Dental Alginate Impressions

Dental Alginate Impressions

Write in detail about properties and uses of alginate.
Answer:

Properties of Alginate (ADA Specification No. 18):

• Taste and Odor: Alginate has a pleasant taste and smell. A variety of colors, odors, and tastes are added to make it pleasant.
• Flexibility: It is 14% at stress of 12.2 N. Lower W/P ratio results in lower flexibility.
• Elastic and Elastic Recovery: Alginate hydrocolloids are highly elastic and about 97.3% elastic recovery occurs. So, permanent deformation is more for alginate.
• Reproduction of Tissue Detail: Detail reproduction is lower as compared to agar hydrocolloids.
• Strength:
  • Compressive strength — 5,000 – 8,000 g/cm²  or 0.5 to 0.9 MPa.
  • Tear strength — 350 – 700 g/cm² Or 0.4 to 0.7 KN/m.
• Dimensional Stability: Alginate has poor dimensional stability due to evaporation, syneresis and therefore cast should be poured immediately.
• Adhesion: Alginate does not adhere well to the tray. Good adhesion is important for accuracy of impression. Retention to the tray is achieved by mechanical locking features in tray.
• Biological Properties: Silica particles present in the dust which rises from the cane after fluffy alginate powder is a possible health hazar

Shelf-life and Storage:

Alginate material deteriorates rapidly at elevated temperature and humid environment. That is why:

• Material is stored in cool, dry environment.
• Lid of bulk package is replaced after every use to minimize moisture contamination.
• Stock only for 1 year.

Dust-Free Alginate

• Dust-free alginate is the newer alginate without silica particles.
• Dust-free alginate is coated with glycol which makes the particles so heavier on puffy or at the time of manipulation the alginate particles does not blow in the air.
• By coating alginate particles with glycol, helps in balancing the composition and maintaining the standards of the composition.
• This type of alginate does not cause any health hazards because no silica particles are present in it.
• The shrinkage of dust-free alginate is less.
• They reproduce good surface details.

They are available in different types of colors and flavors:

• These types of alginate are available with changes in colors which guide and help the dentist as well as are attractive to the patients.
• Their water powder (w/p) ratio is less as compared to older alginate.
• They are available in two types such as fast setting alginate and slow-setting alginate.
• They are more elastic or fragile than older alginate, their tensile strength is also higher than the older alginate also.

 

Disinfection Of Dental Impression

Disinfectants used for impression material are as follows:

• Impression compound: Iodophors, sodium hypochlorite (1:10 dilution).
• ZOE impression: Iodophors, sodium hypochlorite (1:10 dilution).
• Polyether: Iodophors, sodium hypochlorite (1:10 dilution).
• Silicone and polysulphide: Iodophors, sodium hypochlorite, synthetic phenols.
• Wax bites: Iodophors.

Disinfection of impressions is done by immersing the impressions in a plastic bag containing disinfectants or by spraying the impression surface and leaving it for 15 minutes. Polyether and hydrocolloids should be immersed only for 10 minutes. Remove the impressions and rinse in running water, remove excess water, and pour the cast.