Chapter 15 impression Flashcards
An impression is a __ of the oral tissues
A model or cast is a __ reproduction of the oral tissues. A die is a __ reproduction of a single or multiple tooth preparation
An impression is a negative reproduction of the oral tissues
A model or cast is a positive reproduction of the oral tissues. A die is a positive reproduction nof a single or multiple tooth preparation
stock trays
a. Stock trays can be metal or plastic
b. Can be solid or perforated
c. May need adhesive
custom trays
a. Usually constructed in the lab with chemically cured, light-cured, or thermoplastic resins
triple tray
6) Triple Tray: (Double arch or Double bite)
a. Used to make an impression of the teeth being treated
b. Makes an impression of the opposing arch
types of inelastic
1) Dental compound (impression compound)
2) Impression plaster – not used today
3) Zinc oxide eugenol
4) Impresion wax
- A colloid
* Hydrocolloids
- A colloid is a glue-like material composed of two or more substances in which one substance does not go into solution but is suspended within another substance.
- Hydrocolloids are water based colloids that contain large amounts of water, even after they have set
irreversible vs reversible
agar(R) and alginate(IR)
alginate
Most widely used impression material. Used for impression for diagnostic casts, etc. Not accurate enough for final impressions for inlays, onlays, crown and bridge preparations.
agar
introduced in 1925. Glue-like suspension that entraps the water making a colloidal suspension called (sol). When the agar gel is heated, it will reverse its state back into a liquid suspension (sol).
alginate working and setting time
i. Regular Set – 2 to 3 minutes
ii. Fast Set – 1.25 to 2 minutes
b. Setting Time:
i. Regular Set – 2 to 5 minutes
ii. Fast Set – 1 to 2 minutes
elastomer
• Sets by an irreversible chemical reaction and does not have water as a main component, therefore they are more dimensionally stable over long periods of time
zinc oxide eugenol
periodontal dressing
cavity base
temporary cement
temporary restorative material
alginate components :5
calcium sulfate-causes reaction
sodium retards the chemical reaction
potassium sulfate ensures surfaces of stone is good quality
b. Silica fillers – provide “body” & rigidity
e. Quaternary ammonium aids in the disinfection process
Thixotropic Materials
Thixotropic Materials – Liquids that flow more easily under mechanical forces
zinc eugenol is manufactures in 2 forms ?
a) Two Paste System
b) Paste – Liquid formulation
- Catalyst Paste – Brown in color
- Base Paste – White in color
elastomer types
a. Polysulfides
b. Condensation silicones
c. Polyethers
d. Addition Silicones (Polyvinyl Siloxanes)
polyethers
Yields water as a by-product also known as a rubber base. The oldest and most economical of elastomers contain many sulfhydryl (-SH) groups.
sulfhydryl (-SH) groups are known as
mercaptan.
in polyethers
makes sulfur smell and will stain clothes
base of condensation silicone
• The base is a paste that contains a moderately low molecular weight silicone liquid called a dimethylsiloxane which has a reactive -OH group
condensation silicone gives off what as a by product
• Gives off ethyl alcohol as a by-product
addition silicone
- Heavy putty (base & catalyst are supplied in tubs) they are scooped out and mixed by hand or vinyl gloves. No latex. No by-product. Under normal reaction.
which has better mrchanincal properties polyether or polysulfide
polyether Better mechanical properties than those of polysulfides.
in condensation silicone __ is added as a scavenger for the release hydrogen gas
b. Palladium is added as a scavenger for the release hydrogen gas
__ is the component that gives polysulfide its characteristic brown color
a. Lead dioxide is the component that gives polysulfide its characteristic brown color
hand Mixing:
hand Mixing Equal amounts of material are placed on a mixing pad
Static Mixing:
Static Mixing: this technique transforms two fluid or paste like materials into a homogenous mixture without mechanical mixing. Materials make a 180°C turn
Dynamic Mechanical Mixing:
Dynamic Mechanical Mixing: a motor drives parallel plungers forcing the materials into a mixing tip and out into an impression tray or syringe
Requirements of Impression Materials
1) Case of manipulation and reasonable cost
2) Adequate flow properties
3) Appropriate setting time and characteristics
4) Sufficient mechanical strength not to tear or permanently deform during removal
5) Good dimensional accuracy
6) Acceptability to the patient
7) Safety (not toxic or irritating)
8) No significant degradation of properties as a result of disinfection
9) Compatibility with all die and cast materials
10) Good keeping qualities (no deterioration of unused material in the dental office)
