Academic background for impressions for dentures Flashcards
What do we want to record when taking an impression for a denture
- We want the full extend t of the denture bearing area
2. Want the functional depth of the sulcus
List some key anatomical denture bearing areas for a lower denture
- Buccal sulcus
- Buccal shelf
- Pear shaped pad
- Retromolar pad
- Mylohyoid ridge
- Lingual sulcus
Name the muscles that change the shape of the buccal sulcus in the lower arch
- Buccinator
2. incisive muscles
Name the muscles that change the shape of the buccal sulcus in the upper arch
Buccinator
Where is the buccal shelf found
Between the alveolar ridge and insertion of the buccinator into the external oblique ridge
Why is the buccal shelf important when making dentures
It is an area where the denture can extend onto
At the back of the mouth where does the denture bearing area extend up to?
The retormolar pad
What is the pad at the back of the lower arch split into?
- The retromolar pad
2. The pear shaped pad
Where is the pear shaped pad found?
It is the anterior to the retromolar pad
Where is the retromolar shaped pad found?
It is the posterior 2/3rds of the pad
Which pad do we usually cover with our denture?
The pear shaped pad
Where is the functional depth of the sulcus on the posterior lingual side of the lower arch
Extends beyond the Mylohyoid ridge into the posterior retro Mylohyoid area
List some key anatomical denture bearing areas for an upper denture
- Buccal sulcus
- Vibrating line
- Palate
Where do we extend an upper denture up to?
- Extend as far as the buccinator posteriorly
- Palatal coverage unto vibrating line
- Upto to the palatine fovea
What should impressions record in terms of the frenum
Impressions should record the space created when the frenum moved to all possible positions
What is the frenum
It has no muscle fibres excepts at the mid line
What the natural portion of the frenum
Natural portion is perpendicular to the ridge
What can restrict the width of the upper posterior buccal sulci?
The coronoid process
What problems can arise if we don’t consider the coronoid process
We can make a bulky denture that will restrict patients masticatory function
How can we take the coronoid process into consideration when taking an impression?
We can ask the patient to move their jaw from side to Side
List some physical properties of the oral mucosa that can affect impression taking
1, Depth of mucosa over the denture bearing area
- Visco elastic nature of mucosa
- Depth and width of the sulcus
What happens to the elasticity of the mucosa as you get older
It becomes less elastic and if you press the mucosa it doesn’t bounce back into its original position straight away
What can happen if we make a denture that is in essence too tight
It can restrict blood flow to that area
What happens to the depth and width of the sulcus
It moves when you take an impression
At what depth do we need to record the sulus
Functional depth
What is the functional depth determined by
Determined by anatomy and movement
So muscle movement and muscle insertion define the depth
Buccally the functional depth is usually the ___________ depth
Minimum
What is the functional depth limited by lingually?
Limited by the tongues movement to normal physiological positions (so not the minimum depth)
What is the width of the sulcus created by
Created by the action of the muscles and frenum on the impression material
Functional width is a _______ or ________ width
Tolerated
Accepted
Why is the functional width usually a tolerated width
As there is no natural resting width to a sulcus until something is inserted into it
List soem impression philosophies
- Muco-displasive,
- Muco-static
- Differential Pressure
- Functional
What is the muco-displasive impression philosophy
It advocates a high viscosity material giving a high pressure technique which aimed to compress (displace) the mucosa into a loaded portion
What are the benefits of the muco-displasive impression philosophy
Blains to give good retention
What is a disadvantage of the muco-displasive impression philosophy
Likely to increase resorption of alveolar bone
Is the muco-displasive impression philosophy used much today
No it is mostly for historical interest
What has replaced the muco-displasive impression philosophy
The altered cast technique
Name the only time we might use the muco-displasive impression philosophy
In a lower free end saddle
What is the Muco-static principle
It is an attempt to record the mucosa in its rest position
What are the advantages of the Muco-static principle
Comfortable for patient
Preserves underlying bone
What is a disadvantage for the Muco-static principle
- Lack of peripheral seal
- Lack of retention
- Any impression moves the mucosa so mucosa isn’t really static
What is the differential pressure impression philosophy
A broad term that covers all impression which aim to be high pressure in some areas and low pressure in relatively mucostatic in others
What is the functional impression philosophy
It is a closed mouth technique in which an impression is taken beneath functioning dentures
It utilises a slow setting material which is placed beneath the denture
and the patient goes away for a period (2 hours upto 2 days) and
moulds the impression in function
How is the functional impression technique carried out
It utilises a slow setting material which is placed beneath the denture
and the patient goes away for a period (2 hours upto 2 days) and
moulds the impression in function.
What are the advantages of the functional impression technique
The denture bearing area is recorded in function that is said to give a better resultant contour when the denture is loaded
What are the disadvantages of the functional impression technique
The patient need pre existing dentures
Theres hygiene problems when taking the denture
You cannot select the areas to load
When is it useful to take a functional impression
Useful fro re lines of existing dentures
How do we take dentures in Leeds
We use an acrylic, spaced special tray, unperforated from the lab which may be perforated chair side
We use silicone for chrome dentures and alginate for partial acrylic dentures
Which technique have we adopted in Leeds
The relatively mucostatic impressions technique
What material do we use to take an impression for a chrome denture
Silicone
What material do we use to take an impression for a partial acrylic denture
Alginate
What Qualities do we look at when picking our impression material
- Viscosity
- Elasticity
- Dimensional stability
- Hydrophilic
- Handling properties
Do we want a high or low viscosity material for taking impressions?
Ideally low for low pressure relatively mucostatic impressions
BUT high enough viscosity not to run out of the tray
How elastic do we want our impressions material to be?
Enough to emerge easily from undercut without tearing
Why is dimensional stability an important property for impression materials
As the impression must stay the same shape over time until it is cast
Do we want a hydrophilic or hydrophobic material when taking impressions
hydrophilic
Why does out impression material need to be hydrophilic
TO give close adaptation and surface detail
What handling poverties do we need to look at when deciding which impression material to use
- Mixing time
- Working time
- Setting time
Name the ideal impression material
One hasn’t been invented yet
How many impressions do we usually take before creating a denture
2
Primary impression
Secondary impression
What does the primary impression aim to show
Gives us a bold outline of the denture bearing area and which teeth are present
What does the secondary impress allow us to do
Produce a customised tray (special tray)
Describe the type of tray you would use for a low pressure relatively mucostatic impressions
- Rigid material for the tray- acrylic
- Spaced- for a low pressure
- Unperforated
- Stub handles
- Finger rests
- tray adapted or trimmed 2mm short of the functional depth of sulci given on the primary cast
Why do we use a spaced tray for partial dentures
As teeth are present so a spaced tray will allow the impression material to come out of the undercut without tearing
Why do we need stub handles on our impression tray for partial dentures
so we don’t interfere with muscle trimming
Why do we need finger rests on our impression tray for partial dentures
to make it easy to hold the impression intra orally
What do perforation do
They reduce pressure BUT they also create uneven loading
Which factor has the largest effect on impression taking
operator technique
