 Hello everyone welcome back to another session in dentistry and more today's chapter is development of tooth it is a very basic chapter in dental histology or the basic concept of the foundation of dental histology so all the remaining chapters all the future chapters like enamel, dentin, pulp, alveolar bone so everything is connected to this chapter because it is the embryonic stage from which all the other structures are developing so understanding the basic chapter is very important the terminologies the concept in this chapter will give you a good idea or easy to for it will be very easy for you to understand the future chapters if you have the firm grip on this concept so let's see what is the various stages in tooth development from its embryonic state to a full function oral cavity so this is the embryonic cavity so we have future brain or developing forebrain there is a mason kind type of tissue which is covering the forebrain and we have developing stomodium this is a future oral cavity this is a foregut this is a pericardium future heart so this is a embryonic cavity okay and the very early stage of gestation so what happens is we have a structure which is known as primitive oral cavity or stomodium which is lined by stratified scoma sepithelium known as oral ectodum okay so we have a stomodium here this is a future brain this is a future heart pericardium so in between this is a embryonic cavity you might not be able to imagine exactly so this is a very beginning embryonic stage in the first or second third week of gestation so we have a primitive oral cavity which is known as stomodium and which is lined by oral ectodum so what happens after that this oral ectodum contacts the endoderm of foregut so this is a foregut foregut has endoderm here so it contacts with endoderm of foregut which creating buccopharyngeal membrane okay so buccopharyngeal membrane is there it is formed by the endoderm of foregut and the primitive oral cavity that is stomodium so what happens to the buccopharyngeal membrane is it ruptures it ruptures around fourth week that is 27th day of gestation it ruptures so what happens after rupturing once it ruptures there will be a connection between oral cavity that is primitive oral cavity and foregut so foregut and oral cavity a connection established so that is happening at 27th day of gestation so then what happens so at around 3 to 4 week that is 27th day this buccopharyngeal membrane ruptures and connection established and after 2 to 3 weeks so around 6th week what happens we have a structure formation which is known as primary epithelial band because this foregut and this connection we have a special type connected tissue here which is known as neural crestor ecto mesanghymen origin which is creating a primary epithelial band around 6th week of intra uterine or life it is happening after 3 weeks of buccopharyngeal membrane rupturing okay so this is happening at 27th day this is happening at 6th week that is a formation of primary epithelial band because it created from a connected issue which is neural crest or ecto mesanghymen origin so what is the importance of this primary epithelial band it is giving rise to dental lamina and vestibular lamina so dental lamina is nothing but the future tooth are originating from dental lamina okay so this primary epithelial band which has got two structures buccal process and lingual process lingual process is known as dental lamina buccal process is vestibular lamina so this connected tissue formation is not very equal in all the areas so it has cell multiplication at few areas so that few areas there will be rapid cell multiplication so that is giving rise to epithelial band so this epithelial band which invades the underlying ecto mesanghymen along each of the horseshoe shaped future dental arches so we have upper arch and lower arch so this connected tissue proliferation which give rise to epithelial band which invades the horseshoe shaped upper arch and lower arch and which give rise to future teeth so that happens at the 6th week of intrauterine augmentation life after three weeks of buccal pharyngeal membrane rupture so after that what happens it divides into dental lamina and vestibular lamina at around 7th week okay so after one week it divides into dental lamina and vestibular lamina which is buccal and this is lingual process so this dental lamina which is giving rise to the future all deciduous teeth so all deciduous teeth arises from dental lamina and the permanent teeth will be arising from the lingual extension of this dental lamina so there will be a lingual extension from which the future teeth arises and the molas that is permanent molas arise from the distal extension of this dental lamina so dental lamina has all deciduous teeth but from the lingual extension the permanent teeth arises and distal extension the molas that is permanent molas arises so the dental lamina is the most important structure which is giving rise to future tooth so we have seen what is tomodium which is connecting with forget by buccal pharyngeal membrane it ruptures at 27th day or after 2 to 3 weeks there will be continuous multiplication of connective tissue which is neuro cluster ecto mesenchymin origin which is giving rise to a primary epithelial band which is not everywhere it is proliferating certain areas and which invades the whole shoe shape upper and lower arches which has got two process lingual and vestibular the dental lamina is a lingual process which is giving rise to deciduous teeth and the lingual extension giving rise to the permanent teeth and the distal extension of dental lamina giving rise to permanent molas so this is the epithelial band so I have a two different pictures this is from frontal view that is a friend view okay so this is a maxillary or maxilla primitive maxilla and this is a primitive mandible so we have horseshoe shaped arches and this is the epithelial band primary epithelial band from which the future teeth arises okay whereas this is a different view that is a lateral or side view so you have the buccal portion that is a vestibular lamina of primary epithelial band and this is a lingual portion of primary epithelial band which is known as dental lamina from which the future teeth arises so this is a side view and this is a friend view so when you are looking at a person so it looks like this the maxilla mandible or the future bones where the primary epithelial band is in the pink color okay so visualizing this concept is little different because the pictures are not in 3d format so this is a side view or lateral view and this is a friend view okay so this is how primary epithelial band forms it invades into the horseshoe shape arches maxilla and mandible arches and creates epithelial proliferations thereby future dental lamina and vestibular lamina forms so we have learned dental lamina and vestibular lamina are the lingual and buccal portion of primary epithelial band from dental lamina the future teeth arises that is a lingual extension okay the lingual extension so there will be a lingual extension this is a single tooth so we have a set of teeth so the lingual extension will be set so that lingual extension is also known as sucessional lamina because it produces or give rise to the successors teeth that is a permanent teeth okay so lingual portion that is a dental lamina give rise to basically the deciduous teeth so from that we need to get the permanent teeth so it arises from the sucessional lamina which is present in the lingual side of lingual band of primary epithelial band okay we don't get confused dental lamina is a lingual part of epithelial band and lingual part of dental lamina section sucessional lamina arises and we know permanent molars which is coming from the distal extension because we have molars deciduous molars so deciduous molars succession lamina give rise to the permanent pre molars so we don't have any space for permanent molars in epithelial band so it arises from the distal extension of dental lamina that is a permanent molars for second and third molars so what is a job of vestibular lamina which is a buckle portion of you cannot distinguish vestibular lamina and dental lamina here because this is a frontal view so here you can distinguish this is a vestibular lamina and this is the dental lamina this is a lingual side this is a buckle side okay since it is a frontal view the anterior portion will be the buckle and the posterior part will be the dental lamina okay so vestibular lamina which is also known as lip furrow band it is a buckle portion of primary epithelial band it give rise to the vestibule vestibule between the lips and treaks and the tooth bearing area so the vestibule between the lips and treaks and the alveolar bone which bears the teeth vestibular lamina becomes a lip furrow band between the alveolar bone and lips and cheeks so what happens to this dental lamina so usually dental lamina has five-year period or five-year activity so after five-year activity it ruptures when the tooth forms the tooth allows us its connectivity the dental lamina and the remnants might be present in jaw or djunjeva okay so the remnants of dental lamina which is present in the jaw is known as epithelial pearls or islands or epithelial island or epithelial pearl and the remnants of dental lamina which is present in the djunjeva is known as cell rest of sere so this is very important what is epithelial pearl or island and what is cell rest of sere it is the remnants of dental lamina after its activity the remnants might be present in jaw or djunjeva the remnants in djunjeva is known as epithelial pearls or islands and the remnants in djunjeva is known as cell rest of sere so this is dental lamina now we will look into the various stages of tooth formation so before that you need to get this concept clear so it will be like this in future there will be formation of tooth bud from dental lamina so before that this is how it forms the primary epithelial band what is vestibular lamina what is dental lamina and what is lip furrow band what is epithelial pearls and what is cell rest of sere so everything is very important short nodes short essays long essays so there are many questions been asked from this chapter so now let's see the various tooth formation stages so dental lamina so dental lamina in primary epithelial band so what happens to dental lamina so in the epithelial band at 10 points so this dental lamina at 10 different points which represents the future deciduous tooth bud there will be rapid multiplication of ectodermal cells so there will be a knob like structure formation because of the rapid multiplication and it grows into the underlying meson kind okay so it becomes like a enamel organ or it is known as bud stage so it is the first stage so that various stages will be dealing later so it's like a bud so it is by the rapid multiplication of ectodermal cells in the dental lamina at 10 points in maxilla and also in mandible because we have 20 teeth 10 in mandible and 10 in maxilla 20 deciduous teeth so all these points there will be bud formation or enamel organ formation okay so these growth will be towards the ecto meson guy that is the underlying ecto meson guy and it appears first in the mandibular central incisor region the mandibular anterior region so we know the first tooth forms the first two therapsis deciduous lower central incisor so this is a bud stage so at 10 points in dental lamina so dental lamina is nothing but the lingual extension of primary epithelium band so it becomes like a bud stage later more proliferation happens so more proliferation happens it will result into a cap like structures so when there is a cap like structures we have two components that is dental papilla and dental sac or dental follicle so dental papilla is nothing but the inside of this cap the ecto meson camel cells increasing in large number so this tissue appears more denser than the surrounding meson game and represents the beginning of dental papillae so you cannot see a dental papillae here because there will be structure it is more deeper in outline because there will be rapid multiplication of cells and the cells between this inside so the cells within the cap they'll undergo rapid multiplication and it will become more denser compared to the tissue which is present outside so this is known as dental papillae and dental papillae which actually give rise to dentine and pulp okay so dental lamina is this one so dental lamina is soon to be detached from the developing tooth so now let's move on to the dental sac or dental follicle so the surrounding combined enamel organ or dental papilla the third part of the tooth but so it is known as dental sac or follicle and it consists of ecto meson camel cells and fibers that surrounds the dental papillae and enamel organ so this is the enamel organ so covering the enamel organ and dental papillae we have the third structure which is known as dental sac or dental follicle okay so this is covering the enamel organ and dental papillae so dental lamina is here dental lamina is soon to be become rudimentary because it will be detached as the tooth grows so from dental follicle or dental sac there is structures some cementum periodontal ligament and alveolar bone arises so from dental papillae dentine and pulp forms and from dental follicle or dental sac cementum periodontal ligament and alveolar bone forms so we know that this is a tooth and this is a tooth structure okay so you know it looks like a tooth crown so surrounding tissues ultimately develops into the cementum periodontal ligament and alveolar bone so the dental sac or follicle is coming at the lower portion so obviously the future root will be here future cementum will be here and future alveolar bone will be here and the enamel organ that is enamel organ this one it give rise to enamel okay so dental papilla giving dentine and pulp so inside the enamel organ we have pulp and dentine because outer most layer is enamel inside dentine and pulp so the inside structures giving rise to dental pulp and dentine the lower structure that is sac or follicle giving rise to cementum pdl and alveolar bone it is very easy to understand you need to visualize this as a crown of tooth then it is easy enamel organ give rise to enamel papilla give rise to pulp and dentine and the lower portion dental sac giving rise to cement the pdl and alveolar bone so this activity of dental lamina is up to five years after that it continuously disintegrate or detach from the developing tooth and last session we have seen the remnants of dental lamina will be present in jaw or ginger which is known as epithelial pearls or cell rest of rest of saring so that is about butt stage and cap stage so i'll be explaining more about these three stages butt cap and bell stages but before that we need to understand what is enamel organ what is dental papilla what is dental sac and dental follicle and what is dental lamina okay so dental lamina is a most primitive structure from dental lamina the enamel organ develops so as it grows as it develops more and more this dental lamina will become less important or less prominent so now this will go on increasing and it differentiate into various structures so the cells or the organs which giving rise to the future cementum enamel dentine pulp pedodontal ligament and alveolar bone you need to understand from where it is originating and what's happening inside the enamel organ in bell stage history differentiation happens due to the continued growth that is uneven growth of enamel organ it requires a bell shape so in bell stage the crown shape is basically determined so it was thought that the shape of crown is actually determined or influenced by the pressure exerted from dental papillae on the inner enamel epithelium so there will be pressure from dental papillae on the inner enamel epithelium which influences the crown shape at the same time there will be a opposite pressure balancing pressure from the stellate sorry stellate reticulum to balance this pressure which is from the dental papillae and this stellate reticulum opposes this pressure so these both pressure determines the shape of crown and the folding of enamel organ to cause different crown shape which is due to the different rate of mitosis and difference in cell differentiation time so this is basically a crown shape deciding stage and various functions such as amylogenesis and formation of otter blast amyloblast so all are happening in bell stage so inner enamel epithelium which consists of single layer of cells that differentiate prior to amylogenesis into tall column nerve cells which is known as amyloblast so this becomes amyloblast so amyloblast later give rise to enamel so these elongated cells are attached to one another by junctional complexes in lateral position and to cells in the stratum intermedium by desmosomes so it one another attached by junctional complexes and with stratum intermedium by desmosomes so the cells of inner enamel epithelium exerts a strong influence on underlying meson chym on the dental papillae which later differentiate into otter blast so dental papilla exo ecto meson chym in dental papilla will be influenced by the amyloblast here which later becomes otter blast so stratum intermedium is a another structure which we don't have in cap stage which is present in bell stage it is a few layer of squamous cells form stratum intermedium between the inner enamel epithelium and the stellate reticulum so stellate reticulum and inner enamel epithelium we have stratum intermedium stratum intermedium is a new structure which we were not having in cap stage so it is present between inner enamel epithelium inner enamel epithelium is here and this is stellate reticulum between this we have stratum intermedium stratum intermedium so what is the function of stratum intermedium it is essential for the enamel formation so enamel formation is a role it has got a role in enamel formation and next we have stellate reticulum which we had seen in cap stage that is star like cells which is present between outer and inner enamel epithelium so it continues to growth by imbibing fluid from dental papillae so later what happens is as it continuously grows and accumulation of intracellular fluid also increases and finally it collapses and it become a narrow zone thereby reducing the space between outer enamel epithelium and inner enamel epithelium so this will be reduced the space will be reduced and outer enamel epithelium and inner enamel epithelium will be all come in approximation because that space between these two will be completely reduced the outer enamel epithelium it is flattened form low cuboidal cells so this outer enamel epithelium is thrown into folds so thrown into folds which are rich in capillary network and this provides a source of nutrition for the enamel organ so these folds which with the capillary network which provides nutrition for the enamel organ so dandelamina which is extend to lingual site and it is known as successional dandelamina which give rise to enamel organs of permanent successes of deciduous teeth till premolus distal site the molas will be developing and dandel sac exhibit a circular arrangement with circular fibers and resembles a capsule around the enamel organ so these fibers of dandel sac form the periodontal ligament fibers that is between roots and bonds so the junction between inner enamel epithelium and or endoblast outline the future dendeno enamel junction but the major changes are happening during the advanced bell stage so instead of in history differentiation which was in the early bell stage we have more for differentiation so what is happening in advanced bell stage so it is characterized by the commencement of mineralization and root formation so the boundary between inner enamel epithelium and or endoblast outline the future dendeno enamel junction which we had seen earlier and formation of dentine occurs first as a layer along the future dj in the region of future cusps and which proceeds pulpally and epically so there will be dentine formation happens first so there will be first layer of dentine forms along the future dendeno enamel junction so this is a dentino enamel junction so first layer of dentine forms and which forms in the region of future cusp region it forms and proceeds pulpally and epically so it moves towards the pulpal side and epical side and after the first layer of dentine is formed the ameloblast lay down enamel over the dentine in the future incisal and cuspal areas so once the dentine is so dentine is the first thing which is formed after that ameloblast lay down enamel over the dentine in the future incisal and cusp region so then enamel will be formed over the dentine at the incisal and cuspal areas so the enamel formation then proceeds coronally and servically in all the regions from the dj towards surface so from the dj it moves towards coronal and servical direction so coronal direction and servical direction from the dj towards the surface so the enamel forms and which moves coronal and servical direction whereas the dentine which forms and moves towards the epical and pulpal areas so after that what happens the servical portion of enamel organ which give rise to a structure known as hartwick epithelial root treat this hers which outlined the future roots which is responsible for size shape length and number of roots so this will be dealt more in detail about root formation and next stage that is a opposition phase formation of enamel and dentine matrix so opposition is the deposition of matrix of the hard enamel structures so oppositional growth of enamel and dentine is a layer like deposition of extracellular matrix this type of growth is therefore additive so what happens is let it be enamel or dentine it is forming layer by layer so one layer will be added so the the next layer will be added above that then there will be above that so it will be keep on adding so this is a additive effect this layer itself cannot create another layer so the layer has to be added so that is known as additive effect so oppositional growth is characterized by regular and rhythmic deposition of extracellular matrix which is itself incapable of future growth so it cannot create another layer by itself it has to be deposited one by one so layer by layer it will be deposited which is basically incapable of future growth so now we will move on to the root formation so root formation it starts with development of root once the enamel and dentine formation has reached the future cemento enamel junctions so once the dentine formation and enamel formation reached the future cemento enamel junction what happens the root formation starts the enamel organ plays an very important role in root development by forming the structure known as hard wick epithelial root shreeth which models the shape of the root so hers plays very important role which is actually consisting only outer enamel epithelium and inner enamel epithelium as the first layer of dentine has been laid down as the first layer of this black one dentine has been laid down the epithelial root shreeth losses its structural continuity and is close relation to the surface of root so once the dentine is formed the epithelial root shreeth losses its structural continuity that is hers hard wick epithelial root shreeth which losses its continuity and is present in close relation to the surface of root so this remnants persist as an epithelial network of strands or clamps near the external surface of root so it may be present on the external surface of root so it was a sheath continuous sheet so once the dentine is formed this continuity will be lost so the remnants will be present on the root surface as strands or clamps this is known as this epithelial remnants found in the periodontal ligament of eruptive teeth is known as rest of molasses so rest of molasses is nothing but the discontinued hard wick epithelial root sheath present in periodontal ligament otherwise it will be present on the root surface as network of strands or clamps so that is the epithelial rest of molasses so what happens basically in root formation so the prior to beginning of the root formation the root sheath forms a epithelial diaphragm so this is the epithelial diaphragm so it forms a epithelial diaphragm that is the root sheath forms that is hard wick epithelial root sheath forms a epithelial diaphragm and the outer and inner enamel epithelium bend at the future cement enamel junction in a horizontal plane so this is outer and inner enamel epithelium that is this contains only outer and inner enamel epithelium which bend horizontally so this is like this and it bends horizontally so it was supposed to be like this but it bends horizontally and it forms epithelial diaphragm but it creates and it creates the narrowing of white cervical opening so this was very wide so it narrows the cervical opening and the proliferation of cells of epithelial diaphragm is accompanied by the proliferation of cells of connected tissue of pulp adjacent to the so there will be connected tissue proliferation adjacent to the diaphragm when pulp so there will be pulpal tissue proliferation adjacent to this diaphragm so the free end of diaphragm does not grow into connected tissue but the epithelium proliferates coronal to the epithelial diaphragm so it will not grow this direction but coronal direction it proliferates the free end of diaphragm this is the free end of diaphragm which does not grow into the connected tissue but the epithelium proliferates coronal to the epithelial diaphragm so the connected tissue of dental sac so dental sac connected tissue surrounding the root sheath which proliferates and invades this continuous double layer so the continuous double layer it invades this continuous double epithelial air dividing it into a network of epithelial strands so it is by the connected tissue of dental sac so the rapid sequence of proliferation and destruction of heartwicks epithelial root sheath so this is a heartwicks epithelial root sheath explains the fact that it cannot be seen as a continuous layer on the surface of developing root so it will be removed from the root or it present as remnants as a network of strands or clumps near the external surface of root or it may be present in the periodontal ligament of eruptor teeth as cell rest of molasses so in the last stage of root development the proliferation of the epithelium the proliferation of the epithelium in the diaphragm which lacks behind that of the pulpel connected tissue so pulpel connected tissue is here so during the last stages of root development proliferation of epithelium in the diaphragm okay so that lacks behind that of pulpel connected tissue and this wide opening will be reduced by the deposition of dentine and cement at the apex of the root so this will be reduced as a root forms so what happens when tooth is having multi-rooted so this is bi-rooted multi-rooted structure so the differential growth of epithelial diaphragm in the multi-rooted teeth causes the division of the root trunk into two or three roots so during the general growth of enamel organ expansion of its cervical opening occurs in such a way that the long tongue like extension of the horizontal diaphragm develops so this is a cross section okay so there will be a tongue like diaphragm develops so you can see here tongue like develops so before the division of root tongue occurs the free ends of the horizontal epithelial flaps grows towards each other and fuse so it grows towards each other and fuse the single cervical opening is divided into two or three opening two or three opening so how it happens on the pulpal surface of dividing epithelial bridges dentine formation starts and on the periphery of each opening so this is the each opening this is a multi-rooted tooth on the periphery of each opening the root development follows in the same way as described for the single-rooted tooth so this is how multi-rooted tooth formation so the roots in the multi-rooted tooth happens in this way there will be a epithelial tongue like structure forms and there will be splitting of roots so on summarizing we have started from primary epithelial band and we reach the complete tooth formation so we have seen dental lamina which is basically initiating the process which is a lingual portion of epithelial band then we have bud stage and cap stage which is basically proliferation and early build stage is histo differentiation and advanced build stage morpho differentiation and a position phase where the enamel and dentine forms the matrix will be laid down in a position phase so it's a very lengthy session but it has to be done in this way because it has starting from the storm odium the oral cavity the primitive oral cavity and step by step we are moving on we cannot in between stop because it has to be like a continuum so if you're studying bud stage you have to study cap stage and early build stage advanced build stage and how the complete root formation happens including the root formation so the tooth formation both crown and root formation involves so there are many questions been asked from this chapter that is bud stage cap stage or bell stage drawing and explaining cell rest of molasses rest of serre enamel knot enamel cord outer enamel epithelium hard so hard weeks epithelial root sheath and it's commonly asked as a long essay so every answer must be accompanied by proper diagram proper label diagram that is proper use in hematocin used diagrams then only you will get good marks even if you're writing a very good answer without pictures will significantly reduce your marks so I'll come up with a new topic in dental histology thank you