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Some clinical observations regarding the role of the fluid film in the retention of dentures
58 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
parison, and with little regard for ac curately defined criteria of measurement. The personal bias of the examiner is often outstanding, and the validity of the entire evaluation is dubious. A typical example of a nonobjective endorsement has been cited by Beecher: “ I have used the remedy you sent me in several patients. It is my distinct impression that this is the finest thing ever made for the purpose.” — Statement by an Eminent Clini cian.12
Testimonial evidence is almost never ac ceptable.
SUMMARY
This paper briefly sets forth certain basic requirements and concepts for conduct ing sound research in connection with the testing of agents with potential thera peutic usefulness in dentistry. It is in tended to serve both as a guide to those who may contemplate active investiga tions in this field, and as an aid to the critical dentist in evaluating reports of such studies, whether published or pre sented orally. 12. Beecher, H. K. Clinical impression and clinical investigation. J.A.M.A. f51;44 Jan. 3, 1953.
Some clinical observations regarding the role of the fluid film in the retention of dentures R. L. Campbell, D.D.S., M.S.D., Chicago
A brief examination of the dental litera ture for the past hundred years reveals that there is no unanimity concerning the actual physical forces responsible for the retention in situ o f the complete maxillary denture. Adhesion and cohe sion of molecules, capillary attraction, the “ suction” provided by atmospheric pressure, “ interfacial surface tension,” the pressure of the atmosphere relative to that of the fluid film— to cite only the most outstanding— are mentioned as contributors in whole or in part to the picture. The first American writer to speculate at any length on this problem was War ren,1 who in an 1897 revision o f Rich
ardson’s Mechanical Dentistry stated that two forces are utilized in the retention of dentures: atmospheric pressure and adhesion. The adhesion of solids to liquids, described as an extremely pro nounced force, he illustrated by an ex periment in which a polished plate is brought down carefully into contact with the surface of a liquid in such a way that adhesion takes place. Wilson2
Graduate student, Northwestern University Dental School. 1. Warren, George W., editor. Richardson's A prac tical treatise on mechanical dentistry, ed. 7. Philadel phia, Blakiston Co., 1897, p. 214-218. 2. Wilson, George H. A manual of dental pros thetics. Philadelphia, lea & Febiger, ,1914, p. 275-301.
CAMPBELL . . . VOLUME 48, JANUARY 1954 • 59
in 1914 concluded that atmospheric pres sure was of little actual value in reten tion unless a vacuum chamber was in cluded in the design of the plate because of the tendency of the layer of fluid be tween the baseplate and the soft tissues to equalize the pressure without and within. In 1923 Greve3 studied this problem by adapting for the purpose a model of the maxilla in soft vulcanite and a den ture baseplate with a hook in the palate. A film of saliva was introduced between the two surfaces, and weights were hung on the hook. Later, the process was re peated with the whole enclosed in a vacuum. No measurable difference in re tention ensued, so that adhesion was as sumed to be of more importance than atmospheric pressure. At about the same time Le Docte4 contended that the major factor in retention was “ la couche capillaire,” or, as it would be termed in Eng lish, the fluid film, operating through surface tension phenomena. He con cluded also after a series of experiments in which a layer of fluid was interposed between a solid surface and an elastic and deformable one that the greater the elasticity, the better was the retention. Page,5 in advancing the theories un derlying the static school of impressiontaking, wrote that since the only actual factor in denture retention is “ interfacial surface tension/’ operating by virtue of a thin film between two objects in close contact, the most desirable state to be attained in the construction of dentures is such a condition of close contact.5 As a result, he discounted entirely any ef fects of atmospheric pressure, such as had been reported by Snyder6 and a group of Navy colleagues in 1945. The latter had apparently proved by means of tests with denture-wearers in a decom pression chamber that a 50 per cent loss in retentive power of the dentures results from a 70 per cent reduction in atmos pheric pressure. Ostlund/ who in 1947 made labora
tory studies of retention using an elas tomer resin model based on the idea of Greve, proceeded to test baseplates of various constructions and fluid films of various properties. He observed that the less the viscosity and the greater the sur face tension of the fluid film, the greater was the retention. A contemporary analysis o f retention in terms of physical principles was made by Stanitz,8 who used the classic anal ogy of two glass plates with a film of fluid between them to simplify the pic ture of the denture seated in the mouth. Through a series of preliminary mathe matical equations, he arrived at the fol lowing :
F = 1CA a when F is the force, C the coefficient of surface tension, A the area of the plate and a the thickness of the fluid film. Since the preliminary steps included one in which the atmospheric pressure (Pa) minus the fluid pressure (Pf) was shown as being equal to twice the coefficient of surface tension (C ) divided by the thick ness (a) of the film (Pa — Pf) = 2C,
a the part played by the fluid film in re tention could apparently be assumed to be dependent on the pressure o f the at mosphere on it. Thus, although speculation has been abundant, the chief fact in the contro versy evidently remains to be established; namely, whether the weight of the at-
3. Greve, Karl. Luftdruk und Adhäsion der Befestig ung des Zahnersatzes. Deutsche Zahnärztl. Wchnschr. 30:25 Jan. 28, 1927. 4. Le Docte, J. Théorie physique de la rétention des appareils prothétiques du haut et réalîzatîon d'une nouvelle méthode rationnelle de prise d'empreinte. Rev. de stomatol. 29:1076 Dec. 1927. 5. Page, H. L. Mucostatîcs. Chicago, Author, 1946, p. 3. 6. Snyder, F. C., and others. Effect of reduced at mospheric pressure upon the retention of dentures. J.A.D.A. 32:445 April 1945. 7. östlund, S. L. G. Some principles in the retention of dentures. (Abst.) Northwest. Univ. Bui. 49:11 Nov. 22, 1948. 8. Stanitz, J. D. An analysis of the part played by the fluid film in denture retention. J.A.D.A. 57:168 Aug. 1948.
60 • THE JOURNAL OF THE AM ERICAN DENTAL ASSOCIATION
F ig . 1 • P a tie n t w ith nylon lin e, hollow ro d , p u lley a n d m e a su rin g a p p a r a tu s in p lac e. F o r p h o to g ra p h ic p u rp o se s, se v e ral b ars are m iss in g
mosphere or the phenomena related to surface tension and adhesion are mainly responsible for holding maxillary den tures in place. Consequently, it occurred to the writer, in the course of a series of clinical studies on denture retention,9 that if a way could be found to divorce one set of factors from the other, some light might be shed on the subject. A l though Greve, Snyder and others had attempted to nullify the influence of the atmosphere, nevertheless, in every experiment performed the fluid film was present, as far as can be ascertained. When it was demonstrated, therefore, that the fluid film could presumably be eliminated by practical means, a prom ising approach to the problem became apparent. MATERIALS AND M ETH ODS
The current work, the purpose of which was to determine the effects on the re tention of a maxillary denture of the at tempted elimination of the intermediary fluid film layer, was actually the continu ation of a series o f tests on other aspects of retention. For this study the same patient and clinical procedures were util
ized as in the other study. The complete description of the equipment used is re ported elsewhere.9 In brief, two baseplates were con structed, one by the Schlosser technic, now being employed at the Northwestern University Dental School, a technic in which a zinc oxide eugenol wash impres sion is used, and the other with an algi nate impresison. A number of wire sta ples were incorporated into the denture base in various positions. These served as eyes into which a hook could be in serted. By means of the mechanism shown in Figure 1, a static load was ap plied to an eye, perpendicular to the plane of the denture base, for the pur pose of dislodging the denture. If the force required to dislodge the baseplate, as measured by a spring dynamometer, was greater than 192 ounces, it was as sumed that the retention was complete. In the search for an effective “ drying” procedure, a pharmacological agent, such as atropine sulfate, seemed the ob vious means of stopping the formation of the fluid film through suppression of oral secretions. After a fairly lengthy in vestigation by trial and error, it was dis covered that relatively massive doses of this drug, administered orally to the patient after a short period of fasting, were necessary to achieve the desired result. The obliteration of all apparent fluid film was usually brought about after an interval of at least 90 minutes; the absence of the film was the chief crite rion, apart from the safety of the patient, for the dosage of the drug. The amount finally established for use in the experi ments was 1/50 grain. It is interesting to note that, except for extreme dryness of all the oral tissues, the patient in this experiment evidently experienced a minimum of the familiar reactions, such as dilation of the pupils, paralysis of ocu9. Skinner, E. W .; Campbell, R. L;i and Chung, P. A clinical study of the forces^ required to dislodge maxillary denture bases of various designs. J.A.D.A. 47:671 Dec. 1953.
CAMPBELL . . . VOLUME 48, JANUARY 1954 • 61
lar accommodation and gastrointestinal symptoms, normally associated with the use of this drug. The British Pharmaco poeia lists 1/60 grain as the maximum dose o f atropine sulfate. The average dose given clinically is 1/100.10 As to further indications of the dry ing effect of atropine, it was noted that the tissues o f the hard palate, soft palate, uvula and buccal sulcus were bone dry to the touch and exhibited a peculiar, iridescent, glazed appearance. A slight suggestion of dampness was evident in the floor of the m outh; however, since deglutition was prohibited during the tests, there was little possibility of trans fer of such moisture via the tongue. Fur thermore, before each trial, in an at tempt to detect any free moisture, the mouth was wiped out thoroughly with a towel and the palate likewise before, the plate was positioned. O f apparently great significance was the fact that identical conditions remained at the conclusion of each trial; that is, no free moisture could be detected either on the maxil lary surface of the denture or on the tissues in contact with it. In other words, no fluid film was visi ble before and during the time the den ture was seated. The length of time avail able for experimentation under the in fluence of 1/50 grain o f atropine sulfate was sufficient to enable all tests to be completed with the dry field.
T a b l e 1 • Effecf o f the presence or absence o f fluid film on the retention o f Plate 1
Eye no.
W ith fluid film
1 2 3 4 5 6 7 8
oz. 192+ 34.2 53.0 192+ 192+ 48.5 192+ 192+
W ithout fluid film oz. 192+ 73.6 92.8 192+ 192+ 58.8 192+ 192+
T a b l e 2 • Effect o f the presence or absence o f fluid film on the retention of Plate 2
Eye no.
W ith fluid film
W ithout fluid film
1 2 3 4 5 6 7 8 9
oz. 192+ 62.4 44.8 192+ 99.2 76.8 192+ 192+ 59.2
oz. 192+ 131.2 102.4 192+ 192+ 150.4 192 + 192+ 115.2
D IS C U S S IO N
From the tables (Tables 1 and 2) and graphs (Fig. 2 and 3 ), the results for the two plates can be noted. In the case of Plate 1, made from the paste-wash impression, a force of 192 ounces on eye no. 1, the median anterior eye, did not dislodge the plate. When the denture base was seated under ordinary condi tions, however, the area around eye no. 2, in the second molar region, sustained 34.2 ounces, while, when tested later in the dry environment, it was able to sup port 73.6 ounces. In like manner, the area around eye no. 3, also in the molar region, exhibited an increase in retentive force of from 53.0 ounces to 92.8 ounces when tested in the dry mouth. When the dry condi tion existed, the maximum load on eyes no. 4, 5, 7 or 8 did not dislodge the plate; at the same time, the retention in the midline (eye no. 6) increased from 48.5 ounces under the usual conditions to 58.8 ounces in the dry mouth. The results for Plate 2, constructed from an alginate impression, seem quite comparable in every way to those ob tained with Plate 1. The outstanding fact
10. Dorland, W. A. The American illustrated medical dictionary, ed. 20. Philadelphia. W. B. Saunders Co. 1944, p. 1663.
62 * THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
KEY WITH FLUID FILM WITHOUT FtUID FILM
200i 180 160 140i 120 100 80 60 40 20 EYE NO.
' 8 4 5 PLATE I
6
2
3
F ig . 2 • R e su lts fo r P la te 1 in term s o f re ten tion in o u n ces, w ith an d w ith ou t flu id film
again is that, for those eyes on which the applied force dislodged the plate at all, retention is shown to have been substan tially increased under the conditions of the experiment. O n the whole, for this plate, the increases are somewhat greater, as for example, the increase in force on eye no. 6 from 76.8 to 150.4 ounces. The fact that one baseplate was pro duced according to a static principle of impression-taking and the other by a more orthodox method appears to have had no particular bearing on the results. In fact, the over-all pattern for the two seems more remarkable for its consist ency; and the slight variations can prob ably be attributed to experimental vari ations, rather than to any significant differences between the technics them selves. The observation that the apparent ab sence of a fluid film between the denture and the palate seems to increase the re tention of a denture rather than to de crease it cannot be explained readily.
Since factors directly dependent on the fluid film, such as “ interfacial surface tension” and capillary attraction, are therefore seemingly eliminated as forces in denture retention, any practical theory based on these considerations would seem to require re-evaluation. O n the other hand, it may be that retention can be accounted for by some of the other hypotheses, such as adhesion; that is, the attraction of unlike molecules, as mentioned by Warren and Wilson.1’ 2 Although no fluid film could be dis cerned, there is, of course, the possi bility that some type of film was present and remained undetected. In such an event, the film would probably have been extremely thin. If that had been the case, according to the equations of Stanitz,8 the retentive force would have been greatly increased. The possible sources of such a film can only be surmised. Little is known concerning the question of tissue secre tions. If such secretions do exist in minute amounts, then the possible effect cannot
KEY WiTH FLUID FILM WITHOUT FLUID FILM
200 180
160 140 120 100
80
60 40
20 EYE NO- 1
8
4
5
6
2
PLATE n F ig . 3 • R e su lts fo r P la te 2 in term s o f re ten tion in o u n ces, w ith an d w ith ou t flu id film
CAMPBELL . . . VOLUME 48, JANUARY 1954 • 63
be neglected as a consideration in this connection. Another consideration, perhaps of greater likelihood, is that a minute water film was formed by the acrylic resin. The denture bases were stored in water at room temperature when not in use. Al though the denture base was always care fully dried before insertion, it is conceiv able that a syneresis of some nature may have occurred at mouth temperature dur ing the test. Such a situation seems rather improbable, however, since it is a well-known fact that the water-sorption of acrylic resin increases with the temperature and that therefore at body temperature water would be absorbed rather than expelled. At any rate, if any fluid film formed in this manner, it could not be detected by the means at hand during the experiment. SU M M A R Y AND CONCLUSIONS
The retention of acrylic resin maxillary denture baseplates was measured clini
cally with a fluid film and with the mouth surface dry. The following facts were made evident: 1. The absence of the normal layer of fluid between the denture base and the palate did not in any way lessen the retention of the denture. 2. In every case where the denture could be dislodged in a particular area, the amount of force necessary to dislodge it was actually increased by the appar ent lack of the fluid film. 3. In this respect, there appeared to be no significant difference in retention between plates made by the static technic and by a so-called pressure technic of impression-taking 4. The increase in retention of a den ture base without the usual fluid film cannot be explained on the basis of accepted theories.
T h e U n kn ow n N a tu re of P ro te in s • The empirical manner in which research in the protein field must proceed has long been a thorn in the side of biochemists. Besides requiring untold hours of cut-and-try experimentation, it leaves unanswered the fundamental questions on the nature o f proteins. Without proteins there is no life. Proteins exist only as part of and as products of life. Many agents producing disease owe their destructiveness to the proteins they contain. Yet, the structure of not one single protein is known! In spite of the immense variety of proteins and their range from beneficial to harmful, they are known to have many common characteristics. For instance, they can all be broken down into a very few chemical substances, all o f which are called amino acids; this is evidence that the underlying structure of all protein molecules is similar. There is a great deal of other evidence, all pointing in the same direction. However, the structure— the way atoms are arranged and fastened together— in even one kind of protein molecule is still unknown. If this underlying structure were known in the fundamental molecule of a protein, it would doubtless be possible to explain many of the ways that proteins behave and even to predict new things that proteins could do. “ S c ie n c e on the M a r c h ," T h e Sc ien tific M o n th ly 7 7 :1 1 0 A u g u st 1 9 5 3 .
parison, and with little regard for ac curately defined criteria of measurement. The personal bias of the examiner is often outstanding, and the validity of the entire evaluation is dubious. A typical example of a nonobjective endorsement has been cited by Beecher: “ I have used the remedy you sent me in several patients. It is my distinct impression that this is the finest thing ever made for the purpose.” — Statement by an Eminent Clini cian.12
Testimonial evidence is almost never ac ceptable.
SUMMARY
This paper briefly sets forth certain basic requirements and concepts for conduct ing sound research in connection with the testing of agents with potential thera peutic usefulness in dentistry. It is in tended to serve both as a guide to those who may contemplate active investiga tions in this field, and as an aid to the critical dentist in evaluating reports of such studies, whether published or pre sented orally. 12. Beecher, H. K. Clinical impression and clinical investigation. J.A.M.A. f51;44 Jan. 3, 1953.
Some clinical observations regarding the role of the fluid film in the retention of dentures R. L. Campbell, D.D.S., M.S.D., Chicago
A brief examination of the dental litera ture for the past hundred years reveals that there is no unanimity concerning the actual physical forces responsible for the retention in situ o f the complete maxillary denture. Adhesion and cohe sion of molecules, capillary attraction, the “ suction” provided by atmospheric pressure, “ interfacial surface tension,” the pressure of the atmosphere relative to that of the fluid film— to cite only the most outstanding— are mentioned as contributors in whole or in part to the picture. The first American writer to speculate at any length on this problem was War ren,1 who in an 1897 revision o f Rich
ardson’s Mechanical Dentistry stated that two forces are utilized in the retention of dentures: atmospheric pressure and adhesion. The adhesion of solids to liquids, described as an extremely pro nounced force, he illustrated by an ex periment in which a polished plate is brought down carefully into contact with the surface of a liquid in such a way that adhesion takes place. Wilson2
Graduate student, Northwestern University Dental School. 1. Warren, George W., editor. Richardson's A prac tical treatise on mechanical dentistry, ed. 7. Philadel phia, Blakiston Co., 1897, p. 214-218. 2. Wilson, George H. A manual of dental pros thetics. Philadelphia, lea & Febiger, ,1914, p. 275-301.
CAMPBELL . . . VOLUME 48, JANUARY 1954 • 59
in 1914 concluded that atmospheric pres sure was of little actual value in reten tion unless a vacuum chamber was in cluded in the design of the plate because of the tendency of the layer of fluid be tween the baseplate and the soft tissues to equalize the pressure without and within. In 1923 Greve3 studied this problem by adapting for the purpose a model of the maxilla in soft vulcanite and a den ture baseplate with a hook in the palate. A film of saliva was introduced between the two surfaces, and weights were hung on the hook. Later, the process was re peated with the whole enclosed in a vacuum. No measurable difference in re tention ensued, so that adhesion was as sumed to be of more importance than atmospheric pressure. At about the same time Le Docte4 contended that the major factor in retention was “ la couche capillaire,” or, as it would be termed in Eng lish, the fluid film, operating through surface tension phenomena. He con cluded also after a series of experiments in which a layer of fluid was interposed between a solid surface and an elastic and deformable one that the greater the elasticity, the better was the retention. Page,5 in advancing the theories un derlying the static school of impressiontaking, wrote that since the only actual factor in denture retention is “ interfacial surface tension/’ operating by virtue of a thin film between two objects in close contact, the most desirable state to be attained in the construction of dentures is such a condition of close contact.5 As a result, he discounted entirely any ef fects of atmospheric pressure, such as had been reported by Snyder6 and a group of Navy colleagues in 1945. The latter had apparently proved by means of tests with denture-wearers in a decom pression chamber that a 50 per cent loss in retentive power of the dentures results from a 70 per cent reduction in atmos pheric pressure. Ostlund/ who in 1947 made labora
tory studies of retention using an elas tomer resin model based on the idea of Greve, proceeded to test baseplates of various constructions and fluid films of various properties. He observed that the less the viscosity and the greater the sur face tension of the fluid film, the greater was the retention. A contemporary analysis o f retention in terms of physical principles was made by Stanitz,8 who used the classic anal ogy of two glass plates with a film of fluid between them to simplify the pic ture of the denture seated in the mouth. Through a series of preliminary mathe matical equations, he arrived at the fol lowing :
F = 1CA a when F is the force, C the coefficient of surface tension, A the area of the plate and a the thickness of the fluid film. Since the preliminary steps included one in which the atmospheric pressure (Pa) minus the fluid pressure (Pf) was shown as being equal to twice the coefficient of surface tension (C ) divided by the thick ness (a) of the film (Pa — Pf) = 2C,
a the part played by the fluid film in re tention could apparently be assumed to be dependent on the pressure o f the at mosphere on it. Thus, although speculation has been abundant, the chief fact in the contro versy evidently remains to be established; namely, whether the weight of the at-
3. Greve, Karl. Luftdruk und Adhäsion der Befestig ung des Zahnersatzes. Deutsche Zahnärztl. Wchnschr. 30:25 Jan. 28, 1927. 4. Le Docte, J. Théorie physique de la rétention des appareils prothétiques du haut et réalîzatîon d'une nouvelle méthode rationnelle de prise d'empreinte. Rev. de stomatol. 29:1076 Dec. 1927. 5. Page, H. L. Mucostatîcs. Chicago, Author, 1946, p. 3. 6. Snyder, F. C., and others. Effect of reduced at mospheric pressure upon the retention of dentures. J.A.D.A. 32:445 April 1945. 7. östlund, S. L. G. Some principles in the retention of dentures. (Abst.) Northwest. Univ. Bui. 49:11 Nov. 22, 1948. 8. Stanitz, J. D. An analysis of the part played by the fluid film in denture retention. J.A.D.A. 57:168 Aug. 1948.
60 • THE JOURNAL OF THE AM ERICAN DENTAL ASSOCIATION
F ig . 1 • P a tie n t w ith nylon lin e, hollow ro d , p u lley a n d m e a su rin g a p p a r a tu s in p lac e. F o r p h o to g ra p h ic p u rp o se s, se v e ral b ars are m iss in g
mosphere or the phenomena related to surface tension and adhesion are mainly responsible for holding maxillary den tures in place. Consequently, it occurred to the writer, in the course of a series of clinical studies on denture retention,9 that if a way could be found to divorce one set of factors from the other, some light might be shed on the subject. A l though Greve, Snyder and others had attempted to nullify the influence of the atmosphere, nevertheless, in every experiment performed the fluid film was present, as far as can be ascertained. When it was demonstrated, therefore, that the fluid film could presumably be eliminated by practical means, a prom ising approach to the problem became apparent. MATERIALS AND M ETH ODS
The current work, the purpose of which was to determine the effects on the re tention of a maxillary denture of the at tempted elimination of the intermediary fluid film layer, was actually the continu ation of a series o f tests on other aspects of retention. For this study the same patient and clinical procedures were util
ized as in the other study. The complete description of the equipment used is re ported elsewhere.9 In brief, two baseplates were con structed, one by the Schlosser technic, now being employed at the Northwestern University Dental School, a technic in which a zinc oxide eugenol wash impres sion is used, and the other with an algi nate impresison. A number of wire sta ples were incorporated into the denture base in various positions. These served as eyes into which a hook could be in serted. By means of the mechanism shown in Figure 1, a static load was ap plied to an eye, perpendicular to the plane of the denture base, for the pur pose of dislodging the denture. If the force required to dislodge the baseplate, as measured by a spring dynamometer, was greater than 192 ounces, it was as sumed that the retention was complete. In the search for an effective “ drying” procedure, a pharmacological agent, such as atropine sulfate, seemed the ob vious means of stopping the formation of the fluid film through suppression of oral secretions. After a fairly lengthy in vestigation by trial and error, it was dis covered that relatively massive doses of this drug, administered orally to the patient after a short period of fasting, were necessary to achieve the desired result. The obliteration of all apparent fluid film was usually brought about after an interval of at least 90 minutes; the absence of the film was the chief crite rion, apart from the safety of the patient, for the dosage of the drug. The amount finally established for use in the experi ments was 1/50 grain. It is interesting to note that, except for extreme dryness of all the oral tissues, the patient in this experiment evidently experienced a minimum of the familiar reactions, such as dilation of the pupils, paralysis of ocu9. Skinner, E. W .; Campbell, R. L;i and Chung, P. A clinical study of the forces^ required to dislodge maxillary denture bases of various designs. J.A.D.A. 47:671 Dec. 1953.
CAMPBELL . . . VOLUME 48, JANUARY 1954 • 61
lar accommodation and gastrointestinal symptoms, normally associated with the use of this drug. The British Pharmaco poeia lists 1/60 grain as the maximum dose o f atropine sulfate. The average dose given clinically is 1/100.10 As to further indications of the dry ing effect of atropine, it was noted that the tissues o f the hard palate, soft palate, uvula and buccal sulcus were bone dry to the touch and exhibited a peculiar, iridescent, glazed appearance. A slight suggestion of dampness was evident in the floor of the m outh; however, since deglutition was prohibited during the tests, there was little possibility of trans fer of such moisture via the tongue. Fur thermore, before each trial, in an at tempt to detect any free moisture, the mouth was wiped out thoroughly with a towel and the palate likewise before, the plate was positioned. O f apparently great significance was the fact that identical conditions remained at the conclusion of each trial; that is, no free moisture could be detected either on the maxil lary surface of the denture or on the tissues in contact with it. In other words, no fluid film was visi ble before and during the time the den ture was seated. The length of time avail able for experimentation under the in fluence of 1/50 grain o f atropine sulfate was sufficient to enable all tests to be completed with the dry field.
T a b l e 1 • Effecf o f the presence or absence o f fluid film on the retention o f Plate 1
Eye no.
W ith fluid film
1 2 3 4 5 6 7 8
oz. 192+ 34.2 53.0 192+ 192+ 48.5 192+ 192+
W ithout fluid film oz. 192+ 73.6 92.8 192+ 192+ 58.8 192+ 192+
T a b l e 2 • Effect o f the presence or absence o f fluid film on the retention of Plate 2
Eye no.
W ith fluid film
W ithout fluid film
1 2 3 4 5 6 7 8 9
oz. 192+ 62.4 44.8 192+ 99.2 76.8 192+ 192+ 59.2
oz. 192+ 131.2 102.4 192+ 192+ 150.4 192 + 192+ 115.2
D IS C U S S IO N
From the tables (Tables 1 and 2) and graphs (Fig. 2 and 3 ), the results for the two plates can be noted. In the case of Plate 1, made from the paste-wash impression, a force of 192 ounces on eye no. 1, the median anterior eye, did not dislodge the plate. When the denture base was seated under ordinary condi tions, however, the area around eye no. 2, in the second molar region, sustained 34.2 ounces, while, when tested later in the dry environment, it was able to sup port 73.6 ounces. In like manner, the area around eye no. 3, also in the molar region, exhibited an increase in retentive force of from 53.0 ounces to 92.8 ounces when tested in the dry mouth. When the dry condi tion existed, the maximum load on eyes no. 4, 5, 7 or 8 did not dislodge the plate; at the same time, the retention in the midline (eye no. 6) increased from 48.5 ounces under the usual conditions to 58.8 ounces in the dry mouth. The results for Plate 2, constructed from an alginate impression, seem quite comparable in every way to those ob tained with Plate 1. The outstanding fact
10. Dorland, W. A. The American illustrated medical dictionary, ed. 20. Philadelphia. W. B. Saunders Co. 1944, p. 1663.
62 * THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
KEY WITH FLUID FILM WITHOUT FtUID FILM
200i 180 160 140i 120 100 80 60 40 20 EYE NO.
' 8 4 5 PLATE I
6
2
3
F ig . 2 • R e su lts fo r P la te 1 in term s o f re ten tion in o u n ces, w ith an d w ith ou t flu id film
again is that, for those eyes on which the applied force dislodged the plate at all, retention is shown to have been substan tially increased under the conditions of the experiment. O n the whole, for this plate, the increases are somewhat greater, as for example, the increase in force on eye no. 6 from 76.8 to 150.4 ounces. The fact that one baseplate was pro duced according to a static principle of impression-taking and the other by a more orthodox method appears to have had no particular bearing on the results. In fact, the over-all pattern for the two seems more remarkable for its consist ency; and the slight variations can prob ably be attributed to experimental vari ations, rather than to any significant differences between the technics them selves. The observation that the apparent ab sence of a fluid film between the denture and the palate seems to increase the re tention of a denture rather than to de crease it cannot be explained readily.
Since factors directly dependent on the fluid film, such as “ interfacial surface tension” and capillary attraction, are therefore seemingly eliminated as forces in denture retention, any practical theory based on these considerations would seem to require re-evaluation. O n the other hand, it may be that retention can be accounted for by some of the other hypotheses, such as adhesion; that is, the attraction of unlike molecules, as mentioned by Warren and Wilson.1’ 2 Although no fluid film could be dis cerned, there is, of course, the possi bility that some type of film was present and remained undetected. In such an event, the film would probably have been extremely thin. If that had been the case, according to the equations of Stanitz,8 the retentive force would have been greatly increased. The possible sources of such a film can only be surmised. Little is known concerning the question of tissue secre tions. If such secretions do exist in minute amounts, then the possible effect cannot
KEY WiTH FLUID FILM WITHOUT FLUID FILM
200 180
160 140 120 100
80
60 40
20 EYE NO- 1
8
4
5
6
2
PLATE n F ig . 3 • R e su lts fo r P la te 2 in term s o f re ten tion in o u n ces, w ith an d w ith ou t flu id film
CAMPBELL . . . VOLUME 48, JANUARY 1954 • 63
be neglected as a consideration in this connection. Another consideration, perhaps of greater likelihood, is that a minute water film was formed by the acrylic resin. The denture bases were stored in water at room temperature when not in use. Al though the denture base was always care fully dried before insertion, it is conceiv able that a syneresis of some nature may have occurred at mouth temperature dur ing the test. Such a situation seems rather improbable, however, since it is a well-known fact that the water-sorption of acrylic resin increases with the temperature and that therefore at body temperature water would be absorbed rather than expelled. At any rate, if any fluid film formed in this manner, it could not be detected by the means at hand during the experiment. SU M M A R Y AND CONCLUSIONS
The retention of acrylic resin maxillary denture baseplates was measured clini
cally with a fluid film and with the mouth surface dry. The following facts were made evident: 1. The absence of the normal layer of fluid between the denture base and the palate did not in any way lessen the retention of the denture. 2. In every case where the denture could be dislodged in a particular area, the amount of force necessary to dislodge it was actually increased by the appar ent lack of the fluid film. 3. In this respect, there appeared to be no significant difference in retention between plates made by the static technic and by a so-called pressure technic of impression-taking 4. The increase in retention of a den ture base without the usual fluid film cannot be explained on the basis of accepted theories.
T h e U n kn ow n N a tu re of P ro te in s • The empirical manner in which research in the protein field must proceed has long been a thorn in the side of biochemists. Besides requiring untold hours of cut-and-try experimentation, it leaves unanswered the fundamental questions on the nature o f proteins. Without proteins there is no life. Proteins exist only as part of and as products of life. Many agents producing disease owe their destructiveness to the proteins they contain. Yet, the structure of not one single protein is known! In spite of the immense variety of proteins and their range from beneficial to harmful, they are known to have many common characteristics. For instance, they can all be broken down into a very few chemical substances, all o f which are called amino acids; this is evidence that the underlying structure of all protein molecules is similar. There is a great deal of other evidence, all pointing in the same direction. However, the structure— the way atoms are arranged and fastened together— in even one kind of protein molecule is still unknown. If this underlying structure were known in the fundamental molecule of a protein, it would doubtless be possible to explain many of the ways that proteins behave and even to predict new things that proteins could do. “ S c ie n c e on the M a r c h ," T h e Sc ien tific M o n th ly 7 7 :1 1 0 A u g u st 1 9 5 3 .