week 5- impressions technique Flashcards
properties of an impression materials
Accuracy Elastic recovery Dimensional stability Flow Flexibility Workability Hydrophilicity A long shelf life Pt comfort Economics Tear resistance Need to consider the unset,setting and set properties
what level of accuracy do we need to record until
25 microns
what are the types of impression materials
non elastic
synthetic
what are some non elastic impression materials
waxes
compound and plaster
hydrocolloid- reversible/irreversible
what are some synthetic impression materials
- Rubbers – polysulphide
- Polyethers
- Condensation polymers
- Addition polymers
advantages of addition cured silicones
Accurate Suffers little distortion with time Range of viscosities Can be withdrawn from large undercuts suffering no plastic deformation No taste
disadvantages of addition cured silicones
Costly material
Platinum can be poisoned via latex gloves (chloroplatinic acid catalyst is contaminated by sulphur compounds)
Hydrophobic
what happens as the filler content increases
dimensional stability and strength increase but their accuracy and flowability decrease
how do addition cured silicones work
Setting reaction involves a two paste system
Paste 1 is polydimethylsiloxane containing Si-H GROUPS
Paste 2 is polydimethylsiloxane containing Si-CH=CH2 groups
with a PT catalyst
where is the light body impression placed
on the teeth
where is heavy body silicone placement
on the tray at the same time
adhesive on the model 10 mins before
how do we do soft tissue control
retract gingival cuff with gingival retraction cord - in different sizes
how do we place the gingival cord
The cord is placed into the gingival crevice of the tooth all the way round- the condition of the gums and the depth of the sulcus will determine what cord we need to use
what is another example of retraction we can use
Components: acidic paste 15% aluminum chloride
Action is- haemostatic- compression of the tissues and astringent action of aluminium chloride
what are the contra indications for astringent paste
Diseased periodontium
Open furcations
Exposed bone
how do we use the astringent paste
Place 3M ESPE Astringent Retraction Paste into a common composite dispenser, remove cap and discard a small amount of material.
▪ Place the tip of the capsule into the sulcus. While placing the tip into the sulcus the tissue is mechanically retracted from the tooth. The soft edged tip is rounded to prevent
▪ tissue damage.
▪ Extrude retraction paste slowly while going slowly around the prepared tooth. Take care tat the tip of the capsule is subgingival!
what else can we do
paste and cord together
how long do we leave the paste for
two minutes
how do we remove the paste
air-water spray and suction.
benefits of the astringent paste
▪ Easy sulcus access due to the fine capsule tip
▪ Effectively opens the sulcus
▪ Enables a clean, dry sulcus area and long-lasting hemostasis
▪ Application with common composite dispenser
▪ Easy and time saving: 50% faster than cords
▪ Lower risk of bleeding/post haemorrhage than with cords
Easier application into the sulcus and interproximal access than others pastes
what is electro surgery
Use short, sweeping motions
what do we need to consider when doing electro surgery
NO PACEMAKER
no mirror!
burning smell of flesh
what are some applications of the electro surgery
▪ Removing localised ginigival tissue ▪ Exposure of subgingival caries ▪ Exposure of crown margin ▪ Improve contour and shape of tissues ▪ Easy retraction for multiple abutments ▪ Quick Predictable healing
how do we place retraction cords
- Having a healthy periodontal status for the patient prior to crown prep there must be a gingival sulcus of 2-3mm
- Pack the first cord using a flat plastic,wards carver,packer
- Push it firmly into the sulcus
- Place thr second cord- usually larger than the first cord
- Then before placing the light bodied silicone- remove the second cord
- Continue to dispense all around the tooth and cover the adjacent teeth be careful of air bubbles
- Fill the tray with the medium body silicone and ensure this is seated over the light body prior to setting
Set for 5 minutes
when do we place the light body silicone
right after removing the cords
what is the impression assessment
▪ Impression material well-mixed/fully-set
▪ Is the impression still seated in the tray
▪ All teeth in the arch included
▪ No folds between the heavy (or putty) & wash
▪ No drags
▪ No air bubbles
Good impression of adjacent teeth
what does the lab need for an impression
A good impression of the prepared tooth in addition cure silicone
Good impression of the opposing arch
Interocclusal record
Prescription of the type of crown needed, design, shade and any characteristics
what do we use in shade selection
VITA classical shade selection- Four groups: A- brown hues B- yellow hues C- grey hues D- reddish hues
what are the four Cs of patient notes
clear
contemporaneous
concise
complete
