Chapter 46 Flashcards
3 classifications of impressions
Preliminary
Final
Occlusal (bite) registration
Negative
Impressions
Positive
After the impression is poured up it becomes positive
Preliminary impressions are used for:
Diagnostic models Custom trays Provisional coverage Orthodontic appliances Pre treatment and post treatment records
Final impressions are used for:
They produce the most accurate reproduction of the patient’s teeth and surrounding tissues. It provides the dentist or the lab tech the essential information needed to create the indirect restorations such as fixed bridges,crowns ,partials ,full dentures and implants
Bite registration are used for:
To produce a reproduction of the occlusal relationship of the maxillary and mandibular teeth when the mouth is occluded or closed
Impression trays:
- Carry the impression material into the oral cavity
- Hold the material close to the teeth
- Avoid breaking during the removal of the impression
- Prevent warping the completed impression
Three types of impression trays
Quadrant tray
Sectional tray
Full arch tray
Quadrant or sectional mesh trays are used for final impressions. When using these type of trays you eliminate the bite registration portion of the procedure because it does both at the same time
The correct tray must accomplish the following:
- Comfortable for the patient
- Extends slightly beyond the facial surfaces of the teeth
- Extends approximately 2 to 3 mm beyond the third molar, retromolar or tuberosity area of the arch
- Is sufficiently deep enough to allow the material 2 to 3 mm between the incisal or occlusal all of the teeth
Stock trays
What we use on dexter and ourselves to take preliminary impressions .
Custom tray
Used when a more precise impression is needed and we call that a final impression
Types of custom trays
Acrylic resin custom tray
Light cured resin custom tray
Thermo plastic custom tray
Tray adhesives
Used when the use of a smooth tray is recommended to try and create a mechanical lock
Hydrocolloid materials
Used to obtain a preliminary impression. One exception to the rule is a final impression can be taken for partial or full dentures. Alginate or Kromopan pan cannot be brought back to the original state
Packaging and storage for alginate
Containers
Pre measured packaging
Bulk
Shelf like is approx one year
Time for pouring up impressions
Alginate, within one hour
Kromopan , within 100 hours
Two types of setting
Normal set : working time 2 mins, setting time 4.5 mins
Fast set: working time 1.25 mins, and setting time 1-2 mins
Reason to use the fast set
Patient with a severe gag reflex
Operator working alone should use the regular set as it gives them more time to place the impression tray into the patient’s mouth and it also gives them more time to mix the material
Altering the setting time
Room temperature water is the best when mixing Alginate or kromopan . Cooler water will give a bit more time before it sets and warmer water will go faster
Water and powder ratios
Adult man 2 w and 2 p
Adult max 3 w and 3p
Child man 2w and 2p or 1w and 1p
Child max 2w and 2p
Large adult man 3w 3p
Large adult max 4w 4p
Explain to patient what the impression will be like
Will feel cool No taste or smell Breathe through your nose Use left hand if you need anything 1-2 minutes to set
Evaluating and alginate impression
- Centered
- Includes the vestibular areas
- Free from tears and voids
- Sharp anatomical detail of all the teeth
- The retromolar pads are reproduced
- The hard pallet is reproduced
Edentulous
Means no teeth
Reversible hydrocolloid
Reversible means that you can bring it back to its original state. This type of material is not used often today as it needs to go through a process to bring the material back. A conditioning bath if used
