Alginate Seminar

Dr Avreet Sandhu

ALGINATE

First Impressions count

CONTENTSINTRODUCTIONDEFINITIONCLASSIFICATIONPROPERTIESELASTOMERIC IMPRESSION MATERIALIRREVERSIBLE HYDROCOLLOID – ALGINATE

COMPOSITION

PHYSICAL PHASES

PACKING AND STORAGE

CONTENTSMAKING OF ALGINATE IMPRESSIONTROUBLE SHOOTING

INTRODUCTIONThe ability to record consistently good impressions

is both a science and an art. It is worth bearing in mind that the impression influences not only the quality of the subsequent restoration but also the technician’s perception of the dentist’s skill.

An impression is a negative record of the tissues of the oral cavity which constitutes the basal seat of the denture. An impression is made in a material which has plasticity and which hardens or sets while in contact with the tissue.

Definition

Classification of ImpressionsPreliminary impressions

Taken either by the dentist or an expanded-function dental assistant.

Used to make a reproduction of the teeth and surrounding tissues.

Used to make (1) diagnostic models, (2) custom trays, (3) provisional coverage, (4) orthodontic appliances, and(5) pretreatment and post‑treatment records.

Classification of ImpressionsFinal impressions

Taken by the dentist.Used to make the most accurate reproduction of

the teeth and surrounding tissues.Used to make indirect restorations, partial or full

dentures, and implants.

Classification of ImpressionsBite registrations

Taken by the dentist or dental assistant.Make a reproduction of the occlusal relationship

between the maxillary and mandibular teeth.Provide an accurate registration of the patient’s centric

relationship between the maxillary and mandibular arches.

The Ideal Impression Material Easy to mix and handle.

Suitable working time.

Suitable setting time.

Compatible with die and stone

Not toxic or allergenic to the patient.

Dimensionally stable on setting.

Accurate to record the fine details of the prepared tooth

Has acceptable odor and taste.

Adequate strength.

Adequate shelf life.

The Ideal Impression Material Economical

Ready to disinfected without loss of accuracy.

Fluid or plastic when inserted into the mouth.

It must be an exact record of all the aspects of the prepared tooth and sufficient unprepared tooth structure immediately adjacent to margins, to allow the dentist and the technician to be certain of the location and configuration of the finish line.

Other teeth and tissue surrounding the abutment tooth must be accurately reproduced to permit proper articulation of the cast and contouring of the restoration.

It must be free from air bubbles especially in the finish line area.

• High accuracy Biocompatibility

(very small contraction <0.5%)

• High dimensional stability Compatibility to stone• High elastic recovery High tear strength• Ease of use Long shelf life• Hydrophilic Pleasant color &taste

and Hydrophobic• Proper setting time Cost

Elastic recoveryThe amount of rebound after a cylinder of material is strained 10% for 30 seconds.

98%

Impression

Impression Tray

IMPRESSION MATERIALSIMPRESSION MATERIALSKey PropertiesKey Properties

Accuracy

a. Accuracy = ability to replicate the intraoral surface details.

DimensionalStability

b. Dimensional Stability = ability to retain its absolute dimensional size over time.

TearResistance

c. Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.

Properties: Reaction: Set:Rigid:1. Impression Plaster Rigid Irrev (Chem)2. Impression Compound Rigid Rev (Phys)3. Zinc Oxide/ Eugenol Rigid Irrev (Chem)

CLASSIFICATION SYSTEMCLASSIFICATION SYSTEMBased on Properties of Set Materials

Water-Based Gel:4. Alginate (Irreversible Hydrocolloid) Flexible Irrev (Chem)5. Agar-Agar (Reversible Hydrocolloid) Flexible Rev (Phys)

Elastomers:6. Polysulfide (Rubber Base, Thiokol) Flexible Irrev (Chem)7. Silicone (Conventional, Condensation) Flexible Irrev (Chem)8. Polyether Flexible Irrev (Chem)9. Polyvinyl Siloxane (Addition Silicone) Flexible Irrev (Chem)

Impression materials

Impression materialImpression material

ElasticElastic

NonelasticNonelastic

Zinc oxide EugenolZinc oxide Eugenol

Impression CompoundImpression Compound

PlasterPlaster

Non-aqueouselastomers

Non-aqueouselastomers

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

Impression waxes Impression waxes

HydrocolloidsHydrocolloids

AgarReversible

AgarReversible

AlginateIrreversible

AlginateIrreversible

NonelasticNonelastic

Zinc oxide eugenolZinc oxide eugenol

Impression CompoundImpression Compound

Gypsum (Plaster)Gypsum (Plaster)

Impression waxImpression wax

Elastomeric Impression Materials

A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.

ElasticElastic

HydrocolloidsHydrocolloids

AgarAgar

AlginateAlginate

Hydrocolloids

Reversible and Irreversible Introduced by Sears 1939 First elastic Sears AW. Hydrocolloid impression technique for inlays and fixed

bridges.

Irreversible Hydrocolloid Material that cannot return to a solution state

after it becomes a gel.Alginate is the irreversible hydrocolloid most

widely used for preliminary impressions.

Makeup of AlginatePotassium alginate (Alginic Acid) (12-15%)

Comes from seaweed; is also used in foods such as ice cream as a thickening agent.

Calcium sulfate (8-12%)Reacts with the potassium alginate to form the gel.

Trisodium phosphateAdded to slow down the reaction time for mixing.

Makeup of AlginateDiatomaceous earth (70%)

A filler that adds bulk to the material. Controls the stiffness of the set gel

Zinc oxideAdds bulk to the material.

Potassium titanium fluoride (~10%)Added so as not to interfere with the setting and surface

strength. Sodium Phosphate (retarder) (2%)

Coloring and flavouring agents (traces)

Physical Phases of Alginate

The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form. (sol: resembles a solution, but is made up of colloidal particles dispersed in a liquid)

The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.

“gel” entangled framework of solid colloidal particles in which liquid is trapped in the interstices and held by capillary forces (Jello)

There are 2 main reactions occur when powder reacts with water during setting:

• First rxn. provides adequate working time: (Retarder)

2Na3PO4 + 3CaSO4 ----> Ca3(PO4)2 + 3Na2SO4

After the sodium phosphate has reacted, remaining calcium sulfate reacts with sodium alginate to form an insoluble

calcium alginate, which forms a gel with the water:H2O Na alginate + CaSO4 --------> Ca alginate +

Na2SO4 (powder) (gel)

Normal set alginate

Working time of 2 minutes and a setting time of up to 41/2 minutes after mixing.

Fast set alginateWorking time of 11/4 minutes and a setting time of 1 to 2 minutes.

Def : Working timeThe time allowed for mixing the alginate, loading

the tray, and positioning the tray in the patient's mouth.

Setting time The time required for the chemical action to be

completed.

Packaging and Storing of AlginateContainers about the size of a coffee can are the

most commonly used form of packaging. Premeasured packages are more expensive, but

save time by eliminating the need for measurement of the powder.

Shelf life of alginate is approximately 1 year.

Causes for Distortion and Dimensional Change of Alginate

If an alginate impression is stored in water or in a very wet paper towel, the alginate will absorb additional water and expand. This condition is called imbibition.

If an alginate impression remains in the open air, moisture will evaporate from the material, causing it to shrink and distort. This condition is called syneresis.

ADA Specifications <3% deformation with a 10% strain

Altering the Setting Times of AlginateCooler water can increase the setting time if

additional time is needed for the procedure. Warmer water can reduce or shorten the setting

time of the procedure.

Water-to-Powder Ratio An adult mandibular impression generally

requires two scoops of powder and two measures of water.

An adult maxillary impression generally requires three scoops of powder and three measures of water.

Taking an Alginate Impression

Explain the procedure to the patient:The material will feel cold, there is no unpleasant taste,

and the material will set quickly.Breathe deeply through your nose to help you relax and be

more comfortable.Use hand signals to communicate any discomfort.

Mouth Preparation

Rinse and dry the patient's teeth If teeth are too dry, alginate will stick

An Acceptable Alginate Impression The impression tray is centered over the central and

lateral incisors. There is a complete "peripheral roll," which includes all of

the vestibular areas. The tray is not "overseated," which would result in

exposure of areas of the impression tray.The impression is free from tears or voids.There is sharp anatomic detail of all teeth and soft

tissues.The retromolar area, lingual frenum, tongue space, and

mylohyoid ridge are reproduced in the mandibular impression.

The hard palate and tuberosities are recorded in the maxillary impression.

Trouble Shooting Inadequate working or setting time:

temperature of the water, incomplete spatulation W/P too low improper storage of alginate powder

Distortion: Tray movement during gelation or removed from mouth prematurely weight of tray compressing or distorting alginate

impression not poured up immediately

Tearing: removing impression from mouth before adequately set thin mixes (high W/P ratio) presence of undercuts (blocking out these areas before an impression may help) inadequate amount of impression material in tray (avoided by minimum 3 mm of impression

material between tray and oral tissues)

• Loss of detail: removed from mouth prematurely

Consistency: preset mix is too thin or thick The W/P ratio is incorrect (avoid by fluffing powder before measuring;

do not overfill powder dispenser) inadequate mixing (avoided by vigorous spatulation and mixing for

recommended time) using hot water: grainy and prematurely thick mix

• Dimensional change: delay in pouring alginate impression stored in air: results in distorted, undersized cast

due to alginate impressions losing water when stored in air

Porosity: whipping air into the mix during spatulation (proper mixing: after initial wetting of powder by the water, mix alginate so as to squeeze the

material between the spatula blade and the side of the rubber bowl)

• Poor stone surface (of cast) set gypsum remaining in contact with the alginate for too long a period

of time

Stock tray

Rim lock tray Perforated tray

Special tray(Custom tray)

Stock tray

NonelasticNonelastic

Zinc oxide eugenolZinc oxide eugenol

Impression CompoundImpression Compound

PlasterPlaster

Impression waxImpression wax

ElasticElastic

HydrocolloidsHydrocolloids

Non-aqueouselastomers

Non-aqueouselastomers

AgarAgar

AlginateAlginate

PolysulfidesPolysulfides

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

Non-aqueouselastomers

Non-aqueouselastomers

PolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

ElasticElastic

HydrocolloidsHydrocolloidsAgarAgar

AlginateAlginate

• High accuracy Biocompatibility

(very small contraction <0.5%)

• High dimensional stability Compatibility to stone• High elastic recovery High tear strength• Ease of use Long shelf life• Hydrophilic Pleasant color &taste

and Hydrophobic• Proper setting time Cost

(Ideal Properties) (Ideal Properties)

Disinfection of Impression Materials Irreversible Hydrocolloids (Alginate)

Diagnostic Casts: Soak 10 min in Gluteraldehyde

Final Impressions:

Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under damp gauze 10 min

Reversible Hydrocolloid Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under damp gauze 10 min

Addition –reaction Silicones

In Gluteraldehyde 1 hr., Rinse sterile water Soak in fresh solution Gluteraldehyde 10 min

Zinc oxide eugenol Soak in Gluteraldehyde 10 min

Silicone Impressions Soak for 10 min Gluteraldehyde

Polyether Impressions Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min

Fundamentals of Removable Partial Dentures 2nd Ed. CP Owen

Tray Selection CriteriaFeel comfortable to the patient. Extends slightly beyond the facial surfaces of the

teeth. Extends approximately 2 to 3 mm beyond the third

molar, retromolar, or tuberosity area of the arch. Is sufficiently deep to allow 2 to 3 mm of material

between the tray and incisal or occlusal edges of the teeth.

Characteristics of Impression TraysQuadrant tray

Covers one half of the arch. Section tray

Covers the anterior portion of the arch. Full arch tray

Covers the entire arch.Perforated tray

Holes in the tray create a mechanical lock to hold the material in place.

Smooth trayInterior of the tray is painted or sprayed with an

adhesive to hold the impression material.

Impression TraysMust be sufficiently rigid to:

Carry the impression material into the oral cavity.Hold the material in close proximity to the teeth.Avoid breaking during removal.Prevent warping of the completed impression.

Basic Impression Technique1. The material selected depends upon the dentist’s preference

and the type of impression required for the procedure.2. The dentist prepares the tooth or teeth for the impression. 3. The light-bodied material is prepared and loaded into the

syringe and transferred to the dentist.4. The dentist places the light-bodied material over and around

the prepared teeth and onto the surrounding tissues.5. The heavy-bodied material is prepared and loaded into the

tray and transferred to the dentist.6. When the impression material has reached final set, the

impression is removed and inspected for accuracy.7. The impression is disinfected, placed in a biohazard bag,

labeled, and readied for the laboratory technician.

REFERENCESREFERENCES

• Skinner’s Science of Dental Materials

• Dental Materials and Their Selection (William J. O’Brien)

• Introduction to dental materials (Richard Van Noort)

• Science of Dental Materials Phillips 11th Ed. • Mr. Robert Seghi Alginate Impression Materials

(alginate lecture 2006.ppt)