 Hello everyone, welcome back to a new session in dentistry and more. Today's session is about dentine, so we will be covering this under a few sessions. So the first session is about dentine, its formation, its structure and little details about the dentinal reviews and second part is about various types of dentine and the last session we will be covering about the theories relating the dentine transmission of nerve impulses. So let's see one by one, so dentine as we all know it is a tooth layer basically the second layer of tooth which provides the bulk and general form of the tooth and it begins to form slightly before the enamel and it determines the shape of crown including the cusp and ridges and also the number and size of the roots. So let's get into the details of dentine. So dentine the heart structure of tooth just like enamel which is physically and chemically it closely resembles bone and it is said to be a living tissue. Then enamel is not a living tissue it is mostly a vascular, acellular but dentine is a living tissue since tubules present in it contains processes of specialized cell which are odentoblast okay so odentoblast so since it has odentoblast which is known as living tissue we can say that it is a living tissue unlike enamel. So main morphological difference between bone and dentine is that some of the osteoblast, osteoblast are the bone cells exist on the surface of the bone and when one of the cells become enclosed within its matrix it is called an osteocyte okay but the odentoblast cell bodies remain external to dentine okay but their processes exist within the tubules and dentine but the cell bodies remain external to dentine the osteocyte is not there in odentoblast there is no odentocyte in osteocyte it is nothing but when the cell becomes enclosed within its matrix okay but these odentoblast cell bodies remain external to dentine that is a basic difference between bone and dentine or we can say osteoblast and odentoblast we have osteocyte in bone which is enclosed within the matrix and stages of tooth development we have studied in detail the stages of tooth development in enamel it's almost same nothing is different only thing is the odentoblast which is giving rise to dentine first the inner enamel epithelium it influences the pulp to differentiate the odentoblast to form the first layer of dentine then dentine forms when dentine forms it in turn differentiate the amyloblast the inner enamel epithelium into amyloblast so once this dentine pre-dentine is formed the nutritional supply to the inner enamel epithelium is cut and the nutritional will be taken from the dental sac so this is the dentine which forms pre-dentine forms so it forms in the coronal part and even the root part so we have two types of dentine the coronal dentine and root dentine and this is a cervical loop so there will be proliferation at this area this will results in root formation and this is giving rise to hardwicks epithelial root sheath so all this we have covered in detail in the development of tooth and also in enamel chapter so coronal part I mentioned in enamel chapter in detail so the root dentine when the root formation proceeds the epithelial cells from the epith the cervical loop which proliferates apically and influences the differentiation of odentoblast from the dental papillae as well as cementoblast from the follicle okay this is a follicle this is dental papillae so we differentiate the dental papillae to form the root dentine and we differentiate the cells from the dental sac to form cementum so there will be deposition of root dentine and cementum so that is about formation of odentoblast or dentine so the structure of dentine basically the dentinal matrix of collagen fibers are arranged in network so it is arranged in a network and as this dentine calcifies calcifies the hydroxyapatite crystal mass the collagen fibers so the bodies of odentoblast they are arranged in layer on the pulpal surface of the dentine okay so bodies are arranged in so these are arranged this is the pulpal surface so this is the pulp this red color so bodies are arranged this is the pulpal surface okay this is the pulpal surface so the body the odentoblast odentoblast will be like with a projection and will be like this so this is the tail and this is the head part so the bodies of odentoblast arranged in a layer on the pulpal surface so this will be arranged in the layer on the pulpal surface on the dentine and only their cytoplasmic processes are included in the tubules in the mineral matrix okay so each cell will give rise to one process which travels the pre-dentine and calcified dentine within one tubule and terminates in a branching network to the DEJ or CEJ so it goes starts from the pulpal surface and it terminates here this is the enamel the otter most covering and it's it terminates at the DEJ or CEJ which is the root portion where cementum and dentine meets which is known as cemento dentinal junction in crown it meets with enamel which is known as dentino enamel junction okay now let's learn something about dentinal tubules which is basically the course of these tubules follow a gentle curve okay so the gentle curve so it is a double curvature and this is known as s-shaped curve so we have a s-shaped curve this is like this s-shaped curve and it starts at right ankle at the pulpal surface okay so this is a pulpal surface it starts at right ankle to the pulpal surface just like enamel it starts from right ankle to the dentinal surface so it starts right ankle at the pulpal surface and first convexity of this doubly curved course is directed towards apex of tooth okay so it will be like this so the first convexity towards the apex okay this is first convexity and this is second convexity so first convexity towards the apex of tooth and these tubules are perpendicular to d e j and c e j okay so d e j will be on the crown and c e j c not c e j c d j that is cemento dentinal junction this will be in root and d e j will be in crown and this is double curvature double convex and it has a shaped pattern so dentinal tubules are almost straight near the root tip at the root tip which will be almost straight and also straight at the incisal edges and c usps so dentine thickness ranges from 3 to 10 millimeter and the ratio between outer to inner dentine has 5 is to 1 that is outer has 5 tubules compared to the inner tubules ratio between outer to inner number of tubules is 5 to 1 the more tubules are present in the outer portion of dentine that is which is closer to the enamel and number of tubules per square millimeter varies from 15 000 at d e j but the number of tubules is lesser at d e j and more at pulp that is around 15 000 at d e j but 65 000 near the pulp surface so 5 is to 1 was the outer and inner dentinal surface ratio okay 5 is to 1 but this is number of tubules per square millimeter so number of tubules per square millimeter is very low or less than 50 000 or around 15 000 at d e j but it is 65 000 at pulp whereas the outer and inner surface of dentine is about 5 is to 1 okay so outer dentine has 5 with respect to inner dentine 5 times bigger outer dentine compared to the inner dentine and next we have the internal tubules and it has lateral branches throughout the dentine which is termed as canalicule or micro tubules and this enamel spindle we have learned in chapter enamel that is the odentoblast process okay so the odentoblastic processes which extends through the d e j into enamel several millimeters which is known as enamel spindle actually enamel spindle is not an enamel structure which is actually a odentoblastic that is a related dentine which which transfers or which enter into this d e j for few millimeter and it terminates enamel that is why it is known as enamel spindle this is odentoblast which extends from d e j extends through d e j into enamel okay so that is known as enamel spindle so next we have various types of dentine in next session we will be learning about types of dentine such as peritubular dentine, inter tubular dentine, pre-dentine and odentoblastic processes primary dentine, secondary dentine, tertiary dentine so all will be dealt in next session okay thank you