hi everyone this is Miss O'Brien in this presentation we are going to go over chapter 8 of your dental assisting textbook and we're just going to go over the first part of the chapter and this is the chapter on embryology okay so uh what is embryology embryology is the study of prenatal development in the stages before birth so the word is derived from embryo uh you know which is before the baby is fully formed and ology means the study of so it's the study of prenatal development so pregnancy actually begins with conception or fertilization when the sperm fertilizes the egg which I'm sure you're all aware of and then gestation this is the period from fertilization to birth so for humans the gestation period is an average of nine months from conception to birth um or it's 40 weeks as measured from the last menstrual period that's how they a lot of Obstetricians measure it um so the the due date rule of thumb is to count back three months from the last menstrual period of the mother then add a year and a week so um so this is actually an estimate and births can occur two weeks earlier or two weeks later you hear all the time about you know somebody has a certain due date and the baby came early or the baby came late so so again it's just kind of an estimate it's not um you know it's not the date that the baby's definitely going to be there so um now the sex of the baby or the gender of the baby is established at conception and then it starts to become physically apparent in just a few weeks after the conception date and then the developmental age we use this in embryology a lot and this is based on the date of conception which is assumed to be two weeks after the last menstrual period but it it could again it could vary by two weeks in either direction honestly okay so prenatal development it actually consists of three distinct periods and the first period of prenatal development is the pre-implantation period so this occurs at the beginning of the first week of the gestation period And this is when the ovum or the egg is penetrated by the sperm during fertilization so what happens then the egg surface will change so that no other sperm may enter so once it's fertilized by one sperm it can't be fertilized by other sperm then we have the union of the egg and the sperm and this forms a fertilized egg and this is called a zygote so the sperm and the Egg they will each contribute 23 chromosomes to the zygote so there will be a total of 46 chromosomes 23 from the sperm from the father 23 from the egg from the mother and these are what determine inherited characteristics and then the joining of the chromosomes this is a process called meiosis which you may have studied in your previous biology courses okay so um so this obviously is an enlarged picture um this is the sperm uh this is the ovum so once the sperm penetrates the ovum no other sperm can penetrate the ovum the surface changes and then it forms the zygote and then we have meiosis and the forming of the 46 chromosomes or the joining of the 23 chromosomes from each each component okay um and then this is called a kerotype this is just a chromosome mapping tool and you can see they've got the um the various chromosomes they're they're all in pairs and then they have the pair of chromosomes that determine the sex or the gender of the child okay um and then sometimes um certain um certain things can happen during the meiosis period and one of them is something called trismy and that what that is is there instead of a pair of chromosomes on the um the 21st chromosome set there's there's three of them called trismy that means there's there's an extra chromosome so um so chromosome number 21 instead of a pair it's actually a triplet of chromosomes so that leads to there being 47 chromosomes in this person's genetic makeup and this is what we call down syndrome you may have heard of that so down syndrome or sometimes it's called trismy 21 because of the third chromosome on the 21st pair of chromosomes this this results in Down syndrome and um and people with Down Syndrome they often have physical features that that are associated with that um that syndrome and then sometimes there's um various levels of intellectual disability although uh you know a lot of people with Down Syndrome can be very very high functioning so um so some of the some of the physical features the facial features that you see with Down Syndrome are like widely spaced eyes oblique eyelid fissures epicanthic folds so that's a fold in the tissue on the eyelids a broad flat face a flat Bridge nose forward lip sometimes people with Down Syndrome have heart issues like defective heart valves so there's a lot of a lot of physical features associated with Down syndrome and again it all comes down to that extra chromosome on the chromosome number 21. okay and then the prenatal development second period so the second period is the embryonic period And this is when implantation occurs so the zygote is formed in the first period and then it's implanted at the beginning of the second period so from the beginning of the second week to the end of the eighth week this is considered the second period or the embryonic period of prenatal development so in this period the zygote which is pre-implantation becomes an embryo once it becomes implanted then you have the embryo so this is the most critical period as development begins in all major structures so what happens during this period is cells begin to proliferate it means you're you're many many more cells are being created they differentiate into different like organ systems different types of cells and then they integrate they kind of come together and to act as a system or a unit okay so this shows you the embryonic development um so about week five uh that's in letter a week six you can see letter b and then by week eight um the the embryo really kind of takes on more of a you know more classical human features the embryo starts to look more like a human baby around week eight um you know kind of loses some of these uh other features that we don't really associate with babies and then the you know you can see the head becomes more more formed although it's you know disproportionately large it's more you know head shaped okay and then the third period of prenatal development this is the fetal period so um this is from about the ninth week uh until the actual birth of the baby and then body systems continue to develop and mature at this point um the the fetus has ears arms hands legs feet even fingerprints and Footprints at this point all the organ systems have formed so um so the fetus is is less vulnerable to the effects of radiation and viruses and drugs than the embryo is although you know you still want to be careful of course if if you're pregnant and this is a period of growth and maturation so so most of all the systems are already formed they're just growing and maturing and kind of the the completion is happening okay um so this just shows a few different periods during during the gestation so like we said the zygote um that's that's uh the preamp Plantation period um then the um zygote goes through um these various phases at blastocyst and then the blastocyst becomes the disc and then the disc becomes the embryo and then we have the the embryo during the embryonic period and then the embryo continues to you know mature and develop the cells differentiate they integrate you know they been proliferating and then finally you have the fetus and at that point you know once the the once the embryo becomes a fetus really all the organ systems are kind of uh almost complete but they still need to grow and mature okay and then again this kind of shows um the uh the development of the fetus from the 11th week to the 38th week so you can see it's you know at this point is just a matter of of growth and maturation um you know all the the organ systems are kind of formed at that point but you know you just need to um to grow okay um so just a quick learning check uh meiosis this is the joining of chromosomes and it takes place during which period a prenatal development would it be the pre-implantation period the post-implantation period the embryonic period or the fetal period what do you guys think okay so meiosis actually takes place during the pre-implantation period so so before the uh the zygote is even implanted and becomes an embryo the uh the joining of the chromosomes 23 from the sperm 23 from the ovum uh you know before you know before it's even implanted that's when this all takes place so so meiosis takes place during the pre-implantation period okay so let's talk about embryonic development of the face and the oral cavity okay so um so there's three uh primary embryonic layers so this occurs during the third week of development these three embryonic layers are formed so you've got the the ectoderm which is the outer layer and the mesoderm which is the middle layer so I always remember that M you know for mesoderm M's for middle and then endoderm in my mind I always think endoderm like inner layer so so you've got the inner layer the endoderm the middle layer the mesoderm and then the outer layer the ectoderm so the cells in each layer will multiply and differentiate into specialized cells for various organs and tissues so some will become the the skin some will become heart tissue some will become lung tissue so they all start with these these three embryonic layers all right and here you can see on the embryo you know the developing brain is around here this would be the the stomodium or the Primitive mouth uh the developing heart would be in this this area so you know you can kind of see the the pre-fetal features of the embryo you know you can see that the legs would be down here and such and the in the arms would be in this area um so if we uh if we look at the layers um you know the the ectoderm um that can that tissue is the outer layer you can see that it can develop into the the span excuse me the brain and the spinal cord we've got the the mesoderm which would be the middle layer you can see it's developing Into the Heart here and then the endoderm which is the inner layer is developing into the digestive system we've got the oropharyngeal membrane you can see that's in the area of the Primitive mouth or the stomodium they call it um the pharynx you know that would be like in the throat area and then the foregut which will get into the digestive tract so obviously this is going to move you know down further as the as the embryo and the fetal the fetus develop okay um so stomodium so I mentioned that before this is the Primitive math so basically it's just the part of the embryo right in here that will become the mouth later on as the um as the embryo develops into the fetus and then the Primitive pharynx um these these merge during the fourth week so as you know your your mouth and your you know pharynx and your esophagus all that kind of merges together so um so this happens during the fourth week of prenatal development so by the fifth week the site of the face is indicated from above by the region in front of the bulging forebrain and From Below by the first pair of branchial branches so so you can kind of see that here's you know the developing brain or the forebrain is here here's your branchial branches and then here's your stomodium or the the Primitive mouth and this area that's going to become the the eye so um and then you can see here here's the eye or what will become the eye this would be the uh the forebrain the stomodium or the Primitive mouth is here and then just below the stoma diem you have the branchial branches okay um so branchial arches sometimes you hear them called branches sometimes arches so there's six pairs of branchial arches and these form by the end of the fourth week so um so the first branchial Arch this is called your mandibular Arch and um and we have a mandibular bone so your lower jaw bone is the mandible so it's kind of in that area so this mandibular Arch or the first branchial Arch forms bones muscles and nerves of the face as well as the lower lips the muscles of mastication you know that meant when we say mastication we mean chewing and then the anterior portion of the alveolar process of the mandible so the alveolar process that's the bone around your teeth and then the mandible is the lower jaw bone so it forms all that then we have the second brachial Arch and this is also known as the hyoid Arch and this forms the the styloid process the stapes of the ear that's one of the inner bones of the ear or pairs of inner Bones the Stylo hyoid ligament parts of the hyoid bone which is a bone which kind of is well they call it a floating bone it's in your neck and then um this the starch also forms the side and the front of the neck and um and we'll don't worry if you don't know what the styloid process is we're going to be learning about that next week when we study the um head and neck Anatomy the bones um and then the third brachial Arch this forms the body of the hyoid and the posterior of the tongue and then the fourth fifth and sixth brachial arches these form the structures of the the lower throat that should say including the the thyroid cartilage the muscles the nerves of the pharynx and the larynx so you can see from the first brachi large you know you kind of start more at the front of the face like with the lips and then as you go to the sixth branchial Arch you're kind of moving kind of posteriorly and um and inferiorly so you're moving kind of backwards and downwards through the the throat basically okay so hard and soft palettes um so you can if you're not familiar with your hard and soft palettes your hard palate is the you know the hard part of your the roof of your mouth basically so the hard palate is the roof of your mouth and then as you move back a little bit um towards the throat where the bones stop and it's just kind of more soft tissue that's your soft palate so a lot of times if somebody touches your soft palate like if you were to get dental X-rays and they accidentally touch the the soft palate with the um with the sensor then you might gag so that's you know that's kind of where the soft palate begins that usually triggers a gag reflex for somebody so um so the formation of the palette the hard and soft palate it actually takes several weeks to occur it's very complex and it begins in the fifth week of prenatal development um and is formed from two separate embryonic structures so the uh the pallets form from the the primary and the secondary palette we'll see a picture of this in a minute and then the fusion of the primary and secondary palettes they form a y-shaped pattern on the roof of the mouth and if you actually have an infant or know somebody with an infant you could actually maybe see it in their mouth if you looked um so you know so this y shape is it's visible in the infant but you know as the infant ages it's it's not quite as visible as they mature and grow so Fusion of the palettes it begins in the anterior during the ninth week and then it's completed during the 12th fetal week so the palate is actually formed in three stages there's formation of the primary palette then formation of the secondary palette then you have the fusion of the two palettes the primary and secondary so um so this is uh this is really critical in in the development of of the um the fetus because any disruption in this process could lead to a cleft lift or palate and it doesn't happen a lot but it's it's certainly not unheard of either so um so there's you know things like certain medications or drugs and and other you know behaviors can lead to uh to the child developing a cleft Lipper palate so um you know between the um you know about the fifth week to the 12th week it's it's really important that um that a pregnant woman you know take care of herself well and um and stays away from certain substances so that you know so that they're not at an increased risk for the infant having a cleft lip or palate okay um so you can see the the primary palette um there's you know there's four incisor teeth um the maxillary incisors uh are part of the the primary palette then you have the um the secondary palette back here so the so the secondary palette is really the the majority of the palette um the primary is the anterior and it's a bit smaller and the secondary palette is formed from um fused palatal shelves um you can uh you know we'll talk more about those later but you can see the the line the the fusion line between the primary palette and the secondary palette runs between the maxillary lateral incisors and the maxillary canines and you can see this why so you might be able to see this in an infant's mouth if they're young enough and then we were talking about the the hard palate so the the second primary and secondary uh palettes they fuse and they become the hard palate and then portion a portion of the secondary palette becomes the soft palate so um and then there's a suture and an area of a suture where the palatal Shelves come together and this is your median Palatine suture so it's just a an imaginary line that runs down the um you know just down the center of the hard palate and on some people it's you know you can't really see it on some people you can see it a little bit some people it's more pronounced it just depends okay um so this is what happens if there's any disruption of the fusion of those pallets it can lead to a cleft liper pallet so um so luckily um you know these with modern medicine these can be fixed fairly I don't want to say easily but but they can do a really really good job restoring oops restoring the function and the Aesthetics so you can see this is the same child on the left and the right and they were born with a cleft lip at least possibly a cleft palate as well even the you know the um the nostril the left nostril was involved and and they just did a beautiful job restoring that and it doesn't you know you can barely even see a scar so um so it is important that you know babies that are born with cleft lip or palate they need a lot of um a lot of medical assistance because there's there's surgery involved also feeding can be an issue a long time ago and babies were born with cleft liver palette they often didn't survive their infancy because they couldn't feed so um so luckily thank goodness for modern medicine because you know this is the result and it's absolute really amazing okay so facial development development of the human face occurs primarily between the fifth and eighth weeks of you know of the prenatal period so the face develops from the frontal nasal process and the first branchial Arch so we talked about the first brachial Arch and how that forms the lips and some of the bones around the teeth and the the jaw but it also develops from the frontal nasal process which is another part of the embryo so forward growth of mouth structures produce striking age-related changes so at one month of prenatal development the overhanging forehead is the dominant feature so we saw the the pictures of the embryo versus the fetus and you know and there is quite a large forehead or forebrain at one month and then at two months rapid growth of the nose and the upper jaw occurs the lower jaw growth is kind of later than the the upper jaw and then at the three month Mark um you know the the you know you have a fetus that resembles a human but with a disproportionately a large head and then four months the face looks human the hard and soft palates differentiate there's formation of primary dentition has begun and then during the third trimester the the fat is laid down in the cheeks you know when we're talking about facial development and these are also called sucking pads and that just helps with the you know the baby once they're born with the the nursing functions okay and then tooth development so this is you know as Dental professionals this is kind of what we're most interested in so when the embryo is five to six weeks old that's when we see the first signs of tooth development and um and the first signs of tooth development that we see are in the mandibular anterior region so when we say mandibular we mean the lower jaw and the anterior region so those incisors in the front of the of the lower jaw and then the next area we see that develops is the maxillary anterior region so these would be your upper front teeth that we see develop next so first the lower than the upper first the mandibular then the maxillary so tooth development it progresses towards the posterior so it's going from the front to the back basically and it does that in both Jaws both the maxillary and the mandibular and then by the 17th week all the primary teeth are developed and the even the permanent teeth development has occurred at the 17th week in utero so before the baby's even born all the primary teeth are developed and the permanent teeth development has begun as well now that doesn't mean that a baby is born with all these teeth they're still you know underneath the gums they're not erupted yet you know although sometimes babies are born with a tooth or maybe two teeth it just depends I've had a couple of patients over the years that tell me you know I was born with a tooth which you know it happens it's rare but it does happen but usually the the baby is born with no teeth they just haven't erupted yet they're developed they're there uh they're you know it just takes more growth and maturation before they erupt okay so quick learning check uh the Primitive math is called the can you guys think back and remember what that is and then the structure arises from which branchial Arch and that branchial Arts is also known as the what brachial Arch so most of the brachial arches have two two different names a number and a name basically so let's let's see what the answers are so we said the uh the Primitive math is called the stomidium and this structure arises from the first bronchial Arch and that Arch is also known as the mandibular branchial Arch okay okay so let's talk about developmental disturbances these are anomalies which means something out of the ordinary and they're caused by genetic and environmental factors so you know environmental factors pregnant women have to be very careful that they don't take certain medications or that they're not exposed to certain substances because that can result in developmental disturbances of the fetus so that's why you know we want pregnant women to be very careful okay um so genetic factors um so the most common genetic factor of concern is tooth and jaw size so um so a child might inherit a large Jaw from one parent and small teeth or a small jaw and large teeth from you know if you have a father that has a large jaw and a mother that has small jaw and small teeth you know the the child might inherit the large doll in the small teeth in which case there's a lot of spacing in there you know if they inherit maybe a small Jaw from their mother but large teeth from their father then they might have you know malocclusions because they have these large teeth being kind of crammed into a very small space so so that's that's something that's of concern and you know that's basically how the field of Orthodontics has become has developed you know and become necessary so so there can be a large discrepancy in size and the relationship of the teeth and all and this can cause malocclusion which is poor tooth position or contact and that's you know when you have malocclusion you really need to have that corrected not so much for the looks although it does make for a prettier smile but for the function because if you have crowded teeth and you can't clean them well that can lead to gingivitis and periodontal disease and all kinds of issues so um so one I love dogs so you'll see a lot of dogs in my lectures uh but one one way we see this in action is with um smaller dogs so a lot of smaller dogs have been bred you know by dog breeders to be small uh they used to be bigger but they take them down in size with each generation so so what happens with a lot of small dogs is they still have the teeth of bigger dogs you know they've inherited bigger dog teeth from you know their mother or their father or whoever and then all these teeth can't fit in their smaller Jaws so they wind up with this kind of malocclusion so this this can happen with humans as well and it's um you know kind of it sets you up for kind of poor oral health for for your lifetime if you don't have it corrected okay um so environmental factors anomalies are caused by teratogen so a teratogen is some sort of advice excuse me adverse environmental influence so some sort of influence that's not good for the um for the embryo or the fetus so like we said an anomaly is something unusual a lot of times it's something that's not healthy so um so teratogens these can include infections drugs or exposure to radiation so for instance if the the mother has some sort of infection that can lead to you know the infection can affect the fetus and it might lead to like a damaged heart valve for the fetus or you know sometimes if a mother has a high fever it'll affect the teeth of the of the child you know sometimes you can see like a white line through the teeth like during the you know the mother had some sort of fever during um the developmental period when the teeth were developing so you can clearly see evidence of it drugs um certain drugs will affect the development of the baby there was a drug called thalidomide back in the 1960s that a lot of women in Europe took England and Germany in particular and the babies had all kinds of birth defects you know especially with their their arms and their legs but even you know some sometimes it was fatal so so certain drugs you know pregnant women really need to avoid because it can be terrible for the fetus it can um you know develop all sorts of birth defects as a result and exposure to radiation can also harm the fetus so so again when you're pregnant you have to be very very careful so drugs taken during pregnancy may cause birth defects and this can include both prescription or over-the-counter drugs so women really need to be careful even taking aspirin you know aspirin is a blood thinner that can be detrimental to the fetus cold tablets a lot of cold tablets um have some sort of amphetamine in them alcohol even antibiotics pregnant women can take certain antibiotics but um some antibiotics they can't uh one one example is tetracycline this is an antibiotic antibiotic and if it's taken during pregnancy it will cause the child to have yellow gray brown stains on their teeth primary or permanent teeth actually and this is um you know and these are permanent stains it's not something you can bleach out so so tetracycline you really have to be careful if you have a pregnant patient you can't use tetracycline with them or else it could lead to an issue you know for the child later on and and you can't prescribe tetracycline to to young children either because they like again it can stain their their primary teeth or their permanent teeth so women of child bearing age they should avoid teratogens if they miss their menstrual period you know even if they don't know for sure that they're pregnant they need to be careful so the mother's dental health is a concern turn when they're pregnant because even toxins from a dental infection can pass to the infant there's been a lot of correlation between between periodontal disease in pregnant women and low birth weight and premature delivery it actually goes below Beyond correlation to to causation even when a mother has periodontal disease they produce certain chemicals that that can cause premature premature contractions of the uterus and this leads to uh you know premature delivery and a low birth weight baby not to mention bacteria from the oral cavity if you have bleeding gums like you would have with gingivitis or periodontitis bacteria from the oral cavity can get into the bloodstream and you know the mother's blood goes through to the fetus while they're pregnant so so there can be a lot of you know a lot of issues so it's really important that that mothers or people even trying to get pregnant should have you know Dental Care um and a fever and a mother during pregnancy may leave marks on the fetuses developing teeth which then we see later after they erupt when they're older and so it's really critical that the you know the the mother or the pregnant woman even before she gets pregnant has good nutrition because it's critical for the developing child um you know certain nutrients like folate for instance um it's it's critical in the development of the child and if they don't have certain nutrients they could develop things like spina bifida for example so um so it's very important to have that good nutrition okay so this is tetracycline stain this isn't a terrible case of it but you can see these teeth even if you bleach them you won't get rid of this yellowness or this brownness so this is what the tetracycline stain looks like so a lot of people um my age before they really identified that this was an issue um they you know they have this kind of stain and really the only thing you can do for this is maybe like veneers or crowns to to make it look better because again it it won't bleach out and it's you know this isn't a terrible case of it but I've seen like much more staining as a result of tetracycline okay so which of the following drugs is considered a teratogen capable of causing anomalies in the developing teeth of fetus do you guys remember okay so that's actually going to be tetracycline um so so Tylenol is considered safe for pregnant women malox Benadryl those haven't been noted as any sort of teratogen but tetracycline is because it can develop permanent staining in the tooth of the or the teeth of the um the fetus as they grow up and become a child okay so facial development after birth so as you know a great deal of facial development takes place throughout um you know throughout childhood um so face changes from newborn to adult so after the immediate postnatal period most of the facial growth takes place in growth spurts so you guys have probably heard of growth spurts you know somebody you know might be five foot at the beginning of the summer and then at the end of the summer they're five foot six or something so that's That's a classic growth spurt and a lot of times you see that during adolescence and it's particularly pronounced with uh with boys you know they seem to grow a lot very quickly so um so these growth spurts are you know how most of facial growth takes place as well so the facial bones these grow and reshape through deposition of new bone and resorption of existing bones so a lot of people kind of consider bone kind of a static entity but it's really not it's very Dynamic bones are always growing and reshaping even when you're older you know after you're done growing um you know there's there's still deposition of new bone and resorption of existing bone or old bone because you know the old bone becomes not as not as functional so the deposition of bone is achieved by osteoblasts and these are cells that create new bone so um so I always think of you know new bone osteoblasts the B is for bone then the resorption of the bone is achieved by osteoclasts so these resorb bone or breakdown bone that you know that that you don't need or may not be as functional so um so this is a you know this is a kind of fun or um process that takes care takes place in the body you know all the time throughout your lifetime but but a lot more during these periods of growth so um so modeling bone modeling or sometimes is called displacement this describes bone changes which take place along joints we also call joints articulations we have you know joints in our skulls we have uh you know joints all over the body so so they take place along joints as they increase in size and shape to keep up with growth of the surrounding tissue so the bone is always modeling you know or Remodeling and remodeling occurs in response to forces placed on the tooth within a tooth socket so so especially if you're in in Orthodontics if you have braces a lot of remodeling is occurring with the um with the bone within the tooth socket and that's how teeth move and they become stable in their new position so um so when force is applied to a tooth the bone in in front of the tooth will be resorbed and the bone will be deposited behind the tooth to fill in the space so so Orthodontics again is based on this phenomenon so let's take a look at that so you can see the the growth from the newborn to to adult you can see there's a lot of changes the jaw you know becomes a lot more prominent by by the time you reach adulthood and the head is you know it's much larger you know babies have much larger heads in proportion to the rest of the body than an adult does so you can see everything grows the nose grow the ears grow the forehead kind of becomes more proportionate to the face and the jaw jaw certainly grows quite a bit okay so how does the jaw grow well what happens is we have resorption on the the anterior portion of the mandible uh resorption of bone and then we have deposition of new bone on the posterior of the mandible so so in front of the mandible we've got resorption of the bone behind the mandible we have deposition so this helps the jaw grow you know kind of backwards and sort of upwards as well and that's how it enlarges so so this deposition takes place in these growth spurts but you know but it's kind of in a layered kind of way so it doesn't all you know you don't get a couple inches of bone overnight you know might seem like it but you don't okay and then here's how Orthodontics work so Orthodontics works by uh you know these these bands and brackets um well the brackets and the wire uh what they did was they create a tension zone so if you guys have ever worn braces or even Invisalign you know when you get new trays or when they tighten the wires you can feel it it really feels like the teeth are being pushed or pulled so what they do is they create a tension zone for the teeth and then they create a compression zone so this tooth is being pushed towards the compression Zone and when it's pushed towards the compression Zone you have bone resorption in that area and then this tension zone is where oops where new bone is being deposited in this area so this will move the tooth incrementally you know you want to move it very slowly because you don't want to destroy bone without creating new bone you move it very slowly but the tooth you know eventually the tooth will get to the new um you know more more beneficial space for it and and it'll be firmly in place you won't lose bone as long as you do it slowly so you get this bone resorption the bone breaks down in the compression zone so that the tooth can move over and then as it's moving new bone is being deposited in this this tension Zone to hold the tooth in place in its new place okay so let's talk about the life cycle of a tooth this is called odontogenesis this is tooth formation it starts with that okay so odontogenesis or tooth formation this is divided into three primary periods so we have the growth period the calcification period and the eruption period okay so um so the growth period this is the further divided into three more stages so they divide it down quite a bit um so uh so the growth period is divided into the bud cap and Bell stages so we'll talk about all of those so the bud stage this is the very first stage of the three stages of the growth period and again the growth period is the first stage of the three stages of odontogenesis okay so um so the bud stage begins at all okay so this is also called initiation and this is the beginning of development for each tooth it starts with the formation of the dental lamina I will see a picture of this in a minute so the dental lamina this is a thickened band of epithelium so you probably heard of epithelium before it's you know tissue cells it's a certain type of tissue cell so the dental lamina is just a thickened band of that so immediately following this formation of the dental lamina the tooth buds for the primary teeth are formed and there's 10 enlargements of the dental lamina in each Arch so why you know that results in 20 tooth buds all together 10 up top 10 down bottom so and that correlates with you know children have 20 primary teeth normally um 10 maxillary primary teeth and 10 mandibular primary teeth so each tooth Bud eventually becomes a tooth okay so then the dental lamina continues to grow in each arch in a posterior Direction so the tooth buds for for permanent molars develop you know back in the posterior um and then sexadenius teeth these are permanent teeth that replace primary teeth so succidaneous tooth is a permanent tooth and it comes in it succeeds or replaces a primary tooth so for instance your maxillary incisors your maxillary permanent incisors are succidaneous teeth because they replace your maxillary primary incisors so they're succidaneous now your molars your first second and third molar they don't replace any primary teeth you do have primary molars but those are replaced by the permanent premolars your your permanent molars are not they're not replacing any primary teeth or baby teeth so they're not considered succidaneous teeth because they don't replace anything they're just new teeth basically so the succidaneous teeth again these are permanent teeth that replace primary teeth and they develop from tooth buds that are deep in the Dan deep in the dental lamina and they're lingual to the primary teeth so so they're deep obviously they come in after the primary teeth they they come in at some point and they push out the primary teeth when the child is you know when they're growing up okay so here's the dental lamina so you've got the oral epithelium right just a type of cell and then you have this thickened area and that's that's the dental lamina and then within the dental lamina you have the tooth bud and you're going to have um or the developing fetus will have 20 tooth buds 10 up 10 upper and 10 lower 10 maxillary 10 mandibular and then you've got um the the developing alveolar process so the alveolar process that's the bone that's surrounding the tooth so so the um so the oral epithelium thickens becomes the dental lamina and then the tooth buds are within the dental lamina and then you've got the Ecto mesenchyme which which you don't have to worry about we'll talk more about that later okay so um so that was your bud or initiation stage next we have the cap stage so so this is also called proliferation so when we talk about proliferation that means something's increasing in number so in this cap stage the cells of the tooth grow and increase in number so growth causes regular changes in the size and the proportion of the developing teeth they you know they're getting bigger they're getting um you know they're kind of getting their final shape at this point the solid looking tooth Bud changes into a hollow cap like shape and we'll see a picture of that in a minute and that's where the cap stage gets gets its name basically so the ectoderm layer remember the ectoderm is the outer layer this differentiates into the oral epithelium and the oral epithelium will become the enamel organ so this will eventually form the enamel of the developing tooth so so you guys know that your teeth are covered in enamel or the crown of your tooth is covered in enamel so so this is you know the ectoderm layer differentiates differentiates in the oral epithelium and this becomes the enamel organ and that's what's going to basically form the enamel of your tooth so where does your enamel come from the enamel organ okay and that comes from the outer layer or the ectoderm layer um now the mesoderm layer the middle layer this differentiates into connective tissue also called mesenchyme and this will become the dental papilla so the dental papilla will eventually form the pulp and the Dentin of the tooth so underneath the enamel is the Dentin right so so the Dentin forms most of the tooth really you know you have the enamel on the crown of the tooth and then beneath that you have the Dentin which makes up you know the inner part of the crown and then the root of the tooth then in the very very middle of the tooth you have the pulp and the pulp is the there's a hollow part called the pulp chamber and that contains the nerves for the tooth and the blood vessels for the tooth and we will see pictures of all this so you'll understand better so just remember if you're asked you know what where does the pulp in the Dentin of the tooth come from or how does it develop it comes from the dental papilla the enamel organ creates the enamel of the tooth and then the dental papilla creates the pulp in the Dentin of the tooth so is the enamel organ and the dental papilla develop the mesenchyme which is just the connective tissue surrounding them this condenses to form the dental Sac so the dental Sac will eventually give rise to the cementum and the periodontal ligament around the tooth so so again I know these a lot of these terms are new to you they'll make more sense as we go along okay so um so here is the the cap stage so we go from the um the bud to the cap stage but is the initiation stage and the cap stage is next then we've got the um the uh this is called the enamel knot the enamel organ okay the enamel organ is what is going to become the enamel which covers the crown of the tooth then we have the the dental papilla right and just a reminder the dental papilla is going to form the pulp in the Dentin of the tooth okay then we have the dental sac the dental Sac is going to form the pair oops I'm sorry is going to form the cementum and the periodontal ligament of the tooth so if if I were to ask you you know what forms the cementum and the periodontal ligament you're going to say the dental Sac does okay and then down here again we have the developing alveolar process that's the bone around the tooth um and then the successional dental lamina um and the the primordium of the succidaneous teeth so so this occidentus teeth those are permanent teeth so those you know those are kind of hanging out up here okay and then um so let's look at the the tooth structure real quick so you have a better understanding of these you know various uh terms that we're looking at so um so the crown of the tooth the crown of the tooth is what you see in the mouth right so the crown of your tooth is covered in enamel for the most part so this is the enamel and that comes from the the enamel organ right so um so beneath the enamel we have the Dentin so the Dentin is the material it really makes up most of the tooth so so in the crown area the Dentin is covered by enamel and then when you go into the roots of the tooth this is all dent in here this is all Dentin right and the Dentin on the root of the tooth oops sorry about that the Dentin on the root of the tooth it's covered by a substance called cementum so this is the cementum cementum is just like a rough substance and it allows connective tissue to connect to the root of the tooth so the cementum where the we have the cemento enamel Junction so this is where the enamel stops and the the layer of cementum starts so the layer's momentum goes all around the outer part of the root of the tooth and it allows this periodontal ligament to attach to the tooth so this momentum is all around the root of the tooth and then right inside the cementum is the Dentin and then if you go up to the crown of the tooth right inside the enamel is the done okay and then when we go to the very center of the tooth this is where you have your pulp cavity so the pulp cavity it's it's a hollow chamber but it contains blood vessels you can see the red and blue that's uh you know arteries and veins and then the yellow or nerves so the pulp cavity is really it holds everything that keeps the tissue alive the blood vessels and the nerves and um and that's located here so you can see some teeth have more than one root you know they have two or three Roots this this tooth has two Roots so the pulp chamber kind of goes down into both of those roots and you can see here's a maxillary tooth that just has one root so you've got the pulp chamber just you know kind of follows the root of the teeth so um so anything um you know below the enamel is considered the root of the tooth and then you have the the crown of the tooth is from the cej to the to the top of the tooth and then you have your alveolar process this is the mandibular alveolar process because this is lower tooth you know all this is the alveolar process all around and then we've got the maxillary alveolar process because this is a maxillary tooth it's kind of hanging downwards right so that's all the the parts of the two so let's just go back here for a second so the enamel organ okay that becomes the enamel of the two this part okay go back again that oops the dental papilla Dental papilla that becomes the the Dentin and the pulp of the two that's the dental papilla then you have the um the dental Sac remember the dental Sac that gives rise to the cementum and the periodontal ligament so the dental Sac that you see here kind of going around the tooth that purple area that is going to be the cementum okay and then the periodontal ligament is here I don't think it's labeled on here but it's like this pink area that's the periodontal ligament and it helps hold the tooth in place okay all right so let's do a quick learning check the blank layer differentiates into oral epithelium which becomes the blank which will eventually form the enamel of the developing tooth all right think about that for a minute then the next question the blank layer differentiates into connective tissue or mesenchyme which become the blank eventually will form the pulp and the Dentin of the tooth so what did we say forms the pulp and the Dentin and then the blank condenses to form the blank and this will eventually give rise to the cementum and periodontal ligament so um so I'll give you guys a second think about that and let's take a look at the answer so the answer is first of all we have the ectoderm remember Ecto when you see that think outer outer layer so the ectoderm layer differentiates into oral epithelium which becomes the enamel organ and this will eventually form the enamel of the developing tooth the enamel covers the crown then we have the mesoderm layer and our middle layer this differentiates into connective tissue or mesenchyme which will become the dental papilla and the dental papilla will form the pulp and the Dentin and I like to use little memory tricks you know it helps me so when I see Dental papilla I think Denton pulp that kind of helps me remember enamel organ enamel Dental papilla Dentin pulp then we have the mesenchyme and this condenses to form the dental Sac so the dental Sac will eventually give rise to the cementum and the periodontal ligament so hopefully um you know maybe take a little while to remember all that but hopefully you guys understand the basis of it okay um so again we're still in the growth period and like we said the growth period consists of the the bud or initiation stage and the cap stage and our third stage is the Bell stage so now we're on the Bell stage so during the Bell stage the cells differentiate and become specialized and this is known as histo differentiation so they're becoming different and and specialized you know what are they going to do when they grow up kind of thing so epithelial cells come from a myeloblasts and ameloblast are enamel forming cells okay so the epithelial cells they become ameloblast which form the enamel or you know what's on top of the crown of the tooth or the outside of the crown of the tooth then we have peripheral cells of the dental papilla and these will become odontoblasts so remember we said the dental papilla is going to form or Dentin and the pulp so um so the Dentin comes from odontoblast these are your Dentin forming cells then the inner cells of the dental Sac these become cemento blasts so remember we said the the dental Sac forms cementum so the dental Sac it makes sense that it would become the inner cells of that would become cemento blasts so they can form that cementum so so the dental organ assumes a bell shape the dental lamina this connects the dental organ to the oral epithelium this breaks apart during this stage so um so during this stage the basic shape and size of each tooth are established by morphodifferentiation so um so histo differentiation the cells becoming specialized and morphodifferentiation means they're they're taking on a different shape and size so um so the dental enamel and cemento enamel or I'm sorry Denton enamel and cemento dental Junctions these are the um c d e j and c e j these are formed and act as a blueprint for the developing tooth okay so um so this is um those are the blueprints basically for the developing tooth it gives them the basic idea for the shape of the tooth and then emiloblasts these deposit enamel and odontoplast deposit Dentin so remember ameloblaster enamel and adanta Blaster your Dentin and these give the completed tooth its shape and size okay and then the process starts at the top of the tooth and moves downwards towards the root of the tooth so the development of the root begins after the enamel and the Dentin formation has reached the cej and that's the cemento enamel Junction so in our cells of the dental Sac these differentiate into cemento blast and these produce the cementum to covering the developing root tooth so let's uh let's take a look at that so you've got the oral epithelium remember we said it becomes thickened and it becomes Dental lamina and then you have the the bud of the enamel organ here and then we have the we've got a permanent tooth bud and then we've got the ameloblast which form enamel and we've got the odontoblast which form Dentin okay and then we've got the the enamel organ which will eventually form the enamel of the tooth and the dental papilla here which will eventually form the um the pulp and the Dentin of the tooth I'm sorry I kind of went out of order here I should have gone a b c and then D so so we've got the bud of the enamel organ and then this differentiates into the enamel organ and the dental papilla so the enamel organ becomes enamel the dental papilla becomes Dentin and the pulp of the tooth and together these are known as the tooth germ then we get down to letter A we can see the permanent tooth bud is developing and then we've got the ameloblast which eventually form enamel cells and then the uh the Dentin or the Odana blasts which form Dentin and then we can see the the tooth is starting to take shape here so we've got the unmeeler blast which are forming the enamel and then the adanta blasts which are forming the Dentin sometimes you'll see it with the E sometimes not Dentin or dentine they're kind of synonymous and then we've got the the pulp of the tooth in the middle and then the epithelial root sheath so you can see as how the tooth starts to develop over time okay calcification so this is the process by which the structural outline formed during the growth stage is hardened so so during this growth stage you you know you kind of get the basic structure of the tooth but you know it needs to get it needs to become hardened or else you know you can't have soft teeth basically they won't function well so so they become hardened by the deposit of calcium and other mineral salts so calcium is really the the major mineral that hardens them so the enamel it's built layer by layer by ameloblast so it's not like the ameloblasts come in and just lay down one big layer and they're done no the enamel is is very very layered so it you know it's it's very gradual and um and the ameloblast they work outward from the dental enamel Junction starting at the top of the crown and spreading downward over the sides of the tooth okay and then uh pits and fissures so so you probably you know have noticed on your teeth you have you know pits and fissures in your teeth so pits are like little small holes fissures are like deep like little grooves in your tooth and you know that's normal that's a developmental feature of the teeth so um so if you have a multi cusp teeth they have a cap of enamel they develop over each cusp and then the cusps coalescer come together and form a solid enamel covering over the occlusal surface of the tooth but these you know these fissures are created when the cusps kind of come together and those are a little bit of a weaker point of the tooth because the enamel is not quite as thick so so the pits and fissures are formed during this process so a pit results when two developmental grooves cross each other and they form a deep area and this is really it's too small for a toothbrush bristle to clean so so a lot of times you know you could develop cavities in these areas because they can't become cleaned out nowadays they kind of they put sealants in there so that bacteria can't get in there and cause decay um and then a Fisher this is a fault along a developmental groove on the occlusal surface that is caused by incomplete or imperfect joining of the Lubes during tooth formation so a fault is like or a fissure is like a line it's a line across the chewing surface of the tooth you know on the posterior teeth and again it's where the the enamel joins from from two different cusps and it's not perfect you know you have kind of a weak area there so again A lot of times they'll put sealants in those areas because they are at risk for Decay so um so enamel may be thin in these areas and more at risk for Decay but luckily we have sealants to correct that okay so here's um so here's a fissure fissure is a long line and then a pit is like a little dot so um so a pit is kind of hard to see Pits on here that might be a pit but this is you know these are the fissures so basically the enamel it it forms on each cusp these are the cusps here's another cusp another one another one so so the enamel forms on each cusp and then it joins together with the enamel of another tooth but the problem is you you have this fissure where they join it's sort of like a suture or a joint and the enamel just isn't quite as thick so what they've done to um to help these areas that are vulnerable and then the pits are kind of like in you know kind of and these like joining areas of the fissures so what they do is they put sealant or composite material in these fissures these deep areas and then it makes it you know you can clean it better with a toothbrush and um and they're not as vulnerable to Decay so I assume you guys a lot of you guys probably have sealants on your teeth okay um so the eruption of primary teeth eruption is the movement of the tooth into its functional position in the oral cavity so you know the eruption just means your tooth is coming into to place the place where it's supposed to be so that you can um you know chew and eat and speak and all the all the functions of the teeth can take place normally now eruption of primary dentition this is you know what we call baby teeth this takes place in chronological order and then it's followed by the permanent dentition later or the adult dentition so the process involves active eruption and this is a vertical movement of the tooth so think about it the tooth is coming up into the mouth it's moving upwards you know it's breaching that gingiva and then it's finally erupting into its its final place in the mouth so this involves actually many stages it's pretty complex um and then disintegration of the tooth this causes inflammatory response which is commonly known as teething so it can be very very uncomfortable for the baby and if any of you have children or you know younger siblings or whatever you might remember a time when their teeth were coming in and you know because of this inflammation it can be very uncomfortable so the baby can you know cry quite a bit because it does you know it hurts so um so no one can really specify the exact forces that push the primary teeth through the soft tissues um you know scientists haven't really established the exact Force but they know that it happens you know and it happens pretty much to everybody okay and then uh shutting shedding is also known as exfoliation you know when your baby tooth falls out that's shedding or exfoliation and again this is a normal process by which primary teeth are lost as the succinaneous teeth develop so the sexodenus teeth these are permanent teeth that replace a primary tooth so what happens is when that that adult tooth comes into the mouth it kind of pushes that baby tooth out of the way right and then you wind up losing the baby tooth which is what's supposed to happen so so osteoclasts remember we talked about osteoclasts and these are the cells that break down bone or Resort bone so osteoclasts you know have a hand in this shedding or exfoliation what happens is these osteoclast cells they cause resorption of of the primary tooth root and and this begins at the apex of the root you know all the way at the tip of the root and it continues up towards the crown of the of the tooth so um so the tooth is eventually lost due to lack of bone support so so if you've ever lost a baby tooth which I'm sure you have you may or may not remember you know the tooth kind of becomes more and more Wiggly uh right before it's lost so um so this resorption of the tooth root by the osteoclast that's what because causes the tooth become more and more mobile or Wiggly you might say and then finally the tooth just comes out all together so shedding of teeth or exfoliation of these primary or baby teeth is intermittent so um you know so children might lose a few teeth within the span of a month and then they might not lose any for a while so there's we've got eruption and exfoliation charts in here that you guys can look at um so so shedding is intermittent at the same time that the shedding takes place as these osteoclasts are breaking down the um the primary tooth root osteoblasts are actually replacing that resorbed bone so it's very very Dynamic and then odontoblast and cemento blast are replacing resorbed portions of the root so the osteoclasts will break down bone and the root of the tooth and then the osteoblasts they come in they rebuild the the bone around the permanent tooth and then the adanta blast and the cemento blast they they rebuild portions of the primary Mary root or I'm sorry the the permanent tooth root so the primary twos it may become tight after initially being loose sometimes you see that a primary tooth will get a little bit loose and then it'll tighten again but eventually it will become loose and then exfoliate ultimately as the osteoclasts work work at breaking down the bone and the root of the tooth so it is shed okay and then next will come the eruption of the permanent teeth so the process of eruption for succidaneous tooth which is the permanent tooth it's the same as for our primary tooth so so permanent teeth they actually erupt lingual to the roots of the shedding primary anterior tooth or between the roots of the shedding primary posterior tooth so so when you're talking about the the front teeth or the anterior teeth the permanent teeth will come in behind those closer to the tongue when you're dealing with anterior teeth and the permanent teeth when you're talking about posterior teeth what's going to happen is the permanent teeth are going to come up between the roots of those primary molars or baby molars so when a permanent tooth starts to erupt before a primary tooth is fully shed then you can have problems problems may occur so that's when you need to seek an orthodontic console so that you don't have malocclusion as a result because you know sometimes you guys may have experienced it or had kids that you've seen with it but the the permanent tooth might start coming in and the baby tooth just isn't ready to leave yet so so sometimes you have to go to the dentist and have it extracted um you know but but something not normal is going on so um so you really need to have it checked out if that's the case okay so here's uh here's a primary dentition chart so you can see um like if you look over here on the right you can see how the the permanent teeth are coming in you know in the anterior they're coming in lingual to these primary teeth and in the posterior where the primary molars are you have the permanent teeth coming up in between these molars so when the primary or when the permanent teeth are erupting they push they help push the primary teeth out and the primary teeth should be ready to come out because the osteoclasts breaking down the root of the tooth and the bone around the tooth okay so this just shows you what's happening five months in utero seven months in utero you know you have all these developing teeth and then birth you know usually people aren't born with teeth occasionally they are but usually not then you can see around six months uh you know it could be between four and eight months that's one year um anterior teeth start coming in usually the mandibular anterior or lower anterior teeth come in first followed by the the maxillary anterior teeth then you start to have you know some of the um more posterior teeth coming in so um so that's just your basic uh kind of eruption chart for um for primary dentition and then this kind of gives you the um you know the the eruption dates and months for the child and the shutting dates as well so um so you can see in the primary dentition we have one central incisor one lateral incisor one canine and then a first and second molar in each quadrant so so that means that the there's 20 baby teeth or 20 primary teeth right and um and these molars the first and second molar those are replaced in the adult dentition or secondary dentition by the first and second premolar right so um so in the permanent dentition your central incisor your lateral incisor your canine and your first and second premolar those are considered succidaneous but then your adult molars come in behind where the baby molars were so those are not considered succidaneous so again we'll we'll get more into that um but you know you can see the um the upper teeth and the lower teeth the um the central incisors for the lower teeth come in about six to ten months and then the upper teeth about eight to twelve months so you can kind of look at the chart and figure out what the approximate dates are and then the lateral incisors for the mandibular 10 to 16 months for the maxillary 9 to 13 months so you know usually it's the the mandibular first followed by the maxillary but not not necessarily always and then the teeth start shedding around six to seven years old the um the central incisors sorry the central incisors will shed first and then um last you'll you'll probably have the canines and the second molar shedding so it just depends okay and then um so mixed dentition uh usually when the you know we'll see mixed dentition when the child's about seven years old as soon as uh any of those permanent teeth start to come in that's when you have mixed dentition um so usually it happens usually happens around six years old really the um the first permanent molar will come in around six years but around six to seven years is when you'll start seeing the shedding of the the baby teeth or the primary teeth and you can see as the child gets older they have more and more permanent teeth and fewer primary teeth and then um usually when the child's about 12 years old that's when the the second adult molars or second permanent molars will come in and then the third molars usually will come in late teenage years early 20s so all right and then here's the uh the permanent tooth eruption chart so you can see the the mandibular Central incisors are usually the first permanent teeth in at six to seven years old along with the the first permanent molars but the mandibular and maxillary they come in about six to seven years old then you have the maxillary Central incisors at seven to eight and the mandibular lateral sizers at seven to eight so um so you guys will you know you don't have to memorize this all at once you'll start seeing it again and again and again and become more more familiar with the information as we go along okay and that is it for uh for chapter eight part one um I I hope you're not too overwhelmed with the information I know it's a lot to start off with at first but um but again we're going to be going over a lot more information and it'll kind of all start to come together you know in the next few weeks and and you'll be seeing it in other classes as well so um so thank you for listening I hope you all learned something and hopefully enjoyed it and I will see you in class thank you so much bye bye