Impressions and occlusion for conventional dentures Flashcards
What is an impression?
A reverse or negative form of the tissues which is converted into a positive model/cast using plaster or stone or a mixture of both plaster and stone.
What modifications of stock trays can be done?
using soft wax/putty/compound (or greenstick) or by trimming the tray
How to know if a tray is too small or too large?
- Too small – flanges hit the ridge
- Too large – stretches the mouth
or feels uncomfortable or cannot get it in the mouth
What are the limitations of stock trays?
Rarely fit the mouth accurately
Often require modification
May be difficult to obtain necessary border seal
Remember – Do not overload trays; Occasional pre-packing
What should be prescribed after primary impressions always?
special trays
What is border moulding?
using the movement of the patient’s soft tissues to shape the impression edges.
captures muscular attachements and normal movement
What should be evaluted in the impression?
- General adaptation & surfacedetail. -No significant airblows
- Appropriate sulcus depth and shape “functional sulcus”
- Tray placed correctly to ensure ridge is in centre of tray
- All appropriate landmarks are included – entire denture bearing area included including palatal extension to post dam
- Anterior lingual sulcus–tongue has been protruded
- Impression is fixed to the tray
What should you do when you and the supervisor decide to accept an impression?
Remove debris & rinse
Disinfect
Mark extensions with an indelible pencil
Wrap, label & bag
Prescribe for special trays
Take to lab so impression is cast asap
What should be included in your lab prescription?
Stage: What you want done; not what you have done
When: Date/time you want the work for
Label: Patient label (all 3 copies)
Appliance: Full (replica or conventional); material
Who: Student name & email address; Supervisor name & stage signed
What: Is to be done with the work you send & what do you want back Safety: Disinfected
Specifics: Upper/Lower/Both; Shades/moulds/materials; tray handles; postdam(s); special instructions
What are special trays made out?
Light cured acrylic resin, heat / cold cured acrylic resin
Advantages of special trays?
Need less impression material
Ensures even thickness of impression material
- minimise tissue displacement
- maximises dimensional stability of impression material
Less bulky so more comfortable for patient
What are tissue stops and what are they used with?
pre-form space for the impression material
Used with spaced trays - primary and secondary impressions
What do tissue stops do?
To ensure uniform thickness of impression material
To help localise tray during impression taking
Where should the tissue stops be in lower and upper trays?
Lower tray - place in canine region and over retromolar pads
Upper tray - place in canine region and along post dam area
What material is used for tissue stops?
greenstick
What are finger rests used for and where?
Used with lower special trays
Placed in the region of 2nd premolar / 1st molar
Allows fore finger to be placed on either side of the tray, thumb under mandible for support to ensure it is fully seated posteriorly and ensure more even distribution of pressure to the tissues
Help stabilise the tray in the mouth
What are spaced special tray?
what are they used for?
Constructed using material to leave space between the tray and ridge
Commonly used
Usually 3mm spacing
For use with higher viscosity materials eg alginate, heavy body elastomers
Most situations
What are close fitting trays?
what are they used for?
Spacing up to 1mm
For use with light viscosity materials for wash impression eg light bodied elastomers, ZOE
Resorbed ridges; replicas
Are most impressions mucocompressive or mucostatic?
mucocompressive
What is mucocompression?
pressure is applied to the mucosa so that the shape of the tissues under load is recorded
What is mucostasis?
minimum pressure is applied to the tissues to record their shape at rest
How are fibrous flabby ridges recorded in impressions?
Using an impression with perforated special tray with both high and low viscosity material
How is the occlusion recorded? (jaw registration)
record blocks
wax block vs shellac base vs heat cured base
wax block only
- less retentive
- cheap
- lots of space for setting teeth
shellac base
- more stable
- more expensive
- limited space for setting teeth
heat cured base
- very stable
- expensive
- least space for setting teeth
What are the steps for jaw registration?
- Step 1: Adjust upper record block for retention
- Step 2: Adjust upper record block for tooth position
- Step 3: Adjust upper record block for occlusal planes
- Step 4: Lower tooth position & horizontal jaw relationship
- Step 5: Measure vertical dimension & establish face height
- Step 6: Record registration
- Step 7: Select shade, mould & setting
How can the upper record block by adjustment?
- Use the wax knife and hot plate/heated pallet knife to make adjustments
What does overextension of the peripheries result in?
loss of retention
What is the recommended nasiolabial angle?
90 degrees
What is the actual nasiolabial angle in edentulous patients?
96 degrees
LIMBO
lip support
incisal level
midline
buccal corridor
occlusal plane
How can the lip support be checked?
Use of the Alma gauge for checking tooth position
How can the incisal level be checked?
Visual judgement Photographs of natural teeth Lip level
Lip during speech
Age
1-2mm of show
What are the fricatives?
When speaking, the upper front teeth touch the lower lip lightly to produce these sounds.
F and V sounds
How can the occlusal plane be assessed?
Measuring interpupilary for anterior
measuring ala-tragus for posterior
What is the neutral zone?
and in practical terms
the potential space between the lips and cheeks on one side and the tongue on the other; that area or position where the forces between the tongue and cheeks or lips are equal
Anterior teeth - Over ridge
Posterior teeth - Over ridge
Polished surfaces
– No buccal overextension – cheek dislodgement;
lower lingual – wider at base than apex so tongue does not dislodge
What are the skeletal classes?
- Class I skeletal relationship:
Shallow overjet and overbite - Class II Div 1 skeletal relationship:
Increased overjet and shallow overbite - Class II Div 2 skeletal relationship:
Increased overjet and deeper overbite - Class III skeletal relationship:
Edge to edge incisors and posterior crossbite Try avoid reverse overjet anteriorly (retrocline incisors)
What is retruded contact position (RCP)?
Guided occlusal relationship occurring at the most retruded position of the condyles in the joint cavities.
Limited by the lateral ligaments of the TMJ
Remains the same throughout life, assuming nothing adverse happens to the condyles
A reference point for mounting casts on an articulator
What is the muscular position?
The position of closure produced by balanced muscle activity raising the mandible from rest to initial contact
Beware postural class III occlusions – old worn dentures
What is the occlusal vertical dimension?
the distance between a set point on the maxilla and a set point on the mandible when the (denture or natural) teeth are in maximum intercuspation
What is the resting vertical dimesion?
when the mandible is at rest with patient upright
What is the freeway space usually?
2-4mm
What does excessive FWS result in?
Reduced masticatory efficiency
“Overclosed” facial appearance and cheek biting TMJ symptoms
What does inadequate (reduced) FWS result in?
Excessive load on denture bearing area
Continuous muscular activity results in pain
Aesthetic complaints – “Teeth too big”; “Show too much teeth” Noisy dentures
How is the FWS calculated?
RVD - OVD = FWS
What is used to measure OVD and face height?
willis bite gauge
dividers
What are the 2 measuring points usuing dividers?
nose and chin
What are the final checks before recording registration?
Are blocks trimmed so teeth will be in the neutral zone?
Do you have even contact with upper block?
Is OVD correct for patient, with adequate FWS?
Is centre line correct?
Are occlusal planes appropriate?
How is registration recorded?
cut notches on upper and lower blocks
use wax or jaw registration paste
check for heel interferences on the casts
What is the manchester rim?
bite block
Simplified registration
Applicable to General Practice
Time saving
Difficulties if need to outline unusual lower anterior positions
What articulators can be used to assess the jaw registration?
simple hinge - cheap, simple occlude
fixed value lateral and protrusive - used in GDH, great for complete
semi adjustable, individualised by facebow - rarely used with completes, difficult occlusions
