Dental Material Chp 5 and 6 (TERMS ONLY)

Dental Impression Material

a class II device composed of materials such as
alginate or polysulfide intended to be placed on a preformed impression tray
and used to reproduce the structure of a patient’s teeth and gums

Preliminary Impression

the first one taken; usually taken with an irreversible hydrocolloid. Study models/diagnostic casts for treatment planning; fabricating custom trays,
provisional restorations, orthodontic retainers

Final Impression

The more accurate impression taken for fabrication of crowns, bridge, implants; needs to be very detailed and accurate ; most commonly with polyvinyl siloxane and polyether

Bite Registration/Occlusal Impression

Needed for the proper fabrication of the dental restoration; impression of the two opposing arches/teeth; previously taken with wax but polyvinyl siloxane has replaced wax; more accurate

Negative reproduction

The impression itself

Positive reproduction

The poured study model

Elastic

widely used and has rebound meaning when the tray is removed, the material
goes back to its original form

inelastic

not commonly used today and is a impression compound

Key properties of impression materials

Strength, accuracy, tear resistant, and dimensional stability

Stock trays

one size fits all.; Small medium, large, xlarge; usually single-use plastic,
but can also be made of metal(require sterilization); can be solid or
perforated(preferred); if solid referred to as rim-locked trays due to the raised
borders on the inside of the tray; helps to hold material in tray; in addition, need
adhesive

Stock Sectional Trays

same as stock trays; can be full arch, quadrant, anterior, or
for bite registration

Triple Trays/Closed Bite trays

stock sectional tray; captures both arches in centric occlusion at the same time; also called closed-bite, double-bite, dual-arch, check-bite tray

Bite Registration Trays

mesh; double-sided; records proper bite relationship

Custom Trays

fitted to the exact dimensions/shape of a patient’s mouth; usually fabricated in the lab; made of chemically-cured, light-cured, or thermoplastic material

Reversible Hydrocolloids

Agar (it is a gel, but on heating, it becomes a sol)

Irreversible Hydrocolloid

alginate

What is a colloid?

glue-like material made of two or more substances where one substance does not
go into solution but is suspended within another substance

Sol

when the powder is mixed with water it creates a glue-like colloidal
suspension

Gel

when the suspension is chilled it creates

Hysteresis

melting and gelling at different temperatures (reversible)

Syneresis in Irreversible Hydrocolloids

Water exudes and impression contracts/distorted (drys up)

Inbibition in Irreversible Hydrocolloids

Water may be absorbed and impression swells (like a sponge)

Reversible Hydrocolloid is made up of

Agar (colloid), Borax (strengthen gel), Potassium sulfate, Water (dispersion medium)

Advantages of Reversible Hydrocolloid

Good surface detail, Reusable and easily sterilized

Disadvantages of Reversible Hydrocolloid

Need special equipment (water bath for 5 minutes) and special technique, Dimensional instability

Steps of an alginate impression

Uses preliminary impression, working time (the length of time from start of mix to loading the tray): 2-3min, setting time (the length of time from start of mix to final set) : 2-5 min

What factors could change the set time of alginate

Water temperature: hot water- shortening/quickening the setting time ; cold water- lengthens/increases the setting time

Alginate Components

Potassium alginate or sodium alginate, TriSodium phosphate, Diatomaceous earth (silica - Inert filler), Colorants, Flavor, Antimicrobial agents

Two consistency alginate system

Two different mixes, one goes into the tray (high viscosity) and the second mix gets put into the syringe (low viscosity) and then dispensed into the peripheral vestibule, creating a border, molding material

Advantages of using Alginate

Will ‘wet’ the tooth surface, Hydrophilic, Non toxic and non irritant, Good surface detail, Ease of use and mix, Easy pouring, Inexpensive; good shelf life, Setting time can be controlled with the temperature of the water used

Disadvantages of using Alginate

Poor dimensional stability, Syneresis, Imbibition, Setting time is very dependent on the operator handling, Can also be an advantage, Messy to work with

Steps to taking a alginate impression

#1 – explain the procedure to the patient, look into the patients mouth (estimate tray size), Fit the tray (mandibular first), add wax to the tray, Fluff the powder, Dispense powder into a cup, Measure water/place in the mixing bowl, Add powder to the water, Mix with spatula, Load the tray, Back to front –maxilla From the lingual - mandible, Seat the tray (Seat back to front), remove tray, rinse under cold water, inspect, disinfect, pour

What should you not do while waiting for the alginate to set

DO NOT leave patient

How do we disinfect impressions

Rinse impression under water, spray disinfectant, put into ziplock bag (10 mins), take it out and wrap in a damp paper towel, goes back in the bag

Disinfectant solutions

detrays/ inactivates TB/COVID, be on the EPA N list, must be safe to use

How long do you disinfect alginate impression

10 minutes

If an alginate impression is left exposed to the air the water content of the impression will evaporate, causing the impression to shrink, which is called

syneresis

What is the working time

What is the working time of a regular time set alginate

2-3 min