Support Flashcards
saddle
edentulous area
replaces gaps but not necessarily teeth numerically
denture base
connector
flange
replacement tissue extending to vestibular sulcus
- extension from alveolar ridge into buccal or labial sulcus
7 questions to ponder when designing an RPD
Will a prosthesis be made?
- Are they dentally fit to cope? Alternative treatment options?
What type of prosthesis: Fixed or removable?
What teeth will be replaced and why?
- Patient’s expectation is to replace all missing teeth – but will fill gaps but not necessarily numerical value
- What saddles will be restored
How will occlusal loading be resisted by the denture?
- Tooth; Mucosa; Tooth & mucosa
How will the denture be retained?
How the denture will resist horizontal movement
How will the components be joined?
What is Kennedy Classification?
an anatomical classification that describes the number and distribution of saddle (edentulous) areas.
- The most posterior saddle defines the classification
Number of saddle areas present in patient (not number of missing teeth)
third molars in Kennedy classification
third molars are generally ignored unless they play a direct part in the denture design
Kennedy Classification: Class I
bilateral free-end
- arch with 2 free end saddles
Kennedy Classification: Class II
unilateral free-end
- 1 free end saddle on arch
Kennedy Classification: Class III
unilateral bounded
- abutments either side
Kennedy Classification: Class IV
anterior bounded (crossing the midline) - abutments either side of the midline e.g. canine to canine (2 to 2 missing)
what is each additional anterior saddle classification referred to as?
a modification
e. g. if a case had two bounded saddles present it would be classified as a ‘Kennedy Class III modification 1’.
- Do not include classifying saddle in classification
Kennedy Class IV cannot be modified.
- As most posterior saddles determines classification
can Kennedy Class IV be modified?
no
As most posterior saddles determines classification
support
term used to describe the RESISTANCE of a denture to OCCLUSALLY DIRECTED Load
Resistance to vertical seating forces
- E.g. chewing forces
2 options for resisting movement towards the tissue are
- Utility of hard tissue
Teeth long axis via PDL - Spread the load over large surface area
E.g. palate
Teeth in support
prevents/resists movement, directs load through periodontal ligaments of adjacent teeth
- into alveolar bone, natural spread
mucosa in support
Needs large surface area = load distributed over a wide area (Stiletto Heel vs Snow Shoe)
- Through the saddle area or hard palate themselves directly onto alveolar bone
Don’t want a small area of load directly onto bone as accelerate bone resorption in that area
Craddock Classification of Support provides
Craddock provides a simple classification based on support for a removable partial denture.
- Describes how the denture on saddle areas is supported
It only gives the type of support and does not tell anything about the number or distribution of teeth.
3 classes of Craddock Classification
- tooth
- mucosa
- tooth & mucosa
tooth support
Teeth provide a HARD tissue resistance to occlusal loading
- Down through long axis onto PDL into bone
- Added root area gives wide distribution of load
Common for bounded saddles
mucosa support
A LARGE coverage provides resistance to occlusal loading
- Doesn’t involve abutment teeth at all, uses the residual alveolar ridge and all the hard palate (need large denture base)
tooth & mucosa support
A combination of HARD tissue and LARGE coverage when there are reduced number of teeth and large edentulous saddles.
e.g. Free end saddle (cannot avoid abutment loading but can use mesial abutment tooth)
5 positives of tooth support
Transmits load via the periodontal membrane.
- Down onto PDL not compressing tissue
Allows the supported denture base to feel like the natural dentition.
Is more comfortable for the patient.
Protects the soft tissue from trauma.
Is likely to stay in close contact with its supporting structures over a period of time.
- Less spacing
2 downsides of mucosa only support
Must cover as large an area as possible.
- Reduction of the occlusal table
- Denture needs to be larger than it potentially could be
Allows the denture base to move slightly. Sink into the mouth – more conscious for the patient
- Possible damage to adjacent gingival margins
what should be the first considered option for support for an RPD?
tooth support
what are the best teeth for providing support?
those with the largest root area depending on the health of the periodontal attachment.
what does root surface determine?
how much load the tooth can take in addition to itself
A healthy tooth can potentially carry its own load plus one and a half similar teeth
- E.g. molar can carry premolar
strongest to weakest teeth in terms of tooth support
Molar > canines > premolars > anterior teeth
how to determine how supportive a tooth will be?
crown to root ratio
remaining teeth value must be greater than missing teeth value
how many times is the Periodontal membrane support more than the mucosal coverage for a lost tooth?
more than 4-times the mucosal coverage for a lost tooth.
- Diameter of tooth + surface area of root = greater load
what do you need to consider when establishing tooth support?
quality of bone health
how is tooth support carried out?
through metal alloy rests on the surface of adjacent abutment teeth.
The rest should transfer load through the long axis of the tooth.
what are rests?
the components which provide SUPPORT for the denture from vertical opposing forces.
Rest are described by that part of the tooth they contact, e.g. Cingulum, Incisal, Occlusal
3 types of rest
cingulum
incisal
occlusal
2 materials which rests can be made of
cast (norm)
wrought metal (rare)
what movements do rests oppose?
Rests oppose movement of the base towards the tissues.
why is incorporating rests into acrylic resin bases rare?
Incorporating rests into acrylic resin presents a problem due to low base strength.
- Placing a metal component potentially weakens the acrylic surrounding it.
where can cingulum rests be?
- Mainly canines but also upper central incisors
- Rare to have sufficient cingulum on lower anterior
where can incisal rests be?
More on lower than upper arch
See metal, so may not be tolerated by patient
determining size of occlusal rests
Small rests
- Not recommended as they apply large forces per unit area
- Can tip the tooth
Large rests
- Recommended as this can direct force down the long axis
Reach the midline of the tooth to prevent tipping
recommended size for occlusal rests
Reach the midline of the tooth to prevent tipping
incisal rests
- Extended from the denture base framework
- Used mostly on lower anterior teeth
- Poor aesthetic appearance
- May interfere with incisal occlusion
- Not recommended on wear facets
cingulum rests
Extended from the denture base framework
Unless prominent cingulum is available a preparation is required
- If sticks out then can become a food and plaque trap as poorer self-cleansing
Used mostly on maxillary and mandibular canines (can be used on maxillary incisors and laterals too)
Aesthetically superior to incisal rests
Apply less stress at lower level – less rotational forces
Less likely to break
metal framework base (Co Cr)
Rigid and strong
All rests are integral to the base connected to the major connect directly or by minor connectors
Produced by casting using ‘lost wax technique’ – more extensive technique
PMMA (acrylic resin) base
Flexible (not rigid) and poor strength
Rest are incorporated mechanically into (within) the base
- Potential weak point of denture as no chemical bond
Any load resisted by rests through the denture base place an internal stress on the base material
Rests for support within an acrylic base are the exception rather than rule, although can be used when opposing forces are light e.g. complete denture
6 rest roles
Prevent movement of RPD towards the mucosa
Assist in distribution 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 RPDs
primary function of rests
support support the denture against VERTICAL load- that is directed towards the tissue.
2 additional uses (bar support) of rests
- Reciprocation
- Indirect retention
best rest type
occlusal
- will direct occlusal forces down the long axis (root) of the abutment teeth.
what is the default position of the rest for a bounded saddle?
immediately adjacent to the saddle
- may have to be changed depending on the occlusal relationship
Additional rests may be incorporated.
- Might not necessarily require if only replacing one tooth
But go to is 2 for more support
what is the default position of the rest for a free end saddle?
NOT immediately adjacent to the saddle
- On the opposite side of the tooth from saddle
- Prevent axial torqueing
Don’t want to compromise abutment tooth
No rests on distal of free end saddle - always mesial
- Don’t have the space create the space
where should the support be for tooth support bases?
the support should be on the tooth surface nearest to the base.
(bounded saddle)
where should the support be for tooth and mucosa supported bases?
the support should be on the tooth surface which is not next to the base.
(free end saddle)
where should occlusal rests be avoided?
in occlusal centric stop
(occlusal contact that effects the occlusal relationship of the patient – hit heavy)
The denture will be uncomfortable and the rest will interfere with the occlusion
3 consequences of making rest seats
- Loss of occlusal stop when denture is not worn.
- Destruction of tooth surface.
- Exposure of dentine.
craddock class 2 primary support area
hard palate
craddock class 3 support areas
Buccal shelf on lower arch
No lingual surface support - contour vertical, placing too much on floor of mouth
what is mucosal support dependent on?
large an area possible of mucosa being covered.
what is a risk of mucosal support?
accelerated bone resorption
- End up spaces between denture and underlying mucosa
since soft tissue is compressible it is inadvisable to place the base within 3mm of the gingival margins are
- this will place pressure at the gingival margin.
how to mitigate potential accelerated bone resorption in mucosa support?
by spreading over largest SA possible
why do you get accelerated bone resorption in mucosa support?
since soft tissue is compressible it is inadvisable to place the base within 3mm of the gingival margins are
- this will place pressure at the gingival margin.
the Every Partial Denture features
Mucosa borne denture which restores the dental arch; with contact points between the denture and abutment teeth
The gingival margins are not covered by this denture design
- All gingival margins healthy and free as possible
- Very good
- Frictional contact support
Spread load but not compromising health of patient
To ensure the most distal tooth does not drift a posterior wire stop (not clasps) is incorporated
- To prevent loss in frictional contact
why is it good that in the Every PD there is clear gingival margins
All gingival margins healthy and free as possible
Spread load but not compromising health of patient
issues with the Every PD
Designs like these can produce narrow and therefore weak denture base areas
- Metal inserted into acrylic causes an inherent weakness in the denture base
how is distal drift prevented in Every PD
To ensure the most distal tooth does not drift a posterior wire stop (not clasps) is incorporated
- To prevent loss in frictional contact
Craddock Class 3 design complication
difference in compressibility between periodontium (vertical displacement of tooth attachment within it’s socket) and the mucoperiosteum (mucosal covering over alveolar bone may compress by as much as 2.0mm)
- unstable base for RPD
need to try and prevent wobble
free end saddle issue
