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. 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’d Final 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’d Bite 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.
Study model (cast) Oral Examination Primary Impression Treatment Planning • duplicate model Final Impression Mouth and tooth preparation Master model Denture Laboratory procedure • investment cast • refractory cast Delivery
Definition 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 2 nd 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 strength. 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 High elastic recovery Ease of use Hydrophilic and Hydrophobic • Proper setting time Compatibility to stone High tear strength Long shelf life Pleasant color &taste Cost
Elastic recovery The amount of rebound after a cylinder of material is strained 10% for 30 seconds. 98%
Hydrophilic VS Hydrophobic
Which one of the impression materials we choose? • What’s the job you do? primary impression final impression • How accurate do you want? removable denture fixed prostheses • What technique do you use?
IMPRESSION MATERIALS Key Properties a. Accuracy = ability to replicate the intraoral surface details. b. Dimensional Stability = ability to retain its absolute dimensional size over time. c. Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus. Impression Tray Impression Accuracy Dimensional Stability Tear Resistance
PROBLEM ANALYSIS What are tolerable limits for “error” in indirect procedures? a. b. c. d. e. f. g. Impressions Casts, Dies Waxing Investing Casting Finishing, Polishing Cementation Prepped Tooth Width = = = = +/- 0 + 1. 5% +/- 0 8 mm (=8, 000 m) 8, 000 m x 0. 5% = 40 m = 20 m/side Typical clinical error = >100 m/side
CLASSIFICATION SYSTEM Based on Properties of Set Materials Properties: Reaction: Set: Rigid Irrev Rev Irrev (Chem) (Phys) (Chem) Water-Based Gel: 4. Alginate (Irreversible Hydrocolloid) 5. Agar-Agar (Reversible Hydrocolloid) Flexible Irrev Rev (Chem) (Phys) Elastomers: 6. Polysulfide (Rubber Base, Thiokol) 7. Silicone (Conventional, Condensation) 8. Polyether 9. Polyvinyl Siloxane (Addition Silicone) Flexible Irrev (Chem) Rigid: 1. 2. 3. Impression Plaster Impression Compound Zinc Oxide/ Eugenol
Impression materials Plaster Nonelastic Impression Compound Zinc oxide Eugenol Impression waxes Impression material Elastic Non-aqueous elastomers Polysulfides Alginate Irreversible Hydrocolloids Agar Reversible Polyethers Condensation silicone Addition silicone
Nonelastic Gypsum (Plaster) Impression Compound Zinc oxide eugenol Impression wax
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 mix 2. ) irregular shapes of particles prevent them from fitting together tightly Dental Stone • Type III - dental stone (diagnostic casts) • Type IV - high strength dental stone (working models) • Type V - high-strength, high-expansion dental stone Stone is the α hemihydrate form Types of Gypsum Products
Calcination H or other means Mineral gypsum -------- > Model plaster + Water (Ca. SO 4. 2 H 2 O) Dental stone High-strength dental stone (Ca. SO 4. 1/2 H 2 O) Reverse Reaction 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: Ca. SO 4. 1/2 H 2 O + 11/2 H 2 O ---> Ca. SO 4. 2 H 2 O + 3900 cal/g mol
Elastomeric Impression Materials A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.
Elastic Agar Hydrocolloids Alginate
Hydrocolloids 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 -291 Philips Science of Dental Materials 11 th 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 Alginate Potassium 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 phosphate Added to slow down the reaction time for mixing.
Makeup of Alginate cont’d Diatomaceous earth (70%) A filler that adds bulk to the material. Controls the stiffness of the set gel Zinc oxide Adds 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 Alginate Containers 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.
Fig. 46 -7 Examples of packaging for alginate.
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 Alginate Cooler 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.
Fig. 46 -8 Scoop and water measure for alginate.
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
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% water 13% agar Agar is an organic substance derived from seaweed. Additional chemical modifiers are added to aid in the handling characteristics.
Conditioning Bath for Reversible Hydrocolloid § Three Compartments 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.
Types of Reversible Hydrocolloid Tray material Packaged in plastic tubes. Each tube has enough material to fill a full arch, water-cooled tray. Syringe material Packaged 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. 2. 3. 4. 5. 6. A stock water-cooled tray is selected, making sure that the tray does not impinge on any of the teeth or soft tissue. Plastic stops are placed in the tray. Tubing is connected to the tray and to the water outlet for drainage. The material is liquefied and moved to the storage bath. The light-bodied material is placed in the syringe, and heavy-bodied material is placed in the tray. The light-bodied material is expressed around the prepared tooth, and the dentist seats the tray.
Elastic Polysulfides Polyethers Non-aqueous elastomers Condensation silicone Addition silicone
GENERAL FORMULATION For Elastic Impression Materials 1. Flexible Matrix (Continuous Phase): a. Multifunctional Pre-Polymer or Polymer b. Crosslinking Agent c. Curing Agent (Catalyst or Initiator) d. Modifiers (Accelerators, Retarders, Plasticizers, Flavoring Agents, Colorants) 2. Filler or Extender (Dispersed Phase): Polymer (high shrinkage) Filled Polymer (low shrinkage)
ELASTOMERIC IMPRESSIONS Management of Shrinkage Use 2 -step techniques: (a) Light-Heavy Body, OR (b) Wash-Putty Impression Tray Impression Load tray with heavy-bodied IM Cover prep with light-bodied IM from syringe During setting shrinkage, distortion of impression is toward tray. Impression Dies tend to be oversize and so the casting is oversize.
ELASTOMERIC MATERIALS Mixing and Delivery Systems Polyether, Polyvinylsiloxane Polysulfide Rubber, Silicone Rubber Mixing Options: § 2 Pastes on Mixing Pad § 2 Pastes in Mixing Gun § 2 Pastes in Mixing Machine 2 x 2 x 2 = 256 folds
IMPRESSION MATERIALS Management of Distortion During Tray Removal Strain rate sensitive elastomers ! Impression Tray Fast removal Impression VERY FAST (SNAP) Slow removal
IMPRESSION MATERIALS REACTION CONVERSION (%) Distortion Time Related to Setting Reaction 100 VPS Pe PS, Silicone log TIME (minutes)
Polysulfide Impression Material Chemical makeup Base: Mercaptan polysulfide. Cross-linking agent: Sulfur and/or lead peroxide. Catalysts: Copper hydroxides, zinc peroxide, organic hydroperoxide. Fillers: Zinc sulfate, lithopone, or calcium sulfate dihydrate.
Manipulation and Technique Considerations for Polysulfide Material Dispense pastes at the top of the mixing pad. Mix pastes with the tip of a spatula to incorporate the material first. Transfer the material to the fresh surface of the mixing pad. Water, saliva, and blood affect polysulfide material. Impression should be removed quickly after setting do not rock the tray. Adhesive must be thin and dry before adding the impression material. Wait 20 to 30 minutes before pouring the impression for the stress relaxation to occur in the material. Be careful of glove powder contamination of the impression.
Polyether Impression Material Chemical makeup Base: Polyether Cross-linking agent: Sulfate Catalysts: Glycol-based plasticizers Filler: Silica
Manipulation and Technique Considerations for Polyether Material is very stiff, which makes it difficult to remove without rocking. When removing the impression, break the seal and rock slightly to prevent tearing. Water, saliva, and blood affect polyether material. Added moisture will increase the impression’s marginal discrepancy. Increased water absorption occurs if a thinning agent is used.
Silicone Impression Material Chemical makeup Base: Poly dimethyl siloxane Cross-linking agent: Alkyl ortho silicate or organo hydrogen siloxane Catalyst: Organo tin compounds Filler: Silica
Manipulation and Technique Considerations for Silicone Material The material has a limited shelf life. The tray requires a special tray adhesive. No syneresis or imbibition but does respond with shrinkage over time. The material is more flexible, so there is more chance for distortion during removal. Wait 20 to 30 minutes before pouring of models for stress relaxation to occur.
Polyvinyl Siloxane Impression Material Chemical makeup Base: Silicone polym Catalyst: Chloroplatinic acid Filler: Silica
Manipulation and Technique Considerations for Polyvinyl Siloxane Material 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.
POLYSULFIDE RUBBER Chemistry and Setting Reaction CONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts DISPERSED PHASE: Fillers = Mercaptan Functional Polysulfide = Sulfur and/or Lead Peroxide = Pb. O 2 or Copper Hydroxides (Type I) Zinc Peroxide or Organic Hydroperoxide (Type II) = Ti. O 2 or Zinc Sulfate or Lithopone or Calcium Sulfate Dihydrate SETTING REACTION: Stepwise (relatively slow), Exothermic, Affected by temperature
POLYSULFIDE RUBBER Manipulation and Technique Considerations a. b. c. * d. e. f. g. Two-step techniques recommended: Reduces air entrapment and surface tension effects. Material adversely affected by H 2 O, saliva, and blood. Set impression should be removed quickly - do not rock tray. No syneresis or imbibition, but distortion due to continued reaction. Ideally need uniform thickness and at least 2 mm thick for accuracy. (1) Adhesive must be thin (2) Adhesive must be dry 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 15 s to constant color (5) Load syringe or tray (6) Use pad excess to monitor setting time 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 RUBBER Chemistry and Setting Reaction CONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts Modifiers DISPERSED PHASE: Fillers = Polydimethyl Siloxane = Alkyl Orthosilicate or Organo H-Silane = Organo Tin Compounds (e. g. , tin octoate) (but not dibutyl tin dilaurate) = Colorants, Flavorants = Silica SETTING REACTION: Stepwise (relatively slow), Exothermic, Affected by temperature H 2 O by-products
SILICONE RUBBER Manipulation and Technique Considerations a. b. c. d. e. Limited shelf-life: Unstable in tubes. Requires mechanical retention or special tray adhesives No syneresis or imbibition, but continued polymerization shrinkage. Better dimensional stability than RHC but more expensive 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 RUBBER Chemistry and Setting Reactions CONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts Modifiers = Amine-terminated Polyether = Aromatic Sulfonate = = Colorants, Glycol Plasticizers, Flavorants DISPERSED PHASE: Fillers = Silica SETTING REACTION: Stepwise (relatively slow), Exothermic, Affected by temperature
POLYETHER RUBBER Manipulation and Technique Considerations a. b. c. d. e. Excellent impression accuracy and dimensional stability. Stiff and therefore difficult to remove without rocking. Break seal and rock slightly to prevent tearing: Low tear resistance. Negatively affected by H 2 O, saliva, and blood. (1) Since hydrophobic, moisture increases marginal discrepancy (2) Increased water absorption occurs if use thinning agents Can be dispensed from automated extruder and mixer (ESPE Penta. Mix)
POLYVINYL SILOXANE Chemistry and Setting Reactions CONTINUOUS PHASE: Polymer Crosslinking Agent Catalysts Modifiers = Double-bond-functional Silicone Polymer = Chloroplatinic Acid = = Colorants, Flavorants, Plasticizers DISPERSED PHASE: Fillers = Silica SETTING REACTION: Chain (very fast), Exothermic, Affected by temperature Hydrogen gas released by decomposition of crosslinking agent.
POLVINYLSILOXANE Manipulation and Technique Considerations a. b. c. BEST impression material for dimensional stability: Pouring should be delayed at least 4 hours for H 2 out-gassing. Pouring can be delayed up to 7 -to-10 days (or indefinitely). Stiffness makes removal difficult. Most material dispensed using auto-mixing gun and mixing tips
COMMERCIAL PRODUCTS 1980 -1995 Predominantly POLYSULFIDE and SILICONE elastomers before 1995.
COMMERCIAL PRODUCTS 1996 -2004 Predominantly POLYETHER and PVS elastomers after 1996.
IMPRESSION MATERIALS Comparison of Key Properties Poor >-----------------> Good 1. Accuracy (Reproduction of Detail): a. Wetting of Tissues: b. Wetting by Dental Stone: ALG < SIL, PS < PE <= RHC, PVS SIL, PVS < PE <= ALG, RHC 2. Dimensional Stability: (Resistance to Distortion): a. Polymerization Shrinkage b. Thermal Shrinkage c. Loss of Components d. Stress Relaxation ALG <= RHC < PS, SIL < PE, PVS 3. Tear Resistance (Elasticity): a. Elastic Deformation b. Strain Rate Sensitivity ALG, RHC, PE < PVS , SIL < PS
IMPRESSIONS PERCENT CHANGE (%) Dimensional Stabilty PRODUCT EXAMPLES
Stock tray Rim lock tray Perforated tray
Stock tray Special tray (Custom tray)
Nonelastic Plaster Impression Compound Zinc oxide eugenol Impression wax
Elastic Agar Hydrocolloids Alginate Non-aqueous elastomers Polysulfides Polyethers Condensation silicone Addition silicone
Elastic Hydrocolloids Agar Alginate Polysulfides Polyethers Non-aqueous elastomers Condensation silicone Addition silicone
(Ideal Properties) • High accuracy Biocompatibility (very small contraction <0. 5%) • • High dimensional stability High elastic recovery Ease of use Hydrophilic and Hydrophobic • Proper setting time Compatibility to stone High tear strength Long shelf life Pleasant color &taste Cost
Impression plaster ADA type I gypsum product
Impression plaster For edentulous impression Contraindication for undercut
Composition Calcium sulfate hemihydrate Potassium sulfate (Ca. SO 4)2. H 20 Reduce expansion Borax Reduce the rate of setting time Starch Help disintegration of the impression from plaster model
Reaction Calcium sulfate hemihydrate + water calcium sulfate dihydrate
Mechanical properties Very low viscosity (mucostatic) Hydrophilic Good dimension stability 0. 06% Great accuracy
Manipulation Easy to mix, trapping air bubbles W/P ratio must be measured out carefully Use in special tray, thickness of 1. 0 -1. 5 mm. Setting time 2 -3 minutes Must apply separating medium before pouring the impression Powder must be stored in air tight
Advantage Accuracy to soft tissue impression Good accuracy Short setting time
Disadvantage Can not be used in undercut ridge Able to flow to pharynges Heat due to reaction Sensation of dryness
Impression compound Type II Green stick compound
Impression with compound Type II
Composition Natural resin Waxes Stearic acid Filler&inorganic pigment 40% 7% 3% 50%
RESINS Amorphous organic substance which are insoluble in water Make Thermoplastic Shellac, dammar, rosin or sandarac
WAXES Straight chain hydrocarbon CH 3(CH 2)n. CH 3 Tasteless, Odorless, Colorless Make Thermoplastic beeswax and colophany
Stearic acid • Lubricant and Plasticizer Fillers Control degree of flow Minimize shrinkage Improve rigidity Diatomaceous earth, Soapstone, talc
Mechanical properties Thermoplastic Reversible 37 -45 C๐ physical process Very low thermal conductivity High thermal expansion High contraction coefficients High viscosity 0. 3%
Manipulation Soften by heating over the flame or water bath Do not heat too much volatile Take impression Room temperature water cooling Pour impression as soon as possible Warm the impression before take the cast
Water bath Alcohol lamp Alcohol torch
Advantage Can take impression again Compatible with model material
Disadvantage Very technique sensitive High coefficient of thermal expansion => dimensional change Mucocompressive Must be poured within one hour Low detail reproduction
Troubleshooting Distortion -Material is not completely cooled -Flexible tray -Delay in pouring
Troubleshooting Compound is too brittle or grainy -Prolong immersion in the water bath
Zinc oxide-eugenol Impression paste
Zinc oxide-eugenol Impression paste
Zinc oxide-eugenol For full arch edentulous impression without or minor undercut Wash impression Bite registration Temporary cementation Temporary filling
Composition (base) Zinc oxide (Zn. O) Oil Hydrogenated rosin Zinc acetate Trace of water Accelerator Initiator
Composition (reactor) Eugenol Oil Rosin Filler (kaolin) Non eugenol paste 12~15% Carboxylic acids
Reaction Zn. O + eugenol (powder) Zn eugenolate + Zn. O(unreacted) (liquid) (Solid)
Mechanical properties @ Very low viscosity @ Irreversible chemical change @ Low dimensional change 0. 1%
Manipulation
Manipulation Equal length of the two paste is extruded Mixed with stainless steel spatula in paper pad or glass slab Mixing time 45 -60 s Working time 3 -5 min shorten by increase Temperature&Humidity
Advantage Accuracy of soft tissue impression (mucostatic) Good dimensional stability Good surface detail reproduction Inexpensive Adhere well to dental compound
Disadvantage Messiness Non elastic Time Unstable setting May irritating to soft tissue
Troubleshooting Inadequate working or setting time -excessive humidity and/or temperature Distortion -unstable tray
Impression wax KORECTA WAX , IOWA WAX
Manipulation Functional Impression
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 2 nd Ed. CP Owen
REFERENCES • 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 11 th Ed. • Stephen C. Bayne Department of Operative Dentistry School of Dentistry University of North Carolina • Mr. Robert Seghi Alginate Impression Materials (alginate lecture 2006. ppt)
Tray Selection Criteria Feel 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 Trays Quadrant 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 tray Interior of the tray is painted or sprayed with an adhesive to hold the impression material.
Impression Trays Must 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.
Table 46 -1 Types of Stock Trays
Fig. 46 -3 Examples of quadrant, section, and full -arch impression trays.
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 Materials Base Packaged as a paste in a tube, as a cartridge, or as putty in a jar. Catalyst Also 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 Technique 1. 2. 3. 4. 5. 6. 7. The material selected depends upon the dentist’s preference and the type of impression required for the procedure. The dentist prepares the tooth or teeth for the impression. The light-bodied material is prepared and loaded into the syringe and transferred to the dentist. The dentist places the light-bodied material over and around the prepared teeth and onto the surrounding tissues. The heavy-bodied material is prepared and loaded into the tray and transferred to the dentist. When the impression material has reached final set, the impression is removed and inspected for accuracy. 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 Polysulfide Polyether Silicone Polyvinyl siloxane
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 bite Useful when the diagnostic casts are trimmed. The most common technique is to use a softened baseplate wax.
Fig. 46 -27 Wax bite registration.
Types of Occlusal Registration cont’d Polysiloxane 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’d Zinc 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.
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