BiomatII- Final Impressions

8/8/2019 BiomatII- Final Impressions

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TUFTS UNIVERSITY SCHOOL OF

DENTAL MEDICINE

Tissue Management and

Impression Making

Ekaterini Antonellou D.D.S.

Division of Prosthodontics

Department of Prosthodontics and

Operative Dentistry


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After tooth preparation and temporization , we

should make a final impression in order to fabricate

a restoration

Impression= Negative likeness of the teeth

and the surrounding structures.

It is the link between the prepared teeth and

the cast on which we make the crown.


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GOALS FOR A FINAL IMPRESSION

Accurate

Detailed No voids


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PROPERTIES OF IMPRESSION

MATERIALS

Elasticity/rigidity -

Flow-

Tear strength-

Hydrophilic- material to tolerate moisture in an impression site

Accuracy/Dimensional stability- Working and setting time

Ease of manipulation

Cost effectiveness


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Irreversible hydrocolloid(alginate)

Used for diagnostic impressions andremovable dentures and partials

Advantages : - Rapid set

- Straightforward technique- Low cost

Disadvantages:- Poor accuracy and surface

detailPrecautions: - Pour immediately


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Reversible hydrocolloid (agar)

Used for multiple preparations or with problemswith moisture

Advantages : - Rapid set

- Low cost of actual materialDisadvantages: - Low tear resistance

- Low stability

- Equipment needed- Special trays needed

Precautions: - Pour immediately

- Use only with stone


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Polysulfide Polymer

Currently used mostly for removable dentures and partials Advantages : - High tear strength

- Easier to pour than otherelastomers

- Low cost

Disadvantages: - Messy- Unpleasant odor

- Long setting time

- Stability only fair

- Humidity and temperature reduce

working time

Precautions: - Pour within 1 hour

- Use of a custom tray to minimizethe contraction of polysulfide polymerization


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Condensation silicone

Used mostly for lab procedures

Advantages : - Relative short setting time

Disadvantages:- Poor wetting

- By products of polymerizationreaction are alcohol and water. Asa result , evaporation from the setmaterial causes dimensional

stabilityPrecautions: - Caution to avoid bubbles when

pouring


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Polyether (Impregum)

Used for most impressions ,except for very long and thin teeth

Advantages : - Dimensional stability (can be poured morethan once ,even the next day)

- Accuracy

- Low polymerization shrinkage

- Relatively short setting time- Automix available(pentamix machine)

Disadvantages:- Set material very stiff

- Absorption of water (should bestored dry)

Precautions: - Care not to break the teeth whenseparating the cast

- Block undercuts

- Care for perio involved teeth


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Addition silicone(Poly-Vinyl-siloxane)

Used for most impressions

Advantages : - Great dimensional stability (can be poured

more than once ,even the next day)- Accuracy

- Very short setting time

- Automix available

Disadvantages:- Hydrophobic

- Poor wetting-Some materials release Hydrogen .

Newer materials contain scavengers to

prevent the release of gasPrecautions: - Care to avoid bubbles when pouring

- Setting inhibition for some putties by latexgloves


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Tissue Health

Control of periodontal disease

Proper contour, margins and surface of

provisional restoration Oral hygiene

Use of Chlorhexidine (Peridex or Periogard)


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Saliva control

Use of cotton rolls and dry-angles to cover

the salivary ducts

Use of saliva evacuators Use of local anesthesia

Prescription of anticholinergics e.g. atropine

or pilocarpine


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Displacement of gingival tissues

Mechanical displacement with non-impregnated

cord.It is better if it is braided(Gingibraid, Van R)orknitted(Ultrapak ,Ultradent)

Chemically impregnated cord in anastrigent(Hemodent) . They contain aluminum oriron salts that cause ischemia. Aluminum chlorideand ferric sulfate are suitable because they cause

minimum tissue damage. Preimpregnated cords with epinephrine should be

used with caution


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The inner epithelial lining of the gingival sulcus is

removed

Access for a subgingival crown margin

Control of postsurgical hemorrhage

Passage of a high-frequency current through the

tissue from a large electrode to a small one. At

the small electrode the current induces rapidlocalized polarity changes that cause cell


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Electrosurgery

Profound local anesthesia is needed

Not suitable on thin attached gingiva

It should not be used with metal instruments The electrode should not touch any metallic

restoration (can cause pulp damage)

It should not be used on or near patientswith cardiac pacemaker or insulin pump


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Disinfection

Glutaraldehyde 2% 10 min soak (not for

polyether)

Iodophor (1:213 dilution)

Chlorine compounds (1:10 dilution of

commercial bleach)


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Final steps

Re-evaluation of the final impression

Interocclusal record Shade selection


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BiomatII- Final Impressions

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