 Hello everyone, welcome back to another session in dentistry and more today's topic in orthodontics is cephalochordal gradient of growth. So the pattern of growth in human is different. So there is a difference in the relative rates of growth between one part of the body to the other. So the different parts and organs of the body grow at different times and to different extents. This is termed as differential growth. So the differential growth can be expressed through one is Scammon's curve that we already discussed Scammon's curve where I explained you about the neural tissue, genital tissue, general tissues and the lymphoid tissues. That was postnatal growth of all these tissues, how they are getting accelerated at different age throughout the postnatal period. The next one is cephalochordal gradient of growth. So this cephalochordal gradient. So cephalic means we know it is about the head and caudal is the lower portion. So how the head and the remaining portion are proportioned each other during various stages of growth or through the ears from the fetus and to the adult. So there are difference in the relative rates of growth between one part of the body and the other. So overall body proportion changes as one grows from fetal life to adulthood. So there is an axis of increased growth extending from head towards the feet. So this is the head which is changing as the age progresses or once the persons moving to adulthood. So you can see the proportionate change of head, limbs and the body torso. So the head is in advance of the trunk and the trunk in advance of the limbs regarding the growth and maturity at all times. So in fetal life, so this is three months fetus. So you can see the head is nearly one half of the total embryonic life. So this is one half, I am sorry about this picture, it looks weird. Anyway this is one half of the total length that is during the two to three months of intra uterine life. At this stage the limbs are rudimentary and the trunk is underdeveloped. Then what happens then the head grows proportionally more slowly whereas the limbs and trunk grow very faster so that the proportion of the entire body occupied by head is reduced to one quarter of the body length at birth. So at birth the head proportion is one fourth, so this is one fourth because the growth of head is reduced whereas the limb and the trunk grows very faster so that the head portion has become one fourth of the total length. And during childhood what happens the pattern of growth continues with lengthening of the torso and limbs. At adulthood the head is reduced to one eighth of the entire body. So this is one eighth, this is one fourth and the half of this is one eighth. So at adulthood the head becomes one eighth of the entire body length and the lower limb occupies one half of the total length. So the lower limb occupies the one half, so this is the one half of the total length. So this is cephalocodal gradient of growth how the head, limbs and trunk is getting changed over the period from the fetus to the adult. So in phase at birth the naso maxillary complex and mantable is less developed with the cranium representing more than half of the total head. Maxilla being closer to the brain and which grows faster and its growth is completed before mandibular growth. This we had discussed in Scammon's growth curve, maxillary growth completes around 7 to 8 years whereas mandible continues to grow till 18 to 20 years. So mandible being away from the brain completes its growth later than maxilla. So maxilla by 7 to 8 years whereas mandible by 18 to 20 years. So this is related to the phase that is cephalocodal growth in phase. So that's all about the gradient of growth. So the differential growth could be expressed in two ways one is Scammon's curve and cephalocodal gradient of growth. So drawing this picture is little difficult but anyway if it is asked you can just represent the head how the head is changed from one half to one eight. So this is one half, this is one eight and this is one fourth of the limbs become one half. So these two points you can highlight and draw a neat picture. So that's all about cephalopodal gradient of growth. So I will come up with a new topic in orthodontics. Thank you.