Factors in assessing suitablity for Co/Cr
Mobility
- Why is it mobile?
- Periodontal disease
- trauma from occlusion
- periapical infection
- traumatic injury
- pathologic jaw lesion
- Is the cause controlled?
Periodontal disease and cobalt chrome
Acrylic is less hygenic Co/cr can’t accomodate tooth loss as well
Periodontal factors
- Stage and grade
- Prognosis
consideration
Acrylic
- changing dentition
- questionable prognosis
- future extraction likely
- easy to modify/add teeth
- transitional treatment
- flexibility
a well made acrylic denture can be a permanent denture
Co/Cr
- Rigid
- Thin
- Less tissue coverage
- Design-controlled support & bracing
- Potentially more cleansable
decision making process
biology + prognosis + maintenance + cost + time + expectations
Clinical Pathways
Acrylic
Pathway
- Primary impression
- Special tray *
- Definitive impression
- MMR*
- Tooth try-in? *
- Insert
1. Primary impression
- Aim: a diagnostic representation of the dentition and edentulous areas
- Can use a stock tray with modification
- Use putty to widen or extend it
- can also use periphery wax or even green stick
Do we need a secondary impression
- Ask about the edentulous span and what hte impression must achieve
- May not need
- short bounded saddle
- single missing tooth
Cases with minimal tooth loss and bounded edentulous space
As long as the primary alginate impression is good enough it can b used as the final impression
- the purpose of the secondary is to capture more tissue area, but if the dneture is only tooth supported then it doesn’t really matter
Strongly consider cases:
- Kennedy 1/II free-end saddle
- Long Kennedy IV
- Large tissue-supported Kennedy III
2. Special tray - design
- Perforated tray
- alginate —> 3 mm spacer
- Non-Perforated tray
- PVS/PVE —> 2mm spacer
Lab Slip
Example: Dear Lab, Please fabricate Upper and Lower Special tray according to the following : Maxillary perforated special tray with 3 mm spacer for Alginate impression. Mandibular non-perforated special tray with 2mm for PVS impression wiht tissue stops
Tissue stops: Helpful initially until you get more experience with taking impressions as they help to prevent burn through. They are extensions which hit the teeth
Spacer: If special tray isn’t fabricated with a spacer then there is no space for the impression material. spacer is normally wax put on the stone model before creating the special tray
Special tray workflow]
- Seat
- check:
- gross extension
- seating
- interference
- sharp edges
- check:
- . Function
- Cheek/lip manipulation
- tongue movements
- trim
- adjust areas that displace the tray
- reasess
- repeat the same movements
Assessing special tray extension
- put the bare tray in. Do border moulding movements (cheecks and tongue), whenever the denture moves it means it needs to be trimmed
- Tongue:
- move to the left and denture moves = trim right lingual flange and vice versa
- If its moving slightly its ok , just big movements
Do we need border moulding?
Common situations:
- Kennedy I/II free-end saddle
- Long Kennedy IV
- Large tissue-supported saddle
- Posterior maxillary extension where the denture base extends into functionally relevant soft tissue areas
Which materials Options:
- PVS
- most commonly used
- brand: imprint
- Alginate
- PVE
- least commonly used
PVS Available combinations at OCHWA
- Heavy: Imprint 4 heavy body
- Medium : Imprint 4 regular
- Light: Imprint 4 light body
Mixing:
- you can use medium alone
- or heavy + light, medium + light
there is no right or wrong combination all of these rely on clinician reference
Different generations of imprint
Make sure if you are mixing then they are the same genetation of imprint (i.e. imprint 4 and 4 not 3 and 4)
Why light body
- where detail matters
- rest seats
- guide planes
- prepared tooth surfaces
- lingual plate contact
- palatal plate contact
Block outs
- Spot the risk
- black triangles/open embrasures/large interdental spaces
- gingival recession
- tipped teeth
- bridge of pontic undercuts
- mobile/periodontally compromised
- Block out
- periphery wax
- probably one of the easiest
- light cure gingival barrier
- PTFE/Teflon tape
- Oraseal
- Temporary restorative material
- periphery wax
PVE and tray stuck
Blockouts of undercuts are important especially with PVE because the tray can get stuck always block out form the buccal side, that way you have enough lingual extension Main goal: Prevent material from going through buccally to lingual
Judging the definitive iimpression
- Tooth supported/ bounded saddle
- rest seats/guide planes
- saddle anatomy
- Path of insertion infomration and relevant tooth surfaces
- Free-end/long saddle
- abutment teeth
- entire denture-bearing area
- Buccal + lingual extension
- Retromolar pad/tuberosity
- Functional peripheral form
Drag
if the impression has defects such as drag, you can stlil make it work depending on where it is. For example if its in a spot which the denture doesn’t extend then its fine
4. MMR - when do we need it
Required/essential
- Kennedy I/II free-end saddle
- Long kennedy IV
- unstable occlusal stops
- VDO change Although the patient has a stable bite, the model can still move , especially when we have a free-end saddle so even though there is an occlusal stop it is unstable
Not essential
- kennedy III (when hand articulation is possible)
Bite Registration
always take a bite registration, its quick then you can decdied whether you can use it or no
Practical test: - cast-rocking test
- Put the models together
- are they stable?
- are they rocking/sliding?
- can also use articulating paper
- compare the articulator and the patients mouth occlusion
Scanning the bite
More predictable
- short bounded saddle
- stable teeth
- good access + moisture control
- reliable occlusal landmarks
- minimal tissue displacement More challenging:
- long edenulous span
- free-end saddle
- mobile/displaceable tissues
- functional border required
- limited access or difficult otngue/cheek control
- few stable occlusal landmarks
The scan can look beautiful.. but the bit can still be wrong always validate the digital record clinically
Contact only mode for occlusal registration
Digital bite reg algorithms kind of suck , move the scanner to “contact only mode” to actually assess the registration good workflow paper: Guidelines for Digital Interocclusal Records: Part 1 – Dentate and Partially Dentate Patients
5. Tooth try in or direct finish?
tooth try-ins preferred
- multiple teeth
- aesthetic zone
- uncertain tooth positoin
- occlusal uncertainty
- altered VDO
- clinician/student uncertainty Direct finish may be reasonable
- single straightforward tooth
- good neighboring references
- stable occlusion
- minimal aesthetic risk Tooth try-in : what are you approving?
- Tooth position
- Aesthetics
- Phonetics
- Occlusion
- VDO (where relevant)
- Patient acceptance
6. Insertion appointment
DO NOT JAM IT IN!
Path of insertion
- Posterior —> anterior?
- Right —> left?
- Simultaneous seating?
Look for the first contact, then adjust conservatively
- Rigid acrylic interface
- Clasp
Cobalt chrome clinical workflow
- Primary impression
- Preliminary articulation
- Preliminary try in?
- survey + design
- Special tray
- Mouth prep
- Definitive impression
- Framework
- MMR
- Tooth try-in
- Insert
2. Preliminary articulation
- How can I articulate the diagnostic casts?
- pvs bite registration
- Diagnostic MMR
- Base and occlusal rim fabricated intraorally/ on the study model or requested from the laboratory
3. Preliminary try-in
Sometimes you need the teeth before the metal
**consider diagnostic tooth arrangement when **
- anteiror tooth position is uncertain
- class II/III interarch relationship
- Limited prosthetic space
- Framework must support an unusual tooth position
4. Survey and design
The survey answers:
- Undercuts
- path of insertion
- interferences
- support and guidance
Surveyed diagnostic cast should have:
- survey line
- undercut gauge
- proposed rest
- guide plan
- path arrow
Design workflow:
- survey
- design
- prepare the mouth
6. Mouth Preparation
Mouth preparation is design-driven: every preparation should have a reason
- Rest seats
- Guide planes
- Enamel recontouring
- Interference reduction where appropriate
Rest seat preparation
If you have space for the metal you can extend the metal on top of the tooth without preparing one! If the marginal ridge area is more rounded this makes it more favorable as no prep if the marginal ridge area has deep grooves (v shaped) it makes it more favorable to prep
7. Survey master model
- Re-survey the mast cast and ask:
- did we create what we planned?
- Check:
- Path of insertion
- Guide planes
- Useful undercuts
- Rest locations
- Framework design
8. Framework
Prove the framework
Start on the master model and check
- Seating - full adaptation
- Support - rest contact
- Stability - no rocking
- Retention - clasp engagement
- Function - no interference
If it does not seat, do not force it
- find the interference
- Possible sources
- tooth interference
- guide-plane discrepancy
- rest interference
- connector interference
- distorted framework
- incorrect path
Finding interference
Use fit checker or occlusal spray
Examples
- Minor clasp adjustment
- very limited rest adjustment
- Acrylic component adjustment
Major discrepancies necessitate a remake!
8/9 - framework +/- MMR
Framework fits, what’s next? can we save a visit
Option 1:
- send to lab
- lab adds rim
- patient returns
- record mmr
Option 1 used:
- unstable rim
- Major VDO change
- complex jaw relationship
- uncertain tooth position
- inadequate time/skill to make reliable record
Option 2:
- adapt rim chairside —> record MMR today
- saves appointment
- Saves lab free
Marking landmarks
Always mark canine , smile, midline to help the lab place teeth
10. Tooth try-in
What are you assessing?
- Tooth position
- Aesthetics
- Phonetics
- Occlusion
- Retention and stability
- VDO (where relevant)
- Patient acceptance
Check VD
Use shim stock beofre and after putting it in, should have contact either way
11. Insert
Framework discrepancy —? stop + reassess for remake
Assess
- seating - full adaptation
- support - rest contact
- stability - no rocking
- retention - clasp engagement
- occlusion - no interference
- tissues - no impingement
- insertion - correct path
- removal - patient capable Adjust acrylic/occlusion as indicated
Adjust acrylic first
At this stage the framework should already be verified so its probably the acrylic thats the problem