Impressions and Impression Materials Flashcards
What are the aims of definitive, secondary impressions?
Exact duplication of the prepared and uncut tooth beyond preparation to allow evaluation of location and configuration of finishing line
Duplicate other teeth and soft tissue t permit proper articulation of the cast and contouring the restoration
Must be free of bubbles specially at finishing line and prepared surfaces. (bubbles whether small or large make it necessary to repeat the impression)
Work flow for crowns:
Preparation -> Impression or scanning -> Fabrication of models which can be cast and scanned.
Casting -> Manual finishing -> Veneering/polishing -> insert in the mouth
Scanning -> Milling -> Sintering ->
What are the prerequisites of impressions/scanning?
Tissue management
GIngival tissue displacement
Saliva control
Adequate impression/scanning technique
How is tissue management done?
Careful preparation (Hard tissue and soft tissue)
Atraumatic procedure
Well-contoured provisional restoration
Adequate oral hygiene
How should the tooth be prepared?
Supragingival margins if possible
Minimally subgingival or intracrevicular if supragingival not possible
Well-defined, smooth, continuous margins
What are the causes of bad crown preparations?
Defective margins
Inaccurate fit
Roughness of the tooth-restoration surface
Improper crown contour
Violation of the connective tissue attachment
How is gingival displacement achieved for impression?
Most common technique is the retraction cord and copper band (old school for impression)
Surgical widening (Electrosurgery or laser)
Chemicals (Astringent: Aluminum chloride, ferric sulfate)
How is cord inserted into gingival sulcus?
Cord is packed into the sulcus stretching the circumferential periodontal fibers
What are the types of retraction cords?
Braided
Knitted
Twisted
Medicated and nonmedicated
What instruments are used to place a retraction cord?
Serrated and non-serrated packers.
Sometimes both instruments can be used.
What is the difference between single and double cord techniques?
Single cord can be used or double cord. Leave around 3 to 5 minutes before taking impression soft tissue needs time to adapt to the new shape.
What are the indications for a retraction cord?
Shallow sulcus
Thin periodontium
What are the advantages and disadvantages of the single cord?
Least traumatic
little potential for gingival recession
Disadvantages
Haemorrhage and exudate
What are the advantages and disadvantages of the double cord?
Control of bleeding
Excellent lateral displacement
Dis
Time consuming’
Potentially traumatic
What are the advantages and disavantages of electrosurgery
ADv:
Lower cost than lasers
Electrosurgercy cuts rapidle when compared to a laser
When on the proper setting haemostasis is immediate
After cutting the wound is nearly painless.
Disadvanatages
COntraindicated in patients with any electrical device
Patient must be anaesthetied
Burning smell
Risk of overcutting
Because of high heat production it cannot be used around implants.
