Clinical Procedures in Bridge Construction


Uploaded by UMichDent on 08.07.2009

Transcript:
Welcome to the University of Michigan Dentistry Podcast Series promoting oral health care
worldwide.
After proper anesthesia has been given and the 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 lingual of the molar. The purpose of the tracer cuts
is to give you a reference of how much to take off of the tooth on these various peripheral
surfaces. The diamond is carried into the tooth only one-half of its diameter. These
tracer cuts are parallel to each other and parallel to the line of draw of the anterior
abutment tooth which is the bicuspid. It is wise to place pencil marks on the tooth when
you're first attempting to place the tracer cuts. 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 cuts which is again half the diameter of this diamond
instrument. Now the next quarter or the segment of the tooth is going to be reduced and this
will be the mesio-lingual. Again, keeping the diamond instrument parallel to the draw
of the anterior abutment tooth using a high speed and light touch carefully reducing this
area. This then is carried to the distal-buccal area. Now here you'll notice that there's
a check in this particular area and this has to be held away from the rotating instrument.
You'll see now that a chamfer has been established on 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 occlusal surface but this time to the full depth of
the diameter of the diamond instrument. This again will give you an organized approach
to the reduction of this occlusal surface and giving you a standard amount of reduction.
Once the tracer cuts have been placed on the buccal and lingual portion of the occlusal
surface, then the remaining islands are reduced until you have an approximate reduction of
the occlusal surface which is the diameter of the diamond instrument. The instrument
is then turned at right angles and the line angles are rounded with the same diamond instrument.
Here we are trying to be very efficient with the diamond instrument using it to its fullest
ability. Now the amount of occlusal reduction is going to be checked with two thicknesses
of 28 gauge green wax and we can check with the indentations of this wax to see if we
have adequate occlusal reduction going into working and balancing. When the proper amount
of occlusion and occlusal reduction has been obtained a retention groove on the buccal
and lingual is placed. This retention groove is parallel again with the anterior abutment
tooth and this is placed to resist any dislodgement in an anterior posterior movement of the tooth
in occlusion.
A final finishing of the chamfer is placed with a three-quarter A diamond instrument
and this is just a slight beveling of the chamfer 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 disks modeled on a Moore's mandrel. In this particular
case, there's, on a couple areas of caries on a pit, on the buccal and a little bit on
the mesial. This will very carefully be removed and a cement base will be placed in this area.
Now careful examination of the finished preparation is important to see we have all the details
that we have a line of draw, our finishing line is smooth and is carried under the tissue
properly and that we have enough occlusal clearance. Then we're ready to proceed to
the preparation of the bicuspid. A 699-9L diamond is used to do the initial cutting
and slicing. Here it's very important that we do not nick or cut the adjacent tooth so
great care has to be taken with the handling of this rotary instrument and using a light
touch very carefully entering the proximal surface you can open up this area, slice it,
without injuring the adjacent tooth and without giving our tooth too much taper in this particular
area. You'll notice that in this procedure there 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 by using this diamond instrument. The slice as
you can see is slightly concave. Now with a 770-7 diamond, the same diamond you used
on the molar, a tracer cut is placed on the distal and the lingual surface. This again
is to allow us, enough, allow us a guide in the 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 reduce it to the depth of the tracer cut so that
we will have a chamfer established around the lingual surface that will blend into the
mesial slice and a distal slice that will come out to the buccal surface. Great care
must be taken to bring this out far enough to the buccal surface so that we have brought
out our finishing line far enough so that it's in an area of immunity. Now here you
can see blending of that chamfer into the mesial slice. Here again since this is the
bulk of your diamond care must be taken not to nick the adjacent bicuspid. You can see
the detail of the chamfer.
Tracer cuts then are again placed on the occlusal surface of the bicuspid carrying the diamond
to its full depth. To give us a reference of how much to take off of this occlusal surface
and we are going to protect this buccal cusp so we will also extend our tracer cut over
the buccal surface and then, when our tracer cuts have been completed we will reduce the
remainder of the tooth to the depth of our cuts. This is to give us enough clearance
in waxing so that we do not make the gold so thin that the patient will wear through
it. We need enough clearance so we have enough gold for strengthening this occlusal surface.
Once you have the tracer cuts placed, the reduction 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 and saliva to contend with that you will not have
on your Visidont model. Now we are placing the mesial and distal boxes. This is done
with a 770-7 with a diamond held as parallel as possible to the tracer cuts and the retention
grooves cut on the more. You can see now the connection of the mesial and distal boxes
across the occlusal. We're traveling through the isthmus making a box or staple form on
this bicuspid.
Now further refinement of our surface of protection on the buccal surface and using the three-quarter
A diamond we are modifying our chamfer slightly to make a definite sharp margin so that this
margin can be read readily on our dyes and when 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 no roughnesses. Now the occlusion on the bicuspid
which is more anterior can be checked visually by having the patient go into working at balancing.
When you're happy with the preparations and the preparations of the tissue packed with
your Visidont you will not have the soft tissue as you have here and your finishing lines
are above the tissue. This is a very important step in the impression taking, in the patient's
situation. And many a rubber base has been ruined by not having the tissue packed properly.
You'll note here that there's no bleeding involved with this and this will give us room
to place the rubber base once the tissue has been retracted.
After the rubber base has been mixed, the string pack will be removed usually after
five minutes and then the rubber base is injected around the preparations carefully avoiding
any bubbles.
The teeth more anterior are also injected and then custom tray has been fabricated and
this is seated very carefully down to the occlusal 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 removal of the tray is very important. It should be
in the long axis of the tooth and after the impression has been removed, we'll dry it
and examine it. You should examine the margins to 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 surface and the boxes and there are no tears and make
sure that you have a complete mix of rubber.
The temporary crown is fabricated using a plastic wafer that has been pressure-formed
on a study model. This plastic wafer is tried in the mouth and if it does fit, then we'll
fill it with DuraLay, lubricate the teeth and have the patient then close down on this
and when this starts to harden or get warm then this will be removed from the patient's
mouth and then allowed to continue polymerization on 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 need to take an occlusal registration. This is
most readily done and most easily done using DuraLay on the occlusal surface of the tooth
and then have the patient close into the soft DuraLay coping giving us an occlusal registration
of the opposing tooth. By using this and then hand articulation of the rest of the arch,
you'll be able to mount this very accurately.
Now the polished temporary crown is tried in the mouth and margins are checked just
as you would check a finished bridge. The occlusion is checked to make sure that is
correct. And then this will be cemented with a zinc oxide eugenol sedative cement. By having
the patient bite down on the plastic wafer or 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 is cemented we will have the patient drive it
down to the proper occlusal height and hold it there until the temporary cement has hardened.
This will make a very nice temporary and get the patient used to having something in this
denture-less space before you put your final bridge in that area. It will also make a comfortable
dressing to the teeth that you have prepared and removed lots of enamel on.
All the requirements of a finished bridge should be followed on this temporary bridge.
Now after the bridge has been fabricated in the 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 castings and give you a false reading as far as occlusal
in your margins. Careful examination of this bridge before cementing is very important.
You should be able to have a pretty good registration of working and balancing and occlusion on
this bridge. Your margins should be developed so, 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 the mouth. You should have about one millimeter
of space under the pontic so the patient can readily clean. In this particular case, we
have sandblasted the occlusal surface so we can pick up any occlusal registrations that
are out of place. Also, the sandblasting does give us a dull surface, it does not reflect
gold and it's probably a little more desirable than the shiny gold. We have polished the
undersurface and the suture joint area so that this will not collect plaque and will
be very easy to clean. You'll notice that the 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 very carefully seated. Now push it down. If it's
going to hang up it may be on the contact of 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, to make sure that the margins areů good and
you'll note here that the margins have given us the same adaptation here on this natural
tooth as we had on the dyes. Now we'll find that 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 fabricating the bridge, the temporary bridge will wear
and the opposing teeth will extrude down just a bit and you will have some adjustment to
make on the occlusal surface. In this particular case, we are using the articulating paper
to pick up the [...]. Now they have been adjusted and 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 accurate way of checking occlusion and we will place
this on the occlusal surface and pull and we can determine the areas where we're getting
occlusal contact and where we're not. Now the anteriors did not have occlusal contact
before we started the bridge and we will not have 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 has already been filled with the cement and we're
applying it to the tooth. The bridge then will be placed on the teeth and very carefully
pushed down to make sure we're in the right line of draw and once we have this in the
mouth where there's some moisture and there's warmth we have to move pretty fast because
the cement then does set up rather quickly with moisture and heat. We're going to use
an orangewood stick to push the bridge down and then the cement is wiped away from the
margin and then we will again push it down until 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 margins back to the enamel surface. The hydraulic
pressure of cement oozing out of these margins tends to open up the margins and with this
5S burnisher you should try to get to as many of the margins as you can to burnish them
down back to the tooth surface. The bridge is 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 important to clean all the cement away and to take the
areas where there are marks from the burnisher and polish it with a little bit of pumice.
Make sure that all the cement has been removed from under the soft tissue and in the contact
area. The cement can act as an irritant just like calculus and cause gingival problems.
It's important to clean this area and then instruct the patient on the use of dental
floss under the bridge to make that this is kept clean and you've made the surface very
shiny and smooth so they can remove the plaque and it's important they do this at least once
a day to keep this bridge clean.
A final check we make down the margins to make 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 the teeth 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 is part of them and is not a foreign object.
And the bridge would give them many years of good service providing they give the bridge
the necessary home care and you have them back for recalls to check the occlusion and
to check on wear and to check on oral hygiene.
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