Of the cases treated in the Dental Infirmary for pyorrhea, the following systemic conditions were noted: The number of cases treated.. 131

Constipation Rheumatism

1 Kidney trouble

5

T HAS been apparent to many of the profession, and especially to those engaged in teaching, that much of the present literature relative to the question of dental cements is obsolete and has been so for some time. A reference to many of the present text books now in use, and with two or three exceptions, the current literature, shows in the light of this investigation, that the writers of these subjects did not have reliable information concerning the present cements many of which have for several years now been labeled "New Process," "Improved," "Non-Sodium," etc., all of which tending to convey to the user that changes in the product had recently been made. When the writer was called upon to contribute the article on plastics in the fourth edition of the American Text Book of Operative Dentistry he encountered the same difficulties that had confronted other writers on the subject and immediately undertook some work to determine in a limited degree, at least, the changes that had been made in some of the cements in use in dentistry which made the present information appear so antedated. After a little work had been done it was found that the reason that the available literature appeared So much antedated was that we were handling the improved, new process, and non-sodium varieties and had neglected to purchase some of the older makes that were described in the literature.

Every cement in use in dentistry as far as possible was then purchased and an investigation begun to determine if possible, within a short time, what was really available for use in dentistry, by classes, and the result was that three classes of oxyphosphates and the oxychlorides were mentioned.

This hurried, and superficial investigation served to point out the enormous size of the task to get the constitution and properties of these products, and led to the placing of Mr. R. M. McCormick, M. S., in the laboratories of the University of Michigan by the Research Commission of the National Dental Association to aid in carrying on more work along the same line. With the assistance of Mr. McCormick careful qualitative analyses were made of the principal cements sold in the Middle West, including many of those that had been studied previously and which had caused many to think that much of the present literature on the subject was obsolete. With these qualitative analyses it soon became apparent that the statement of the writer that "the principal cements available consisted of three classes of oxyphosphates and the oxychlorides" was not sufficient to convey much of an idea of our present products.

Practically all the information relative to the composition of the cements that is mentioned in Volume No. 2 of Black's Operative Dentistry under the head of cements is contained in the fol

lowing: "The coments are received from the dealer in two separate bottles, the one containing the powdered oxide of zinc or oxide of copper and the other the prepared phosphoric acid." Regarding the properties of these products, Black states that "As yet there has been very little careful examination of the physical properties of these cements." Later in the chapter, however, he discusses some of the properties as seen from recent observations.

In Johnson's Text Book of Operative Dentistry, under the heading Cement, three kinds of cement are considered: oxychloride of cement, oxyphosphate of cement, and the oxyphosphate of copper. Regarding the oxyphosphate cement, it is claimed that it is "principally composed of glacial phosphoric acid and zinc oxide, to which is added, for the purpose of increasing hardness and lessening solubility, several foreign ingredients, e. g., sodium phosphate gives the liquid a glassy consistence in handling. A chemical analysis of cements shows the following impurities: arsenic, antimony, lithium phosphate, cadmium sulphide, fluorhydric acid, nitric acid, sodium carbonate, powdered glass, silex and water glass, sodium borate, magnesium oxide, magnesium nitrate, so dium phosphate, silicate of alumina, and phosphate of alumina. The fineness of the powder varies not only with different makes, but occasionally with different lots put out by the same maker. The finer it is the quicker it sets." Concerning the oxychlorides the following is given in the same chapter, viz.: "The powder of the oxychloride of zinc is composed chiefly of oxide of zinc, calcium oxide being often added to hasten setting, and other ingredients to obtain certain other properties, as silicate of alumina, magnesium oxide, sodium borate, silex, powdered glass, etc." The third class mentioned, the oxyphosphate of copper it is claimed, "is composed of the same liquid as the

foregoing, and cuperic oxid, with or without addition of other metallic oxides."

The widely used dental metallurgy, Hodgen-Millberry, refers to the dental cements as being composed of three varieties, viz., "The Phosphate, the oxychloride and the oxysulphate." The powder is said to be prepared by calcining a quantity of the purest zinc oxide, luted in a sand or French clay crucible, for several hours, as a white heat, or by electric furnaces, thus avoiding possible contamination with products of combustion." The liquid is said to be "usually made by dissolving glacial (metaphosphoric) acid, HP03, in distilled water and evaporating it to a syrupy consistence." In a foot note on the same page (149) it is pointed out that metaphosphoric acid becomes orthophosphoric acid at a temperature of 99°C. (HPO3+ H20—H3PO4), thereby implying that orthophosphoric rather than metaphosphoric acid is used. In another part of the chapter on cements such oxides as aluminum, magnesium, and tin are said to be mixed with the zinc oxide to improve the properties of the powder, and that native oxide of titanium, powdered rutile, slate, etc., are sometimes added for the purpose of giving the powder a variety of shades. The oxychlorides are said to be composed of deliquesced zinc chloride and prepared zinc oxide, the two being mixed together. The oxysulphates are not described.

In H. Carlton Smith's book entitled "Chemistry for Dental Students" under the heading "Dental Cements," we find the following, viz: "Dental Cements, largely used as temporary fillings and linings of cavities, contain oxide of zinc, oxide of copper, or rarely sulphate of zinc, combined, at the time the cement is used, with phosphoric acid or a solution of zinc chloride." Later in the chapter the following appears: "It is not intended to give the impression that the liquid should consist only of glacial

phosphoric acid or the powder only of oxide of zinc. A cement thus made would set so rapidly that it would be of no pratical value. The resulting mass would also probably be crumbly. The powder or the liquid, one or the other, is usually mixed with phosphates of the heavy metals which would be insoluble in water, but which would dissolve in strong phosphoric acid." Later in the chapter ferric oxide is mentioned as increasing resistance to disintegration. The oxychlorid, oxysulphate, oxyphosphate of copper, a tin cement, and artificial enamel are merely spoken of in a very brief kind of a way.

and

In the more recent English publication "The Science and Practice of Dental Surgery" by Norman G. Bennett, under Cements," the heading "Osteo-Plastic there appears the following, viz., "There are five varieties in common use; of these, four are basic zinc compounds, oxychloride, viz., oxyphosphate, oxysulphate of zinc, and oxyphosphate of copper, whilst the fifth is a silicious compound. There is no standard formula for any variety, each manufacturer slightly modifying his particular product, both with regard to its composition and method of preparation; nor have the chemical and physical properties of these cements been investigated to the same extent as those of dental amalgams. The powder is composed of calcined zinc oxide to which small quantities of other materials are added for the purpose of increasing the hardness of the cement and modifying its color; the liquid is one of the forms of phosphoric acid, often modified by the addition of small amounts of zinc oxide and alumina." Later in the article appears the following, viz., "The substances added with the object of imparting hardness and better wearing qualities to the cement include silex, borax, powdered glass, oxide of tin, and oxide of bismuth. To make the cement set more quickly, the oxides of magnesium and aluminum

in small quantities are sometimes incorporated with the powder. To secure a desired shade, coloring matters of the nature of yellow ochre, ferric oxide, titanium oxide, gold oxide, powdered slate, etc., are employed."

Of the contributions appearing in the current magazines there are many that seem to be based upon statements made in the literature several years previously and appear to have little or no relation to the plans that are being followed out by some of the present makers of these products. There are contributions, however, from three makers of our present cements that are worthy of consideration, not that they contain very much information regarding the constitution and properties of these products, but because there are what appear to be very nicely guarded hints in them that can be understood by one who has acquired a more or less intimate knowledge of the cement making properties of all the materials available for the purpose. Such an article may be found in Items of Interest for 1902, by Herman Fleck, Ph. D., another by W. V. B. Ames, D. D. S., appearing in the Journal of the Allied Societies for December 1911, and a third by Paul Poetschke, of the Caulk Laboratories, appearing in the Journal of Industrial and Engineering Chemistry for March 1915. The latter one by Mr. Poetschke, while it does not reveal the secrets of what has been to us the most difficult task yet undertaken, viz., to synthesize a product after an analysis had been made thus verifying the analysis, seems like the most unrestricted presentation of the products used by the company he represents for the class of cements under consideration that may be found in present dental literature.

Dr. Fleck, in the article referred to, in summing up some discussion of the cements divides them into two classesClass 1 consists of cements resulting from a mixture of some form of zinc oxide with orthophosphoric acid that has