Chapter 46 Flashcards
Three classifications of impressions
- Preliminary
- Final
- Occlusal (bite) registration
Five things preliminary impressions are used for
– Diagnostic models
– Custom trays
– Provisional coverage(temporary fixed bridge or crown)
– Orthodontic appliances
– Pre-treatment and post treatment records
Impression trays must be sufficiently rigid to:
– Carry the impression girl into the oral cavity
– Hold the material close to the teeth
– Avoid breaking during the removal of the impression
-Prevent wrapping the complete impression
The three ways Impression trays are supplied:
Quadrant tray – only covers one quadrant at a time
Sectional tray – only covers the anterior teeth
Full arch tray – covers the whole arch
Four things the correct size of the tray must accomplish:
– Comfortable for the patient
– Extend slightly beyond the facial services of the teeth
-Extends approximately 2-3 mm on the third molar, retromolar, or tuberosity area of the arch
-is sufficiently deep enough to allow the material 2-3 mm between the tray and the incisal or occlusal edges of the teeth
Two types of impression trays
Stock trays and custom trays
Three types of custom trays
- acrylic resin custom tray
- light cured resin custom tray
- thermoplastic custom tray
Three ways Alginate can be purchased
Containers, pre-measured packaging and Bulk
Water and powder ratios for impression material
ADULT: mandibular 2 water 2 powder
ADULT: maxillary 3 water 3 powder
CHILD: mandibular 2 water 2 powder or 1 water 1 powder
CHILD: maxillary 2 water 2 powder
ADULT XLARGE ARCH: mandibular 3 water 3 powder
ADULT XLARGE ARCH: maxillary 4 water 4 powder
Explaining the procedure to patient
Breathe through your nose No taste or smell Cold to the touch Raise hand if you need anything Take one to two minutes to set
Evaluating an Alginate impression
- impression should be centred
- complete “peripheral rolls” which includes the vestibular areas
- free of tear and voids
- Sharp anatomical portions of all teeth
- Retromolar pads and tuberosites are reproduced
- Hard palate is reproduced ( maxillary)
3 compartments of conditioning bath
- Liquefying
- storage
- Tempering
3 different forms of elastomeric materials
- Light bodied
- Regular bodied
- Heavy bodied
Elastomeric materials are supplied in 3 different ways
- Paste system (tube) base and catalyst
- Cartridge base and catalyst
- Putty ( containers)
A bite registration with an elastomeric material provides the lab tech and dentist the following benefits
- Material is fast setting
- Paste has no odour or taste to the patient
- gains dimensional stability over time
- Convenient to use
Tray set up
- Mirror
- Alginate
- water
- water measure
- mixing bowl
- spatulas
- impression tray
- utility wax
- Baggie
- paper towel
- mouthwash (Dixie cup)
- air/Wyler syringe
- saliva ejector
- Pts mirror
- PPEs
- Pts glasses
- bib
- bib clips
- chart
Impressions
Impressions are negative reproduction of those structures. Once an impression is poured with plaster or stone it becomes a positive.
Perforated stock trays
Most commonly used stock tray because the material has an opportunity to ooze out instead of going into the patients mouth
Final Impression are used for
Produce the most accurate reproduction of the patients teeth and surrounding tissues
Essential info needed to create indirect restoration such as fixed bridges, crowns, partials, full dentures and implants
Bite registration are used:
Produce a reproduction of the occlusal relationship of the maxillary and mandibular teeth when the mouth is closed. Provides an accurate registration of the patients centric relationship between the max and the man arches for the the dentist or technician.
Impression trays
Used to hold the material for taking the impressions.
Perforated trays
Most commonly used stock trays because the material has an opportunity to ooze out instead of going into the patients mouth. Have a mechanical lock that is why the material is able to stay in the tray.
Quadrant or sectional mesh tray
Used for final impressions. Eliminates the bite registration portion of the procedure because it does both at the same time.
Custom trays
Used for a more precise impression when needed. Called a final impression.
Stock trays
Used on dexter and ourselves to take preliminary impression (first)
Tray adhesives
Used when the use of a smooth tray is recommended (non perforated) to try and create a mechanical lock.
Hydrocolloid materials
Hydro (water) colloid (gel) used to obtain a preliminary impression.
Irreversible Hydrocolloid materials
Means you cannot bring them back to their original state ( alginate or kromopan)
Alginate
Should be poured up with stone or plaster within 1 hour. Most widely used for preliminary impressions
Kromopan
Should be poured up with stone or plaster within 100 hours
Reasons to use fast set
Patient with a severe gag reflex
Setting time
Room temp water is the best when mixing Alginate or kromopan. Colder water will give you more time with the material and setting while warm water will give you less time with the material but is good if you don’t have fast set material available.
Edentulous
Means no teeth.
Reversible Hydrocolloid
Like ice cream
Reversible means you can bring it back to original state
Not used often today it need to go through a process to bring it back to its original state. Conditioning bath is used.
Four types of elastomeric materials
Polysulfide
Polyether
Silicone
Polysiloxane
Polysulfide
Available in light bodied, regular and heavy bodied
Two paste system
Disadvantages: strong odour and stains clothing
Long working and sitting times
Flexible
Polyether
Better mechanical properties than polysulfide Less dimensional change then silicone Includes a thinner Two-paste system or cartridge Equal length not equal amount
Silicone
Odour free, non-staining, easy to mix
Less deformation than polysulfide
Superior dimensional stability
Base is paste, catalyst is a liquid ,cartridges or putty
polysiloxane
High dimensional stability Low tear resistance No taste, no odor Light bodied,regular and heavy bodied Cartridges are putty
Acceptable maxillary impression the 6 criteria
- impression tray is centred over the central and lateral incisors
- tray is seated for accurate representation of the heigh /depth of the vestibule and surrounding tissues
- Impression is free from tears or voids in the soft tissues
- sharp anatomic detail of the teeth
- palate is reproduced
- tuberosities are reproduced
Acceptable mandibular impression the five criteria
- impression tray centred over the central and lateral incisors
- tray is seated for accurate representation of the height/depth of the vestibule and surrounding tissues
- impression is free from tears or voids in the soft tissues
- sharp anatomical detail of teeth
- retromolar area is reproduced
Elastomeric materials
Used when a more precise impression is needed. Are self curing and supplied as a base and catalyst.
Occlusal bite registration material
Procedure is done to show that you’re closer relationship between the maxillary and mandibular teeth. Most popular materials used for bite registration is polysiloxane (blu-bite) and wax bite
Light bodied
Used because of its ability to flow into and around the details of the prepared teeth.
Can be place with a syringe or with a tip from the auto mix cartridge with the extruder gun.
Regular and heavy bodied materials
Referred to a tree type materials.
Much thicker than light bodied impression materials and use to fill the tray.
Initial set
Stiffening of the paste without the appearance of elastic properties. Material may be manipulated only during this stage.
Final set
Begins with the appearance of elasticity and proceeds of elastic properties and proceed through gradual change to a solid rubbery mass.
Final cure
Occurs within 1 to 24 hours.
Only slight dimensional change is noted
Three Curing stages
Initial set
Final set
Final cure
