Guidelines for the Fabrication of Custom Maxillary and Mandibular Visible Light Cure Impression Trays Using a Wash Impression Technique
- Outline the casts for the custom edentulous trays as indicated in the Handbook for Complete Denture Prosthodontics on pages 45 and 46.
- Outline any undercuts on the cast, being sure to visually survey the cast and decide upon the best path of insertion and withdrawal. Remember that in most cases this path is not going to be straight up and down. Also refer to the handbook, pages 46, 47, and 48.
- Fill in the undercuts with only enough pink occlusion rim wax to block out the undercut. Do not place excessive wax within the outline and be sure that no wax is in the peripheral roll area.
- Coat the cast and wax with a thin layer of model release agent or petroleum jelly.
- Remove a sheet of VLC tray material from its protective pouch and lay it over the cast.
- Give the material a moment to slump onto the impression surface of the cast.
- With an instrument or an index finger coated in petroleum jelly, gently press the material to place with no voids, into the palate, the peripheral rolls, and/or the lingual areas. Be sure that the hamular notches and/or the retromolar pads are completely covered.
- Using a sharp instrument and/or scissors, trim excess material up to the custom tray outline which you previously drew in the cast. The material may be cut slightly beyond this outline and after curing trimmed back. Never, however, have the custom tray trimmed short of the outline on the cast at this point.
- Fabricate handles as illustrated on a separate guideline sheet. Be careful with the handles because you are frequently required to wait in line to use one of the curing machines. Handles can easily slump out of shape as you wait for your turn. To prevent this, partially cure the handles with your laboratory lamp to prevent slumping.
- Place the cast and tray into the VLC curing unit and process for two minutes.
- When the machine stops, take out the cast and tray. Carefully pry the tray away from the cast and apply a coat of air barrier coating on the tray, if you wish to use this material.
- Return the tray to the curing unit and process for an additional six minutes.
- Be sure that the carousel in the curing unit is in the lowest position. Have no more than two trays being processed at any one time.
- Adjust and finish the borders of the trays to the tray outlines previously drawn on the casts. Scrub the trays with soap and water.
- If you did not apply a coating of ABC to your trays, apply a thin layer of petroleum jelly and place them in the curing unit for an additional two minutes. Wash with soap and water.
For informational purposes:
VLC (Visible Light Cure) resins are urethane dimethacrylate based interpenetrating polymer networks. These materials also contain a small amount of silica, an organic filler, and a photoinitiator, camphoroquinone, and are cured with visible light in the blue light range of 400-500 nm. These resins are devoid of methylmethacrylate, packaged in opaque containers, and are presently available in three forms – sheet, rope, and gel.