Laboratories Rely On Accuracy Of Impression Materials

How many times have you and your dental laboratory argued over a poorly fitting restoration?  The dentist claims it is a laboratory error and the laboratory argues it is due to a poor impression.

Efforts to solve this ongoing argument, plus the increasing use of impression materials for duplicate models for cosmetic restorations, have stimulated our interest in impression materials.

Dental manufacturers are challenged into making a predictable, accurate impression, which dentists can confidently send to a laboratory to have a restoration fabricated.  An impression material must be not only accurate but also able to resist distortion over time so that, if the dentist desires, the impression can be delivered to the laboratory for pouring working models.

Working Time Of The Impression Material

The dentist’s working time with an impression material is a crucial factor in the ultimate fit.  Towards the end of the working time, the impression material starts to form a memory and will “remember” the first position to which it begins adhering. 

Additional pressure applied further alters the impression, but it still has a tendency to rebound slightly to the original position when the pressure is removed. The short working times are desirable unless multiple preparations are being impressed at the same time.

Successful Impression Material

A successful impression material must have certain properties to allow for clinical success.  These properties include the following:

• The accuracy to reproduce surface detail of the tooth proportion and soft tissue surrounding the teeth.
• The accuracy to reproduce the same arch tooth relationships and dimensions (important for fabrications of fixed bridgework) and for establishing a correct relationship when mounting the maxillary and mandibular models.
• Dimensional stability over time.
• The elasticity and elastic recovery for removal form the mouth where undercuts exist as well as not to distort when removed form the mouth.
• The tear resistance to allow for making subgingival impressions with gingival retraction.
• A tray adhesive that will retain the impression material when it is removed from the mouth.

A comparison of the different impression material classes will help you in selecting the appropriate material for the specific clinical situation.  POLYSULFIDES offer a medium to long working time, but are difficult to mix.  They provide good surface detail and resistance to tearing, but they have a bad odor and can be a bit messy to use. Some common brand names: PERMLASTIC, COE-FLEX, NEOPLEX.

POLYETHERS: These materials are much more dimensionally stable than the polysulfide.  Pouring can be delayed many hours, even days, and double pouring is possible.  But these benefits are costly with polyethers earning the “most expensive” label. 

Surface reproduction in resultant casts is very good, but the rigid set of the material makes removal from undercut areas a bit difficult. 

Some common brand names: IMPREGUM, POLYGEL, PERMADYNE.  

POLYSULFIDES. These materials are usually used in putty/reline system since shrinkage upon setting is the main drawback here.  Impressions need to be poured rather quickly, certainly within the hour. These materials are not as rigid as the polyethers and they resist deformation better than polysulfides. 

Some common brand names: CITRICON, ACCOE, CUTTERSIL, XANTOPREN/OPTOSIL, COLTOFLAX/COLTEX.

ADDITIONAL SILICONES (aka vinyl polysiloxane):

These materials are touted as being the most accurate of all materials.  Pouring can be delayed for days, and the material is right behind the polyethers in the terms of cost. New developments in this category of impression materials have improved its hydrophilic properties and the suppression of the release of hydrogen gas upon setting now allows for immediate pouring if desired. 

Some common brand names: EXTRUDE, MIRROR-3, REFLECT, CINCH VINYL, EXCEL, PERMAGUM, PRESIDENT, REPROSIL, EXPRESS-H, POL-E-LASTIC.

POLYETHENE: This material has good dimensional stability and gives three to five minutes working time.  Polyethene is tear resistant and give good reproduction of surface detail. 

Some common brand name: POLYLASTIC. 

Although these new classes of impression materials are usually twice the cost of polysulfide impression materials, the advantages and convenience for using them will usually outweigh the cost factor.

"Impressive Dental Studio has been successfully providing dentists with various dental restorations for the past 50 years. Our special expertise means we can bring back  beautiful, healthy smile... and restore some of the most challenging  cases."

For more information about Impressive products you can call Toll Free 1-800-944-1244 or email us at info@impressivedental.com.