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Table of Contents
Vol. 38, No. 3, 2004
Issue release date: May–June 2004
Caries Res 2004;38:236–240
(DOI:10.1159/000077760)

How Much Saliva Is Enough for Avoidance of Xerostomia?

Dawes C.
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Man., Canada
email Corresponding Author

Abstract

Xerostomia, the subjective sensation of dry mouth, occurs when the salivary flow rate is less than the rate of fluid loss from the mouth by evaporation and by absorption of water through the oral mucosa. Evaporation can only occur during mouth-breathing but could reach a maximum rate of about 0.21 ml/min at rest, although normally it would be much less. Water absorption through the mucosa can occur because saliva has one sixth the osmotic pressure of extracellular fluid, thus creating a water gradient across the mucosa. The maximum absorption rate is calculated to be about 0.19 ml/min, declining to zero as the saliva reaches isotonicity. A recent study found the residual saliva volume, the volume of saliva left in the mouth after swallowing, to be 71% of normal in patients with severe hyposalivation and whose mouths felt very dry. Saliva in the residual volume is present as a thin film which varies in thickness with site. The hard palate has the thinnest film and when this is <10 µm thick, evaporation during mouth-breathing and/or fluid absorption may rapidly decrease it to zero, resulting in xerostomia. This is also generally associated with reduced secretion from the soft palate minor glands, which may contribute to the film on the hard palate. Thus, xerostomia appears to be due, not to a complete absence of oral fluid, but to localized areas of mucosal dryness, notably in the palate. Unstimulated salivary flow rates >0.1–0.3 ml/min may be necessary for this condition to be avoided.


 goto top of outline Key Words

  • Xerostomia
  • Hyposalivation
  • Dry mouth
  • Residual volume
  • Salivary film
  • Evaporation
  • Mucosal fluid absorption
  • Flow rate
  • Palatal dryness

 goto top of outline Abstract

Xerostomia, the subjective sensation of dry mouth, occurs when the salivary flow rate is less than the rate of fluid loss from the mouth by evaporation and by absorption of water through the oral mucosa. Evaporation can only occur during mouth-breathing but could reach a maximum rate of about 0.21 ml/min at rest, although normally it would be much less. Water absorption through the mucosa can occur because saliva has one sixth the osmotic pressure of extracellular fluid, thus creating a water gradient across the mucosa. The maximum absorption rate is calculated to be about 0.19 ml/min, declining to zero as the saliva reaches isotonicity. A recent study found the residual saliva volume, the volume of saliva left in the mouth after swallowing, to be 71% of normal in patients with severe hyposalivation and whose mouths felt very dry. Saliva in the residual volume is present as a thin film which varies in thickness with site. The hard palate has the thinnest film and when this is <10 μm thick, evaporation during mouth-breathing and/or fluid absorption may rapidly decrease it to zero, resulting in xerostomia. This is also generally associated with reduced secretion from the soft palate minor glands, which may contribute to the film on the hard palate. Thus, xerostomia appears to be due, not to a complete absence of oral fluid, but to localized areas of mucosal dryness, notably in the palate. Unstimulated salivary flow rates >0.1–0.3 ml/min may be necessary for this condition to be avoided.

Copyright © 2004 S. Karger AG, Basel


 goto top of outline References
  1. Becks H, Wainwright WW: Human saliva. XIII. Rate of flow of resting saliva of healthy individuals. J Dent Res 1943;22:391–396.
  2. Brennan MT, Shariff G, Lockhart PB, Fox PC: Treatment of xerostomia: A systematic review of therapeutic trials. Dent Clin North Am 2002;46:847–856.
  3. Camner P, Bakke B: Nose or mouth breathing? Environ Res 1980;21:394–398.
  4. Collins LMC, Dawes C: The surface area of the adult human mouth and thickness of the salivary film covering the teeth and oral mucosa. J Dent Res 1987;66:1300–1302.
  5. Dawes C: Physiological factors affecting salivary flow rate, oral sugar clearance, and the sensation of dry mouth in man. J Dent Res 1987;66(special issue):648–653.
  6. Dawes C, Odlum O: Salivary status in a treated head and neck cancer patient group. J Can Dent Assoc 2004, in press.
  7. DiSabato-Mordarski T, Kleinberg I: Measurement and comparison of the residual saliva on various oral mucosal and dentition surfaces in humans. Arch Oral Biol 1996a;41:655–665.
  8. DiSabato-Mordarski T, Kleinberg I: Use of a paper-strip absorption method to measure the depth and volume of saliva retained in embrasures and occlusal fossae of the human dentition. Arch Oral Biol 1996b;41:809–820.
  9. Ganong WF: Review of Medical Physiology, ed 19. Stamford, Appleton & Lange, 1999, p 620.
  10. Healy CM, Cruchley AT, Thornhill MH, Williams DM: The effect of sodium lauryl sulphate, triclosan and zinc on the permeability of normal oral mucosa. Oral Dis 2000;6:118–123.
  11. Howie NM, Trigkas TK, Cruchley AT, Wertz PW, Squier CA, Williams DM: Short-term exposure to alcohol increases the permeability of human oral mucosa. Oral Dis 2001;7:349–354.
  12. Jha N, Seikaly H, Harris J, Williams D, Liu R, McGaw T, Hofmann H, Robinson D, Hanson J, Barnaby P: Prevention of radiation induced xerostomia by surgical transfer of submandibular salivary gland into the submental space. Radiother Oncol 2003;66:283–289.
  13. Lagerlöf F, Dawes C: The volume of saliva in the mouth before and after swallowing. J Dent Res 1984;63:618–621.
  14. Lear CSC, Flanagan JB Jr, Moorrees CFA: The frequency of deglutition in man. Arch Oral Biol 1965;10:83–99.
  15. Lesch CA, Squier CA, Cruchley A, Williams DM, Speight P: The permeability of human oral mucosa and skin to water. J Dent Res 1989;68:1345–1349.
  16. Nederfors T: Xerostomia and hyposalivation. Adv Dent Res 2000;14:48–56.
  17. Niedermeier W, Huber M, Fischer D, Beier K, Müller N, Schuler R, Brinninger A, Fartasch M, Diepgen T, Matthaeus C, Meyer C, Hector MP: Significance of saliva for the denture-wearing population. Gerodontology 2000;17:104–118.
  18. Niinimaa V, Cole P, Mintz S, Shephard RJ: Oronasal distribution of respiratory airflow. Respir Physiol 1981;43:69–75.
  19. Odlum O: Preventive resins in the management of radiation-induced xerostomia complications. J Esthet Dent 1991;3:227–229.
  20. Proctor DF: The upper airways. I. Nasal physiology and defense of the lungs. Am Rev Respir Dis 1977;115:97–129.
  21. Proctor DF: Form and function of the upper airways and larynx; in Fishman AP, Macklem PT, Mead J, Geiger SR (eds): Handbook of Physiology. Bethesda, American Physiological Society, 1986, section 3, vol III, pp 63–73.
  22. Schwartz A, Shaw JH: Studies on the effect of selective desalivation on the dental caries incidence of albino rats. J Dent Res 1955;34:239–247.
  23. Siegel IA, Izutsu KT, Watson E: Mechanisms of non-electrolyte penetration across dog and rabbit oral mucosa in vitro. Arch Oral Biol 1981;26:357–361.
  24. Sreebny LM, Banoczy J, Baum BJ, Edgar WM, Epstein JB, Fox PC, Larmas M: Saliva: Its role in health and disease. Int Dent J 1992;42:291–304.
  25. Weast RC, Astle MJ: CRC Handbook of Chemistry and Physics, ed 59. West Palm Beach, CRC Press, 1978–1979, p E-41.
  26. Weast RC, Astle MJ: CRC Handbook of Chemistry and Physics, ed 61. Boca Raton, CRC Press, 1980–1981, p D-261.
  27. Wolff M, Kleinberg I: Oral mucosal wetness in hypo- and normosalivators. Arch Oral Biol 1998;43:455–462.
  28. Wolff M, Kleinberg I: The effect of ammonium glycopyrrolate (Robinul®)-induced xerostomia on oral mucosal wetness and flow of gingival crevicular fluid in humans. Arch Oral Biol 1999;44:97–102.

 goto top of outline Author Contacts

Dr. C. Dawes
Department of Oral Biology, Faculty of Dentistry
University of Manitoba, 780 Bannatyne Avenue
Winnipeg, Man. R3E 0W2 (Canada)
Tel. +1 204 789 3512, Fax +1 204 789 3943, E-Mail colin_dawes@umanitoba.ca


 goto top of outline Article Information

Number of Print Pages : 5
Number of Figures : 0, Number of Tables : 0, Number of References : 28


 goto top of outline Publication Details

Caries Research (Journal of the European Organization for Caries Research (ORCA))
Journal founded 1967 by Y. Ericsson; edited 1970–1987 by K.G. König; 1987–1994 by J.M. ten Cate; 1994–2000 by J. Tenovuo

Vol. 38, No. 3, Year 2004 (Cover Date: May-June 2004)

Journal Editor: R.P. Shellis, Bristol
ISSN: 0008–6568 (print), 1421–976X (Online)

For additional information: http://www.karger.com/journals/cre


Copyright / Drug Dosage / Disclaimer

Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher or, in the case of photocopying, direct payment of a specified fee to the Copyright Clearance Center.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in goverment regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

Abstract

Xerostomia, the subjective sensation of dry mouth, occurs when the salivary flow rate is less than the rate of fluid loss from the mouth by evaporation and by absorption of water through the oral mucosa. Evaporation can only occur during mouth-breathing but could reach a maximum rate of about 0.21 ml/min at rest, although normally it would be much less. Water absorption through the mucosa can occur because saliva has one sixth the osmotic pressure of extracellular fluid, thus creating a water gradient across the mucosa. The maximum absorption rate is calculated to be about 0.19 ml/min, declining to zero as the saliva reaches isotonicity. A recent study found the residual saliva volume, the volume of saliva left in the mouth after swallowing, to be 71% of normal in patients with severe hyposalivation and whose mouths felt very dry. Saliva in the residual volume is present as a thin film which varies in thickness with site. The hard palate has the thinnest film and when this is <10 µm thick, evaporation during mouth-breathing and/or fluid absorption may rapidly decrease it to zero, resulting in xerostomia. This is also generally associated with reduced secretion from the soft palate minor glands, which may contribute to the film on the hard palate. Thus, xerostomia appears to be due, not to a complete absence of oral fluid, but to localized areas of mucosal dryness, notably in the palate. Unstimulated salivary flow rates >0.1–0.3 ml/min may be necessary for this condition to be avoided.



 goto top of outline Author Contacts

Dr. C. Dawes
Department of Oral Biology, Faculty of Dentistry
University of Manitoba, 780 Bannatyne Avenue
Winnipeg, Man. R3E 0W2 (Canada)
Tel. +1 204 789 3512, Fax +1 204 789 3943, E-Mail colin_dawes@umanitoba.ca


 goto top of outline Article Information

Number of Print Pages : 5
Number of Figures : 0, Number of Tables : 0, Number of References : 28


 goto top of outline Publication Details

Caries Research (Journal of the European Organization for Caries Research (ORCA))
Journal founded 1967 by Y. Ericsson; edited 1970–1987 by K.G. König; 1987–1994 by J.M. ten Cate; 1994–2000 by J. Tenovuo

Vol. 38, No. 3, Year 2004 (Cover Date: May-June 2004)

Journal Editor: R.P. Shellis, Bristol
ISSN: 0008–6568 (print), 1421–976X (Online)

For additional information: http://www.karger.com/journals/cre


Copyright / Drug Dosage

Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher or, in the case of photocopying, direct payment of a specified fee to the Copyright Clearance Center.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in goverment regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

References

  1. Becks H, Wainwright WW: Human saliva. XIII. Rate of flow of resting saliva of healthy individuals. J Dent Res 1943;22:391–396.
  2. Brennan MT, Shariff G, Lockhart PB, Fox PC: Treatment of xerostomia: A systematic review of therapeutic trials. Dent Clin North Am 2002;46:847–856.
  3. Camner P, Bakke B: Nose or mouth breathing? Environ Res 1980;21:394–398.
  4. Collins LMC, Dawes C: The surface area of the adult human mouth and thickness of the salivary film covering the teeth and oral mucosa. J Dent Res 1987;66:1300–1302.
  5. Dawes C: Physiological factors affecting salivary flow rate, oral sugar clearance, and the sensation of dry mouth in man. J Dent Res 1987;66(special issue):648–653.
  6. Dawes C, Odlum O: Salivary status in a treated head and neck cancer patient group. J Can Dent Assoc 2004, in press.
  7. DiSabato-Mordarski T, Kleinberg I: Measurement and comparison of the residual saliva on various oral mucosal and dentition surfaces in humans. Arch Oral Biol 1996a;41:655–665.
  8. DiSabato-Mordarski T, Kleinberg I: Use of a paper-strip absorption method to measure the depth and volume of saliva retained in embrasures and occlusal fossae of the human dentition. Arch Oral Biol 1996b;41:809–820.
  9. Ganong WF: Review of Medical Physiology, ed 19. Stamford, Appleton & Lange, 1999, p 620.
  10. Healy CM, Cruchley AT, Thornhill MH, Williams DM: The effect of sodium lauryl sulphate, triclosan and zinc on the permeability of normal oral mucosa. Oral Dis 2000;6:118–123.
  11. Howie NM, Trigkas TK, Cruchley AT, Wertz PW, Squier CA, Williams DM: Short-term exposure to alcohol increases the permeability of human oral mucosa. Oral Dis 2001;7:349–354.
  12. Jha N, Seikaly H, Harris J, Williams D, Liu R, McGaw T, Hofmann H, Robinson D, Hanson J, Barnaby P: Prevention of radiation induced xerostomia by surgical transfer of submandibular salivary gland into the submental space. Radiother Oncol 2003;66:283–289.
  13. Lagerlöf F, Dawes C: The volume of saliva in the mouth before and after swallowing. J Dent Res 1984;63:618–621.
  14. Lear CSC, Flanagan JB Jr, Moorrees CFA: The frequency of deglutition in man. Arch Oral Biol 1965;10:83–99.
  15. Lesch CA, Squier CA, Cruchley A, Williams DM, Speight P: The permeability of human oral mucosa and skin to water. J Dent Res 1989;68:1345–1349.
  16. Nederfors T: Xerostomia and hyposalivation. Adv Dent Res 2000;14:48–56.
  17. Niedermeier W, Huber M, Fischer D, Beier K, Müller N, Schuler R, Brinninger A, Fartasch M, Diepgen T, Matthaeus C, Meyer C, Hector MP: Significance of saliva for the denture-wearing population. Gerodontology 2000;17:104–118.
  18. Niinimaa V, Cole P, Mintz S, Shephard RJ: Oronasal distribution of respiratory airflow. Respir Physiol 1981;43:69–75.
  19. Odlum O: Preventive resins in the management of radiation-induced xerostomia complications. J Esthet Dent 1991;3:227–229.
  20. Proctor DF: The upper airways. I. Nasal physiology and defense of the lungs. Am Rev Respir Dis 1977;115:97–129.
  21. Proctor DF: Form and function of the upper airways and larynx; in Fishman AP, Macklem PT, Mead J, Geiger SR (eds): Handbook of Physiology. Bethesda, American Physiological Society, 1986, section 3, vol III, pp 63–73.
  22. Schwartz A, Shaw JH: Studies on the effect of selective desalivation on the dental caries incidence of albino rats. J Dent Res 1955;34:239–247.
  23. Siegel IA, Izutsu KT, Watson E: Mechanisms of non-electrolyte penetration across dog and rabbit oral mucosa in vitro. Arch Oral Biol 1981;26:357–361.
  24. Sreebny LM, Banoczy J, Baum BJ, Edgar WM, Epstein JB, Fox PC, Larmas M: Saliva: Its role in health and disease. Int Dent J 1992;42:291–304.
  25. Weast RC, Astle MJ: CRC Handbook of Chemistry and Physics, ed 59. West Palm Beach, CRC Press, 1978–1979, p E-41.
  26. Weast RC, Astle MJ: CRC Handbook of Chemistry and Physics, ed 61. Boca Raton, CRC Press, 1980–1981, p D-261.
  27. Wolff M, Kleinberg I: Oral mucosal wetness in hypo- and normosalivators. Arch Oral Biol 1998;43:455–462.
  28. Wolff M, Kleinberg I: The effect of ammonium glycopyrrolate (Robinul®)-induced xerostomia on oral mucosal wetness and flow of gingival crevicular fluid in humans. Arch Oral Biol 1999;44:97–102.