Every dental student knows how much time and energy is spent making a perfect master impression. But for many of us, the job does not end after the impression is made. Improperly boxing and pouring the impression can lead to critical errors. Once you have collected the proper materials, this method of creating a land on any type of impression is simple and cost-effective.
1. Impression (If using a stock tray, the handle will need to be cut off.)
2. Hard plastic mobile surface
3. Red Boxing Wax (1 for each impression)
5. Alginate (Fast set is best.)
6. Bowl and Spatula
7. Sharp Blade (#15 ideally)
9. Vaccuform Mixer
10. Stone (Your choice depending on cast use.)
11. Vibrating table
After the Impression is set:
12. Hot water bath
13. Buffalo Knife
14. Model Trimmer
Place the impression on the hard plastic mobile surface. Shape the red boxing wax around the impression so that there is 3-5 mm of space between the edge of the impression and the red boxing wax. Join the ends of the boxing wax with digital pressure. Gently remove the impression from inside the red boxing wax and off of the hard plastic mobile surface. Place a thin layer of Vaseline on the inside of the red boxing wax and return to hard plastic mobile surface.
Mix a 4 parts alginate power to 5.5 parts water. (The suspension should be runny.) Pour into red boxing wax, which is placed on the hard plastic mobile surface. Place impression into the alginate suspension in a centered fashion. Push down until 2-5 mm of the buccal flange is showing. Do not pull the impression back up or move side to side. (It is okay if the alginate runs over the posterior portion of the impression.) Let the alginate set.
Without breaking the red boxing wax pattern, gently slide red boxing wax off of alginate/impression unit. Holding the blade horizontally, remove excess alginate from the unit. Ideally, 2-3 mm of the impression is showing from the top of the buccal flange to a horizontal alginate base. There should not be an undercut between the contact area of the alginate and impression/tray or else your tray will be difficult to remove once poured and set. If an undercut is present, add play-dough to recreate horizontal plane.
Replace the non-broken red boxing wax around alginate impression. Leave 1.0 – 1.5 cm of alginate showing.
Vacuum mix your choice of stone. Place the red boxing wax unit on hard plastic mobile unit onto a table vibrator. Slowly place stone into the red boxing wax unit from one area. Confirm that stone is vibrating into all crevices. Once the impression and alginate unit is covered in stone, fill the remaining area until level with the top portion of the red boxing wax. Repeat procedure with other impressions.
Once the cast is set (1), removed alginate (2) and red boxing wax (3) from unit. Place unit into to a hot water bath (1 min) so that compound becomes soft. Using a buffalo knife gently remove impression from cast (4). Trim models on model trimmer to proper specifications depending upon use (5).
~Jennifer A Neese, Indiana ’14, District 7 trustee