chapter 46: Impressions

Dental impressions

Taken for the fabrication of indirect restoration, dentures, bleaching trays, mouth guards, and retainers

Dental impressions are a _____ reproduction of teeth

Negative

Models are a _____ reproduction of teeth

positive

What are the two types of dental impression techniques?

Traditional (material) based and digital

Types of material based impressions

Preliminary, Final, occasional (bite) registration

Preliminary impressions

Use to create an accurate reproduction of teeth and surrounding areas

What are preliminary impressions used for?

Diagnostic models, custom trays, provisional coverage, orthodontics

Final impressions

Use to create EXACT detail of teeth and surrounding areas

What are final impressions used for?

Indirect cast restorations, partial or full dentures, and implants

Bite (occlusal) registrations

Used to produce reproduction of occlusal relationship of teeth when mouth is occluded

Impression trays

Used to hold impression material within the mouth

Types of impression trays

Stock trays and custom trays

Stock trays

Designed for different areas in the mouth and comes in different sizes and styles

What are the different type of stock trays?

Quadrant, section and full arch

Quadrant trays

Covers half of an arch

Section trays

Covers anterior portion of arch

Full arch trays

Covers entire arch

Perforated surface trays

create mechanical lock

How long should a tray extend beyond the third molar?

2-3mm beyond

What should be used to extend a tray?

Utility wax

Custom trays

designed to fit the mouth of specific patients and make most accurate impressions

Custom trays are used for?

Dentures, inlays, crowns, bridges

What can help ensure that impressions remain firmly attached ?

Tray adhesive

Hydrocolloid material

The oldest dental impressions used to preliminary and final impressions

Irreversible hydrocolloid are changed by

chemical factors

Reversible hydrocolloid are changed by

Thermal factors

Irreversible hydrocolloid (alginate)

Material that CANNOT return to sol state after becoming gel

Alginate is used for what type of impressions

Preliminary (material)

Function of potassium alginate in alginate

Used as a thickening agent

Function of calcium sulfate in alginate

Forms a gel

Function of trisodium phosphate in alginate

Slows down mixing time

Function of diatomaceous earth

Bulks the material

Function of zinc oxide in amalgam

Add additional bulk to material

Function of potassium titanium fluoride in alginate

Protect setting and surface strength

Physical phases of alginate

Sol (solution) Ang gel (solid) form

How long do you have to “pour up” the alginate

one hour

What is the working time and setting time for normal set?

2 minutes working time and 4 ½ minute setting time

What is the working time in setting time for fast set

1 ½ minute working time and 1-2 minute setting time

What can increase the setting time when mixing alginate?

Using cold water

What is the water to powder ratio for mandibular impression?

2 scoops powder , 2 measurements water

What is the water to powder ratio for maxillary impression?

3 scoop powder, 3 measurement water

How is alginate mixed

With a spatula and a rubber bowl or alginator

How to reduce the gag reflex

Breathe through nose, drool and distraction

Reversible hydrocolloid

material that changes its physical state from sol to gel and back to sol

Resversible hydrocolloid is made of

85% water, 13% agar and additional chemicals

What is used to change reversible hydrocolloid from one consistency to another

Specialized conditioning bath

Light Bodied material

A syringe type that is dispensed directly onto the teeth

Heavy and regular bodied

A type types used to fill the tray, used for a more accurate and detailed impression

Paste mix system

Supplied in tubes and mixed when Dentist is ready

Auto mix system

Has appropriate amount without waste

Mixing unit system

On a tabletop or wall mounted that provides no access material and infection control

Potty mixing system

Supplied as a putty and has a high viscosity

What food resembles reversible hydrocolloid

Ice cream

Types of elastomeric materials

Polysulfide, polyether, condensation silicone and poly silo and

Polysulfide

Used as a final impression, strong odor, hard to mix and long setting time

Polyether

Has an acceptable order and taste, easy to mix and short setting

Condensation silicone

Odor-free and easy to mix

Polysiloxane

No taste or odor and low tear resistance

Occlusal (bite) registration

Used to show centric relationship of upper and lower arches

Polysiloxane bite registration paste

Most popularly used bite registration with no odor or taste

Wax bite registration paste

Used to show occlusal relationship and lacks stability

ZOE bite registration paste

Used when durable materials

Digital impressions

Replaces traditional material based impressions by using technology to scan a replica of oral cavity

Two types of digital impressions techniques

Digital photographs and digital video