RPD PROS Flashcards
What is the working order for creation of an RPD denture? (Clinical visits)
History and examination, provisional diagnoses
Primary impressions
(Preliminary jaw reg and denture design/definitive diagnoses/treatment plan)
Master impressions
(Metal framework try-in)
Jaw registration
Wax try-in
Denture delivery
Review
What is the working order for creation of an RPD denture? (Clinical and lab stage)
Flow chart
What do/can the lab do after primary impressions?
Cast the primary impressions
Survey your cast
Make preliminary casts for a preliminary jaw registration and then articulate those primary casts
Make a custom tray to take master imps
What might you do before master impressions are taken?
Denture design
Any necessary tooth preparation
What do the lab do after you have taken master imps?
Cast master imps
Make registration rims (+ metal framework)
What do the lab do after you’ve done a jaw reg?
Articulate the master casts
Set the teeth and make a try-in denture
What do the lab do after the try-in stage?
Process and finish denture
What upper anatomy do you want to record from impressions?
Teeth
Gingival margins
Any residual ridges
Maxillary tuberosities and hamular notches
Functional labial and buccal sulci including frenae
Hard palate and it’s junction with the soft palate
What upper anatomy do you want to record from impressions?
Teeth
Gingival margins
Any residual ridges
Maxillary tuberosities and hamular notches
Functional labial and buccal sulci including frenae
Hard palate and it’s junction with the soft palate
What lower anatomy do we want to record from impressions?
Teeth
Gingival margins
Any residual ridges
Retromolar pads
Functional labial buccal sulci including fraenae
Lingual sulcus, lingual frenum, mylohyoid ridge and retromylohyoid area
What equipment do you need for impressions?
Stock trays and handles
Spatula
Adhesive
Alginate (correct of scoops)
Mixing bowl
Measuring cup
What are the options for filling a space?
No treatment
Bridge - fixed prosthesis
Denture - removable prosthesis
Implants
(Ortho)
What are the options for filling a space?
No treatment
Bridge - fixed prosthesis
Denture - removable prosthesis
Implants
(Ortho)
What should you always always always do because deciding on a treatment plan?
GET A DEFINITIVE DIAGNOSIS!!
Good practice involves getting articulate and surveyed study casts
What should you get from a history of pros patients?
Address their opening presenting complaint?
Dental history, attendance patterns, previous treatment
How long since teeth have been missing and why - eg trauma, caries, perio, never had?
Denture history
Medical history
Social history - age, sex, employment, how they got to the appt, smoking and drinking
What denture history questions should you ask the pt?
• How long have you had the dentures you currently wear?
• Were they made as a set?
• When did you first start wearing dentures?
• How many dentures have you had in the past?
• Which were the most comfortable? Do you still have them?
• Have you noticed any changes to your dentures?
• Have the problems with your dentures come on recently or were they there when you first had them?
What should you check in your clinical examination of pros patients in particular?
(all the normal stuff)
Charting, mobility
Saddles and ridges, bone
Dentures in and out of the mouth
Special tests - radiographs if justified eg for bone levels and underlying pathology, vitality tests?
What are the Kennedy classifications?
• Position of denture saddles around arch with intention to replace teeth
• Class I-IV - bilateral free end saddle, unilateral free end saddle, bounded saddle, anterior bounded saddle (with modifications except class IV!)
• Posterior most saddle regarded first, further saddles are designated modifications
What do you want to check of the existing dentures (in and out of the mouth)?
Age
Type and material
Tooth, mucosa, or tooth and mucosa borne
Kennedy classification
Design
Fractures/repairs
Extension retention stability
Tooth relationships
FWS
Aesthetics/planes
Tolerance to existing RPDs
What is the purpose of preliminary impressions?
Study casts
Diagnosis and surveying
Treatment planning
Outline support
Fabrication of a suitable special tray
What is the purpose of articulated study casts?
To allow an accurate examination of tooth contours and the occlusion - essential in designing a denture
What is the purpose of articulated study casts?
To allow an accurate examination of tooth contours and the occlusion - essential in designing a denture
What might we need to consider for saddles in preliminary impressions?
Impression compound
What is impression compound and what is it’s purpose?
High viscosity
Thermoplastic - can be softened by heat
Stable - rigid once cooled and set
It is a bulk filler for trays
What is the softening temperature of impression compound?
55-60°
What do we want to capture with the impression compound?
Buccal and distolingual extensions of the free end saddles
Retromolar pad regions (key supporting areas in the lower arch)
What would you do right before taking the preliminary impression?
Carefully select the dentate stock tray (with handles) - check extension in the mouth
Modify the tray if necessary to record appropriate denture bearing areas
Select appropriate impression material (eg alginate)
Use an adhesive and leave it to dry
What instructions do you send to the lab after a preliminary impression?
Cast up preliminary impressions (50/50 or dental stone is suitable)
Fabrication of occlusal rims if required OR
Fabrication of special trays
What special tray variants are there to prescribe?
Materials: PMMA (VLC/SC/HC), shellac/thermoplastic materials, (metal, old)
Spacing: 0.5-3mm depending on impression material
Perforated/non-perforated/selectively perforated
Handle design (slubs or L shaped or no handles)
Extension into sulcus: generally 2mm short of sulcus (so imp material makes up the periphery of the impression)
What must you consider if you are going to use an addition silicone (PVS) or polyether for a master imp?
The tray design must reflect this - HOW??
What special tray would you create if your master imps were in alginate (upper and lower)?
Upper: 3mm spaced tray, non-perforated, anterior L shaped handle, VLC acrylic
Lower: ???
What special tray would you create if your master imps were in alginate (upper and lower)?
Upper: 3mm spaced tray, non-perforated, anterior L shaped handle, VLC acrylic
Lower: ???
Why is 3mm the optimum thickness for alginate?
If too thin then alginate can tear
If too thick then alginate can set at different rates and can lead to distortions
Spacing for different impression materials are a function of their inherent properties. What are the different spacings required for different custom trays?
3mm alginate
2mm plaster of Paris (not really used anymore)
2mm PVS/polyether
0.5-1mm ‘close fitting’ ZnOE
What features of a custom tray should you check before placing it in the patients mouth?
Check against the stone model
That it covers the periphery and is relived slightly shy of the full depth of the sculls
Full coverage of hard and soft palate
Handle cranked away from labial region
Cracks/voids
What features of a custom tray should you check in the patients mouth?
(DISINFECT FIRST!)
Look to ensure the periphery of the tray doesn’t extend right into the sulcus (adjust if it does)
Why don’t we want the periphery of the special tray to go all the way into the sulcus?
Want to ensure that alginate can flow over the periphery of the tray so we can capture the functional depth of the sulcus all the way round.
What should we ask the patient to do before we take an alginate imp and why?
What should we ask the patient to do before we take an alginate imp and why?
Rinse mouth thoroughly, teeth should be clean, food bits and debris not good
How does asking pt to rinse their mouth ensure good surface accuracy of the imp and the cast stone model?
Alginate mixed with water is hydrostatic and requires tooth and mucosa surfaces to be sufficiently moist and free from salivary mucin and proteins in order for the alginate material to flow close to the tooth surfaces to produce a detailed impression.
Salivary mucins and proteins have been shown to affect the setting of gypsum dental stone
What is alginate?
An irreversible hydrocolloid
What is alginate?
An irreversible hydrocolloid
What are the 2 phases of alginate setting?
- SOL phase - stage at which mixed material should be inserted in the mouth when it is sufficiently fluid to record detail. No gelation should occur at this stage. WORKING TIME.
- GEL phase is stage at which fibrils are formed within the polysaccharide chains and the alginate goes through an irreversible setting process. It is after this stage that the impression tray should be removed from the mouth. SETTING TIME.
Composition of alginate powder impression material
Trisodium phosphate - controls setting time
Polysaccharides - causes setting to be irreversible
Calcium salt - reacts with sodium alginate to allow the setting reaction
Filler - decreases viscosity of alginate, allowing it to handle well
What should you do before putting alginate in bowl?
Shake alginate container tub
(to eliminate the segregation of powder particles that may occur during storage and to incorporate the surface layer which is often contaminated with moisture picked up from the atmosphere in the container)
What should you consider when putting alginate in bowl and about the water?
Gently fill the alginate scoops
Measure water at eye level
Temperature of water should be room temp (20-22°)
What should the consistency of alginate be?
Smooth mixture devoid of air bubbles and lumps. Needs to be sufficiently fluid to record maximum soft tissue detail, and sufficiently viscous to displace the lingual soft tissues in order than full depth of the sulci can be recorded.
What would happen with a thin/runny mix or a thick/firm mix of alginate?
Thin/runny mix would result with the material running out from under the tray causing the pt to gag and impression record might have voids lacking detail
Thick/firm mixture would not allow the alginate to flow around the teeth and anatomical soft tissue areas when the tray is seated in the mouth, resulting in a granular appearance and lack of detail in the final impression
How many scoops of alginate per tray?
Large imp tray needs 4 scoops, 3 for a medium (upper)
3 for an upper custom tray
Minus 1 for the lower for all of these
How can you change the mixing timing?
Temperature - higher temp = quicker setting (thus use cold water)
Changing amount of trisodium phosphate
Why do we use a perforated impression tray?
To allow mechanical locking of the alginate material to the impression tray. Reduces risk of tearing/separating the set alginate impression on removal from the mouth.
How do you disinfect?
10% sodium hypochlorite solution for 1min
What happens if the alginate imp is left in the open?
Syneresis and evaporation occurs. Syneresis is the loss of moisture from the gel (set) phase of alginate causing shrinkage of the impression and occurs even if stored correctly. Important to cast a model from the alginate impression as soon as possible, even if stored in 100% humidity.
What happens if alginate is stored in wet conditions?
Imbibition occurs, water is a robed but the gel (set) phase of the alginate, causing localised expansion of the impression where it has contacted water.
What is the purpose of a preliminary jaw registration?
Allows definitive treatment planning on articulated study casts. Allows for the assessment of space and positioning of teeth.
What are the 3 categories of occlusion in RPDs, and how do you do a preliminary jaw reg for each?
- Patients with at least balanced 3-point contact (one anterior and 2 posterior contacts in each buccal segment). Registration possible using wax wafer (no rims), use ICP.
- Patients with occlusal contact which is insufficient to allow casts to be placed in ICP without rims. A risk or rims are required, use ICP.
- Patients without an occlusal stop to indicate the correct intercuspal position. Rims required, use RCP.
When do you not need a primary jaw registration?
If there is no tooth contact (ie a partially dentate arch opposing an edentulous one)
What are the 2 positions that we can record the jaw in?
ICP and RCP
What is ICP?
Tooth based position - so pt can reproducibly get their bit together in the same way
Maximum number of teeth interdigitate
What is RCP?
Based on where the condyle of the jaw sits in the glenoid fossa
Condyle should be in the most superior position to be stable and bony
Needed to TMJ is balanced for the patient
Better for when there is no/less teeth so we do not cause TMD and are stretching the ligaments of the TMJ
What is a surveyor?
An instrument used to determine the relative parallelism of 2 or more surfaces of the teeth or other parts of the cast of a dental arch.
What is a surveyor?
An instrument used to determine the relative parallelism of 2 or more surfaces of the teeth or other parts of the cast of a dental arch.
What are the 4 steps to surveying?
Identify, mark, measure, eliminate
What instrument do you use to identify undercuts during a primary survey?
Analysing rod
What happens if the space between an undercut and the denture is not bigger than 3mm in diameter?
As long as space is >3mm in diameter, it is big enough to allow things to flush and wash through. If less, then it will cause a food trap.
What can gaps at the front of the denture cause?
Can leave black triangles which are unaesthetic?
What are interferences?
Stop the denture from being constructed or designed properly or fitted inside the mouth, eg:
- bony prominences (eg canine eminence)
- inclined teeth (eg in lower arch angled back toward the tongue)
What is the benefit of tilting the cast heels up or heels down?
Ensures denture can go into the mouth at an angle to benefit certain spaces in the mouth
Allows denture to engage in areas that would otherwise be dead space
Avoid interferences
Insertion/removal paths change; undercut position changes
What is the normal path of removal for a denture?
Denture will remove perpendicular to the denture bearing area
If denture has been angled what does this mean?
It can only go out at a certain angle
How do guide planes exist?
Can be naturally existing or artificially prepared - dont cut off more than enamel.
Can add composite to make them.
What is a guide surface?
Where the whole surface is tight fit against the denture, rather than a single point of contact with the denture - allows for better retention.
(by having friction surfaces either side, the denture is bound to only come in one way and come out one way)
When you use a graphite marker on a cast, what are you marking?
Marks the most bulbous portion of the tooth. Everything below the survey line is the undercut.
(do after tilting, mark all of the teeth!)
What instrument do you use to measure?
Undercut gauge
What does the undercut gauge help us determine?
Helps determine at which point/depth we need to engage the clasp
When is cast cobalt chromium flexible?
Cast cobalt chrome is flexible if you have an element of it extended to >15mm (must be 15mm to have ideal properties).
Only flexible to engage an undercut of upto 0.25mm.
What might happen is the undercut is less than 0.25mm for cobalt chromium?
Less than 0.25mm might break the clasp or the tooth because the clasp wont flex.
0.25mm is the maximum retentive force - less is less retentive. The less of an undercut you go into, the less effective the clasp.
Which part of the clasp engages the undercut?
Only the terminal third of the clasp engages the undercut (is under the survey line)
What depth undercut can wrought metal or stainless steel engage upto?
Can engage upto 0.5mm on the tooth because it is more flexible.
When do we tend to use wrought wire clasps?
With acrylic dentures, embedded within this.
Do we ever use a 0.75mm undercut?
It is too deep to engage.
Why do we measure the undercut?
Undercuts allow metal components, CLASPS, to engage and retain the denture.
What are the maximum engagement depths of the different materials?
0.25mm cast cobalt chrome
0.5mm wrought metal (stainless steel)
0.75mm too deep to engage
Why cant we use occlusally approaching clasps on premolars or smaller etc? (CoCr?)
Because you cannot get the 15mm length that is needed. Thus must use a gingivally approaching clasp to get that length.
Is wrought wire or cobalt chrome more flexible?
Wrought wire is more flexible (hence why it does not need the 15mm length)
What is elimination?
Blocking out/eliminating unwanted undercuts with wax. Done by lab. Prevents acrylic being processed into unwanted undercuts.
What are unwanted undercuts?
Where the connector of the denture sits flush against the tooth. We don’t want the connector to engage in any of the undercuts on the side, or the denture will get stuck.
Where do we want the denture to finish?
Smooth the wax off, parallel to path of insertion, so when the denture goes in, it will sit flush to the survey line but not below it. Want denture to finish flush against the teeth.
How do you record the tilt?
Can mark the side of the stone cast
Tripoding: mark 3 points on the inner surface of the palatal aspect of the stone model, to give the lab a triangulation as to which way the tilt is.
(also write on the lab ticket, heels up/heels down etc etc to give more info).
How thick do heat cured acrylic dentures need to be?
At least 3mm thick to be strong enough
Any less we would need to move to metal which can be 1mm.
What is a saddle?
The part of the denture that rests on the oral mucosa
Space to be filled by a denture
Bounded or free end
What is support?
The resistance to a vertical displacing force directed towards the mucosa
What is support?
The resistance to a vertical displacing force directed towards the mucosa
What are the classifications of support?
Tooth supported
Mucosa supported
Tooth and mucosa supported
What are the classifications of support?
Tooth supported
Mucosa supported
Tooth and mucosa supported
What is tooth support?
Denture projections sit on teeth, on rests, to help spread load amongst adjacent teeth
Creation of rest seats
What is mucosa supported?
No projections onto teeth
All force directed to mucosa
What is tooth and mucosa support?
Most common in free end saddles
Utilising rest and rest seat at front end but more posteriorly support gained from mucosa alone
What is tooth and mucosa support?
Most common in free end saddles
Utilising rest and rest seat at front end but more posteriorly support gained from mucosa alone
What is retention?
Acts to resist movement or displacement away from the denture bearing area.
How is mechanical retention achieved in RPD?
Clasps - terminal portion of a clasp engages an undercut area on a tooth surface
What is a major connector?
Component of a denture which unites saddles
Can be cast metal CoCr or acrylic
Benefits of having a metal major connector over acrylic?
Stronger, thinner, can have less coverage of the palate (more feedback from palate)
What are the advantages of acrylic denture creation?
CHEAP and EASY to construct and modify
What are the disadvantages of acrylic dentures?
Weak (reduced longevity)
Not rigid (slight flex increases chances of fracture - lower elastic modulus will fracture under force)
Bulky (3mm)
Radiolucent (cannot be found if swallowed)
What are the indications for acrylic dentures?
IRD - bone will resorb and acrylic is easier to add to
Transitional dentures (teeth need to be added to in the future)
What are the advantages of metal based dentures?
Strong and rigid
Thin
Can be designed for precision fit and to favour periodontal health
How does metal dentures favour periodontal health?
Can go around crowns for precision eg and is smaller and thinner so doesn’t cover as much mucosa and gingival margins, helping plaque stay away
What are the disadvantages of a metal denture?
COMPLEX to design and EXPENSIVE to construct
Requires stability of abutment teeth
Unaesthetic for some
What are the indications for metal dentures?
Stable dentition as a definitive prosthesis
EXAM Q - how do you design RPDs?
Stone model study casts, surveyed and ideally articulated
1. Saddles
2. Support
3. Retention
4. Reciprocation
5. Bracing
6. Connector
7. Indirect retention
Why do we replace teeth?
Occlusal stability
Function
Aesthetics
Speech
Soft-tissue support
What does a saddle include?
Covers alveolar ridges
Where flanges originate
Artificial teeth and gum-work
Saddle can go further back than the last tooth - eg covers the mucosa where the 8 is
How can you design the occlusal surface?
Reduce surface area of the posterior occlusal table
Use narrow posterior teeth or remove lingual cusps - (buccal cusps are functional in lower)
Omit last tooth only or all molar teeth with a third premolar instead
Why would you extend the base of the saddle so the acrylic covers upto 2/3 of the Retromolar pad and why might you not?
It will maximise the stability - extend the flange to cover the BUCCAL SHELF
Care when extending lingually in the lower (can be painful in a resorbed ridge). Trimming it back will cause the denture to not be as stable but will be more comfortable.
What is the polished surface?
Aspects of the saddle that touch the tissues/tongue etc.
Can shape the flanges to create concavity to allow the glossal, buccinator and mentalis muscles to engage the denture and enhance the retention for a mandibular RPD
What is the polished surface?
Aspects of the saddle that touch the tissues/tongue etc.
Can shape the flanges to create concavity to allow the glossal, buccinator and mentalis muscles to engage the denture and enhance the retention for a mandibular RPD
The material for the fitting surface - what is the difference between on the ridge and off the ridge retention?
On the ridge retention - metal on mucosa (usually indicated if there is insufficient space eg vertical dimension too small)
Off the ridge retention - acrylic on mucosa
Why is off the ridge retention favoured?
Since acrylic is much easier adjusted than metal
Eg for adjusting the surface or adding a reline etc.
How much space if needed between teeth occlusion (for a rest)
Needs at least 1mm space between teeth occlusion
When are rests not suitable?
If there is more than 50% bone loss, or really mobile teeth
What should you consider for rests?
Health of abutment tooth (bone levels, pulp health, mobility)
Extent of saddle
Expected force on the saddle - Consider the opposing arch and what the occlusion is like eg denture, natural teeth or implants.
Eg denture will have little force, teeth have PDL fibres to feel, implants will smash through cos they are strong
What is the ideal rest position?
In a bounded and tooth supported saddle: as close to the saddle as possible
When is a rest seat needed?
Rest seat will be needed if insufficient occlusal space. Drill into enamel of teeth only.
When is a rest seat needed?
Rest seat will be needed if insufficient occlusal space. Drill into enamel of teeth only.
What provides better support?
Tooth better than mucosa because mucosa is soft and relies on retention
What element of tooth support is there in acrylic dentures?
When you finish the acrylic at the survey line rather than at the gingival margin (called colleting) (don’t want gum stripper design). Draw denture line on teeth.
Why is a free-end saddle a problem?
Due to a differential of pressure, the denture will move in a free ended saddle and mucosal part may move up. Too much pressure on the abutment tooth will displace it distally and we don’t want it to become mobile.
What can we do to protect the abutment tooth in a free-end saddle situation?
RPI method:
R = mesial rest
P = distal guide plate
I = I-bar gingivally approaching clasp
Should be no coverage of the tooth lingually, allowing the denture to disengage. Method allows the saddle to move without harming the tooth, and to disengage in a controlled healthy way.
What can we do to protect the abutment tooth in a free-end saddle situation?
RPI method:
R = mesial rest
P = distal guide plate
I = I-bar gingivally approaching clasp
Should be no coverage of the tooth lingually, allowing the denture to disengage. Method allows the saddle to move without harming the tooth, and to disengage in a controlled healthy way.
What is the free-end saddle shortened dental arch concept?
8-10 pairs of occluding units
The retention of a natural, aesthetic, functional dentition of no less than 20 teeth.
What are the types of RPD retention?
Clasps
Guide surfaces (main 2)
Neuromuscular forces (shaping polished surfaces)
Physical forces (saliva)
Precision attachments
Why do acrylic partial dentures need clasps?
Because they cannot attain a great peripheral seal
Is a clasp flexible?
A clasp should be the only part of a denture that is flexible
What are the 3 types of gingivally approaching clasps?
I bar
J bar
T bar
What are the types of occlusally approaching clasps?
Ring
3-arm/E
What are the types of occlusally approaching clasps?
Ring
3-arm/E
What factors must you consider when clasping teeth?
Position of undercut
Sulcus shape - risk of food trap
Clasp material
Clasp length
Clasp cross section
Appearance/aesthetics
Periodontal status
How does position of undercut affect clasp?
Only the terminal third of the clasp should flex and engage
How does sulcus shape affect food trapping?
GA clasps with big undercuts might allow for food trapping between soft tissues and clasp
How does clasp material affect which clasp to use?
Cast metal - CoCr = stiffer
Wrought wire - stainless steel = flexible
Is cast metal or wrought wire more effective?
Cast cobalt chrome is stiffer but more effective
Can you use cast metal on acrylic dentures?
Cast cobalt chrome can only be used on metal based dentures
What clasp material do we usually use for acrylic dentures?
Wrought wire (but can use cast metal)
Which clasp material will give better retention for dentures?
Cast metal will give better retention than wrought wire.
How does clasp cross section affect choice of clasp use?
Circular clasps flex in all different directions so are less effective at retaining the denture. Semi-circular (cast CoCr) clasps flex in the most appropriate way in comparison to wrought wire circular clasps.
How do aesthetics affect what clasp to use?
Might not what to clasp an anterior tooth
How do clasps affect periodontal status?
For teeth that are periodontally not idea, you might not was to use rigid or stiffer clasping. More relaxed (like wrought wire) clasping will put less lateral pressure and load on the teeth.
Which clasp material do you use for healthy and unhealthy teeth (periodontally)?
Healthy teeth want CoCr
Less healthy teeth want wrought wire.
Where do you want to clasp a tooth?
Usually strongest and bulkiest teeth want to be clasped (usually molars)
Position a clasp as close to the saddle as possible.
Should be a clasp on either side of the arch and ideally at least one clasp per saddle.
What depths of undercut can each material reach and why?
Cast metal = 0.25mm
Wrought wire = 0.5mm
IF undercut is too deep, clasp will engage it and it will be too deep for the clasp to come out. So only engage at required depth.
What happens if you position a clasp deeper than these depths?
Clasp fracture
Tooth fracture
What happens if you position a clasp shallower than these depths?
Less depth reduces effectiveness of the clasp.
How do guide surfaces work?
Limits the number of directions/paths that dentures can displace away from the denture bearing area. Hence enhances retention. Denture parallel to a tooth surface - denture can only go in at one angle.
They provide a definitive path of insertion and removal.
What is reciprocation?
Prevents unwanted tooth movement (due to the forces acting on the tooth by a clasp). Balances the lateral pressure a clasp places on a tooth (stops it from wobbling).
What factors can act as reciprocation?
Reciprocating arms
Ring clasp terminal third is retentive, other aspect is reciprocative.
Major connector
What is bracing?
Prevents lateral movement of the denture during function. Whilst the denture is fully seated.
Examples of bracing
natural bracing eg flange, major connector, resting against teeth etc
What does a connector do?
Connects ALL components of the denture together to form a rigid stucture
What are the different types of upper major connectors?
Anterior palatal bar or plate
Middle palatal bar or plate
Posterior palatal bar or plate
Full coverage palatal plate
Ring (plate) or skeletal (bar) connector
What are the different types of lower major connectors?
Lingual bar
Sublingual bar
Lingual plate
Dental bar
Kennedy bar
Labial bar
READ ABT THE DIFFERENT TYPES IN PAPER
READ
Make brainscape on this
What is indirect retention?
Prevents rotation of the denture around a clasp axis
How do you achieve indirect retention?
To prevent rotation around a clasp axis, the INDIRECT RETAINER must be positioned on the opposite side of the clasp axis to the saddle.
Indirect retainer can be a rest on a tooth or extension of the connector onto the hard palate.
Describe how plaque retentive and how actual retentive the different gingivally approaching clasps are?
T is the most plaque retentive but most retentive
I bar gives least amount of retention but least plaque retention
J bar in between
(remember that if the plaque is retaining not near to the gingival margin then it wont cause inflammation)
What class of dentures do guide surfaces work best on?
Kennedy class III
What are the types of rests?
cingulum rests
occlusal rests
What can rest seats be incorporated into?
bonded metal crowns
bonded composite contours
surveyed crowns
(treatment plan early!!)
What can happen if you have rests on a crown?
Galvanic action - issues with dissimilar metals touching and currents - some patients prone to this.
Eg cobalt chrome touching gold alloy
How do you modify a custom tray, with what and why do you do it?
Greenstick modification to achieve a good peripheral seal at the hard soft palate junction and also allow for spacing when taking the alginate impression
Can extend it into a free end saddle region (want to capture hamular notch here)
Explain how to do a greenstick mod?
Vaseline the greenstick
Warm it in hot water bath
Place on tray where needed (posterior edge, free end saddle, centre)
Put whole tray in water to allow for better adhesion
Ensure warm before placing in patients mouth
Ensure not in any teeth areas
After adaptation, run final greenstick under cold water and spray the tray ready for alginate imp
Why do we put greenstick in the centre of the custom tray?
It will maintain the 2-3mm spacing to ensure alginate is at the correct thickness around the teeth and tissues. Will help relocate tray to a good position.
How do you take a master impression?
Dry water residue
Adhesive and allow to dry
Shake alginate tub
Put scoops into bowl
Add water and mix
Ensure no air bubbles
Tray handle away from lip
Border moulding
Pt to breathe through nose
Relieve and remove impression
What do the lab do after you have taken master imps?
They cast the imps for master casts. They will make the wax rims for the next stage (occlusal registration rims)
What material are the casts made from?
Teeth, palate, flange areas are replicated in dental stone. Base of cast is plaster of paris.
What is the purpose of occlusal registration rims?
To record the patients jaw relationship and establish where the teeth are to be set.
What information will the dentist identify (6) from the wax rims?
Occlusal plane
Lip support
Centre line
High smile line
Vertical dimension
Centric relation (upper and lower jaw relationship)
What is in the wax rim?
wire strengthener so the reg rim doesnt distort when used in pt mouth since pt mouth is warm.
What should you do first when the wax reg rim is returned from the lab?
Check it on the master model:
- check extensions of the rim extend to the full depth of the sulcus
- wire strengthener fully embedded
- reg blocks in saddles are appropriate width and height according to adjacent teeth present
Will the wax rim have good retention and stability?
Only wax so might not have absolute retention
Stability - should sit firmly on model and not rock of move around
Why do you put models to soak?
so the wax doesnt stick to them later
What should you check initially after placing the rim in the mouth without too much pressure?
Fully seated. Extension, retention, stability (no rocking?). Tell pt not to bite together at this stage.
What do you need to consider if there is an anterior flange?
Consider lip support
Naso-labial angle 90 degrees
If too large, add wax to buccal surface. If too small remove wax from this surface.
What should you consider about incisal height?
Ensure height of rim is level with the adjacent teeth.
If anterior flange what information do you need to provide the lab with?
Centre line - vertical mark midline of face.
Smile line - usually 70-80% but varies. Ask pt to smile and draw horizontal mark.
What must you ensure when registering the bite (in ICP)?
Ensure rims are trimmed down sufficiently so they dont distort when pt bites together - teeth should make slight contact and wax should not interfere too much
How far should the pt bite down?
We only want cusp tip indentations inside the wax
If you are doing a metal denture, before/at jaw reg stage you will get a metal framework try-in. What must you check with this?
Initially examine on the cast: check component fit, adequate dimensions, correctly located. Want to ensure it is accurately sitting in and following out design. Ensure no interference from metal framework with occlusal relationship.
What should you not forget at the jaw reg stage!
To take shade and mould
Why would you do a trial of metal framework without wax>
Easier to spot errors and adjust
What will the lab give back after you have done a jaw reg?
Articulated study casts with the teeth set up on the wax try-in.
What are the types of articulator?
Hand articulation
Simple hinge articulator
Average value articulator
Semi-adjustable articulator
Fully adjustable articulator
What movements does an average value articulator allow?
Lateral movement and anterior-posterior movement.
What is the condyle angle on average value articulator?
30 degrees
How do you articulate casts?
Set articulator incisal pin to 0 degrees
Position mounting plate and occlusal table
Check casts fit together precisely
Place upper cast in position with anterior reg rim in contact and centreline corresponding with the V on occlusal table
If rocking is present secure with ribbon wax
Check incisal pin contacts the incisal table with sufficient room for the plaster
Mix 60ml with plaster of paris. Create a mound on top of model and while soft gently close the arm of the articulator.
Ensure incisal pin and table are in contact!
Tidy plaster
After set unscrew and smooth
Place upper back on articulator and position lower cast - articulator should be upside down
Repeat steps for lower
Briefly describe how lab techs set up teeth
Centrals first
Laterals and incisors - follow arch shape, observing overjet and overbite
Posterior teeth
Soften wax with hot wax knife and push tooth into place. Tungsten bur can remove excess acrylic. Ensure interdigitation with opposing teeth. After each tooth is set ensure incisal pin is touching incisal table.
Ensure buccal corridor. Carve gingival margins with Ash 5 or Le Cron.
Which teeth should be contacting for a class I occlusion?
Upper 2nd premolar - cusp tip positioned between lower 2nd premolar and 1st molar
Upper 1st molar - mesialbuccal cusp fits into buccal groove of lower 1st molar
Upper 2nd molar - mesialbuccal cusp fits into buccal groover of lower 2nd molar
What should you check in a trial denture assessment? (more detail in C/C)
Extension retention stability
Soft tissue support
Incisal height
Occlusal plate
Centre line/canine line/smile line
Occlusion
Speech, appearance, tooth position
What will the lab do after the try-in stage?
They will make the acrylic denture.
Please see RPD8 for details. Add to pros labs flashcards.
When should you place a finished denture in the patients mouth (in practice)?
Until payment has been made
What must you check before fitting the denture at delivery?
Correct denture?
Is it fit and safe, eg check for sharp/rough areas
Dirty, disinfect it and rinse it.
Examine the fit surface under a good light
What should you check on the fit surface?
Check flanges for overextensions/roughness
Check fit surface for roughness
Check for acrylic pearls
Should you fit the denture or let the pt fit the denture?
You should fit the denture for the first time as the pt will be unfamiliar. Seat it carefully and slightly. If there is resistance then remove and assess. Try again but don’t force denture. Adjustment might be required.
Assessing the denture: where should the denture extend to?
Should reach the functional depth of the sulcus
Don’t want it to dig into soft tissues if overextended, and needs relief at fraenal attachments
Assessing the denture: how retentive should a denture be?
Lower - should not move around with the tongue and should have resistance
Relies on clasps engaging undercuts on teeth - wire adjustment, adams cribs plyers?
Assessing the denture: what are you checking for stability?
How well, when the denture is fully seated, does the denture stay in the same spot, not moving around, pivoting, catching on something etc
Should not rock
Assessing the denture: how do you assess occlusion?
Should be in ICP
Use articulating paper to identify marks
Red marks might need to be adjusted down to allow the patient to bite properly
Sometimes occlusion needs to be increased (usually want it to conform to patients ICP bite)
What should you tell the patient do with the denture before they leave after you’ve checked the initial treatment plan and checked the denture meets the objectives?
Let pt have a look. Make them try it in and out 3 times with a mirror before they leave and document this
What 8 instructions should be given to patients before they leave?
- May be difficult to eat. Cut food into smaller pieces and avoid sticky foods.
- Removal may be difficult initially - practice
- Remove and clean after meals
- Reinforce necessity to clean natural dentition and denture
- Remove dentures at night and soak in room temp clean water
- Pain and soreness may occur
- No DIY
- Can be a difficult experience.
Why should you remove dentures at night and soak in room temp water?
Expansion or contraction of the denture if the water is too hot or cold and might warp it. Allow mouth to re cleanse itself overnight.
What should you say for the review period?
1-2 weeks
What should you advise if the denture causes significant pain or trauma?
Discontinue wear but start wearing again 24hrs before review appt - to see on soft tissues where damage or soft spots is occurring
What is the good standard for cleaning dentures?
Soap and warm water and a soft brush
Clean after meal if they can
What is the rationale for denture cleaners?
Basic denture hygiene
Prevent plaque/calculus build up
Reduce fungal infection (Candida) (can grow into denture acrylic)
Maintain long-term periodontal health
Prevent halitosis
Increase denture longevity
What should you consider after soap and water for a denture brush and cleaning paste?
Not toothpaste - too abrasive, will wear denture acrylic down
Helps prevent debris buildup
Bulky handle on brush - better dexterity for older patients
What effervescent peroxides are there and how are they used?
Steradent (original and deep clean)
Boots original
Maximum 5mins. Released bubbles - release energy which damages the surface of the denture, reducing its shine and making the denture more plaque retentive.
What alkaline hypochlorites are there and how do you use them?
NaOCl/NaOH
Dentural
Milton solution
Max 15mins, in room temp water. No mechanical cleaning action, purely disinfection mechanism. Care when using with metal dentures because can rust.
What other denture cleaners are there?
Antimicrobials, eg corsodyl (stains with long term use)
Enzymatic systems
Acids
What are the problems/how to avoid problems with denture cleaners?
DO NOR use with hot or warm water (to prevent shape warping)
DO NOT use dilute household toilet bleach
DO NOT use sodium hypochlorite for long periods (bleaches and makes brittle)
DO NOT use effervescent peroxides for long periods (weakens metal and acrylic)
Specifically with metals - don’t use sodium hypochlorite with warm water, don’t use acid cleaners, corrosion will weaken the metal work leading to failure
DO NOT soak in denture cleaner overnight
Why do we soak dentures in water overnight?
Because they are 2/3’s moisture, so don’t want to dry it out otherwise will warp
What history should you take at the review?
One week later - how are you getting on?
Pain history
Any other problems eg phonation, mastication, social, looseness
What should you do in your clinical examination of the patient at the review?
Assess dentures in and out of mouth and check soft tissues
Check remaining teeth and mobility
Not all ulcers and erythematous areas are painful
Check standard of cleaning of denture and remaining teeth
What should you do in your clinical examination of the patient at the review?
Assess dentures in and out of mouth and check soft tissues
Check remaining teeth and mobility
Not all ulcers and erythematous areas are painful
Check standard of cleaning of denture and remaining teeth
What are some common problems at the review stage?
Ulceration or erythma of the soft tissues
Tooth discomfort
Phonetics
Cheek biting
Aesthetics
What can cause soft tissue ulceration and how do we solve this?
Overextended denture base?
Not always painful.
May look translucent prior to frank ulceration - before the ulcer fully breaks the epithelial barrier it becomes slightly lighter pink
Adjust the denture to solve
What can cause soft tissue erythema and how do we solve this?
Roughness of the denture base or occlusal error. Always check occlusion first, then look at fit surface.
Run gauze of a fingertip across fit surface to check the sharp areas.
Pressure indicator paste (where it rubs off the denture is where adjustment is needed)
Adjust the denture as a solution
What might be causing tooth discomfort?
Pressure from the RPD
Occlusal trauma
Check tooth for caries and periodontal disease (can flare up at same time of denture fit)
Solution: manage dental pain/ease the denture
How do you solve pressure from the RPD?
Use occlude: fine spray paint.
Paint the fit surface of the denture. When the denture sits on the tooth, the fine spray wipes off the denture. Adjust only where it is rubbing. Guides adjustment.
What might be causing phonetics issues?
Incorrect placement of anterior maxillary teeth (changes in contour of anterior palate)
Premolar positioning - if too lingual it can impede the tongue movement, if too buffalo can allow air to escape
What is the solution for phonetics issues?
Allow time for adaptation. Could take several weeks, but tongue will eventually adapt. If it hasn’t after 6 months then needs to be adapted.
Solution: very difficult to solve immediately, aim to check speech at try-in stage, not waiting until review for it to be an issue.
What is the cause of cheek biting and how do you solve this?
Insufficient horizontal overlap of maxillary and mandibular posterior teeth
Round the buccal mandibular cusps to create a greater horizontal overlap.
How do you solve tongue biting?
Lingual lower cusp needs rounding
What problems can occur with aesthetics and how do we solve this?
Should be confirmed at wax-try in.
Shade selection, shape selection
Solution: remake the denture/replace the teeth
