Taking of an impression with the help of Shellac base plate is a bit out dated now but still in practice in some places. The primary aim of base plate is to make a replica of the structures of the oral cavity on the cast by application of pressure.
This procedure is cost effective so it is still in application in many small cities. It’s handling is also easy but it’s back drops are that the sulcus depths and some minute structures cannot be registered in the impression.
* Shellac Base plate (both mandibular and maxillary)
* Spirit lamp
* Primary cast
* Mandibular shellac base plate
* Maxillary shellac base plate.
The shellac base plate is taken(for maxillary it is Triangular in outline and for mandibular it is horseshoe shaped), the base plate is then heated partially on the flame not until it melts but till it softens so that it can be adapted onto the cast. After ideal softening the softened base plate is taken and adapted to the cast with hands and by using cotton so the the base plate can be adapted well into the sulcus. After adapting the wax to the cast the excess which is projecting out is cut off using a scissor. Then wait for some time as it gets hard and then remove it and the impression is read for use.
It is a temporary impression and can change dimensions in change of temperature so handling should be done carefully.
It is a rigid material and the impression taken is used for primary casts.