1. Impression Materials Chapter 46 1
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2. Chapter 46 Lesson 46.1
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3. Learning Objectives Pronounce, define, and spell the Key Terms.
List the three types of impressions taken in a dental office.
Describe the types of impression trays and their characteristics of use.
(Cont’d)
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4. Learning Objectives
(Cont’d)
Discuss hydrocolloid impression materials and their uses, mixing techniques, and application.
Mix alginate impression material at a competent level.
Take maxillary and mandibular preliminary impression at a competency level.
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5. Impressions are a negative reproduction of dental structures.
Introduction
Impression materials are used to obtain an impression of teeth, the surrounding oral tissues, or both.
Impressions are a negative reproduction of dental structures.
How many students have had impressions taken?
For what reasons?
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6. Preliminary Impressions
Taken either by the dentist or the expanded-function dental assistant
Used for the making of:
Diagnostic models
Custom trays
Provisional coverage
Orthodontic appliances
Pretreatment and posttreatment records
Preliminary impressions are almost always taken by a competent dental assistant.
What are diagnostic models used for?
What are custom trays used for?
What is provisional coverage?
What types of orthodontic appliances can be made?
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7. Final Impressions Taken by the dentist
The most accurate reproduction of the teeth and surrounding tissues
Used to make:
Indirect restorations
Partial or full dentures
Implants
Final impressions are never taken by the dental assistant.
What are some examples of indirect restorations?
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8. Fig. 46-10 Example of a final impression.
Which tooth is involved in this impression?
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9. Bite Registrations Taken by the dentist or dental assistant
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
Why are bite registrations important in the fabrication of indirect restorations?
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10. Fig. 46-16 Example of a bite registration
Fig Example of a bite registration. (Courtesy of 3M Dental Products, St Paul, Minn.)
Example of a polysiloxane bite registration
What arch is this?
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11. 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
Are impressions a positive or negative reproduction?
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12. 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
Has holes in the tray to create a mechanical lock to hold the material in place
Smooth tray
Interior painted or sprayed with an adhesive to hold the impression material
Are impression trays metal or plastic?
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13. Fig. 46-1 Types of stock trays.
What is a triple tray?
What are the advantages of using a triple tray?
Which of these impression trays needs to have an adhesive applied?
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14. Fig. 46-3 Examples of quadrant, section, and full-arch impression trays.
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15. Tray-Selection Criteria
Must feel comfortable to the patient
Should extend slightly beyond the facial surfaces of the teeth
Should extend approximately 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch
Depth to allow 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth
Try the tray in the patient’s mouth before mixing material.
Explain the procedure to the patient.
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16. Tray Adhesives VPS adhesives (blue) Rubber base adhesive (brown)
For polyvinyl siloxane and polyether impression materials.
Rubber base adhesive (brown)
Used with rubber base impression materials.
Silicone adhesive (orange-pink)
Used with silicone impression materials.
Tray adhesives should be applied after the tray has been tried in the patient’s mouth.
How long should the tray adhesive be applied to the tray before the impression material is added?
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17. Hydrocolloid Impression Materials
These materials are used to obtain preliminary and final impressions.
Hydro mean “water.”
Colloid means “gelatin substance.”
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18. Irreversible Hydrocolloid
Material cannot return to a solid state after it becomes a gel.
Alginate is the irreversible hydrocolloid most widely used to take preliminary impressions.
What can alginate impressions be used for?
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19. Makeup of Alginate Potassium alginate Calcium sulfate
Comes from seaweed; also used in foods such as ice cream as a thickening agent
Calcium sulfate
Reacts with the potassium alginate to form the gel
Trisodium phosphate
Added to slow the reaction time for mixing.
(Cont’d)
No taste.
Flavors are available. (Cherry is the most common.)
Odor-free.
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20. Makeup of Alginate Diatomaceous earth Zinc oxide
(Cont’d)
Diatomaceous earth
A filler that adds bulk to the material
Zinc oxide
Adds bulk to the material
Potassium titanium fluoride
Added so as not to interfere with the setting and surface strength
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21. Physical Phases of Alginate
First phase
In the sol (as in solution) phase, the material is in a liquid or semiliquid form.
Second phase
In the gel phase, the material is semisolid, similar to a gelatin dessert.
On completion of both phases, alginate is susceptible to tearing and stretching.
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22. Packaging and Storing of Alginate*
Containers
Premeasured packages
*The shelf life of alginate is approximately 1 year.
Alginate should be stored at room temperature.
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23. Fig. 46-5 Packaging of alginate.
Alginate impression materials come in a reusable tub with a measuring scoop. This is the most common form of alginate.
Premeasured foil packets are available at a slightly higher cost.
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24. Cause for Distortion and Dimensional Change
Imbibition
Alginate impression stored in water or a very wet paper towel will absorb the additional water and expand.
Syneresis
If an alginate impression remains in the open air, its moisture will evaporate, causing the impression to shrink and distort.
How long after the impression is obtained should we proceed to pouring?
Storing the impression in a plastic bag can help prevent distortion.
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25. Alginate Settings Normal-set alginate Fast-set alginate Working time
Working time of 2 minutes and a setting time of up to 4½ minutes after mixing
Fast-set alginate
Working time of 1¼ minutes and a setting time of 1 to 2 minutes
Working time
The 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.
Which setting time would be preferred for a patient who has a sensitive gag reflex?
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26. Altering the Setting Time 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.
Which water temperature would be preferred for a patient who has a sensitive gag reflex? Why?
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27. Water-to-Powder Ratio
Adult mandibular impression
Two scoops of powder and two measures of water
Adult maxillary impression
Three scoops of powder and three measures of water
These ratios are only guidelines for measurement.
Check the manufacturer’s directions before measuring.
Adjustments may have to be adjusted, because not all patients are the same.
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28. Fig. 46-6 A plastic scoop and plastic cylinder are supplied with alginate.
Do not pack powder into scoops.
Use a spatula to level the top of the scoop.
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29. 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 relax and feel more comfortable.
Use hand signals to communicate any discomfort.
Never leave the patient alone during this procedure.
Would we ask the patient whether he or she has a sensitive gag reflex? Why or why not?
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30. An Acceptable Alginate Impression
The impression tray is centered.
The "peripheral roll," including all of the vestibular areas, is completed.
The tray is not "overseated."
The impression is free of tears or voids.
Sharp anatomic detail of all teeth and soft tissues is captured.
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.
If these criteria are not met, you must retake the impression.
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31. Fig. 46-7 How an impression must appear.
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32. Reversible Hydrocolloid
This impression material changes its physical state from a sol to a gel and then back to a sol.
Not commonly used in dental offices.
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33. Chemical Makeup of Reversible Hydrocolloid
85% water
13% agar
Agar is an organic substance derived from seaweed.
Additional chemical modifiers are added to improve the substance’s handling characteristics.
Additional equipment is required to obtain an impression.
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34. Conditioning Bath for Reversible Hydrocolloid
Three compartments
A “conditioner” bath liquefies the semisolid material at 212° F and is then cooled to 150° F.
A “storage” bath, readies the material for the impression in its tubes.
A “tempering” bath keeps material at 110° F in the syringe and tray.
Longer steps are required to obtain this type of impression.
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35. Types of Reversible Hydrocolloid
Tray material
Packaged in plastic tubes, each with enough material to fill a water-cooled full-arch tray
Syringe material
Packaged in plastic or glass cartridges that fit a syringe or in preloaded syringes or preformed sticks that are used to refill special hydrocolloid inlay syringes.
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36. Application of Reversible Hydrocolloid Impression Material
A stock water-cooled tray is selected.
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.
Is this type of material used for preliminary or final impressions?
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37. Chapter 46
Lesson 46.2
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38. Learning Objectives
Discuss elastomeric impression materials and their uses, mixing techniques, and application.
Competently mix a paste final impression material.
Competently prepare an automix impression material.
(Cont’d)
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39. Learning Objectives
(Cont’d)
Describe the importance of the occlusal registration and its use in a procedure.
Take a wax bite.
Prepare and assist in a closed-bite registration procedure.
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40. Elastomeric Impression Materials
Elastomeric impression materials are used when an extremely accurate impression is essential. The term elastomeric means “having elastic or rubberlike qualities.”
Commonly used in dental offices.
Easier to use than reversible hydrocolloids.
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41. Characteristics of Elastomeric Impression Materials
Base
Packaged as a:
Paste in a tube
Cartridge
Putty in a jar
Catalyst
“Accelerator” packaged as a:
Liquid in a bottle with a dropper top
Very accurate impressions are obtained with the use of this material.
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42. Forms of Elastomeric Materials
Light-bodied
Also referred to as syringe type or wash type
Used because it can flow into and around the details of the prepared tooth
Placed on and immediately around the prepared teeth with the use of a special syringe or extruder
(Cont’d)
The syringe may be disposable or sterilizable and reusable.
Extruder tips are disposed of after each use.
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43. Forms of Elastomeric Materials
(Cont’d)
Regular and heavy-bodied
Also referred to as “tray-type” materials, they are much thicker. As the name implies, they are used to fill the tray. Their stiffness helps 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.
Would this material be used to define details of the prepared tooth?
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44. Basic Impression Technique
The material selected depends on 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 on 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 its 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.
What is the process for tray selection?
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45. 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 takes 1 to 24 hours.
Do these impressions need to be disinfected before delivery to the dental laboratory?
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46. Types of Elastomeric Materials
Polysulfide
Polyether
Silicone
Polyvinyl siloxane
All of these materials are very similar products, and all provide the same outcome.
Dimensional stability is a main concern.
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47. Polysulfide Impression Material
Chemical makeup
Base: mercaptan polysulfide
Crosslinking agent: sulfur, lead peroxide, or both
Catalysts: copper hydroxides, zinc peroxide, organic hydrogen peroxide
Fillers: zinc sulfate, lithopone, or calcium sulfate dihydrate
Also known as rubber base.
Has a strong odor.
Can stain clothing.
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48. 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.
The impression should be removed quickly after setting; do not rock the tray.
The adhesive must be thin and dry before the impression material is added.
Wait 20 to 30 minutes before pouring the impression to allow stress relaxation to occur in the material.
Be careful to avoid glove-powder contamination.
Has a long working time.
Has a long setting time.
Would this material be used on a patient with a sensitive gag reflex?
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49. Polyether Impression Material
Chemical makeup
Base: polyether
Crosslinking agent: sulfate
Catalysts: glycol-based plasticizers
Filler: silica
A thinner can be used with this material.
What is a thinner used for?
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50. Manipulation and Technique Considerations for Polyether Material
The material is very stiff, making it difficult to remove without rocking.
When removing the impression, break the seal and rock it 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.
Supplied in a two-paste system or cartridge system.
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51. Silicone Impression Material
Chemical makeup
Base: poly dimethyl siloxane
Crosslinking agent: alkyl orthosilicate or organo hydrogen siloxane
Catalyst: organo tin compounds
Filler: silica
Odor free.
Does not stain.
Very good dimensional stability.
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52. Manipulation and Technique Considerations for Silicone Material
The material has a limited shelf life.
The tray requires a special tray adhesive.
Silicone material is not subject to syneresis or imbibition, but it does respond with shrinkage over time.
The material is more flexible, so the more chance of distortion during removal is greater.
Wait 20 to 30 minutes before pouring of models for stress relaxation to occur.
Supplied in a tube for the base and a bottle or smaller tube for the catalyst.
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53. Polyvinyl Siloxane Impression Material
Chemical makeup
Base: silicone polymer
Catalyst: chloroplatinic acid
Filler: silica
Also known as polysiloxane.
High dimensional stability.
Low tear resistance.
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54. Manipulation and Technique Considerations for Polyvinyl Siloxane Material
For dimensional stability, this is the best impression material.
Pouring of the model can be delayed as long as 7 to 10 days.
Stiffness of the material makes removal of the tray difficult.
The material is dispensed with the use of an auto-mixing unit and mixing tips.
Most commonly used impression material.
No odor.
Tasteless.
Available in light-, regular-, and heavy-bodied forms.
Supplied in cartridges or putty form.
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55. Occlusal Registration
Occlusal registration is an accurate registration of the normal centric relationship of the maxillary and mandibular arches. Also commonly referred to as the bite registration.
What is centric occlusion?
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56. Types of Occlusal Registration
Wax bite
The wax bite is useful when the diagnostic casts are trimmed.
The most common technique involves the use of a softened baseplate wax.
Equipment needed: laboratory knife and heat source.
What type of heat source is used?
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57. Fig. 46-17 Wax bite registration.
How long should the wax bite registration stay in the patient’s mouth?
Does this impression need to be disinfected?
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58. Types of Occlusal Registration
Polysiloxane bite-registration paste:
Supplied both as a paste system and also as cartridges
Fast-setting
No resistance to biting forces
No odor or taste for the patient
Gains dimensional stability over time
Convenient to use
(Cont’d)
Widely used.
Does not require a heat source.
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59. Types of Occlusal Registration
(Cont’d)
Zinc oxide–eugenol (ZOE) bite-registration paste
ZOE paste offers little or no resistance to bite closure and is fast-setting material.
The material is supplied in a paste system and dispensed onto a paper pad, mixed, and placed on a gauze tray for the patient to bite into.
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