Chapter 46: Impression materials and techniques Flashcards
three classifications of impressions
- preliminary
- final
- occlusal (bite registration)
A preliminary impression is indicated for the following procedures:
diagnostic models/casts
custom trays
provisional coverage
orthodontic appliances
pretreatment and post treatment records
who can take occlusal registrations or bite registrations
dentist and DA
these are used to hold the impression material within the mouth.
impression trays
Impression trays are of two basic types:
stock trays custom trays
Impression trays are supplied in one of the following ways
- quadrant trays (cover half the arch)
- section trays (covers anterior portion of arch)
- full arch trays
thisi tray allows the impression material to ooze through the holes of the tray, creating a mechanical lock to hold the material in place.
perforated tray
when this 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 material securely in the tray.
smooth surface tray
The correct size of tray accomplishes the following:
- patient comfort
- Extends 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch
how would you extend an impression tray ? what material would you use
utility wax
____ helps ensure that an impression remains firmly attached to the tray on removal from the mouth so as not to cause deformity.
tray adhesives
specific adhesives used with specific impression materials are as follows:
- VPS adhesives (blue)—used with polyvinyl siloxane (polysiloxane) and polyether impression materials
- Rubber base adhesives (brown)—used with rubber base impression materials
- Silicone adhesives (orange-pink)—used with silicone impression materials
a material used to obtain preliminary and final impressions
hydrocolloid
Depending on the type of hydrocolloid, the physical change from ______to ______can be irreversible (changed by chemical factors) or reversible (changed by thermal factors).
sol (solution)
gel (solid)
Hydrocolloid impression materials that cannot return to the sol state after they become a gel are termed
irreversible hydrocolloids.
an irreversible hydrocolloid that is most widely used for preliminary impressions.
alginate
The main components of alginate include the following:
- Potassium alginate,
- Calcium sulfate
- Trisodium phosphate
- Diatomaceous earth
- Zinc oxide
- Potassium titanium fluoride
Hydrocolloid impression materials have two physical phases:
sol ( solution)
gel (solid)
The gel strength of hydrocolloid is not as great as that of _____ impression materials. The hydrocolloids have difficulty withstanding tensile stress (tearing) and elastic strain (stretching).
elastomeric impression
Alginate impression materials must be “poured up” within _ hour of taking the impression
one hour
If an alginate impression is stored in water or in a saturated paper towel, the alginate acts like a sponge and will absorb the additional water and expand. This condition is called
:
imbibition
Storage of the disinfected impression in a plastic biohazard bag covered with a slightly moistened towel will provide an atmosphere close to 100% relative humidity, which causes the least amount of distortion
t or f.
true
Alginate is available in two settings:
normal set
fast set
Normal-set alginate has a working time of _ minutes and a setting time of up to __ minutes after mixing.
2
4 1/2
Fast-set alginate has a working time of __ minute and a setting time of _ to _ minutes .
1 1/4
1-2 mins
time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient’s mouth is called :
working time
what is the difference in the makeup of the completed impression between the two setting types of alginates.
no difference.
The decision as to which type to use is based on time-related factor
which temperature is best when mixing alginate
70 f / 21 c
the term used to describe the change in temperature that causes the reversible hydrocolloid material to transform from one physical state to another.
hysteresis
Reversible hydrocolloid material is approximately __% water and __%
agar
85%
13%
also referred to as “tray-type materials”
regular and heavy body materials
also referred to as syringe-type or wash-type material, is dispensed directly onto the prepared and surrounding teeth.
light bodied material
This material is less
viscous (has a lower
viscosity) than tray material and is used because of its ability to flow into and around the details of the prepared tooth.
light bodied material
polymerization stages
- initial
- final set
- final cure
most common mixing technique for use with impression materials
preparing the light-bodied material first, then the heavy-bodied material.
The four types of elastomeric impression materials most often used in dental practice are
polysulfide
polyether
polysiloxane
silicone
Of concern when using elastomeric materials are:
dimensional stability
permanent deformation
the ability of the material to keep its shape after it has been removed from the mouth.
dimensional stability
the ability of the material to resist permanent change caused by stresses during removal from the mouth.
deformation
means that the material was changed and will not regain its previous shape.
permanent deformation
also reffered to as rubber base
polysulfide
Disadvantages of rubber base material
strong odor and can easily stain clothing.
this elastomeric material has high dimensional stability and low tear resistance, making them easy to handle when taking final impressions
Polysiloxane (polyvinyl siloxane)
also referred to as rubber base.
polysulfide
this elastomeric material includes a third component called a thinner to reduce thickness and improve finished impression
polyether
The term ______indicates “having elastic or rubber-like qualities.”
elastomeric
Reproduction of a patient’s bite with the use of wax or elastomeric material
occlusal registration
a registration of the normal centric relationship of the maxillary and mandibular arches
occlusal (bite) registration
A wax bite registration is used to show the occlusal relationship of the :
maxillary and mandibular teeth
One of the most popular materials used for bite registrations:
Polysiloxane Bite Registration Paste
When a more durable material is needed for a bite registration, _________ material may be selected.
Zinc Oxide–Eugenol Bite Registration Paste (ZOE)
Taking an alginate impression of an edentulous arch differs from taking other alginate impressions in two ways:
(1) The height of the teeth is missing
(2) must include more extensive tissue details.
