see the video: http://www.learnerstv.com/video/Free-video-Lecture-4716-Dental.htm
In this presentation we will discuss the anatomy of the primary teeth. Our objectives in today’s presentation are to identify these teeth by name and location and the positions of them, to discuss a little bit about occlusion and to discuss rather extensively the differences between the primary teeth and the permanent teeth, to discuss the morphology on some of these primary teeth as well as the differences and terminology, and to get some identifying characteristics of some of these teeth. If we look to our skull here of a youngster of approximately 4 or 5 years of age, we can start to identify our primary teeth. We have 20 in number and if we divide these down into quadrants of 5 here, we’ll identify them individually. We have a maxillary right primary central incisor, our lateral incisor and our cuspid.
The interiors are essentially the same. If we look to our posteriors now we have a first molar and a second molar. This means that we have no premolars or bicuspids in our primary teeth and we have no third molars. This just leaves 5 in quadrant. With four quadrants it will give us our 20 teeth. Now in the permanent teeth we identified these teeth by number, for record purposes, and we had 1 through 32, starting with the maxillary right posterior tooth. In our just primary dentition we’re discussing these teeth by letters and we’ll start with a maxillary right posterior and this will be number A and then we’ll go, as we did with the permanent ones, around to the maxillary left posterior, which should be 10 letters around to the letter J and we’ll drop directly below to a mandibular second primary molar K. And continue on around until we come to the 20th letter in our mandibular right molar which would be T. I called these teeth primary teeth. You may well recognize that there are other terms for them. Deciduous teeth has been a technical term for these teeth for a long time and it is in a lot of the literature. Primary teeth has been more recently accepted official name for these teeth so we’ll try to refer to them as primary although still [Roll?] refer to them as deciduous I’m sure because of a habit. Also these are called baby teeth. Of course parents most commonly know these as baby teeth and not by other terms although they are continuing to be educated here on this.
Frequently they can be called milk teeth. Some of these have gotten stained from the glue and dirt, what have you, but these teeth frequently are very white and oftentimes much wider than the permanent test. So they’re called milk teeth as a slang term. If we look to the occlusion on these teeth we’ll find essentially the occlusion is basically the same as the permanent teeth. Our mandibular teeth are smaller in the anterior and they’re…develop an arc which is inside of the maxillary arc and they’re biding to the lingual of our maxillary teeth. And this occurs all the way around. We have the same type of an overbite and an overjet situation in the anterior and in the posterior. We’ve got the buccal cusp of our mandibular posterior teeth occluding into the central fossas and grooves of our maxillary teeth. One thing in relation to the occlusion is a little bit different and that is if we look all the way back to our posterior teeth, frequently we’ll have in this area what is called a flush terminal plane. Our anterior teeth in the mandible are much smaller but our mandibular teeth on the molars become much wider and they help to make up for this difference and often times will end up with the same plane at the posterior here. This makes quite the significance in the eruption of the permanent teeth here. We might look to the eruption here a little bit. We’ve got a cutaway section and if you take the labial plate or cortical plate of bone I should say off of these skulls we’ll find that underneath we have a tremendous number of teeth developing. Got a central and the lateral and a cuspid, our two premolars. And all of these teeth are basically called succedaneous teeth, which is a term which we should identify. To define, a succedaneous tooth is a tooth which replaces one of the primary teeth. One the reasons we can call this a 4 to 5 year old is because these first permanent molars which erupt at 6 years of age are not quite coming through the bone yet. They are still down underneath the cortical plate of the bone in some of the areas. Maxillary one started through, a mandibular one is completely under the cortical plate of bone. Some people ask why we don’t study the primary teeth first, particularly since they are the first in the mouth, as in this 18 month old child. But there are many reasons. First of all our primary teeth do not have well-defined landmarks or grooves, fossas, ridges, depressions.
They are just not as distinct as they are in the permanent teeth. These teeth are generally smaller and harder to study from size standpoint. And availability of them is not very good. The good fairy has a way of getting most of these teeth and we have a hard time getting a selection to study. Our text book lists the primary teeth after the permanent teeth but they do have a rather large number of good diagrams and photographs which you may have to use to supplement your study on these teeth. We also have a fairly decent collection of these primary teeth in the [Kaiden?] Center which can be checked out for studying and looking at in the [Kaiden?] Center. Let’s look at the differences that exist between these permit and primary teeth. We have 8 general differences. The first one is size. We’ve got some permanent teeth and some primary tooth next to each other and just overall general size is very significant. This is obvious. We’ve also got a size variation in relation to the crown height. The crown height on these deciduous or primary teeth are very short and squatty. The distance from the cervical to the occlusal is considerably shorter in proportion to the permanent teeth. We can go back to the slides here, we can see that there is a number two difference, is a significance color variation. We can see some permanent teeth coming in down here and they’re often times yellower. Our primary teeth are whiter and this is where they pick up the term milk teeth. This is a big problem with parents when these permanent teeth usually start coming in on their first children, I bet you I’ve seen a hundred of them or more in more practice, they come running in and say “Something’s wrong with my child’s permanent teeth. They are all yellow.” And there’s supposed to be that difference and you have to point out to them the difference and why. This also points out, I think rather significantly, the size variation. For instance on our central incisor of the primary tooth we’re wider from the mesial to the distal than we are from the incisor to the cervical. This is one of the reasons why they’re getting a short squatty type of terminology to the crown. Third major difference is basically number. Again, easy one. We got 20 primary teeth. We have no premolars. We have the same 6 anterior, 4 mandibulars and the 4 maxillaries…6 of maxillaries. Mandibulars. And then we have 2 molars.
So the ones we’re missing are basically third molars and our premolars and these are simply termed first primary molar and second primary molar. You can see the first permanent molars starting to come in here in this section. This is not a deciduous tooth here and very important that we learn eruption of these because parents don’t recognize that these are not, as they would term them, baby teeth and they’re very frequently likely to get into a great amount of disease and trouble before they know that they are permanent. One of the things that’s number four main difference is that our primary teeth have no mammelons. You can see permanent teeth here. Very strong mammelons when they first come in. Primary teeth have no mammelons, even when they’re present to begin with. 5th major general difference is in pulp chamber size. Pulp chambers in the primary teeth are proportionally larger than they are in permanent teeth. And this is significant. Number 5… number 6 main difference would be that the enamel is thinner on the primary teeth. We can see how the enamel is thinner and rather even in comparison to the enamel on the permanent tooth. This is the first permanent molar here. This is your second primary molar. The large size of these primary pulps becomes very important when removing decay and in preparing these teeth for restorative fillings. We’ve got a major root difference on these teeth and actually we divided this into three differences. So I’ve listed number 7 as root differences on the molars, molar root differences, in three basic areas. One is that the roots are widely spread and you can see the succedaneous tooth developing right here, which would be your second permanent mandibular premolar, a number 20 developing right in between the roots of the primary teeth. So these roots are spread wide. They are often times said to be bold or flared in this area. Number two, the roots are frequently thin from mesial to distal. Quite broad as we’ll study…find as we study the individual teeth. Quite broad from the buccal to the lingual but quite narrow mesially distally. Gives them a ribbon shaped appearance, particularly on these mandibular molars. Third major difference is this root trunk. They are trifurcating or bifurcating. In this instance it would be trifurcating. Here it would be bifurcating. Very close to the cervical of the tooth and in some instances there is no root trunk whatsoever left. We’ve got a very short, very small root trunk on these. Number 8 major difference is the cervical ridge. A cervical ridge is very prominent on primary teeth.
Whether you want to call this buccal deflecting ridge or the deflecting ridge of the teeth or the buccal ridge. Here it would be labial ridge. Or whether we want to say that the cervicals constrict. Sometimes they’ll say cervical constricts but nevertheless you get a large cervical roll on the primary teeth in comparison to the permanent. Our maxillary permanent teeth have a heavier cervical roll or cervical ridge than what the mandibulars do. But this is even much more prominent in the deciduous teeth. And this becomes very important from many operative and restorative standpoints. Again, here is a cuspid. Just a general outlined form. You can see a very much more prominent roll on the cervical. We back and look at these teeth on the individual basis. We’ll go through each one of them fairly promptly. We’ll find that the differences aren’t real tremendous. For instance if we were to take a primary central incisor. Aside from the general differences that I’ve been pointing out to you, um, we find that the ridges on here are not nearly as prominent. For instance we haven’t got these labial ridges that develop from these 3 mammelons or depressions I should say. Labial depressions that develop from the mammelons because we basically don’t have the mammelons present on the primary teeth. On the lingual surface our marginal ridges are just not real prominent. Our mesial distal marginal ridges are indistinct. The cingulum looks proportionally larger on it. But again this is prominently due to the fact that this shortness of the crown from incisor to the cervical and often times our lingual cingulum will be kind of prominent but it’s, as I say, short and squatty. Other than this we haven’t got a large number of differences. Our main roll at the cervical is very important difference. Our cervical line is not nearly as prominent in its curvatures. It still has the same basic curvature as a tooth has all the same basic anatomy as the permanent ones but it’s just not real prominent or characteristic.