DENT 718: Removable partial dentures: design considerations

Uploaded by UMichDent on 25.03.2009

Welcome to the University of Michigan Dentistry podcast series promoting oral health care
So what do we want to look at today are design considerations for the various types of partial
dentures so we run through the class I, the class II, class III and class IV partials.
So when we look at class I partials generally, okay, we may have, whether we look at premolar
abutments they will be in either arch, we may have canine abutments in either arch.
Sometimes we might have a premolar uh a canine or a lateral incisor, very rarely to have
a lateral incisor as an abutment. So if you look at different types of fulcrum lines again
in your text page 96 talks about different fulcrum lines and rather than bore you and
go over all that what you want to look at is thereís going to be a fulcrum line axisóor
a fulcrum line axis for tissue directed forces meaning when people bite down on hard foods.
And if we have free-end distal extension partial, we expect the distal extension portion of
the partial to be compressed toward the tissue a little bit. Again the tissue is more compressible
than the teeth are intrudable. So if you think of biting down on a tooth on a tooth socket
that's got a periodontal ligament, suspending it so you bite down on the tooth, it literally
intrudes in its socket a tiny little bit. So if you have a class I partial that has
a bilateral distal extension and youíve got bicuspid abutments when you bite on the partial,
the bicuspid abutments intrude a little. And the soft tissue that supports the distal extension
basis of the partial also squashes down so the compressability of the tissue is several
factors many magnitudes more than the intrudability of the teeth into their socket which results
in a distal pipping a little bit of the partial. So thatís your fulcrum line or your primary
axis on tissue-ward directed toward forces. Thereís also another fulcrum line thatís
the retentive fulcrum line meaning if you eat sticky foods when youíre opening your
mouth and thereís something sticking to the distal extension aspect of the partial trying
to pull the partial denture away from the tissue. Thereís also a fulcrum line for that
and that fulcrum line is typically going to pass through the retentive tips of the clasps.
So if you have a clasp on either side of the arch and the object or that part of the partial
denture that is going to resist movement that would try to lift it out of the mouth are
the clasps. And where is the retentive aspect of the clasps? Itís at the terminal third,
where they are most retentive and they go into the undercut so a line passing through
the terminal third of the clasp tips would be the fulcrum line on a force going away
from the tissue. So youíve got a couple different fulcrum lines not just the one going toward
the tissue but another fulcrum line for forces trying to take the partial away from the tissue.
This has been gone over extremely thoroughly on the chart on page 96. Indirect retention,
what happens with indirect retention is when you have a partial denture framework the finished
partial denture thatís trying to be taken away from the tissue youíve got your primary
fulcrum line for retention and then the indirect retainer helps brace the base. Now the biggest
purpose for a third point of reference or indirect retention on distal extension partials
comes into play when we are doing relines of the partials. So if you have a patient
in for a periodic recall. How many people have had a patient in for just a check-up,
youíre doing a prophy on them, and you're gonna go ahead and check them up and they've
either got a combination case thatís denture versus a partial denture or theyíve got a
partial denture in one or both arches. So how many people have had a patient like in,
just to do a follow-up? Three of you? Maybe a third of you? So the point is what do you
look at? When we say evaluate their partial. So, how do you evaluate partial? I donít
know. [Scattered chuckling] Howís it doing? Okay good. Did you evaluate the partial? Yup.
How did you do that? I asked Mrs. McGillacuty if it was doing okay. What did she say? She
said it was fine. Did you do anything else? Ehhne. And so one of the things that one would
do in a distal extension partial is how would you determine whether or not a distal extension
partial might benefit from a re-line. One of the things was PIP a simpler way is if
we know when the framework was constructed, letís say for the sake of argument, that
the lower partial denture was done so that the teeth we had for this lower partial that
youíre imagining is we had first bicuspid through first bicuspid left in the patient.
So we made a lower partial denture framework and we made a lingual plate on it. So we had
an occlusal rest and a clasp on each of the first bicuspids and we had a lingual plate
that went around the lingual aspect of the rest of the front teeth. So if I would say
how do you know if the partial denture needs a reline or not just try to make it go tetter-totter
across the primary fulculm line. Can you see if you take one finger--gloved hand of course--and
hold the lingual plate against the teeth and put another finger on the first molar area
of the partial and see if you can tetter-totter it front to back everybody with me now? And
if you can see the lingual plate area thatís on the lingual of the anterior of the teeth
noticeably lift up off the teeth so when you push down on the first molar area you can
see that the back end of the partial tilts down and then that part of the partial framework
that fit against the lingual aspect of the lower anterior teeth lifts up in the air and
comes up away from the teeth, can you see the only thing that can cause that is if the
gum tissue on the underside of the distal extension base has remodeled, has reabsorbed
and reshaped itself? So the gums under the distal extension base donít fit up under
the partial as good as they did when it was first made. So when a brand new partial was
put in and you look at it to see if it will tetter-totter front to back if itís bilateral
distal extension you don't expect to see a lot of this tipping back and forth on a new
partial. Over time a year, two, three, four, whatís going to happen is the soft tissue
is going to remodel a little bit so when you go to do that same pushing back and forth
the tissue isnít supporting the back end of the partial, it goes down and your indirect
retainer is your point of reference because if that lifts up off the teeth itís telling
you that you got tetter-tottering. Question?
[Question inaudible]
Professor: Uh-huh. Tetter-totters a lot. Uh-huh.
[Question continues]
Professor: The question was if you have a class III partial thatís hypothetically tooth
supported at all four corners so there is no distal extension and at least according
to the record as much as we can believe the record, the provider at the time said things
fit well and everything was okay at the time it was delivered. You are now the poor sucker
whoís doing the recall a year later and youíre cleaning their teeth or youíre doing whatever
and you try this class III partial denture in and it seems like it rocks quite a bit.
It doesnít fit on the teeth very well. Weíll go over class IIIs in a little bit here but
basically if your partial denture is tooth supported all the way around, would any change
in the soft tissue okay, if the gumís reshaped a little bit would that in theory have an
effect on the fit of a class III partial?
Nothing to do with it because itís tooth supported all the way around. Now typically
if a patient is being compliant. Iíll say that again. If ñ underline three times ñ
if a patient is being compliant and wearing their partial on a regular basis would you
expect that the partial denture framework fitting on the teeth will help stabilize the
teeth in that position? When the partial is delivered? If in fact things fit well which
they said it did in the record? Is that a reasonable assumption?
So if the patient fits like socks on a roster or something really bad okay when you eliminate
the impossible everything left however improbable is probably the cause. So the patient was
either non-compliant and didnít wear it which allowed the teeth to shift. Itís sort of
like I donít know how many of you have undergone orthodontics and for those of you who did
orthodontics did you wear retainers for some period of time? And if you got lazy because
youíre just a human being and you went several days or a couple weeks without wearing your
retainer when you put your retainer back in, it felt like it didnít fit so good. It fit
pretty bad in fact. And just after a day or two things seem to settle in and the teeth
readjusted themselves to fit your retainer. Same thing happens with a partial denture.
So if I have a situation like you have I either assume one of two things. The patient was
non-compliant and didnít wear their partial for some period of time, it's been in the
dresser drawer for some period of time and put it in when they came in to see you so
now itís your fault because it doesnít fit or they dropped it or the dog got a hold of
it because patients lie. You know, itís all my fault. Youíre stopped by the cops so you
see the gum machine come up in your rear view mirror, right? So whatís the first words
out of his mouth? Do you know how fast you were going maíam? You know? [In higher toned
voice] No officer I didn't have any idea. Iím the Virgin Mary here. What happened?
You know so it's sort of like people are not the best at saying: I was doing 20 over, Iím
in a hurry, itís my fault. Put the cuffs on me. Itís all my fault. Probably if you
said that you could blow the officer over with a feather and theyíd let you off with
a warning just ëcause theyíd be so blown away that someone was just upright honest
with them. So to answer your question my greatest suspicion in that circumstance is they were
either non-compliant when wearing the partial and teeth shifted or they dropped it and it
got bent. Go ahead.
[Question inaudible]
Did the tooth in question that had this sort of miniscule resi on one tooth, did it have
any lingual or buccal bracing on the tooth or that was theñ? Okay so the point is you
can somewhat of a miniscule resi. But if there is some sort of retentive arm or bracing arm
or clasp arm on the buccal or lingual of the tooth itís unlikely that itís gonna shift
that much if itís being worn on a moderately regular basis.
[Question inaudible]
Uh-uh. Again if the tooth ñ if the partial is being worn on a fairly regular basis. If
they are not wearing it absolutely itís probably going to keep tilting over mesially. But if
the partial is in place it runs slam into the proximal plate on the partial so even
if the occlusal rest were to break off you might get a little tissue irritation around
that tooth because in that area the partial would be freely--you see what Iím saying?
Slide up and down around the tooth but because of the proximal plate on the partial the tooth
would have a heck of a time tilting more mesially. If the partial was being worn. So again when
I see those kinds of things especially with an all-tooth supported partial, the first--and
with students because again they push you all over the place I canít tell you how many
years itís been--thatís one of the advantages in dentistry of getting gray hair. Okay, I
canít tell you how many times over the years I come into the cubicle and I tell the patient
verbatim exactly what you just told them six minutes before I got there and theyíre going,
ìYes, doctor, okay doctor, uh-huh, okay doctor,î and then they leave. And then you come up
to me after clinic and you go I want to send that person to the moon because I said exactly
the same thing you did and they said are you sure? I donít agree with you dudda-this dudda-that
so when you get more gray hair they just sort of tend to and you say the same thing they
just donít fight back as much or push back as much. But many times also if you, itís
sort of like the [clears throat] DNA on the dress, you sort of deny, deny, deny right?
Right up until thereís incontrovertible proof to the contrary right? And so if you ask the
person were you wearing this? Oh yes! Yes. Of course. And we donít have the DNA on the
dress so to speak, to sort of make people change their story. But thatís another matter.
So if we look at a class I partial here basically. Whatís a fairly common circumstance of a
class I partial? Youíve got a bilateral distal extension. Youíve got primary retainers,
in this case, bicuspids. This happens to be a lingual bar not a lingual plate so we have
an indirect retainer here. Again if we imagine our primary fulcrum line here. We imagine
sticky foods a Milk Dud or a JuJu Bee, a gummy bear stick in here and try and lift this away
from the tissue, the fulcrum line is going to be through the clasp tips and by fact of
this touching the indirect retainer or if I have a lingual plate and the plate touches
the lingual of the anterior teeth thatís going to resist the back end of this thing
tipping up in the air. But adds are more important than that because really if anyone eats gummy
bears with these theyíre coming out in their lap anyway. They wonít stay in that tight.
The biggest reason and the biggest advantage of having indirect retainers is an indexing
position for the partial to determine whether it needs a realign and then if you choose,
and say gee, it does need a realign. How are we going to do the realign on a partial? Unlike
a complete denture, unlike a complete denture. For a partial denture what you are not going
to do, what you're not going to do is load up the underside of these bases with a little
bit of PVS, seat it in the mouth and just tell the patient to bite together. Youíre
not going to do that. How come?
Can you see that over time the partial denture base settle down a little bit because it lost
tissue support? Itís very possible that the opposing teeth if they were natural teeth
extruded a little bit? So if you just let them bit down theyíll just tilt it to the
same orientation it had. So if you go ahead and put your PVS in the underside of the bases,
seat the partial denture framework in and carefully hold firmly the partial denture
framework so that the primary occlusal rests are down and the indirect retainers down.
If itís a lingual plate you hold it so that youíre sure that that lingual plate holds
down and tight against the teeth. So youíre holding the framework in its proper orientation
to the teeth which is essentially suspending the free end of the partial in space over
the top of the gums and your impression material is making up the difference retreading a tire.
People get that okay? You send it off to the lab, the lab realigns it so now it comes back
itís got new plastic under it. You fit it in the patientís mouth, you ask them to bite
down, what do you expect to see concerning the occlusion? Itís too high in the back.
So then you just adjust the occlusion on the partial as necessary to get it so now the
partial doesnít rock front to back, the biteís even. But we have adjusted the occlusion on
the partial a little bit because if in fact the distal aspect of the partial sank down
because of loss of support where the tissue changed, itís reasonable to assume that the
occlusion of the opposing arch followed it down which is why you donít just have the
patient quote ìbite togetherî when youíre realigning a partial. You orient the framework
correctly to the teeth and thatís where the indirect retainers come in as a really good
third point of reference for situating the framework on the teeth and knowing itís well
seated. Itís also a great, as I said, it's a great device for telling whether the partial
denture is rocking. Has it lost base support? Easiest way to tell is to seat it as a tetter-totter.
So you look at, hereís an upper case. Now you donít see that much tissue change over
time with maxillary partials. Theyíve got a lot more real estate to cover. Thereís
a lot more square millimeters of gums to support them. This whole area across the center of
the palate, okay, is pretty good support so I donít see the need to realign maxillary
partials anywhere near the rate at which we need to realign free-end mandibular partials.
Because weíve got a lot more tissue support for upper partials.
And here just shows one in the mouth. So you basically got your indirect retainer, youíve
got your lingual bar, and youíve got your clasps. So you check things out and you see:
do things rock?
Here is a lower, weíve got canine abutments. Now in this particular case can you see looking
straight down on the top of the canines that weíve built, weíve done crowns on them both
and weíve created raised cingula on the two crowns because again on the lingual of a cuspid
as it normally exists, itís just that slope that goes all the way down to the gum is just
not a good vertical resting spot. So if the tooth does not otherwise need a crown, you
can build that lingual aspect up with composite to create a ledge on the lingual of it and
composite. You could also go to the thickest portion of the canine, the very thickest portion,
down on the cingulum, take a parallel-sided flat ended bur and cut a small ledge, a fairly
narrow ledge, or you can build it up with composite. Any of the three. My main goal
isnít to leap immediately to doing crowns on teeth if they donít otherwise need a crown
other than for creating a resting spot. You can do that other ways. Sometimes when canines
are rotated weíll actually put a small, little notch on the incisal edge of the canine so
that this framework fits on that little notch. Canines are rotated a bit that does not wind
up being aesthetically unpleasing. Now many times we would not use incisal hooks if we
thought this was going to show very much. Rather than use this my own prejudice would
be if I could, to try and use a little bit of a ledge down on the cingulum at the lingual.
When we look at canine abutments in the maxilla, as much as I possibly can, what I try to do
in the maxillary arch is avoid this if I can. Because again one of the biggest complaints
patients are going to have about partial dentures in general, removable partial dentures, it's
actually two things. One they come in and out.
Can you give me anything thatís fixed that doesnít come in and out? Well depending on
the number and distribution of teeth you may not have that choice. So one big complaint:
gee, they come in and out. Second biggest complaint is theyíre ugly. I donít like
that big clasp showing on my tooth. Which is why anytime, and I mean anytime, you get
a maxillary partial denture in which youíre going to have a canine as an abutment try
to survey it in such a wayóif this is the canine and this is the front of the mouth
here ñ try to work things in such a way that you see if you can come down with a infrabulge
clasp arcing toward the distal. So this is the greatest convexity of the tooth if you
look at this from the incisal edge. Cuspid teeth or canine teeth when you look at them
from the incisal have two faces. Thereís sort of a distal face and a mesial face and
it sort of comes around like this and if this is the front of the mouth anything you can
get from here back tends to hide. So the cheek is hiding it a little bit. If you can create
an infrabulge clasp with a modified tear and eye at the distal, labial aspect of the tooth
as close to the gums as you can get it. Again when youíre surveying these casts the whole
idea about trying to reshape the labial aspect of the tooth to get the height of contour
as low as you can towards the gums. Iíd like my 10,000th of an inch of undercut to happen
ideally about .5 millimeters from the gums because you can see the closer you get your
clasp to the gums two things happen. One is itís better mechanically because youíre
grabbing closer to where the tooth comes out of the bone but secondarily itís just nicer
looking aesthetically because on an upper case if the clasp is way up toward the gum
depending on where the patient smiles their lip doesnít come up above the clasp so you
donít see it and if youíre hiding it around the distal labial of the tooth you donít
see it. So over the years I just see lots and lots of partials on maxillary cases where
thereís a canine involved and as far as Iím concerned are just butt ugly. Because somebody
didnít take the time to take a study model and survey the darn thing and say where is
the height of contour? Can I come up with the survey that will give me the height of
contour that tries to be at the distal labial? Then I try to get a good enough impression
so I hope I donít have a lot of undercut of soft tissues to content with up deeper
in the vestibule from where I want to come down on that tooth. Because if Iíve got real
severe undercut up in the soft tissue in that area then itís difficult to do an infrabulge
clasp but on maxillary partials whenever thereís a cuspid involved, I really like to do an
infrabulge clasp if I can at all and thatís whatís drawn on here. The thing I would change
on the drawing is I would not take it to the mid-labial. I would take it to the distal-labial
sneaking it around this back corner. Now if I do that, one of the other principles Iíve
got to do is that Iíve got to grab around that tooth more than 180 degrees so that the
tooth doesnít move over time away from the partial denture framework. So that means I
need to get some aspect of my framework as far up around that mesial-lingual as far up
there as I possibly can so if my clasping is at the distal labial I need to get my indirect
retention or my occlusal restore-something as far around the corner around the mesial
lingual as I can so I get more than 180 degrees of encirclement of the tooth so it doesnít
move over time.
And so here are some other cases where weíll do these this is starting to get to the right
idea but it's sort of is like if we carried it right over to the mesial labial corner
and then went back, right idea but itís sort of like hmmm screwed that one up a little
bit. Because if we were doing this anyway why didnít we just come down, arc up a little
further and have the anterior most aspect of that T-bar be just about mid-labial on
the cuspid or little bit distal to the mid-labial? So my clasp engaging was right here because
this when the patient smiles jumps right out at you. Itís like this chrome hub cap looking
at you when they drive by. Pretty, who did that for you? Dr. Shotwell. Well Iíll be
sure to tell all my friends. Not bad. Thatís great.
And if you have a modification space same thing here. Youíve got your class I because
itís bilateral distal extension happens to have an anterior modification space. Class
IIs. Okay, what weíve got? Class II is a unilateral free-end upper or lower. So what
have weíve got here. Basically youíve got your primary occlusal rest, your primary occlusal
rest, indirect retainer. Your fulcrum line runs through the occlusal rest if weíre talking
about the fulcrum line that is concerned with tissue-ward movement. If you bite down on
food in this area and you try to push this down your fulcrum line runs across these occlusal
rests. Your retentive fulcrum line is sticky foods that are trying to lift the partial
away from the tissue is gonna go through the retentive tips of this clasp and this clasp.
So this is your fulcrum line if it is for occlusal-ward forces. If itís for sticky
forces trying to remove the partial in the retentive fulcrum line goes from the tip of
the cuspóor Iím sorryóthe tip of the clasp to the tip of the clasp. So that would be
the removal fulcrum line.
Class II upper. Same kind of a thing. Youíve got a unilateral distal extension. Okay we
basically have up here our primary retainer, our primary retainer, indirect retainer third
point of reference. Here again they happen to put a T-bar clasp on this what I would
do a lot of times if I could take a high speed handpiece or a carbide disk. If I had a reasonable
retentive contour at this distal labial aspect Iíd try to recontour this and cut this part
off. Again the curvature of this infrabulge aspect if I can get that to come down a little
bit distal to the point of greatest convexity, Iíd hide the whole thing better. Now with
a lot of these patients when youíre assessing the patient and youíre thinking about what
you might be doing for clasp design on any of these patients male or female when theyíre
in and you take your preliminary impressions one of the things to do with the patients
is to get them so they moisten their lips. Lips are nice and relaxed. You ask them to
smile. Then you ask them to put a really fakey smile on thatís so hard itís going to break
their face and see how high they can really fakey smile and you may get some people that
even on the fakey smile their lip doesnít get up far enough so that itís an issue but
thatís useful information. Thatís useful information because if a person has a really
high smile line then you want to do anything you can to try to hide or diminish how obvious
the clasp is. And to that end itís going to work out better if you survey these things
and be looking real hard for retention at the distal labial aspect of the tooth. Hope
that you do not see a frenum attachment coming in there or a big soft tissue undercut. Soft
tissue undercuts bother me more than frenum attachments. If aesthetics is a big deal,
the patient canít afford a precision attachment of some sort and I got a frenum in there what
do you suppose Iím going to do?
Iím going to call up my friendly neighborhood periodontist or if you do it yourself, Iím
going to do a frenectomy. Iím just going to cut it out of the way. So I can put my
clasp where will it be aesthetically the most pleasing and Iíll just lose the frenum at
that point. If thereís a huge soft tissue undercut thatís a little more difficult to
deal with. But if itís a frenum thatís in the way you can consider doing a frenectomy
to maximize the asethics of your clasp. Okay a II, class II weíve got a modification space
either a front or a back modification space so hereís your class II unilateral distal
extension and thereís another spot that's dential so here itís bounded by teeth so
we have a distal abutment here. So this would be a class II-P. Okay so here basically is
the framework of that which shows you the posterior modification space, thereís the
posterior modification space when weíre ready to get a bite on it. Same kind of thing in
the mouth. Okay hereís our class II posterior modification space with the molar. Primary
occlusal unit our primary uh, primary retentive unit. Another one over here primary retainer.
Thatís the word Iím grasping for is ëretainerí which consists of an occlusal rest, a retentive
arm, and a reciprocal component. Thatís either gonna be a lingual reciprocal arm or itís
going to be a lingual plate that goes across the lingual of the tooth so we have occlusal
rest, clasp component and reciprocation component, okay? So you can also have a class II. Here's
your distal extension, free end and weíve got both an anterior and a posterior modification
space on this. So again itís still a class II. It happens to have two modification spaces.
And so here is that case in the mouth. Combination case. Youíve got an upper denture, you've
got a lower partial, youíve got your free inside with the clasp okay? Weíve got some
modification spaces then on over the other side.
Thereís the same thing in a maxillary case. Again here weíve tried to make moreóthese
were done several years ago when we took these pictures and over time what weíve tried to
do with these I-bars isóI tend to like a modifed T-bar rather than an I-bar and the
reason I like a modified T-bar rather than an I-bar is it just hasÖ
It has a bigger footprint. It touches more tooth than this. And again if I can try to
hide this around the back corner of the tooth, I donít think Iíd pay an aesthetic price
for that. But it used to be one of our former faculty loved doing these and he would try
to make these things like jewelry so they really got so they were really fine, barely
showed up at all. What do you suppose the down side of that was?
That they didnít necessarily break they just came out of retention real quick. So you didnít
have a big enough foot print and this arm that came down just wasnít stiff enough that
they were back all the time getting it adjusted which over time led to what one individual
said is a break. So if Iíve got just a slightly more robust arm here and it doesnít have
to be a truck bumper okay on a Kenworth semi going down the road. It doesnít have to be
that big but I find that the little foot going toward the distal just gives me more square
millimeters of contact with the tooth than that little area of the I-bar will. But again
I try not to have this thing come down mid-labial on the tooth I want it to come down toward
the distal labial aspect. Because itís going to give me a more aesthetic partial and depending
on the patientís smile line, they just donít show up that much it works out really well.
Class IIIs. Which pertain to one of the questions asked earlier. If Iíve got a class III hypothetically
I shouldnít have to deal very much with the resorption of the dentureless ridges. So if
Iíve got an area in here or an area in here when you get to the mouth both of these areas
where itís dentureless are bounded by teeth. So when this person bites down really hard
on their partial, theyíre not squashing the gums. Because the partial is tooth-supported
all the way around. So if this was delivered last year and you wind up getting the patient
11 or 12 months after this was delivered and theyíre telling you it doesnít fit worth
the tankerís darn again all you can go by is whatís written down on the form six. So
if the form six says everything fit just peachy at the time it was delivered and the occlusion
was good and it doesnít fit so good now my first supposition is the patient either has
not been compliant about wearing it or it got dropped. It got dropped. And in either
case whatís going to happen is if the framework gets sprung you can try to fiddle and fix
it but itís not going to work well. If the partial is not being worn as was asked before
this distal molar and this distal molar itís very likely that they may in fact be pounded
a little more mesially so that distance from the mesial marginal ridge to this tooth to
the distal proximal of this tooth will have decreased a little bit. And if you try to
seep the partial down in itíll seem really, really, really tight because whatís happening
is your partial denture is now acting like an orthodontic appliance. And youíre trying
to see if you can get those distal teeth pushed upright again so depending on long the patient
was non-compliant about wearing it you may or may not be able to get that much movement.
You may or may not. So hereís another one. Now many times people will ask if Iíve got
a class III partial thatís completely tooth supported itís very common that I will tend
to use a metal base with bead retention. Because again if Iíve got a completely tooth supported
partial I donít plan on having to realign the underside of that partial. Because I donít
expect the gums are going to change much because Iím not putting much pressure on them. Not
putting any pressure on them. So when Iím doing a completely tooth supported partial
pretty common in the dentureless areas. Iím just going to put a cast metal base with bead
retention. Occasionally weíve done this if Iíve got tooth in this area. So hereís a
tooth thatís, a partial thatís entirely tooth supported but weíre laying right over
the top of this tooth and you may or may not be able to see very well sometimes what happened
with these teeth is the tooth basically is cut off pretty much at the gum line and occasionally
these will have a post and coping put on them. Now can anyone imagine a reason why I might
have my partial denture just go over the top of that tooth? Any thoughts?
Sometimes if you take study models and mount these cases the tooth in this area sits way
up above the plane of occlusion. Itís almost in contact with the upper gums. And when you
look at it itís real obvious from the front that this tooth in the back because it was
unopposed for some period of time extruded. So if you were going to leave that tooth at
the height it showed up at the plane of occlusion on that side in the patient would be going
way the heck up in the air where upon youíve got no room to work on the upper arch. So
one of the things you want to do with study models is evaluate the orientation of your
plane of occlusion and in other areas where do you suppose you learn, where you do learn
how to evaluate the orientation of the plane of occlusion? Where do you learn that? With
your denture patients. Yeah? So whatís a reasonable plane of occlusion? Even with the
anterior teeth to the center of the retromolar pad that you do with the denture. So what
happens to students all the time when they get these bigger cases if thereís teeth there,
no matter how screwed up or crooked the teeth are with the anatomic landmarks somehow you
people think the teeth came down off Mount Sinai with Moses or something.
Oh theyíre sacrosanct. Oh my god they canít be touched! Oh we got ñ how can we possibly
work with it Dr. Shotwell eheheh well, where are your anatomic landmarks? So maybe on a
tooth like this in some cases maybe it was already endodontically treated and Iím not
even thinking about putting a crown on it Iím going to hose that puppy right off at
the gum line. And many times how many of you have had it, you get a tooth thatís the terminal
tooth in the lower arch. Very last tooth in the lower arch. What do you often see concerning
the gums at the distal marginal ridge of the last tooth in the lower arch? The gums are
right up even with the marginal ridge of the tooth. Anybody had one of those? Theyíre
fun to do crowns on, arenít they? Because itís real easy to get that axial wall on
the distal. You people are freaking out and you know I say give me the anesthetic but
theyíre really profoundly numb Dr. Shotwell, I gave them an infraorbital. I know they are.
Now was I speaking Klingon or what? Give me the anesthetic. And then I go and infiltrate
the daylights out of this tissue right here. Till it turns about as white as my lab coat.
ëCause what am I about to do?
Rotary gingitage. Okay? Weíre going to vaporize it. Because Iíve got to get a hold of that
tooth. There are many times depending on where this has extruded to, itís way above where
a reasonable plane of occlusion ought to be. So Iím smoking that puppy down until itís
at a reasonable plane of--- just like you would if you were going to adjust the wax
rim on a denture. So the denture stuff really does come back to help you even when youíve
got teeth there. Look at your landmarks. And so the reason one might consider making a
partial like this is this side of the mouth is extruded. The tooth perhaps was already
endodontically treated so they cut this puppy right down even below the height of the gums
at the distal marginal ridge. We smoke that too. And then put a bevel around this whole
thing and all I do is haul out the whole pulp chamber so when I get this coping back, this
post and coping, it sort of looks like a mushroom? This mushroom stem coming down that sort of
goes down where the pulp chamber was, people following me okay? And the occlusal is just
a flat occlusal that doesnít try to go much higher than the gums. It just covers the occlusal
of the tooth and it goes down to the bevel that I created on it. So now I got this thing
about the right height or a little below the height of an ideal plane of occlusion. Then
I can take my partial and rest it right over the top of it. Iíll have no intention of
putting a tooth on top of this. My teeth are going to be up here but my plane of occlusion
will now be even and level. And it wonít be going way the heck uphill on the side where
the tooth was extruding so look at some of those things when youíre thinking about these.
So here is a class III all tooth supported with an anterior modification space. Hereís
another class III in a maxillary case so you basically got teeth over here okay? You can
see it just come across the palate sometimes you affectionately refer to these things as
a closed-palate or a toilet seat for obvious reasons and so you can go ahead and not cover
too much of the palate but the thing here is if you look at this and say well why wouldnít
I just choose to do that longer span? Youíd have three pontics. Can anyone give me some
reasons why I *might* not chose to do that as a fixed partial denture?
Why wouldnít I do it as a bridge? Do people feel comfortable about that length of a span?
Itís getting pretty long. Now youíre going ahead and putting a crown on it, crusting
it, putting a crown on a molar. Again the thing you do is you remember way back in the
depths and the recesses of your brain, in Dr. Mayís lecture something called Anteís
Law. Does anyone vaguely remember what Anteís Law talked about?
Okay, number of square millimeters of root surface in contact with bone. Iím not talking
about anatomical root surface, Iím talking about clinical root surface. So if a person
has lost some attachment and theyíve lost some bone height, can you see they still got
the same anatomical root surface but they donít have the same clinical root surface?
People follow the difference between those two? So suddenly if you lose bone your clinical
crown gets taller and your clinical root gets shorter. So now you start looking at how many
square millimeters of tooth root do I have here and how many millimeters of tooth root
do I have here in bone? And is that equal to or greater than? Preferably greater than
the square millimeters of tooth root of all the teeth that are being replaced, all the
pontic teeth. Now the other thing that happens when you have a longer span bridge in the
upper or the lower jaw, what do you suppose one of the forces happens on the fixed partial
denture here is that just really beats the periodontium up a lot? Itís not straight
down vertical forces itís buccal lingual forces. Forces that try to rack this thing
buccal lingually. And can you see that if you do this with a partial denture this is
what weíre talking about when we talk about cross arch stabilization? So the fact that
the partial comes over here and gets a good grip on this tooth on the other side of the
arch can you see this is now like a three-legged milk stool? Itís pretty stable so if any
forces try to take this side and wiggle it buccal lingually it gets braced off this.
So longer span from front to back is not always ideally treated as a fixed partial denture.
If you can put implants in there not a problem but long span with a fixed partial denture
can spell heartache especially if you ever get a long span in this anterior tooth and
I see it over and over again is a cuspid that has been endodontically treated and has a
post-end core in it. So I canít tell you over the years how many of these long span
fixed partial dentures Iíve seen in which the anterior abutment is a cuspid that was
endodontically treated that had a nice cast gold post and core and a really nice fitting
PFM crown. What do you suppose I see happen to these teeth three to 10 years down the
road? Vertical root fracture. Now we are in the vernacular scra-hood because now I no
longer have a cuspid to hang onto, Iím up to a lateral incisor. Lot of support there,
isnít there? Thatís a real peach. So now letís a longer span bridge using a lateral
as our primary abutment. Duh. Well because the lateral is not too good letís just pull
the lateral and let's splint the two centrals together. Now youíre just getting insane.
Just donít even come to me with that okay? Now youíre thinking really hard about implants.
Youíre thinking really hard about some sort of a partial. So longer spans are not always
the best treatment with fixed partial dentures because of the buccal lingual force that will
go on those long span bridges and the partial can give us cross arch stabilization. So it
really helps mitigate the buccal lingual forces on those teeth. So basically here is just
another example of a class III. Tooth supported all the way around. Again we try to keep getting
these things Iím much happier if theyíre tucked around the distal, labial, or the distal
buccal corner.
Then we get to the class IVs. Class IVs are always tough because your replacement teeth
are always in front. And sometimes these tend to be tippy and itís really hard to get all
the tippiness out of these. So over your practicing lines what you may want to consider is a lot
of these class IV partial denture cases can really be treated successfully if you can
find one spot somewhere under this anterior area to put a single implant. And the advantage
of doing it with a partial denture is the location of the implant doesnít have to line
up exactly with the tooth. Now if youíre in practice for very long what youíre going
to see is some genius with no planning puts some implants in the anterior area and the
location of the implant is exactly in the interproximal embrasure area of where the
tooth ought to be. So now how do you get that so it looks pretty when youíre trying to
put fixed work on it? Does it go: It takes restorative ingenuity itís sort of like yeah
right itís called paint porcelain to try to cover up your screw-up, okay? So on these
when youíre doing it with a partial denture you can just put a single implant anywhere
across here put a zest locator on it and itís going to work really well. Very seldomóto
show you this oneóit doesnít happen often if you have one of these people that's got
class III lower arch. It seems like all the teeth sort of tow in lingually. When you survey
it you canít feel anything on the lingual of the teeth, not very often, but occasionally
we will do a labial bar. So all the teeth are leaning so far lingually we canít fit
anything down lingually so the partial goes out here and as luck would have it in most
of these cases the lip conceals that pretty well. Most of the time now would you choose
to do that as an implant? Absolutely you would choose to do it as an implant. On these big
cases the more teeth youíre replacing up here the more difficult it is to not have
that anterior tipping phenomena. And in your practicing lives, unlike mine, one of the
things I try to tell anyone with this situation is try to get A: an implant up here somewhere
to brace the anterior aspect of this. Many a time with class IVs when they come back
for recalls this is what you see because of that tippiness. You can beat yourself up about
this but you canít always get rid of this. Try as you might. Try as you might.
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