partial denture designing

7/27/2019 Partial Denture Designing

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Partial Denture Designing

Tony Johnson and Duncan Wood

University of Sheffield

School of Clinical Dentistry

Academic Unit of Restorative DentistryOctober 2011


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What you need to design

partial dentures:

Study models

Model surveyor

Patients previous partial denture history

Details regarding the patients oral andgeneral health


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The model surveyorUses:

To locate accurately the height of survey lines on teethfor a given path of appliance insertion

To determine the best path of appliance insertion

to precisely position clasp arms and determine thedesign which ensures that the metal has the necessaryresilience to prevent trauma to the teeth or claspfracture

To establish soft tissue and tooth undercuts whichmust be blocked out prior to model duplication ordenture construction


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The model surveyorUses continued:

To establish soft tissue undercuts which may requiresurgical removal or be used for added retention whencompatible with the path of insertion.

To provide information for the design of the entire partial, ,

rests, location of bars, plates and retention elements.

To aid in the restorative procedures necessary on abutmentteeth.

To trim wax patterns of crowned teeth to coincide with thepath of insertion and improve the fit of the appliance andaid reciprocal action.


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A system of design Denture support

o

Tooth or tissue borne Saddles

Surveying the model

o Design criteria and options for direct retainers

Reciprocation

Support

Connectorso Design criteria and options for connectors

Indirect retention


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The shortened dental arch

principle

A reduced dentition may actually be adequate for

many patients and it is more important in these cases tomaintain the teeth that remain than replacing themissing ones

The World Health Organization have set a standard forgood oral health as having 20 natural teeth throughout

adulthood. However, in the context of having a

functional occlusion it may be less important than thenumber of teeth that occlude with each other to permit

acceptable oral function


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principleSome reasons for not providing an RPD for

patients who have 20 occluding teeth are: RPDs that replace molar teeth may not provide

the patient with any immediate masticatory

skills to effectively use the appliance A high standard of oral hygiene is required by the

patient if further tooth loss is to be avoided.

Older patients may find this harder to achieve At least 50% of all free-end saddle RPDs are not

worn!


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principleSome potential disadvantages of not providing an RPD forpatients who have 20 occluding teeth are:

Could be an increased risk of anterior tooth wear

Subsequent provision of an RPD, due to further tooth loss,may be harder for the patient to habituate to due to

larger masticatory role and its inability to accommodate thenew prosthesis placed into a space it had previouslyoccupied

Could be an increased risk of TMJ dysfunction. However,

there is no evidence to confirm this and free-end saddleRPDs would not necessarily prevent TMJ dysfunctionanyway.


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Tissue Borne RPDsFactors to think about:

Teeth to be replacedo What teeth should be chosen? The narrower the teeth the

less pressure they exert on the denture and underlyingtissues use premolars not molars!

Saddle extensionso Always extend the base to the maximum denture bearing

area even if only a few teeth are being replaced thesnow shoe effect!

Path of insertiono Can the path of insertion be altered from the path of

displacement? This improves retention and aesthetics


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Chromium/cobalt RPDsFactors to think about:

All the factors mentioned for tissue borne dentures areapplicable here as well

How sound are the teeth needed for clasping or resting?

Is there enough undercut for clasps to usefully engage?

What depth of undercut should the clasps engage?o Based on the tooth to be clasped and the type of clasp and

material being used

Major connectors and there extension Which type and

how far do they need to extend? Always check the patients old denture if they have one to

ascertain what problems, if any, they had with it no pointcreating the same problems.


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Transferring your design to the

technician Clear easy to understand instructions are essential if you and the patient

are to get the RPD you both want.

The best method of transferring your design to the technician is to draw itprecisely onto the surveyed study models.

Detailed drawings and written instructions detailing every aspect of yourdesign are required to enable the technician to produce the RPD youre uested.

The factors you should detail are: direct retainer types on which teeth andengaging what undercut depth; the type of connector and its exactextension; the position of occlusal or incisal rests; saddles, extension andthe number and type of teeth they hold; reciprocal elements, types andextension; indirect elements; general instructions including the surfacefinish of metal denture bases, mirror or stippled. The colour of the acrylicresin denture base can have an important effect on aesthetics, particularlywhen involving anterior teeth; you may need to use an acrylic resin shadeguide to achieve a good match between the natural tissue and thedenture base.


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A final word on design!All partial dentures exact a biological price from the

patient. The dentists role is to minimize the price. The design should be as simple as possible, so long as it

is compatible with the requirements for support,.

Inappropriate design causes more damage than thewrong choice of materials.

When replacing upper teeth the case for an acrylic

base denture is strengthened by the presence of thehard palate and the support it provides.


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A final word on design (contd) Permanent mandibular partial dentures should make use of

soft tissue support as much as possible to prevent trauma

to the soft tissues. This will usually dictate the use of a castmetal major connector since although it is possible toconstruct metal rests which can be incorporated into anacr lic resin denture it is not cost-effective.

Provision of a denture saddle posterior to a natural molarabutment cannot be justified. An unopposed tooth in theopposite jaw does not alter the importance of thisstatement.

Special impression techniques (such as the altered casttechnique) for mandibular free-end saddle partial denturesare highly recommended in order to provide a more stableresult for this often poorly tolerated prosthesis.

partial denture designing

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