Impression sem/Dental implant courses by Indian dental academy

Elastomeric impressions, most accurate when used with a cross sectional thickness of 2 mm -> best achieved with custom tray.

STOCK TRAYS - Stock plastic trays - Stock metal trays : perforated  Non-perforated  Rim lock trays  Denticular - Clear trays Edentulous Stock plastic trays (Pic. BDJ. Article) - Can be used for impression of one or two single units.

- Trays do not have sufficient rigidity - Low cost - Contra indicated with fixed bridge work because its flexibility adversely affects inter preparation, cross arch and anteroposterior dimensions Stock metal trays (Pictures) - Coated steel or stainless steel trays combine the convenience of stock plastic trays with the rigidity of custom trays.

- Perforated or rim lock trays indicated for putty wash impressions for mechanical retention in addition to tray adhesive (adhesion of putty to its impression adhesives is not as reliable as with other viscosities).

Custom trays - Custom tray improves the accuracy of an elastomeric impression by limiting the volume of the material, thus reducing two sources of error: • Stresses during removal.

• Thermal contraction - Custom trays, constructed on the diagnostic cast using one layer of bae plate wax as a spaces - Trays can be fabricated because (Picture page 364 – 68) Roseinsteil - Pollymethylmethecrylate - Photo-cure bisacryl materials (Triad) - PVS putty materials - Thermoplastic trays - PMM trays should be fabricated at least 24 hours in advance to in sure stability.

- Tray should extend 3-5 cm for gingival margin, wax spaces covered with tin foil.

- Thermoplastic trays with elastomers not recommended as the plasticizers in elastomers attack and soften the compound.

- Occlusal stops – critical for proper orientation of tray in the mouth.

- Three stops ideal, with atleast one posterior to prepared teeth.

- Should be placed on non-functioning cusps so that distortion will not interfere with inter cuspal relationship.