 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 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 told 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 amylogenic amylogenic and non amylogenic 90 percentage of the total protein belong to amylogenic which is low molecular weight Which is rich in proline histidine amino acids also glutamine and leucine But as non amylogenic 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 shock 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 brown Lines are enamel and the pink lines are dentin 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 these 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 Tentino enamel junction. Okay, so why it is important because of inter woven network of roads teeth can resist Masticatory forces up to 20 to 30 pounds per tooth. That is why it is clinically Significant because of its 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 9 micrometer in length and 5 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 occlusion or incisal surface So occlusion or incisal surface the enamel rod bodies will be seen and the tails. Okay, so the tails will be at the Surveillance area. So if this is particularly a tooth Okay, so at this area occlusion 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 apatite crystals So they are arranged parallel to the long axis of rod which has point 05 to 1 micrometer with 90 micrometer which has pyramidal shape and hydroxy apatite crystals are Placed within this hexagonal shape so that is about Enamel rods and hydroxy apatite 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 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 hypo calcified 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 Into 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 In size LH 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 In size LH 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 it's 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 and 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 not 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 a 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 null enamel and this is a optical appearance at the incisal Tip or cusp edges So in addition the enamel roads 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 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 roads, null enamel and enamel spindle Now we have very important structure which is known as Honder-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, Interprismatic substances and the variation 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 Honder-Schrieger bands, incremental lines of Red-CS And various surface structures such as perichymata, prismless structure, enamel cups, enamel broaches that comes under enamel rodents, neonatal line, enamel cuticle that is Nasmids 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, Honder-Schrieger bands and various surface structures in my next video. Thank you