RPD DESIGN - SUPPORT Flashcards by Roisin Mousa

What is support defined as

RESISTANCE of a denture to OCCLUSALLY DIRECTED load

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During function, what are the forces transmitted through

the denture saddle

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What is the forces transmitted during function resisted by

bone

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Describe a tooth borne denture

The denture is supported by the adjacent teeth by components such as occlusal rests, the force is transmitted to bone via teeth and periodontal ligaments

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How does a tooth borne denture work

It provides a HARD tissue resistance to occlusal loading

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Describe a mucosa borne denture

The denture rests on the MUCOPERIOSTEUM then the force is transmitted through that tissue

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What is required for mucosal support

a LARGE SURFACE AREA is required to distribute the load over a wide area

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How do mucosa borne dentures work

the large coverage provides resistance to the occlusal loading

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What is a mucosa and tooth borne denture

Where there is a combination of HARD and LARGE coverage when there are reduced number of teeth and large edentulous areas

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What is craddock class 1

tooth borne denture

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What is craddock class 2

mucosa borne denture

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What is a craddock class 3 denture

tooth and mucosa borne

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What are the advantages of a tooth support denture

Allows the supported denture base to feel like natural dentition
Is more comfortable to the patient
Protects the soft tissue from trauma
Is likely to stay in close contact with its supporting structures over a period of time

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What is the disadvantage of a mucosal supported denture

allows the denture base to move slightly

possible damage to adjacent gingival margins

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Where is a mucosa borne denture most likely to be successful

A mucosa borne denture is more likely to be successful in the maxillary jaw as palatal coverage ensures more effective support - a mucosa borne denture in the mandibular jaw often causes tissue damage

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What does planning support depend on

root area of abutment teeth
extent of saddles
expected force on saddle

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What do you think about when looking at root area of abutment teeth

Area of root available to accept vertical forces governed by type of tooth and periodontal health

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What is the tooth with the least root

mandibular incisors

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What is the issue with periodontal disease in planning support

If PDL has been partly destroyed by periodontal disease (periodontal disease often first attacks the widest part of the root and so its greatest area) the full support potential of the tooth cannot be used

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What fibres is vertical force generally transmitted by and what can impact the function of these fibres

oblique

will not function effectively if the teeth are tilted mesially (issue w/ mandibular molars)

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How does extent of saddle effect support

Smaller the saddle, lower the forces

What do you look at when looking at expected force

Is the opposing dentition natural or artificial

Functional force created by an opposing denture is less than that of natural teeth

What are rests made out of

cast or wrought metal

Why can incorporating rest into acrylic resin be problematic

due to low base strength

placing a metal component potentially weakens the acrylic surrounding it

What size of rest do we want

We want LARGE RESTS as these can direct the force down the LONG AXIS of the tooth

What are the different type of rests

occlusal cingulum incisal

What are occlusal rests used on

Premolars and molars

What are cingulum rests used on

maxillary canines mandibular canines (requires tooth prep) maxillary central and lateral incisors

What are the advantages of cingulum rests

Aesthetically superior to incisal rests | Apply stress at lower level due to less rotational forces

What are incisal rests used for

mandibular canines | incisors

What are the disadvantages of incisal rests

○ Not preferred due to aesthetics ○ May interfere with incisal occlusion ○ Not recommended on wear facets

What are the functions of rests

assist in distribution of occlusal load distribution of horizontal force maintaining components in correct position protecting the denture/abutment tooth junction providing indirect retention reciprocation preventing overeruption determine the axis of rotation for free end saddle RPD direct retentive elements to work in a planned matter providing bracing for anterior teeth

How do rests distribute horizontal force

○ Some rests will transfer some of the horizontal functional force - this is known as the BRACING function

How do rests maintain components of the denture in the correct position

The rests prevents the other components of the denture sinking into the soft tissues

How do rests protect the denture/abutment tooth junction

○ Can provide a 'roof' to the space between the saddle and abutment tooth ○ Prevents food being forcibly pushed down by the denture into the GM

How do rests provide reciprocation

○ Rest placed in a box shaped preparation in a molar or premolar tooth can provide effective reciprocation for a retentive clasp

How do rests prevent over eruption

○ Tooth is best maintained in position by contact with an opposing natural or artificial tooth ○ In the absence of an opposing tooth, a well retained occlusal rest is able to prevent overeruption

Describe rests as part of a metal framework base

All rests are integral to the base connected to the major connector directly or by minor connectors

How are rests incorporated into PMMA

Rests are incorporated mechanically into (within) the base

What is the issue with rests incorporated into PMMA

Any load resisted by rests through the denture base place an internal stress on the base material

When is it ok to use rests in PMMA denture

They can be used when opposing forces are light e.g complete denture

Where is the default position for a rest

for a bounded saddle is IMMEDIATELY adjacent to the saddle | the default position may have to be changed depending on the opposing dentition

What is the default position for a free end saddle rest

NOT immediately adjacent to the saddle - it is placed on the MESIAL side of the abutment tooth

Where should you avoid putting rests

Avoid placing a rest in an occlusal centric stop - will interfere with occlusion

What is the possible consequences for preparing rest seats

Loss of occlusal stop when denture is not worn Destruction of tooth surface Exposure of dentine

Where should mucosal support bases be placed in regards to the gingival margin

3mm | will place pressure at the GM otherwise

What is a every partial denture design

for mucosal support restores the dental arch; with contact points between the denture and abutment teet connector borders kept 3mm away from GM

In an every design denture what is used to prevent distal drift

a wire stop is placed posteriorly

What is the issues with an every design denture

Some designs such as these can produce narrow and therefore weak denture base areas Metal inserted into acrylic causes an inherent weakness in the denture base

What is an issue with tooth and mucosal support denture

difference in compressibility between periodontium and mucoperiostium (0.1mm vs 2mm) can cause denture to rock