EF- ch46: alginate and bite registration

What are impression materials used for?

Obtain an impression of teeth, surrounding oral tissues, or both

Impressions are a ___ reproduction of dental structures

negative

what are the three classifications of impressions taken in dental procedures consist of…

preliminary, final, and occlusal (bite registration)

What determines the type of dental material a dentist selects to take impressions?

The type of dental material selected by the dentist to take these impressions will depend on what will be constructed from the impression

What impression can be taken by either dentist or EFDA?

preliminary impressions and bite registrations

What are the following reasons why preliminary impressions are used?

diagnostic models, custom trays, provisional coverage, orthodontic appliances, pretreatment and post-treatment records

what impression is taken by the dentist only?

final impressions

Why are final impressions are used?

It’s used to produce the most accurate reproduction of the teeth and surrounding tissue

When providing the essential information for the dentist and dental lab tech during a final impression, what can it be used to make?

indirect restorations, partial or full dentures, implants

What does a bite registration shows?

It makes a reproduction of the occlusal relationship of the maxillary and mandibular teeth when the mouth is occluded

What does the bite registrations provide after it’s been excreted and hardened on the teeth?

It provides an accurate registration of the patient’s centric relationship between the maxillary and mandibular arches

What are used to hold the impression material when impression are taken?

Impression trays

impression trays must be sufficiently rigid to…

carry the impression material into the oral cavity, hold the material close to the teeth, avoid breaking during removal, prevent warping the completed impression

what are the two types of impression trays?

stock trays and custom trays

stock trays are manufactured in ___ ways

several

What is available in a range of sizes and styles?

stock trays

how many different types of impression trays are there?

quadrant tray, section tray, full arch tray

what is a quadrant tray?

it’s used to cover half of an arch

what is a section tray?

it’s used to cover the anterior portion of the arch

what is a full arch tray?

covers the entire arch

what are the two kinds of characteristic a surface tray (impression) can have?

perforated or smooth

what happens when the perforated surface tray is used?

the impression material oozes through the holes in the tray, creating a mechanical lock to hold the material in place

what happens when a smooth surface tray is used?

there is no mechanical lock so the interior of the tray is painted or sprayed with an adhesive to hold the impression

In terms of impression tray sizing, how do you know the tray is correct?

is comfortable to the patient

extends slightly beyond the facial surfaces of the teeth

extends approximately 2 to 3mm beyond the third molar, retromolar, or tuberosity area of the arch

is sufficiently deep to allow 2 to 3 mm of the material between the tray and incisal or occlusal edges of the teeth

What can be used to add length to the tray?

utility wax to the border of the tray

why is it necessary to add utility wax on a tray?

if the tray doesn’t completely cover the 3rd molar AND it’s used for patients with an unusually high palate so the wax can be added to the palate area of the impression tray

what is a custom tray?

it’s used to fit the mouth of a specific patient

how is a custom tray made?

The custom tray is constructed in the laboratory from a diagnostic model made from a preliminary impression of the arch before the dentist has prepared the teeth 

What can custom trays be made from?

A custom tray may be constructed by using acrylic resin, light-cured resin, or a thermoplastic resin technique 

what are the 3 tray adhesives that can be used?

VPS, rubber base, silicone

Which impression material can VPS adhesives go on?

For polyvinyl siloxane and polyether impression materials 

Which impression material can rubber base adhesive go on?

used with rubber base impression materials

which impression material can silicone adhesive go on?

silicone impression materials

hydrocolloid materials are used to obtain what type of impressions?

preliminary and final impressions

what does hydro mean?

water

what does colloid means?

gelatin substance

depending on the type of hydrocolloid, the physical change from sol to gel can be ___ or ___

irreversible or reversible

What caused a hydrocolloid to be irreversible?

changed by chemical factors

what caused a hydrocolloid to be reversible?

changed by thermal factors

Hydrocolloid impression materials that cannot return to the sol state after they become a gel are termed

irreversible hydrocolloids

what irreversible hydrocolloid is most widely used for preliminary impressions?

alginate

what is the main ingredients of alginate?

potassium alginate, calcium sulfate, trisodium phosphate, diatomaceous earth, zinc oxide, potassium titanium fluoride

what is potassium alginate?

derived from seaweed

what does calcium sulfate reacts with in the composition and chemistry of alginate?

potassium alginate to form the gel

why is trisodium phosphate needed in the composition and chemistry of alginate?

added to slow the reaction time for mixing

why is diatomaceous earth needed in the composition and chemistry of alginate?

a filler that adds bulk to the material

why is zinc oxide needed in the composition and chemistry of alginate?

adds bulk to material

why is potassium titanium fluoride needed in the composition and chemistry of alginate?

added so as not to interfere with the setting and surface strength of the product used when making a model

What are the two physical phases in hydrocolloid impression materials?

Sol (solution) phase and gel (solid) phase

what is the sol phase material like?

It’s in a liquid or semi-liquid form

what is the gel phase material like?

it’s semisolid, similar to a pudding dessert

T or F: The strength of the material will continue to increase even after it appears to be set

True

T or F: Leaving the impression in the mouth for the full length of time recommended by the manufacturer is important toward achieving maximum strength 

True

Most alginate materials must be poured up within _ hours of taking the impression to avoid dimensional change

1 hour

T or F: Alginate can be purchased in a variety of ways 

True

T or F: Containers about the size of a coffee can are the most common form of packaging 

True

Premeasured, individual packages are more ___, but they save time by eliminating the need for measurement of the powder 

expensive

T or F: The material is also supplied with flavoring as well as changes in color when set 

True

Meaning of Imbibition

If an alginate impression is stored in water or in a soaked paper towel, it will absorb the additional water and expand

meaning of syneresis

if an alginate impression remains in the open air moisture will evaporate, causing the impression to shrink and distort

what is normal set alginate time for working and setting?

working time of 2 minutes and setting time of up to 4.5 minutes after mixing

what is fast set alginate work time and setting time?

work time is 1 ¼ minutes and setting time of 1 to 2 minutes

What is working time when doing alginate?

the time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient’s mouth

What is setting time when doing alginate?

The time required for the chemical action to be completed, after which the impression is ready to be removed from the patient’s mouth 

What is the best temperature water to use when mixing alginate?

room temperature water

what temperature water will increase the setting time if additional time is needed for the procedure?

cooler water

what temperature water will reduce or shorten the setting time of the procedure?

warmer water

T or F: The manufacturer supplies a plastic scoop for dispensing powder and a plastic cylinder for measuring the water 

True

What is the adult mandibular impression water to powder ratio?

2 scoops of powder and 2 measures of water

what is the adult maxillary impression water to powder ratio?

3 scoops of powder to 3 measures of water

what is the most common mixing technique with alginate

spatulation with a rubber bowl and beavertail wide spatula

what is another mixing technique that involves electrical component?

alginator which is a rubber flexible bowl with low or high speed

When EFDA is taking an alginate impression, it’s important to be competent in…

mixing the alginate

loading the tray

keeping the patient comfortable while taking the impression

what does a patient need to know when taking an impression?

• The material will feel cool, there is no unpleasant taste, and the material will set quickly 

• Breathing deeply through the nose will help the patient relax and feel more comfortable 

• The patient can use some type of hand signals to communicate any discomfort 

When evaluating alginate impression it should be…

• The impression tray should be centered 

• There is a complete “peripheral roll,” including all of the vestibular areas 

• The tray is not “overseated” 

• The impression is free from tears or voids 

• Sharp anatomic detail of all teeth and soft tissues is provided 

• 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 

How does taking an alginate impressions of an edentulous arch differs from taking other alginate impression in two ways

• The height of the teeth is missing 

• It is important to include more extensive tissue details 

How is edentulous tray different from other trays?

it’s not as deep as other trays used for alginate impressions

A change of __ causes the reversible hydrocolloid material to transform from one physical state to another

temperature

What does hysteresis means?

used to describe the change in temperature that causes the reversible hydrocolloid material to transform from one physical state to another 

__% water in hydrocolloid

85%

__% agar in hydrocolloid

13%

What is agar?

organic substance derived from seaweed 

For the reversible hydrocolloid to change from one consistency to another… What is used?

specialized conditioning bath is used

A “conditioner” bath liquefies the semisolid material at ___ F and is then cooled to ___F 

212F and 150F

A ___ bath readies the material for the impression in its tubes

“storage”

A “tempering” bath keeps material at ___F

110F

A reversible hydrocolloid tray material is packaged in…

plastic tubes and each tube hold enough material to fill a full arch, water cooled tray

The material needs enough __ to keep the material from flowing out of the tray when dispensed at __F 

viscosity; 150F

Why is a Reversible Hydrocolloid impression tray filled and immersed in 110F bath for a few minutes?

further increase viscosity and reduce the temperature to a comfortable level for the patient 

What is Reversible Hydrocolloid Syringe Material?

• A conventional hydrocolloid is dispensed directly onto the prepared tooth and surrounding teeth 

• Less viscous than tray material 

What is Reversible Hydrocolloid Syringe Material packed in?

plastic or glass cartridges that fit a syringe or in a preloaded syringe or comes in preloaded syringes or preformed sticks that refill special hydrocolloid inlay syringes 

Syringe material is liquefied by placing it in the same __F storage bath as the tray material

150F

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; the dentist seats the tray 

When are elastomeric impression materials used?

when an accurate impression is essential

What does elastomeric means?

having elastic or rubber-like qualities

What is the Characteristics of Elastomeric Impression Materials 

self curing and supplied as a base and a catalyst

What’s a base?

Packaged as a paste in a tube, in a cartridge, or as putty in a jar 

what’s a catalyst?

Packaged as a paste in a tube, in a cartridge, or as a liquid in a bottle with a dropper top 

What are the 2 materials forms of elastomeric impression materials?

light bodied; regular and heavy bodied materials

what is light bodied material used for? what’s it referred to as?

• Also referred to as syringe-type or wash-type 

• Used because it can flow into and around the details of the prepared tooth 

• A special syringe, or extruder, is used to apply light-bodied material immediately around prepared teeth