alternative use polyvinyl acetate in the dental laboratory
TRANSCRIPT
TIPS FROM OuR READERS Alternative use for polyvinyl acetate in the dental laboratory
J. Fraser McCord, BDS, DDS, a A. Patel, RDT, b R. Richmond, BSc, c and P. W. Smith, BDS d University Dental Hospital of Manchester, Manchester, United Kingdom
Dental laboratories are regarded as potential hazard areas where flammable materials, gas supplies, casting machines, pumice trays/pumice slurries, and polishing leathers are potential areas for problems and cross- infection.I, 2 Safety problems also exist in the on-off switches for lights, fans, and polishing lathes that must be switched on and off with water-moistened hands. This article offers a solution, by using a polyvinyl acetate (PVA) stent to cover the switch and render its inner assembly remote from water vapor.
P R O C E D U R E
A Skillbond lathe (Skillbond Limited, Bucking- hamshire, U.K.) with lathe apparatus (Fig. 1) was used to demonstrate this procedure. The lathe is disconnect- ed and an impression of the switch assembly on the outer casting is recorded in polyvinyl siloxane laborato- ry putty (Zetalor, Zhermack, Rrvigo, Italy). When set, a master cast is formed in dental stone. As the switch on the lathe rotates during the on-off switching, space must be created to allow for this movement when the cover is in place. This space is created by adding 2 mm of plaster around the periphery of the gypsum tem- plate. A sheet ofpolyvinyl acetate polyethylene (Akorn Polymers, Bolton, England) is heat-pressed onto the template (Fig. 2). The stent is then trimmed and placed over the switch (Fig. 3).
No replacements have occurred in 1 year of service and the lathe switches have not required servicing because of the abrasive nature of the pumice slurry- contaminated atmosphere adjacent to the lathes. The resilience of the PVA allows the on-off switch to be dis- placed appropriately and adds to the health and safety of the laboratory.
Reprint requests to: PROF J, F. MCCORD TURNER DENTAL SCHOOL UNIVERSITY DENTAL HOSPITAL OF MANCHESTER HIGH CAMBRIDGE ST MANCHESTER M15 6FH UNITED KINGDOM FAX: 44-161-275-7822
Copyright © 1999 by The Editorial Council of The Journal of Prosthetic Dentistr)~.
0022-3913/99/$8.00 + 0. 10/4/95793
aprofessor and Head, Unit of Prosthodontics. bDental Technician, Unit of Prosthodontics. cDental Instructor, Unit of Prosthodontics. dLecturer, Unit of Prosthodontics. J Prosthet Dent 1999;81:496.
Fig. 2. A, PVA laboratory putty template. B, Stone model with 2 mm space added to all 4 external flat surfaces (original dimension illustrated by lines). C, PVA stent before trimming.
Fig. 1. Typical switch on laboratory lathe. Fig. 3. Completed PVA stent in position.
496 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 81 NUMBER 4