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
