Impression and Tissue Management Flashcards by Rodwan Halimi

Why are impressions taken?

Restorations that can fit exactly are:

More efficient and faster working

Aid periodontal prophylaxis and prevent caries

Are aesthetic

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What is the aim of an impression?

Produce a dimensionally stable “negative” that can serve as the mould for a model or be scanned

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What are the objectives of a definitive secondary impression?

Exact duplication of the prepared and uncut tooth beyond the preparation to allow evaluation of location and configuration of finishing line

Duplicate other teeth and soft tissue to permit proper articulation of the cast and controuing the restoration

Must be free of bubbles specially at finishing line and prepared surface

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What are the prerequisites of a impression/scanning?

Tissue management

Gingival tissue displacement if needed

Saliva control

Adequate impression/scanning technique

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What can of tissue management needs to be done for impression/scanning?

Careful preparation (Hard tissue/soft tissue)

Atraumatic procedure

Well-contoured provisional restoration

Adequate oral hygiene

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What should the tooth preparation look like for adequate tissue management?

Supragingival margins is possible

Minimally subgingival or intracrevicular if not possible to be supragingival

Well-defined, smooth and continuous margins

Well-finished and tidy preparation

Atraumatic to gingival tissues

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What is the maximal subgingival depth allowed if preparation is subgingival?

Maximum around 0.7mm

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Why are subgingival margins such a bad idea?

Defective margins

Inaccurate fit

Roughness of the tooth-restoration interface

Improper crown contour

Violation of the connective tissue attachment

Greater pathogenicity of the subgingival dental plaque

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Why is the gingiva displaced for a crown prep?

Enlargement of the gingival sulcus

Tissue deflection horizontally and vertically to displace the margin and root surface. (Finishing line for the restoration and development of adequate emergence profile)

Control of gingival bleeding and exudate

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What are the methods of gingival displacement?

Mechanical displacement:

Retraction cord

Copper band

Surgical widening:

Electrosurgery

Laser

Chemicals:

Astringent (Aluminum chloride, ferric sulfate)

Adrenaline (Transient ischaemia and epithelial tissue shrinkage)

Combined:

Retraction cord + Chemical

Expasyl (Kerr)

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How does the copper band work?

It is placed around the tooth within the gingival sulcus thus spreading the sulcus outwards

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How does the retraction cord work?

Cord is packed into the sulcus stretching the circumferential periodontal fibers 0.3 - 0.4mm

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What are the types of retraction cords?

Braided

Twisted

Knitted

Medicated and nonmedicated

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How is a retraction cord placed?

Using a cord packers (Can be serated or non-serrated)

Using 2 instruments it is pushed in

Leave the cords in place 3 to 5 minutes.

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How many cords are placed into the gingival sulcus?

Can be a single or double cord

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What is the function of the double cord?

Primary cord is important for vertical retraction and secondary cord for horizontal displacement

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What are the indications for a single cord?

Shallow sulcus

Thin periodontium

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What are the indications of double cord?

Thick periodontium

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What are the advantages and disadvantages of single cord?

Advantages:

Least traumatic

Little potential for gingival recession

Disadvantages:

Haemorrhage and exudate

What are the advantages and disadvantages of using double cord?

Advantages:

Control of bleeding

Excellent lateral displacement

Disadvantages:

Time consuming

Potentially traumatic

Least predictable gingival response

How is surgical widening done?

Remove the inner epithelial lining to get better access to the finish line and control haemorrhage

What should practitioners be careful of when using surgical widening?

Risk of permanent damage to gingiva (recession)

Avoid for thin gingiva

What are the methods of surgical widening?

Electrosurgery and laser

What are the advantages and disadvantages of surgical widening with electrosurgery?

Advantages:

Lower cost than lasers

Electrosurgery cuts extremely rapidly when compared to a diode laser

When on the proper setting homeostasis is almost immediate

After curring the wound is nearly painless

What are the disadvantages of surgical widening with electrosurgery?

Contraindicated in patients with any electrical device You must anaesthetize patients Burning smell Risk of overcutting Because of high heat production while cutting, electrosurgery should not be used around implants

What are the advantages of surgical widening with laser?

Minimal LA needed Does not harm dental tissue Can be used around implants Can be used around full metal, PFM crowns, amalgam or gold alloy restorations

What are the disadvantages of surgical widening with laser?

Cost Cuts much slower than electrosurgery Cutting large pieces of soft tissue is time consuming Danger of laser beam

What are the issues with chemical displacement?

Causing transient ischaemia Shrinkage of gingival tissues Reduce flow of gingival fluids Adrenaline can cause tachycardia so other medications are preferred

What are some examples of chemical displacement agents?

Aluminum chloride Aluminum sulfate Potassium sulfate Ferric chloride Ferric sulfate

What combination is commonly used for tissue retraction?

Retraction chord + astringents

What is contained in expasyl?

Combination of aluminum chloride and kaolin

What is contained in traxodent?

Aluminum chloride paste

How is saliva control achieved?

Absorbents block salivary ducts (eg cotton rolls and absorbing cards) Saliva evacuator LA (Controls blood and saliva) Anticholinergic meds

How must gingival tissues be treated to achieve a good impression? Why is this important?

Gingival health must be achieved before embarking on definitive impressions If gingiva isn't healthy it is impossible to prepare a predictable intracrevicular margin. Impressions are difficult due to uncontrollable haemorrhage As soon as periodontal resolution occurs there will be recession

What materials are used for impressions?

Monophase (medium body) = polyether Multiphase (heavy body and light body) = Polyvinyl siloxane

What are the important keys to correct impression technique?

Adequate manipulation of the material Proper thickness of the material Proper pressure applying during impression making

What is the purpose of an intraoral custom tray try in?

Check for clearance and comfort To adjust if required

How long must the adhesive be applied to impression tray before the impression?

15 minutes

What are the steps to gingival displacement with retraction cord and astringent?

Isolate prepared teeth Cut sufficient cord length Soak cord in astringent Loop the cord around the tooth and gently insert it into the sulcus Avoid overpacking Dry the teeth (do not dessicate) Evaluation (Visualize all the margins of the preparation, no soft tissue folding on the cord)

How is impression material mixed?

If using "cartridge" system extrude a little impression material at first ensuring an even mix of material and no blockage in the cartridge Addition silicone: base and catalyst are mixed

How much base and catalyst should be used for addition silicone?

Equal amounts of base and catalyst

How should the tray be loaded?

Load tray such that impression material is slightly below the lip of the tray Apply light body material around the prep and load the tray with heavy body material Light bodied material should be applied intraorally after 10 - 15 seconds of removing cord and assessing gingival tissues Inject the material slowly around the preparation margins. The tip shold follow the material and continue in one direction staying close to the sulcus Once the sulcus is filled continue over the rest of the tooth Gently air blow the material

How should tray be inserted?

Position the tray first into the mouth Clear lips from the tray Using one continuous motion seat tray until resistance stops

How should the tray be removed?

Hold the tray in the mouth until the impresison is set and remove in one fluid movement Optimum removal of impression tray for upper jaw is to loosen tray on opposing side Optimum removal of impression from lower jaw is loosening tray on prep side. Finger and air stream should be used together to loosen impression

What should be inspected after taking an impression?

All gingival margins should be clear and defined Uniform layer of material Detailed with accurate occlusal surfaces Distal surfaces of molars are captured

What should not be present on a successful impression?

No bubbles, voids, thin walls, shifts, or double imprints that compomise dental anatomy.