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Biological Demands of Complete Dentures
Biological demands of complete dentures M . M . D eV a n , D .D .S., Philadelphia
It is not enough for the dentist to look into the mouth o f a patient and deter mine what type o f denture will be ade quate; he must take all factors into con sideration. T h e successful wearing o f com plete dentures requires assets o f three types: (1 ) structural, (2 ) psychologic and (3 ) biologic. A patient should pos sess sufficient oral structure to support dentures; namely, sufficient mass and distribution o f alveolar and basal bone, satisfactory thickness and rigidity o f m ucoperiosteum , structurally sound tem porom andibular joints and adequate muscle tissue, favorably attached. In addition, the patient must have the phys ical stamina and ability to make use o f the tissue-supported dentures. T h e neces sary psychologic factors are certain per sonality traits, especially the will to per severe in the initial and continued wearing o f com plete dentures and the emotional stability to ensure a satisfac tory salivary reaction. This paper deals with the third type o f factors, the biologic. O f these the most im portant are (1 ) tissue tone, (2 ) mus cle tone, (3 ) bone quality and (4 ) character and quantity o f saliva. A ge and general health o f the patient are not listed as separate factors since they are associated with each o f these fou r fa c tors; an aged and sickly individual may not be able to m eet the biological d e mands for com plete dentures; his tissues, both the soft and the osseous, may lack
the quality to meet the needs o f mucosaadherent artificial dentures. T IS S U E T O N E
Tissue tone is an index to the nutritional and circulatory condition o f the patient. T h e color and surface texture o f the facial skin and oral m ucosa should be observed. T o the prosthodontist thin, anemic, blotchy facial skin usually means protracted and prolonged adjustments after the dentures are inserted. T h e thin, drawn face o f early senescence may be indicative o f insufficient adipose tissue in the oral mucosa to offer the cushioning effect required fo r the com fortable wear ing o f com plete dentures. Inflamed oral mucosa is usually super sensitive. Patients with tissues o f this type experience difficulty in becom ing accustom ed to com plete dentures both during rest periods and while chewing. W hen they speak, they feel a so-called tenderness in making the various tongueteeth contacts required fo r the enuncia tion o f the consonants. In addition, the supersensitiveness o f these tissues causes patients with com plete dentures to be slow in acquiring chewing facility. C om -
Presented before the Section on Full Denture Pros thesis combined with the Section on Oral Surgery, ninety-second annual session of the American Dental Association, Washington, D. C., O ctober 17, 1951. Professor and chairman of the departm ent, of pros thetic dentistry, University of Pennsylvania School of Dentistry. 524
DE VAN . . . VOLUME 45, NOVEMBER 1952 • 525
plete denture patients should be recalled yearly, primarily to observe mucosal tone. I f the color o f the mucosa covered by the denture is noticeably dissimilar to that o f the mucosal covering o f the tongue, lips and cheeks, an examination should be made to ascertain probable causative factors. Every phase o f denture construc tion should be considered carefully; only those procedures should be follow ed which result in dentures that leave n o in flammatory telltale signs o f excessive or insufficient tissue pressure. This is an extremely im portant point: dentures do not meet biological demands if the m ucosa to which they adhere shows signs o f inflammation. F or this reason the use o f a peripheral seal, including the customary post-dam m ing, is to be avoided whenever possible. M ucosal tone is most nearly normal when oral tissue is registered in the impression in an un disturbed condition. There is danger in excessive tight peripherally sealed dentures. T hey may cause atrophy o f the soft tissues and re sorption o f the underlying bone.1 T he biological demands o f com plete dentures require that the wearing o f the dentures should cause little or no change in tissue tone. M USCLE TONE
T h e proper preparation o f fo o d requires power, pow er furnished by the muscles o f the face, m outh and jaws. Besides mastication, the musculature, supported by com plete dentures, must maintain normal facial appearance and assist in the production o f articulate speech. A l though chewing capacity is im portant, in many instances it may be inadvisable to concentrate on that function at the ex pense o f appearance and speech. By care ful selection and preparation o f food prior to ingestion an individual can cope successfully w ith the problem o f reduced masticatory powers, but he alone can do little or nothing with his facial structure
and his ability to speak well. T h e social status o f m any a m an or w om an is such that he or she may deem it necessary to require o f the dentures the m axim um in the way o f appearance and speech, per haps at the expense o f masticatory effi ciency. Thus, the dentist must consider the contour o f the labial flanges. It is cus tomary to extend the labial flanges to the m ucolabial fold in order to develop the m axim um retention o f the dentures and thereby to increase chewing efficiency. I f this is done, the normal appearance o f the superior portion o f the upper lip in cluding the base o f the nose may be altered. O n the low er denture such ex tensions usually destroy the esthetic dip associated with the juncture o f the lower lip and the chin. A consideration o f ap pearances is justly within the scope o f a discussion o f the biological demands o f com plete dentures. Labial flanges should be contoured primarily fo r appearance rather than fo r the retention o f dentures. T h e tonicity o f the enveloping muscles must be considered in developing flange height, thickness and contour. I f muscle tone is high, the denture flange should be short to minimize displacing tendencies. T h e occlusal vertical dimension o f the com plete dentures should be less than the postural rest vertical dimension.2 Patients should be told to keep their lower jaw relaxed. T h e follow in g ditty repeated several times may help: “ From this rule never d ep a rt: lips together, teeth apart.” T h e relaxed position allows rest periods fo r the elevator group o f muscles. T he horizontal muscles such as the buccinators and the orbicularis oris need support from the dentures. Kingery3 has advanced a significant idea in his statement that the teeth con-
1. Weinmann, J. P., and Sicher, H. Bone and bones; fundamentals of bone biology. St. Louis, C . V. Mosby Co.. 1947. 2. Sears, V. H. Principles and technics for complete denture construction. St. Louis, C. V. Mosby Co., 1949. 3. Kingery, R. H. Personal communication.
526 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
stitute only a third o f the masticatory machine, that the other two thirds con sists o f the tongue and cheeks. These muscle organs serve as steering agents, guiding, directing and m aintaining the fo o d morsel between the teeth. T h e pa tient’s kinesthetic sense and his neuro muscular skills play an important role in the successful use o f com plete dentures. B O N E Q U A L IT Y
In the act o f mastication, the teeth, both the natural and the artificial, function as intermediaries, receiving the muscular force only to transmit it through the associated connective tissue to the under lying bone. C om plete dentures require the continued preservation o f the bony foundation on w hich they rest. A con tinual periodic rebasing and remaking o f dentures is not satisfactory. Every possi ble effort should be made to build den tures within the physiologic and biologic limits o f the available osseous structure. I f alveolar bone is scant and its density is slight, an attempt should not be made to restore to position, proportion or form the structure that is missing. T o d o so w ould be to build beyond the structural foundation, contrary to the laws o f statics.4 Placing the posterior teeth ou t side the base area requires the m axim um in the way o f retention. Setting teeth within the ridge area helps to stabilize the denture and thus requires fo r fu n c tion the m inim um in the way o f reten tion. It is extremely im portant to stabilize com plete dentures. T h e usual objective o f developing m axim um retention only does not supply a m uch-needed preven tive factor. T h e objective should be the constant preservation o f what remains rather than the meticulous restoration o f what is missing. T h e terms retention and stability should be understood clearly. Stability is that state wherein forces that tend to cause m otion are successfully resisted without loss o f equilibrium. A stable d en
ture is one that resists successfully the magnitude and direction o f functional forces that tend to alter the positional relation o f the denture to its osseous sup port. Actually, a so-called stable denture is only relatively stable, for absolute sta bility in any edentulous patient is im possible. In the above definition o f a stable denture, it is im portant to note that the term osseous support and not mucosa is used; during function a den ture may lose stability and yet maintain its positional relation to the mucosa. U n der such circumstances the denture still possesses retention. Retention may be d e fined as that state o f a denture wherein functional forces are unable to destroy the adhesion existing between the den ture and the mucoperiosteum. It is ap parent that a denture may be unstable and yet possess sufficient retention to re sist dislodgment. As long as the denture under functional loads does not lose its grip upon the mucosa, it m ay be said to possess an adequate degree o f retention but not stability. I f a denture does not m ove noticeably in' function, displacing the mucoperiosteum , it is said to be stabilized. Stable dentures are the most effective means o f preserving the denture fou n da tion, which is com posed o f alveolar bone with its overlying m ucoperiosteum and its underlying basal bone. Stable dentures are difficult, if not impossible, to con struct when large amounts o f alveolar bone have been lost, since the setup can not be centralized sufficiently to satisfy the law o f statics, that is, to exert force within the supporting structure and at a right angle to it. I f bone quality is high, dentures that are retentive but not stable can be worn with m inim um bone loss. Patients w ho need com plete dentures, however, usually possess bone o f low density. T h eir m etabolic processes have slowed dow n because o f age or degener-
4. DeVan, M. M. Basic considerations in full denture planning. J. 2nd. Dist. D. Soc. (N.Y.) 25:451 (April) 1940.
DE VAN . . . VOLUME 45, NOVEMBER 1952 • 527
ative disease processes. B y roentgenographic study o f the character o f the trabeculae, the bone quality is identified as close-meshed or rarefied. Likewise the nature o f the border o f the bony ridge is characterized as smooth o r jagged. T h e patient’ s health and age also are im por tant factors in bone quality. C H A R A C T E R A N D Q U A N T IT Y O F SA L IV A
Patients with dry m ouths are usually difficult patients. W hen saliva is sub normal in quantity, it is usually abnor mal in viscosity. R opy, sticky saliva is an unfavorable factor in the task o f stabil izing the com plete denture. W hen sali vary viscosity is high, the moisture film between the mucosa and th e denture base is increased in thickness. T h e e ffect o f this film is to cause a greater separation between the denture base and the under lying bone. T h e tendency to skid and to displace the denture is thereby increased. P R A C T IC A L S U G G E S T IO N S
1. T h e oral surgeon should hesitate to render a patient com pletely edentulous
until he has considered the physical, b io logic and psychologic factors pertinent to the case. Better still, he should defer extractions until a prosthodontist has been given an opportunity to appraise the patient’s ability to wear com plete dentures satisfactorily at that particular time. In some instances, the retention o f a few natural teeth to serve as abutments fo r provisional partial dentures may ease the transition from natural to artificial teeth. A slight delay in rendering the patient com pletely edentulous may have favorable physical, biological and psy chological results. 2. T he oral surgeon should find out from the patient whether or not impres sions o f the natural teeth were taken prior to their rem oval; he should explain the desirability o f having immediate re placements constructed before the natural teeth are removed. 3. In the removal o f teeth, the oral surgeon should retain as m uch bone as possible, especially the buccolabial cor tical plates above and the lingual cortical plates below.
Search for Error • For the layman, the most im portant thing about science is this: that it isn’ t a search for truth but a search for error. T he scientist lives in a w orld where truth is unattainable, but where it’ s always possible to find errors in the long-settled or the obvious. . . . So-called “ scientific” books that are supposed to contain final answers are never scientific. Science is forever self-correcting and ch angin g; what is put forth as gospel truth cannot be science. R udolf Flesch, T he A rt of Clear Thinking.
It is not enough for the dentist to look into the mouth o f a patient and deter mine what type o f denture will be ade quate; he must take all factors into con sideration. T h e successful wearing o f com plete dentures requires assets o f three types: (1 ) structural, (2 ) psychologic and (3 ) biologic. A patient should pos sess sufficient oral structure to support dentures; namely, sufficient mass and distribution o f alveolar and basal bone, satisfactory thickness and rigidity o f m ucoperiosteum , structurally sound tem porom andibular joints and adequate muscle tissue, favorably attached. In addition, the patient must have the phys ical stamina and ability to make use o f the tissue-supported dentures. T h e neces sary psychologic factors are certain per sonality traits, especially the will to per severe in the initial and continued wearing o f com plete dentures and the emotional stability to ensure a satisfac tory salivary reaction. This paper deals with the third type o f factors, the biologic. O f these the most im portant are (1 ) tissue tone, (2 ) mus cle tone, (3 ) bone quality and (4 ) character and quantity o f saliva. A ge and general health o f the patient are not listed as separate factors since they are associated with each o f these fou r fa c tors; an aged and sickly individual may not be able to m eet the biological d e mands for com plete dentures; his tissues, both the soft and the osseous, may lack
the quality to meet the needs o f mucosaadherent artificial dentures. T IS S U E T O N E
Tissue tone is an index to the nutritional and circulatory condition o f the patient. T h e color and surface texture o f the facial skin and oral m ucosa should be observed. T o the prosthodontist thin, anemic, blotchy facial skin usually means protracted and prolonged adjustments after the dentures are inserted. T h e thin, drawn face o f early senescence may be indicative o f insufficient adipose tissue in the oral mucosa to offer the cushioning effect required fo r the com fortable wear ing o f com plete dentures. Inflamed oral mucosa is usually super sensitive. Patients with tissues o f this type experience difficulty in becom ing accustom ed to com plete dentures both during rest periods and while chewing. W hen they speak, they feel a so-called tenderness in making the various tongueteeth contacts required fo r the enuncia tion o f the consonants. In addition, the supersensitiveness o f these tissues causes patients with com plete dentures to be slow in acquiring chewing facility. C om -
Presented before the Section on Full Denture Pros thesis combined with the Section on Oral Surgery, ninety-second annual session of the American Dental Association, Washington, D. C., O ctober 17, 1951. Professor and chairman of the departm ent, of pros thetic dentistry, University of Pennsylvania School of Dentistry. 524
DE VAN . . . VOLUME 45, NOVEMBER 1952 • 525
plete denture patients should be recalled yearly, primarily to observe mucosal tone. I f the color o f the mucosa covered by the denture is noticeably dissimilar to that o f the mucosal covering o f the tongue, lips and cheeks, an examination should be made to ascertain probable causative factors. Every phase o f denture construc tion should be considered carefully; only those procedures should be follow ed which result in dentures that leave n o in flammatory telltale signs o f excessive or insufficient tissue pressure. This is an extremely im portant point: dentures do not meet biological demands if the m ucosa to which they adhere shows signs o f inflammation. F or this reason the use o f a peripheral seal, including the customary post-dam m ing, is to be avoided whenever possible. M ucosal tone is most nearly normal when oral tissue is registered in the impression in an un disturbed condition. There is danger in excessive tight peripherally sealed dentures. T hey may cause atrophy o f the soft tissues and re sorption o f the underlying bone.1 T he biological demands o f com plete dentures require that the wearing o f the dentures should cause little or no change in tissue tone. M USCLE TONE
T h e proper preparation o f fo o d requires power, pow er furnished by the muscles o f the face, m outh and jaws. Besides mastication, the musculature, supported by com plete dentures, must maintain normal facial appearance and assist in the production o f articulate speech. A l though chewing capacity is im portant, in many instances it may be inadvisable to concentrate on that function at the ex pense o f appearance and speech. By care ful selection and preparation o f food prior to ingestion an individual can cope successfully w ith the problem o f reduced masticatory powers, but he alone can do little or nothing with his facial structure
and his ability to speak well. T h e social status o f m any a m an or w om an is such that he or she may deem it necessary to require o f the dentures the m axim um in the way o f appearance and speech, per haps at the expense o f masticatory effi ciency. Thus, the dentist must consider the contour o f the labial flanges. It is cus tomary to extend the labial flanges to the m ucolabial fold in order to develop the m axim um retention o f the dentures and thereby to increase chewing efficiency. I f this is done, the normal appearance o f the superior portion o f the upper lip in cluding the base o f the nose may be altered. O n the low er denture such ex tensions usually destroy the esthetic dip associated with the juncture o f the lower lip and the chin. A consideration o f ap pearances is justly within the scope o f a discussion o f the biological demands o f com plete dentures. Labial flanges should be contoured primarily fo r appearance rather than fo r the retention o f dentures. T h e tonicity o f the enveloping muscles must be considered in developing flange height, thickness and contour. I f muscle tone is high, the denture flange should be short to minimize displacing tendencies. T h e occlusal vertical dimension o f the com plete dentures should be less than the postural rest vertical dimension.2 Patients should be told to keep their lower jaw relaxed. T h e follow in g ditty repeated several times may help: “ From this rule never d ep a rt: lips together, teeth apart.” T h e relaxed position allows rest periods fo r the elevator group o f muscles. T he horizontal muscles such as the buccinators and the orbicularis oris need support from the dentures. Kingery3 has advanced a significant idea in his statement that the teeth con-
1. Weinmann, J. P., and Sicher, H. Bone and bones; fundamentals of bone biology. St. Louis, C . V. Mosby Co.. 1947. 2. Sears, V. H. Principles and technics for complete denture construction. St. Louis, C. V. Mosby Co., 1949. 3. Kingery, R. H. Personal communication.
526 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
stitute only a third o f the masticatory machine, that the other two thirds con sists o f the tongue and cheeks. These muscle organs serve as steering agents, guiding, directing and m aintaining the fo o d morsel between the teeth. T h e pa tient’s kinesthetic sense and his neuro muscular skills play an important role in the successful use o f com plete dentures. B O N E Q U A L IT Y
In the act o f mastication, the teeth, both the natural and the artificial, function as intermediaries, receiving the muscular force only to transmit it through the associated connective tissue to the under lying bone. C om plete dentures require the continued preservation o f the bony foundation on w hich they rest. A con tinual periodic rebasing and remaking o f dentures is not satisfactory. Every possi ble effort should be made to build den tures within the physiologic and biologic limits o f the available osseous structure. I f alveolar bone is scant and its density is slight, an attempt should not be made to restore to position, proportion or form the structure that is missing. T o d o so w ould be to build beyond the structural foundation, contrary to the laws o f statics.4 Placing the posterior teeth ou t side the base area requires the m axim um in the way o f retention. Setting teeth within the ridge area helps to stabilize the denture and thus requires fo r fu n c tion the m inim um in the way o f reten tion. It is extremely im portant to stabilize com plete dentures. T h e usual objective o f developing m axim um retention only does not supply a m uch-needed preven tive factor. T h e objective should be the constant preservation o f what remains rather than the meticulous restoration o f what is missing. T h e terms retention and stability should be understood clearly. Stability is that state wherein forces that tend to cause m otion are successfully resisted without loss o f equilibrium. A stable d en
ture is one that resists successfully the magnitude and direction o f functional forces that tend to alter the positional relation o f the denture to its osseous sup port. Actually, a so-called stable denture is only relatively stable, for absolute sta bility in any edentulous patient is im possible. In the above definition o f a stable denture, it is im portant to note that the term osseous support and not mucosa is used; during function a den ture may lose stability and yet maintain its positional relation to the mucosa. U n der such circumstances the denture still possesses retention. Retention may be d e fined as that state o f a denture wherein functional forces are unable to destroy the adhesion existing between the den ture and the mucoperiosteum. It is ap parent that a denture may be unstable and yet possess sufficient retention to re sist dislodgment. As long as the denture under functional loads does not lose its grip upon the mucosa, it m ay be said to possess an adequate degree o f retention but not stability. I f a denture does not m ove noticeably in' function, displacing the mucoperiosteum , it is said to be stabilized. Stable dentures are the most effective means o f preserving the denture fou n da tion, which is com posed o f alveolar bone with its overlying m ucoperiosteum and its underlying basal bone. Stable dentures are difficult, if not impossible, to con struct when large amounts o f alveolar bone have been lost, since the setup can not be centralized sufficiently to satisfy the law o f statics, that is, to exert force within the supporting structure and at a right angle to it. I f bone quality is high, dentures that are retentive but not stable can be worn with m inim um bone loss. Patients w ho need com plete dentures, however, usually possess bone o f low density. T h eir m etabolic processes have slowed dow n because o f age or degener-
4. DeVan, M. M. Basic considerations in full denture planning. J. 2nd. Dist. D. Soc. (N.Y.) 25:451 (April) 1940.
DE VAN . . . VOLUME 45, NOVEMBER 1952 • 527
ative disease processes. B y roentgenographic study o f the character o f the trabeculae, the bone quality is identified as close-meshed or rarefied. Likewise the nature o f the border o f the bony ridge is characterized as smooth o r jagged. T h e patient’ s health and age also are im por tant factors in bone quality. C H A R A C T E R A N D Q U A N T IT Y O F SA L IV A
Patients with dry m ouths are usually difficult patients. W hen saliva is sub normal in quantity, it is usually abnor mal in viscosity. R opy, sticky saliva is an unfavorable factor in the task o f stabil izing the com plete denture. W hen sali vary viscosity is high, the moisture film between the mucosa and th e denture base is increased in thickness. T h e e ffect o f this film is to cause a greater separation between the denture base and the under lying bone. T h e tendency to skid and to displace the denture is thereby increased. P R A C T IC A L S U G G E S T IO N S
1. T h e oral surgeon should hesitate to render a patient com pletely edentulous
until he has considered the physical, b io logic and psychologic factors pertinent to the case. Better still, he should defer extractions until a prosthodontist has been given an opportunity to appraise the patient’s ability to wear com plete dentures satisfactorily at that particular time. In some instances, the retention o f a few natural teeth to serve as abutments fo r provisional partial dentures may ease the transition from natural to artificial teeth. A slight delay in rendering the patient com pletely edentulous may have favorable physical, biological and psy chological results. 2. T he oral surgeon should find out from the patient whether or not impres sions o f the natural teeth were taken prior to their rem oval; he should explain the desirability o f having immediate re placements constructed before the natural teeth are removed. 3. In the removal o f teeth, the oral surgeon should retain as m uch bone as possible, especially the buccolabial cor tical plates above and the lingual cortical plates below.
Search for Error • For the layman, the most im portant thing about science is this: that it isn’ t a search for truth but a search for error. T he scientist lives in a w orld where truth is unattainable, but where it’ s always possible to find errors in the long-settled or the obvious. . . . So-called “ scientific” books that are supposed to contain final answers are never scientific. Science is forever self-correcting and ch angin g; what is put forth as gospel truth cannot be science. R udolf Flesch, T he A rt of Clear Thinking.