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Surface tension in retention of complete dentures
Surface
tension
in retention
Whammed
Aleem
Abdullah,
Dental
Madras
Medical
Wing,
of corn
dentures
M.D.S.* College,
Madras,
India
R
etention of complete dentures is that state wherein functional forces acting away from the mucous membrane are unable to destroy the attachment existing between the dentures and the underlying mucousmembrane. Retention of complete dentures is accomplished by mechanical, biologic, and physical factors. The thin film of saliva interposed between the mucosa and the dentures acts as a fluid medium and establishesphysical forces of adhesion, cohesion, and surface tension.lV5These physical factors, though of small magnitude, hold the dentures in place. Atmospheric pressure and gravity are other physical factors of retention. Adhesion, cohesion, and surface tension require explanation. The three states of matter (liquid, gas, and solid) depend upon the variation in the aggregation of molecules.6Kronig,? Maxwell,8 and Boltzmanns postulated that the molecules of gas are in a state of motion and hence attain no form. Even in liquids the molecules separate from each other with difficulty. In solids, each molecule has a definite position about which it vibrates. The binding intermolecular force in the solid state of matter is very high. Hence, the moleculesare fixed. RETENTION OF COMPLETE DENTURES Cohesion. The intermolecular forces, referred to as van der Waals forces, wherein atoms and hence moleculesare attracted to one another, are electrical in nature.“~ lo-l2 This intermolecular force is cohesion, and it is explained on the basisof the atomic structure of matter. The atoms of a molecule consistof a positive nucleus and negative electrons moving in an orbit. In forming a molecule, atoms share their electrons and move very close to one another. If the center of gravity of electrons does not coincide with that of the molecules, the atom is supposedto have a separation of charge or dipole, When two dipoles are close, they attract each other. This attractive force existing between the dipoles of atoms and hence molecules of the same matter is known ascohesive force.13 *Lecturer
in Prosthetic
Dentistry.
141
142
Abdullah
J. Prosthet. Dent. August, 1972
Adhesion. A molecule with a separation of charge or dipole is capable of inducing a separation of charge in a molecule of different matter and establishingan attractive force. This phenomenon is known as adhesion. Thus, a permanent dipole of a molecule of water induces a temporary separation of charge in the molecule of glass, establishesan attractive force, and adheres to the glasssurface. Though most liquids exhibit this phenomenon, mercury is an exception. Surface tension. The cohesive force acting on the surface of liquids is responsible for still another phenomenon, namely surface tension. Ramsay and ShieldsI stated that the phenomenon of surface tension was due to unbalanced molecular attraction at the surface of liquids. The molecules in the bulk of the liquid are attracted in all directions by the adjacent molecules, and the resultant force on the molecule is zero. However, the molecules oriented at the surface of the liquid are mainly attracted toward the bulk of the liquid, becauseno such cohesive force exists just above the surface. This results in an unbalanced molecular attraction. The resultant effect is that the molecules at the surface are pulled toward the bulk of the liquid. This contractile force at the surface is referred to as surface tension or surface free energy. The molecules at the surface gained potential energy, becausethey are oriented in the field of cohesive f0rce.l This potential energy is capable of performing work; in other words, it has the capacity to reduce the surface area of the liquid when it is subjected to a stretching force. Thus, surface tension is also referred to as surface potential energy. When two nomniscible liquids are in contact, a definite amount of surface energy exists at the interface between the two surfaces of liquids. This surface energy is known as the intrinsic interfacial energy of the liquids or inter-facial surface tension. The surfaces of both liquids and solids possesssurface energy. However, the effects of surface energy are apparent only when the surface is mobile.13The free surface energy of solids is much more difficult to measure than that of liquids because of the ability of solids to support shear stress.The free surface energy of solids is higher than that of liquids. A thin metal foil shrinks when heated. This shrinkage or “creep” according to Chapman and BorteP is due to the free surface energy, and it is calculated from creep measurements. The surface tension of gold (22 carats) calculated by the creep method is 1.510 dynes/cm. Among the liquids, mercury has the highest surface tension of 475 dynes/cm. at room temperature. The surface tension of water at 20’ C. is 72.75 dynes/cm., while that of most organic liquids lies between 25 and 30 dynes/cm. Cushman and associateP determined surface tension of saliva obtained from 25 subjects and found it to vary from 49.6 to 57.4 dynes/cm. Ropaczewesky17reported this value to vary from 69.7 to 71.4 dynes/cm. Both investigators used the Du Nocy tensiometer13for the determination of the surface tension of saliva, Craig and associates* collected saliva by stimulation with paraffin wax. They determined surface tension using the Du Noiiy tensiometer and observed values that varied from 53.4 to 57.0 dynes/cm. They conducted an experiment to analyze the forces of adhesion, cohesion, and surface tension in retention by using glassand acrylic resin plates. The reduction of pressurewas calculated by the application of the Stan& fomula.*Q Craig and co-workers2 argued that if the film thickness was approximately 10 P,
Volllme 28 Number 2
Surface
tension
in retention
of dentures
143
the radius of curvature would be 5 J.L Using this value of radius of curvature (5 EL) and surface tension of saliva as 54 dynes/cm., the pressure reduction would be approximately 0.08 pound per inch. This pressure difference would represent 0.5 pt:l cent of atmospheric pressure. From this study, they concluded that reduced pressure in the film of saliva contributed little to the retention of complete dentures. is the principal factor, According to Craig and associates, 2 the force of capillarity in retention of complete dentures. They maintained that capillarity is a combined result of cohesion, adhesion, and surface tension. DISCUSSION Craig and co-workers2 realized the role of adhesive force, calculated its magnitude, and introduced it in an equation to determine the retentive force. Stanitz”’ also mentioned the importance of adhesive force. However, he did not include it in: the equation to assess the force of retention. The theory that reduced atmospheric pressure in the thin film of saliva is thr only means of holding the dentures in place was subjected to criticism by the proponents of the mucostatic technique. Snyder and other? reported that a 70 per cent reduction in atmospheric pressure resulted in less than a 50 per cent reduction ol retention. Craig and associate? maintained that reduced atmospheric pressure in the film of saliva contributed little to the retention of dentures. Thus, reduced atmospheric, pressure alone is not the principal factor of retention. Due to its position, the upper denture is constantly acted upon by gravitational forces. This dislodging force is overcome by adhesion and cohesion, because when a layer of saliva comes in contact with the impression surface of the denture, thr adhesive force starts to operate, By definition, the force necessary to counteract adhesion is that required to separate the unit cross-sectional area of the interface hetween two plates interposed by a film of liquids.G Surface tension is potential energy that is capable of performing work such as contracting or minimizing the surface area of liquids when they are subjected to stretching forces.G Therefore, surface tension operates only when it is called uporr. The force of surface tension is effective when the dentures are dislodged away from the denture-bearing mucous membrane. cohesion, and surface tensiorl According to Schultze, 21 the forces of adhesion, are maximum when the thickness of the interposed film of water is minimum ( 10 F, Therefore, accurate adaptation of the denture base aids the physical factors of saliva in operating at their optimal level.
SUMMARY Adhesion, cohesion, and surface tension are explained on the basis of the atomic. structure of matter. Surface tension is considered as potential energy in that it is capable of performing work such as contracting or minimizing the surface area of liquid when it is subjected to a stretching force. Surface tension operates when the dentures are dislodged. Adhesion, cohesion, and surface tension operate at their optimal levels when the thickness of the fluid film is 10 p. Accurate adaptation of the denture base is conducive to good retention.
144
J. Prosthet. Dent.
Abdullah
August, 1972
References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
17. 18. 19. 20. 21.
Findlay, A.: Introduction to Physical Chemistry, ed. 3, London, 1960, Longmans, Green & Company, p. 534. Factors Related to Denture ReCraig, R. G., Berry, G. C., and Peyton, F. A.: Physical tention, J. PROSTHET. DENT. 10: 459-467, 1960. Cambell, R. L.: Some Clinical Observations Regarding the Role of the Film in the Retention of Dentures, J. Am. Dent. Assoc. 48: 58-63, 1954. Lammie, G. A.: The Retention of Complete Dentures, J. Am. Dent. Assoc. 55: 502-508, 1957. Ostlund, S. G.: Saliva and Denture Retention, J. PROSTHET. DENT. 10: 658-663, 1960. 1961, McGraw-Hill Book Company, Gordon, M. B.: Physical Chemistry, New York, Inc., p. 411. Kronig, A.: Kinetic Theory of Gases, Annalen der Physik. Poggendorff Jubdband. 99: 322-327, 1856. Maxwell, C.: Kinetic Theory of Gases, Phil. Mag. 19: 22-29, 1860. Boltzmann, L.: Varlessungen Ober Gas Thearie, ed. 1, Leipzig, 1898, StGchiometrie und Verwandtschaftsbhre. Debye, P.: Inter-molecular Forces, Physik. Z. Leipzig 21: 178-185, 1920. Keeson, W. H.: van der Waal’s Forces, Physik. Z. Leipzig 22: 129-135, 1921. London, F.: Inter-molecular Forces, Z. Physik. Chemie. B. 11: 222-227, 1930. Walter, J. M.: Physical Chemistry, ed. 3, New York, 1959, Prentice-Hall, Inc., p, 499. Ramsay, V., and Shields, J.: Surface Tension Determination, Philosoph. Trans. R. Sot., 184: 647-654, 1893. Chapman, C. L., and Borter, K.: Surface Potential Energy in Solids, J. Phys. Chem. 25: 422-429, 1953. Cushman, F. H., Etherington, J. W., and Thompson, G. E.: Relationship of Salivary Surface Tension and Rate of Flow to Dental Caries in an Adolescent Group, J. Dent. Res. 20: 251-253, 1941. Ropaczewesky, E. W.: Salivary Viscosity and Calculus Formation in Man, Arch. Oral Biol. 9: 65-71, 1964. Du Noiiy, L.: Surface Equilibria of Organic and Biological Colloids, New York, 1926, The Chemical Catalog Company, Inc. Stanitz, J. D.: An Analysis of the Part Played by the Fluid Film in Denture Retention, J. Am. Dent. Assoc. 37: 168-172, 1948. Snyder, F. C., Kimball, H. D., Bunch, W. B., and Beaton, J. H.: Effect of Reduced Atmospheric Pressure Upon Retention of Dentures, J. Am. Dent. Assoc. 32: 445-450, 1945. Schultze, W.: Uber AshIsion Und Luftadruck Und ihre Verwendung bei der Fixierung kiinstlicher Gebisse, Dtsch. Zahnaerztl. Z. 24: 538-547, 1921. 103 MADHAVARAM PERAMBUR, INDIA
MADRAS-~
HIGH 1
RD.
tension
in retention
Whammed
Aleem
Abdullah,
Dental
Madras
Medical
Wing,
of corn
dentures
M.D.S.* College,
Madras,
India
R
etention of complete dentures is that state wherein functional forces acting away from the mucous membrane are unable to destroy the attachment existing between the dentures and the underlying mucousmembrane. Retention of complete dentures is accomplished by mechanical, biologic, and physical factors. The thin film of saliva interposed between the mucosa and the dentures acts as a fluid medium and establishesphysical forces of adhesion, cohesion, and surface tension.lV5These physical factors, though of small magnitude, hold the dentures in place. Atmospheric pressure and gravity are other physical factors of retention. Adhesion, cohesion, and surface tension require explanation. The three states of matter (liquid, gas, and solid) depend upon the variation in the aggregation of molecules.6Kronig,? Maxwell,8 and Boltzmanns postulated that the molecules of gas are in a state of motion and hence attain no form. Even in liquids the molecules separate from each other with difficulty. In solids, each molecule has a definite position about which it vibrates. The binding intermolecular force in the solid state of matter is very high. Hence, the moleculesare fixed. RETENTION OF COMPLETE DENTURES Cohesion. The intermolecular forces, referred to as van der Waals forces, wherein atoms and hence moleculesare attracted to one another, are electrical in nature.“~ lo-l2 This intermolecular force is cohesion, and it is explained on the basisof the atomic structure of matter. The atoms of a molecule consistof a positive nucleus and negative electrons moving in an orbit. In forming a molecule, atoms share their electrons and move very close to one another. If the center of gravity of electrons does not coincide with that of the molecules, the atom is supposedto have a separation of charge or dipole, When two dipoles are close, they attract each other. This attractive force existing between the dipoles of atoms and hence molecules of the same matter is known ascohesive force.13 *Lecturer
in Prosthetic
Dentistry.
141
142
Abdullah
J. Prosthet. Dent. August, 1972
Adhesion. A molecule with a separation of charge or dipole is capable of inducing a separation of charge in a molecule of different matter and establishingan attractive force. This phenomenon is known as adhesion. Thus, a permanent dipole of a molecule of water induces a temporary separation of charge in the molecule of glass, establishesan attractive force, and adheres to the glasssurface. Though most liquids exhibit this phenomenon, mercury is an exception. Surface tension. The cohesive force acting on the surface of liquids is responsible for still another phenomenon, namely surface tension. Ramsay and ShieldsI stated that the phenomenon of surface tension was due to unbalanced molecular attraction at the surface of liquids. The molecules in the bulk of the liquid are attracted in all directions by the adjacent molecules, and the resultant force on the molecule is zero. However, the molecules oriented at the surface of the liquid are mainly attracted toward the bulk of the liquid, becauseno such cohesive force exists just above the surface. This results in an unbalanced molecular attraction. The resultant effect is that the molecules at the surface are pulled toward the bulk of the liquid. This contractile force at the surface is referred to as surface tension or surface free energy. The molecules at the surface gained potential energy, becausethey are oriented in the field of cohesive f0rce.l This potential energy is capable of performing work; in other words, it has the capacity to reduce the surface area of the liquid when it is subjected to a stretching force. Thus, surface tension is also referred to as surface potential energy. When two nomniscible liquids are in contact, a definite amount of surface energy exists at the interface between the two surfaces of liquids. This surface energy is known as the intrinsic interfacial energy of the liquids or inter-facial surface tension. The surfaces of both liquids and solids possesssurface energy. However, the effects of surface energy are apparent only when the surface is mobile.13The free surface energy of solids is much more difficult to measure than that of liquids because of the ability of solids to support shear stress.The free surface energy of solids is higher than that of liquids. A thin metal foil shrinks when heated. This shrinkage or “creep” according to Chapman and BorteP is due to the free surface energy, and it is calculated from creep measurements. The surface tension of gold (22 carats) calculated by the creep method is 1.510 dynes/cm. Among the liquids, mercury has the highest surface tension of 475 dynes/cm. at room temperature. The surface tension of water at 20’ C. is 72.75 dynes/cm., while that of most organic liquids lies between 25 and 30 dynes/cm. Cushman and associateP determined surface tension of saliva obtained from 25 subjects and found it to vary from 49.6 to 57.4 dynes/cm. Ropaczewesky17reported this value to vary from 69.7 to 71.4 dynes/cm. Both investigators used the Du Nocy tensiometer13for the determination of the surface tension of saliva, Craig and associates* collected saliva by stimulation with paraffin wax. They determined surface tension using the Du Noiiy tensiometer and observed values that varied from 53.4 to 57.0 dynes/cm. They conducted an experiment to analyze the forces of adhesion, cohesion, and surface tension in retention by using glassand acrylic resin plates. The reduction of pressurewas calculated by the application of the Stan& fomula.*Q Craig and co-workers2 argued that if the film thickness was approximately 10 P,
Volllme 28 Number 2
Surface
tension
in retention
of dentures
143
the radius of curvature would be 5 J.L Using this value of radius of curvature (5 EL) and surface tension of saliva as 54 dynes/cm., the pressure reduction would be approximately 0.08 pound per inch. This pressure difference would represent 0.5 pt:l cent of atmospheric pressure. From this study, they concluded that reduced pressure in the film of saliva contributed little to the retention of complete dentures. is the principal factor, According to Craig and associates, 2 the force of capillarity in retention of complete dentures. They maintained that capillarity is a combined result of cohesion, adhesion, and surface tension. DISCUSSION Craig and co-workers2 realized the role of adhesive force, calculated its magnitude, and introduced it in an equation to determine the retentive force. Stanitz”’ also mentioned the importance of adhesive force. However, he did not include it in: the equation to assess the force of retention. The theory that reduced atmospheric pressure in the thin film of saliva is thr only means of holding the dentures in place was subjected to criticism by the proponents of the mucostatic technique. Snyder and other? reported that a 70 per cent reduction in atmospheric pressure resulted in less than a 50 per cent reduction ol retention. Craig and associate? maintained that reduced atmospheric pressure in the film of saliva contributed little to the retention of dentures. Thus, reduced atmospheric, pressure alone is not the principal factor of retention. Due to its position, the upper denture is constantly acted upon by gravitational forces. This dislodging force is overcome by adhesion and cohesion, because when a layer of saliva comes in contact with the impression surface of the denture, thr adhesive force starts to operate, By definition, the force necessary to counteract adhesion is that required to separate the unit cross-sectional area of the interface hetween two plates interposed by a film of liquids.G Surface tension is potential energy that is capable of performing work such as contracting or minimizing the surface area of liquids when they are subjected to stretching forces.G Therefore, surface tension operates only when it is called uporr. The force of surface tension is effective when the dentures are dislodged away from the denture-bearing mucous membrane. cohesion, and surface tensiorl According to Schultze, 21 the forces of adhesion, are maximum when the thickness of the interposed film of water is minimum ( 10 F, Therefore, accurate adaptation of the denture base aids the physical factors of saliva in operating at their optimal level.
SUMMARY Adhesion, cohesion, and surface tension are explained on the basis of the atomic. structure of matter. Surface tension is considered as potential energy in that it is capable of performing work such as contracting or minimizing the surface area of liquid when it is subjected to a stretching force. Surface tension operates when the dentures are dislodged. Adhesion, cohesion, and surface tension operate at their optimal levels when the thickness of the fluid film is 10 p. Accurate adaptation of the denture base is conducive to good retention.
144
J. Prosthet. Dent.
Abdullah
August, 1972
References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
17. 18. 19. 20. 21.
Findlay, A.: Introduction to Physical Chemistry, ed. 3, London, 1960, Longmans, Green & Company, p. 534. Factors Related to Denture ReCraig, R. G., Berry, G. C., and Peyton, F. A.: Physical tention, J. PROSTHET. DENT. 10: 459-467, 1960. Cambell, R. L.: Some Clinical Observations Regarding the Role of the Film in the Retention of Dentures, J. Am. Dent. Assoc. 48: 58-63, 1954. Lammie, G. A.: The Retention of Complete Dentures, J. Am. Dent. Assoc. 55: 502-508, 1957. Ostlund, S. G.: Saliva and Denture Retention, J. PROSTHET. DENT. 10: 658-663, 1960. 1961, McGraw-Hill Book Company, Gordon, M. B.: Physical Chemistry, New York, Inc., p. 411. Kronig, A.: Kinetic Theory of Gases, Annalen der Physik. Poggendorff Jubdband. 99: 322-327, 1856. Maxwell, C.: Kinetic Theory of Gases, Phil. Mag. 19: 22-29, 1860. Boltzmann, L.: Varlessungen Ober Gas Thearie, ed. 1, Leipzig, 1898, StGchiometrie und Verwandtschaftsbhre. Debye, P.: Inter-molecular Forces, Physik. Z. Leipzig 21: 178-185, 1920. Keeson, W. H.: van der Waal’s Forces, Physik. Z. Leipzig 22: 129-135, 1921. London, F.: Inter-molecular Forces, Z. Physik. Chemie. B. 11: 222-227, 1930. Walter, J. M.: Physical Chemistry, ed. 3, New York, 1959, Prentice-Hall, Inc., p, 499. Ramsay, V., and Shields, J.: Surface Tension Determination, Philosoph. Trans. R. Sot., 184: 647-654, 1893. Chapman, C. L., and Borter, K.: Surface Potential Energy in Solids, J. Phys. Chem. 25: 422-429, 1953. Cushman, F. H., Etherington, J. W., and Thompson, G. E.: Relationship of Salivary Surface Tension and Rate of Flow to Dental Caries in an Adolescent Group, J. Dent. Res. 20: 251-253, 1941. Ropaczewesky, E. W.: Salivary Viscosity and Calculus Formation in Man, Arch. Oral Biol. 9: 65-71, 1964. Du Noiiy, L.: Surface Equilibria of Organic and Biological Colloids, New York, 1926, The Chemical Catalog Company, Inc. Stanitz, J. D.: An Analysis of the Part Played by the Fluid Film in Denture Retention, J. Am. Dent. Assoc. 37: 168-172, 1948. Snyder, F. C., Kimball, H. D., Bunch, W. B., and Beaton, J. H.: Effect of Reduced Atmospheric Pressure Upon Retention of Dentures, J. Am. Dent. Assoc. 32: 445-450, 1945. Schultze, W.: Uber AshIsion Und Luftadruck Und ihre Verwendung bei der Fixierung kiinstlicher Gebisse, Dtsch. Zahnaerztl. Z. 24: 538-547, 1921. 103 MADHAVARAM PERAMBUR, INDIA
MADRAS-~
HIGH 1
RD.