Impression Materials BDS 3. Dr M Slabbert Dept Prosthodontics Wits. First Impressions count. Classification of Impressions. Preliminary impressions Taken either by the dentist or an expanded-function dental assistant. Used to make a reproduction of the teeth and surrounding tissues. - PowerPoint PPT Presentation
Text of Impression Materials BDS 3
Dr M Slabbert Dept Prosthodontics Wits
First Impressions count
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 Impressions cont’dFinal 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 Impressions cont’dBite 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.
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.
Prof Owen Fundamentals of Removable partial dentures 2nd Ed pg. 124 -131
Wits Pros Book Vol 2 Pg. 14
Study pages 14- 31 Vol 2
www.health.wits.ac.za/Prosthodontics Primary impressions in alginate…
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 shelf life.
The Ideal Impression Material cont. 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.
Hydrophilic VS Hydrophobic
Which one of the impression Which one of the impression materials we choose? materials we choose?
Dental Plaster• Type I – impression plaster• Type II – model (laboratory) plaster (used for mounting casts)plaster is composed of the β form of calcium sulfate hemihydrate Crystals•plaster is weaker than dental stone due to:
1.) porosity of the particles, requiring more water for a plaster mix2.) irregular shapes of particles prevent them from fitting together tightly
Dental Stone• Type III - dental stone(diagnostic casts)• Type IV - high strengthdental stone (workingmodels)• Type V - high-strength, high-expansion dental stone
Stone is the α hemihydrate form Types of Gypsum Products
H or other meansMineral gypsum ---------------- > Model plaster + Water(CaSO4 . 2H2O) Dental stone High-strength dental stone (CaSO4 . 1/2H2O)
When calcium sulphate hemihydrate (dental plaster, stone, etc.) is mixed with water, the reverse reaction takes place, and the hemihydrate is converted back to the dihydrate:
A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.
Reversible and Irreversible Introduced by Sears 1939 First elastic Sears AW. Hydrocolloid impression technique for inlays and fixed
bridges. Dent Digest 1937; 43: 230-234.Lin C, Zeiber G J. Accuracy of impression materials for complete
arch fixed partial dentures. J Prosthet Dent 1988; 59: 288-291Philips Science of Dental Materials 11th Ed. Part 2 Pg. 231
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 Alginate cont’dDiatomaceous 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)
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.
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
Reversible Hydrocolloid An impression material that changes its physical
state from a sol to a gel and then back to a sol.
Chemical Makeup of Reversible Hydrocolloid
85% water13% agar
Agar is an organic substance derived from seaweed.Additional chemical modifiers are added to aid in the
Conditioning Bath for Reversible Hydrocolloid
The first bath is for liquefying the semisolid material. A special water bath called a “hydrocolloid conditioner” at 212° F liquefies the material. After liquefying, the preset thermostat cools the temperature to 150° F automatically.
The second bath becomes a storage bath that cools the material, readying it for the impression. At this temperature, the tubes are waiting for use.
A third bath is kept at 110° F/44° C for tempering the material after it has been placed in the tray.
Three Compartments Three Compartments
Types of Reversible Hydrocolloid Tray material
Packaged in plastic tubes. Each tube has enough material to fill a full arch, water-cooled tray.
Syringe materialPackaged in plastic or glass cartridges that fit a
syringe or in preloaded syringe or preformed sticks that refill special hydrocolloid inlay syringes.
Application of Reversible Hydrocolloid Impression Material
1. A stock water-cooled tray is selected, making sure that the tray does not impinge on any of the teeth or soft tissue.
2. Plastic stops are placed in the tray.3. Tubing is connected to the tray and to the water
outlet for drainage.4. The material is liquefied and moved to the storage
bath.5. The light-bodied material is placed in the syringe,
and heavy-bodied material is placed in the tray.6. The light-bodied material is expressed around the
prepared tooth, and the dentist seats the tray.
1. Flexible Matrix (Continuous Phase):a. Multifunctional Pre-Polymer or Polymerb. Crosslinking Agentc. Curing Agent (Catalyst or Initiator)d. Modifiers (Accelerators, Retarders,
Plasticizers, Flavoring Agents, Colorants)
2. Filler or Extender (Dispersed Phase):
GENERAL FORMULATIONGENERAL FORMULATIONFor Elastic Impression MaterialsFor Elastic Impression Materials
Polymer (high shrinkage)
Filled Polymer (low shrinkage)
During setting shrinkage, distortion of impression is toward tray.
Dies tend to be oversize and so the casting is oversize.
ELASTOMERIC IMPRESSIONSELASTOMERIC IMPRESSIONSManagement of ShrinkageManagement of Shrinkage
Impression TrayUse 2-step techniques:
(a) Light-Heavy Body, OR(b) Wash-Putty
Load tray withheavy-bodied IM
Cover prep withlight-bodied IM
ELASTOMERIC MATERIALSELASTOMERIC MATERIALSMixing and Delivery Systems
Mixing Options: 2 Pastes on Mixing Pad 2 Pastes in Mixing Gun 2 Pastes in Mixing Machine
For dimensional stability, this is the best impression material.
Pouring of the model can be delayed up to 7 to 10 days.
Stiffness of the material makes removal of the tray difficult.
Material dispensed using auto-mixing unit and mixing tips.
Manipulation and Technique Considerations for Polyvinyl Siloxane
Manipulation and Technique Considerations for Polyvinyl Siloxane
CONTINUOUS PHASE:Polymer = Mercaptan Functional PolysulfideCrosslinking Agent = Sulfur and/or Lead PeroxideCatalysts = PbO2 or Copper Hydroxides (Type I)
Zinc Peroxide or Organic Hydroperoxide (Type II)
DISPERSED PHASE:Fillers = TiO2 or Zinc Sulfate or
Lithopone or Calcium Sulfate Dihydrate
SETTING REACTION:Stepwise (relatively slow), Exothermic, Affected by temperature
POLYSULFIDE RUBBERPOLYSULFIDE RUBBERChemistry and Setting ReactionChemistry and Setting Reaction
POLYSULFIDE RUBBERPOLYSULFIDE RUBBERManipulation and Technique ConsiderationsManipulation and Technique Considerations
a. Two-step techniques recommended: Reduces air entrapment andsurface tension effects.
b. Material adversely affected by H2O, saliva, and blood.c.* Set impression should be removed quickly - do not rock tray.d. No syneresis or imbibition, but distortion due to continued reaction.e. Ideally need uniform thickness and at least 2 mm thick for accuracy.
(1) Adhesive must be thin(2) Adhesive must be dry
f. Paste-Paste Mixing Recommendations:(1) Dispense pastes at the top of the mixing pad(2) Mix pastes with tip of spatula only for 5 seconds(3) Transfer mass to fresh surface at center of mixing pad(4) Wipe spatula off with paper towel; Strop mass for 15s to constant color(5) Load syringe or tray(6) Use pad excess to monitor setting time
g. Pouring of models:(1) Wait 20-30 minutes before pour for stress relaxation to occur(2) RB is non-reactive with model and die materials(3) Be careful of glove powder contamination of impression(4) RB can be electroplated
SILICONE RUBBERSILICONE RUBBERChemistry and Setting ReactionChemistry and Setting Reaction
CONTINUOUS PHASE:Polymer = Polydimethyl SiloxaneCrosslinking Agent = Alkyl Orthosilicate or Organo H-SilaneCatalysts = Organo Tin Compounds (e.g., tin octoate)
(but not dibutyl tin dilaurate)Modifiers = Colorants, Flavorants
DISPERSED PHASE:Fillers = Silica
SETTING REACTION:Stepwise (relatively slow), Exothermic, Affected by temperatureH2O by-products
SILICONE RUBBERSILICONE RUBBERManipulation and Technique ConsiderationsManipulation and Technique Considerations
a. Limited shelf-life: Unstable in tubes.b. Requires mechanical retention or special tray adhesivesc. No syneresis or imbibition, but continued polymerization shrinkage.d. Better dimensional stability than RHC but more expensivee. Pouring of models:
(1) More flexible so more chance for distortion during removal(2) Wait 20-30 minutes before pour for stress relaxation to occur
POLYETHER RUBBERPOLYETHER RUBBERChemistry and Setting ReactionsChemistry and Setting Reactions
SETTING REACTION:Stepwise (relatively slow), Exothermic, Affected by temperature
POLYETHER RUBBERPOLYETHER RUBBERManipulation and Technique ConsiderationsManipulation and Technique Considerations
a. Excellent impression accuracy and dimensional stability.b. Stiff and therefore difficult to remove without rocking.c. Break seal and rock slightly to prevent tearing: Low tear resistance.d. Negatively affected by H2O, saliva, and blood.
(1) Since hydrophobic, moisture increases marginal discrepancy(2) Increased water absorption occurs if use thinning agents
e. Can be dispensed from automated extruder and mixer (ESPE PentaMix)
POLYVINYL SILOXANEPOLYVINYL SILOXANEChemistry and Setting ReactionsChemistry and Setting Reactions
are insoluble in waterMake ThermoplasticShellac, dammar, rosin or sandarac
WAXESStraight chain hydrocarbon
Tasteless, Odorless, ColorlessMake Thermoplasticbeeswax and colophany
FillersControl degree of flowMinimize shrinkageImprove rigidityDiatomaceous earth, Soapstone, talc
•Lubricant and Plasticizer
High contraction coefficients 0.3%
Very low thermal conductivity
Reversible physical process
Thermoplastic 37-45 C๐
High thermal expansion
ManipulationSoften by heating over the flame or water bathDo not heat too much volatileTake impressionRoom temperature water coolingPour impression as soon as possibleWarm the impression before take the cast
Water bathAlcohol lampAlcohol torch
Compatible with model material
Can take impression again
Must be poured within one hour
=> dimensional change
Very technique sensitive
High coefficient of thermal expansion
Low detail reproduction
-Material is not completely cooled
-Delay in pouring
TroubleshootingCompound is too brittle or grainy
-Prolong immersion in the water bath
Zinc oxide-eugenol Impression paste
Zinc oxide-eugenol Impression paste
Zinc oxide-eugenolFor full arch edentulous impression without or minor
Temporary cementation Temporary filling
Composition (base)Zinc oxide (ZnO)OilHydrogenated rosinZinc acetate AcceleratorTrace of water Initiator
@ Irreversible chemical change@ Irreversible chemical change
Manipulation Equal length of the two paste is extruded
shorten by increase
Working time 3-5 min
Mixing time 45-60 s
Mixed with stainless steel spatula in paper
pad or glass slab
AdvantageAccuracy of soft tissue impression (mucostatic)
Inexpensive Adhere well to dental compound
Good surface detail reproduction
Good dimensional stability
Disadvantage MessinessNon elastic TimeUnstable setting May irritating to soft tissue
TroubleshootingInadequate working or setting time
-excessive humidity and/or temperature
Impression waxKORECTA WAX , IOWA WAX
Manipulation Functional Impression
Disinfection of Impression Materials Irreversible Hydrocolloids (Alginate)
Diagnostic Casts: Soak 10 min in Gluteraldehyde
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
•Skinner’s Science of Dental Materials
•Dental Materials and Their Selection (William J. O’Brien)
•Introduction to dental materials (Richard Van Noort)
•Dr Sukontip Arwatchanakan
•Science of Dental Materials Phillips 11th Ed.
•Stephen C. Bayne Department of Operative Dentistry School of DentistryUniversity of North Carolina
•Mr. Robert Seghi Alginate Impression Materials (alginate lecture 2006.ppt)
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.
Tray Adhesives VPS adhesives (blue)
For polyvinyl siloxane and polyether impression materials.
Rubber Base Adhesive (brown) Used with rubber base impression materials.
Silicone Adhesive (orangish-pink)Used with silicone impression materials.
Characteristics or Elastomeric Impression MaterialsBase
Packaged as a paste in a tube, as a cartridge, or as putty in a jar.
CatalystAlso known as the accelerator, is packaged as a
paste in a tube, as a cartridge, or as a liquid in a bottle with a dropper top.
Forms of Elastomeric Materials Light-bodied
Also referred to as syringe type, or wash type. This material is used because of its ability to flow in and about the details of the prepared tooth. A special syringe, or extruder, is used to place the light-bodied material on and immediately around the prepared teeth.
Forms of Elastomeric Materials cont’d Regular and heavy-bodied
Often referred to as tray‑type materials, they are much thicker. As the names imply, they are used to fill the tray. Their stiffness helps to force the light‑bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation.
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.
Curing Stages of Elastomeric Materials Initial set
The first stage results in stiffening of the paste without the appearance of elastic properties. The material may be manipulated only during this first stage.
Final set The second stage begins with the appearance of
elasticity and proceeds through a gradual change to a solid rubberlike mass. The material must be in place in the mouth before the elastic properties of the final set begin to develop.
Final cure The last stage occurs from 1 to 24 hours.
Types of Elastomeric Materials
Occlusal Registration An accurate registration of the normal centric
relationship of the maxillary and mandibular arches. Also commonly referred to as the bite registration.
Types of Occlusal Registration
Wax biteUseful when the diagnostic casts are trimmed.The most common technique is to use a softened
Types of Occlusal Registration cont’dPolysiloxane bite registration paste: Supplied
both as a paste system and also as cartridges.The material is fast setting.There is no resistance to biting forces.There is no odor or taste for the patient.It gains dimensional stability over time.It is convenient to use.
Types of Occlusal Registration cont’dZinc oxide-eugenol (ZOE) bite registration paste
ZOE paste has little to no resistance to bite closure and is a fast-setting material.
Material is supplied in a paste system and dispensed onto a paper pad, mixed, and placed onto a gauze tray for the patient to bite into.