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