Alginate Flashcards
(24 cards)
What is impression material?
A substance or combination of substances used to make an impression or negative reproduction of the oral environment
What is the purpose of dental impressions?
Used in preparation of casts by filling the impression with dental stone or other model material
List the ideal requirements of an impression material
- Pleasant taste, odor, and esthetic color
- Non-toxic and non-irritating
- Cheap
- Adequate shelf life
- Easy to use with minimum equipment
- Dimensional stability
- Adequate strength
- Elastic recovery properties
- Ability to be electroplated
- Compatibility with die and cast materials
- Adequate wettability of oral tissues
- Readily disinfected without significant loss of accuracy
What are the two main categories of hydrocolloid impression materials?
- Reversible hydrocolloid
- Irreversible hydrocolloid
Define hydrocolloids
Materials that exist in sol (viscous liquid) or gel (jelly-like) form, with water as the solvent termed hydrocolloid
What are the two types of hydrocolloid impression materials?
- Agar (reversible hydrocolloid)
- Alginate (irreversible hydrocolloid)
What is alginate?
An irreversible hydrocolloid developed as a substitute for agar, derived from a mucous extract of brown seaweeds
What is the mixing time for normal setting alginate?
1 minute
What is the mixing time for fast setting alginate?
45 seconds
What happens with over mixing alginate?
Reduction of final strength and working time
What happens with under mixing alginate?
Inadequate wetting, lack of homogeneity, and poor recording of detail
What is the effect of water temperature on alginate setting time?
Colder water results in longer gelation time; warmer water results in shorter gelation time
What is the composition of alginate?
- Sodium or potassium triethanolamine alginate (15%)
- Calcium sulfate dihydrate (16%)
- Zinc oxide (4%)
- Potassium sulfate (3%)
- Potassium titanium fluoride (3%)
- Diatomaceous earth (60%)
- Sodium phosphate (2%)
- Coloring and flavoring agents (traces)
What is the setting reaction of alginate?
Gelation involving calcium sulfate and sodium phosphate to form calcium phosphate and sodium sulfate, and calcium sulfate with sodium alginate to form insoluble calcium alginate
How is alginate impression material disinfected?
By immersion in 1% Sodium Hypochlorite or 2% Gluteraldehyde for less than 10 minutes, or preferably by spraying with disinfectant
What affects the dimensional stability of hydrocolloid impressions?
The ability to gain or lose water (imbibition, syneresis, dehydration) leading to deformation
List applications of alginate impression materials
- Making primary impressions
- Final impressions for complete dentures
- Impression for repairs to dentures
- Wash material over primary impressions
- Impressions for study models and working casts
- Fabrication of mouth guards and provisional restorations
What are some advantages of alginate?
- Easy to mix and manipulate
- Low cost
- Comfort to patients
- Hygienic
- Good surface detail
What are some disadvantages of alginate?
- Cannot be electroplated
- Cannot be corrected
- Poor dimensional stability
- Poor tear strength
- Distortion may occur if not handled properly
What is a dust-free alginate?
Alginate achieved by coating the material with glycerine or glycol to reduce dust
What is chromatic alginate?
Alginate that contains an acid/base indicator to indicate the setting time
What causes grainy material in alginate?
Improper mixing, prolonged mixing, excessive gelation, or low water/powder ratio
What can cause tearing of alginate impressions?
Inadequate bulk, premature removal, moisture contamination, or prolonged mixing
What results from improper handling of alginate?
Issues like irregularly shaped voids, external bubbles, and distortion
