PRD 131 : Quiz 3 (alginates/ gypsum, provisionals) Flashcards
what are the common impression materials
hydrocolloids and synthetic elastomeric polymers
what are the desirable qualities for impression (just read )
- odor/taste/color
- non toxic
- good results/economics
- shelf life
- easy /minimal equipment
- setting meets clinical needs
- consistency/texture good
- wets oral tissues
- elastic for easy removal and recovery after removal
- strength to prevent breaking/tearing
- stability w/temp and humidity ranges in clinical and lab procedures lasting long enough to make cast or die
- compatibility with cast and die materials (?)
- accuracy in clinical use
- readily disinfected without loss of accuracy
- no release of gas/byproducts during setting
what is alginic acid from agar plants (chemically)
-what do the properties depend on
block copolymer of anhydro B-D mannuronic acid and anhydro-B-D-guluronic acid
solution with calcium makes ca alginate
- properties depend on degree of polymerization and ratio of guluronan and mannuronan blocks in the polymeric molecules
- mannuronan regions are stretched/flat and guluronan regions contribute less flexibility and they bidn w calcium.
- guluronan-> brittle gels. mannuronan-> weaker more flexible
what is the gel forming ability of alginates related to
proportion of L-guluronan blocks (guluronan makes it less flexible, binds calcium)
whats in the alginate forming powder, what is the chem reactions that occur in the process
calcium sulfate dihydrate, soluble alginate, and sodium phosphate in powder…
- calcium phosphate is formed. (rather than Ca alginate) because of lower solubility? so sodium phosphate is called a retarder– slows down the process. sodium phosphate makes for longer worker time!
- then after phosphate ions are depleted, ca ions react w soluble alginate to form the insoluble alginate, which combo with h20 makes irreversible Ca alginate gel!
- the ca alginate is insoluble in h20 and it gels up.
- level of sodim phosphate produces regular or fast set alginates!!
what fillers are used in alginate and what does it do
diatomaceous earth or fine siliceous particles are used as fillers (WEAR A MASK , dont breathe these in) - this controls flexibility of the set from soft to hard sets
what does adding organic glycols do to alginate powder
reduces dust
how can you know a set is complete by adding something to alginate
add pH indicator- changes color when set is comlete
what are injectable alginates
more fluid before set and flexible after set I think? slide 11
what can be impacted if the proportions are off in alginates
consistency, setting time, strength and quality of the impression.
what is regular alginate mixing time? for fast set? what is wrong with over or under mixing?
regular is 1 minute! fast set is 45 seconds
-strength is impacted if over or under mixed
what is working time for alginate
available time from start of mix to seating of impression before the gel state occurs
what is a regular set time for alginate impression? range?
usually 3 minutes, up to 4.5 minutes. mix time of 60 seconds allows 2 to 3.5 minutes of working time
range is 1-5 minutes
how long after placed in tray do you seat?
immediately
what is too cold water for alginate
10 celsius or cooler is not recommended for comfort of patient
how do you detect clinical setting time and how much longer should you leave in mouth
loss of tackiness - leave in mouth 2 to 3 minutes longer to maximize tear strength and elastic recovery
how much is alginate compressed upon removal in areas of undercuts? what does the magnitude of the compression depend on? what is elastic recovery?
how does time impact elastic recovery?
alginate is compressed about 10% upon removal in areas of undercuts (?) magnitude depends on extent of undercut and space b/w tray and teeth. elastic recovery is the return to dimensions at set or gel state of the mouth
ansi/ada spec says recovery may be at least 95% when compressed 20% for 5 seconds
-when % compression is lower theres higher elastic recovery , also when time of compression is lower and after longer recovery time there is more elastic recovrey
what is the amount of flexibility needed for alginate impressions
ansi/ada range is 5 to 20% , most like 14%. some lower that would hurt
-its needed to take impression OUT OF the mouth!!!
what do you do after taking impression (real person) to prepare for gypsum? what if sitting for a while? how to store it
must be rinsed well in cold water to remove saliva and blood (interfere with gypsum set)
- free water must be removed to avoid pooling in deep parts like cusp tips- would dilute gypsum mix and make a softer surface.
- reflective surface should look dull (no more water)
- if sits for 30+ minues should be rinsed with cool water to remove alginat eexudate caused by syneresis (?) the exudate will retard gypsum set. best to wrap rinsed impression in a moist paper towel and put in a plastic bag to avoid moisture loss.
- set gypsum shouldnt remain in contact w alginate as the soluble ca dihydrate of gypsum will react w/water in the gel, causing surface quality loss.
(alginate impressions loes water by evaporation and shrink when standing in air ,30 mins can void for clinical use)
how do you clean a alginate impression
usually spray
or immersion *not significant dimensional changes
methylmacrylate trays
slide 21! ? custom, requires a model, two visits. can be border molded. relief to assure thickness of alginate critical
features of rimlock metal trays
no adhesive required
autoclavable
cant be heat formed like plastic can
solid color trays features for alginate impressions
perfed for retention of alginate to the tray
- can be heat molded
- cant visualize implant heads or teeth?
- diff colors for diff sizes.
- cant visualize underlying structures.
what is the tray in clinic/features
ribbed for rigidity
- can be heat molded
- ribs make heat molding more difficult
- ribs block view of underyling structures somewhat
