1. alginate

what structure provides legal proof of pt current occlusion?

mounted diagnostic case on an articulator

explain the land areas and thickness requirements for a trimmed cast:

• maxillary lingual land area thickness

• mandibular lingual land area thickness

• peripheral land area thickness

• vestibular depth

• maxillary lingual land area: 10-15mm deepest part

• mandibular lingual land area thickness: 10-15 mm

• peripheral land area thickness: 3-5mm

• vestibular depth: 3mm

what are the two materials most commonly used to make impressions?

• hydrocolloids 

• synthetic elastomeric polymers 

impressions create positive or negative reproductions of the tissue?

negative

filling an impression with dental stone or other model material makes a negative or positive cast?

positive

what are the some desirable qualities of impression materials?

• Pleasant odor, taste, and color

• Absence of toxic or irritant constituents

• Adequate shelf life

• Economic

• Easy to use

• Good setting characteristics

• Satisfactory consistency and texture

• Readily wets oral tissues

• Resistance to permanent distortion

• Adequate strength

• Dimensional stability over temperature and humidity normally found in clinical and laboratory setting

• Compatibility with cast and die materials

• Accuracy in clinical use

• Readily disinfected without loss of accuracy

• No release of gas during the setting of the impression or cast and die material

what are the six types of impression materials?

• Alginate hydrocolloid (A.K.A. irreversible hydrocolloid)

• Agar hydrocolloid (A.K.A. reversible hydrocolloid)

• Elastomeric materials Zinc oxide-eugenol materials

• Gypsum

• Compound impression material

what is the most widely used impression material in dentistry?

alginate (hydrocolloids)

which an an advantge and disadvantage of alginate hydrocolloids?

• adv: accurate if handled properly

• disadv: dimensionally unstable (syneresis vs inhibition)

alginate powder composed of what substances:

• Sodium or Potassium alginate (12 to 15%)

• Calcium sulfate dehydrate (8 to 12%)

• Sodium phosphate (2%)

• Reinforcing filler (~70%)

• Potassium sulfate or alkali zinc fluorides (~10%)

• Coloring and flavoring agents

what are the two main reactions of alginate hydrocolloids?

what slows alginate reaction?

retarders/chelating agents ike trisodium phosphate or sodium hexametaphosphate - bind to free calcium ions preventing immediate cross-link of alginate chains delaying reaction

how to manipulate alginate:

• Powder should be lightly shaken for aeration

• One scoop of powder should be used for one measure of water

• Always add water to the mixing bowl first

• One minute of thorough mixing for the regular setting and 45 seconds for fast-set

• Set time is around 3.5 minutes after mixing

add powder or water to bowl first

water

how long to mix for regular vs fast-set?

• regular: 1 min

• fast-set: 45 sec

set time for alginate after mixing

3.5 min

1 scoop of powder in grams vs water in ml

• 1 scoop of powder = 16g

• 1 measure of water = 38 ml

lower or higher W/P ratio: increase in strength

lower W/P

lower or higher W/P ratio: increase in tear strength (resisatnce to pulling)

lower W/P

lower or higher W/P ratio: “better” consistency

lower W/P

lower or higher W/P ratio: decrease in working time

lower W/P

lower or higher W/P ratio: decrease in setting time

lower W/P

lower or higher W/P ratio: decreased flexibility 

lower W/P

lower or higher W/P ratio: decrease in strength

higher W/P

lower or higher W/P ratio: decrease in tear strength 

higher W/P

lower or higher W/P ratio: runny consistency 

higher W/P

lower or higher W/P ratio: increase in working time

higher W/P

lower or higher W/P ratio: increase in setting time

higher W/P

lower or higher W/P ratio: increased flexibility

higher W/P

(cold/hot) water will increase the working and setting times

cold

syneresis

storage in air

loss of water due to hydration that causes shrinkage

syneresis

imbitbition

storage in water

tendency to absorb water that results in swelling 

imbibition

how long can an impression be stored in 100% himidty?

30 min prior to pouring

disinfection of impression accomplished by immersion in what two substances?

sodium hypochlorite or iodophors

water temp should be btwn 

65-75℉

undercuts and not enough material could lead to

tearing

consistency is related to what three things?

• water-powder ratio

• water temp

• spatulation

porosity can be related to what

incorrect spatulation

poor stone surface is related to what?

extended contact btwn gypsum and alginate - separate 45-60 min after pouring

what are the features of ideal mandibular and maxillary impressions?

infection control of impression in operatory:

• Rinse impression using cold running water to remove blood and debris

• Rub impression using Cavi Wipe

• Wrap it with Cavi-Wipe and place in plastic bag

infection control in lab

• Place impression on a paper towel

• Spray with Cavicide in 4th Fl Lab and leave it for 3 mins

• Rinse impression using cold running water

• Pour impression with Type III or IV dental stone

gypsum or alignate: refer to various forms of calcium sulfate (hydrous and anhydrous)

gypsum

gyspum or alginate: manufactured by the calcination of calcium sulfate

gypsum

gypsum products are manufactured by the (BLANK) of calcium sulfate dihydrate

calcination

what are the five gypsum products?

• impression plaster - ISO type 1

• (white) plaster - ISO type 2

• high strength plasters:

  • (yellow) stone - ISO type 3

  • stone, high-strength, low-expansion - ISO type 4

  • stone, high-strength, high expansion - ISO type 5

what is the worst thing about acrylic resin?

shrinkage

for metal base, crowns and bridges what ISO type used

4 bc low expansion 0-0.15%

white impression plaster

1

white mounting plaster of Paris

2

yellow stone study class

3

working cast for C&B

4

green working cast aka Die Keen aka C&B (tooth/implants), metal rpd frame

5

type 1 setting expansion % and compressive strength psi

• 0-0.15%

• 580-1160 psi

type 2 setting expansion % and compressive strength psi

• 0-0.30%

• 1300 psi min

type 3 setting expansion % and compressive strength psi

• 0-0.20% 

• 2900 psi min

type 4 setting expansion % and compressive strength psi

• 0-0.15%

• 5100 psi min

type 5 setting expansion % and compressive strength psi

• 0.16-0.30% 5100 psi min

yellow stone

3

green stone

5

for a maxillary complete denture what stone is used?

3

for a mandibular metal base rpd what stone is used?

5

for a mandibular acrylic resin (shrinkage) rpd what stone is used?

3

for immediate maxillary complete and mandibular resin based rpd what stone should be used?

3

type ? allows expansion to compensate for acrylic shrinkage

3

type ? provides limited expansion - good for prosthesis that require high precision like crown and bridge, fixed prosth like dental implant restoration and metal based rpd

4 or 5

what are the two products of partial dehydration of gypsum

plaster and stone

traditional hemihydrate plaster is produced by

dry calcination (Beta Hemihydrate)

medium and high strength plasters/stoens manufactured by wet calcination havea (stronger/weaker) set mass

stronger Alpha Hemihydrate 

setting process

• 2 stages, thick slurry

• reverse of first stage of dehydration & exothermic 

slurry water defined as

saturated calcium sulfate solution made by placing stone debris in a container of water

using tap water or slurry water for gypsum:

• decrease setting time or shorten setting time

• decrease compressive strength (not good)

• increase dimensional change (not good)

slurry water

lab plaster W/P ratio and ISO (gypsum setting process)

47, 2

dental stone W/P ratio and ISO (gypsum setting process)

30, 3

mounting stone W/P ratio and ISO (gypsum setting process)

26, 3

microstone W/P ratio and ISO (gypsum setting process)

28, 3

die-keen W/P ratio and ISO (gypsum setting process)

21, 4

four stages of gypsum setting process

1. fluid

2. plastic

3. friable

4. carvable

setting reaction causes a (decrease/increase) in true volume of reactants

decrease

what will affect the chemical reaction during the setting of gypsum products?

water/powder ratio

↑ temp of water

↓ setting time

(high/low) water/powder ratio harden more quickly, and will produce less microporosities related to residual unreacted water

]It will, however, (decrease/increase) microporosity related to crystal growth

low, increase

(more/less) spatulation turns = lower setting time

more

setting expansion is (inversely/proportional) to w:p

inversely

strength is (inversely/proportional) to w:p

inversely proportional

using (low/high) w:p for maximum strength also increases setting expansion

low

Removal of uncombined water from cast gypsum by low-temperature drying approximately (halves/doubles) the strength

doubles

hand mix or power-driven mix w vacuum:

• lower setting time

• higher compressive strength

• lower setting expansion %

• lower viscosity

power-driven mix w vacuum

what:

• serves as complement tool to clinical exam

• provides legal proof pf pt current occlusion

• allows clinician to modify occlusal pre-tx plan prior to definitive tx plan

• evaluate pt occlusion in centric and eccentric positions

• determine interarch distance - make alterations to clinician’s desire w/o pt

mounted cast on an articulator

what is the relationship between teeth and alveolar ridge?

interarch distance