RPD - Saddles and Supports Flashcards
What is meant by the term ‘saddle’?
- An edentulous area
What is meant by the word ‘flange’?
- Replacement tissue extending to the vestibular sulcus
What is Kennedy Classification?
- An anatomical classification that describes the number and distribution of saddle (edentulous) areas
What defines the Kennedy classification of a mouth?
- The most posterior saddle in the mouth
What is Kennedy class 1?
- Bilateral free-end saddle
What is Kennedy class 2?
- Unilateral free-end saddle
What is Kennedy class 3?
- Unilateral bounded saddle
What is Kennedy class IV?
- Anterior bounded saddle (crossing the midline)
What is each additional saddle area referred to as in Kennedy classification?
- A modification
Which Kennedy class cannot be modified?
Kennedy Class 4
What is meant by ‘support’ in relation to RPD’s?
- A term used to describe the RESISTANCE of a denture to OCCLSALY DIRECTED load
What are the options for resisting movement towards the tissues in the support of RPD’s? (2 points)
- Utility of hard tissues
- Spread the load over a large surface area
Which classification is based on the support for a RPD?
- Craddock’s classification
What is Craddock’s class 1?
Tooth - Teeth provide a HARD tissue resistance to occlusal loading
What is Craddock’s class 2?
Mucosa - A LARGE coverage provides resistance to occlusal loading
What is Craddock’s class 3?
Tooth and mucosa - A combination of HARD tissue and LARGE coverage when there are reduced number of teeth and large edentulous saddles
- You cannot avoid mucosal loading when you have a free end saddle
How do tooth supported RPD’s transmit load?
- Via the periodontal membrane
What does tooth support of an RPD allow?
- Allows the supported denture base to feel like the natural dentition
- It is more comfortable to the patient
What do tooth supported RPD’s support the soft tissue from?
- Protects the soft tissue from trauma
What must mucosal supported RPD’s cover?
- As large an area as possible
- Reduction of the occlusal table
What does mucosal supported RPD’s allow which may cause possible damage to adjacent gingival margins?
- Allows the denture base to move slightly
Which teeth are the best for providing support for a RPD?
- Those with the largest root area depending on the health of the periodontal attachment
How many times more is the periodontal membrane for support compared to the mucosal coverage for a lost tooth?
4 times
How much of a load can a healthy tooth carry?
- Potentially carry its own load plus one and a half similar teeth
What should you think about when thinking about whether a tooth is suitable for support?
- Think of the root to crown ratio
What should the rest on the teeth supporting RPD’s transfer the load through?
- The long axis of the tooth
What are ‘rests’ in tooth support of RPD’s?
- The components which provide SUPPORT for the denture from vertical opposing forces
Rests are describes by that part of the tooth they contact. What are the 3 types of rest?
- Cingulum, incisal, occlusal
What are ‘rests’ made of?
- Cast or wrought metal
- Rests are best used as part of a CAST METAL denture framework
Can rests be incorporated into acrylic bases?
- Yes, but this is very rare
- Incorporating rests into acrylic resin presents a problem due to low base strength. Placing a metal component potentially weakens the acrylic surrounding it
Theoretically all rests should be on a rest seat. Why does this not always happen?
- Doesn’t usually happen due to the ethics of removing healthy tooth tissue
Why are small occlusal rests not recommended?
- As they apply large forces per unit area
Why are large occlusal rests recommended?
- As this can direct forces down the long axis
- Need to be big enough to ensure the loading goes onto the long axis of the tooth
- Think about size of rest coming to at least the midline of the tooth - this is ideal
Where are incisal rests mostly used?
- On lower anterior teeth
- This is due to a poor aesthetic appearance
What may incisal rests interfere with?
- May interfere with incisal occlusion
Where are incisal rests not recommended?
- On wear facets
Where are cingulum rests mostly used?
- On maxillary and mandibular canines, can be used on maxillary incisors and laterals
What are 2 properties of metal framework bases (CoCr)?
- Rigid and strong
What are rests like on a metal framework base?
- ALL rests are integral to the base connected to the major connect directly or by miner connects
How are metal framework bases produced?
- By casting using a ‘lost wax technique’ - more extensive technique
What are 2 properties of acrylic resin dentures?
- Flexible and poor strength
How are rests incorporated into acrylic resin dentures?
- Incorporated mechanically into the base
What does any load resisted by rests on an acrylic denture cause?
- They place an external stress on the base material
- Rests for support within an acrylic base are the exception rather than the rule
What are the 6 main things rests on RPD’s do?
- Prevent movement of an RPD towards the mucosa
- Assist in distribution of occlusal load
- Direct retentive elements to work in a planned manner
- Prevent over-eruption of unopposed teeth
- Provide bracing on anterior teeth
- Determine the axis of rotation for free-end saddle RPD’s
What is the purpose of a rest?
- To support the denture against VERTICAL load - that is directed towards the tissue
Why are rests often pla c ed on the occlusal surface of a tooth?
- Since this will direct occlusal forced down the long axis (root) of the abutment teeth
Where is the default position to place a rest for a bounded saddle?
- IMMEDIATLY adjacent to the saddle
- Additional rests may be incorporated
- The default position may have to be changed depending on the opposing dentition
Where is a rest places for a free end saddle?
- NOT immediately adjacent to the saddle
Where should rests be places for tooth supported bases?
- The support should be on the tooth surface nearest to the base
For tooth and mucosa supported bases, where should the rests be positioned?
- The support should be on the tooth surface which is not next to the base
Why should you avoid placing a rest in an occlusal centric stop?
- The denture will be uncomfortable and the rest will interfere with the occlusion
What are centric stops?
- The stable points of contact between occluded maxillary and mandibular teeth
Rest seat can be prepared but there are downsides to this. What are 3 of the consequences?
- Loss of occlusal stop when denture is not worn
- Destruction of tooth surface
- Exposure of dentine
What is mucosal support (Craddock’s class 2&3) dependent on?
- Dependent upon as large an area as possible of mucosa being covered
- However since soft tissue is compressible it is inadvisable to place the base within 3mm of where the gingival margins are, this will place pressure at the gingival margin
What is the ‘every’ partial denture design?
A mucosa borne denture which restores the dental arch; with contact points between the denture and the abutment teeth
- To ensure the most distal tooth does not drift posteriorly a wire stop is incorporated
In an ‘every’ partial denture are the gingival margins covered by the denture design?
- No
Bounded saddle cases are tooth supported unless the saddles are what?
- Longer than 3 teeth
What are ‘every’ design dentures?
- They are less harmful mucosa-borne dentures
Why are mandibular mucosa supported dentures generally not recommended?
- As there is insufficient area to provide support unless this denture is being used as a training appliance in preparation for a complete denture or overdenture
