Burdrop

Transcription

Welcome to the University of Michigan Dentistry Podcast Series promoting oral health care worldwide. Today we're going to talk about occlusal lingual openings for endodontic therapy. The objective of this sequence is to allow you the student to be able to design and prepare adequate endodontic access preparations for any tooth you're assigned in the clinic. After the rubber dam is in place, the next step for endodontic therapy is to gain access into the pulp. Access is necessary in order to clean out the infected and necrotic pulp tissue, to smooth and enlarge the canals and also to get the canal ready to receive the filling material. Now since the pulp lives inside the tooth where you can't see it, you have to use guides in order to visualize the size, shape, and position of the pulp. We generally useówe rely on three guides to give us this information. The three guides that we use are the simple knowledge that the pulp is always located in the center of the tooth, we use the initial radiograph to give us information on the pulp and also we use the outline form of the crown that we're working on to give us information of the outline form of the pulp. Now let me go back and explain what we mean by these three guides. Here are some teeth sectioned in cross-section. As you can see in each case, the pulp is about the same shape as the outline of the tooth only it's in the exact center. You can see the pulp almost forms a bull's eye right in the middle of the tooth. Here are some mandibular central incisors sectioned mesio-distally and labio-lingually. You can see that the pulp is located in the center of the tooth throughout the entire length of the tooth. Knowing the position of the pulp mainly that it's in the center of the tooth, the problem then is to visualize the overall size and shape of the pulp. To do this, at least in the mesio-distal directionóview, we use the initial radiograph. Here is the radiograph of the maxillary central incisor. Note that you can see, in a mesio-distal view, the shape and position of the pulp. You can also see the shape of the pulp chamber and pulp horns and you can see the relative distance from the pulp horns and chamber to the surface of the tooth through the secondary dentin formation. Okay, we know the position and the mesio-distal size and shape of the pulp. Now the only problem is to visualize the overall three dimensional shape of the pulp and the guide that we use for this is the overall shape of the crown of the tooth that we're working on. Here is a model of a maxillary central incisor with the crown shape accentuated. As you can see it's very broad at the incisal and narrows out at the cingulum area forming kind of a triangular shape. From this, and from the information that we get from the radiograph we would visualize that the shape of the pulp would be triangular right in the middle of that crown surface very similar to the shape of the crown. We've quickly gone through the three guides to pulpal morphology namely the centralized location of the pulp, the initial radiograph and the shape of the crown that we're working on. Now I want you to quickly try and test yourself to see if you understand these principles. Here is a radiograph of a mandibular central incisor. Study it. Look at the shape and the size of the pulp. Now here are some models of mandibular central incisors. Which would you suppose would be the proper outline form for the shape of the pulp? I hope you chose the one on the right. You'll notice from the radiograph that the pulp was very narrow. But the crown shape tells you it was a triangular crown shape much as the maxillary central incisor was only the tooth is very long, labio-lingual direction. So the outline form of the pulp will be somewhat triangular, very narrow mesio-distally and very long labio-lingually. Study the radiograph. You can see the pulp chamber and the mesio-distal size and shape of that pulp. Here are some models of the crowns of those teeth. Study the shape of the crown. Would you suppose it would be the one on the right or the one on the left? You should have chosen the one on the right. The crown, although it's fairly wide mesio-distally, the X-ray shows you that it is a very narrow pulp and the crown is very broad buccal-lingually so you would have a very narrow, very broad pulp as indicted by the radiograph and the shape of the crown. Let's move onto the mandibular molar. Here's a radiograph where the pulp has been somewhat accentuated and comes up to the occlusal surface. Many students have trouble visualizing in a mesio-distal direction the dimensions of the pulp so study the pulp, study the radiograph, note that the pulp on the mesial comes about halfway between the central pit and the marginal ridge and on the distal, the pulp comes to about the distal pit. Now take a look at these models. Would you suppose the shape of the crown would be more like the one on the right or the one on the left? This time you should have chosen the one on the right once again. The mesial part of that crown is very square and you can see from the radiograph that the pulp extends just distal to the marginal ridge. Towards the distal of the tooth, the pulp, the crown shape, becomes very somewhat triangular and as a result the pulp should also take on a triangular outline form. So putting the information together you should be able to visualize the shape of the pulp. The maxillary molars show a slight variation from the principles previously mentioned. The entire crown shape is not representative of the shape of the pulp. The shape of the pulp most closely resembles the part of the crown that is bound by the mesio-lingual, the mesio-buccal and the distal-buccal cusp. This forms a triangular outline shape as you can see on the model of this maxillary molar. In deciding on the shape of the pulp, you should disregard the distal-lingual cusp. Test yourself on this variation. Study this radiograph of the maxillary molar. Note the shape and mesio-distal size of the pulp and where it transfers to the surface of the tooth. In this case the pulp is slightly mesial of the center. Now study the crown shape of these models. Try to decide which should be the outline form of the pulp. You should have said the one on the left. The area founded by the mesio-lingualómesio-buccal and distal-buccal cusps forms a triangular area with the pulp very much in the center of that area. We've gone through a detailed description of the procedure of access preparation on maxillary central incisors. Now I'm going to very briefly go through some other examples on other teeth pointing out only the differences in variations in this, these procedures. All the other teeth are almost exactly the same so we'll only point out variations. In the maxillary biscuspid, the pulp is so narrow mesio-distally, that students have been gouging the tooth in that direction. To guard against this, after you drop into the pulp chamber with a number four low-speed round bur, switch to the flame-shaped bur to unroof the pulp chamber. Put the bur into the channel that you've prepared to the pulp and extend in the buccal-lingual direction only. Here is the maxillary molar with the pulp as we visualized it. Part of the tooth is bonded by the mesio-buccal, the distal-buccal and the mesio-lingual cusp forms a triangular outline form right in the middle of that area. Once again we establish that tentative outline form with a 1057 high-speed penetrating right down to the dentin. When we reach dentin we stop, switch over to the number six, low-speed round bur penetrate into the pulp. Once again on these molars the pulp can be a far distance away so don't be nervous and start looking around for it blindly. Angulate the handpiece, center it over the central pit, the pulp will be underneath the central pit and dive straight down to it. When you reach the pulp you'll feel the bur drop in and stop your handpiece. You don't want to continue on and hit the bifurcation. Okay, you feel for the roof. You come on down and unroof that tooth working from the inside out. Staying away from the floor and walls of the pulp chamber. You don't want to look for the canals right now you wait until the pulp chamber is completely unroofed and then look for the canals. You have the final preparation completely unroofed the floor is left untouched. The walls are left untouched. The roof is off and the pulp chamber is clean. You have been listening to a presentation from the University of Michigan's School of Dentistry which is dedicated to supporting open learning and open educational resources. This recording is licensed under the creative comments. It may be reused and redistributed for nonprofit use. Please attribute materials to the University of Michigan's School of Dentistry and redistribute under this same license. For more information on how this and other University of Michigan School of Dentistry recordings may be used visit www.dent.umich.edu/license.