Februari 25, 2017
welcome to the university of michigan dentistrypodcast series promoting oral health care worldwide. after proper anesthesia has been given andthe necessary radiographs and study models are available, the preparation is commenced.a 770-7m diamond is used to cut tracer cuts on the mesial, buccal, distal, and lingualof the molar. the purpose of the tracer cuts is to give you a reference of how much totake off of the tooth on these various peripheral surfaces. the diamond is carried into thetooth only one-half of its diameter. these tracer cuts are parallel to each other andparallel to the line of draw of the anterior abutment tooth which is the bicuspid. it iswise to place pencil marks on the tooth when
you're first attempting to place the tracercuts. then the tooth is reduced in sections. the mesio-buccal section now is being reduced,carrying the finishing line just to the gingival tissue and to the depth of the tracer cutswhich is again half the diameter of this diamond instrument. now the next quarter or the segmentof the tooth is going to be reduced and this will be the mesio-lingual. again, keepingthe diamond instrument parallel to the draw of the anterior abutment tooth using a highspeed and light touch carefully reducing this area. this then is carried to the distal-buccalarea. now here you'll notice that there's a check in this particular area and this hasto be held away from the rotating instrument. you'll see now that a chamfer has been establishedon the lingual-mesial just along the buccal
of this tooth just above the gingival tissue.the next step is reducing the occlusal surface. tracer cuts are again placed on the occlusalsurface but this time to the full depth of the diameter of the diamond instrument. thisagain will give you an organized approach to the reduction of this occlusal surfaceand giving you a standard amount of reduction. once the tracer cuts have been placed on thebuccal and lingual portion of the occlusal surface, then the remaining islands are reduceduntil you have an approximate reduction of the occlusal surface which is the diameterof the diamond instrument. the instrument is then turned at right angles and the lineangles are rounded with the same diamond instrument. here we are trying to be very efficient withthe diamond instrument using it to its fullest
ability. now the amount of occlusal reductionis going to be checked with two thicknesses of 28 gauge green wax and we can check withthe indentations of this wax to see if we have adequate occlusal reduction going intoworking and balancing. when the proper amount of occlusion and occlusal reduction has beenobtained a retention groove on the buccal and lingual is placed. this retention grooveis parallel again with the anterior abutment tooth and this is placed to resist any dislodgementin an anterior posterior movement of the tooth in occlusion. a final finishing of the chamfer is placedwith a three-quarter a diamond instrument and this is just a slight beveling of thechamfer to make it sharp and to add just a
little tiny lip of gold around the chamfer.this is carried completely around the tooth. the final finishing is done with sand disksmodeled on a moore's mandrel. in this particular case, there's, on a couple areas of carieson a pit, on the buccal and a little bit on the mesial. this will very carefully be removedand a cement base will be placed in this area. now careful examination of the finished preparationis important to see we have all the details that we have a line of draw, our finishingline is smooth and is carried under the tissue properly and that we have enough occlusalclearance. then we're ready to proceed to the preparation of the bicuspid. a 699-9ldiamond is used to do the initial cutting and slicing. here it's very important thatwe do not nick or cut the adjacent tooth so
great care has to be taken with the handlingof this rotary instrument and using a light touch very carefully entering the proximalsurface you can open up this area, slice it, without injuring the adjacent tooth and withoutgiving our tooth too much taper in this particular area. you'll notice that in this procedurethere is very little bleeding of the soft tissue if the diamond is handled properly.now from this occlusal view you can see the amount of slice that has been obtained byusing this diamond instrument. the slice as you can see is slightly concave. now witha 770-7 diamond, the same diamond you used on the molar, a tracer cut is placed on thedistal and the lingual surface. this again is to allow us, enough, allow us a guide inthe reduction of these surfaces. this is carried
just one-half the depth of this diamond instrument.now with the same diamond we will take that remaining area of enamel and dentin and reduceit to the depth of the tracer cut so that we will have a chamfer established aroundthe lingual surface that will blend into the mesial slice and a distal slice that willcome out to the buccal surface. great care must be taken to bring this out far enoughto the buccal surface so that we have brought out our finishing line far enough so thatit's in an area of immunity. now here you can see blending of that chamfer into themesial slice. here again since this is the bulk of your diamond care must be taken notto nick the adjacent bicuspid. you can see the detail of the chamfer.
tracer cuts then are again placed on the occlusalsurface of the bicuspid carrying the diamond to its full depth. to give us a referenceof how much to take off of this occlusal surface and we are going to protect this buccal cuspso we will also extend our tracer cut over the buccal surface and then, when our tracercuts have been completed we will reduce the remainder of the tooth to the depth of ourcuts. this is to give us enough clearance in waxing so that we do not make the goldso thin that the patient will wear through it. we need enough clearance so we have enoughgold for strengthening this occlusal surface. once you have the tracer cuts placed, thereduction of the occlusal surface really becomes very simple just a step-by-step procedure.you'll notice in this particular case in the
mouth that there are tongue and cheeks andsaliva to contend with that you will not have on your visidont model. now we are placingthe mesial and distal boxes. this is done with a 770-7 with a diamond held as parallelas possible to the tracer cuts and the retention grooves cut on the more. you can see now theconnection of the mesial and distal boxes across the occlusal. we're traveling throughthe isthmus making a box or staple form on this bicuspid. now further refinement of our surface of protectionon the buccal surface and using the three-quarter a diamond we are modifying our chamfer slightlyto make a definite sharp margin so that this margin can be read readily on our dyes andwhen you're in practice a technician will
be able to read those margins very easily.further refinement of the preparation is done with a sand disk to make sure there are noroughnesses. now the occlusion on the bicuspid which is more anterior can be checked visuallyby having the patient go into working at balancing. when you're happy with the preparations andthe preparations of the tissue packed with your visidont you will not have the soft tissueas you have here and your finishing lines are above the tissue. this is a very importantstep in the impression taking, in the patient's situation. and many a rubber base has beenruined by not having the tissue packed properly. you'll note here that there's no bleedinginvolved with this and this will give us room to place the rubber base once the tissue hasbeen retracted.
after the rubber base has been mixed, thestring pack will be removed usually after five minutes and then the rubber base is injectedaround the preparations carefully avoiding any bubbles. the teeth more anterior are also injectedand then custom tray has been fabricated and this is seated very carefully down to theocclusal stops that you've placed on the formatray and after the impression has been seated,it will sit there now for 10 minutes until a rubber base has completely set up. the removalof the tray is very important. it should be in the long axis of the tooth and after theimpression has been removed, we'll dry it and examine it. you should examine the marginsto make sure that you have registered the
sharp, finishing lines of your preparation.you should examine to see if you have all the other details on the occlusal surfaceand the boxes and there are no tears and make sure that you have a complete mix of rubber. the temporary crown is fabricated using aplastic wafer that has been pressure-formed on a study model. this plastic wafer is triedin the mouth and if it does fit, then we'll fill it with duralay, lubricate the teethand have the patient then close down on this and when this starts to harden or get warmthen this will be removed from the patient's mouth and then allowed to continue polymerizationon the bench top or in a cup of warm water and then it will be trimmed and cemented.
before the patient is dismissed we will needto take an occlusal registration. this is most readily done and most easily done usingduralay on the occlusal surface of the tooth and then have the patient close into the softduralay coping giving us an occlusal registration of the opposing tooth. by using this and thenhand articulation of the rest of the arch, you'll be able to mount this very accurately. now the polished temporary crown is triedin the mouth and margins are checked just as you would check a finished bridge. theocclusion is checked to make sure that is correct. and then this will be cemented witha zinc oxide eugenol sedative cement. by having the patient bite down on the plastic waferor form, the bridge usually will be about
the thickness of that wafer shy of the occlusion.this will be picked up by the thickness of cement in cementing. so once the bridge iscemented we will have the patient drive it down to the proper occlusal height and holdit there until the temporary cement has hardened. this will make a very nice temporary and getthe patient used to having something in this denture-less space before you put your finalbridge in that area. it will also make a comfortable dressing to the teeth that you have preparedand removed lots of enamel on. all the requirements of a finished bridgeshould be followed on this temporary bridge. now after the bridge has been fabricated inthe laboratory, the patient returns and the temporary bridge is very carefully removed.it's important to remove all the temporary
cement because this can hang up your castingsand give you a false reading as far as occlusal in your margins. careful examination of thisbridge before cementing is very important. you should be able to have a pretty good registrationof working and balancing and occlusion on this bridge. your margins should be developedso, so that you should be able to go from tooth to dye and not pick up any catches,on the dye, and if you have an accurate impression then this should fit exactly the same in themouth. you should have about one millimeter of space under the pontic so the patient canreadily clean. in this particular case, we have sandblasted the occlusal surface so wecan pick up any occlusal registrations that are out of place. also, the sandblasting doesgive us a dull surface, it does not reflect
gold and it's probably a little more desirablethan the shiny gold. we have polished the undersurface and the suture joint area sothat this will not collect plaque and will be very easy to clean. you'll notice thatthe castings are clean. there is no investment, no bubbles. the periphery of this casting,the bridge is very shiny, polished to a very high luster. the occlusal surface is sandblasted. now the bridge is taken to the mouth and verycarefully seated. now push it down. if it's going to hang up it may be on the contactof the mesial portion here of this bridge and that should be very carefully checked.when the bridge is seated, you should check it with an explorer, a sharp explorer, tomake sure that the margins areå¯ good and
you'll note here that the margins have givenus the same adaptation here on this natural tooth as we had on the dyes. now we'll findthat very often that the occlusion will change even though our bite registration was accurate.the patient wearing the temporary bridge for three or four weeks while you're fabricatingthe bridge, the temporary bridge will wear and the opposing teeth will extrude down justa bit and you will have some adjustment to make on the occlusal surface. in this particularcase, we are using the articulating paper to pick up the [...]. now they have been adjustedand now we are seating the bridge back again to check the occlusion finally before we cement.now we're checking this with a shim stock and this mylar shim stock is a very accurateway of checking occlusion and we will place
this on the occlusal surface and pull andwe can determine the areas where we're getting occlusal contact and where we're not. nowthe anteriors did not have occlusal contact before we started the bridge and we will nothave it at this particular time. the cementation procedure is the same as cementing an in-lay.in this particular case, we are using a zinc oxide eugenol eba cement and the bridge hasalready been filled with the cement and we're applying it to the tooth. the bridge thenwill be placed on the teeth and very carefully pushed down to make sure we're in the rightline of draw and once we have this in the mouth where there's some moisture and there'swarmth we have to move pretty fast because the cement then does set up rather quicklywith moisture and heat. we're going to use
an orangewood stick to push the bridge downand then the cement is wiped away from the margin and then we will again push it downuntil no more cement will come out from under the bridge and around the bridge margins.it is very important also before the cement completely hardens to burnish the marginsback to the enamel surface. the hydraulic pressure of cement oozing out of these marginstends to open up the margins and with this 5s burnisher you should try to get to as manyof the margins as you can to burnish them down back to the tooth surface. the bridgeis being held now with a cooley peg to keep it under pressure while we are cementing it.the margins can be adjusted with a sand disk and after the cement has hardened, it's importantto clean all the cement away and to take the
areas where there are marks from the burnisherand polish it with a little bit of pumice. make sure that all the cement has been removedfrom under the soft tissue and in the contact area. the cement can act as an irritant justlike calculus and cause gingival problems. it's important to clean this area and theninstruct the patient on the use of dental floss under the bridge to make that this iskept clean and you've made the surface very shiny and smooth so they can remove the plaqueand it's important they do this at least once a day to keep this bridge clean. a final check we make down the margins tomake sure we have all the adaptation that we need and have the clearance under the pontic.the occlusal surface and the margin should
blend in harmoniously with the rest of theteeth in the oral environment. if you've fabricated this bridge properly, then the occlusal registration,occlusal pattern, should be correct. the patient should leave feeling as if that bridge ispart of them and is not a foreign object. and the bridge would give them many yearsof good service providing they give the bridge the necessary home care and you have themback for recalls to check the occlusion and to check on wear and to check on oral hygiene. you have been listening to a presentationfrom the university of michigan's school of dentistry which is dedicated to supportingopen learning and open educational resources. this recording is licensed under the creativecomments. it may be reused and redistributed
for nonprofit use. please attribute materialsto the university of michigan's school of dentistry and redistribute under this samelicense. for more information on how this and other university of michigan school ofdentistry recordings may be used visit www.dent.umich.edu/license.
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