Impression Techniques, Materials and Shade-Selection Flashcards
List some ideal properties of impression material
- Accuracy
- Elastic recovery
- Dimensional stability
- Flows and is flexible
- Workable
- Hydrophilic
- Long shelf life
- Comfortable for patient t
- Economic and tear resistant
How accurate does our impression material need to be
Must be able to record detail of 25 microns
What groups can the different types of impression materials be split into
- Non elastic
2. Synthetic elastomers
List the different types of impression materials
- Waxes
- Hydrocolloids
- Rubbers- polysulphide
- Polyethers
- Condensation polymers
- Addition polymers
What are the advantages of using addition cured silicones for impressions
1, Accurate
- Suffers little distortion over time
- Range of viscosities
- Can be withdrawn from large undercuts suffering no plastic deformation
- No taste
What are some of the disadvantages of addition cured silicones
- A little bit expensive
- Platinum can be poisoned via latex gloves
- Hydrophobic
What happens to impression material as we increase the filler content
The dimensional stability and strength increase BUT the accuracy and flowabilty decrease
How do we take an impression an addition cured silicone gun
- . the light-bodied silicone is placed around the prepared tooth without any air voids. include the adjacent teeth
- Seat a impression tray with heavy bodied silicone into the mouth and wait for it to set
Why do we need to include the adjacent teeth when applying the light bodied silicone
That is where the contact point will be
What dow ended to control when taking silicone impressions
Soft tissue control eg bleeding and exudate from the adjacent soft tissues
What can we do if we have concerns that gingival may ruin the impression
We can temporarily retract the gingival cuff to allow entry of impression material into the gingival crevice
What do we use to temporarily retract the gingiva
Gingival retraction cords
What are the different types of gingival retracted cordn
- Knitted type
2. Rope twisted
How is a gingival retraction cord inserted into the mouth
- The cord is placed firmly into the gingival crevice of the tooth all the way round.
- Firm pressure is required to do this.
- Pack firmly 360degrees round the tooth
How do we decide what size cord to use when carrying out gingival retraction
The gingival condition and the depth of the sulcus will determine the size of the cord used.
What is an alternative to using gingival retraction cords
Astringent retraction paste
Electro surgery
What is our aim when we use astringent retraction paste
To temporarily displace the marginal gingiva in healthy periodontium to provide a dry sulcus
When might we need to achieve a dry sulcus?
- For impressions
- Provision of temporary restorations
- Cementation of restoration
- Class II and V restorations
What are the contraindications of Astringent retraction paste
- Diseased periodontium
- Open furcations
- Exposed bone
What are the components of Astringent retraction paste
Acidic paste made up of 15% aluminium chloride
What is the action of Astringent retraction paste
Haemostatic – compression of tissues and astringent action of aluminium chloride.
How do we use the Astringent retraction paste
- Place 3M ESPE Astringent Retraction Paste into a composite dispenser,
- Place the tip of the capsule into the sulcus.
- While placing the tip into the sulcus the tissue is mechanically retracted from the tooth.
- Extrude retraction paste slowly while going slowly around the prepared tooth.
- Leave the paste for at least two minutes.
- Completely remove astringent retraction paste with air-water spray and suction.
What can happen if we leave the astringent on for too long
A too long application of the paste may harm the soft tissue.
What are the key benefits of using Astringent retraction paste
- Easy sulcus access due to fine capsule tip
- Effectively opens the sulcus
- Enables a clean, dry sulcus area and Long lasting haemostats
- Application is with common composite dispenser
- Easier and quicker to do than just retraction cord
- lower risk of bleeding
What is electro surgery
Removal of gingival tissue to expose clear preparation margins
