Replica-casting method

Figure 4.9 Schematic of (A-C) the fabrication of the mold for making the PDMS replica using the resin casting method, (D) the casting of the device and (E) the convex shape of the resulting emitter tip. (Reprinted with permission from ref. 22).

Casting liquid prepolymers on microfabricated molds is the simplest and cheapest method of replication. Masters can be fabricated as discussed above or by simply defining structures in photoresist on a variety of substrate materials. Once the masters have been fabricated, they are often treated with a mold release agent prior to use. The liquid polymer is poured over the molds and placed under vacuum in order to completely fill the features and remove any air bubbles. Finally, the material is thermally cured, and the replica is cut or peeled from the mold. This process is schematically represented in Fig. 3. 

The results of this research demonstrate an accurate transfer of the implant replica position by virtual implant insertion into both a pre-operative and a postoperative cast, obtained from impressioning. In previous studies, the evaluation of the implant positions has required a post-surgical CT scan. With the indirect methods, using laser scanning techniques, this extra radiation exposure of the patient can be eliminated. 

Investment Casting. A process for the casting of small metal components to a close tolerance. In the usual process a wax replica of the part to be cast is coated ( invested ) with refractory powder, suitably bonded, and the whole is then warmed (150°C) to melt out the wax - hence the alternative name Lost-wax Process the refractory mould is then bred at 1000-1100 C. The refractory used may be powdered sillimanite or alumina, or specially prepared cristobalite the latter is particularly used in the application of the process in dentistry. B.S 1902 Pt 10 specibes methods for the determination of resistance to deformation at elevated temperatures permeability and standard air bow capacity at elevated temperatures thermal proble determination, for refractories for investment casting shell mould systems prefabricated brickwork, in which reinforcement is provided by steel rods running horizontally across perforations in the blocks. 

An excellent review of freeze fracturing is found in a chapter by McNutt [362]. The method has been described for preparation of biological membranes. An older, improved version of the method was described by Steere [363] and Moor et al. [364], while a review of the method and application to membranes was described by Branton [365]. The method involves cementing a 1-2 mm piece of the material onto a copper disk with gum arabic dissolved in 20% glycerin and then transferring the material to liquid Freon 22 (chlorodifluoromethane). The specimen is fractured with a cold knife in a vacuum evaporator, and it may be etched prior to replication. A replica can be cast on the surface of the hydrated... 

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