There is the taking the impression part which is an art form in it self with implications of everything else that goes with it. You do not want to make life more difficult knowing that your great detailed impression taken is now great to look at but dimensionally unstable due to the properties within the material altered.
Dentist: Patient is a gagger, edentulous, impression taken with all anatomical landmarks, border moulding, all vestibule areas are very nicely detailed within the impression, "I am happy with the result and believe that I will get a really nice denture to fit".
Lab: Great impression, dentist has taken accurate impressions, models casts with all areas maintained, all denture stages followed, dentures finished, "great, off you go to get fitted".
Dentist: "F/F does not fit, please remake". (The dreaded words for Dentist & Technicians)
As you can see from the example it shows one person is missing, where is the person who mixed the impression material which is the most important job, more important than taking the impression as they are creating the material for you to take the impression. I always have all of my models, denture acrylics etc mixed to manufactures water and powder ratios this way I know it is done correctly and if it is not correct its a manufactures error as i am accurately following guidelines.
Its similar to someone making a chicken sandwich but then giving you something that looks like chicken and tastes like chicken but it sure is not chicken.
(PS. This is not a guide to blame some one else for impressions not coming out the way you would like or the reason why your prosthesis is not fitting, there is a multitude of reasons. )
Mixing Alginate Procedure for Dental Professionals
- Spray adhesive inside of the tray and on the outside.
- Check size of the tray and determine how many scoops of powder is needed:
- Small – 2 scoops.
- Medium sized – 3 scoops.
- Large – 4 scoops.
- Use scoop to obtain powder & scrape excess off with a spatula into the container without compacting or pushing the powder down into the scoop.
- Place all scooped powder in bowl, with your spatula make a separation line between the powder, which creates an empty channel with alginate powder on each side for the water to flow in-between and soak the powder. (By creating a channel, that allows you to soak all of powder from the inwards to the outward surface, rather than water sitting on top)
- Fill measuring cup exactly to the ratio of powder scoops (use measuring cup supplied) place water into the hole of the alginate.
- (5 seconds) Slowly mix the powder and liquid make sure all powder is wet and soaked. Turn the bowl with your stationary hand, mix with your working hand, hold bowl towards stomach to stabilise the bowl.
- (10 seconds) Hold the bowl away from you, turn with stationary hand and squeeze alginate clockwise against the sides of the bowl with a spatula in your working hand. Place the edge of the underneath of the bowl on the table to stabilise. (This releases air out and you should air popping sounds)
- (5 seconds) Scoop all alginate together as if you are going to load the tray and place it on the side of the bowl & push towards you to get rid of excess air.
- Take a little bit at a of material at a time, load the anterior section from the middle of the tray to the labial side and then turn the tray around and load alginate from middle backwards to the posterior. ( You are pushing the air out of the tray by loading it this way).
- More alginate placed anteriorly, sloping down posteriorly. ( A personal preference, ask your clinician what he prefers, I do this to stop air bubbles forming labially and yes it works)
- Turn the tap on (not running to fast) place fingers under the running water and place wet fingers to drip water over the top of the impression and slightly pat down and compress onto the impression material. (allows easier flow ability of the material and acts as a surface tension glaze on adjacent teeth to stop air bubbles)
- Setting time in mouth usually about 45 seconds to 1 min and 50 seconds. (Check manufactures instruction)
- After setting and removal from the mouth, place directly under water and rinse.
- Disinfect impression, do not leave longer than the recommend time as this can distort the material. (Usually 10 mins)
- Rinse impressions under the tap and place into a bag, do not compress or place into a tight bag. Label disinfected.
- Wait for material to set inside bowl and with a wet wipe, wipe down the bowl, spatula and any other instrument used.
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