Elastomeric Impressions

Impressions create what type of reproduction?

Negative reproduction (mold)

Casts/models are what type of reproduction?

Positive reproduction (stone/plaster poured into mold)

When seating an impression tray, were do you insert first and why?

Posterior first 

• Controls material flow 

• Prevents gagging 

• Better adapation

What Is the term for a material changing into a gel-like substance in the presence of water?

Hydrocolloid 

Agar is derived from what?

Seaweed

Is agar reversible or irreversible ?

Reversible (changes in temperature) 

What special equipment does agar require?

Water bath (hydrocolloid conditioner) + special trays with cooling system

What are agar impressions used for?

Final impressions (reproduce fine detail)

What quality do elastomeric materials have? 

Rubber-like 

When are elastomeric impressions used?

For final impressions with high detail

• (indirect restorations)

Elastomeric impressions are supplied as?

Base + catalyst (self-curing) 

What are the 3 viscosities of elastomeric material?

• Light-bodied (flows, detail)

• Regular (medium, balanced)

• Heavy bodied/Putty (thick, fills tray, pushes light into detail)

List mixing techniques for elastomeric materials?

• Paste-to-paste

• Automix

• Putty

• Syringe

• Gun

What are the 4 types of elastomeric materials?

• Polysulfide 

• Polyether 

• Silicone 

• Polyvinylsiloxane (PSV) 

What are some characteristics of Polysulfide?

• Used for final impressions (removable prosthesis)

• Long setting time (9 min)

• Wait 20-30 min before pouring

• Dispensed as paste

What are some disadvantages of Polysulfide?

• Unpleasant sulfur odor

• Can stain clothing

What are some characteristics of Polyether?

• Paste-to-paste system 

• Very stiff when set 

• Moisture sensitize (tooth must be dry) 

• Provides excellent detail reproduction) 

What are some characteristics of Silicone?

• Odor free, nonstaining, easy to mold

• Paste-to-paste or putty + catalyst

• No syneresis (water loss) or imbibition (water gain)

• Responds with shrinkage over time

• Wait 20-30 min before pouring

What are some characteristics of Polyvinylsiloxane (PVS)?

• High dimensional stability (doesn’t change size)

• No taste or odor 

• Paste-to-paste in cartridge or putty 

• Various viscosities 

What is the purpose of bite registration?

Record occlusal relationship between maxillary and mandibular teeth

What two materials are used for bite registration?

• Wax

• Polyvinylsiloxane (PVS)

What are some advantages/disadvantages of wax bite registration?

• Easy and inexpensive 

• No special equipment 

• Disadvantage: easily distorted 

What are some advantages of PVS bite registration?

• More stable

• Great detail

• Very accurate

What is a centric relationship?

Natural jaw position when relaxed

What is centric occlusion?

Normal way teeth bite together 

• Back teeth touch 

What is protrusive movement?

Lower jaw moves forward

• Back teeth do not touch