A system of design for cobalt chrome dentures Flashcards
State the 4 principles for cobalt chrome dentures
- Avoid gingival coverage
- Provide a denture that has good support
- Make sure the connector is rigid to distribute evenly the loads the denture will endure
- Keep it simple
Why is it important that we avoid gingival coverage when designing a cobalt chrome denture
As it will promote plaque accumulation and can encourage periodontal disease
Why do we need to make sure the denture has good support?
To ensure it does not sink and lead to gum stripping
List the 8 steps to design cobalt chrome dentures
- Saddles
- Support
- Retention
- Bracing/reciprocation
- Indirect retention
- Guide planes
- Connectors
- Review principles of design
What are saddles?
Edentulous areas in the mouth
When designing our saddle what do we need to consider?
Do we need to replace every tooth?
Do we need to replace every tooth?
No we need a reason for each tooth we put on the denture
What might be a reason to replace a tooth
- Aesthetics
- Masticatory efficiency
- Prevent drifting/ tilting/ over eruption
- Phonetics
What might a reason we avoid replacing a tooth
- Plaque trap
- Trauma
- Patient tolerance
- Cost
According to kaisers research when can masticatory efficiency be reduced?
Below ten occluding units (10 teeth in each arch)
Are dentures as good at chewing as natural teeth?
No
Implants are a lot better but more expensive
Ultimately what/ who decides if the masticatory efficiency of a patient has been reduced?
The patient
What is phonetics referring to?
Speech
ie patient asking for dentures to improve their speech
What is the major disadvantage for replacing teeth
Plaque retention which can lead to:
- Periodontal disease
- Caries
- Fungal infections
Which structures in the mouth can be traumatised due to dentures?
- Soft tissues
2. Pulp (fixed bridge work can lead to plural necrosis)
How can patient tolerance become a disadvantage for replacing teeth?
- Gag reflex
2. Psychology and patient expectations
Where do saddles usually extend to?
Saddles usually extend to the full extent of the denture bearing area
Describe the position of the saddle in the lower arch
Saddles extend to the functional depth of the sulcus and as far back as the pear shaped pad in the lower arch
Describe the position of the saddle in the upper arch
Saddles extend to the functional depth of the sulcus and as far back as the hamualar notch in the upper arch
Why do saddles usually extend to the full extend of the denture bearing area?
To distribute the vertical and lateral load over as greater area as possible and so decrease the pressure on the underlying mucosa
What is support on a denture usually provided by?
Rest seats
Where can rest seats be placed?
- Occlusal
2. Cingulum
For a bounded saddle where do we usually place the support?
On the nearest surface of each abutment tooth
For a free end saddle where do we usually place the support?
On the medial side of the abutment tooth
Why do we look for support on the medial side of the abutment tooth for a free end saddle?
As this reduces the torque on the abutment tooth
When placing a rest what do we NEED to check?
Need to check occlusion to make sure the position of the rest seats are possible and don’t interfere with the patients bite
What might we need to do if the patients occlusion is tight?
May need to provide a deep rest seat preparation
OR
May move the occlusal rest to a convenient nearby position which is
free of the occlusion.
How do we asses each rest seat position?
By using an articulated study cast
Do we always need a rest seat?
NO remember keep your design simple
How do clasps work?
They engage the undercut to gain retention
What is the undercut
It is the area below the survey line
What is the survey line
The line of maximum bulbosity on the tooth
What determines the size of the retentive force on a tooth?
The horizontal depth of the undercut
How can clasps approach the tooth?
Occlusally
OR
Gingivally
Name the two types of occlusal approaching clasps
- Simple 3 arm clasp
2. Ring clasp
Name the 3 types of gingival approaching clasps
- I bar
- T bar
- L bar
What should each saddle ideally have on a bounded saddles
Should ideally have a clasp on at least one abutment tooth unless aesthetics dictate
What do we need to look at when thinking about retention on a bounded saddles
For each saddle, look, initially for retention on both abutment teeth
What do we need to look at when thinking about retention on a free ended saddles
Usually look for retention on the abutment tooth of the saddle
What can we do if we haven’t got an undercut where we want it
We can ad composite on natural teeth to gain undercut
What can we do if we have too mcc undercut on a tooth?
We can re shape the tooth by cutting a guide plane or adding composure then re shaping
When thinking about bracing/ reciprocation clasps what should we check for?
Check for resistance to lateral and anterior/posteriro movement
How do we check for resistance to lateral and posterior/anterior movement
Engage flanges to the functional depth of each sulcus
Where do we need to add reciprocative clasps
Opposite to each retentive clasp arm
What is indirect retention
It is resistance to rotational displacement in a tooth and mucosa borne denture
What happens when sticky food pulls a free end saddle away from the mucosa
The denture can rotate around the clasp
How is indirect retention is usually achieved?
By placing an occlusal rest on a tooth anterior to the clasp
Where is the best place t put indirect retention clasps
As far from the clasp axis as possible
Why are guide planes important
- For a single path of insertion
- For reciprocation
- For indirect retention
- To create a path of insertion radically different from the path of displacement
- To use with the RPI clasp system
What does the horizontal depth of an undercut determine?
The size of the retentive force
What do we achieve if we place guide planes across the teeth in an arch that are parallel to each other
We effectively create one path of insertion for the denture
What is the benefit of creating one path of insertion for the denture
Increases retention as the denture can only be removed if it is taken out in a certain direction
Describe connectors
They are rigid
Describe connectors we can use in the upper arch
Need to Clear the gingival margin by 3mm
Give examples of where we can place connectors in the upper arch
- Anterior palatal bar
- Mid palatal bar
- Posterior palatal bar
Name some connectors we can use in the upper arch
- Horse shoe
- Palatal plate
- Ring
Give examples connectors we can place in the lower arch
- Lingual bar
- Sublingual bar
- Lingual plate
- Dental bar
- Buccal bar
Name the most common connector for the lower arch
Lingual bar
How much depth do we in the lingual sulcus need to be able to place a lingual bar
6mm
Where does the sublingual bar sit?
At the bottom of the lingual sulcus
What does a sublingual bar need
Requires a special accurate impression of the lingual sulcus as the depth of the lingual sulcus changes as we move our mouth
How much depth do we in the lingual sulcus need to be able to place a sublingual bar
5mm
What is different about a lingual plate from the other lower arch connectors
You don’t need 3mm clearance
Where does a dental bar connector sit?
Entirely on the teeth
What do we need to be able to place a dental bar
Long clinical crown needed
