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Complete dentures

Physical factors in retention of complete denturesZora Bkhov6, M.U.Dr., and Milan Neuman, M.U.Dr.Charles University, Plzen, Czechoslovakia

S metimes complete dentures that appear to be correctly made have inadequateretention, even though the anatomic conditions of the basal seat are good, Becauseof this, we investigated the physical factors which influence denture retention todetermine their part in providing retention.A number of theories about retention have been proposed. Denture retentionis often confused or identified with denture adhesion, even in someprosthetic text-books. Denture retention is defined as its resistance against dislodging from thebasal seatl; Herland? considers denture retention to be the resistance against theinfluence of chewing forces, gravity, etc.

Among the physical factors that influence denture retention are : (1) adhesionand cohesion, (2) negative atmospheric pressureunder the denture, (3) capillarity,and (4) the viscosity of saliva. All of these factors were subjected to a thoroughphysical and mathematical analysis, and their application to denture retention willbe explained. In addition, a model of the mechanisms nvolved in denture reten-tion was developed.ADHESION AND COHESION

Adhesion and cohesion are important physical factors in denture retention. Thelimit of the effect of molecular forces is of the order of 10Vscm. per 0.000001 cm.Between the surface of the denture and the mucous membrane of basal seat, thereis a layer of saliva which has the thickness of the order of lo-* em. per 0.01 cm.(Fig. 1) .3-6Evidently the existence of forces of adhesion between the mucous mem-brane and the denture is not a consideration. Adhesion in denture retention playsa part only in connection with the wetting of the capillary space, Even in it, how-ever, there is no relationship of direct proportion. Therefore, including adhesion inthe first place among the physical factors of retention is not correct. Since forcesof cohesion with water, and approximately with saliva as well, are in the order of1 Gm. on 1 cm.*, this force is sufficient for overcoming the weight of the denture.However, cohesion is a negligible force in denture retention and need not be con-sidered (Fig. 2).230

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Volume 25K umber 3 Physical factors in retention of complete dentures 231. .._................. . . . . . .. . . .._ . . . . . . . . . . . . . . . . . . . . MUCOSA

SALIVA

MATERIALOF DENTURE

u= &cm

Fig. 1. The distance r demonstrates the extent of molecular power and is essen tially smallerthan the distance a which is between the muco us membrane and the denture.

Fig. 2. A glas s plate laid on the surface of the water is drawn up by power I. Th is demon-strates that cohesion is a milder power than adhesion, because the water column is brokenand the plate remains wet.

ATMOSPHERIC PRESSUREThe theory of atmospheric pressure in retention of dentures is supported by a

number of authors.3-51 7p8 The authors assume that when the denture is dislodgedfrom the basal seat, a lower atmospheric pressure is formed under the denture incomparison with the pressure of the surrounding atmosphere. The force created by

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232 Blahova and Neuman J. Prosth. Dent.March, 1971. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . ...** MUCOSA

--~---SA L I VA --=---=-\

MATERIALOF DENTURE

Fig. 3. Capillary attraction (F) does not act on the surface of the liquid only. It acts in thewhole column of the liquid, even on the walls of the capillary fissures w hich attracts themto each other.

Salivary glands and even blood in capillaries create pressure which tends to balancethe rapid pressure differences which arise under the denture. Therefore, atmosphericpressure in itself cannot be the cause of denture retention. The cause for retentionmay be only the difference of pressures under the denture and outside it. How-ever, atmospheric pressure is effect ive during dislodging of dentures and sets inaction a more complicated mechanism.CAPILLARY ATTRACTION

Capillary attraction is sometimes mentioned as a factor in denture retention.6, +I3When the denture is adjusted on the tissue surface, a space of about 0.1 mm. iscreated between the denture and the mucous membrane. In this way, the conditionfor the capillary attraction to come into action is developed.

The quantity of capillary attraction has been mathematically calculated on atheoretical basis.g However, the important fact is that capillary attraction comes intoaction also between two bases. The capillary attraction does not act only on thesurface of the liquid as it is usually explained by examples of capillary elevationand depression, but it works in the whole column of the liquid. The same force thatdraws the meniscus at the surface of the fluid, attracts two capillary walls to eachother (Fig. 3).The magnitude of the capillary attraction created by the space between the den-ture base and the mucous membrane is one half in comparison with the exampleof the attraction in the tubes. The more narrow the space, the greater the attrac-tion, When good wetting of the walls of the space occurs, the attraction inside theliquid is lowered because of capillary attraction. In the case of the mucous mem-brane, saliva, and the denture base, the denture is attracted to the mucous mem-brane by a force whose magnitude responds to the difference of the attraction ofthe exterior atmosphere and the saliva under the denture. Thus, capillary attractionmay be the force which results in denture retention.VISCOSITY OF SALIVA

Saliva, a relatively viscous liquid, is present in the space between the denturebase and the mucous membrane. The viscos ity depends on the proportion of secre-tion of the serous and mucous glands.

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Physical f ac O IF in retention of complete dentures., 233The movement of a viscous liquid can be imagined as a successive shifting of

infinitesimal layers. During this shifting, friction develops which tends to impede theshift ing. At a suffic iently small distance between the denture and the mucous mem-brane, the layer of saliva is parallel to both walls and the resistance of this layer isindirectly proportional to the distance. Dislodgment of denture is rendered possiblein the initial phase only by the fact that the quantity of saliva between the mucousmembrane and the denture base increases by a certain volume from the surround-ings and from palatal glands. lo, I23 I4 Viscosity of saliva, then, is not a direct sourceof the force which retains the denture. However, viscosi ty of saliva helps preventthe dislodgment of denture, especially in the initial phase, and so it becomes animportant factor in retention.

The effect of the viscosity of saliva, in contradiction to other physical phenom-ena, is also related to mobil ity. This problem deals mainly with the displacement ofa :substance in relation to time. This fact explains the problem of expressing capillaryattraction and viscosity mathematically as the application of equations of motionbecomes necessary.lOJ 1*-14MODEL FOR DENTURE RETENTION

When the denture is pressed to place on the mucous membrane, only a thinlayer o f saliva of about 0.1 mm. thickness remains under the denture. At the sametime, the mucous membrane is elastically deformed to the outline of the denture.In this way, a suitable condition for capillary attraction comes into action which issuffic iently powerful to hold the denture on the basal seat in static conditions. How-ever, a positive relationship has been found between the degree of the load on thedenture and the time after which retention fails.l*

Viscosity is the only factor in retention of complete dentures that is dependentupon time. A difference in pressure arises in the layer of saliva which brings thesaliva into motion. The speed of this motion is dependent on many factors such asthe viscosi ty of the saliva, and the width of the space between the denture base andthe mucosa. As this space gradually increases and is filled with saliva, the capillaryat traction, whose magnitude was at first sufficient for denture retention, is reducedto such an extent that the retention fails (Fig. 4) .A question still unexplained involves the failure of capillary attraction to main-ta.in retention after a certain time. The deformed mucous membrane returns slowlyto the original condition and at the same time releases energy which was accumu-la.ted by the force of the denture. The released energy manifests itself by motion inthe layer of saliva under the denture. The saliva increases and the capillary attrac-tion decreases as the space under the denture becomes larger, thus reducing reten-tion (Fig. 5).

For the denture to maintain retention during resting conditions, it is necessaryfrom time to time to deform the mucous membrane to conform with thedenture base. This is performed easily by the patient when he sucks and swallowssaliva which has increased under the denture and, at the same time, pushes thedenture back into place on the mucosa.

Capillary attraction in a capillary tube or space ceases to be effective if thetube is submerged under the surface of the same liquid. A similar situation occurs

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234 Bldhovli and Neuman J. Prosth. Dent.March. 1971

.\,MUCOUS MEMBRANE

Fig. 4. A cross section of the upper jaw and denture. If a downward force (P) is exertedon the denture, the thickness of the layer of saliva increases, the capillary attraction decreases,and retention is reduced.

Fig. 5. A cross section of the upper jaw and denture. Th e mucous membrane is deformed bypressure on the denture PI. However, in time the mucos a is dislodged from the denture,saliva flows under the denture, the capillary space enlarges, and the denture falls off.

in lower complete dentures. The basal seat tissues of the lower jaw are wetted bysaliva far more intensively than the basal seat tissues of the upper jaw. Therefore,the capillary attraction in lower complete dentures functions only very little andfor a short period of time in many instances as saliva accumulates.SUMMARY

None of the physical factors involved in complete denture retention can be to-tally explained. However, some of them participate commonly in the intricate mech-anism which is set in action at the moment of dislodgment of the denture. A mostimportant factor in retention seems to be capillary attraction. Another factor is theviscosity of saliva which affects the motion of saliva under the denture. Denture

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Volrmw. 25Number 3 Physical factors in retention of complete dentures 235retention is enhanced by the elasticity of the mucous membrane of the basal seatarea and by a good border seal which keeps the space between the denture and themucosa as small as possible.ReFerences

1. Boucher, C. O., Frechette, A. A., and Gehl, D. H.: Glossary of Prosthodon tic Terms ,Ed. 2, J. PROSTH. DENT. 1: 39,196O.

2. Herlands, R. E.: Removable Partial Denture Terminology, J. PROSTH. DENT. 8: 964-791, 1958.

3. Kantorovicz, A.: Innen-und ausen-W entil, Adhls ion und Luftdruck, D. Z. Z. 5: 784-791, 1956.

4. Kuba li, H. N.: The Theore tic Ba sis of the Functional Vacuum Method for CompleteDenture Construction, J, PROSTH. DENT. 10: 673-681, 1960.

5. Kuck, M.: Adhlsio n und Luftdruck, D. Z. Z. 5: 792-797, 1956.6. Lammie, G. A.: The Retention of Complete Dentures, J. Amer. Dent. Ass . 55: 502-508,

1957.7. Campbe ll, R. L.: Relief Chambers in Complete Dentures, J. PROSTH. DENT. 11: 230-

236, 1961.8. Stam oulis, S.: Phys ical Factors Affecting the Retention of Complete Dentures, J. PROSTH.

DENT. 12: 857-869, 1962.9. Betzler, H., and Riedel, H.: Die Ursachen und Gesetze be im Halt der Prothese, Stoma

14: 117-134,, 182-209, 1961.10. Graig, R. G., Berry, G. C., and Peyton, F. A.: Physic al Factors Related to Denture

Retention, J. PROSTH. DENT. 10: 459-467, 1960.11. Lawson, W. A.: Die Haftfahigkeit der Vollprothese, Linformation dent. 48-24: 2625-

2635, 1966.12. Ostlund, S. G.: Saliva and Denture Retention of Complete Dentures, J. PROSTH. DENT.10: 658-663, 1960.

13. Stanitz, J. D.: An Analys is of the Part Played by the Fluid Film in Denture RetentionJ. Amer. Dent. Ass . 37: 168-172, 1948.

14. Campbe ll, R. L.: Effects of Water Sorption on Retention of Acrylic Resin Denture Bases ,J. Amer. Dent. Ass . 52: 448-454, 1956.

KYJEVSKA 75PLZENCZECHOSLOVAKIA