Elastic impressions (hydrocolloids)
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Transcript of Elastic impressions (hydrocolloids)
Elastic Impression MaterialsHydrocolloids
Vinay Pavan Kumar .K 1st year MDS
Dept of ProsthodonticsAECS Maaruti College of Dental Sciences
Hydrocolloids
Definition
Classification
Composition
Properties
Manipulation
Advantages and disadvantages
Impression
Negative record of tissues of mouth used to reproduce the form of teeth and the surrounding
tissues (GPT 8)
Impression material
Any substance or combination of substances used for making an impression or negative
reproduction (GPT 8)
Colloid “Kola” means “glue”“oid” means “like”
First described by Thomas Graham (1861)
Colloidal state
State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm
Colloid
Solution - a homogeneous mixture consisting of a single phase
Colloid - a heterogeneous mixture of not readily differentiated two phases
Suspension - a mixture of two distinct phases
Colloid has 2 phases:
Dispersed phase
Dispersion phase
Type
Solid Liquid SolSolid Gas Solid AerosolLiquid Liquid EmulsionLiquid Gas AerosolGas Liquid FoamGas Solid Solid Foam
•Dispersed phase
•Dispersion phase
Gelation
There is a phase change from
SOL GEL• Gel state - the dispersed phase agglomerates to
form a chain of fibrils called “micelles”
• Fibrils form a “brush heap structure”
• The dispersion medium is held in the interstices between the fibrils by capillary attraction
Elastic impression material
Hydrodocolloids
Agar
Alginate
Non-aqueouselastomers
Polysulfide Polyether
Condensation siliconeAddition silicone
What is hydrocolloid?
Colloid that contains water as the dispersion phase
Hydrocolloid impression material are based on colloidal suspensions of polysaccharides in water.
Exists in two forms• Sol form - fluid with low viscosity• Gel form - a jelly like elastic semisolid
Types of hydrocolloid impression material
Based on the mode of gelation:Reversible – Agar• Secondary bonds hold the fibrils together• Bonds break at slightly elevated temperatures
and become re-established
Irreversible – Alginate• Fibrils are formed by chemical action
ImbibitionProcess of water sorption i.e. the gel swells whenplaced in water
SyneresisExpression of fluid on to the surface of gel structure
A. Shrinkage phenomena occur if syneresis forces (F syneresis) are higher than osmotic forces (F osmotic). B. Osmotic active ingredients within color-changing irreversible hydrocolloid shift force balance towards F osmotic, resulting in overall expansion of material.
Schematic drawing illustrating presumed processes within irreversible hydrocolloid on molecular level.
Erbe C, Ruf S, Wöstmann B, Balkenhol M Dimensional stability of contemporaryirreversible hydrocolloids: Humidor versus wet tissue storage
J Prosthet Dent 2012;108:114-122
Liquifaction TemperatureTemperature at which gel changes to sol (70 -100°C)
Gelation TemperatureTemperature at which sol changes to gel (37-50°C)
Hysteresis – Temperature lag
REVERSIBLE HYDROCOLLOID - AGAR
• Agar is an organic hydrophillic colloid (polysaccharrides) extracted from certain types of seaweed.
• 1937 – Agar was introduced by Sears.
Component Function Composition
Agar Brush heap structure 13 – 17%
Water Reaction medium >80%
Borax Strength 0.2-0.5%
Sulfate Accelerator 2%-5%
Wax Filler 0.5%-1%
Thymol and glycerine Bactericidal and plasticiser
1,3- linked â-D-galactopyranose and 1,4-linked 3,6-anhydro-á-L-galactopyranose
Agarose, is a strongly gelling, non-ionic polysaccharide
Agaropectin, is more complex polysaccharide having sulfate groups
• Sol: random coils• Gelation I : Double helices• Gelation II :aggregation of helices
Manipulation
Agar hydrocolloid requires special equipment:Hydrocolloid Conditioning unit
“Conditioning unit” is a thermostatically controlled unit having 3 compartments:•Boiling compartment --- water at 1000 C.•Storing compartment --- water at 650 C•Tempering or conditioning compartment --- water at 450 C.
•Water cooled rim lock trays
Conditioning unit
Liquefying Store Tempering 1000 C 650 C 460 C
Steps in impression preparation
1.Liquefaction - at 1000 C2.Store in 650 C
3.Load agar in tray
4.Temper at 460C 5.Seat in patient’s mouth6.Cool with water of 180 C – 210 C for 5mins 7.Remove by snap action 8.Pour the mold material
StrengthThe tear strength of agar - 0.8 to 0.9 N/mm ANSI/ADA Specification - 0.75 N/mm
Compatibility with Gypsum More compatible than alginates
Dimensional stability•Less stable due to imbibition and syneresis•Cast to be poured immediately •Agar is best stored in 100% humidity for maximum of 1hr
Advantages:
•Dimensionally accurate •Hydrophilic - displace moisture, blood, fluids•No custom tray or adhesives required•Pleasant •No mixing required•Stone casts easily removed•Cheap compared to synthetic elastic materials•Can be reused when used as duplicating material
Disadvantages:
•Initial expense –special equipment•Material prepared in advance •Tears easily•Dimensionally unstable•Cannot be electroplated•Difficult to disinfect•Only one model can be poured
Irreversible hydrocolloid – Alginate
• Developed by S. William Wilding in 1941
• As a substitute to agar during World War II
• Alginic acid prepared from marine brown sea weed
Examples◦Jeltrate (Dentsply/Caulk)◦Coe Alginate (GC America)
(a) β-D-mannuronic acid. (b) α-L-guluronic acid. (c) Structural formula of sodium alginate molecule
Alginate composition
Composition
Component FunctionWeight
percentage
Sodium or potassium triethanolamine alginate
Dissolves in water and reacts with calcium ions
15%
Calcium sulphate dehydrate
Reactor 16%
Zinc oxide Filler particles 4%Potassium titanium fluoride
Accelerator 3%
Diatomaceous earth Filler particles 60%
Sodium phosphate Retarder 2%
Coloring and flavoring agent
Give coloring change when setting is complete
Traces
FORMS OF ALGINATE
• Powder
• Sol – Plaster of Paris acts as reactor
• 2 paste system - alginate sol
calcium reactor
Setting reaction:
A reaction of soluble alginate with calcium sulphate and the formation of an insoluble calcium alginate gel
Na alginate + CaSO4 Ca alginate + Na2SO4
(Powder) (Gel)
Irreversible chemical reactionWorking and setting times are determined by the rate of release of calcium ions
(CaSO4).2H2O 2Ca2+ + 2SO42- + H20
Gelation of homopolymeric blocks of α-L-guluronic acid junction with calcium ions. Binding of divalent cations by alginate: the “Egg-box” model
Retarder•Calcium ions will react preferentially with the phosphate ions to form an insoluble calcium phosphate
2Na3PO4 + 3CaSO4 Ca3(PO4)2+3Na2SO4
Water powder ratio•16g of powder is mixed with 38ml of water- gelation in 3 to 4 minutes
Controlling setting time
•Type-I : Fast setting (1- 2 minutes)
•Type-II : Normal setting (4 - 5 minutes)
Comparison Of Regular And Fast Set Alginate
Regular set Fast Set
Mixing Time 1 min 45 sec
Working Time 3 min 1.25 to 2 min
Setting Time 4 to 5 min 1.5 to 3 min
• Manufacturers adjust the concentration of sodium phosphate to produce regular and fast-set alginates
• Setting time can be altered by change in
temperature of the water
• Higher the temperature, faster the setting
• 1-minute reduction in setting time occurs for each 100 C temperature increase
Manipulation
• Weigh powder- W/P ratio (16 g powder, 38 ml water)
• Powder added to water• rubber bowl• vacuum mixer
• Mixed for 45 sec to 1 min• Place tray• Remove after 2 to 3 minutes or after gelation
(loss of tackiness)
Alternatives to Hand Mixing
• Two alternatives exist for mixing alginates other than manual manipulation of the impression material.
• The Alginator and the Vac-U-Mix automatically mix the alginate through the use of motorized electrical equipment
Stock trays-perforated – 20 holes per Sq Inch, distance between holes – 2mm
Customization of trays :
Modifications-wax/tracing stick impression compound/heavy-bodied silicone
IMPRESSION TRAYS
TRAY ADHESIVES FOR ALGINATE
Liquid
• Diethylenetriamine polymer
• Xylene
• Erythrosine
Spray
Solvents - used to remove this adhesive
PropertiesFlexibility• ANSI/ADA Specification permits a range of 5% to 20% at a
stress of 0.1MPa and most alginates have a value of 14%.
•Strength• ANSI/ADA Specification :compressive strength of 0.35 MPa• Compressive strength - 0.5 to 0.9 MPa• Tear strength range from 0.37 to 0.69 MPa
Sketch of tear strength specimen with load applied in the directions of the arrows; the specimen tears at the V-notch.
Elastic recovery
Recovery >95% when the material is compressed 20% for 5 seconds. Alginate – 98.2%
Variation of compression set with time of an alginate impression material at strains of 10%, 20%, and 30% applied for 5 and 10 seconds.
Shelf Life • One year• It deteriorates rapidly at high temperature
Dimensional Stability • It has poor dimensional stability because of either
syneresis or imbibition• Impressions should be stored in 100% relative
humidity
Reproduction of tissue details • low when compared with agar
Representative photographs of alginate impressions after each storage time.
JeltratePlus after (a) 30 minutes, (b) 48 hours, and (c)100 hours; Alginmax after (d) 30 minutes, (e) 48 hours, and (f) 100 hours; and Kromopan 100 after (g) 30 minutes, (h) 48 hours, and (i) 100 hours.
WORKING TIME
The working time of alginate is determined by the help of the penetrometer (from the start of mixing to the start of gelation)
Fast set : 1.25 – 2mins
Regular set : 2 – 4.5mins
SETTING TIMEThe initial setting time of alginate is determined by placing
a flat Polymeric cylindrical rod in contact
The cylinder is withdrawn and is repeated till no alginate
is sticking to its surface
TESTS FOR COMPRESSIVE STRENGTH• The compressive strength should exceed 0.35Mpa
Tear Strength and Compressive Strength for CA37 (0,95 N/mm – 1,06 MPa) and Orthotrace (0,83 N/mm – 1,06 MPa) were significantly higher than for Hydrogum (0,54 N/mm – 0,69 MPa), Aroma Fine(0,51 N/mm – 0,57 MPa) and Blueprint(0,49
N/mm – 0,61 MPa)
WOORTMAN.R, KLEVERLAAN.C.J, IPPEL.D, FEILZER.A.J Tear strength as indicator for the stability of Alginates
Taste and Odor • Pleasant taste and odor
Compatibility of agar and alginate with gypsum• Agar and alginate cause retardation of gypsum• Overcome by immersing the impression in a
solution of gypsum accelerator (2% potassium sulphate)
• Incorporating a plaster hardener
Model plaster poured against alginate
Dental stone poured against the same alginate
Disinfection
Immersion in 1% Sodium Hypochlorite or 2% Gluteraldehyde < 10 min immersion or sprayed with disinfectant
Current protocol (by centre for disease control and prevention) :
Use of household bleach (1-10 dilution)IodophorSynthetic phenol
Storage• Storage at 100% relative humidity (RH) reportedly results
in minor dimensional changes
Placed on pane of clear acrylicresin on top of wet sponge inside
air-tight humidor
Wrapped in wet tissues in contact with entire specimen surface and placed in
zipper plastic storage bag
If humidor storage is used, IH impressions should be poured within 4 hours. If bag/tissue storage is used, non-color change IH impressions should, preferably, be poured within 2 hours
Erbe C, Ruf S, Wöstmann B, Balkenhol M Dimensional stability of
contemporaryirreversible hydrocolloids: Humidor versus wet tissue storageJ Prosthet Dent 2012;108:114-122
There is a greater chance for distortion the longer the impression is stored
New alginates have improved long-term storage ranging from 48 to 120 hours when stored in a plastic bag
Advantages
Easy to mix and manipulate Minimum requirement of equipment Hydrophilic ,gives good surface detail even in
saliva Low cost Comfortable to the patient Hygienic ,as fresh material must be used It records fine details in patients with undercuts Good surface details are recorded even in
patients with excessive salivation
Disadvantages
Poor tear strength Dimensionally unstable Lower detail production Difficult to disinfect High permanent distortion Cannot be electroplated It cannot be corrected
Dustless alginate
• Inhaling fine airborne particles from alginate impression material can cause silicosis and pulmonary hypersensitivity
• Dustless alginates were introduced which give off or no dust particles so avoiding dust inhalation
• This can be achieved by coating the material with glycerine or glycol. This causes the powder to become more denser than in uncoated state
• Introduced by Schunichi, Nobutakwatanate in 1997
• This of comprises sepiolite and a tetraflouroethylene resin having a true specific gravity of from 2-3
• The material generates less dust, has a mean particle size of 1-40microns
Low dust alginate :
Antiseptic alginate :
• Introduced by Tameyuki Yamamoto, Maso Abinu patented in 1990.
• An antiseptic containing alginate impression material contains 0.01 to 7 parts by weight of an antiseptic such as glutaraldehyde and chlohexidine gluconate per 100 parts by weight of a cured product of an alginate impression material.
• The antiseptic may be encapsulated in a microcapsule or clathrated in a cyclodextrin.
Chromatic alginate
• The alginate impression material with color indications avoiding confusion about setting time.
• Color changes are visualizing the major decision points in impression making
pH of fluid mass changes during setting Acid /base indicator in their formulation.
Ex : KromaFaze (Dux Dental), Integra (Dux Dental)
Agar Alginate
Preparation Boil, temper, store Powder, water
Ease of Use Technique sensitive Good
Patient Reaction
Thermal Shock Pleasant, clean
Ease of removal Very easy Very easy
Disinfection Poor Poor
Handling Properties
Agar Alginate
Working Time (min)
7 – 15 2.5
Setting Time
(min)
5 3.5
Stability 1 hour 100% RH Immediate pour
Wettability and castability
Excellent Excellent
Cost Low Very low
Laminate (Agar-Alginate) technique:
Inject syringe material around the prepared tooth
Seat the tray loaded with alginate & allow it to set
Cool alginate gels the agar
Advantages:Equipment cost is lowerLess preparation time is required
Disadvantages:Bond between agar and alginate is not
always soundAlginate materials displaces the agar
during seating
Wet field technique:
Wet the tooth surface with warm water
Syringe materials applied over the occlusal and incisal portion
Seat the tray with material
Hydraulic pressure forces the fluid material down the tooth displacing the blood & debris
TRIPLE TRAY TECHNIQUE
• In this technique one impression records both the mandibular, maxillary arches and the occlusal relationship
Effect Causes
Agar Alginate
Grainy materialInadequate boilingStorage temperature too lowStorage time too long
Improper mixingProlonged mixingExcessive gelation W/P ratio too low
Separation of tray and syringe material
Water soaked tray material surface not removedPremature gelation of either material
Not applicable
Tearing
Inadequate bulk
Premature removal from mouth
Syringe material partially gelled when tray was seated
Inadequate bulk
Premature removal from mouth
Moisture contamination
Prolong mixing
Effects of mishandling:
Effect Causes
Agar Alginate
Irregularly shaped voids
Material too cold Moisture or debris on tissue
Rough or chalky stone model
Inadequate cleansing of impression
Premature removal of die
Improper manipulation of stone
Excess water or hardening solution left in the impression
Air drying the impression before pouring
Inadequate cleaning of impression
Premature removal of impression
Improper manipulation of stone
Excess water left in impression
Model left in impression too long
Effect Causes
Agar Alginate
External bubblesGelation of syringe material prevents flow
Undue gelation preventing flow
Air incorporated during mixing
Distortion
Impression not poured immediately
Movement of tray during gelation
Premature removal of impression
Improper removal from mouth
Use of ice water during initial stages of gelation
Impression not poured immediately
Movement of tray during gelation
Premature removal of impression
Improper removal from mouth
Duplicating Materials
Both types of hydrocolloids are used for duplication of casts and models in dental laboratory for fabrication of prosthetic appliances and orthodontics models
The composition of hydrocolloid type for duplicating materials are same
Agar hydrocolloid is more popular in labs because it can be used many times
Errors during impression making
•Mix too thick•Continuous pressure
•Movement during setting•Separation of alginate from tray
•Inadequate working time limiting flow•Teasing the impression while removal
•Too much air blown to dry the impression•Moist towel or cotton over impression for storage
Rudd RW and Rudd KD. A review of 243 errors possible during the fabrication of a removable partial denture: Part I. J Prosthet Dent 2001;86:251-61.
ALGINATE IMPRESSION TECHNIQUE IN HIGH PALATE VAULT
Nandini VV, Venkatesh K V, Nair K C Alginate impressions: A practical perspective, J Conserv Dent 2008;11: 37-41.
SINGLE STEP APPROACH TO MAKE DIAGNOSTIC IMPRESSIONS OF BOTH THE ARCHES & FACE BOW TRANSFER
Komuravelli AK, Suresh Sajjan MC ,Single step approach to make diagnostic impressions of both the arches and face bow transfer: a novel technique. Indian J Dent Res. 2012 Jan-Feb; 23(1):2-6
CONCLUSION
Hey……What are you doing???
I’m trying to make a really good first “IMPRESSION”
REFERENCES•Craig G R, Powers J M, Sakaguchi R L Restorative Dental Materials,13th edition, USA, Elsevier publications, 2012, pg 277- 86.
•Ferracane J L, Materials in Dentistry, 2nd edition, USA, Susan Katz publishers, 2001, pg 173 - 99.
•Anusavice, Sheen, Rawls, Philips Science of dental materials, 12th edition, Florida, Elsevier Health Sciences, oct 2012, pg 168 - 77.
•Rudd R W and Rudd KD, A review of 243 errors possible during fabrication of a removable partial denture: part 1. J Prosthet Dent 2001;86:251- 61.
•Walker.M.P,Burckhard.J,Mitts.D.A,Williams.K.B Dimensional change over time of extended-storage alginate impression materials. AngleOrthod. 2010;80:1110 – 1115.
•O’Brien W J, Dental materials and their selection, 2nd edition, Canada, Quintessence publications, 1997,pg 127 - 32.
• Nandini V V, Venkatesh K V, Nair K C Alginate impressions: A practical perspective, J Conserv Dent 2008;11: pg 37 - 41.
• Keita Kashima and Masanao Imai. Advanced Membrane Material from Marine Biological Polymer and Sensitive Molecular-Size Recognition for Promising Separation Technology, Advancing Desalination,2012.
Erbe C, Ruf S, Wöstmann B, Balkenhol M, Dimensional stability of contemporary irreversible hydrocolloids: Humidor versus wet tissue storage, J Prosthet Dent 2012;108: pg 114 - 122
Hiraguchi H et al, Effects of Disinfection of Combined Agar/Alginate Impressions on the Dimensional Accuracy of Stone Casts, Dent Mater Journal 26 (3): 457 - 462, 2007
Komuravelli A K, Suresh Sajjan M C ,Single step approach to make diagnostic impressions of both the arches and face bow transfer: a novel technique. Indian J Dent Res. 2012 Jan-Feb; 23(1):2-6