design principles of RPDs Flashcards
what kind of support should be the aim with bounded saddles and why
tooth support
not likely to get as much alveolar absorption
teeth will move a little but the mucosa tends to move a lot
what kind of support should be the aim with free end saddles
tooth and mucosa support
where do you want the rest in a bounded saddle
want this as close as possible to the bounded saddle
where do you want the rest in a free end saddle
on the mesial of the abutment tooth
if it was on the distal there is a risk the tooth would tip backwards
what is the advantage of posterior tooth preparation
allows the rest seat to fit nicely on the tooth
doesn’t feel rough to the tongue
won’t affect the occlusion
usually easier to do it this way
why should you be aware of metal crowns when preparing teeth
can be perforated
this means you would need to create a new metal crown for the patient at your own expense
when do you not want support as close as possible to the saddle
If the last molar is tilted (angle of the mandible) then a rest seat on the mesial will cause the tooth to tilt so in this case the rest seat should go on the distal
what do you look for in direct retention
triangular pattern of clasping
triangle cannot rock
when can precision attachments be useful
when you dont have many teeth
what clinical problems can arise with the RPI design
creates a small gap where food traps can occur
patients dont like these
not a good choice if the patient’s oral hygiene is not good
what is bracing
lateral resistance to movement of the denture
what is reciprocation
associated with newton’s third law = for every fore there is an equal and opposite one
if you don’t reciprocate the clasp then the tooth will move
what are disadvantages of the plate connector
patient loses sense of taste
speech may be affected
can cause small food traps
why do clinicians design the denture
They have seen the patient ○ Tooth condition ○ Periodontal condition ○ Motivation § The success rate of denture depends on good oral hygiene and good dental care ○Cost
what are alternative treatments to a RPD
- no active treatment
- fixed prostheses
> conventional
> resin-bonded - implants
what are the 7 aspects of design
- saddles
- support
- retention
- indirect retention
- bracing / reciprocation
- connectors
- review and simplify
what is the saddle area
the teeth being replaced
name the classification system for saddles
kennedy denture classification
what is kennedy class I
bilateral free end saddle
what is kennedy class II
unilateral free end saddle
what is kennedy class III
bounded saddle
what is kennedy class IV
anterior bounded saddle crossing the midline
what is support
the resistance of the denture to occlusally directed load
what is stopping the denture going through the mucosa
name the classification system for support
craddock’s classification
what is class I of craddocks classification
tooth borne support
what is class II of craddocks classification
mucosa borne support
what is class III of craddocks classification
combination of tooth and mucosa
what is retention
resistance of the denture to vertical displacement (lifting away from the tissues)
what are the methods of retention
- clasps
- soft tissue undercuts
- adhesion
- friction
- path of insertion
- precision attachments / implants
what is indirect retention
resistance to rotational displacement
need to have things on both sides of the axis of rotation of the denture - need a balance
what is reciprocation
prevents a clasp arm moving the clasped tooth
what do major connectors do
connect all the components
what do minor connectors do
connects rests, clasps and bracing arms
what are the advantages of the bar design
gingival margins clear gives good depth comfortable for patient simple design doesn't affect taste
what are the advantages of a mid palatal bar / strap
comfortable for patient
works well
what are the advantages of the horse shoe design
- works well
- keeps palate clear for patient
if patient has a heavy bite which causes the denture to break how can this be resolved
rise the connector up higher on the prosthetic teeth anteriorly
metal backing means the denture cannot be broken due to the heavy bite
this q is v specific to the horse shoe design given as an example in this lecture x
what are the advantages of a plate design
if the longevity of teeth is poor then it is easy to add new teeth onto the denture
can also extend the plate further back to give indirect retention and make denture more stable
what are the disadvantages of a plate design
covers palate so taste will be affected
name types of connectors
- ring
- bar
- plate
- spoon (every)
- horseshoe
what are the different types of lower CoCr bars
- lingual
- sublingual
- dental
what are the advantages of a flanged saddle
- gives good retention
- stops food trapping
- appearance stays the same
what are the advantages and disadvantages of gum fitted / open faced saddles
looks good initially
- no flange
- as resoprtion occurs there will be a gap
what needs to be considered for tooth / mucosa support
- periodontal condition of abutments
- size and position of saddle / abutments
- condition of supporting mucosa
- occlusion / chewing capability
- aesthetics
what is involved in direct retention
- clasps
- engaging soft tissue undercuts
- hydrostatic pressure
- path of insertion
- muscle control (more important for complete denture)
what is included in the review stage of design
studying the design and deciding if you can make the design simpler, less fussy or have less components
