel They are like deciduous teeth when they develop Partly before and partly after birth So the boundary between these two portions in enamel Is marked by accentuated incremental lines of ritzius Which is known as neonatal line So neonatal line Neonatal line is nothing but accentuated ritzius Line of ritzius which is showing the demarcation of the portion Which is formed before and after the birth So some teeth which partly develop before birth And after some portion after birth So these are inter These are the line which is differentiating these two r Known as neonatal line or ring So these results from abrupt change in the environment and nutrition of newborn infants So prenatal enamel is better developed than postnatal enamel And perichemata are absent in prenatal enamel So that was about enamel Neonatal line Now we move on to enamel cuticle They are delicate membrane Covers the crown of newly erupted tooth Which is known as Nasmith's membrane Which is very important Nasmith's membrane Nasmith's membrane is nothing but Covering of newly erupted tooth So these Nasmith membrane are delicate membrane which covers the crown of newly erupted tooth Or which is also known as primary enamel cuticle So Nasmith's membrane is enamel cuticle This is secreted after the epithelial enamel organ retracts from the cervical region during tooth development It protects the surface of enamel from resorptive activity of adjacent vascular tissue So the primary enamel cuticle or Nasmith membranes Job is to protect the tooth from adjacent resorptive activity So we have primary enamel cuticle and secondary enamel cuticle So primary enamel cuticle which covers the entire crown of newly erupted tooth Which is removed by mastication Which is secreted by postemuloblast Whereas the secondary enamel cuticle which covers the cervical area of enamel Thickness of 210 micrometer which is continuous with cementum Which is probably mesodermal origin And that is the difference between primary enamel cuticle and secondary enamel cuticle So these all are short notes enamel cuticle Handle, sugar bands, incremental lines of ritzius, ferricahemata Enamel roads, Nasmith membrane, enamel cuticle Now we have enamel lamellae These are leaf-like structures Enamel lamellae are leaf-like structures So it will be like leaf-like structures That extends from enamel surface towards DEJ So this is external surface So this is DEJ So it starts from here towards DEJ And which is basically organic And a little bit of mineral composition Which originates in plains of tension When enamel road cross such a plane They may not fully calcify So when tension is there There will not be proper calcification So that places A crack may develop So this crack is filled either by surrounding cells If it has occurred in unerupted tooth Or by organic material If it has occurred after eruption So the tension happens So during such plains If tension is happening While eruption What happens They will not completely calcify And if the disturbance is very severe There will be a crack formation And if it is before the tooth eruption The crack is filled by surrounding cells And if it has occurred after Then there will be organic content So that is known as enamel enamel Basically it has three types Type A, type B and type C Type A is restricted to enamel So this is enamel This is enamel And this is dentine This is dentine This is enamel So type A is restricted To enamel So this will be here So it starts from outer enamel surface It will be here that is type A Type B may reach up to dentine So if it starts It may reach till here And it is mostly degenerating cells So type C is containing organic material And it may invade It may cross this one Dendino enamel junction That is type C So the significance is It is a site of weakness in tooth And may form a road of entry of bacteria And initiate dental caries Because it is poorly calcified There is no proper calcification happens here And the next structure is enamel Tufts So enamel enamel if you finish enamel tuft Is thin ribbon like structure Which is resembling a tuft or grass It is similar to like Similar to enamel enamel So this is like tufts or grass Which is created by examining such area Under low magnification of ground section So we can observe it when we Check it under low magnification in ground section So these consist of basically Hypocalcified enamel rods And inteprismatic substances So that is enamel tufts So they arise from DEJ So enamel enamel which is Arranged from Outer surface But this enamel tufts Arranged from DEJ Arranged from outer surface enamel to towards DEJ So enamel tufts arise from DEJ And it reach up to One fifth to one third of its thickness And the presence and the development Are consequences of an adaptation to spatial Condition of enamel That is an adaptation mechanism So it basically Significance of enamel tufts It prevents enamel fracture So next we have dentino enamel junction So this particular Blue line is dentino enamel junction Which is basically scalloped structure So surface of dentin at dentino enamel junction is pitted And shallow depression of dentin Which fit round at projection of enamel It appears scalloped due to the mixing of crystals of dentin And enamel each other So there will be mixing of enamel and dentino crystal So it creates a scalloped structure That is dentino enamel junction So enamel spindles We have enamel spindles Next enamel spindles are Odentoblastic processes which Pass across DEJ into enamel Their end is known as enamel spindles So sometimes odentoblastic process Is termed dentin And it crosses the DEJ and reach up to enamel With a thickened end And they have been termed as enamel spindles So this direction of spindles And rods are divergent As rods are formed at right ankle to ameloblast And spindles are parallel to ameloblast So enamel spindle is always parallel Enamel spindle Which is parallel to ameloblast Whereas Enamel rods are right ankle to ameloblast So that is about enamel spindles So we have covered The structure, surface structures and other structures Of enamel So we are finishing our part one Second part is amelogenesis The formation of enamel So we will be checking in detail Already we know how enamel forms In our tooth formation stages Anyway let's Wind up the session one of enamel So we have learned about thickness, color, hardness, solubility, permeability, translucency, chemical properties Various proteins And various structures So structures are rods, road sheath, inter prismatic substances More about striations, more about direction of roads And hunter, sugar bands, incremental lines of red sea ice And various surface structures Such as pericameter, prism less structure Enamel cuticle, enamel amelay Enamel tufts, orientoblastic crosses And enamel spindle Dentino enamel junction Enamel cuticle which is also known as Nasmids membrane Enamel road ends Enamel caps and enamel brush So all are various structures which is present in enamel So it can be asked as a short note A short essay and a long essay So it's a very very important session So I'll come up with enamel Formation or amelogenesis In my next video of enamel Thank you So let's continue our sessions in enamel So in this session I'll be explaining about The amelogenesis The various layers of advanced bell stage Where the actual enamel formation happens The process of amelogenesis, life cycle of ameloblast And mineralization and theories of mineralization So Advanced bell stage We have seen the bell stage in tooth formation So hope you remember this We have four distinct layers in advanced bell stage So we have butt stage, calf stage and bell stage Then advanced bell stage This is the last stage Where the more four differentiation happens So in this stage we have Four layers That means outer enamel epithelium The late reticulum stratum inter medium And inner enamel epithelium Which ultimately give rise to the enamel So let's see one by one How the enamel formation happens So in advanced bell stage So at advanced bell stage Preceding the formation of our structures That is dentine and enamel The enamel organ consists of four distinct layers Such as outer and inner enamel epithelium Stelite and stratum inter medium So what is the role of outer enamel epithelium It consists of a single layer of cuboidal cells So at highest convexity This is the highest convexity This outer enamel epithelium becomes irregular in shape And the capillaries in the connective tissue Which surrounds epithelial enamel organ Which proliferates and protrudes towards the enamel organ So immediately before enamel formation starts The capillaries enter into stelae triticulum So this increased vascularity ensures rich metabolism When a plentiful supply of bloodstream to the inner enamel epithelium is required So basically the outer enamel epithelium provides the Blood network or the rich supply of blood For the inner enamel epithelium for the formation of ameloblast So during enamel formation the cells of outer enamel epithelium Which develop willae cytoplasmic vesicles And large number of mitochondria All indicating specialization for active transport of material So all the materials required for the enamel formation Will be transported from the outer enamel epithelium Through the stelae triticulum Via cytoplasmic vesicles, mitochondria and willae Which develops in the outer enamel epithelium During the process of enamel formation So what is the role of stelae triticulum Stelae triticulum is middle part of enamel organ Which consists of cells that are star shaped That is why it's got that peculiar name star shaped Which has long processes reaching in all directions From the central body So it reaches from all directions From central body And these neighboring cells are separated by wide intracellular spaces So we can see wide intracellular spaces between the cells Which has large amount of intracellular fluid And these cells connected by each other And to the cells of stratum intermedium And outer enamel epithelium by desmosomes The stratum intermedium is here Outer enamel epithelium is here So these cells connected with each other To the stratum intermedium And to the outer enamel epithelium by desmosomes So what are the functions of stelae triticulum So basically it act as a buffer against physical forces That might distort the developing dentino enamel junction Giving rise to morphology So it act as a resistance, it act as a cushion And it permits only limited flow of nutrition elements Overlying the blood vessel to formative cells Because when the first layer of dentine is laid down It collapses to bring the blood vessels near So when the dentine is formed This will be collapsed and bring the blood vessel Near to the dentine Which is formed just now Whereas stratum intermedium which is a flat or cuboidal cells Which is situated between stelae triticulum and outer enamel epithelium The function is not fully understood But it is believed to play a role in production of enamel itself Either by controlling the fluid diffusion Into and out of amylablast or by the actual contribution Of necessary formative elements or anything So it has a significant role But it is not very clear what is its exact role That is stratum intermedium Which is present between the stelae triticulum and outer enamel epithelium Whereas the inner enamel epithelium Which is derived from the basal layer of oral epithelium So before enamel formation begins These cells assume a columnar form And differentiate into amyloblast That produces enamel matrix So it would determine the crown pattern It intues differentiation of odendoblast So enamel intues differentiation of odendoblast From dental papillae So from dental papillae We have formation of dentine happen So this amyloblast intues Formation or differentiation of odendoblast From cells of dental papillae So enamel formation after differentiation into amyloblast And we have cervical lop also So this part is known as cervical lop So this is a cervical lop So which is the border of wide basal opening of enamel organ Where the inner and outer enamel epithelium Become approximated It will become two-layer cell So this is when the crown has been formed The cells of this portion giving rise to a structure Which is known as heart wick epithelial root sheath Okay Heart wick epithelial root sheath Which is very vital for root formation So which is known as cervical lop Which is giving rise to heart wick epithelial root sheath So that is cervical lop and heart wick epithelial root sheath So this is how enamel formation the basic step Now let's see the life cycle of amyloblast one by one So according to the function of life span of the cells of inner enamel epithelium The life cycle of amyloblast Which can be divided into six stages Those are morphogenic stage, organizing stage Formative stage, maturity stage, protective stage And desmolytic stage Okay And the morphogenic stage Which is before the amyloblast are fully differentiated Inter enamel epithelium interacts with adjacent mesenchymal cells Determining the shape of tentin enamel junction and crown Okay So during the stage cells are short, columnar and large oval nuclei Which fills almost entire body So morphogenic stage which is Just before the amyloblast are fully differentiated What happens this inner enamel epithelium It interacts with adjacent mesenchymal cells And adjacent mesenchymal cells And which differentiate the shape of DJ and crown Okay So in this stage Golgi apparatus and centrioles are located in the proximal end of the cell And mitochondria are evenly dispersed throughout the cytoplasm So the changes happening in morphogenic and organizing stage Okay So in organizing stage what happens The inner enamel epithelium becomes taller The reversal of functional polarity Before that in morphogenic stage we have Golgi apparatus and centrioles located at the proximal end And mitochondria is evenly distributed Okay So let this be the nucleus So what happens in organizing stage The polarity will be changed Okay That is the Golgi apparatus and centrioles Comes to the distal end and mitochondria to proximal end So these two will be at distal end And mitochondria will move to or segregate to the proximal end So this is a change happening in organizing stage Okay So in morphogenic stage it was opposite And the reversal happening in organizing stage That is The Golgi apparatus and centrioles move to the distal end The evenly distributed mitochondria goes to the proximal end Okay Then the next change is disappearance of cell free zone So in morphogenic stage we have a cell free zone So that will be that will be disappeared Okay That is morphogenic stage So what happens So in later or terminal stage Audentoblast These are the Audentoblast Which begin to secrete dentine Which is a critical phase in life cycle of inner enamel epithelium That differentiate into amyloblast Okay So when Audentoblast begin to secrete dentine This orange one this is Audentoblast Towards the pulp or the dental papillae Once the dentine formation starts This inner enamel epithelium differentiate into amyloblast So along with this amyloblast are cut off From their original source of nutrition That is connected tissue of dental papillae Because this dentine is a hard structure Which cut off the rich source of nutrients from dental papillae Towards the inner enamel epithelium Because it will act as a barrier Okay Between dental papillae and inner enamel epithelium So what happens it has to anyway get the nutrition So it was getting nutrition from dental papillae But now dentine is becoming a barrier Because Audentoblast is secreted dentine Which is acting as a barrier So inner enamel epithelium Which takes up nutrition from dental sac Okay So that is a very critical phase Hope you don't get confused This is dental papillae This is dental sac which is covering outside Dental sac is covering outside Not this one this is stellate epithelium So the covering outer dental sac will be providing nutrients Once the dentine formation happen So there will be reduction and gradual disappearance of stellate epithelium This minimizing the distance between capillaries So as the formation of dentine and enamel happens This distance will be reduced The stellate reticulum will be collapsed And providing the capillaries closer to the inner enamel epithelium Okay So we finish two stages Mophogenic stage Mophogenic stage and organizing stage Hope you clear this The movement of this reversal of polarity of centrioles And Golgi apparatus and mitochondria Now we have formative stage That is secretory stage with and without Tom's process So formative stage is also known as secretory stage Where the first layer of dentine is necessary For the beginning of enamel matrix formation Because Audentoblast secretes dentine Thereby enamel Inner enamel epithelium is converting into amyloblast Okay So during the formation of enamel matrix earliest change is the development of blunt cell processes On amyloblast surfaces Which penetrates basal lamina and enter pre-dentine Which is known as Tom's processes Okay this is very important short note Tom's processes Tom's processes Tom's process which is penetrating the basal lamina and pre-dentine Okay dentine is this yellow orange one And the closer to enamel is the pre-dentine Which is the first dentine which forms So during the formation of enamel matrix The first change is the development of a blunt process A blunt process on amyloblast surface Okay which penetrates basal lamina and enter pre-dentine So basal lamina which separates enamel and dentine Which penetrates pre-dentine which is known as Tom's process So this happens in formative stage So in the beginning secretory stage Where the first layer of dentine is formed So Tom's process does not happen So as it goes as it grows The Tom's process enters pre-dentine Okay that is a formative stage Now we have maturity stage So enamel maturation occurs after the most of the thickness of enamel Has been formed in occlusal and incisal edge So once the occlusal and incisal thickness of enamel is achieved Then enamel starts maturing Okay so during this phase Amyloblast are slightly decreased in length Okay this is amyloblast Which reduces its length And they display microvilli at distal end So this stratum intermedium cells Lose the cuboidal cells Cuboidal shape on regular arrangement And assume spindle shape So in enamel maturation Amyloblast are involved in cyclic process In which organic material is removed And inorganic material is introduced And this process is reflected on morphology of cells Okay so organic material will be removed And inorganic material will be placed That is a maturity stage And the protective stage So when enamel has completely developed And only calcified The amyloblast stop to be arranged in a well defined layer And can no longer be differentiated from cells of stratum intermedium And outer enamel epithelium This is stratum intermedium And this is outer enamel epithelium When the enamel has completely developed and calcified Though amyloblast This is amyloblast Amyloblast stop to be arranged in a well defined layer And can no longer be differentiated from stratum intermedium And outer enamel epithelium So all will be looking a similar pattern So these cell is from a stratified epithelium Covering the enamel Which is known as reduced enamel epithelium Which is very very important So how the reduced enamel epithelium forms It is actually the outer enamel epithelium Steletroticulum And inner enamel epithelium So these three cells are very distinctive Very clearly demarcated But what happens when the enamel has completely developed and calcified These amyloblast They stop to be arranged in a well defined layer And it can no longer be differentiated from the cells of Outer enamel epithelium And stratum intermedium So these three cell is forms a stratum A stratified epithelium which covers the enamel Which is known as reduced enamel epithelium Okay So inner enamel epithelium Further known as reduced enamel epithelium And the next stage is the small etic stage So the reduced enamel epithelium Which proliferates and induces atrophy of the connective tissue Separating it from the oral epithelium So that the fusion of two epithelium can occur So this is completely formed tooth It erupts into the oral cavity So oral cavity there will be oral epithelium So in the small etic stage what happens The reduced enamel epithelium Proliferates and induces atrophy of the connective tissue There will be atrophy of connective tissue above the tooth Okay so it can easily erupt into oral cavity So there will be fusion of oral epithelium And reduced enamel epithelium happens So reduced enamel epithelium has enzymes Which can destroy the connective tissue fiber That is why it is known as the small etic stage So this is how tooth erupts into the oral cavity Finally the fusion of oral epithelium And reduced enamel epithelium happens Okay so there will be morphogenic stage Where the cell polarity matters And the organising stage the reversal happens Formative stage that is secretory stage Where the tom's process which enters pre-dentine Maturity stage where the enamel and dentine Actually forms and protective stage where the Inner enamel epithelium is known as reduced enamel epithelium And the small etic stage finally It enters into oral cavity where the Reduced enamel epithelium and oral epithelium Which joins and there will be enzyme activity It destroys the connective tissue above the tooth And it erupts into the oral cavity So what is the function of reduced enamel epithelium Okay so it is to protect the mature enamel From degeneration until the tooth erupts Okay that is the basic function Of reduced enamel epithelium Now we move on to amelogenesis Amelogenesis is on basis of ultrastructure and composition There are two process happening that is matrix formation That is organic matrix formation and mineralisation So organic matrix formation is ameloblast Begin the secretory activity when small amount of dentine Has been laid down okay when small amount of dentine That is a pre-dentine is formed The ameloblast which is here okay Begin the secretory activity So ameloblast lose their projection that has penetrated base lamina And islands of enamel matrix are deposited along the pre-dentine So first dentine is formed pre-dentine So the ameloblast starts Forming enamel matrix along the pre-dentine So as enamel deposition proceeds A thin continuous layer of enamel is formed All along the dentine This is known as dentino enamel membrane Okay after that toms process forms So as ameloblast begins to secrete enamel matrix They move away from dentinal surface So each cell forms a conical projection This projection is known as toms process which enters into pre-dentine So that is the role of toms process So this toms process contain basically primary secretory granules And small vesicles Whereas cell body cytoplasm contains abundant synthetic organelles And distinction between this toms process and cell body Is clearly marked by the terminal bars Which are localized condensation of cytoplasmic substances Associated with cell membrane So that is how this enamel forms Now after that mineralization happens And maturation of enamel matrix So ameloblast which covers enamel or mature enamel Are involved in cyclic process that is organic material is removed And enamel matrix will be introduced Okay so there will be a ruffle border Associated with inorganic material and smooth border Which is associated with removal of protein and water So mineralization has basically three theories Booster theory, seeding theory and matrix vesicle theory And mineralization of enamel takes place in basically two stages One is primary or partial mineralization Second is maturation Partial mineralization is around 25-30% of total mineralization happens At this stage immediate partial mineralization occurs in matrix segment And inter prismatic substances So we have two types of mineralization That is partial and maturation Partial mineralization only 25-30% happens So whereas in maturation it is characterized by Gradual completion of mineralization So this mineralization starts at heights of the clown And progresses servically So it starts here and it progresses servically However at each level maturation seems to begin at the dental end of roads So at each level it begins at the dental ends of roads Thus there is an integration of two processes That is each road matures from depth to surface It starts from here to outer surface And maturing roads is from the cusp or incisal edge towards the cervical end So it is happening in two directions That is from here to here and here to here One is from depth to the surface This is depth to the surface And this is from cusp or incisal edge towards the cervical end Okay this is how maturation happens So that is about maturation And now we have few changes that is age changes We know what happens in enamel Age changes most commonly attrition or wearing of enamel will be there And we have learnt a lot of abnormalities which related to enamel formation That is mainly amylogenesis, hatches and teeth in continental syphilis So these are the changes happens or abnormalities during amylogenesis Okay so that's all about enamel formation So we have completed in three parts Okay this is actually part three So in first part we were explaining about the basic characteristics and various structures present In the second part we were seeing about the Hunter Shrieker bands Incremental lines of just see its pericameter and all those things And the third part which is basically highlighting the formation of enamel Based on the advanced belt stage structure that is four structures Amylogenesis and the life cycle of amyloblast So you can expect a lot of questions Amylogenesis, terms, processes, life cycle of amyloblast And reduced enamel epithelium And the advanced belt stage, cellate reticulum, the dentine formation So dentine formation will be dealt in detail In the next session that is dentine Now we are finishing enamel So enamel to understand enamel So I repeat you need to go through the entire chapter That is tooth formation chapter If you have very good knowledge in tooth formation this is very easy So it is little bit confusing first dentine forms Then enamel forms before first dentine The amyloblast induces dental papilla to lay down Dentine formation again in turn induces amyloblast Inner enamel epithelium to change amyloblast So that confusion is there to avoid confusion You need to start from the basics That is the tooth formation stages Burnt stage, cap stage and belt stage And regarding the root formation You need to know what is cervical loop Harvicks epithelial root sheath So if you are thorough with the basic topics The further topics will be very easy So I will come up with dentine in my next session Thank you