A study cast is a
Permanent record of a patient's present condition; missing teeth, anomalies in size, shape or number, rotation, shifting, tilting, drifting
The mandibular impression should be taken
First
The maxillary impression should be taken
Second
What materials and equipment/armamentarium should be selected for an impression?
Patient bib, towel and mouth rinse
Appropriate impression tray sizes; cleaned and sterilized
Clean, dry mixing bowl
Spatula, clean, dry and stiff with rounded end
Saliva ejector
Dental materials - Utility wax, alginate, measuring devices for both powder a
What dental materials are needed for taking an impression?
Utility wax
Alginate
Measuring devices for both water and powder
Why is it so important for the operator to wear a mask when taking am impression?
Prevents inhalation of powders; dangerous
How should the patient's head be when taking an impression?
Upright and stable
How is the patient prepared for taking an impression?
Review the medical history/ antibiotic premedication
Explain procedure to patient and the need for it
Position patient - head upright and stable
Remove any removable appliances - in container
Provide pre-procedural mouth rinse for patient to remove debris
How can gagging be prevented?
Avoid excessive material
Topical anesthetic agent or salt
Tilt head forward; lift one leg up
How should the maxillary tray be seated?
Posterior to anterior
How should the patient be instructed to breathe?
Deeply through their nose; this helps to avoid gagging
What should be considered for the width when selecting the impression tray?
Must allow for adequate thickness of the material on facial and lingual
What should be considered for the length when selecting the impression tray?
Must allow for coverage of the Retromolar pad and maxillary tuberosities
How much clearance should there be on the anterior labially to the most protruded incisor?
1/4 inch (2-3 mm)
Where should the clinician be standing when trying in the maxillary tray?
At the side to the back of the patient
Where should the clinician be standing when trying in the mandibular tray?
At the side to the front of the patient; instruct the patient to raise their tongue
What is the purpose of using the beading wax (wax rim)?
Prevents metal tray from causing discomfort to the soft tissues
Beading wax can be used to seat the vestibular periphery _________ into position with reduced _____________ on the displaced tissue
firmly
pressure
Beading wax can be used to prevent ___________________ of incisal or occlusal surfaces through the ___________
penetration
alginate
What type of patients might beading wax be used on?
Patients with high vaulted palates
Beading wax can also be used to
extend the length of the tray
How can beading wax be used to prevent gagging?
It can be used to create a posterior palatal seal
How does beading wax allow retention of alginate?
It provides a slight undercut at the rim
How should the right-handed operator be positioned when seating the mandibular tray?
7 -9 o'clock
How should the left-handed operator be positioned when seating the mandibular tray?
4 o'clock
How should the lip be retracted when placing the mandibular tray?
using the non-dominant hand
How should the impression tray be placed in the mouth?
rotate the tray and position to the centre allowing a 1/4 inch to the facial
What should the patient be instructed when mandibular tray has been placed?
Raise the tongue and relax lips and cheeks
When holding the impression tray in position, which fingers should be used and where should they be placed?
Middle fingers of both hands placed over the premolar area
How should the seal be broken when removing the impression tray?
By elevating cheek on edge of impression
What is important to remember when removing the impression tray?
Do not rock the impression back and forth
Once the impression has been removed, it should be
rinsed under cold water and disinfected, then wrapped in a wet towel
How should the right-handed operator be positioned when seating the maxillary tray?
10-11 o'clock
How should the left-handed operator be positioned when seating the maxillary tray?
1 o'clock
Why would the patient be instructed to form a tight "O" with their lips during a maxillary impression?
To mold the impression material
The water temperature too high might result in
Inadequate working time
How might a non-homogenous mixture occur?
Incomplete spatulation or premature setting
What may cause distortion of the impression?
Not removing the impression from the mouth rapidly, rocking the impression back and forth when removing, or placing the impression on a table upside down
What is important to remember about thin mixes?
They are more prone to tearing and tear strength increases with the rate at which stress is applied; desirable to remove impression quickly
What might cause loss of detail?
Premature removal of impression while its setting
How can dimensional change be avoided?
Pour the model up ASAP or store the impression in a moist sealed plastic bag
What might be the cause of a porous impression?
Whipping air into the mixture during spatulation, squeeze material between spatula and bowl
How can improper consistency of present mix be avoided?
Make sure the powder is fluffed and measure accurately to eliminate too thin or too thick mixes
When evaluating impressions, what are we looking for?
Proper extension of tuberosity/Retromolar pad
No air bubbles or voids on the teeth
Minimal bubbles on gingiva and tissue
Frenums are visible and the tray centered
Visible peripheral roll, palate reproduced
Complete reproduction of the height of the vestib
For disinfection, what has been tested and is effective with no distortion of an alginate impression when used 10-15 minutes before pouring?
Iodophor (1:213) and Sodium Hypochlorite (1:10)
What is the main component potassium alginate used for?
Dissolves in water to form a sol (liquid)
What is the main component calcium-sulphate used for?
It helps to gel (form solid)
What is the main component trisodium phosphate used for?
It slows down the mixing time
What are the main components diatomaceous earth and zinc oxide used for?
Fillers; to add bulk to the mixture
What is the main component potassium titanium fluoride used for?
It adds surface strength
The impression is the _____________ reproduction
negative
The model is the ________________ reproduction
positive
What is the working time for normal set alginate to set?
2 minutes
What is the working time for fast set alginate to set?
1 1/4 minutes
What is the setting time for fast set alginate?
1 to 2 minutes
What is the setting time for normal set alginate?
Up to 4 minutes
What should the water temperature be when mixing the alginate material?
20 to 21 degrees C (68 to 70 F)
How does colder water affect the setting time?
It will lengthen the setting time
How does warmer water alter the setting time?
It will shorten the setting time
How does warmer weather and higher humidity alter setting time?
It will cause it to set more rapidly
What tray should be selected for mechanical lock?
Perforated trays
What is imbibition?
Too much water is absorbed and the impression swells and is distorted
What is syneresis?
Loss of water and the impression shrinks