Apparatus for dental purposes, namely, dental impression trays; apparatus for dental use, namely, dental impression trays; apparatus for fabricating dental prostheses specifically adapted for dental use, namely, prosthetic instruments for dental purposes; apparatus for use in the fitting of dental prostheses, namely, prosthetic instruments for dental purposes; apparatus for use in the preparation of dental prostheses, namely, prosthetic instruments for dental purposes; dental moulding apparat...