Impression for Indirect Restorations Flashcards
What factors will make a good impression?
Tray choice inc. size
Appropriate technique
Good soft tissue management
Appropriate choice/use material
What different trays are available?
- Metal (e.g rim-lock)
Reusable, can be perforated
Adv: rigid- help support material to maintain pressure
Disadv - need sterilising - Plastic
Disposable
Disadv: not as rigid - more prone distortion
How can you assess size of tray?
Space space for seating and adequate room for imp
Place in mouth and hold handle - rotate lateral (if contact posterior suggest too small)
How can trays be more retentive?
Grooves, perforation
Use adhesive
Define accuracy?
Ability to replicate the hard and soft tissues
Define resolution/ precision?
Ability to reproduce surface detail
What is dimensional stability?
Maintenance of material in terms of size and shape over prolonged period of time
What are the classifications of impression materials?
- Hydrocolloids - reversible or irreversible (alginate)
2. Synthetic elastomers - polysulphides/polyetheres/ silicones
What are ideal characteristics for imp material?
High accuracy, good dimensional stability, elastic, good tear strength, easy use, good working and setting time, tolerant disinfection, cheap, acceptable taste
Properties/ use of alginate?
Poor reproduction surface detail
Poor dimensional stability
Not suitable definitive indirect impression
Used for opposing arch imps
Properties/ use of polysulphides?
Not used
Adv = long working time, flexible, good tear resistance, long shelf-life
Disadv = long working time, poor dimensional stability, stick, unpleasant smell, need special try
What is condensation silicone?
Cheaper than addition silicones
By product = alcohol
Adv: easy to use, good surface detail, good tear resistance
Disadv: dimensionally unstable, hydrophobic
What are addition silicones?
Most commonly used imp material for indirect restorations
Addition reaction between silane and vinyl groups when catalyst and base pastes are mixed
No-by product
Adv and disadv of addition silicones?
Adv: excellent dimensional stability, excellent surface detail reproduction, biocompatible, simple mixing, reasonable working time
Disadv: expensive, hydrophobic, setting time affect by temp, difficult to remove from cast, some latex glove inhibit setting
What are different formulation of addition silicones?
Putty
Heavy bodied
Medium bodies
Light bodied
What are different properties of formulations of addition silicones?
Light/ medium - more flowable and high detail reproduction
Putty - increased filler content (increase dimensional stability)
Heavy bodies - lack of contraction, dimensional stability
Use of polyether as imp material?
Option for fixed prosthodontics
Rigid - favoured for things such as implants but makes difficult to remove from mouth (may remove periodontally compromised teeth)
Adv and disadv of polyether?
Adv: good dimensional stability and surface reproduction, one viscosity - shear thinning allows flow, hydrophilic
Disadv: very stiff/ rigid, swell w/ water if kept damp environment, bitter taste
Why do imps need to be disinfected?
Remove blood/saliva contaminant
Rinse to remove visible debris then follow procedure
What are the 3 types of soft tissue management?
Mechanical - retraction cord
Chemical - retraction paste, homeostatic agent
What is gingival retraction?
Downwards and outward movement of free gingival margin
Allows syringe imp material beyond prep margins
Doesn’t control inflammation
What is retraction cord and what techniques can be used?
Cord = packed into gingival sulcus to retract gingiva
Single cord technique - most common removed prior to imp
Double cord - fine cord used initial (vertical) then pack largest above (vertical and lateral) - leave fine cord for imp
What is haemostatic agent?
Aluminium chloride/ epinephrine to control bleeding
What is retraction paste?
Viscous agent syringe into gingival sulcus to provide retraction and haemostats
More expensive
