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IMPRESSION TECHNIQUES OF FPD A variety of techniques have evolved over time and selection of the specific technique depends on experience and an evaluation of an individual patient. Time, expense and accuracy must all be considered in making the selection. PUTTY WASH / STOCK TRAY TECHNIQUE: Mixing method: double mix and single mix Stock trays can also be used with medium and heavy bodied elastomers normally used with custom trays. If a single mix technique is anticipated with a stock tray, the polyvinyl siloxanes are used. Place the patient in supine position and the operator at 9 o’clock position. Select the tray shape and size based on patient’s arch shape and size. Coat the tray evenly with adhesive on the inside and rim Isolate the areas to be impressed with cotton rolls and dry preparations with short bursts of compressed air. The sulcus should be dry, but do not dessicate the dentin.

IMPRESSION TECHNIQUES OF FPD

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Page 1: IMPRESSION TECHNIQUES OF FPD

IMPRESSION TECHNIQUES OF FPD

A variety of techniques have evolved over time and selection of the specific

technique depends on experience and an evaluation of an individual patient.

Time, expense and accuracy must all be considered in making the selection.

PUTTY WASH / STOCK TRAY TECHNIQUE:

Mixing method: double mix and single mix

Stock trays can also be used with medium and heavy bodied elastomers

normally used with custom trays.

If a single mix technique is anticipated with a stock tray, the polyvinyl

siloxanes are used.

Place the patient in supine position and the operator at 9 o’clock position.

Select the tray shape and size based on patient’s arch shape and size. Coat

the tray evenly with adhesive on the inside and rim

Isolate the areas to be impressed with cotton rolls and dry preparations with

short bursts of compressed air. The sulcus should be dry, but do not dessicate

the dentin.

Choose a braided cord to push the tissue aside and physically enlarge the

sulcular space by measuring the sulcus depth and width with periodontal

probe. Subgingival areas of the finish line that need tissue displacement.

Cut approximately 1 – 1 ¼ inch of cord.

Choose a dull, blunted acking instrument with a width that fits comfortably

into the sulcus.

Wrap the cord around the tooth and from the buccal, grasp the two ends with

your thumb and forefinger. Slide the cord down toward the sulcus.

Page 2: IMPRESSION TECHNIQUES OF FPD

Choose the mesiofacial or distofacial line angle to gently pack 1mm of cord

into sulcus. This holds the cord in place to facilitate further sulcular

displacement.

Continue packing the proximal sulcus and proceed toward the lingual, not

the facial surface. Continue around the lingual toward the opposite proximal

surface.

Control the buccal ends of the cord while pushing the cord with a hand

instrument toward the tooth.

Then roll it into the sulcus while pushing toward the already packed cord.

This prevents the cord from being displaced.

Observe the gingiva being displaced laterally from the tooth. Do not push the

cord down apically; this strips the attached gingiva.

Determine the final length of the cord and allow 1mm overlap plus 2mm

excess for uncomplicated removal. Cut the cord with sharp scissors to

prevent tugging on the cord.

Complete the packing at the facial surface. This varies according to the

position of the finish line, supragingival or subgingival.

Evaluate tissue displacement; if you cannot see the finish line in a certain

area(s), then additional cord(s) with increasing diameter is/are indicated.

Use alum (aluminum sulfate) to control of fluids from the walls of the

gingival sulcus.

If the gingival sulcus is healthy and not lacerated, this medicament is

sufficient.

Use epinephrine (8 percent) to control minor hemorrhage, but do not use on

patients with lacerated tissue, cardiovascular disease, diabetes, or

hyperthyroidism. Consult a current Physicians' Desk Reference (PDR) for

drug contraindications.

Page 3: IMPRESSION TECHNIQUES OF FPD

If no medicaments are applied to the dry cord, then slightly moisten the cord

with water. This will help prevent its sticking to the sulcular tissue upon

removal.

If inflammation is present and seepage cannot be controlled, remove the cord

and repeat the above steps or use electrosection.

If inflammation is present and seepage cannot be controlled, then verify the

temporary restoration's fit and surface texture. Cement the provisional and

allow gingival healing before making another impression.

Observe the finish line. If you cannot see all areas of the finish line, repeat

the steps. If you can see at least 0.5 mm below the finish line, continue.

Leave cord(s) in place for 8 to 10 minutes. While the cord is displacing the

gingiva, it is compressing the blood vessels.

Prolonged retention can cause belated gingival sloughing and migration.

Block out undercuts around the teeth in the arch with red rope wax. The

tissue is dry but not dehydrated when applying the wax.

This facilitates impression removal, reduces distortion, and averts tearing.

Prepare syringe:

Lubricate syringe "0" -ring lightly. Trim tip. Open orifice to increase rate of

flow or close orifice to decrease rate of flow. Orifice must be smooth and

without cracks.

Measure arch length of tray to guide in dispensing the amount of elastomer

RULE:

Dispense one times the length of the tray for the low-viscosity elastomer

(syringable).

Making final impression:

Page 4: IMPRESSION TECHNIQUES OF FPD

Choose a large mixing pad, approximately 6 by 8 inches. Some brands of

impression material have mixing devices that resemble a caulking gun and

do not need a mixing pad. These dispense material by placing a replaceable

cartridge and mixing tip into the gun and squeezing the trigger to express the

material.

Choose a spatula that is large enough to pick up the mixed impression

material, yet sufficiently pliable to mix the material against the pad.

Place the pad near the edge of a table about waist high.

Mix the low-viscosity impression material according to manufacturer's

instructions.

First use a circular motion combining the two strands, then a figure eight

motion to blend and flatten the mixture onto the mixing pad. Flattening the

mixture and limiting the number of times you lift the spatula from the pad

reduces the number of voids in the mixture.

Mix according to manufacturer's instructions to obtain a streak-free mixture

in less than 1 minute.

Load the syringe by holding it at a slight angle while scraping the pad. Wipe

off excess at the tip with a paper towel, screw on the tip, and insert the

plunger. Express a small amount before handing to the dentist.

While the plunger is inserted into the syringe, the dentist initiates cord

removal.

NOTE:

If using stock tray with single mix method, refer to section on stock tray, and

then continue.

Grasp the 2 mm excess of cord with forceps and slowly tease the top cord

toward the occlusal with a gentle continuous pressure. Repeat for all cords.

Evaluate the retraction site for seepage, hemorrhage, or debris.

Page 5: IMPRESSION TECHNIQUES OF FPD

Quickly blow away seepage with short bursts of compressed air or dry with

cotton pledgets.

If seepage cannot be controlled, Syringe inaccessible areas first, e. g., distal

lingual finish line.

Position the syringe so the elastomer is ahead of the tip's orifice

Insert tray:

For stock tray (putty wash) double mixing technique, insert the low-viscosity

impression material into the tray without overfilling the tray.

Fill the inside slightly less than the depth of the external borders.

Note that the excess flows to the back of the tongue or throat and causes

discomfort.

For stock tray (putty wash) single mixing technique, the unset high-viscosity

impression material should already be in the tray, and the preparations

syringed with low-viscosity impression material.

Spread the checks one at a time, first with the tray and then with an index

finger.

Position the tray over the arch. Seat from posterior to anterior, allowing the

excess to extrude anteriorly.

Apply force in a vertical direction until further seating is impossible.

Evaluate final position and adjust tray quickly if necessary.

Evaluate final impression:

Stabilize the tray and wait the minimum time as suggested by the

manufacturer to achieve the final set. Extended periods are usually

advocated by researchers.

Perform "clinical final set test".

Page 6: IMPRESSION TECHNIQUES OF FPD

Remove tray:

Insert two fingers under each side of the tray to break the seal.

Remove the tray parallel to the preparation(s) path of withdrawal and

transfer to assistant. This is crucial with cross arched impression.

Rinse impression with ambient water, and dry with short, small bursts of

compressed air.

Some elastomers are hydroscopic, so remove all the water.

Retraction cord(s) remaining in the impression material are removed

carefully. Check sulcus for residual impression material and remove any

debris and clean the oral cavity.

Evaluate set impression:

Elastomeric material should be present 0.5 mm beyond visible finish line.

Note presence of bur marks, the junction of smooth root surface, and

continuous finish line.

There should be no tray show-through in any areas of the impression, except

at tissue stops.

There should be no shiny smooth areas; if present, they suggest moisture

contamination.

There must be no voids present; if present, they suggest mixing problems or

contamination.

Disregard small voids in unimportant areas.

Review for tears (subtle undercuts to be "blocked out"). Polysulfides can

distort without tearing, but sometimes reveal excessive distortion by a

lightened colour.

There should be no thin areas leaving the finish line unsupported. These

areas distort under the weight of the stone.

Page 7: IMPRESSION TECHNIQUES OF FPD

Making working cast:

Position the dowels into the impression. Insert one extra dowel pin on either

side of the working dies. This ensures die removal despite errors during

sectioning.

Check dowel(s) position(s) in impression for parallelism and retention and -

add paper clips or orthodontic wire for retaining the second pour to the first.

The Pindex System allows immediate pouring of impression.

Pour first layer of stone. Wait for initial set of stone. Lubricate die areas.

Bead and box impression. Pour second layer of stone for the base.

Page 8: IMPRESSION TECHNIQUES OF FPD

CUSTOM TRAY

Synonyms: Acrylic tray

Mixing technique: Single

Advantages:

1. Less impression material is needed than with stock tray.

2. Because the trays are used only once, sterilization is not a problem.

3. A uniform thickness of impression material minimizes distortion resulting

from curing shrinkage.

4. Pre curing of the tray material is not required.

Disadvantages :

1. Construction of the custom tray is time consuming.

2. The tray must "age" for 24 hours to minimize further distortion.

3. The monomer may be a sensitizer for some personnel.

Technique:

Soak replicas of the diagnostic casts in slurry water for 10 minutes.

Paint a layer of tinfoil substitute (or petroleum jelly) on the cast as a

separating medium to prevent the resin from adhering to the cast.

Draw a pencil line on the cast as a guide in defining the tray extensions

Warm and adapt two sheets of base plate wax (total thickness, 2 mm) to the

cast.

NOTE:

For more rigid materials, polyethers and poly vinylsiloxanes, 3 mm is

required to facilitate removal from the mouth and removal of the replica cast.

Trim the excess wax to the pencil line with a knife.

Page 9: IMPRESSION TECHNIQUES OF FPD

Cover the wax with a thin tinfoil (or polyethylene) sheet to protect resin

from wax during the exothermic cure.

Remove wax to create four wide-spaced hard tissue stops at least 3 mm" and

located on non functional cusps. Stops may be placed on firm tissue as a last-

resort.

Measure monomer (liquid) and polymer (powder) according to the

manufacturer's recommended ratio.

Insert both (liquid first, then powder) into a suitable paper cup; most kits

contain cups.

Mix according to manufacturer's recommendations.

Wait until doughy stage is reached, not sticky to the touch.

Form dough patty into a flattened shape approximately 4 mm thick.

Adapt flattened patty to tin-foiled diagnostic cast. Trim excess to pencil line

while resin is still doughy. Use excess resin to form handle on the tray, this

will help in removal from the mouth.

Moisten the unset tray surfaces with monomer (liquid) before joining.

Observe exothermic stage of curing acrylic resin.

Wait for the final set according to manufacturer's instructions (approximately

15 minutes). Gently lift the tray from the cast. Remove the wax spacer with

the protector. Observe that all wax has been removed.

Trim and polish the tray using slow speed, continually checking for

excessive heating of the acrylic resin.

Store at room temperature for 24 hours before making impression to

minimize distortions.

The adhesive can also be placed now.

Gingival displacement and management

See section on stock tray

Page 10: IMPRESSION TECHNIQUES OF FPD

Prepare syringe:

See section on stock tray

Making final impression:

Select medium to high-viscosity elastomer to line the tray. Choose low-

viscosity elastomer for syringe preparations.

"Provide two large mixing pads, approximately 6 by 8 inches. Some brands

of impression material have mixing devices that resemble a caulking gun

that do not need a mixing pad or spatula. These work by inserting a

replaceable cartridge and mixing tip into the gun and squeezing the trigger to

express the material into a tray or directly into the syringe.

Obtain two spatulas that are shaped to manipulate the mixed impression

material and pliable enough to mix the material against the pad.

Place the pads near the edge of a table about waist high.

Mix the low-viscosity impression material according to manufacturer's

instructions. First use a circular motion combining the two strands, then a

figure eight motion to blend and flatten the mixture. Flattening the mixture

and limiting the number of times you lift the spatula from the pad reduces

the number of voids in the mixture.

Mix according to manufacturer's instructions, obtaining a streak-free mixture

in less than 1 minute.

Load the syringe by maintaining a slight angle while scraping the pad.

Wipe off excess at the tip with a paper towel, screw on the tip, and insert the

plunger. Express a small amount before handing to the dentist.

Mix the higher-viscosity impression material.

While the plunger is inserted into the syringe, the operator initiates cord

removal.

Grasp the 2 mm excess of cord with forceps and remove the top cord slowly

with a gentle continuous tug toward the occlusal. Do the same for all cords.

Page 11: IMPRESSION TECHNIQUES OF FPD

Evaluate tissue for seepage, hemorrhage, or debris.

Quickly blow away seepage with short bursts of compressed air or dry with

cotton pledgets.

If seepage is evident, see section on stock tray, Syringe inaccessible areas

first, i. e. distal lingual finish line.

Allow the elastomer to extrude ahead of the tip's orifice.

Insert high-viscosity impression material into tray without overfilling the

tray. Fill the inside slightly less than the depth of the outside borders.

Note that the excess flows to the back of the tongue or throat and causes

discomfort, and propels saliva under the tray causing bubbles.

The patient is seated in an upright position to avoid this.

Spread the cheeks one at a time, first with the tray and then with your index

finger.

Position the tray over the arch.

Seat from posterior to anterior, allowing excess to extrude in an anterior

direction.

Continue seating in a vertical direction until the tray stops prevent further

progress.

Evaluate final position and adjust tray quickly if necessary.

Evaluate final impression:

See section on stock tray.

Remove tray:

See section on stock tray.

Evaluate set impression:

See section on stock tray.

Page 12: IMPRESSION TECHNIQUES OF FPD

CLOSED BITE DOUBLE ARCH METHOD

Synonyms: Dual quad tray, double arch, triple tray, Accu-bite, closed mouth

impression

Minimum conditions:

1. The articulator must have a vertical dimension holding stop such as an

incisal pin or other metal-to-metal contact. If the articulator's design does

not provide for a positive stop, there must be sufficient natural teeth

remaining to maintain vertical dimension. This approach is limited to

single castings in patients with suitable interdigitation.

2. There should be sufficient space distal to the terminal tooth in the arch to

allow tray approximation.

Advantages:

The physical deformation of the mandible during opening is minimized.

The shifting of teeth occuring during maximum intercuspation is captured.

Less elastomeric impression material is needed so the patient is more

comfortable.

Less gagging may occur.

Disadvantages:

Tray is not rigid; depends on impression material for rigidity.

Is not a functionally generated technique, so it is limited to one casting per

quadrant.

The distribution of the impression material is not uniform.

Page 13: IMPRESSION TECHNIQUES OF FPD

Technique:

While waiting for anesthesia or after completion of tooth preparation.

Evaluate the fit of the tray in patient's mouth.

Position the tray's crossbar distal to last tooth in the arch. Instruct patient to

close the mouth. Observe the complete bilateral closure and the patient's

comfort.

Adjust the tray, select new tray size, change brand, or modify technique.

Practice until patient is familiar with tasks.

Gingival displacement and management:

See section on stock tray

Prepare syringe:

See section on stock tray.

Tray is inserted to determine the clearance laterally and distally.

Making final impression:

Choose a large mixing pad, approximately 6 by 8 inches. Some brands of

impression material have mixing devices resembling a caulking gun that do

not need a mixing pad.

These are activated by placing a replaceable cartridge and mixing tip into the

gun and squeezing the trigger thus expressing the material.

Select a spatula that is sufficiently large to elevate the mixed impression

material, yet pliable enough to mix the material against the pad. Place the

pad near the edge of a table about waist high.

Mix the low-viscosity impression material according to manufacturer's

instructions. First use a circular motion combining the two strands, then a

smooth figure eight motion to blend and flatten the mixture onto the mixing

Page 14: IMPRESSION TECHNIQUES OF FPD

pad. Flatten the mixture and limit the lifts of the spatula from the pad to

reduce the number of voids in the mixture.

Mix according to manufacturer's instructions to obtain a streak-free mixture

within 1 minute.

Load the syringe by maintaining it at a slight angle while scraping the pad.

Wipe off excess at the tip with a paper towel, screw on the tip, and insert the

plunger. Express a small amount before handing to the dentist. While the

assistant is inserting the plunger into the syringe, initiate cord removal.

Grasp the 2 mm excess of cord with forceps and tease the top cord slowly

with a gentle continuous pressure toward the occlusal. Repeat for all cords.

Evaluate site for seepage, hemorrhage, or debris.

Quickly remove seepage with short bursts of compressed air or dry with

cotton pledgets.

If seepage is uncontrolled, see section on stock tray.

Syringe inaccessible areas first, i.e. distal lingual finish line; interproximal.

Allow the elastomer to extrude ahead of the tip's orifice.

Mix the high-viscosity elastomer and "overfill" bilaterally. Manually seat

tray on maxillary arch.

For quadrant trays, position the crossbar distal to the last tooth in that arch.

Instruct patient to slowly close mouth.

Evaluate complete closure by observing the interdigitation on the opposite

arch.

Secure patient's comfort.

Evaluate final impression:

Wait the time suggested by the manufacturer to achieve the final set, plus 2

minutes.

Perform clinical final set test.

Page 15: IMPRESSION TECHNIQUES OF FPD

Tray removal:

Instruct the patient to open. The impression adheres to one arch.

Place a finger on either side of the tray. Remove with equal pressure

bilaterally to minimize the distortion of the tray. Do not use the handle to

remove tray. Remove residual impression material in sulcus or interproximal

areas.

Rinse impression with ambient water, and dry with short bursts of

compressed air. Retraction cord(s) in the impression material is/are removed

carefully. Check sulcus for residual impression material.

Remove debris and clean the oral cavity.

Pour die:

Trim excess impression material with a surgical knife.

"Vibrate the die stone and overfill the prepared tooth. Position dowel pin and

allow stone to set. Place a bead of wax around the edges of the die to remove

undercuts.

Lubricate the dowel pin and die stone with separating media.

Making working cast(s) and attaching to articulator:

Box the impression.

Choose hinge articulator with incisal pin or vertical dimension stop

(Recommended for neutron occlusion and one uncomplicated casting)

Place sticky wax around circumference of tray. Cut a strip of boxing wax in

half length-wise. Soften the wax uniformly over a gas flame.

Adapt and box both upper and lower arches at one time. Seal the area at the

junction of boxing wax and tray to prevent the stone from entering the

opposite side of the impression.

Page 16: IMPRESSION TECHNIQUES OF FPD

Cut small openings to accommodate the articulator so that correct

positioning of the impression is possible.

Position the tray, bisecting the inter articulator distance from top to bottom,

parallel to the table top, and centered from side to side. Pour the opposing

side (side without dies) first and close articulator arm into unset stone.

Evaluate impression tray position and secure the dowel pins so they are not

interfacing with the closure of the articulator and on the working side. Wait

45 minutes for initial set of gypsum.

Lubricate the die(s) with a separating media. Pour prepared side (with die) of

impression with gypsum product.

Close articulator arms until incisal pin contacts the lower arm. Remove unset

stone around tip of dowel pin(s) to facilitate removal.

Place a rubber band around upper and lower arms of the articulator arm.

Wait 45 minutes.

Removing impression tray from articulator:

Remove rubber band and pull articulator arms apart slowly, separating the

casts from the impression tray.

Evaluate casts and separate die(s).

Page 17: IMPRESSION TECHNIQUES OF FPD

COPPER BAND TECHNIQUE

The copper tube or band is used to salvage an impression of multiple

preparations when there are only vague margins on one or two preparations that

are not adequately replicated in the impression. The patient's condition, the

extent of the aberration evaluated, and judgement determines whether the

copper band technique saves time or whether a remake of the original

impression is more appropriate.

The steps for a copper band impression of a single prepared tooth are:

Fitting copper band to preparation:

Select copper band diameter by trial and error by deforming the tubes to

semi ellipsoidal cross section and trying in.

Anneal selected tube by heating in flame and quenching in alcohol.

Mark approximate position of finish line with a sharp explorer tip.

Cut with scissors and smooth rough edges with carborundum stone.

Impression materials and techniques:

Evaluate fit; band should extend approximately1 mm beyond finish line and

produce minimal tissue blanching. Do not remove from preparation.

If fit is tight at finish line area, rock the tube gently from side to side. A

space between finish line and copper band approximating the width of an

explorer tip is optimum.

Cut orientation hole in top one-fifth of facial surface of tube.

Make compound plug:

Cover fingers with a light coat of petroleum jelly.

Gently heat red stick compound over a Bunsen burner flame; compress the

warm mass with the lubricated fingers.

Page 18: IMPRESSION TECHNIQUES OF FPD

Evaluate viscosity and temperature; reheat or temper in a warm water bath if

necessary.

Insert warm compound mass and fill approximately the top one-third of

copper tube.

Seat and orient band onto preparation. Compress excess into hand lightly

with lubricated finger.

NOTE:

The amount of compound is critical to the success of this step. The

compound should just touch the occlusal surface. Cool tube with water.

Using Backup towel clamp, grasp top one-fifth of copper band and remove

from mouth. Evaluate preparation side of band. Only part of the occlusal

surface should be impressed.

Relieve any excess by cutting. Slow speed with No. 6 or 8 carbide bur is

suggested. Stop frequently to air cool or blow away debris. Remove 0.2 mm

of compound from the impressed occlusal surface. This creates a space for

the heavy body polyvinylsiloxane.

Using a long shank No. 6 round carbide bur, drill a hole through the center

of the compound plug. This will decrease hydraulic pressure to facilitate

seating of the copper band.

Making impression:

Cut approximately four or five evenly distributed holes with a sharp No. 4 or

No. 6 round carbide 2 to 3 mm above the bottom of the copper tube. Be

careful not to heat the tube.

These holes will retain the polyvinylsiloxane impression material and

provide a suitable space at the finish line area. This additional space prevents

marginal tearing.

Page 19: IMPRESSION TECHNIQUES OF FPD

Coat the internal surface sparingly with adhesive. Spot the internal surface;

do not coat the entire area. The adhesive can occupy too much space in the

finish line areas.

Clean and isolate preparation.

Prepare the syringe tip by securing a hole size approximating the diameter of

the shank of a long shank bur.

NOTE:

Some poly vinylsiloxane impression systems have an auto mixing device to

facilitate the next two steps.

Mix 1 inch of heavy-viscosity, but not putty, elastomeric impression

material.

Inject the elastomeric into the copper band, filling the space completely from

the compound to copper band edge.

Position fingers on top edge of band, orient and seat customized copper tube.

Evaluate tube position; if incorrect, reposition.

Stabilize band and compress excess into plug’s hole with lubricated finger.

Note excess expressed at gingival area. Remove fingers; protect copper band

from movement and await final set.

Grasp top one-fifth of impression with sharp backup towel clamp and gently

remove from tooth.

Evaluating impression and making die: Evaluate impression; if the area

needed is accurately impressed, proceed. With a sharp surgical knife remove

excess elastomeric.

Using masking tape, box the impression and pour in die stone.

Trim die stone to form elongated tapered cylinder base for convenient

manipulation during wax up.

Page 20: IMPRESSION TECHNIQUES OF FPD

The defective areas can be relieved on the original full arch impression and

the waxing of the margin created from the copper band die and transferred to

the relieved die for adjustment of proximal contacts and occlusion.