PRD 131 : Quiz 3 (alginates/ gypsum, provisionals)

Question 1

what are the common impression materials

Answer 1

hydrocolloids and synthetic elastomeric polymers

Question 2

what are the desirable qualities for impression (just read )

Answer 2

• 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

Question 3

what is alginic acid from agar plants (chemically)

-what do the properties depend on

Answer 3

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

Question 4

what is the gel forming ability of alginates related to

Answer 4

proportion of L-guluronan blocks (guluronan makes it less flexible, binds calcium)

Question 5

whats in the alginate forming powder, what is the chem reactions that occur in the process

Answer 5

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!!

Question 6

what fillers are used in alginate and what does it do

Answer 6

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

Question 7

what does adding organic glycols do to alginate powder

Answer 7

reduces dust

Question 8

how can you know a set is complete by adding something to alginate

Answer 8

add pH indicator- changes color when set is comlete

Question 9

what are injectable alginates

Answer 9

more fluid before set and flexible after set I think? slide 11

Question 10

what can be impacted if the proportions are off in alginates

Answer 10

consistency, setting time, strength and quality of the impression.

Question 11

what is regular alginate mixing time? for fast set? what is wrong with over or under mixing?

Answer 11

regular is 1 minute! fast set is 45 seconds

-strength is impacted if over or under mixed

Question 12

what is working time for alginate

Answer 12

available time from start of mix to seating of impression before the gel state occurs

Question 13

what is a regular set time for alginate impression? range?

Answer 13

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

Question 14

how long after placed in tray do you seat?

Answer 14

immediately

Question 15

what is too cold water for alginate

Answer 15

10 celsius or cooler is not recommended for comfort of patient

Question 16

how do you detect clinical setting time and how much longer should you leave in mouth

Answer 16

loss of tackiness - leave in mouth 2 to 3 minutes longer to maximize tear strength and elastic recovery

Question 17

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?

Answer 17

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

Question 18

what is the amount of flexibility needed for alginate impressions

Answer 18

ansi/ada range is 5 to 20% , most like 14%. some lower that would hurt

-its needed to take impression OUT OF the mouth!!!

Question 19

what do you do after taking impression (real person) to prepare for gypsum? what if sitting for a while? how to store it

Answer 19

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)

Question 20

how do you clean a alginate impression

Answer 20

usually spray

or immersion *not significant dimensional changes

Question 21

methylmacrylate trays

Answer 21

slide 21! ? custom, requires a model, two visits. can be border molded. relief to assure thickness of alginate critical

Question 22

features of rimlock metal trays

Answer 22

no adhesive required
autoclavable
cant be heat formed like plastic can

Question 23

solid color trays features for alginate impressions

Answer 23

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.

Question 24

what is the tray in clinic/features

Answer 24

ribbed for rigidity

• can be heat molded
• ribs make heat molding more difficult
• ribs block view of underyling structures somewhat

Question 25

what are features of crystal clear tray

Answer 25

• can read text thru tray
• great for implants
• clarity makes underlying structures obvious
• ribless so easier to heat mold

Question 26

what is damit

Answer 26

prevents intrusion of material into throat. post dam - flexible and increases vertical hydraulics. combines phjysically with material (unlike wax?)

Question 27

what are the 3 raw materials derived from partial dehydration of gypsum rock

what are the 4 types of gypsum products used in dentistry
and which do we use at school rn

Answer 27

1. plasters (fluffy and porous)
2. hydrocal (higher density and more crystallline)
3. density /densite (densest)

these form basis for the four types used in dentistry:

• Type 2: plaster
• Type 3: low to moderate strength dental stone (this is what we will use in class)
• Type 4: high strength/low expansion dental stones
• type 5: high strength/high expansion dental stones

(types 2,3,4,5 in ANSI/ADA spaces)

Question 28

what is spatulation of gypsum

Answer 28

mixing of gypsum products is spatulation? has impact on setting time and expansion: an increased speed or amount of spatulation (mixing) will shorten the setting time

Question 29

how does temp impact gypsum setting

Answer 29

increase temp from room temp to body temp increases rate of reaction and shortens set time. if you heat over 37 celsius the rate o frxn decreases and set time increases.

Question 30

how should gypsum be stored

Answer 30

closed container! avoid imbibition (water from environment)

Question 31

what are the important properties of gypsum

Answer 31

fluidity at pouring, setting time, near setting expansion, comp strength, hardness/abrasion resistance, reproduction of detail

Question 32

why are provisionals important for tooth position

Answer 32

prevents mesial drift and supraeruption

teeth tend to move mesial

Question 33

what is the provisional preference at pacific (what we use)

Answer 33

bis-acrylic resin

Question 34

what to consider for provisional materials

Answer 34

esthetics, strength, dimensional stability, working time, setting time, ability to finish and polish, biocompatibility

Question 35

what are the advantages and disadvantages to stainless steel for provisional crowns

Answer 35

advantages: wear resistant and affordable
disadvantages: poor esthetics, require adjustment to fit, reline required (?), can irritate soft tissue

Question 36

what are the advantages and disadvantages to a polycarbonate shell for provisional crown

Answer 36

advantages: good esthetics (sizes and shades), useful for dental emergencies
disadvantages: need to have a large stock (high initial cost), reline required, marginal staining

Question 37

what are the advantages and disadvantages to a laboratory processed shell for crown provisional

Answer 37

advantages: great esthetics, wear resistant, longevity
disadvantages: must send models to lab before prep appt, laboratory fee, reline required

Question 38

what are the advantages and disadvantages to methyl or ethyl methacrylate provisional crowns

Answer 38

advantages: wear resistant, affordable, easy to adjust/repair
disadvantages: color instability, about 7% shrinkage, exothetmic setting reaction

Question 39

what are the advantages/disadvantages to bis-acrylic resin

Answer 39

advantages: esthetic, easy to adjust/repair, vety little exothermicity
disadvantages: will fracture under heavy load, material can lock into undercuts, moderately expensive

Question 40

what is exothermicity in terms of provisionals/why it matters

Answer 40

elevation of intrapulpal temperature by 5.5 degrees celsius !!! caused pulpitis/pulpal necrosis in 15% of teeth in monkeys!!!

bis-actylic resin is less exothermic than other materials

Question 41

what is ideal for more elastic recovery?

Answer 41

• the greatest amount of alginate between teeth and tray
• good retention in tray
• rapid removal from mouth
• time for recovery (disinfection is enough)

Question 42

what is an indicator of compatibility for alginate and gypsum combination

Answer 42

v shaped grooves reproduction (test done)

Question 43

how can you reduce tearing with impressions

Answer 43

fast removal! it occurs in thin areas

Question 44

what type of gypsum do we use for our alginate?

Answer 44

type 3 or low to moderate dental stone

Question 45

what affects gypsum setting time

Answer 45

-mixing speed, temperature of water and enviornment, (increase temp shortens settng time but if passed 37 celsius it decreases and set time lengthens)