Part 2 Physical research

Part 2 Physical research

PART 2 G. C. PAFFENBARGER, D.D.S., & W ILM ER SOUDER, Ph.D., WASHINGTON, D.C. Physical research in dentistry is con­ cerned primarily with material...

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Physical research in dentistry is con­ cerned primarily with materials used to replace lost tissues and to correct defec­ tive dental conditions. As the use of these special dental materials constitutes a ma­ jor portion of dental health service, the American Dental Association has for many years supported research in this area. The paucity o f reliable data on restor­ ative materials available as recently as 50 years ago made it difficult for the den­ tist to select appropriate materials and technics. Reports on dental materials given in the early Transactions of the Association are to be found in the reports of the Committee on Mechanical Dentistry.1 SCIENTIFIC FOUNDATION AND RESEARCH COM M ISSION

The spark that started the National Den­ tal Association on the road to active participation in physical research on ma­

terials was a report given at the 1912 meeting.2 At the end o f this report a motion was made that the president of the section appoint a committee to re­ quest the Executive Council of the Asso­ ciation to take some action about the testing of amalgam. A committee o f three was named to report at the next meeting o f the Association. The members of this Special Committee on Scientific Founda­ tion Fund were Weston A. Price, chair­ man; Arthur R. Melendy and C. M. McCauley.3 No time was wasted by Dr. Price. The next year this committee of three was reorganized with a membership of 25 un­ der the title The Scientific Foundation and Research Commission. The 1913 re­ port of this Commission4 showed that four research associates had been em­ ployed by the Association. One o f these, Frank A..Fahrenwald, was working under the direction of Dr. Price and members of the faculty of Case School o f Applied Science. This school’s laboratories were


Lab oratory at the N ational ureau of Standards

made available without cost to the Asso­ ciation. The first work dealt with substi­ tutes for platinum and other dental metal­ lurgical problems.5 M uch of the financing of these studies was done by voluntary subscriptions of dentists and dental so­ cieties solicited largely by Dr. Price. Mostly through his efforts the Research Institute of the National Dental Associa­ tion was founded in Cleveland. The work in metallurgy which had been carried on at Case was transferred to the new Research Institute. Here the work con­ tinued until World War I when the As­ sociation withdrew the support. Accord­ ing to Homer C. Brown,6 this withdrawal was caused by the drafting of most of the workers at the Research Institute and the adoption of a policy of making grants to universities. Another report by Dr. Brown7 presents many interesting facts on the early re­ search activities of the Association. An

extensive bibliography of the papers pub­ lished up to 1939 on research financed in whole or in part by the American Dental Association is given in another of Dr. Brown’s historical reports.8 This bibliog­ raphy refers to the outstanding work in physical research which was contributed by Weston A. Price and associates at the Research Institute of the National Dental Association, and by John Shell and asso­ ciates at the University of California. Cooperative dental research supported by the National Bureau of Standards, the American Dental Association and the Armed Forces at the National Bureau of Standards developed out of a request in 1919 from the War Department for as­ sistance in formulating a specification for amalgam.6 From 1919 to 1922, the Bu­ reau carried on the work alone under the direction of Wilmer Souder. The Bureau did not have sufficient funds to carry out the research program on dental

PA FFEN BA R G ER — S O U D E R . . . V O L U M E 58, J U N E 1959 • 99

materials that seemed appropriate. In 1922 the Bureau called to the attention o f various dental organizations, including the American Dental Association,6 the research associate plan by which outside organizations could cooperate in programs o f general interest to an organization and to the government. The Weinstein R e­ search Laboratories was the only organ­ ization that offered to support research associates to work at the Bureau. This offer was accepted. Work commenced in January 1922.° It continued until April 2, 1928, when the American Dental Associa­ tion completed arrangements, which were begun in 1924, for participating in the program.6 PERSON N EL

Wilmer Souder of the Bureau’s staff was in direct charge of the cooperative dental research program from its inception until 1945, when he became chief o f the Divi­ sion of Metrology. I. C. Schoonover, at present an associate director of the Na­ tional Bureau o f Standards, was chief from 1945 to 1953 when he was succeeded by W. T. Sweeney, the present chief. The senior research associate o f the American Dental Association for the three year period (1928-1931) was N. O. Taylor, now vice-president o f the S. S. White Dental Manufacturing Co. From 1931 to 1941 and from 1946 on, George C. Paffenbarger has served in this capacity; during the war years John R. Beall was senior research associate. In the latter part of 1943 the Research Commission offered the services of John R. Beall and Harold J. Caul to the Bureau for employ­ ment in the direct war effort.10 The Bureau promptly accepted the offer. Mr. Beall was assigned to the guided missile program and Mr. Caul to a project relat­ ing to the extraction o f aluminum from ores other than bauxite.11,12 Each con­ tributed valuable service in the national emergency. In 1959 there were eight permanent

and nine temporary representatives of the Association at the Bureau. The nine tem­ porary associates were hired on grants-inaid to the Association from the U. S. Public Health Service. SCOPE OF T H E PROGRAM

A convenient division of the dental re­ search work includes: the preparation of specifications for dental materials; a cer­ tification program for dental materials; the measurement o f physical and chem­ ical properties and the influence of technics on these properties; the develop­ ment of new materials, instruments and test methods; research on the structure and properties o f the hard tooth tissues; the communication of research findings to clinical practice via motion pictures, reports, clinical demonstrations and ex­ hibits. SPECIFICATIONS

The Association now has 15 standards for dental materials.13 Standards for ten ad­ ditional materials are being formulated with the assistance of the dental ma­ terials group o f the International Asso­ ciation for Dental Research. CERTIFICATION PROGRAM

The certification by the manufacturers that their materials comply with the Asso­ ciation’s standards and the testing and listing o f such certified materials by the Association give the dentist reliable in­ formation for the selection of highest quality dental materials. M EASU REM EN T OF PROPERTIES AND IN FLU E N C E OF TECH NIC

The measurement of pertinent properties and the determination o f the effects on them of the technics o f using dental ma­ terials have received major emphasis in the cooperative program on dental re­

100 • T H E J O U R N A L O F T H E A M E R IC A N D EN T A L A S S O C IA T IO N

search at the National Bureau of Stand­ ards. The data obtained are the basis of the specifications and the certification program and provide the background for the tremendous influence that the re­ search program has had on dental health service both here and abroad. A summa­ tion o f the work up to 1941 is given in Circular C433 o f the National Bureau of Standards.14 The 1958 edition of the man­ ual American Dental Association Speci­ fications for Dental Materials carries the “ Bibliography o f Publications on Dental Research Conducted at the National Bu­ reau o f Standards.” 13 Approximately 300 reports have been printed. N E W T E ST M E TH O D S, MATERIALS AND


Among the various accomplishments of the dental research program at the Na­ tional Bureau o f Standards are the fol­ lowing : 1. The development o f analytical methods for determining the exact com ­ positions of dental amalgams, gold alloys and mercury and for determining the extent o f polymerization o f acrylic resins. 2. The development of new test meth­ ods for amalgam, gold and base-metal alloys, accessory materials used in dental casting processes, impression materials, mercury, dental cements, synthetic resins, gypsums and porcelains, and for measur­ ing mucosal contours. 3. A n explanation of the dentist’s re­ sponsibility for excessive expansion and corrosion o f many amalgam restorations. 4. The demonstration of fluid ex­ change at the margins of dental restora­ tions. 5. An explanation of the setting reac­ tion between zinc oxide and eugenol. 6. An explanation for some of the mechanisms of hydroscopic expansion in dental investments and of the dimensional changes in amalgam.

7. The determination of levels of radi­ ation in and about the head during dental roentgenographic examinations. 8. The development of a panoramic dental x-ray machine and of a fluid turbine contra-angle handpiece. 9. The development of alginate tin­ foil substitute and a new type of alginate impression material. 10. The application of cristobalite in­ vestments. 11. The synthesis of pure hydroxyapatite (the chief mineral constituent of the calcified tissues) and of apatites de­ ficient in divalent cations. 12. The measurement o f the fluo­ rescence of teeth and its application as a means of investigating their structure. 13. The experimental remineralization of dentin. 14. The measurement of the physical properties of enamel and dentin. EFFECT OF T H E RESEARCH PROGRAM

Dental health practice has been signifi­ cantly affected by the cooperative research on dental materials and the hard tooth tissues. Almost every technic that the dentist uses in the handling of restor­ ative and prosthetic materials reflects some application of the research findings. In dental education the effect o f the research program is manifested by the large proportion of course and textbook content stemming from the cooperative work. The quality control equipment and tests employed in the manufacturing of dental materials are taken directly from the publications.13 Even more important are the improvements in the materials that can be traced to these researches. Thus, it is fitting at this time, the Cen­ tennial of the American Dental Associa­ tion, to point out that one of its major activities is the cooperation with the fed­ eral government at the National Bureau

P A F F E N B A R G E R — SO U D E R . . . V O L U M E 58, J U N E 1959 • 101

of Standards in establishing standards for and improvements in dental materials, in developing new materials and instru­ ments and in demonstrating to the dentist how these unique materials which he employs can be used to the best advan­ tage in dental health service to the public. The Association, in carrying on its share in this cooperative research program on dental materials, has expended approxi­ mately $855,000 over the 30 years 1928 to 1958.


N . D . A . T r a n s a c t io n s

1912, p. 334.

4. N . D . A . , S c ie n t if ic F o u n d a t io n a n d R e se a rc h C o m ­ m issio n . R e p o r t o f p r o g r e s s . O ff. Bui. N . D . A . 1:15 N o v . 1913. 5. P rice, W e s t o n A ., a n d F a h r e n w a ld , F ra n k A . M e t a l ­ lu r g ic a l, p h y s ic a l a n d e le c t r o - c h e m ic a l re s e a rc h e s. O ff. Bui. N . D . A . 1:71 O c t . 1914. 6. B ro w n, H o m e r C . H is t o r ic a l re v ie w o f re s e a rc h a c ­ t iv itie s o f o r g a n iz e d d e n tistry . J . A . D . A . 22:1172 J u ly 1935. 7. B ro w n, H o m e r C . L e g is la t iv e a n d re s e a r c h a c t iv itie s o f th e A m e r ic a n D e n ta l A s s o c ia t io n , t o g e t h e r w ilh a ré s u m é o f s o m e e s se n tia l f a c t o r s c lo s e ly re la t e d to o u r p r o f e s s io n a l a d v a n c e m e n t . J . A . D . A . 17:51 J a n . 1930. 8. B ro w n, H o m e r C . S u p p le m e n t a l ré s u m é o f th e r e ­ se a rc h a c t iv it ie s o f o r g a n iz e d d e n t îs ir y , lis t in g p u b lis h e d r e p o r t s a n d p a p e r s . J . A . D . A . 26:477 A p r i l 1939. 9. C o le m a n , .R. L., J r. P h y sic a l p r o p e r t ie s o f d e n t a l m a te r ia ls . Bur. S t a n d a r d s J . Res. 1:867 D e c . 1928. 10. A . D . A . T r a n s a c t io n s

1943, p . 22.


1943, p. 357.

A . D . A . T r a n s a c t io n s

12. N e w s o f d e n t is tr y . R e se a rc h a s s o c ia t e w o rk s on B u re a u o f S t a n d a r d s p ro je c t. J . A . D . A . 34:631 M a y I, 1947. D r. P a f f e n b a r g e r Is se n io r re s e a rc h a s s o c ia t e o f the A m e r i c a n D e n ta l A s s o c i a t io n a t th e N a t io n a l B u re a u o f S t a n d a r d s . D r. S o u d e r is c o n s u lt a n t t o th e a s s o c ia t e d ir e c t o r o f 1he N a t io n a l B u re a u o f S t a n d a r d s . 1. A . D . A . T r a n s a c t io n s


2. M c C a u l e y , C . M . G r e a t n e e d o f im p r o v e m e n t in the m a n u fa c t u r e o f a llo y s . N . D . A . T r a n s a c t io n s I9 I2 , p . 127.

13. P a ffe n b a r g e r , G e o r g e C . ; S t a n fo r d , J o h n W ., a n d Sw e e n e y, W . T. A m e r i c a n D e n ta l A s s o c i a t io n s p e c if ic a ­ t io n s f o r d e n t a l m a t e r ia ls . 1958. C h i c a g o , A m e r i c a n D e n ­ tal A s s o c ia t io n , 1958. 14. S o u d e r , W îlm e r , a n d P a ffe n b a r g e r , G e o r g e C . P h y sic a l p r o p e r t ie s o f d e n t a l m a t e r ia ls . C ir c u l a r C 4 3 3 o f th e N a t i o n a l B u re a u o f S t a n d a r d s . W a s h in g t o n , D . C ., U . S , G o v e r n m e n t P r in t in g O ffic e , 1942.

T h e R esearch W orker • T he research worker deals with the undefined boundaries o f knowledge and with the frayed edges o f sound inform ation. He does not m arch with the procession, but he must do lonely outpost and scouting duties. T heobald Smith.