Outcome 2 - Take an Accurate Preliminary Impression

Question 1

What are preliminary impressions?

Answer 1

Preliminary impressions record details of the teeth and surrounding tissues. The impression produces an accurate three dimensional duplicate of the patient’s oral anatamoy.

Question 2

What is a negative reproduction?

Answer 2

Which when poured in stone to form models which can be used as diagnostic aids, for the fabrication of dental appliances and as a pre-treatment and post-treatment records.

Question 3

General Armamentarium to record preliminary impression:

Answer 3

1. Impression trays
2. Small saliva ejector, air/water syringe tip, mouth mirror (optional)
3. Alginate mixing bowls: clean, dry, flexible rubber or plastic with smooth, unscratched surface
4. Alginate mixing spatulas: clean, dry, with a wide blade end that will reach every part of the bowl without scraping or cutting the surface
5. Dental materials:
   -alginate - measuring scoop and calibrated water measure
   -room temp water
   -utility wax (as per patient oral cavity conditions)

Question 4

What IPC must be followed for impression trays?

Answer 4

• multiple use trays must be sterile, and free of any debris
  -single use trays must be disenfected, and free of any debris

Question 5

For maximum visibility when assessing tray size:

Answer 5

patient chair should be placed in supine position, however, placement of patient in upright seating position is also acceptable. Clinical observation must be preformed prior to tray selection.

Question 6

These intra-oral conditions must be considered when choosing the tray size:

Answer 6

Presence of..
-tori
-high palate
-crowded or rotated teeth
-lesions
-mobile teeth

Question 7

What to consider for tray width?

Answer 7

-must allow for adequate thickness of impression material on the facial and lingual of each tooth to provide strength and rigidity to the impression

• tray flanges may be spread to accomodate extra width in the molar regions, particularly lingual to the mandibular molars in the mylohyoid region.
• when a tooth is prominent labio-, bucco-, or linguoversion, a minimum thickenss of 1/4 inches is suggested, but even then, the fragitlity of the impression material in that area is increased.

Question 8

What to consider for tray length?

Answer 8

• must allow for coverage of the retromolar area of the mandible and the tuberosity of the maxilla

-on the anterior, there should be at least 2-5mm clearance labial to the most protruded incisor without impingement on the lingual gingiva

Question 9

Operator Position for Mandibular Tray Try-in?

Answer 9

Right handed: 7 to 9 o’clock
Left handed: 3 to 5 o’clock

Question 10

Operator Position for Maxillary Tray Try-in?

Answer 10

For the best outcome, tray is tried from two different positions

Right handed: 9 and 12 o’clock
Left handed: 3 and 12 o’clock

Question 11

How to evaluate the size of hte tray..

Answer 11

Gently lower the front of the tray while holding the posterior border in place and examine the relationship of the posterior border to the most posterior molars and the tuberosity areas to determine whether there will be ample coverage. By moving the tray up and down it is possible to observe the relation to the facial surface of all teeth, mal-aligned teeth, protuberances and other features to assess the space allowed for impression material.

Re-select larger and smaller trays as indicated and repeat try-in; when in double the LARGER TRAY is used, rather than smaller.

Question 12

Patient management techniques for impression tray placement

Answer 12

• Approach ith confidence to reassure the patient
  -Work as quickly and efficiently as possible

-Use topical anesethetic:
*cold water or an ice cube held in the mouth has some anesthetic effect.
*Salt (1/4 tsp) on the tongue to swallow just before the tray is to be insterted may releive tissue retractions
-Topical anesthetic may be applied to posterior palatal area, or patient may rinse with a commercial topical agent. A spray topical prepartion is contraindicated because of the proximity to throat, where coughing may be initiated.

-Technique considerations:
*avoid excessive impression material in the tray
*seat the maxillary tray from posterior to anterior
-instruct patient to breathe deeply through his nose before tray is inserted and to continue after insertion, bring head forward.

Question 13

When may tray adaption be required?

Answer 13

May be required to accommodate various intra oral patient anatomy, prevent or minimize patient gag reflex, create palatal seal with high palate or minimize discomfort during impression taking during presence of tori.

Question 14

What may be used to extend the impression tray during impression taking?

Answer 14

Dental Wax

Question 15

Dental waxes are categorized into 3 classifications:

Answer 15

1. Pattern waxes
2. Processing waxes
3. Impression Waxes

Question 16

Example of impression waxes are:

Answer 16

Utility Wax (Rope strips)

Occlusal registration wax: Baseplate wax

Question 17

How to load the impression tray

Answer 17

1. Do not overload; fill to a level just below the edge of the rim
2. Wet your index finger with water and pass lightly over the surface of the impression material.

Question 18

Factors relating to the impression material that contribute to a satisfactory impression:

Answer 18

-Powder
-Water
-Strength and Quality

Question 19

The alginate material (powder) deteriorates on standing, particularly at higher temperatures and humididty. Do the following:

Answer 19

-keep container tightly closed; store in cool place
-Use individually sealed packages except when large numbers of impressions are made regularly
-Refrigerate indivudual packages in hot weather, provided the powder is used immediately upon opening. If left exposed, water condenses on the powder. The bulk container cannot be refrigerated for that reason.

Question 20

Ideal water for impressions:

Answer 20

-temperature controls gelation time

-room temperature provides adequate working time
-colder water will prolong mixing and setting time. Control in hot, humid weather; use cooler water and refrigerate the bowl and spatula.

Question 21

The strength and quality of the finished impression depend on the following factors:

Answer 21

• powder to water ratio accurately weighed and measured
  -firm spatulation will allow chemical reactions to proceed uniformly
  -holding the impression material in position for an optimum period. Distortion can result when the impression is left in the mouth too long or removed prior to setting of material.

Question 22

What steps are involved in order to record dental impressions?

Answer 22

-Prepare armamentarium as per patient appointment

• Communicate and explain procedure to the patient

-Clinical Observation: access patient oral conditions, determine tray size required

-Impression Tray Size Fitting: try mandibular tray first, try maxillary tray second, consider tray modification if required (adding utilty wax for tray extension, patient comfort)

-Mixing and Loading Impression Material

-Recording Mandibular Impression First

-Recording Maxillary Impression Second

• Outcome
• IPC / Safety Procedures
• Charting

Question 23

Steps for Mixing & Loading Impression Material

Answer 23

• Follow manufacture instructions for product mixing

-Mix impression material to smooth consistency

-Spread the alginate against the side of the bowl with the spatula while turning in the palm of your hand
*For mandibular: load tray from lingual and/or buccal rims and press material down into base, load more material anterior
*For maxilllary: Load tray from posterior to anterior, press material down into base, load more material anterior

• Smooth the surface of the alginate by wiping a moistened finger along the surface

Question 24

How to Record the Mandibular Impression?

Answer 24

Done 1st

-Support tray evenly with index fingers around premolar areas on both sides until impression is set

• Ensure patient is seated at the dental assistant height for correct ergonomics
• Attend to patient needs before examining and evaluating the impression

Question 25

How to Record the Maxilary Impression

Answer 25

Done 2nd

-Support tray evenly with index finger around premolar areas on both sides until impression is set

• Ensure patient is seated lower as the impression is taken from 11-12 for right handed operators & 12-1 for left handed operators.
• attend to patient needs before examining & evaluating the impression

Question 26

How to evaluate an impression?

Answer 26

Observe presence of surface details, proper extension over retromolar area or tuberosity, and the peripheral roll (rounded border of the impression) generally.

• Repeat the impression if required. Correct mistakes, rather than be satisfied with substandard impression.

Question 27

IPC / Safety for Impression Taken

Answer 27

• Rinse impression under running cool tap water to remove saliva and/or debris. Disinfect and rinse impression again to prevent disinfection chemical from distorting the impression.

-Ensure moisture is removed before wrapping impression in moist paper towel.

Question 28

Criteria required for Mandibular Impression

Answer 28

• There must be retromolar area included in the impression
  -The impression should be centered in the tray
  -The tray size must provide an adequate peripheral roll both facial, and lingual.
  -The impression must be free of voids & tears (except interproximal)
  -Anatomical detail must be sharp & clear
  -Bone height must be visible throughout
  Tray must be fully seated.

Question 29

Criteria Required for Maxillary Impression

Answer 29

• The hard palate and maxillary tuberosity area must be included in the impression
  -The impression must be centered in the tray
  -The tray size must provide an adequate peripheral roll into the facial vestibules
  -The impression must be free of void & tears (Except interproximal)
  -Anatomical detail must be sharp & clear
  -Bone height must be visible throughout
  -Tray must be fully seated

Question 30

What are bite registrations or occlusal records?

Answer 30

In order for the prosthesis to fit and function properly in the mouth, an accurate record of the patient’s bite must be obtained. These are often called bite registrations or occlusal records. There are various materials and different procedures that can be used depending on the extent of the treatment and the number of teeth involved.

Question 31

What is the purpose of bite registration/ occlusal records?

Answer 31

• To relate the maxillary and mandibular cast correctly
  -To place between the cast during trimming and storage to prevent breakage of teeth
  -To provide an indication for a special need, when there are problems such as open bite, cross bite, edentulous areas, end-to-end, or edge-to-edge relations

Question 32

What is a facebow?

Answer 32

A facebow is a dental tool that measures the relationship between a patient’s teeth and jaw, and transfers that information to a dental articulator.

Question 33

What is an articulator?

Answer 33

Once the facebow transfer is taken, the casts can be mounted on an articulator. The articulator is a device that simulates the movements of a patient’s jaw. The dental lab will often use these devices to achieve an accurate fit for the prostheses. They can be simple devices with hinges that simulate only up and down motions, or more complex where they simulate side to side motions as well.

Question 34

How to use a face bow & articulator?

Answer 34

Each manufacturer of facebow/articulator models will have specific set of instructions to follow.

Question 35

How to chart impressions?

Answer 35

The procedure must be entered on the Services Rendered portion of the patient’s chart. When entering services rendered, document procedure steps/materials by order of use.

Question 36

What should be included in Services Rendered for Impressions?

Answer 36

-the reason the impression was taken
-impression tray(s) size used
-brand name of the product used
-wax type if used and reason
-setting time of the material used: fast set or regular set?
-flavour if available
-include any additional comments such as: patient had strong gag reflex, etc.

Question 37

IPC Safety For Impression Taking?

Answer 37

DA role is to understand, implement, and maintain infection control during patient appointment. During impression taking, patient may experience gag reflex and/or coughing. This can produce large particles of spatter containing saliva, blood and other debris. Spatter can travel far and land on upper surfaces of the wrist and forearms, upper arms, and chest of the operator. Best work practices will minimize spatter such as: ensure the impression material is not placed heavy along the posterior tray as this will minimize patient gag reflex.

Standard IPC protocols must be maintained prior, during and after patient dental appointment.

Disposable impression trays or any heat sensitive or single used items must be disinfected with the high -level disinfectant and rinsed prior use, multiple use impression trays must be sterilized after each patient use.

Question 38

According to Spaulding Classification, impression trays are classified as…

Answer 38

Semi-Critical as they come in contact with mucous membranes or non-intact skin

Question 39

Prior to impression, how to explain the procedure to patient?

Answer 39

• what to expect during impression recording: sensation, drooling

-Identify approx. time impression stays in the mouth: as per manufacture instructions

• Ask patient to follow directions closely during impression taking
• Explain briefly purpose of tray size fitting

Question 40

During impression taking, how to maintain patient safety and comfort?

Answer 40

-Ask patient to lift tounge when asked (during mandibular tray seating)
-Ask patient to breath through nose (during maxillary tray seating)
-ask patient to lean forward when advised

Question 41

After impression is taken, how to maintain patient safety and comfort?

Answer 41

-instruct patient to rinse with water to remove any excess alginate
-provide patient with tissue to clean impression debris from around the face
-use of floss may be required to remove alginate
-patient can eat and drink right away