Alginate and Dental Stone Flashcards
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the ideal impression material
EASY TO MIX AND HANDLE. SUITABLE WORKING TIME. SUITABLE SETTING TIME. COMPATIBLE WITH STONE NOT TOXIC OR ALLERGENIC TO THE PATIENT. DIMENSIONALLY STABLE ON SETTING. ACCURATE TO RECORD THE FINE DETAILS HAS ACCEPTABLE ODOR AND TASTE. ADEQUATE STRENGTH. ADEQUATE SHELF LIFE. ECONOMICAL READY TO BE DISINFECTED WITHOUT LOSS OF ACCURACY. FLUID OR PLASTIC WHEN INSERTED INTO THE MOUTH. IT MUST BE AN EXACT RECORD OF ALL THE ASPECTS OTHER TEETH AND TISSUE SURROUNDING IT MUST BE FREE FROM AIR BUBBLES ESPECIALLY IN THE FINISH LINE AREA.
key properties of impresion materials (2)
accuracy
dimensional stability
accuracy
ability to replicate the intraoral surface details
dimensional stability
ability to retain its absolute dimensional size over time
nonelastic impression materials (4)
gypsum (plaster)
impression compound
zinc oxide eugenol
impression waxes
elastic impression material (2)
hydrocolloids
non aqueous elastomers
hydrocolloids (2)
agar reversible
alginate irreversible
non aqueous elastomers (4)
polysulfide
polyethers
condensation silicone
addition silicone
ALGINATE
(IRREVERSIBLE HYDROCOLLOID)(IRREVERSIBLE HYDROCOLLOID) was developed as a substitute for
AGAR IMPRESSION
MATERIAL WHEN ITS SUPPLY BECAME SCARCE DURING WORLD
WAR II.
ALGINATE IS BASED ON A NATURAL SUBSTANCE EXTRACTED FROM CERTAIN — —. THE SUBSTANCE IS CALLED
BROWN SEAWEED
ANHYDRO-Β-D-
MANNURONIC ACID OR ALGINIC ACID
THE PRINCIPAL FACTORS RESPONSIBLE FOR THE SUCCESS OF THIS
TYPE OF IMPRESSION MATERIAL ARE THAT IT IS (3)
EASY TO MANIPULATE,
COMFORTABLE FOR THE PATIENT,
AND RELATIVELY INEXPENSIVE SINCE IT DOES NOT REQUIRE ELABORATE EQUIPMENT
THE CHIEF ACTIVE INGREDIENT OF THE IRREVERSIBLE
HYDROCOLLOID IMPRESSION MATERIALS IS ONE OF THE SOLUBLE
ALGINATES, SUCH AS (3)
SODIUM,
POTASSIUM,
OR TRIETHANOLAMINE ALGINATE
WHEN THE SOLUBLE ALGINATES ARE MIXED WITH WATER,
THEY FORM A – QUITE READILY
SOL
alginate composition (6)
potassium alginate calcium sulfate zinc oxide potassium titanium fluoride diatomaceous earth sodium phosphate
potassium alginate
function:
weight percentage:
soluble aginate
15
calcium sulfate
function:
weight percentage:
reactor
16
zinc oxide
function:
weight percentage:
filler particles
4
potassium titanium fluoride
function:
weight percentage:
accelerator
3
diatomaceous earth
function:
weight percentage:
filler particles
60
sodium phosphate
function:
weight percentage:
retarder
2
THE TYPICAL SOL-GEL REACTION CAN BE DESCRIBED SIMPLY
AS A REACTION OF
SOLUBLE ALGINATE WITH CALCIUM SULFATE
AND THE FORMATION OF AN INSOLUBLE CALCIUM ALGINATE
GEL
IN THE CLINICAL SETTING, IT IS TEMPTING TO ALTER THE
SETTING TIME BY CHANGING THE W/P RATIO OR THE MIXING
TIME. THIS SLIGHT MODIFICATION CAN HAVE MARKED EFFECTS
ON THE (3)
PROPERTIES OF THE GEL,
THE TEAR STRENGTH,
AND THE ELASTICITY
THE CLINICIAN, HOWEVER, CAN SAFELY INFLUENCE THE
SETTING TIME BY ALTERING THE — OF THE
WATER.
TEMPERATURE
ALGINATE IMPRESSION MATERIALS ARE —, SO
MOIST TISSUE SURFACES ARE NOT A PROBLEM
HYDROPHILIC
GENERALLY, ALGINATES ARE USED AS A
FIRST PRELIMINARY
IMPRESSION TO CONSTRUCT A CUSTOM TRAY FOR A MORE
ACCURATE SECOND IMPRESSION OR TO MAKE STUDY MODELS
TO HELP WITH TREATMENT PLANNING AND DISCUSSIONS WITH
THE PATIENT.
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MAKING AN ALGINATE IMPRESSION (7)
- THE MEASURED POWDER IS SIFTED INTO PREMEASURED WATER THAT
HAS ALREADY BEEN POURED INTO A CLEAN RUBBER BOWL. - THE POWDER IS INCORPORATED INTO THE WATER BY CAREFULLY
MIXING WITH A METAL OR PLASTIC SPATULA THAT IS SUFFICIENTLY
FLEXIBLE TO ADAPT WELL TO THE WALL OF THE MIXING BOWL. ALL OF
THE POWDER MUST BE DISSOLVED. - THE RESULT SHOULD BE A SMOOTH, CREAMY MIXTURE THAT
DOES NOT READILY DRIP OFF THE SPATULA WHEN IT IS RAISED
FROM THE BOWL. - BEFORE SEATING THE IMPRESSION, THE MATERIAL SHOULD HAVE
DEVELOPED SUFFICIENT BODY SO THAT IT WILL NOT FLOW OUT OF
THE TRAY AND GAG THE PATIENT. - THE MIXTURE IS PLACED IN A SUITABLE TRAY, WHICH IS THEN
PLACED IN THE MOUTH. IT IS IMPERATIVE THAT THE IMPRESSION
ADHERE AND BE RETAINED TO THE TRAY SO THAT THE
IMPRESSION CAN BE WITHDRAWN FROM AROUND THE TEETH. - ALGINATE IS VERY WEAK; THEREFORE THE TRAY MUST
FIT THE PATIENT’S ARCH SO THAT THERE IS A
SUFFICIENT BULK OF MATERIAL. THE THICKNESS OF THE
ALGINATE IMPRESSION BETWEEN THE TRAY AND THE
TISSUES SHOULD BE AT LEAST 3 MM. - ALGINATE HYDROCOLLOID MATERIALS ARE STRAIN-
RATE DEPENDENT. THUS THE TEAR STRENGTH IS
INCREASED WHEN THE IMPRESSION IS REMOVED
WITH A SNAP.
mixing time
45 s to 1 min
THE THICKNESS OF THE
ALGINATE IMPRESSION BETWEEN THE TRAY AND THE
TISSUES SHOULD BE AT LEAST - MM.
3
impression disinfection
disinfectant soaked paper towel/plastic bag, 10 min
does disinfection affect VPS?
not adversely affected
HYDROCOLLOIDS
•• IMBIBITION:
EXPANSION AFTER 10 MIN
POLYSULFIDE, POLYETHER
•• POTENTIAL EXPANSION,
increase exposure time
digital impressions (2)
- LESS FOCUS ON RESEARCH AND DEVELOPMENT OF IMPRESSION MATERIALS
- DIGITAL IMPRESSIONS, SCAN AND THEN SEND ELECTRONIC FILE
SOME CURRENT digital impression SYSTEMS: (3)
crerec
itero element
LAVA
which digital impression system will we use in lab?
cerec
CHEMICALLY, THE GYPSUM PRODUCED FOR DENTAL APPLICATIONS
IS NEARLY PURE
CALCIUM SULFATE DIHYDRATE
DIFFERENT — FORMS OF GYPSUM HAVE BEEN USED FOR
CENTURIES FOR CONSTRUCTION PURPOSES AND FOR MAKING
ARTIFACTS.
CRYSTALLINE
GYPSUM PRODUCTS ARE USED IN DENTISTRY FOR THE
PREPARATION OF STUDY MODELS FOR ORAL AND MAXILLOFACIAL
STRUCTURES AND AS IMPORTANT AUXILIARY MATERIALS FOR
DENTAL LABORATORY OPERATIONS THAT ARE INVOLVED IN THE
PRODUCTION OF DENTAL PROSTHESES.
WHEN PLASTER IS MIXED WITH FILLERS, SUCH AS DIFFERENT
FORMS OF SILICA, IT IS KNOWN AS A
GYPSUM DENTAL
INVESTMENT
THE PRINCIPAL CONSTITUENT OF GYPSUM-BASED PRODUCTS SUCH
AS DENTAL PLASTERS AND STONES IS
CALCIUM SULFATE
HEMIHYDRATE
VARIOUS GYPSUM PRODUCTS REQUIRE DIFFERENT AMOUNTS OF
WATER AND THESE DIFFERENCES ARE ACCOUNTED FOR
PRINCIPALLY BY THE
SHAPE AND COMPACTNESS OF THE
CRYSTALS. THESE FACTORS ARE REGULATED BY THE
MANUFACTURER
THE — THEORY PROPOSES THAT WHEN MIXED WITH
WATER, PLASTER ENTERS INTO THE COLLOIDAL STATE
THROUGH A SOL-GEL MECHANISM.
COLLOIDAL
THE — THEORY SUGGESTS THAT REHYDRATED
PLASTER PARTICLES JOIN TOGETHER THROUGH HYDROGEN
BONDING TO THE SULFATE GROUPS TO FORM THE SET
MATERIAL.
HYDRATION
HOWEVER, THE MOST WIDELY ACCEPTED MECHANISM IS THE — — THEORY BASED ON DISSOLUTION OF PLASTER AND INSTANT RECRYSTALLIZATION OF GYPSUM, FOLLOWED BY INTERLOCKING OF THE CRYSTALS TO FORM THE SET SOLID
DISSOLUTION PRECIPITATION
THE SETTING REACTION OF GYPSUM OCCURS BY: (4)
DISSOLUTION OF CALCIUM SULFATE HEMIHYDRATE
FORMATION OF A SATURATED SOLUTION OF CALCIUM SULFATE
AGGREGATION OF LESS SOLUBLE CALCIUM SULFATE DIHYDRATE, AND
PRECIPITATION OF THE DIHYDRATE CRYSTALS.
THE – RATIO IS AN IMPORTANT FACTOR IN DETERMINING
THE PHYSICAL AND CHEMICAL PROPERTIES OF THE FINAL
GYPSUM PRODUCT.
W/P
Mixing time (MT)
DEFINED AS THE TIME FROM THE ADDITION OF
THE POWDER TO THE WATER UNTIL THE MIXING
IS COMPLETED.
MECHANICAL MIXING OF STONES AND PLASTERS
IS USUALLY COMPLETED IN
20 TO 30 SEC.
HAND-SPATULATION GENERALLY REQUIRES AT
LEAST — TO OBTAIN A SMOOTH MIX.
A MINUTE
WORKING TIME (WT)
WORKING TIME IS THE TIME AVAILABLE TO USE A
WORKABLE MIX, ONE THAT MAINTAINS A UNIFORM
CONSISTENCY TO PERFORM ONE OR MORE TASKS.
SETTING TIME (ST)
THE TIME THAT ELAPSES FROM THE BEGINNING OF MIXING
UNTIL THE MATERIAL HARDENS
PROBABLY THE MOST EFFECTIVE AND PRACTICAL METHOD FOR
CONTROLLING THE SETTING TIME IS THE
ADDITION OF CERTAIN
CHEMICAL MODIFIERS TO THE MIXTURE OF PLASTER OR DENTAL
STONE.
IF THE CHEMICAL ADDED DECREASES THE SETTING TIME, IT IS
KNOWN AS AN—; IF IT INCREASES THE SETTING TIME, IT
IS KNOWN AS A —
accelerator
retarder
THE CRYSTALLIZATION PROCESS IS PICTURED AS AN
OUTGROWTH OF CRYSTALS FROM NUCLEI OF
CRYSTALLIZATION. ON THE BASIS OF THE ENTANGLEMENT OF
THE DIHYDRATE CRYSTALS, CRYSTALS GROWING FROM THE
NUCLEI CAN INTERMESH WITH AND OBSTRUCT THE GROWTH
OF ADJACENT CRYSTALS.
WHEN SUFFICIENT CRYSTALS FORM TO PRODUCE THE
OUTWARD THRUST BY IMPINGEMENT,
SETTING EXPANSION
FOLLOWS
SOMETIMES A SETTING EXPANSION IS ADVANTAGEOUS FOR A
DENTAL PROCEDURE; SOMETIMES IT IS DISADVANTAGEOUS,
BECAUSE IT MAY BE A SOURCE OF —.
ERROR
SETTING EXPANSION MUST BE CONTROLLED TO OBTAIN THE
DESIRED — IN DENTAL APPLICATIONS.
ACCURACY
THE MOST EFFECTIVE METHOD FOR CONTROLLING THE SETTING
EXPANSION IS THROUGH THE ADDITION OF CHEMICALS BY THE
MANUFACTURER. THE SETTING EXPANSION CAN BE REDUCED
BY ADDING EITHER (3)
POTASSIUM SULFATE, SODIUM CHLORIDE,
OR BORAX.
IMPRESSION PLASTER (TYPE I) (2)
COMPOSED OF PLASTER OF PARIS, TO WHICH MODIFIERS
HAVE BEEN ADDED TO REGULATE THE SETTING TIME AND
THE SETTING EXPANSION.
RARELY USED ANYMORE FOR DENTAL IMPRESSIONS.
MODEL PLASTER (TYPE II) (2)
IT IS USUALLY MARKETED IN THE NATURAL WHITE COLOR,
THUS CONTRASTING WITH STONES THAT ARE GENERALLY
COLORED.
TYPE II MODEL PLASTER IS RELATIVELY WEAK
AS EVIDENCED BY A COMPRESSIVE STRENGTH AS LOW
AS 9 MPA AND A TENSILE STRENGTH OF 0.6 MPA.
DENTAL STONE (TYPE III)
TYPE III STONES ARE PREFERRED FOR CASTS USED
TO PROCESS DENTURES, BECAUSE THE STONE HAS
ADEQUATE STRENGTH FOR THAT PURPOSE AND THE
DENTURE IS EASIER TO REMOVE AFTER PROCESSING.
DENTAL STONE, HIGH STRENGTH (TYPE IV)
A HARD SURFACE IS NECESSARY FOR A DIE STONE,
BECAUSE THE CAVITY PREPARATION IS FILLED WITH
WAX THAT IS CARVED FLUSH WITH THE MARGINS OF
THE DIE.
DENTAL STONE, HIGH STRENGTH, HIGH EXPANSION (TYPE V)
THE TYPE V DENTAL STONE GYPSUM PRODUCT EXHIBITS
AN EVEN HIGHER COMPRESSIVE STRENGTH THAN DOES
THE TYPE IV DENTAL STONE.
THE SETTING EXPANSION HAS BEEN INCREASED FROM A MAXIMUM OF (TYPE V)
0.10% TO 0.30%.
THE RATIONALE FOR THE INCREASE IN SETTING EXPANSION
LIMITS IS THAT
CERTAIN NEWER ALLOYS, SUCH AS BASE
METAL, HAVE A GREATER CASTING SHRINKAGE THAN DO THE
TRADITIONAL NOBLE METAL ALLOYS. THUS HIGHER EXPANSION
IS REQUIRED IN THE STONE USED FOR THE DIE TO AID IN
COMPENSATING FOR THE ALLOY SOLIDIFICATION SHRINKAGE.
Maximum
Intercuspation
All the teeth
contact in a
stable way
Centric Occlusion
Contact:
First contact when
leaf gauge is in
place on the
anterior teeth
CR: Condyle in the most — position
anterior-superior
