02. Prelimin Impressions

7/29/2019 02. Prelimin Impressions

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Preliminary Edentulous Impressions


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Preliminary Edentulous Impressions

Preliminary impressions

needed for diagnostic casts for

making custom trays


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Custom Tray

Required to accurately register

moveable mucosa

Create seal for retention


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Stock Trays

Stock trays can result in

distortion and shortening of the

final denture flange


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Alginate Syringe Technique

Irreversible hydrocolloid

Ensures capture of critical

anatomy - sometimes missedwith just a tray


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Border Molding

Minimizes distortion of the

movable vestibular tissues

Displacement could lead todislodgment during function


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Irreversible Hydrocolloid Storage

Pre-weighed pouchesEasier dispensing

Minimizescontamination

Bulk materialStore in cool dry airtight

containers


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Irreversible Hydrocolloid Storage

Deteriorates if:Stored above 54C

Repeated openings Deterioration results in:

Thin mixtures

Reduced strength

Permanent deformation


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Tray Selection

5 mm of clearance

with soft tissues

Hydrocolloid requires

bulk for accuracy,

strength and stability


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Tray Selection

Maxillary trays should extend

slightly beyond vibrating line

Mandibular trays should coverthe retromolar pads


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Tray Selection

Sto-K edentulous trays

Short flanges, so dont distort

vestibule


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Tray Modification

Trays can be modified with

compound to extend the tray if

desired


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Irreversible Hydrocolloid Syringe Technique

Critical anatomy registrationRetromylohyoid area

Hamular notchesRetrozygomal area


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Patient Preparation

Practice placing tray

Rotate into place


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Patient Preparation

Dry the mucosaDry the maxilla with folded gauze

Pack 3 gauze in mandibleDont let patient close


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Mark Vibrating Line

Prior to making

preliminary & final

impressions

Fovea should not be used


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Vibrating Line

If denture terminates anteriorly,

poor seal

If terminates posteriorly, soft palatemovement may cause it to dislodge

Denture may be unretentive and/or

uncomfortable


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Locate & Mark the Hamular Notch

Posterior border of a

complete denture

Between the bony

tuberosity & hamulus


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Locate & Mark Hamular Notch

Denture border must terminate on

soft displaceable tissue

Provides comfort and retention

Notch may be posterior to

depression in soft tissue


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Locate & Mark the Hamular Notch

Use the head of a

mirror, to palpate

the notch Mark with an

indelible marker

HamularNotch

Tuberosity

mucosa soft palate

mouth mirror

visual determination ofhamular notch

actual positionhamular notch


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Locate Posterior Border of Hard Palate

Ensure the denture

terminates

posteriorly bypalpating


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Indelible Marks Prior to Impression

Transfer to the impression and

cast when it is poured

Eliminates error

Tissue should be relatively dry

to be most effective


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Syringe Preparation

12 cc disposable syringe

Cut off the tip where it

begins to curve 5 mm orifice


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Plunger Preparation

Vaseline plunger

Ease of extruding material

Use:Uncontaminated bowl,

spatula

Regular set alginate


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Measuring Powder

Fluff (shake) the powder,

measure, tap and flatten

the scoop with powder Use three scoops for

syringe impressions


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Mixing

Assistant mixes for at least

45 seconds

Smooth creamy homologousmixture that glistens

Not granular or lumpy


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Syringe Loading

The assistant loads

the syringe nearly

full from the backand inserts plunger


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Syringe Technique

Syringe a broad rope into

the vestibule

Begin at the posterior Move quickly toward

anterior

Fill the vestibule to labial

frenum


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Cheek Retraction

Use a mirror,

instead of a

finger

Provides better

visibility, more

maneuverability


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Maxillary Impressions

Begin opposite the

tuberosity

Inject until alginate is

seen in the hamular notch

before moving forward


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Mandibular Impressions

Start with the buccal

vestibule adjacent

retromolar pad

Move forward to the labial

frenum

Repeat on the opposite side


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Lingual Vestibule

Roll syringe tip under tongue

Inject into retromylohyoid

space until alginate appears

between tongue & ridge

Move anteriorly, filling to

lingual frenum

Repeat on the opposite side


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Deep Palatal Vaults

Material can be syringed into the

palate

Smooth with a finger, or voids

may occur


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Partially Edentulous

Syringe a small amount of

hydrocolloid on the

occlusal surfaces Force into the occlusal

surfaces with finger


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Cleaning the Syringe


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Preliminary Impressions

The assistant loads the tray

while the clinician is

syringing Place the anterior portion of

the tray first, then seat the

posterior of the tray


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Less gagging if the patient is lying

down

Tongue position avoids gagging

Mold the vestibular area

Pull on the cheeks and lips to

activate muscles and frena


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Support the tray

during setting - do

not leave thepatient

Movement causes

distortion


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Use water to break peripheral seal

Remove quickly (to avoid

permanent deformation)

Evaluate impression

Pour within 12 minutes


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Rinse thoroughly with water

Gently shake to remove excess

water


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Spray with disinfectant to coat

all surfaces, and seal in a bagfor ten minutes


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Sample Impressions


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Sample Impressions


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Syringe Technique Problems

Vestibular material may not

join the tray material

Saliva contaminationInsufficient material


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Syringe Technique Problems

Omitting plunger

lubrication may make it

difficult to express the

alginate

Trapping tongue under the

tray will result in

underextension of thelingual vestibule

Problems with Syringe


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Problems with Syringe

Technique

Severe gaggers poor tolerance

for intraoral motion

Use traditional technique


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Diagnostic Casts


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Pouring a Model

Weighing powder,

measure water

Vacuum mix (less time,stronger cast)

Use a two pour

technique


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Two Pour Technique


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Pouring a Model

Modulate speed of pouring by

tilting back and forth or pressing

the tray more firmly ontovibrator


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Pouring a Model

Model moist during trimming

Soak in slurry water, or soak

with base of cast in water


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Pouring a Model

Casts should be a minimum of 12

mm (.5 inch) in thinnest part

Separate the alginate impressionfrom the stone cast after 45

minutes


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Trimming Casts

Trim the base on the

model trimmer parallel

to the residual ridges

Leave the vestibular

reflection intact for

making a custom tray


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Trimming Casts

All anatomical surfaces

should be included with

minimum voids

02. Prelimin Impressions

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