PLASTER-OF-PARIS; THE EFFECTS OF VARIOUS SUBSTANCES UPON ITS RATE OF SETTING AND THE SUBSEQUENT STRENGTH AND DURABILITY OF THE CAST

1st.—The orthopedic surgeon should select for his use a pure, well made and well kept unadulterated brand of plaster-of-Paris. Such a plaster will set in about 7 minutes, which is fast enough for all ordinary work and yields a cast of the highest strength and durability.

2d.—The use of starch crinoline bandages as the support in the application of the plaster does not interfere materially with either its rate of setting or its tensile strength. The various forms of wire gauze bandages yield a cast of increased tensile strength and therefore a lighter cast.

3d.—Portland cement when used with plaster-of-Paris in amounts varying from 10 to 20 percent yields a cast of superior hardness, strength and durability. It is especially adapted for use about the foot, ankle, and about the thigh in the Lorenz operation.

4th.—Moisture disintegrates, softens and dissolves plaster casts.

5th.—The waterproofing of plaster casts by gauging the plaster bandages in a solution of sodium silicate is impractical. The finished cast should be thoroughly coated with sodium silicate solution after hardening. The hardening of plaster models, shells, corsets, etc., can readily be accomplished by dipping or painting them with a hot alum solution.

6th.—The addition or use of any form of accelerator yields a soft and friable set and the cast is of insufficient tensile strength and resistance to abrasion to possess the lasting qualities demanded by the majority of orthopedic procedures. The worst accelerators in this regard are common alum and potassium sulfate. The practice of using poor plaster and then "doctoring it up" with an accelerator to make it harden rapidly should be abandoned.

7th.—The use of "quick setting dental impression" plaster is also to be condemned for the same reasons. They almost invariably contain considerable amounts of potassium sulfate which renders them brittle and friable. The regular slow setting dental plasters obtainable on demand almost everywhere in our country are pure and unadulterated, and when kept in clean, dry containers present the ideal material for orthopedic casts; they can be wound into bandages with starch, crinoline or wire gauze and where especially heavy wear is expected can be advantageously mixed with 10 to 20 percent of Portland cement.

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