Impression and Tissue Management Flashcards
Why are impressions taken?
Restorations that can fit exactly are:
More efficient and faster working
Aid periodontal prophylaxis and prevent caries
Are aesthetic
What is the aim of an impression?
Produce a dimensionally stable “negative” that can serve as the mould for a model or be scanned
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
What are the prerequisites of a impression/scanning?
Tissue management
Gingival tissue displacement if needed
Saliva control
Adequate impression/scanning technique
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
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
What is the maximal subgingival depth allowed if preparation is subgingival?
Maximum around 0.7mm
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
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
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)
How does the copper band work?
It is placed around the tooth within the gingival sulcus thus spreading the sulcus outwards
How does the retraction cord work?
Cord is packed into the sulcus stretching the circumferential periodontal fibers 0.3 - 0.4mm
What are the types of retraction cords?
Braided
Twisted
Knitted
Medicated and nonmedicated
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.
How many cords are placed into the gingival sulcus?
Can be a single or double cord
What is the function of the double cord?
Primary cord is important for vertical retraction and secondary cord for horizontal displacement
What are the indications for a single cord?
Shallow sulcus
Thin periodontium
What are the indications of double cord?
Thick periodontium
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.
