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Review of Dental Materials Research in 1960
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9. Glimcher, M. J. Specificity of molecular structure of organic matrices in mineralization. In Calcification in biological systems, R. F. Sognnaes, editor, W ashing ton, D. C., A m . Assoc. Advance. S cj , I960, p. 421*487. 10. Solomons, C. C.; Irving, J. T., and Neuman, W. E. Calcificatiqn of dentin matrix. In Calcification in biological systems, R. F. Sognnaes, editor. W ash ington, D. C., Am. Assoc. Advance. Sc., I960, p. 203216. 11. Gonzales, F., and Sognnaes, R. F. Electronmicroscopy of dental calculus. Science 131:156 Jan. 15, I960. 12. Zander, H.; Scott, D. B., and Hazen, S. P. M in
eralization of dental calculus. Proc. Soc. Exper. Biol. & Med. 103:257 Feb. I960. 13. Watson, M . L. Extracellular nature of enamel tn the rat. J. Biophys. & Biochem. Cytol. 7:489 June I960. 14. Piez, K. A., and Likens, R. C. Nature of collagen. II. Vertebrate collagens. In Calcification In biological systems, R. F. Sognnaes, edtior. Washington, D. C., Am . Assoc. Advance. Sc., I960, p. 411-420. 15. Eastoe, J. E. O rganic matrix of tooth enamel. Nature 187:411 July I960. 16. Frank, R. M., and Sognnaes, R. F% Electron mi croscopy of matrix formation and calcification in rat enamel. Arch. O ral Biol. 1:339 March I960.
REVIEW OF DENTAL MATERIALS RESEARCH IN 1960
Gunndr Ryge* D.D.S., M.S., Milwaukee A review of the research reports pub lished in 1960 points out that the trend toward increased emphasis on the bio logical responses to dental materials ob served by Paffenbarger1 is gaining mo mentum. Also, the clinical significance of research findings concerning the physics, chemistry and metallurgy of dental materials was explored and inter preted by several investigators. Two new dental materials textbooks2,3 were published during 1960, and both reflect the clinical and biological trends. Both books not only give excellent and up-to-date coverage of the science of den tal materials but also yield valuable in terpretation of recent research findings and present practical discussions of auxiliary and restorative dental materials. They seemingly base the coverage in the field on the assumption that clinical den tistry can be classified to a large extent as applied dental materials. This as sumption, on the other hand, places the obligation on the dental materials re searcher to widen his sights to acknowl edge and include the biological and clinical aspects. The number of research reports pub lished on dental materials in 1960 is so
large that only a representative group of papers can be covered in this review. Only 3 of the 53 research reports pre sented to the Dental Materials Group of the International Association for Dental Research in M arch 1960 are included in this review; abstracts of the 53 papers were printed in the July-August 1960 issue of the Journal of Dental Research. T IS S U E R E SPO N SE S
Brannstrom and Nyborg4 studied pulp reaction to zinc oxyphosphate cement on a total of 25 contralateral pairs of teeth on dog and man with and without the use of a calcium hydroxide, zinc oxide, poly styrene liner. All teeth with unlined cavi ties showed pulpal changes, but in nine teeth with lined cavities there was no such impairment. Changes beneath un lined cavities included reduction of the predentin zone, pronounced loss of odontoblasts, or the presence of exudate cells amounting to more than slight infil tration. Burke 5 used zinc phosphate cement as one of his control materials in a study of pulpal response in rat molars to cavity cutting and acrylic resins containing
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fluoride. On the basis of histopathological studies, 87 per cent of pulpal re actions under acrylic resins containing fluoride were classified as mild or mod erate, whereas 13 per cent were classified as severe. Little or no difference was found between these reactions and those observed under control restorations (acrylic resin free of fluorides and zinc phosphate cements). Boyd and Mitchell6 implanted 19 phosphate and resin cements subdermally in rats and observed gross reactions and histologic changes at 2, 16 and 32 days after implantation. Zinc phosphate ce ments generally produced mild to mod erate reactions. Cements containing more zinc oxide and less additives produced the milder responses. When silver and copper salts, silicates or antibiotics were added, more severe responses were elicited. Mitchell and co-workers7 determined the ttimorigenicity of subdermal implants of dental materials in rats. Sarcomas de veloped around nickel pellets and nickelgallium alloy pellets. No tumors occurred around ten common dental materials. Kydd 8 studied the toxicity of diethylenetriamine, which is the amine curing agent for epoxy resins. Using standard patch tests on 50 human subjects, he found the agent to be no more toxic than monomeric acrylic acid. Toxicity of cured epoxy resin was studied by Kapsimalis .9 Powdered, cured, unfilled resin produced neither signs of sensitization nor evidence of primary irri tation in patch tests, whereas aluminafilled resins caused inhibition of cell growth and cell degeneration when intro duced in tissue cultures seeded with HeLa cells. Mjor and co-workers10 found that an increase in hardness of the dentin re sulted from the use of calcium hydroxide as a base covering. Increase of hardness under amalgam fillings was found to be insignificant. Fluorine uptake from various dental
materials was studied by Norman and co workers,11 who reported that the fluorine content of enamel was increased by resins and silicate cement that contained fluoride. The release of fluoride occurred relatively quickly and was correlated with reduction in enamel solubility. Fluoridefree silicate and zinc phosphate cements decreased the fluorine content of enamel, thus increasing its solubility. Radioactive phosphoric acid was used by Takada and others 12 to determine the cause of pulpal lesions under unlined sili cate cement in dogs’ teeth. By radioauto graphic examination it was found that radioactive phosphorus had reached the pulp cavity through the dentinal tubules after four days. Histological, radiochemi cal and dye penetration methods were used by Johnson and Wick 13 to study phosphoric acid penetration of cavity liners. SEALING PROBLEM S
The efficiency of various cavity lining materials was studied by Gillings and co workers,14 Swartz and Phillips,15 John son and Wick13 and Massler and Mansukhani.16 Different methods were em ployed in these studies and the results obtained seem to depend to some extent on the testing schemes used. In general, zinc phosphate cements gave virtually no protection to penetration by dyes, acids or radioisotopes, whereas zinc oxideeugenol and some of the resin liners showed somewhat better sealing proper ties. It appears that several of the test methods employed in these studies may give useful information as preliminary screening methods for new liners prior to or in connection with clinical testing and bio-assay of such materials. Marginal adaptation of many filling materials also received considerable at tention by research workers. Going and co-workers17 studied marginal penetra tion of dental restorations by different radioactive isotopes and pointed out that
R EV IEW O F I960 D EN T A L R ESEA R C H
the charge on the tracer and its chemical affinity greatly influence its adsorption on the surface of the filling material and on the tooth surface. The order of marginal permeability was found to vary with dif ferent isotopes. Later, the same authors 18 reported on marginal penetration by crystal violet dye and iodine131. Old silver amalgam and silicate cement restorations appeared to show less penetration at their margins than did fresh restorations. Some degree of penetration by iodine 131 oc curred with all filling materials. There was a complete lack of sealing in zinc phosphate cement and acrylic restora tions. Menegale and others19 reported a quantitative method for computing the area of leakage at margins of restorations. Their study showed that the surface con dition of the cavity wall is an important consideration in the study of marginal leakage, and it was found that rough-surfaced cavity walls considerably improved the resistance to marginal leakage for mat gold, cohesive gold foil, amalgam, silicate and, to some extent, resin restora tions. Parris and Kapsimalis20 studied the cavity sealing properties of nine filling materials (eight temporary filling mate rials and amalgam) at room temperature and after repeated temperature changes, by dye penetration. Only zinc oxideeugenol, amalgam and one commercial temporary filling material (Cavit) re sisted dye penetration at room tempera ture. Zinc oxide-eugenol showed some leakage after ten cycles of temperature change, whereas Cavit maintained a leakproof seal even after repeated tem perature changes. Marginal adaptation of amalgam and gold inlays was studied by Bjorndal and Sahs21 by comparative photomicrography. By this method, amalgam showed better adaptation than gold inlays, which al ways showed a cement line under magni fication. Burnishing of gold did not cover the cement line, but left a ragged margin.
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PH Y SICA L PRO PERTIES OF VARIOUS MATERIALS
Cement Bases • Hoppenstand and Mc Connell22 found that amalgam restora tions in deep cavities with extensive zinc oxide-eugenol underbases failed under relatively small loads, but when the same material was confined to a well-supported cavity preparation, the load sustained was similar to that sustained by amalgam over zinc phosphate cement or by amal gam alone. The authors indicated that the low values obtained in deep cavities may have been due partly to the weakening of the ivorine model teeth used. Lyell23 measured the ultimate crush ing strength of certain base forming materials and discussed the transfer of condensation pressure for amalgam to the base forming material. Zinc oxideeugenol does develop sufficient strength to withstand amalgam condensation, and, in view of the pulpal irritation from zinc phosphate cement, use of a modified zinc oxide-eugenol combination is sug gested with delay of amalgam condensa tion until a subsequent appointment. Present high-speed multiple cavity prepa ration lends itself to this technic. Smith 24 described a quick-setting zinc oxide-eugenol mix, and Fonterrada Vieira 23 studied the setting time of five commercial zinc oxide-eugenol impres sion pastes. Shorter initial and final setting times were observed with high powder-liquid ratio, extended mixing time, and raised temperature. The addi tion of water increased the setting time for some brands and decreased it for others. Comparison with Enamel and Dentin • Stanford and co-workers26 published data on compressive properties (modulus of elasticity, proportional limit, and strength in compression) of hard tooth tissues, di rect filling resins, plastic teeth, zinc phos phate cement, amalgam, silicate cement and three inlay golds. The stiffness
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(modulus) of enamel is higher than that of the restorative materials tested with the exception of the medium and hard gold alloys. The compressive strength of dentin is higher than that of the restora tive materials with the exception of amal gam (compressive strength of gold alloys could not be determined ). Die Materials • The surface hardness of seven stone die materials was studied by Rinne ,27 who obtained most uniform re sults with mechanical mixing under vacuum and routine proportioning of water and powder. So-called hardening treatments reduced the surface hardness. Lubricant should not be applied until the dies have aged sufficiently. Epoxy resin as a die material was studied by Ostlund and Akesson.28 Aluminum oxide as a filler was found to give best surface hardness and cutting re sistance. Dimensional stability was excel lent (less than 0.03 per cent contraction). Bending strength values equal to those for amalgam, and considerably higher than those for dental stones, were re ported. When the molds were filled by centrifugation, none had porosities, whereas practically all vibrated models showed air bubbles. Epoxy resin is well suited for use with impression materials on rubber base, but cannot be used in combination with aqueous impression materials. , Amalgam • The Council on Dental Re search of the American Dental Associa tion adopted the Fédération Dentaire Internationale Specification for Alloys for Dental Amalgam ,29 and the general assembly of the F.D.I. adopted a specifi cation for dental mercury .30 New equipment for the removal of mercury from amalgam was studied by Mosteller and co-workers.31 The repro ducibility of results with both centrifuge machines was good; the strength values and mercury contents compared favor ably with those obtained with a well-
standardized hand technic. Karlstrom 32 described a relatively high-frequency vi brator for amalgam condensation. Skinner and Mizera38 tested the prop erties of amalgam condensed by the Eames low-mercury, high-alloy condensa tion technic with small condensers. The most important feature of the Eames technic was found to be the high early strength obtained. Equal parts of mer cury and alloy can be used; the amalgam should be condensed very rapidly, with small condensers, otherwise layering will occur. Even with the 1:1 ratio, mercury will appear on the surface, and it should be removed before the next increment is condensed. Sweeney and Burns34 studied the effect of alloy-mercury ratios from 1:1 to 1:10 and found that the physical properties of amalgam are not significantly altered by the original alloy-mercury ratio. It should be noted, however, that the residual mer cury content of their specimens varied a maximum of 3 per cent for any one alloy. Tests by Jendresen and Ryge35 pointed up the fact that as particle size decreases, the amalgam exhibits more contraction (or less expansion), and in creased early strength. Amalgam made from alloys containing zinc produces more favorable results in compressive strength and flow tests and in dimen sional stability. Research in Australia • An extensive sur vey of the properties of 21 certified amal gam alloys and 22 noncertified alloys was published by Ware 36 and, on the basis of a thorough review of recent literature, a practical guide to the proper handling of amalgam was set forth .37 • The October 1960 issue of the Aus tralian Dental Journal was devoted to papers especially prepared by the direc tor and staff of the Commonwealth Bu reau of Dental Standards. General infor mation and original data are presented on physical properties of glass fiber mate rials,38 various impression materials ,39,40
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stainless steel,41 gypsum products,42'44 trability of the tin-foil substitute, and re tungsten carbide burs ,43 dental cements46 lease of internal stresses due to sorption and porcelain teeth .47 of water during polymerization. Tsurumaki73 found that crazing cracks in re Impression Materials • The large num pairs did not significantly change their ber of studies concerned with impression strength. The best results were obtained and duplication materials 48'53 is a good with heat-curing resins. Monomer should indication of the importance of and in be applied to establish adhesion. terest for increased knowledge of the The effects of four commonly used properties and behavior of these mate metal reinforcements for acrylic resin rials. were tested by Jennings and Wuebbenhorst.74 Two of these (stainless steel mesh Casting and Soldering • Problems con and braided wire plate) showed no nected with the casting and soldering significant increase in the transverse processes and the materials used in these strength of the resin, whereas the two procedures also received considerable others (stainless steel lingual bar and attention from research workers in 1960. .040 stainless steel wire) did increase the Mahler and Ady54 explained hygroscopic strength of the material. expansion in terms of surface tension Barnhart 75 suggested the use of a forces, and papers were published on combination of silicone rubber and properties of wax ,55’36 investment,57'61 methyl methacrylate for somatoprosthesis gold alloys,62,63 chrome cobalt alloys64 and studied the application of a silicone and soldering.65 rubber as a resilient denture base mate rial .76 Denture Materials • Woelfel and co Leathen 77 studied the microbiology of workers06' 67 reported extensive data on plastic dentures and found the predomi accuracy of fit of complete dentures. Con nating bacteria to be those of the resident ventional acrylic resins processed with the flora of the oral cavity. Odors occurring usual dental technic are as stable in di in some dentures may be attributed to mension as special resins. the resident flora of the tooth sockets of Cornell and co-workers08 found that dentures. Lauffer and Maderner 78 found impact resistance was improved by cross- that phenylmercuric borate in 4 per cent linking of the monomer but decreased by solution was an efficient disinfectant for plasticizers and fiber glass, silica or acrylic resin dentures. alumina oxide fillers. The compressive strength of dental Travaglini and co-workers69 studied gypsum was studied by Fairhurst,79 who Shore hardness and flow of resilient liners found that significant loss of strength re and evaluated ten commercial products. sulted from minute amounts of water ab Grant 70 in a clinical survey found that sorbed and, also, from storage of stone acrylic resin dentures with porcelain at elevated temperatures. The data help teeth fractured nine times more fre explain plastic deformation of denture quently than vinyl resin dentures with models caused by the preheating and processing. vinyl resin teeth. McCrorie and Anderson 71 found that Basic studies of physical factors related repairs with self-curing resins were 57 per to denture retention were reported by cent as strong as the original heat-cured Craig and co-workers.80 Capillary forces material. The slower the rate of poly were found to be responsible for reten merization, the stronger the repair. tion, and the relation of retention to film Causes of cracks in resin dentures were thickness and surface tension of saliva, identified by Miyamoto 72 as water pene area of the film and the receding con
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tact angle of saliva against plastic were studied. Reviews and Surveys • A number of re view or survey articles were published during 1960. The subject matter in these articles included amalgam ,81'84 dental cements,85 silicate cement,86,87 gold foil,88,89 restorations for deciduous teeth ,90 Class V restorations,91 impres sion materials ,02 casting investment,93 casting procedure ,94 porcelain fused to metal,95'98 occluding porcelain to resin teeth 99 and dental materials in gen eral.1,100'103 Some of these articles give original data, whereas others bring to gether a digest of recent developments in limited fields and, quite often, attempt to interpret research findings in terms of specific recommendations for the intelli gent use of methods and materials. Many other articles discussed dental materials and their manipulation exten sively in terms of the refinement of tech nics or the development of new methods. Most articles of this nature were not in cluded in this review even though they may well represent dental materials re search in its applied form. In several in stances such articles are based on empiri cal experimentation and some or all of the elements of organized research methods were not utilized. It should be realized, however, that the originators of such refined technics and improved methods based their work on the results of previous research efforts, and even if their articles may be classified as technic or clinic-type papers, the advancements that result are achieved because of—and will cause further advances in—dental materials research. 604 North Sixteenth Street
•Professor and chairman, department of dental mate* rials, Marquette University School of Dentistry. 1. Paffenbarger, G. C. Dental materials 1956-1958: a review. J.A.D.A. 60:600 M a y I960. 2. Peyton, F. A., and others. Restorative dental materials. St. Louis, C. V. M o sb y Co., I960.
3. Skinner, E. W., and Phillips, R. W . Science of dental materials, ed. 5. Philadelphia, W . B. Saunders Co., I960. 4. Brannstrom, M., and Nyborg, H. Dentinal and pulpal response. IV. Pulp reaction to zinc oxyphosphate cement— a m orphologic study on d og and man. Odont. Revy 11:37 No. I, I960. 5. Burke, G. W., Jr. Pulpal response in rat molars to cavity cutting and fluoride-containing acrylics. (Abst.) J. D. Res. 39:735 July-Aug. I960. 6. Boyd, J. B., Jr., and Mitchell, D. F. Subcutaneous connective tissue reaction of rats to Implanted dental cements. (Abst.) J. D. Res. 39:711 Juty-Aug. I960. 7. Mitchell, D. F.; Shankwalker, G . B., and Shazer, S. Determining the tumorlgenicity of dental materials. J. D. Res. 39:1023 Sept.-Oct. I960. 8. Kydd, W . L. Toxicity evaluation of diethylenetria* mine. J. D. Res. 39:46 Jan.-Feb. I960. 9. Kapsimalis, P. Toxicity studies of cured epoxy resins. J. D. Res. 39:1072 Sept.-Oct. I960. 10. Mjor, I. A.; Quigley, M . B., and Finn, S. B. Microchanges in sound human dentin. (Abst.) J. D. Res. 39:715 July-Aug. I960. 11. Norman, R. D.; Phillips, R. W., and Swartz, M . L. Fluoride uptake by enamel from certain dental mate rials. J. D .'R e s. 39:11 Jan.-Feb. I960. 12. Takada, Y., and others. Experimental study on radioactive phosphoric acid in silicate cement. Shikwa Gakuho 10:1 Oct. 1958. 13. Johnson, W . W., and W ick, J. H. Investigation of the penetration of cavity liners by phosphoric acid. (Abst.) J. D. Res. 39:752 July-Aug. I960. 14. Glllings, B.; Buonocore, M., and Sanda, O. In vitro evaluation of cavity liners. D. Progress 1:57 Oct. I960. 15. Swartz, M. L., and Phillips, R. W . Permeability of cavity liners to certain agents. (Abst.) J. D. Res. 39:752 July-Aug. I960. 16. Massler, M., and Mansukhaní, N. Testing liners under cements in vitro. J. Pros. Den. 10:964 Sept.-Oct. I960. 17. Going, R. E.; Massler, M., and Dute, H. L. M arginal penetration of dental restorations by dif ferent radioactive isotopes. J. D. Res. 39:273 MarchA p ril I960. 18. Going, R. E.; Massler, M., and Dute, H. L. M arginal penetration of dental restorations as studied by crystal violet dye and I131. J.A.D.A. 61:285 Sept. I960. 19. Menegale, C.; Swartz, M . L., and Phillips, R. W . Adaptation of restorative materials as influenced by roughness of cavity walls. J. D. Res. 39:825 July-Aug. I960. 20. Parris, L., and Kapsimalis, P. Effect of tempera ture change on thesealing properties of temporary filling materials.O ral Surg., O ral Med. & Oral Path. 13:982 Aug. I960. 21. Bjorndal, A . M., and Sahs, E. A . Comparative m icrophotographic study of marginal adaptation of am algam and go ld inlay restoration. Iowa D. J. 46:12 Feb. I960. 22. Hoppenstand, D. C., and McConnell, D. M e chanical failure of am algam restorations with zinc phosphate and zlnc-oxide/eugenol cement bases. J. D. Res. 39:899 Sept.-Oct. I960. 23. Lyell, J. S. Base form ing materials for restora tions of silver am algam . Austral. D. J. 3:132 June I960. 24. Smith, D. C. Quick-setting zinc-oxide/eugenol mixture. Brit. D. J. 108:232 March 15, I960. 25. Fonterrada Vieira, D. Pastas zinquenólicas. C on tribución al estudio de su tiempo de fraguado. Rev. A. odont. Argentina 47:145 M ay 1959. 26. Stanford, J. W., and others. Compressive proper ties of hard tooth tissues and some restorative mate rials. J.A.D.A. 60:746 June I960. 27. Rinne, V. W . Effects of various treatments on the surface hardness of stone die materials. J. Nebraska D. A . 36:14 March I960. 28. Óstlund, S. G., and Akesson, N. A. Epoxy resins as die material. Odont. Revy 11:225 No. 3, I960. 29. Council adopts F.D.!. Specification for Alloy for Dental Am algam . J.A.D.A. 60:773 June I960.
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30. Specification for dental mercury adopted by the general assembly. Fédération Dentaire Internationale. Internat. D. J. 10:256 June I960. 31. Mosteller, J. H.; Nadal, R., and Phillips, R. W . Preliminary study of the characteristics of two centrifuge machines for removal of mercury from amalgam. J. South. California D. A . 26:161 M ay I960. 32. Karlstrôm, S. New vibrator for amalgam con densation and removal of calculus. J. Pros. Den. 10:586 May-June I960. 33. Skinner, Ë. W., and Mizera, S . T. The Eames am algam condensation technique. D. Progress 1:13 Oct. I960. 34. Sweeney, W . T., and Burns, C. L. Effect of alloymercury ratio on the physical properties of amalgam. (Abst.) J. D. Res. 39:754 July-Aug. I960. 35. Jendresen, M. D., and Ryge, G. Effects of particle thickness of zinc and non-zinc alloys. D. Progress 1:25 Oct. I960. 36. Ware, A. L. Control of dental amalgam. Austral. D. J. 5:298 Oct. 1960. 37. Commonwealth Bureau of Dental Standards. Practical guide to successful silver amalgam restora tions. Guide No. I, I960. Melbourne, Australia, C om monwealth Bureau of Dental Standards, I960. 38. Dental products containing glass fibre. Austral. D. J. 5:260 Oct. I960. 39. Donnison,J. A . Zinc oxide-eugenol impression pastes. Austral. D. J. 5:262 Oct. I960. 40. Donnison,J. A., and Docking, A. R. Alginate impression materials. Austral. D. J. 5:280 Oct. I960. 41. Wilkinson, J. V. Effect of high temperatures on stainless steel orthodontic arch wire. Austral. D. J. 5:264 Oct. I960. 42. Donnison,J. A.; Chong, M . P., and Docking, A. R. Calorim etric study of the hygroscopic setting of calcined gypsum. Austral. D. J. 5:269 Oct. I960. 43. Ware, A . L., and McLaverty, V. G. Gypsum products. Austral. D. J. 5:273 Oct. I960. 44. Docking, A. R. Some experiments on the precipi tation of gypsum. Austral. D. J. 5:306 Oct. I960. 45. Chong, M. P., and Docking, A . R. Testing of tungsten carbide burs. Austral. D. J. 5:282 Oct. I960. 46. Griffith, J. R., and Ware, A. L. Evaluation of dental cements. Austral. D. J. 5:285 Oct. I960. V-47v,? Docking, A . R., and Chong, M. P. Note on the testrn'g of porcelain teeth. Austral. D. J. 5:292 Oct. I960. 48. Miller, W . A . C., Jr., and others. Physical proper ties of synthetic-rubber-base dental impression mate rials. J.A.D.A. 60:211 Feb. I960. 49. Miller, W . A . C., Jr., and others. Proposed specification for impression material; synthetic rubber base, dental. J.A.D.A. 60:224 Feb. I960. 50. C raig, R. G., and Peyton, F. A . Physical proper ties of elastic duplicating materials. J. D. Res. 39:391 March'-April I960. 51. Ayers, A. D., Jr., and others. Dental duplication test used to evaluate elastic impression materials. J. Pros. Den. 10:374 March-April I960. 52. Myers, G. E., and Stockman, D. G. Factors that affect the accuracy and dimensional stability of the mercaptan rubber-base impression materials. J, Pros. Den. 10:525 May-June I960. 53. Chase, W . W. Adaptation of rubber-base im pression materials to removable denture prosthetics. J. Pros. Den. 10:1043 Nov.-Dec. 1960. 54. Mahler, D. B., and Ady, A. B. Explanation for the h y g ro sc o p ic setting expansion of dental gypsum products. J. D. Res. 39:578 May-June I960. 55. Hollenback, G. M., and Rhoads, J. E. Thermal expansion of pattern wax. J. South. California D. A. 28:6 Jan. I960. 56. Hollenback, G % M., and Rhoads, J. E. C om parison of the expansion of the mold cavity with the linear casting shrinkage of gold. J. South. California D. A. 28:73 March I960. 57. Hollenback, G. M., and Rhoads, J. E. C o m parison of the linear expansion of investment with the linear casting shrinkage of gold. J. South. California D. A. 28:40 Feb. I960. 58.
Hollenback, G.
M., and Rhoads, J. E. Correla
tion of castings to mold dimension. J. South. California D. A. 28:183 June I960. 59. Earnshaw, R. Investments for casting cobaltchromium alloys. Brit. D. J. 108:389 June 7, I960. 60. Bell, R. D. New investing process. Brit. D. J. 108:179 March I, I960. 61. Hollenback, G. M., and Rhoads, J. E. Study of the separation of ingredients of investing materials. J. South. California D. A . 28:384 Dec. I960. 62. O'Brien, W . J. Physical properties of dental gold alloys. D. Labor 7:266 Nov. 10, 1959. 63. Caul, H. J.; C la b a u gh, W. S., and Susa, M. E. Procedure for the determination of the noble metal content of dental gold alloys. J.A.D.A. 61:439 Oct. I960. 64. Harcourt, H. J. Investigation into oxy-acetylene melting of chrome-cobalt alloys and its effect on sur face texture and homogeneity in castings. Brit. D. J. 108:139 Feb. 16, I960. 65. Parker, J. H. Im proved soldering technic. Angle Orthodont. 30:95 April I960. 66. Woelfel, J. B., and Paffenbarger, G. C. Dimen sional changes occurring in artificial dentures. Internat. D. J. 9:451 Dec. 1959. • 67. WoelfeJ, J. B.; Paffenbarger, G. C., and Sweeney, W. T. Dimensional changes occurring in dentures dur ing processing. J.A.D.A. 61:413 Oct. I960. 68. Cornell, J. A.; Tucker, J. L., and Powers, C. M. Physical properties of denture-base materials. J. Pros. Den. 10:516 May-June I960. 69. Travaglini, E. A.; G ibbons, P., and Craig, R. G. Resilient liners for dentures. J. Pros. Den. 10:664 JulyAug. I960. 70. Grant F. D. Clinical observations of number of fractures of acrylic and modified copolymer vinyl dentures. J.A.D.A. 61:578 N ov. I960. 71. McCrorie, J. W., and Anderson, J. N. Transverse strength of repairs with self-curing resins. Brit. D. J. 109:364 Nov. I, I960. 72. Miyamoto, M. Study on causes of crack in resin material-for denture plate. J. Nihon Univ. School Den. 2:163 March I960. 73. Tsurumaki, K. Study regarding strength on the development of crazing cracks in resin denture base. J. Nihon Univ. School Den. 2:141 March I960. 74. Jennings, R. E., and Wuebbenhorst, A . M . Effect of metal reinforcements on the transverse strength of acrylic resin. J. Den, C hild re n 27:162 3rd Quart. I960. 75. Barnhart, G. W. New material and technic in the art of somato-prosthesis, J. D. Res. 39:836 Ju!y-Aug. I960. 76. Barnhart, G . W. Silicone rubber as a resilient denture-base material. J. D. Res. 39:1077 Sept.-Oct. I960. 77. Leathen, W . W., and others. M icrobiology of plastic dentures. J.A.D.A. 60:164 Feb. 1960. 78. Lauffer, H .p and Maderner, F. Zur Frage der Desinfektion von zahnärztlichen Kunstoff-Arbeiten. Deut, zahnärztl. Zschr. 14:486 M arch 15, 1959. 79. Fairhurst, C. W . Com pressive properties of dental gypsum. J. D. Res. 39:812 July-Aug. I960. 80. Craig, R. G.; Berry, G . C., and Peyton, F. A. Physical factors related to denture retention. J. Pros. Den. 10:459 May-June 1960. 81. Weinstock, A . Biophysical properties of silver am algam — its use and abuse. J. Canad. D. A. 26:210 A pril I960. 82. Richardson, D. E. Som e considerations In pre venting amalgam failures. S. Carolina D. J. 18:19 M ay I960. 83. Roberts, E. W . Q u ality amalgam restorations. Texas D. J. 78:4 July I960. 84. Ambrose, E. R. Sound clinical procedures for amalgam restorations. J. C anad . D. A . 26:538 Sept. I960. 85. Dental cements; a review of their physical and chemical properties. J. Den. Children 27:113 2nd Quart. I960. 86. KaWer, F. W., Jr. C a vity restoration with silicate cement. J. Michigan D. A . 42:228 June I960. 87. McConnell, D., and Brawley, R. G . Compressive
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strength of "re in fo rc e d " silicate cement. J, Pros. Den. 10:1092 Nov.-Dee. I960. 88. Kramer, W . S.; Trandall, T. R., and Diefendorf, W . L. C om parative study of the physical properties of variously m anipulated go ld foil materials. J. Am. Acad. G o ld Foil O perators 3:8 M ay I960. 89. Astaff, A., and Morris, M. E. Use and abuse of mat gold. J. California D. A . & Nevada D. Soc. 36:23 Feb. 1960. 90. Ireland, R. L. Cavity preparation and restoration for primary teeth. J. Tennessee D. A . 40:161 July I960. 91. Mosteller, J. H. Class V restorations. J. Pros. Den. 10:561 May-June 1960. 92. Feuerstein, R. M. Physical properties and use of rubber-base impression material. J. Pros. Den. 10:179 Jan.-Feb. I960. 93. Shell, J. S. Milestones in the development of modern dental casting investment. D. Survey 36:616 M ay; 770 June I960. 94. O'Brien, W . J, Practical application of current casting research. J. Pros. Den. 10:558 May-June i960. 95. Cohen, R. Improved esthetics and greater strength using porcelain fused to metal crowns and bridges. New York J. Den. 30:168 M ay I960.
96. Johnston, J. F. Porcelain veneers bonded to precious metal castings. J. Canad. D. A. 26:657 Nov. I960. 97. Stiver, M.; Klein, G., and Howard, M . C. Evalua tion and comparison of porcelains fused to cast metals. J. Pros; Den. 10:1055 Nov.-Dee. I960. 98. Brecker, S. C. Porcelain fused to gold. J. C a li fornia D. A. & Nevada D. Soc. 36:425 Dec. 1960. 99. Sears, V. H. Occluding porcelain to resin teeth. A clinical evaluation survey. D. Survey 36:1144 Sept. I960. 100. Peyton, F. A. Review of dental materials re search in 1959. J.A.D.A. 60:577 M ay 1960. 101. American Dental Association, Bureau of Eco nomic Research and Statistics. Survey of dentist opinion. VI. Dental materials. J.A.D.A. 60:264 Feb. I960. 102. American Dental Association, Bureau of Eco nomic Research and Statistics. Survey of dentist opinion. V III. Summary. J.A.D.A. 60:787 June I960. 103. American Dental Association, Council on Dental Research. List of certified dental materials revised to June I, I960. J.A.D.A. 61:377 Sept. 1960.
Parkinson’s Law in Medicine • A successful candidate for an institutional job, a promotion or any society membership needs to produce a certain number of publications, and this is well justified. Less is known, however, about the following mechanism by which an astronomic proliferation of publications is brought about: The candidate presents a preliminary report in a local meeting and has it locally published. He reports the same insignificant group of experimental and clinical data, with a slight variation of title, in three or four journals. He gives a paper on the same subject to various national, state and county organizations, each of which demands a manuscript to feed its own anemic journal. He delivers an oration before an august body of national or international scope, again resulting in a slightly modified contribution. Finally, he writes a reappraisal of the originally proposed method or concept, retracting or modifying it. to a point where its validity has been destroyed. Thus, an original, prematurely published material may result in 1 to 20 papers. The profession is so used to this that it will not take notice of any new idea until it is seen again and again as a form of ‘nuisance’ type of advertisement. . . . Geza de Takats, Parkinson’s Law in Medicine. New England J. Med. 262:126 Jan. 21, 1960.
9. Glimcher, M. J. Specificity of molecular structure of organic matrices in mineralization. In Calcification in biological systems, R. F. Sognnaes, editor, W ashing ton, D. C., A m . Assoc. Advance. S cj , I960, p. 421*487. 10. Solomons, C. C.; Irving, J. T., and Neuman, W. E. Calcificatiqn of dentin matrix. In Calcification in biological systems, R. F. Sognnaes, editor. W ash ington, D. C., Am. Assoc. Advance. Sc., I960, p. 203216. 11. Gonzales, F., and Sognnaes, R. F. Electronmicroscopy of dental calculus. Science 131:156 Jan. 15, I960. 12. Zander, H.; Scott, D. B., and Hazen, S. P. M in
eralization of dental calculus. Proc. Soc. Exper. Biol. & Med. 103:257 Feb. I960. 13. Watson, M . L. Extracellular nature of enamel tn the rat. J. Biophys. & Biochem. Cytol. 7:489 June I960. 14. Piez, K. A., and Likens, R. C. Nature of collagen. II. Vertebrate collagens. In Calcification In biological systems, R. F. Sognnaes, edtior. Washington, D. C., Am . Assoc. Advance. Sc., I960, p. 411-420. 15. Eastoe, J. E. O rganic matrix of tooth enamel. Nature 187:411 July I960. 16. Frank, R. M., and Sognnaes, R. F% Electron mi croscopy of matrix formation and calcification in rat enamel. Arch. O ral Biol. 1:339 March I960.
REVIEW OF DENTAL MATERIALS RESEARCH IN 1960
Gunndr Ryge* D.D.S., M.S., Milwaukee A review of the research reports pub lished in 1960 points out that the trend toward increased emphasis on the bio logical responses to dental materials ob served by Paffenbarger1 is gaining mo mentum. Also, the clinical significance of research findings concerning the physics, chemistry and metallurgy of dental materials was explored and inter preted by several investigators. Two new dental materials textbooks2,3 were published during 1960, and both reflect the clinical and biological trends. Both books not only give excellent and up-to-date coverage of the science of den tal materials but also yield valuable in terpretation of recent research findings and present practical discussions of auxiliary and restorative dental materials. They seemingly base the coverage in the field on the assumption that clinical den tistry can be classified to a large extent as applied dental materials. This as sumption, on the other hand, places the obligation on the dental materials re searcher to widen his sights to acknowl edge and include the biological and clinical aspects. The number of research reports pub lished on dental materials in 1960 is so
large that only a representative group of papers can be covered in this review. Only 3 of the 53 research reports pre sented to the Dental Materials Group of the International Association for Dental Research in M arch 1960 are included in this review; abstracts of the 53 papers were printed in the July-August 1960 issue of the Journal of Dental Research. T IS S U E R E SPO N SE S
Brannstrom and Nyborg4 studied pulp reaction to zinc oxyphosphate cement on a total of 25 contralateral pairs of teeth on dog and man with and without the use of a calcium hydroxide, zinc oxide, poly styrene liner. All teeth with unlined cavi ties showed pulpal changes, but in nine teeth with lined cavities there was no such impairment. Changes beneath un lined cavities included reduction of the predentin zone, pronounced loss of odontoblasts, or the presence of exudate cells amounting to more than slight infil tration. Burke 5 used zinc phosphate cement as one of his control materials in a study of pulpal response in rat molars to cavity cutting and acrylic resins containing
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fluoride. On the basis of histopathological studies, 87 per cent of pulpal re actions under acrylic resins containing fluoride were classified as mild or mod erate, whereas 13 per cent were classified as severe. Little or no difference was found between these reactions and those observed under control restorations (acrylic resin free of fluorides and zinc phosphate cements). Boyd and Mitchell6 implanted 19 phosphate and resin cements subdermally in rats and observed gross reactions and histologic changes at 2, 16 and 32 days after implantation. Zinc phosphate ce ments generally produced mild to mod erate reactions. Cements containing more zinc oxide and less additives produced the milder responses. When silver and copper salts, silicates or antibiotics were added, more severe responses were elicited. Mitchell and co-workers7 determined the ttimorigenicity of subdermal implants of dental materials in rats. Sarcomas de veloped around nickel pellets and nickelgallium alloy pellets. No tumors occurred around ten common dental materials. Kydd 8 studied the toxicity of diethylenetriamine, which is the amine curing agent for epoxy resins. Using standard patch tests on 50 human subjects, he found the agent to be no more toxic than monomeric acrylic acid. Toxicity of cured epoxy resin was studied by Kapsimalis .9 Powdered, cured, unfilled resin produced neither signs of sensitization nor evidence of primary irri tation in patch tests, whereas aluminafilled resins caused inhibition of cell growth and cell degeneration when intro duced in tissue cultures seeded with HeLa cells. Mjor and co-workers10 found that an increase in hardness of the dentin re sulted from the use of calcium hydroxide as a base covering. Increase of hardness under amalgam fillings was found to be insignificant. Fluorine uptake from various dental
materials was studied by Norman and co workers,11 who reported that the fluorine content of enamel was increased by resins and silicate cement that contained fluoride. The release of fluoride occurred relatively quickly and was correlated with reduction in enamel solubility. Fluoridefree silicate and zinc phosphate cements decreased the fluorine content of enamel, thus increasing its solubility. Radioactive phosphoric acid was used by Takada and others 12 to determine the cause of pulpal lesions under unlined sili cate cement in dogs’ teeth. By radioauto graphic examination it was found that radioactive phosphorus had reached the pulp cavity through the dentinal tubules after four days. Histological, radiochemi cal and dye penetration methods were used by Johnson and Wick 13 to study phosphoric acid penetration of cavity liners. SEALING PROBLEM S
The efficiency of various cavity lining materials was studied by Gillings and co workers,14 Swartz and Phillips,15 John son and Wick13 and Massler and Mansukhani.16 Different methods were em ployed in these studies and the results obtained seem to depend to some extent on the testing schemes used. In general, zinc phosphate cements gave virtually no protection to penetration by dyes, acids or radioisotopes, whereas zinc oxideeugenol and some of the resin liners showed somewhat better sealing proper ties. It appears that several of the test methods employed in these studies may give useful information as preliminary screening methods for new liners prior to or in connection with clinical testing and bio-assay of such materials. Marginal adaptation of many filling materials also received considerable at tention by research workers. Going and co-workers17 studied marginal penetra tion of dental restorations by different radioactive isotopes and pointed out that
R EV IEW O F I960 D EN T A L R ESEA R C H
the charge on the tracer and its chemical affinity greatly influence its adsorption on the surface of the filling material and on the tooth surface. The order of marginal permeability was found to vary with dif ferent isotopes. Later, the same authors 18 reported on marginal penetration by crystal violet dye and iodine131. Old silver amalgam and silicate cement restorations appeared to show less penetration at their margins than did fresh restorations. Some degree of penetration by iodine 131 oc curred with all filling materials. There was a complete lack of sealing in zinc phosphate cement and acrylic restora tions. Menegale and others19 reported a quantitative method for computing the area of leakage at margins of restorations. Their study showed that the surface con dition of the cavity wall is an important consideration in the study of marginal leakage, and it was found that rough-surfaced cavity walls considerably improved the resistance to marginal leakage for mat gold, cohesive gold foil, amalgam, silicate and, to some extent, resin restora tions. Parris and Kapsimalis20 studied the cavity sealing properties of nine filling materials (eight temporary filling mate rials and amalgam) at room temperature and after repeated temperature changes, by dye penetration. Only zinc oxideeugenol, amalgam and one commercial temporary filling material (Cavit) re sisted dye penetration at room tempera ture. Zinc oxide-eugenol showed some leakage after ten cycles of temperature change, whereas Cavit maintained a leakproof seal even after repeated tem perature changes. Marginal adaptation of amalgam and gold inlays was studied by Bjorndal and Sahs21 by comparative photomicrography. By this method, amalgam showed better adaptation than gold inlays, which al ways showed a cement line under magni fication. Burnishing of gold did not cover the cement line, but left a ragged margin.
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PH Y SICA L PRO PERTIES OF VARIOUS MATERIALS
Cement Bases • Hoppenstand and Mc Connell22 found that amalgam restora tions in deep cavities with extensive zinc oxide-eugenol underbases failed under relatively small loads, but when the same material was confined to a well-supported cavity preparation, the load sustained was similar to that sustained by amalgam over zinc phosphate cement or by amal gam alone. The authors indicated that the low values obtained in deep cavities may have been due partly to the weakening of the ivorine model teeth used. Lyell23 measured the ultimate crush ing strength of certain base forming materials and discussed the transfer of condensation pressure for amalgam to the base forming material. Zinc oxideeugenol does develop sufficient strength to withstand amalgam condensation, and, in view of the pulpal irritation from zinc phosphate cement, use of a modified zinc oxide-eugenol combination is sug gested with delay of amalgam condensa tion until a subsequent appointment. Present high-speed multiple cavity prepa ration lends itself to this technic. Smith 24 described a quick-setting zinc oxide-eugenol mix, and Fonterrada Vieira 23 studied the setting time of five commercial zinc oxide-eugenol impres sion pastes. Shorter initial and final setting times were observed with high powder-liquid ratio, extended mixing time, and raised temperature. The addi tion of water increased the setting time for some brands and decreased it for others. Comparison with Enamel and Dentin • Stanford and co-workers26 published data on compressive properties (modulus of elasticity, proportional limit, and strength in compression) of hard tooth tissues, di rect filling resins, plastic teeth, zinc phos phate cement, amalgam, silicate cement and three inlay golds. The stiffness
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(modulus) of enamel is higher than that of the restorative materials tested with the exception of the medium and hard gold alloys. The compressive strength of dentin is higher than that of the restora tive materials with the exception of amal gam (compressive strength of gold alloys could not be determined ). Die Materials • The surface hardness of seven stone die materials was studied by Rinne ,27 who obtained most uniform re sults with mechanical mixing under vacuum and routine proportioning of water and powder. So-called hardening treatments reduced the surface hardness. Lubricant should not be applied until the dies have aged sufficiently. Epoxy resin as a die material was studied by Ostlund and Akesson.28 Aluminum oxide as a filler was found to give best surface hardness and cutting re sistance. Dimensional stability was excel lent (less than 0.03 per cent contraction). Bending strength values equal to those for amalgam, and considerably higher than those for dental stones, were re ported. When the molds were filled by centrifugation, none had porosities, whereas practically all vibrated models showed air bubbles. Epoxy resin is well suited for use with impression materials on rubber base, but cannot be used in combination with aqueous impression materials. , Amalgam • The Council on Dental Re search of the American Dental Associa tion adopted the Fédération Dentaire Internationale Specification for Alloys for Dental Amalgam ,29 and the general assembly of the F.D.I. adopted a specifi cation for dental mercury .30 New equipment for the removal of mercury from amalgam was studied by Mosteller and co-workers.31 The repro ducibility of results with both centrifuge machines was good; the strength values and mercury contents compared favor ably with those obtained with a well-
standardized hand technic. Karlstrom 32 described a relatively high-frequency vi brator for amalgam condensation. Skinner and Mizera38 tested the prop erties of amalgam condensed by the Eames low-mercury, high-alloy condensa tion technic with small condensers. The most important feature of the Eames technic was found to be the high early strength obtained. Equal parts of mer cury and alloy can be used; the amalgam should be condensed very rapidly, with small condensers, otherwise layering will occur. Even with the 1:1 ratio, mercury will appear on the surface, and it should be removed before the next increment is condensed. Sweeney and Burns34 studied the effect of alloy-mercury ratios from 1:1 to 1:10 and found that the physical properties of amalgam are not significantly altered by the original alloy-mercury ratio. It should be noted, however, that the residual mer cury content of their specimens varied a maximum of 3 per cent for any one alloy. Tests by Jendresen and Ryge35 pointed up the fact that as particle size decreases, the amalgam exhibits more contraction (or less expansion), and in creased early strength. Amalgam made from alloys containing zinc produces more favorable results in compressive strength and flow tests and in dimen sional stability. Research in Australia • An extensive sur vey of the properties of 21 certified amal gam alloys and 22 noncertified alloys was published by Ware 36 and, on the basis of a thorough review of recent literature, a practical guide to the proper handling of amalgam was set forth .37 • The October 1960 issue of the Aus tralian Dental Journal was devoted to papers especially prepared by the direc tor and staff of the Commonwealth Bu reau of Dental Standards. General infor mation and original data are presented on physical properties of glass fiber mate rials,38 various impression materials ,39,40
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stainless steel,41 gypsum products,42'44 trability of the tin-foil substitute, and re tungsten carbide burs ,43 dental cements46 lease of internal stresses due to sorption and porcelain teeth .47 of water during polymerization. Tsurumaki73 found that crazing cracks in re Impression Materials • The large num pairs did not significantly change their ber of studies concerned with impression strength. The best results were obtained and duplication materials 48'53 is a good with heat-curing resins. Monomer should indication of the importance of and in be applied to establish adhesion. terest for increased knowledge of the The effects of four commonly used properties and behavior of these mate metal reinforcements for acrylic resin rials. were tested by Jennings and Wuebbenhorst.74 Two of these (stainless steel mesh Casting and Soldering • Problems con and braided wire plate) showed no nected with the casting and soldering significant increase in the transverse processes and the materials used in these strength of the resin, whereas the two procedures also received considerable others (stainless steel lingual bar and attention from research workers in 1960. .040 stainless steel wire) did increase the Mahler and Ady54 explained hygroscopic strength of the material. expansion in terms of surface tension Barnhart 75 suggested the use of a forces, and papers were published on combination of silicone rubber and properties of wax ,55’36 investment,57'61 methyl methacrylate for somatoprosthesis gold alloys,62,63 chrome cobalt alloys64 and studied the application of a silicone and soldering.65 rubber as a resilient denture base mate rial .76 Denture Materials • Woelfel and co Leathen 77 studied the microbiology of workers06' 67 reported extensive data on plastic dentures and found the predomi accuracy of fit of complete dentures. Con nating bacteria to be those of the resident ventional acrylic resins processed with the flora of the oral cavity. Odors occurring usual dental technic are as stable in di in some dentures may be attributed to mension as special resins. the resident flora of the tooth sockets of Cornell and co-workers08 found that dentures. Lauffer and Maderner 78 found impact resistance was improved by cross- that phenylmercuric borate in 4 per cent linking of the monomer but decreased by solution was an efficient disinfectant for plasticizers and fiber glass, silica or acrylic resin dentures. alumina oxide fillers. The compressive strength of dental Travaglini and co-workers69 studied gypsum was studied by Fairhurst,79 who Shore hardness and flow of resilient liners found that significant loss of strength re and evaluated ten commercial products. sulted from minute amounts of water ab Grant 70 in a clinical survey found that sorbed and, also, from storage of stone acrylic resin dentures with porcelain at elevated temperatures. The data help teeth fractured nine times more fre explain plastic deformation of denture quently than vinyl resin dentures with models caused by the preheating and processing. vinyl resin teeth. McCrorie and Anderson 71 found that Basic studies of physical factors related repairs with self-curing resins were 57 per to denture retention were reported by cent as strong as the original heat-cured Craig and co-workers.80 Capillary forces material. The slower the rate of poly were found to be responsible for reten merization, the stronger the repair. tion, and the relation of retention to film Causes of cracks in resin dentures were thickness and surface tension of saliva, identified by Miyamoto 72 as water pene area of the film and the receding con
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tact angle of saliva against plastic were studied. Reviews and Surveys • A number of re view or survey articles were published during 1960. The subject matter in these articles included amalgam ,81'84 dental cements,85 silicate cement,86,87 gold foil,88,89 restorations for deciduous teeth ,90 Class V restorations,91 impres sion materials ,02 casting investment,93 casting procedure ,94 porcelain fused to metal,95'98 occluding porcelain to resin teeth 99 and dental materials in gen eral.1,100'103 Some of these articles give original data, whereas others bring to gether a digest of recent developments in limited fields and, quite often, attempt to interpret research findings in terms of specific recommendations for the intelli gent use of methods and materials. Many other articles discussed dental materials and their manipulation exten sively in terms of the refinement of tech nics or the development of new methods. Most articles of this nature were not in cluded in this review even though they may well represent dental materials re search in its applied form. In several in stances such articles are based on empiri cal experimentation and some or all of the elements of organized research methods were not utilized. It should be realized, however, that the originators of such refined technics and improved methods based their work on the results of previous research efforts, and even if their articles may be classified as technic or clinic-type papers, the advancements that result are achieved because of—and will cause further advances in—dental materials research. 604 North Sixteenth Street
•Professor and chairman, department of dental mate* rials, Marquette University School of Dentistry. 1. Paffenbarger, G. C. Dental materials 1956-1958: a review. J.A.D.A. 60:600 M a y I960. 2. Peyton, F. A., and others. Restorative dental materials. St. Louis, C. V. M o sb y Co., I960.
3. Skinner, E. W., and Phillips, R. W . Science of dental materials, ed. 5. Philadelphia, W . B. Saunders Co., I960. 4. Brannstrom, M., and Nyborg, H. Dentinal and pulpal response. IV. Pulp reaction to zinc oxyphosphate cement— a m orphologic study on d og and man. Odont. Revy 11:37 No. I, I960. 5. Burke, G. W., Jr. Pulpal response in rat molars to cavity cutting and fluoride-containing acrylics. (Abst.) J. D. Res. 39:735 July-Aug. I960. 6. Boyd, J. B., Jr., and Mitchell, D. F. Subcutaneous connective tissue reaction of rats to Implanted dental cements. (Abst.) J. D. Res. 39:711 Juty-Aug. I960. 7. Mitchell, D. F.; Shankwalker, G . B., and Shazer, S. Determining the tumorlgenicity of dental materials. J. D. Res. 39:1023 Sept.-Oct. I960. 8. Kydd, W . L. Toxicity evaluation of diethylenetria* mine. J. D. Res. 39:46 Jan.-Feb. I960. 9. Kapsimalis, P. Toxicity studies of cured epoxy resins. J. D. Res. 39:1072 Sept.-Oct. I960. 10. Mjor, I. A.; Quigley, M . B., and Finn, S. B. Microchanges in sound human dentin. (Abst.) J. D. Res. 39:715 July-Aug. I960. 11. Norman, R. D.; Phillips, R. W., and Swartz, M . L. Fluoride uptake by enamel from certain dental mate rials. J. D .'R e s. 39:11 Jan.-Feb. I960. 12. Takada, Y., and others. Experimental study on radioactive phosphoric acid in silicate cement. Shikwa Gakuho 10:1 Oct. 1958. 13. Johnson, W . W., and W ick, J. H. Investigation of the penetration of cavity liners by phosphoric acid. (Abst.) J. D. Res. 39:752 July-Aug. I960. 14. Glllings, B.; Buonocore, M., and Sanda, O. In vitro evaluation of cavity liners. D. Progress 1:57 Oct. I960. 15. Swartz, M. L., and Phillips, R. W . Permeability of cavity liners to certain agents. (Abst.) J. D. Res. 39:752 July-Aug. I960. 16. Massler, M., and Mansukhaní, N. Testing liners under cements in vitro. J. Pros. Den. 10:964 Sept.-Oct. I960. 17. Going, R. E.; Massler, M., and Dute, H. L. M arginal penetration of dental restorations by dif ferent radioactive isotopes. J. D. Res. 39:273 MarchA p ril I960. 18. Going, R. E.; Massler, M., and Dute, H. L. M arginal penetration of dental restorations as studied by crystal violet dye and I131. J.A.D.A. 61:285 Sept. I960. 19. Menegale, C.; Swartz, M . L., and Phillips, R. W . Adaptation of restorative materials as influenced by roughness of cavity walls. J. D. Res. 39:825 July-Aug. I960. 20. Parris, L., and Kapsimalis, P. Effect of tempera ture change on thesealing properties of temporary filling materials.O ral Surg., O ral Med. & Oral Path. 13:982 Aug. I960. 21. Bjorndal, A . M., and Sahs, E. A . Comparative m icrophotographic study of marginal adaptation of am algam and go ld inlay restoration. Iowa D. J. 46:12 Feb. I960. 22. Hoppenstand, D. C., and McConnell, D. M e chanical failure of am algam restorations with zinc phosphate and zlnc-oxide/eugenol cement bases. J. D. Res. 39:899 Sept.-Oct. I960. 23. Lyell, J. S. Base form ing materials for restora tions of silver am algam . Austral. D. J. 3:132 June I960. 24. Smith, D. C. Quick-setting zinc-oxide/eugenol mixture. Brit. D. J. 108:232 March 15, I960. 25. Fonterrada Vieira, D. Pastas zinquenólicas. C on tribución al estudio de su tiempo de fraguado. Rev. A. odont. Argentina 47:145 M ay 1959. 26. Stanford, J. W., and others. Compressive proper ties of hard tooth tissues and some restorative mate rials. J.A.D.A. 60:746 June I960. 27. Rinne, V. W . Effects of various treatments on the surface hardness of stone die materials. J. Nebraska D. A . 36:14 March I960. 28. Óstlund, S. G., and Akesson, N. A. Epoxy resins as die material. Odont. Revy 11:225 No. 3, I960. 29. Council adopts F.D.!. Specification for Alloy for Dental Am algam . J.A.D.A. 60:773 June I960.
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30. Specification for dental mercury adopted by the general assembly. Fédération Dentaire Internationale. Internat. D. J. 10:256 June I960. 31. Mosteller, J. H.; Nadal, R., and Phillips, R. W . Preliminary study of the characteristics of two centrifuge machines for removal of mercury from amalgam. J. South. California D. A . 26:161 M ay I960. 32. Karlstrôm, S. New vibrator for amalgam con densation and removal of calculus. J. Pros. Den. 10:586 May-June I960. 33. Skinner, Ë. W., and Mizera, S . T. The Eames am algam condensation technique. D. Progress 1:13 Oct. I960. 34. Sweeney, W . T., and Burns, C. L. Effect of alloymercury ratio on the physical properties of amalgam. (Abst.) J. D. Res. 39:754 July-Aug. I960. 35. Jendresen, M. D., and Ryge, G. Effects of particle thickness of zinc and non-zinc alloys. D. Progress 1:25 Oct. I960. 36. Ware, A. L. Control of dental amalgam. Austral. D. J. 5:298 Oct. 1960. 37. Commonwealth Bureau of Dental Standards. Practical guide to successful silver amalgam restora tions. Guide No. I, I960. Melbourne, Australia, C om monwealth Bureau of Dental Standards, I960. 38. Dental products containing glass fibre. Austral. D. J. 5:260 Oct. I960. 39. Donnison,J. A . Zinc oxide-eugenol impression pastes. Austral. D. J. 5:262 Oct. I960. 40. Donnison,J. A., and Docking, A. R. Alginate impression materials. Austral. D. J. 5:280 Oct. I960. 41. Wilkinson, J. V. Effect of high temperatures on stainless steel orthodontic arch wire. Austral. D. J. 5:264 Oct. I960. 42. Donnison,J. A.; Chong, M . P., and Docking, A. R. Calorim etric study of the hygroscopic setting of calcined gypsum. Austral. D. J. 5:269 Oct. I960. 43. Ware, A . L., and McLaverty, V. G. Gypsum products. Austral. D. J. 5:273 Oct. I960. 44. Docking, A. R. Some experiments on the precipi tation of gypsum. Austral. D. J. 5:306 Oct. I960. 45. Chong, M. P., and Docking, A . R. Testing of tungsten carbide burs. Austral. D. J. 5:282 Oct. I960. 46. Griffith, J. R., and Ware, A. L. Evaluation of dental cements. Austral. D. J. 5:285 Oct. I960. V-47v,? Docking, A . R., and Chong, M. P. Note on the testrn'g of porcelain teeth. Austral. D. J. 5:292 Oct. I960. 48. Miller, W . A . C., Jr., and others. Physical proper ties of synthetic-rubber-base dental impression mate rials. J.A.D.A. 60:211 Feb. I960. 49. Miller, W . A . C., Jr., and others. Proposed specification for impression material; synthetic rubber base, dental. J.A.D.A. 60:224 Feb. I960. 50. C raig, R. G., and Peyton, F. A . Physical proper ties of elastic duplicating materials. J. D. Res. 39:391 March'-April I960. 51. Ayers, A. D., Jr., and others. Dental duplication test used to evaluate elastic impression materials. J. Pros. Den. 10:374 March-April I960. 52. Myers, G. E., and Stockman, D. G. Factors that affect the accuracy and dimensional stability of the mercaptan rubber-base impression materials. J, Pros. Den. 10:525 May-June I960. 53. Chase, W . W. Adaptation of rubber-base im pression materials to removable denture prosthetics. J. Pros. Den. 10:1043 Nov.-Dec. 1960. 54. Mahler, D. B., and Ady, A. B. Explanation for the h y g ro sc o p ic setting expansion of dental gypsum products. J. D. Res. 39:578 May-June I960. 55. Hollenback, G. M., and Rhoads, J. E. Thermal expansion of pattern wax. J. South. California D. A. 28:6 Jan. I960. 56. Hollenback, G % M., and Rhoads, J. E. C om parison of the expansion of the mold cavity with the linear casting shrinkage of gold. J. South. California D. A. 28:73 March I960. 57. Hollenback, G. M., and Rhoads, J. E. C o m parison of the linear expansion of investment with the linear casting shrinkage of gold. J. South. California D. A. 28:40 Feb. I960. 58.
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Parkinson’s Law in Medicine • A successful candidate for an institutional job, a promotion or any society membership needs to produce a certain number of publications, and this is well justified. Less is known, however, about the following mechanism by which an astronomic proliferation of publications is brought about: The candidate presents a preliminary report in a local meeting and has it locally published. He reports the same insignificant group of experimental and clinical data, with a slight variation of title, in three or four journals. He gives a paper on the same subject to various national, state and county organizations, each of which demands a manuscript to feed its own anemic journal. He delivers an oration before an august body of national or international scope, again resulting in a slightly modified contribution. Finally, he writes a reappraisal of the originally proposed method or concept, retracting or modifying it. to a point where its validity has been destroyed. Thus, an original, prematurely published material may result in 1 to 20 papers. The profession is so used to this that it will not take notice of any new idea until it is seen again and again as a form of ‘nuisance’ type of advertisement. . . . Geza de Takats, Parkinson’s Law in Medicine. New England J. Med. 262:126 Jan. 21, 1960.