Rema Almudallal Prostho #24 22/4/15

Today , we will talk about jaw relation registration ,occlusion and how to do try in for RPD .

Last time ,we talked about metal framework try in and altered cast technique.

Today , we will gonna talk about the next step .

*After we ensure that the metal framework does seat properly and we do altered cast technique , now it’s time to take jaw relation registration or (bite registration).

Jaw relation means :- *vertical jaw relation.

*horizontal jaw relation.

*how to use face bow in these cases.

*we know from complete denture RVD and OVD , inter-occlusal distance which is the distance between RVD and OVD (free way space) , these principles are the same we gonna apply in our RPD patients .

*In natural dentition , here we talk about RPD not complete denture , there is few differences but the idea behind free way space (where we get it from?) , we get it from average reading of dentate patients. For example , when we are setting at rest in the lecture , there is separation between upper and lower teeth , which is 2-4 mm , we called free way space .

How does jaw relationship in RPD differ from jaw relationship in complete denture ?

**In complete denture , occlusion is totally dependent on residual anatomy (we don’t have any remaining teeth as a reference to our occlusion) ,that’s why we

Rema Almudallal Prostho #24 22/4/15

always use horizontal relationship and centric relation (centric relation is the only reproducible position) , otherwise we don’t have any other reference .

As a result ,we suppose we do bite on the habitual position of the patient (not the centric relation) what the result of that ? the result of that is malocclusion (it means we take the bite without we do proper guidance to the patient for centric relation , in try in we ask the patient to bite down , the patient will bite anywhere because there is no reference ,that’s why in try in stage we notice improper in interdigitation in the teeth , so the result will be malocclusion. If we don’t notice this in try in stage and I went further to the processing step , in the long term , always there will be complains from the patient , the patient doesn’t satisfied the denture , always there is ulcer (not related to pressure area but as a result of malocclusion).

**As oppose to RPDs , In RPD, the occlusion is not totally dependent on the residual anatomy like in complete denture but it depends on the residual ridge plus remaining dental structure (regardless the number of remaining teeth).

Malocclusion if it happens (as we talked in complete denture , it results in instability of the denture and ulceration of the surrounding tissues) , In RPD the malocclusion translates into instability and torquing of the abutments teeth , so after a while of delivery , the RPD with improper occlusion , this will result in mobility of the abutment teeth and ultimately they need extraction . that’s why occlusal relationship must be recorded accurately and the loads are evenly distributed between denture teeth and natural teeth in order not to over-load the natural teeth .

Rema Almudallal Prostho #24 22/4/15

CD vs. RPD

Today , we look about three scenarios :

^^ stable occlusal contacts provided from existing natural dentition (it means , we have enough number of remaining natural teeth we depend on them in bite registration).

^^ stable occlusal contacts not provided from the existing natural dentition (it means , we take it from the teeth and the wax rims).

^^ How about do we have a partially dentate jaw opposed by a completely edentulous jaw .

***Generally ,no matter what the case was, and what the scenario had, you always (you never obtain any bite not only in RPD even we do single crown ), you always have to have three widely separated tripod points of occlusal contacts to relate the two cast accurately (2 points posteriorly –one each side- and one anteriorly ).

Rema Almudallal Prostho #24 22/4/15

***These contact points mainly tooth to tooth or tooth to interocclusal recording material ( basically the wax rims).

If we have enough natural teeth gives these contacts ,so no need to fabricate a wax rim .

If we don’t have enough three widely separated tripod points, then we need to fabricate a wax rims and related to each other.

***A stable orientation of the opposing casts may exist if sufficient teeth remain and in these patients , no inter-occlusal relation recording is necessary (always and forever , the most accurate way to relate two casts together and mount them on articulator is hand articulation). For example , if we have enough teeth to put the upper and lower cast opposing each other , just by hand articulation .

You look at this case , for example , there is a missing area , ideally of coarse will not gonna even think of RPD in such case , but we go for implant therapy but supposedly for what ever reason , this patient had to have an RPD. In such case ,we have opposing and posteriorly , there is enough contact on both side and also all the anterior teeth are present. So , I suggest to put the cast opposing to each other by hand articulation . ( no need to make a wax rim for

Rema Almudallal Prostho #24 22/4/15

this area , just wasting your time , also no need to bring wax and softening in form of horse shoe and ask the patient to bite down on it ( also it is useless).

As I can to articulate the casts on each other by hand articulation , no need to use any recording medium .

The doctor shows us another case , depending on the opposing , for example we have 2 posterior contacts on each side and 2 anterior contacts , in this case we depend on the opposing , if the opposing is completely dentate … the answer yes we have 3 widely separated contacts . If the opposing is distal end saddle on one side for example , we need to fabricate a wax rim . in this case , the opposing gives enough contact (2 posterior on each side and anterior contacts) .

While the patient in the checked , we caught them opposing to each other , we look to the patient mouth , we make sure that the contact in the patient mouth look exactly like this , then we go ahead and mounted directly on the articulator without any wax rim or recording medium .

The doctor shows us a case that needs to fabricate a wax rim on the edentulous area .

Q/ what to take your bite registration where ?

-In complete denture , we take it by wax .

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-Some people take it with zinc oxide.

Any other material we can use it in the clinic ?

-Silicon material or polymerizing resin .

Q/ How to obtain the bite registration ?

-we suppose, the opposing arch is dentate, we take the reference as the anterior teeth , we ask the patient to bite down , there will be touch between lower and upper anterior teeth , we want this relation to stay the same , we take the occlusion of the patient (we don’t return to the centric relation) , then we put the wax rim , we make sure that the contacts with the wax rim or without the wax rim are the same between the remaining natural teeth and then the rims should be placed just out of contact (it means , we trim from the wax , so we make a space between the wax rim and opposing teeth just about 1 mm in order to put our recording medium ( zinc oxide , silicon , wax ) , we put it in the posterior area here then guide the patient and obtain the impression .

**Clinical procedure step by step :-

- Metal framework try in … ( verifying the fit and occlusion of metal framework ).

- Posterioirly , on the saddle area , there is base plate with wax rims .- The framework with the attached record block is first tried in the mouth for

reconfirming the fit of the framework . ( it is possible when we do fabrication of the base plate and wax rim , parts of the base plate and wax

Rema Almudallal Prostho #24 22/4/15

rim materials go underneath the saddle area , so the fit of the framework will not be proper .So , the first step after fabrication of wax rim is to reassure the metal framework is properly placed.

- The height of the wax occlusion rims are adjusted intraorally , so that 1mm of space exists between the opposing teeth and the rims . this 1mm of space for example we fill it with zinc oxide eugenol . The goal of this ( regardless the material we use it ) is to get fine emprence of the opposing dentition in the wax rim .

As oppose to this scenario here ( not other way to take the bite ) but this case show you what not to do , we have sufficient amount of anterior teeth ( which they are the guidance and reference ), when the patient bite down , I should be able to see the contacts between lower teeth and upper teeth , like in this pic , I able to see the upper and lower teeth are completely in contact , at this time the only thing you should do is to add material posteriorly in order to obtain the three widely separated points .

But when I make horse shoe wax and ask the patient to bite down , will not sure about anything ( maybe the vertical dimension is open or no contacts between the anterior and other teeth ). There is really no way to tell how to take it , so always avoid doing this (squashed bite) , they just heat the wax and ask the patient to bite down ( there is no any contact , and also posteriorly there is no wax rims ). It’s really not helpful .

The proper way is by fabrication wax rims and get the intense of your opposing dentition on the wax rim .

Rema Almudallal Prostho #24 22/4/15

**Recording occlusal plane orientation :In complete denture is very easy , cuz anything is under your control , no natural dentition in the way , we use the fox plane and make a proper occlusal plane orientation . If we have natural dentition, especially if it is like this pic , there is some teeth are more over erupted than others , they get in the way , but generally , you can notice the wax rim no longer than adjacent teeth , posteriorly the orientation of fox plane should be parallel to the campers line or the ala- tragus line .

*inter-occlusal recording is most often after fabrication of the RPD framework and the record base fabricated on the edentulous area of the framework on the master cast , after that you add the occlusal rims to the distal extension and obtain the bite .

As we talked, we need three widely separated tripods points of occlusal contacts and these contact points maybe tooth to tooth or tooth to inter-occlusal recording material .And also we talked about hand articulation which is the most accurate way .

If you look to this pic and we suppose that the opposing arch is completely edentulous , how are you gonna obtain your bite registration ??Here we don’t have any reference from anterior teeth of from the natural teeth , so we go for centric relation . ( we forget about these teeth and deal with it as a complete denture ), there is no differences , we star with upper wax rim , we do all the adjustment steps , and then we put the mandibular

Rema Almudallal Prostho #24 22/4/15

wax rim , we make sure it gets with an intimate contact with upper arch , then we start doing our measurements for the free way space ,then we take the bite in the same way , but there is one difference , here the midline is actually already there , there is a natural tooth , this actually make the job a little easier .The over eruption of these teeth in comparison with the wax rim , you have to accommodate it by the mandibular wax rim , mandibular wax rim in the area opposing to these teeth you have to soften it and get the indentation of these teeth in the wax rim , in addition to the grooves and notches that we make it posteriorly , this way to get your three contact points , three contact points ( ant. From natural teeth and post. There is no natural teeth , so we provided through the grooves and notches and obtain it with wax like in complete denture ) .

So , for the patients whom are arches is edentulous , we need to obtain a free way space of 3-4 mm as we all do usually .

Look at this pic :

Rema Almudallal Prostho #24 22/4/15

This case is a good example of an upper partially edentulous arch opposed by mandibular completely edentulous arch , here the orientation of upper occlusal plane is reversed , posterior teeth are soaping downward , in comparison to the orientation of the campers line, and this is one of the compromises when we have partially edentulous opposed by completely edentulous and we have to deal with .In this case , there is a discrepancy but not sever to the point that we say we need to extract these teeth or go for another mode of treatment , so we will have to accept the occlusal plane orientation of the mandible gonna be some what compromised and the difficulty that will result is not easy to obtain the balanced occlusion , so its more challenging how to obtain the balanced occlusion + forces used to chose specific type of denture teeth in order to be able to obtain the balanced occlusion .

## regardless of what the type of case (either opposed by natural teeth or by complete denture ) , the next step is to obtain face bow transfer for the maxillary cast (we mount the maxillary cast on the articulator using face bow fork and then we already have the bite registration for mandibular to maxillary arch , we fit the articulation then we mount the mandibular cast according to our bite).Now, we do setup for the teeth or we do try in , setup of the teeth depends on which occlusal scheme are you gonna choose for the patient, generally

Rema Almudallal Prostho #24 22/4/15

what occlusal schemes do we have ? – canine guidance , - group function(either unilateral or bilateral) , - balanced occlusion (applied only in complete denture patients).

Q/How about the case when we have complete denture opposed by a partial denture which occlusal scheme are you gonna use ?-we look for a complete denture either single arch or both arches you have to go for balanced occlusion ( take it as a rule) .Whenever the opposing arch is completely edentulous , you have to go for balanced occlusion .

How to differentiate between canine guidance and group function ?

-It depends on the existing situation:

^^ if a physiologic state exits , maintain maximum inter-cuspation

- You always have to have bilateral simultaneous contacts posteriorly in the restored occlusion regardless the classification of the RPD either bounded saddle or distal extension or what the extent of the edentulous area . In the final result , you have to have simultaneous bilateral contacts in the centric occlusion .

- Multiple points of posterior occlusal contact to improve chewing cycle and decrease the potential for wear . Remember : here we deal with RPD, we have mixture of natural teeth and denture teeth , wear resistance of denture teeth is much less than natural teeth . So , you have to follow up the patient every year , you will notice after a period of time wear of acrylic teeth and maximum load is on the natural dentition . If this happened , you should change the acrylic teeth of the RPD.

- You never alter the existing occlusal scheme except to remove a pathologic process. ( before we fabricate the RPD, we evaluate the existing occlusion ,

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if there is any pathology in the existing occlusion , we remove it first and then we carry on with our treatment ).

^^If the lateral guidance is needed , definitely go for canine guidance .

We all know the advantages that associated with canine guidance , for dentate patient the occlusal scheme of choice is canine guidance because it is protective , upon lateral movement there is no destructive forces on the posterior teeth .

- Select if canine are present and sound .- If I have periodontaly compromised canine , I can’t do canine guidance any

more , I have think about group function .- It helps to reduce lateral forces .- It promotes a more vertical chewing cycle .- It allows for greater selection of occlusal morphologies .( occlusal

morphologies that we have ,-anatomic ,-semi anatomic ,-zero degree (not anatomic) .More lateral guidance or canine guidance ….> it means when the pt glides laterally , there will separation posteriorly …> so we go for anatomic teeth .

When we do group function (contacts unilateral on one side of the posterior teeth …> we go for semi anatomic teeth ( we can’t use teeth with very developed cusps ) .

And that's if the canine was sound, but if the canine was periodontally compromised, we go for group function (unilateral or bilateral)

Bilateral group function is called balanced occlusion and it's something destructive in natural dentition, and we need it to overcome certain problems in complete dentures only.

Rema Almudallal Prostho #24 22/4/15

Always when we have lateral movement, we need to have separation on the other side. So if not canine guidance, then unilateral group function. Only if we have an opposing complete denture, you go for balanced occlusion.

So, again we establish group function guidance, if the canines are missing or weak, we should never permit non-working contact on natural teeth unless we had a complete denture.

In conclusion, no single occlusal scheme are present as a recipe, treatment depends only on the clinical situation, and selection of occlusal scheme is multi factorial, as we need to check the remaining dentition, patient's bite, is the patient a bruxist .. etc.

So far no supporting evidence that could support and occlusal scheme over the other, the only thing that has evidence is that canine guidance is advantageous, even for complete dentures, some studies say that even balanced occlusion isn't a necessity there!

Nowadays conventional complete dentures aren't the standard of care, but the implant-retained overdentures!

Especially in dentate patients, no occlusal scheme has been shown to have a superiority, so you have to use your clinical judgement for every our aim in RPD is protecting the natural dentition first then replace the missing areas.

Next step is; try-in

In rpds it should be very simple as the remaining natural teeth are the ones giving us the reference.

Before inserting the framework with the teeth, we look inside the mouth and memorize the bite; the contact between the anterior teeth and then we put the metal framework along with teeth try-in, the contacts between natural teeth should look exactly the same, with and without the metal framework, we make sure we have bilateral contacts posteriorly, we make sure of the shade selection that it's proper and matches natural dentition and then we go for patient's approval and processing.

Rema Almudallal Prostho #24 22/4/15

Next step is processing

Processing of rpd is in essence the same like complete dentures, no differences as far as laboratory steps; flasking > first, second and third pour then burn out and then packing the acryl.

But what is the only difference? In rpd we have the frame work with the teeth, so we have undercuts! In complete denture, we do the first pour up to the cast then second pour and the final pour only covers the teeth, we do burn out to the wax then we open the flasks; we separate the upper and lower members then we pack acryl and close then we put it under pressure, in rpds as we said, we have undercuts, if we put plaster around the metal frameworks and teeth, what would guarantee that the metal framework stays on the teeth! Here comes the only difference which is that we extend the first pour; which is made of plaster to the land area of the cast in complete dentures while in rpd we extend it above that to cover the framework and blocks any undercuts there!

Finishing; we use the same burs to finish and polish the acrylic part as in complete dentures.

The metal framework should have already been polished before the metal framework try-in.

Once again before we fit the finished denture in patient's mouth we make sure it fits on the master cast.

You have to remember the only difference between this step and the metalframework try-in is the acrylic part! So if you have a problem here, you should check the acrylic part if it's causing impingement on the soft tissues and preventing it from complete seating, so here, the same as in complete dentures, we use pressure indicating medium and put it on the acrylic parts that are in intimate contact with the abutments or the soft tissues, we get show throughs and we relief them and the denture will go down eventually and we check occlusion once again.

Good luck