differences between primary and permanent dentition hi Ria a passionate undergrad was excited to be posted in the department of pediatric dentistry from now on she will not only be able to treat adults but also young children but a constant thought that troubled her was how can primary and permanent teeth be differentiated she needed a quick revision so she gathered a few models something she already knew was that primary teeth are also called deciduous teeth as they shed off this temporary set of dentition is present in the oral cavity from 6 months to 6 years after which they are replaced by permanent teeth by the age of 21 after the eruption of the third Moler a complete set of permanent dentition is present in the oral cavity as she observed the models she noticed that although the primary and permanent teeth resembled each other they also had certain morphological and hystological differences the first difference was the number of teeth primary teeth were only 20 a number 10 in each Arch and five in each quadrant while the permanent teeth were 30 22 in total 16 in each Arch and eight in each quadrant the difference in the number was because of the absence of premolars and a third molar in the primary dentition based on this difference the dental formula is as follows next she observed the difference in the size all the dimensions in the primary teeth were smaller than the permanent teeth because children have smaller arches as the Arches grow they accommodate the larger permanent teeth next she looked at the difference in the color the primary teeth were lighter and had more of a bluish white appearance while the permanent teeth were darker appearing gray or yellow white this color difference is because of two factors first is that the primary teeth have a thinner layer of Dentin while the thicker layer of Dentin in permanent teeth makes the tooth look yellowish the second reason is that since the enamel and Denton of primary teeth are formed in utero there is no exposure to environmental factors during teeth formation this enhances the quality of the enamel and Dentin in primary teeth pop quiz as Ria began to look at each tooth closely she noted the morphological differences she began with the clinically visible structure in the oral cavity the crown the crowns of the primary enzers appeared wide that is the Miso distal Dimension was greater than cico incisal they looked like Ria's teacup in comparison the crowns of permanent incizors were long like a tall glass as their cervical incisal Dimension was greater another unique feature she observed of permanent incizors is the presence of mamons they were absent in primary incizors instead she noticed a physiology ol ological atrion of the incisal surface did you know permanent incisal develop from three Developmental loes and these appear as elevations on the incisal surfaces called mamons she then moved onto the primary canines which were thin and conical with a prominent singul while the permanent canines were slightly bulbus and less conical without a prominent singul all the primary teeth had a marked cervical constriction at the neck of the crowns whereas the cervical end of permanent teeth were broader now she moved further posteriorly to the primary MERS the first Moler in primary dentition was smaller in dimension when compared to the second Moler unlike the permanent ones where the first was larger than the second crowns of the primary MERS were more bulbous with flat buckle and lingual resembling a bell on the other hand the permanent teeth were less bulbous with rounded buckle and lingual surfaces apart from this the convergence in the Buckle and lingual walls of the MERS narrowed down the accusal table in primary MERS in a buol lingual plane while the permanent mullers had a broader accusal table due to a lack of convergence this difference is clinically significant because the width of the cavity is Limited in the case of accusal cavity preparation in the primary Moler the relatively flat proximal surfaces of primary MERS made a broad contact area with the adjacent teeth in contrast the curved proximal surfaces of the permanent teeth had maximum convexity centered at a point thereby having contact points to adjacent teeth Ria wondered if this was clinically significant during the class 2 cavity preparation in primary Moler the gingival seat of the proximal box must be placed below the contact area by doing so the class 2 restoration falls into a self cleansing area and prevents accumulation of plaque Ria continued with her observation a unique feature of the primary first Moler was the more pronounced cervical Ridge on the Buckle aspect a feature absent in permanent MERS this difference is clinically relevant as the pronounced cervical Ridge provides natural retention to the stainless steel crowns therefore the Buckle and lingual surfaces of primary teeth remain unprepared during Crown preparation in addition to the above differences Ria also noticed that the primary molers had many supplemental grooves unlike the permanent teeth these grooves act as plaque retentive areas and increased the incidence of dental carries in the primary dentition cusps of primary molers were shorter sharper and more pointed these become relatively flat as the teeth undergo physiological attrition during the mixed dentition stage now Ria observed the roots of both the teeth first thing she noticed in the roots was the difference in length and thickness the roots of primary teeth were long and slender while those of permanent teeth were short and robust the second thing that was well appreciable was the Divergence of Roots the Roots of primary teeth were more Divergent and fled to accommodate the permanent tooth Bud below while the roots of the permanent teeth were less Divergent the third difference was the roots of the primary MERS had a short trunk placing the forcation area more cervical and close to the pulp chamber however the root trunk of the permanent Moler was larger thereby pushing the fation area further apik the root surfaces in primary teeth were not smooth and even and Ria wondered if this was a pathology but the answer is no this was a physiological resorption of the roots as these teeth Shed off however if this type of resorption is seen in the roots of permanent teeth it is considered to be path ological these were the differences Ria could see but there was a lot more that needed to be observed under a microscope she began to observe from outside inwards the first visible layer was the enamel primary teeth had thinner enamel with a consistent thickness of about 1 mm throughout the crown whereas the permanent teeth had a thicker layer of enamel that measured about 2 to 3 mm but the thickness varied at different areas the enamel rods were oriented cervically in primary teeth and gingivally ined permanent teeth primary teeth had more organic mineralized enamel the bands of Rus were less common in primary teeth thereby imparting a bluish white color another striking feature that Ria instantly observed was that all primary teeth showed neonatal lines but only first permanent MERS exhibit them this is because the formation of the primary teeth as well as permanent first MERS takes place in utero resulting in a clear line called the neonatal line demarcating the enamel formed in utro and after birth the second layer she observed was the Dentin the Dentin and primary teeth was half the thickness of that in the permanent ones hence tooth structure covering the pulp chamber was less in primary teeth but the thickness of Dentin at the accusal fer of the primary teeth was comparatively thicker why is this significant for a dental student deep cavities prepared in primary teeth end up in the pulp therefore to allow restoration the depth of the cavities in primary dentition must not exceed 1.5 mm within the Dentin the dentinal tubules in primary teeth were irre regly placed and did not follow the characteristic compactly arranged s tubules as seen in permanent dentition does this have clinical importance yes it does the carries and primary teeth progress faster because of the irregularly placed dentinal tubules other features of Dentin were the absence of interglobular Dentin in primary teeth a flat Dentin enamel Junction in primary teeth and a scalloped Junction in permanent teeth Ria had now reached the third layer of the tooth the pulp first she looked at the size of the pulp chamber of primary teeth which was larger in relation to the crown and had higher pulp horns which ran close to the outer surface she figured that if the pulp chamber was larger the cellularity and vascularity would be abundant allowing the primary te teeth to have a high potential for repair this is not so in permanent teeth because of their lower vascularity and cellularity and low potential to repair therefore the reparative Dentin below the arrested carries in primary teeth is more extensive next she observed the outline of the pulp it closely followed the dento enamel Junction as if it was Guided by the Dej to take its out of form this was not so in the permanent teeth her Focus now was on the root canals the primary canals were thin tortuous and branching like the roots of a plant they typically looked ribbonlike while the permanent root canals were well defined and less branched this important feature is kept in mind when placing Barbed brooches into the primary canals for pulp exceptation the ribbon shape of the canals may cause breakage of the instrument which is why brooches are avoided in primary teeth the Tor ofous course of canals and ramifications make it difficult to attain complete debridment of the canals a very distinct feature noted by Ria was the position of the axis canals the pulp chamber floor in primary dentition was porous due to the presence of accessory canals in the forcation areas the permanent teeth accommodate them in the AAL region the clinical significance is that the presence of accessory canals leads to the infection in primary molers draining into the fural area forming a fcal apsis in permanent teeth this infection drains into the peria pyal area forming a per apical absis as she observed the apical area of the roots the apical foramin in primary teeth appeared wider than the permanent where the foramin is restricted this caused es the infection in primary teeth to be inflammatory and less localized however the restricted foramin reduces the blood supply of the permanent teeth and favors healing by calcification of canals as a regressive change finally she spotted the course of nerve fibers in the teeth the nerve fiber terminated in the odontoblastic region as free nerve endings in primary teeth while the nerve fibers in the permanent teeth terminate ated within the odontoblast and Beyond reaching the predentin did you know the primary teeth are less sensitive when compared to permanent teeth because they have fewer nerve Innovations during physiological root resorption in primary teeth the blood vessels in the pulp maintain their normal structure at all stages although an increase in vascularity and blood flow is observed D the vascular changes in the pulp are accompanied by De Innovation which decreases sensitivity as she observed the cementum she noticed that the primary cementum was thin in primary teeth the secondary cementum was characteristically absent this reduces the fitness of the Anchorage to the alviola bone making it easily extractable secondary cementum in permanent teeth is firmly attached to the alviola Bone did you know because alviola atrophy is absent in children gingervitis in a healthy gingiva is rarely seen after understanding all the listed differences between primary and permanent teeth R was sure she would now be able to clinically Implement all that she learned pop quiz [Music] [Music] [Music] let us end this video with the importance of listing out the difference between primary and permanent teeth first of all it is clinically very important to identify the tooth for treatment planning and diagnosis second it helps us to estimate the dental age of the patient third it provides an insight into the eruption status of the child finally it is of great importance in forensic odontology to estimate the age and identity of an individual we hope you had fun learning with us [Music]