dental materials chapter 14 part 2 2013

7/27/2019 Dental Materials Chapter 14 Part 2 2013

1/30

Chapter 14

Impression MaterialsPart 2


2/30

Impression

Material used

Reproduce the form of teeth

CASTING RESTORATION

PREPARATIONS FOR RESTORATIONS

FORM OF THE ORAL HARD AND SOFT

TISSUES

Known as a negative replica of the teeth


3/30

IMPRESSION TRAYS

Used to carry the impression material

to the mouth and support it until it sets

Can be made for edentulous and full

dentition

Full arch/ or quad

Metal or plastic Adults, children

Solid or perforated with holes


4/30


5/30

Solid impression trays

Have raised borders, expensive

Internal surfaces that help lock in the

material (need to clean!)

Known as rimlock trays

May need adhesive

Retain material Prevent distortion


6/30

Plastic trays

Inexpensive

Disposable


7/30

Custom Trays

Constructed in lab

Chemical cured

Light-cured

Resins on casts

Custom fit the mouth of the individual


8/30

Triple Trays

Also called

Double-bite

Dual-arch

Check-bite

Used to make an impression of the

teeth being treated and the opposing

arch


9/30

Bite Registration Trays

Typically U-shaped plastic frames with

a fiber mesh stretched between the

sides of the frame

Place material on both sides of the

mesh


10/30

Alginate

Irreversible hydrocolloid

Most widely used impression material

Easy to manipulate

Inexpensive No special equipment needed

Reasonable accurate Dental casts, partial denture frameworks,

repair of broken partial/dtr, fluoride andbleaching trays, mouth guard, preliminaryimpressions

Not accurate enough for final impressions


11/30

Composition

Main act iveingredient

Potassium or sodium alginate = 15-20%

Colloidal particles as basis of the gel

Produced from derivatives of seaweed

Other ingredients Calcium sulfate dihydrate

Creates irreversible gel with alginate

Potassium sulfate

Ensures set of gypsum materials

Trisodium phosphate and diatomaceous earth

Retarder to control setting time and filler

Flavoring agents, coloring agents

Color, reduce dust, antibacterial action, taste


12/30

Setting reaction

Regular set 2 5 minutes

Fast set

1 2 minutes

Setting time lengthened

Cold water

Setting time shortened

Hot water Should leave the impression in the mouth for

additional 1-2 minutes after it appears set


13/30


14/30

Removing the Impression

Need a thickness of 2-4 mm between

impression tray and the teeth

Thin alginate will tear more easily

Remove

Rapidly

With a snap

Loosen the back of the tray by pushing

down on the edge of the tray


15/30

Dimensional stability

Alginate

Sensitive to moisture losswill shrink Remove from mouth

Rinse and disinfect

Wrap in damp paper towel, seal in zip lockbag

Need to create 100% humidity

Syneresis squeezing out some liquid fromcontracting gels; appears on surface of

impression


16/30


17/30

Impression Making

Objective

To reproduce the oral structures with an

acceptable accuracy

Tray selection

Need adhesive?

Perforated trayno

Rim lockno but recommended Solid trayyes

Size selected needs to cover teeth

Extends posteriorly to include

Retromolar pad, hamular notch


18/30

Dispensing

Manufacturers directions

Supply measuring tools

Powder has scoop

Liquid has measuring cup

Need to fluff powder Turn canister end-over-end a couple of

times Powder will pack tightly while shipping and

ingredients will settle

Will not mix correctly if ingredients are not evenlydispensed in alginate powder

MAKE SURE YOU WEAR MASK


19/30

Mixing

Moderate large maxillary tray/arch

3 scoops of powder

Small maxillary tray/arch 2 scoops of powder

Most lower trays/arch

2 scoops

One unit of water per scoop of powder

Room temperature water in one bowl

Scoops of powder in another bowl

Cold water will retard the set

Consider pt. sensitivity


20/30

Mixing

Warm water will accelerate the set Add powder to water

Powder stirred into water so that powderis wet

Mix against the sides of the bowl

Aggressively mix

Creamy not grainy

Regular set

Mix for 45 seconds

Fast set Mix for 30 seconds


21/30

Loading the tray

Pick up large amounts on spatula andforce into the depth of the tray

Forces air out

Load quickly Alginate should be even to the sides of

the tray

Wet your gloved finger with water andsmooth the surface of alginate and

create shallow trough


22/30

Seating the tray

Wipe alginate on occlusal surfaces of teeth andplace alginate up in the maxillary vestibule

Regular set

2 minutes of working time

45 seconds of that is mixing time

1 minute and 15 seconds to manipulate

Fast set

Setting time 75 seconds(1.25 seconds-2minutes) 30 seconds for mixing

45 seconds to manipulate and seat tray


23/30

Seating the lower tray

Seat the lower

impression Stand in front of the

patient

Use the tray to retract

the pt.s left cheek Use a mirror/or gloved

finger to retract thept.s right cheek

Seat the posterior firstand then continueanteriorly with the seat


24/30

Seating the lower tray

as you move the trayanteriorly, have thepatient lift up theirtongue and then

have them sit it downand extend it forward

Stabilize the traywith your fingers tohold it in place

You have to hold thetray in place


25/30

Seating the maxillary tray

Operator stands just behind the patient at 11o clock

Retract the right corner of cheek with tray

and left corner with finger Rotate tray into position

Seat posteriorly first and gently seat towardanterior

Allows alginate not to flow down the throat Patient can be in supine position

However, upright prevents gagging andalginate/saliva from going down the throat


26/30

Removing the tray

Check the alginate left in the mixing bowl for

completeness of set Leave impression in the mouth for 2 minutes

after the set Patient gags, cannot do this

Use a finger at the side of the tray to applypressure to break the seal while pulling thetray quickly away form the teeth with asnap

Rinse with water

Disinfect the impression


27/30

Evaluate the impression

Need to evaluate impression in case you

have to re-do the impression

Alginate will cover all areas of interest

Will not have a grainy surface

Inadequate mixing

Minimal voids of trapped air Alginate seated in tray and not pulled

free

Free of debris


28/30

Acceptable Impression

All teeth and alveolar processes

recorded Peripheral roll and frenums included

No large voids and few small bubbles

present

Good reproduction of detail

Free of debris

No distortion

Aglinate firmly attached to tray


29/30

Maxillary Criteria

Palatal vault

Vestibule

Hamular notch area included

All teeth

No holes


30/30

Mandibular arch

Retromolar areas included

Lingual extensions recorded

dental materials chapter 14 part 2 2013

Documents