RPD Flashcards
Kennedy’s classification - what is class I?
Posterior bilateral free ended saddle
Kennedy’s classification - what is class II
Posterior unilateral free ended saddle
Kennedy’s classification - what is class III
Posterior unilateral bounded saddle
Kennedy’s classification - what is class IV
Anterior bounded saddle
What classes have modifications? What are these?
I, II, III
Number of extra edentulous area
e.g. missing UL1 and UL8,7,6 = class II mod I
What is an RPD?
A removable appliance which replaces 1 or more missing teeth, not the whole arch
Why can metal components be added to mucosa borne RPDs?
For strength and clasping
What attaches the metal framework of toothborne dentures to the fake teeth?
Acrylic or composite
What makes up mucosa borne dentures?
Metal framework
Acrylic forms the fitting surface and provides support in the saddle areas
When are RPDs only purely tooth borne?
For bounded saddles
When are toothborne dentures provided?
OH is good and stable
Abutment teeth - sound/good condition
What are the requirements of an RPD?
Aesthetics Comfort Retention Distribution of occlusal forces Mastication Space maintenance OVD maintenance
Advantages of RPDs?
Non-invasive
Removable - plaque control
Acrylic ones - additions after bone resorption or tooth loss
Reversible - keep tx options open
Maintains OVD
Prevents tooth movement
Function
Aesthetics - replace the whole dento-alveolar complex
Effective permanent or transitional option
Disadvantages of RPD?
Aesthetics - clasps Pt difficulty adjusting Intolerance - major connector Poor distribution of occlusal forces Tooth tissue loss Plaque accumulation Caries, PD, gingivitis, chronic atrophic candidosis Direct trauma to structures
Name a temporary denture
Spoon denture
Every denture features?
Borders 3mm from margins
Posterior wire stops to prevent posterior drift and loss of contact
List the stages of designing a denture
- Design saddle areas
- Support
- Retention
- Reciprocation
- Bracing
- Connectors
- Indirect retention
- Preparatory work
What is support?
Resistance to vertical forces down towards the mucosa
Options to gain support?
Support = Resistance to vertical forces directed towards the mucosa
Mucosa borne dentures
- Denture footprint being as large as possible to spread the load over a wide area
Tooth borne dentures
- Occlusal, cingulum and incisal rests
- With bounded saddles occlusal rests should be as close to the saddle as possible to ensure the load is transmitted to the tooth efficiently
Tooth/mucosa borne dentures
- Free end saddles mean that the free end of the denture is mucosa borne
- Free end saddles = rests should be as distant from the saddle as possible (at least the opposite side of the clasp tip). This is to improve support, indirect retention and cross arch bracing as the distant rest seat changes the axis of rotation.
- Support is increased as when vertical forces are applied down towards the mucosa, the clasp disengages the undercut and moves towards the mucosa, preventing tooth displacement
- Indirect retention is increased as when forces are applied away from the mucosa, the clasp tip engages the undercut and moves up the tooth bodily rather than causing the denture to rotate and displace
- Cross arch bracing of free end saddles provided to prevent movement
Occlusal rests require rest seats to not affect the occlusion
Occlusal rests provide support, indirect retention, can improve occlusal contacts, prevent overeruption and direct the load down the long axis of the tooth
What do occlusal rests do?
Do not interfere with occlusion due to rest seats
Transmit force down the long axis of the tooth
Improve support, occlusal contacts
Can prevent overeruption
How much tooth prep is needed for different occlusal rests?
CoCr 0.25mm
Gold 0.5mm
SS 0.75mm
Where are occlusal rests located in bonded saddles (tooth borne dentures)?
As close to the bonded saddle area as possible
Where are occlusal rests located in free ended saddles?
Further away from the free end saddle (e.g. mesial of the adjacent tooth) and opposite side of the clasp tip
What is retention?
Resistance to movement of the RPD away from the mucosa (upwards)
How to gain retention?
Physical forces - Saliva creating a peripheral seal
Muscular forces - Through occlusal surfaces of the teeth and polished surfaces of the denture
Mechanical retention: MODELS NEED TO BE ON A SURVEYOR:
- Path of insertion that differs to path of displacement:
When POI differs to POD, in bounded saddles 1 undercut is engaged and the other is blocked out
In free end saddles the undercut is engaged.
An undercut is the area under the surveyor line which indicates the maximum bulbosity of a tooth in the plane of the path of displacement.
POD is perpendicular to the occlusal plane and at a right angle to the occlusal plane.
Clasps
- Provide direct retention by engaging the undercut relative to the path of displacement
- Ensure the abutment teeth are sound and there is enough undercut for the clasp to engage
- Clasps need reciprocation
- Can be gingivally apporaching (I bar - RRPI system for free end saddles) or occlusally approaching
Where is the survey line?
The most bulbous part of the tooth
What is an undercut?
Area under the survey line. Undercut is relative to the path of displacement
How to make the POI equal to POD?
Block out both undercuts adjacent to the bonded saddle
Where do you put a clasp arm?
At the undercut to gain retention relative to upwards direction
What are survey models used for?
Find undercuts relative to the POD and for clasping
Find areas of soft tissue that can be retentive
Why reciprocate clasping?
As the clap arm moves up to the survey line it exerts a sideways load on the tooth that can cause tooth movement. This sideways load can be balanced to prevent tooth movement and make clasp more effective
How to reciprocate clasping?
Put reciprocating arm on the opposite side of the tooth to maintain forces
- Difficult to do
Reciprocating arm with a guide plane:
- Create a flat surface on side of tooth (using a slow speed) and reciprocating arm at bottom of flat - reciprocating arm moves to the most bulbous part of the tooth to stop movement when the clasp arm is exerting it’s forces
Put reciprocating plate on side of tooth as part of connector
- Reciprocating plate stays in contact with the most bulbous part of the tooth (opposite side of the clasp) to prevent tooth movement
What do reciprocating plates contact?
The most bulbous part of the tooth
Define bracing
Resistance to sideways movement of the denture
How to achieve bracing?
Usually provided by other components - connector, maximum saddle extensions and the reciprocating arms of clasps
In free end saddles = needs crossarch bracing to prevent movement. Achieved by occlusal rests being distal to the free end saddles.
What are the types of connectors?
Major:
- Connects saddle areas
- Provides denture rigidity - Provides denture hygiene (should be 3mm away from the gingival margin where possible or above the survey line)
- Mx connectors: Ring, skeletal or open design
- Md connectors: Lingual bar/plate, sublingual bar, dental bar, kennedy bar
Minor:
- Join up components of the major connectors
Define indirect retention.
Methods to achieve indirect retention?
= Resistance to rotation about the clasp axis by acting on the opposite side to the displacing force - prevents rocking e.g. by position of clasps, rests and type of connector
Gain indirect retention by:
- Free end saddles, occlusal rests should be distant from the saddles so the clasp tip moves bodily along the long axis of the abutment tooth
- Altered cast technique for free end saddles
How to make POI = POD?
Block out both undercuts with PoP after surveying it = denture can be removed
When to engage the undercut?
When missing molars (free end saddles) or class IV K.C
What is the POD a right angle to?
The occlusal plane
Name the maxillary connectors
Ring
Skeletal
Open
Name the mandibular connectors
Lingual bar or plate
Sublingual bar
Dental bar
Kennedy bar
How to write your RPD prescription?
Draw design Extent of saddles, no and size of teeth Position of occlusal rests Clasp types on which teeth and corresponding reciprocation Type of connectors and their extension Colour of acrylic base
What is the RPI system?
Provides indirect retention for free end saddles
- Occlusal rests (distant from the saddle/opposite side of clasp)
- Distal guide plane
- Gingivally approaching I bar
Minor connector and distal plate provide reciprocation to the I-bar
Indications for acrylic RPDs?
Remaining teeth have a poor prognosis - can have additions
Young patient/pagets to allow growth
Where bone loss is occuring
When few teeth remain
Temporary denture
Where there is inadequate support from the remaining teeth for a tooth-borne denture (when teeth are not used for support)
Cheaper, made quicker
BUT weak and bulky, can cause soft tissue damage
Indications for CoCr RPDs?
When sufficient, healthy, tooth support can be obtained
Thinner base so more acceptable to the patient
More secure as retained by clasps
Less extensive soft tissue coverage
Strong and transmit load well
BUT cannot be modified
Shortened dental arch?
Less than 20 teeth
9-10 pairs of occluding teeth
Adequate function achieved with reduced dentition
Disadvantages of a shortened dental arch?
Increased risk of anterior tooth wear
RPD provision in future may be more challenging due to fewer teeth, tongue space and controlling a larger denture
Define a functional dentition
The retention throughout life of a functional aesthetic dentition of no less than 20 teeth and not requiring a prosthesis
