hey everyone Ryan here and welcome to this series on orthodontics so this is my personal favorite specialty since I'm currently studying orthodontics as a resident we're gonna cover a ton of great content now the board examiners combined orthodontics and pediatric dentistry into one category in their guidelines but I think it's honestly more helpful to focus on each one individually so I've already made the pediatric dentistry series if you want to go check that out so that being said like all my videos I'm gonna focus on the highest yield things that you need to know for the exam and my hope is that these videos will help you prepare for the board exam and also give you an overview for clinical application and general knowledge so we're gonna start by talking about growth and development and I like to think of growth and development as two sides of the same coin there are two distinctly different things but they work in harmony towards the same goal the growth is all about an increase in size or number an increase in size of cells is called hypertrophy an increase in number of cells is called hyperplasia and growth has to do with anatomic things height weight length width they're all quantitative numbers now development is an increase in complexity or specialization of functions and this is more physiological or behavioral so it's more qualitative things day to day function how you learn how you act and behave and things like that Griffen development follow three basic laws there's a pattern so they're predictable changes in how a body will grow over time there's general timing ages where we expect growth and ages where we don't but there is also some variability and how an individual person will grow and develop with time so there's a pattern timing and variability one such pattern is the cephalocaudal growth gradient so this is saying that body parts closer to the cranium grow fast early on while body parts further from the cranium grow more later on so another way to think of it is the brain is the Trailblazer and everything else has to catch up later on so we can see some examples of this phenomenon in these pictures so two months in utero this baby has a head that comprises 50% of its total length but once we get to 3 to 4 months in utero now the head only comprises 30% at Birth the head is 25% and then as an adult the head is about 12% of the total height you can also look at the upper limbs versus the lower limbs so the upper limbs grow more earlier and then the lower limbs have to catch up later on in life the same can be said for the maxilla and the mandible the maxilla will fully mature earlier than the mandible does because the maxilla is closer to the cranium so one visual depiction of a typical growth pattern and timing of that pattern is thus Kamen's growth curves so these growth curves show age on the x-axis and years and tissue size on the y-axis so from top to bottom we have the lymphoid growth curve so that's your immune tissues the neural growth curve so that's like your brain then we have maxilla mandible general body tissues like bones and muscles and then finally genital tissues on the bottom so each of these has a unique pattern to it and neural tissues including the brain grow rapidly after birth the steepest of these curves and then reach near adult size by about age 6 or 7 and then it kind of levels out lymphoid tissues also grow rapidly reaching twice their sighs by age ten to note that this is a percent of adult size and so we're actually surpassing what the lymphoid tissue mass will be as an adult so we're way up here at about ten years and then they involute or shrink during the pubertal grow spurt to reach their final growth adult size at a hundred percent the genital tissues do not grow much at all until you hit the pubertal growth spurt and then they rapidly increase to that one hundred percent adult size the general body tissues grow rapidly after birth they kind of slow down in childhood and then grow rapidly again during the period growth spurt and then finally we have the maxilla and mandible and so the maxilla follows a bit closer to the neural growth curve because it's closer to the brain and the mandible follows more closer to the general growth curve because it's further away from the brain so we see that a cephalopod growth gradient manifesting in these really neat growth curves so notice how the lymphoid and genital curves after age 10 so if we mark off here and here they kind of act opposite to each other they're like mirror images the lymphoid goes way down and the genital goes way up during that growth spurt and that's because as the concentration of sex hormones estrogen and testosterone increases they drive the growth spurt and this inhibits the further growth of lymphoid tissue which actually begins to shrink eventually reaching that normal adult size so scam ins is one way then we also have distance and velocity human growth curves to represent growth over time so let's look at the distance curve first now pediatricians often keep track of their patients growth with charts the patient will stand against the wall mark how tall they are and that's your distance curve and in black it's showing how much size you've accumulated over time so that's never really gonna go down it's only gonna increase the velocity curve in gray shows the rate of growth so if you remember in physics it's showing the slope of the distance curve so if you have a big increase in a high slope in the beginning that high slope is going to be indicated by the velocity curve being way up here and then as that grow starts to taper off our velocity curve shows that as well and then once we get to that growth spurt at around 12 13 14 we can see an acceleration and growth and how the velocity increases to show that what's happening on the distance curve so the distance curve tracks actual height each year while the velocity curve tracks the change in height which allows you to more easily observe growth velocity like the growth spurt so these are specific velocity curves for boys and girls and it shows that girls hit their growth spurt earlier and mature mature earlier than boys do in general and boys mature more and later on in their lifetime so the average peak growth for girls it is at around age 12 that peak growth time for boys is at around age 14 a little bit later generally the earlier your peak growth is that means the shorter duration that growth spurt will be and the less overall growth that you will see so we looked at some growth patterns and we talked about some of the things that happen with specific tissues in humans and boys and girls now let's talk more about timing of growth so there are a number of different things you can go off of to determine how much sure someone is the easiest thing would be to go up their chronological age because everybody knows their age but that's often not a good indicator of maturity because there's variability some people mature early some people mature late so we have other things to help us judge just how much her that person is one of those things is dental age and this is based on their state of dental development how many primary teeth they have how many primary primary teeth have exfoliated how many permanent teeth have come in but this is unfortunately a pretty poor indicator of maturity the next thing we have is skeletal age and this can be measured by two methods one of them is the CBM staging which is the cervical vertebral maturation so you take a cephalo metric x-ray you look at how their a cervical vertebrae are shaped on that cephalo metric and that gives you an indication of how much her that individual might be the other popular method is not as popular anymore which is called the hand wrist method where you take a take an actual x-ray of that person's hand and you can look at the the finger bones and the wrist bones and see how those are developing to determine someone's maturity this is a better indicator of maturity but not the best so biologic or developmental age is based on certain markers of maturation like we can see here menarchy or first menstruation which occurs just after the peak velocity of growth also you can go off secondary sex characteristics like facial hair and this is the best indicator of an individual's growth status and maturity so we kind of go from worst to best in this list all right so now let's talk about how does growth actually happen so we have growth sites and we have growth centers so a site is any area where growth is occurring a center is a site of growth so growth is occurring also at centers but they also have the ability to grow independently on their own so growth centers kind of have a mind of their own and they can control their own growth and sometimes even control the growth of other growth sites as far as craniofacial structures go most of the things we're going to be talking about our sites the only true growth Center is a sin condor osis sutures surfaces and the mandibular condyle czar all sites and we'll talk more about this a little bit later so there are two main modes of growth the first one is endochondral ossification which I equate with interstitial growth so this is growth from the inside and it results in an increase in length of bones so we start with an embryonic cartilage model or template that grows first and is eventually replaced by bone so we have this zone of resting cartilage we're looking at an epiphyseal plate here and the zone of resting cartilage is at the very end of this bone so this is we're looking at an epiphysis and this is the very end of that bone so the resting cartilage will have these small little Conger sites and they're really hard to see here but they're just these little tiny chondrocyte cells nestled in cartilage then we have this zone of proliferation and so we're getting hyperplasia rapid mitotic division and it results in these columns of cells that are parallel with the direction of growth and this is in contributing to that increase in length then we get to the zone of maturation where we see hyper your fee the cells are starting to get bigger but the walls of the cells are getting thinner then we get to the zone of calcified cartilage or calcification where mineral is deposited and the conger sites are actually destroyed you can note that there are a net outlines that are missing nuclei so now we have some dead cells but with the beginnings of calcification and mineralization and then finally we have the zone of ossification where these empty spaces are invaded by capillaries that form centers of ossification they dump off these progenitor cells that become osteoblasts that's that can secrete osteoid which eventually becomes bone so an endochondral ossification bone develops from a pre-existing cartilage model and it's under more direct genetic control so we see this in at the Physiol place of long bones synchondrosis of the cranial base and also in the condylar cartilage of the mandible now the other one here is the intramembranous ossification and this I equate with a positional growth or mesenchymal growth and so this is growth from the outside and it results in an increase in thickness or diameter so now we're looking at the sides of the bone and as you get more circumferential lamellae laid down along the outside you get more diameter now at the same time bone is being resorbed by osteoclasts in the center from the inside in the medullary cavity so the bone growth stays proportional throughout childhood and adolescence so here osteoblasts are secreting their osteoid matrix directly within the connective tissue lining and then it calcifies without any intermediate cartilage at all so here bone develops from fibrous connective tissue and it's influenced more from environmental forces like stresses so this is what happens at your sutures or on the surfaces of the cranial vault the maxilla and other craniofacial structures so we'll talk more about those specifics in a little bit but I just wanted to lay the foundation for endochondral which you can and a piece apart to mean within cartilage and intramembranous within the membrane those are two big the two big modes of bone growth now there are three different mechanisms that have been proposed for growth and no one theory explains all of craniofacial growth control so we kind of have to consider all three of these working in concert so how hairy citric aim up with the suture theory this is where direct genetic control determines how bone is going to grow and bone will determine its own growth and sutures act as growth centers that push stuff apart this one is mostly debunked as false because we know that the growing brain pushes skull bones apart and new bone is laid down at the sutures in response so sutures aren't really there more so reactive they're not really proactive so they're gross sites they're not growth centers as hairy suture pointed out the James Scott came up with the cartilage theory and this posits that epigenetic birth control has cartilage pushing and pulling stuff apart so in the cartilage Theory cartilage is the growth center that determines growth and bone simply follows along now this one definitely has some truth to it if we look at this example of a condylar fracture condylar fractures usually happen on the condylar neck on the side opposite to the side of impact and then that disconnected condyle gets pulled away it gets resorbed and then 75% of the time it regenerates and 25% of the time it doesn't leading to growth problems like jaw asymmetry but how could it regenerate by itself if it didn't have some kind of intrinsic control so perhaps there is some truth that cartilage has some intrinsic growth potential and then Melvin Moss came up with the functional matrix theory and this is where this is governed by environmental growth control so chewing speaking and other functions caused the nasal and oral cavities to get bigger which serve as the primary determinants of growth for the maxilla and the mandible so here the soft tissue matrix determines growth and bone and cartilage follow that so there's really good evidence for this and it's what we used before to disprove the suture theory that the growing brain which is a soft tissue pushes the skull bones apart and the sutures are reacting to that pressure and laying down bone between those skull bones so all three theories even though suture theory is mostly proved work in concert describe the different mechanisms by which the craniofacial structures grow so some pretty cool stuff and here are the five main regions of the cranium and face we have the cranial vault the cranial base the nazo maxillary complex the mandible and then the two dento alveolar processes supporting the teeth and we'll go through how each of those grows specifically so the cranial vault is the top part of the skull that encases the brain at birth the cranial bones are widely separated by this loose connective tissue called fontanelles so these wide spaces enable delivery of the baby through the birth canal a bonus laid down along the membranes of these bones and that eventually will shrink down these spaces at which point they're called sutures so sutures are thinner spaces that separate the cranial bones in childhood adolescence and then they eventually fuse later in adult life so as the brain grows these cranial bones are being pushed apart and so in order to keep this space from opening wider and wider new bone is being laid down along these membranes and that will occur at these sutures so this is an example of intramembranous ossification intramembranous results in an increase in diameter so the entire skull is getting wider and wider and the bone will be filling in at the fontanel's and sutures to keep up with the growing brain but also you have direct opposition of bone outside of the skull and resorption or removal a bone from the inside so if we go back to this image you can imagine that in addition to what's happening at the sutures new bone is being laid down at the outside which we call a position and bone is being removed from the inside which is be called resorption so we're getting intramembranous ossification not only at the sutures but also at the surfaces as well the cranial base consists of the ethmoid sphenoid and occipital bones at the base of the skull now these three bones are initially cartilage they're part of the cod roe cranium in the fetus and they later transform into bone now we're left though with three bands of cartilage that stick around that are important growth centers called sin Conger sees so each synchondrosis acts like a two-sided epiphysial plate that we saw before so you can imagine that there's this really tiny fin zone of resting cartilage in the center and then maturing cartilage is being pushed out in either direction in order to expand the bone at that zone so these bones are being literally split apart from each other by the Simkin grossest which continues to grow and increases the length of this structure so this is of course an example of endochondral ossification because we're dealing with a cartilage model the intersteno synchondrosis will fuse and close first it's about inactive at by h3e no ethmoid by h7 and Safina occipital is the last one to become an active next let's talk about the maxilla so growth occurs at the sutures posterior and superior to the nasal maxillary complex and its connections to the cranial vault and the cranial base so this is this area right here is this cranial base that we looked at right here it's kind of like a midsagittal slice of the skull and that's that component right there the cranial vault is of course this part right here and so we're getting a position of bone at view sutures because soft tissue that's the nasal and oral cavities which are expanding are pulling this maxilla downward and forward away from the cranial base simultaneously there's also surface remodeling that includes resorption of bone anteriorly an opposition of bone inferiorly at the palate and then also at the alveolar ridges as the teeth erupt down there's also additional bone at the tuberosity posteriorly to make room for second and third molars so the ultimate result of all of this is a downward and forward translation of the maxilla away from the cranial base the mandible has some interesting steps to it so develops in the embryo just lateral to the car the cartilage of the first pharyngeal arch which is called meckel's cartilage but the confusing part is that this is not endochondral growth so meckel's cartilage isn't being replaced by bone the mandible which is here just happens to be created inter membranous Li right next to it so meckel's cartilage actually will disintegrate and contribute to the malleus incus and Pinot mandibular ligament now meanwhile while this is going on we have the condylar cartilage which develops independently and later fuses with the developing mandibular ramus at about four months in utero so here we have the condylar cartilage and here is the part that we were looking at right over here so although the cone-shaped cartilage is replaced by bone eventually its upper end will persist as a site for growth that Conell or cartilage we will see in the next slide so that mandibular Connell or cartilage proliferate and is transformed into bone as the mandible grows downward and forward again away from the cranial base so both jaws are being moved downward and forward but by totally different modes or mechanisms and this creates a gap between the two jaws into which the teeth can erupt now in addition to this endochondral ossification occur at the collar cartilage were also getting surface a position which occurs along the posterior surface of the ramus to try to match and keep up with what the condyle is doing you also get some a position at the coronoid process as well as a little bit at two chin surface resorption occurs along the anterior surface of the ramus which makes room for the second and the third molars to erupt which is opposite with what was happening at the maxilla where we had a position to give room for the second and third molars whereas here we have to take bone away in order to free up a route for those second and third molars to erupt now just like the maxilla you also get alveolar bone growth vertically as the teeth erupt into position so we're getting in the mandible a mix of endochondral ossification and intramembranous ossification now as the mandible grows it can stay at the same angle or it can tend to rotate because it has this axis at the condyle so it can either rotate open in this direction or closed in this direction so an average growth rotation is where the condylar growth roughly is equal to the amount of molar eruption so the mandible truly just grows downward and forward at roughly the same orientation as you can see here now if we have a closing rotation or counter clockwise growth that means that the growth of the condyle is greatly exceeding the amount of molar eruption that we're seeing so that would lead to a shorter lower anterior face height and a skeletal deep by tendency the opposite is opening rotation or clockwise growth this is where the condylar growth is less than the amount of molar eruption leading to a long anterior face height and skeletal anterior open bite tendency so here's a summary of everything that we talked about the cranial vault it were and will kind of focus mostly on this row here and mesenchymal is synonymous with intramembranous so we're seeing intramembranous growth at the sutures and the surfaces because there's no cartilage in the cranial vault the cranial base we see endochondral growth at the cencon josie's we also have a nominal amount of intramembranous growth that happens laterally to make the cranial base grow wider but don't worry too much about that part the maxilla has purely intramembranous growth that's at both sutures and the surfaces directly again no cartilage here and the mandible we mostly get intramembranous growth at its surfaces but we're also getting endochondral growth at that condyle which is pushing that mandible downward and forward which is a very important growth mechanism and of course there are no sutures in the mandible so that intramembranous growth is purely at the surfaces the last high yield fact that i want to cover is a general trend and we talked about all the different regions of the cranium in the face and each of those skull bones exists in three planes of space there's width length and height or more commonly referred to as transverse anteroposterior or AP and vertical and these will come up all throughout the series so generally transverse the transverse dimension stops growing first at around age 10 to 12 then AP at 14 to 16 and finally vertical at eighteen to twenty or even further on into later adult life there are exceptions to this but this is the general overarching trend that drives many treatment decisions that we'll cover later in the series so that's it for this video thank you so much for watching please like this video if you enjoyed it and consider subscribing to this channel for more on dentistry if you're interested in supporting this channel and what I do please check out my patreon page a huge thank you to all of my patrons for all of their support you can unlock extras like access to my video slides to take notes on and practice questions for the board exams with explained answers so go check that out the link is in the description thanks again for watching everyone I'll see you in the next video