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Organic or metal bases for dentures
Organic
or metal bases for dentures
F. D. Moore,
Ph.B., D.D.S.
Chicago, Ill.
S
cientific research, development, and progress in the last fifty years has moved faster than at any time in the history of mankind. Dentistry and the study of dental materialslm6 have participated in this forward thrust. However, there is a gap’ between the performance of most dental research and its clinical evaluation and utilization. Smith7 states that many problems in dental materials are capable of solution in general practice. More dental clinicians should be encouraged to participate in research. The purpose of this article is to evaluate and consider the weaknesses, strengths, and most favorable conditions for the use of organic and metal bases in preserving the residual ridges and oral tissues for placement of removable dentures. THE PROBLEM
OF REMOVABLE
RESTORATIONS
The problem* is to provide the edentulous patient with a substitute for his dentition when the mucoperiosteum has replaced the periodontal membrane as the attaching medium. The prosthetic problem revolves about the basic fact that dentures must be related to the underlying bone through the mucoperiosteum, and not through the periodontal membrane as the dentition is related.8 Formulations of the denture problem that do not begin with this essential difference are illogical and misleading. THE
ROLE OF THE
CONNECTIVE
TISSUE
Certain characteristics’ of connective tissue must be clearly perceived for comprehension of the denture problem. These are: (1) Connective tissue is the connecting medium between the teeth (both natural and artificial) and the underlying bone. We cannot directly attach to bone, but only through connective tissue of some sort. (2) Connective tissues vary in thickness, rigidity, location, and site of attachment. An understanding of these differences is of extreme importance in perception and formulation of the nature of the problem. (3) C onnective tissue possesses the property of elasticity. The moment the displacing force is removed, sufficient hydrostatic force is available to bring the soft tissue back to rest position, (4) Water comprises over 80 per cent of the connective tissue. The laws of hydrostatics apply
227
228
J. Pros. Dent. March. 1967
Moore
under these circumstances, wherein force is transmitted undiminished as equal pressure acting in all directions. (5) Connective tissue membranes associated with teeth manifest a greater resistance to axial or vertical loads than to transverse or horizontal loads. BONES,
THE
BODY,
AND
DENTURE
SUPPORT
The prosthetic problem7 requires an understanding of bone, Some of the important characteristics of bone are: (1) Bones form the framework of the body providing both attachment and support to the soft tissues. (2) Essentially, bone is of two types, cancellous and compact. (3) The conversion of an original mass of cancellous bone into compact bone is the result of tensile and shear forces. (4) Cancellous bone is adequate to counteract compressive stresses (the type of stress that requires support). (5) Compact bone is required to counteract tensile stress (the type of stress required to resist muscle pull). (6) Compact bone arranged in a tubular form is required where resistance must be provided for compressive, tensile, and shear stresses combined. This combination of stresses must be resisted when the same bone must provide support to the weight of the body above it and attachment to the muscles around it. (7) Bone is essentially passive-it reacts, but does not act of its own accord; is responds to force, but does not initiate force. (8 ) The alveolar process develops with the teeth, but does not necessarily disappear with the teeth. (9) The widespread disappearance of the alveolar process following removal of teeth is due to unwise surgical procedure during extraction, and disuse and/or abuse atrophy. CLINICAL
OBSERVATIONS
AND
RESEARCH
Acrylic resin dentures have not met all of the requirements for conserving the denture-bearing tissues of patients for whom long satisfactory use was expected. Acrylic resin base+ 6, 9 warp during processing, and after being placed in service. SkinnerI” stated, “The results are in definite agreernent with those of Worner that the dimensional accuracy of the modern acrylic resins is not as good as that of vulcanite of past years.” An important criterion in selection of a denture base material is accuracy of fit; or the ability of the base to reproduce the original impression. Woelfel, Paffenbarger, and Sweeney’l reported that no resin denture accomplished this because “once a denture is removed from the gypsum cast on which it has been cured, the denture when replaced on the cast will not fit it.” However, this discrepancy was not considered significant by other researchers.4. ‘l-l3 Their conclusion, that the dimensional changes are not clinically significant, may not be entirely objective. Any prosthetic restoration that exerts undue pressure on the bony support is an orthodontic appliance as well as a prosthesis. Some of these warping dentures do exert undue pressure. Lammie” outlines four instances in which the combined use of hard and soft plastic may give superior results : ( 1) in the complete lower denture, when the patient shows a marked senile atrophy of the residual ridge; (2) in developing maximal retention, when the residual ridges are bilaterally undercut; (3) in mouths where a hard median palatal raphe is associated with poor retentive potentiality; and (4)
Organic
or metal bases for
dentures
229
in obturators for acquired and congential clefts of the palate. To these four should be added: (5) in patients with controlled cancer of the jaws; and (6) in immediate dentures. A radioisotope technique, using a mechanism known as a Positron Camera, has been developed that will permit scientists to map the distribution of bone marrow in living human subjects. I4 In this technique, a short-lived radioisotope of iron is used. After the isotope concentrates in the bone marrow, a sensitive detector translates it into dots on film. According to Van Dyke,14 the method has already disclosed previously undetected variations in bone marrow distribution associated with such ailments as polycythemia vera and Paget’s disease. The warped,+ I1 distorted, or deformed2 denture base can just as surely alter the distribution of the bone structure under a denture, causing resorption, and disappearance of the bone. Dental research could avail itself of this scientific technique and determine if the inaccuracies of acrylic resins * -4s 6, I13 I51 I6 have a destructive effect on the oral mucosa and its supporting bony structures. Regli and Gaskill concluded that the ability of the denture base to resist deformation is an important factor in adequate distribution of stress to supporting tissues. Their studies indicated that: ( 1) D uring mastication, plastic denture bases exhibit greater deformation than metal denture bases, or dentures with metal inserts. (2) Dentures constructed for high ridges exhibit torsional deformation. (3) Dentures constructed for flat ridges exhibit compression (inward toward the median line movement). (4) D uring deglutition, the dentures for high ridges exhibit extension, while those for flat ridges exhibit very little extension. Skinner and Jones6 found that the curing shrinkage of cold-curing acrylic resin was practically negligible; whereas, in the bases constructed with heat-curing resin, shrinkage was approximately a third of one per cent. When dentures were heated during processing, the curing shrinkage was greater in every instance, whether a heat-curing or a cold-curing resin was used.
THE ALUMINUM
INSERT BASE
Prothero17 reported that the first known casting of an aluminum complete denture base in the United States was in 1867 by Bean in Baltimore. Since that time, improved equipment and alloys have been developed.gp 18-21 An ordinary aluminum alloy contains 3.75 per cent magnesium, and the balance is aluminum of 99.95 per cent high purity. The aluminum alloy used in my dentures has from 2 to 4 per cent magnesium and 5 per cent silicone. Aluminum is characterized by its excellent fit and reproduction of the cast’s detail. Aluminum is the lightest of the metallic bases, when allowance is made for the thinner palate. A denture cast in this alloy is as light as acrylic resin. Aluminum is indicated when a metal base is necessary, especially when bad retentive factors exist. Some important physical properties of denture base materials are compared in Table I.
TECHNIQUE FOR CASTING ALUMINUM
BASES
The equipment for casting aluminum bases consists of a heavy-duty centrifugal casting machine, a high temperature electric furnace, and a blow torch and accessories. In addition to the common oxidation difficulties, there is the problem of
230
Moore
Table I Physical properties
of aluminum
Properties Density Hardness
Aluminum
(Brinell)
Ultimate tensile strength (tons per sq. inch) Melting range (C.) Percentage elongation The
aluminum
“Sizeland-Coe,
alloy*
in the chart
alloy1
compared Acrylic
with resin
2.66 60-68
1.18 23-29
9.6
3
those of other / Chrome
580-640 4 contained
cobalt
8.2-8.6 280 49 1270-1305 5
materials Gold
alloy 15
Soft 138 Hard 210 Soft 26 Hard 49 870-985 Soft 4-25 Hard l-6
4.5 per cent magnesium.
J, W.79
molten gas inclusion (particularly of hydrogen) which may be liberated by the magnesium in the alloy. The residual water will remain in the refractory crucible. The heating of the ingots is begun with a brush flame, and the dross and oxide are wiped away as they appear. In the refractory crucible, which has been heated in the electric furnace one and one half hours, the molten metal is cast at 700’ F. (when it is not yet in the highly liquid state). In view of the low specific gravity of the alloy, it is necessary to use a highly initial velocity of the centrifugal casting machine. The aluminum ingots must not be overheated at the instant of casting. ADVANTAGES
OF CAST METAL
BASES
Over a period of twenty years, my experiences with the insert cast aluminum denture base and other metal inserts confirm the findings of FaberSg The advantages of the aluminum or other cast metal bases, as determined by clinical impressions, are : 1. The metal base prevents warpage during processing, while acrylic resin does not. 2. The metal base is stronger than acrylic resin, and is less subject to breakage. 3. The fit of aluminum is more accurate, and tissue detail is reproduced more faithfully than with acrylic resin bases. 4. Less tissue change seems to occur under aluminum or other metal bases than under those of acrylic resin. 5. A metal base is less porous than organic material. 6. Metal is a better thermal conductor than is acrylic resin. 7. Dentures made with metal bases show less lateral deformation in function’ than do others. 8. Patients appear to master the use of dentures made with metal bases morr quickly than they do with others. 9. The problems of patients with poor ridges have been treated more successfully with metal bases than with others. 10. A snugness of fit, attainable with metal base dentures, seems to be absent in acrylic resin denture bases.
Organic
or metal
bases for
dentures
231
Summary Research findings indicate that all denture resins exhibit dimensional changes during processing. Such warpage is likely to be damaging to the tissues that support removable dentures. Therefore, the scientific method requires the use of discrimination when organic (acrylic) resin complete denture bases are used. Aluminum and other metal denture bases can aid in conserving the supporting tissues of the denturebearing area (basal seat) of dentures. References 1. Van Huysen, G., Fly, W., and Leonard, L.: Artificial Dentures and the Oral Mucosa, J. PROS. DENT. 4: 446, 1954. 2. Regli, C. P., and Gaskill, H. L.: Denture Base Deformation During Function, J. PROS. DENT. 4: 548, 1954. 3. Cornell, J. A., Tucker, J. L., and Powers, C. M.: Physical Properties of Denture-Base Materials, J. PROS. DENT. 10: 516, 1960. 4. Woelfel, J. B., Paffenbarger, G. C., and Sweeney, W. T.: Changes in Dentures During Storage in Water and in Service, J. A. D. A. 62: 643, 1961. 5. Lammie, G. A., and Storer, R.: A Preliminary Report on Resilient Denture Plastics, J. PROS. DENT. 8: 411, 1958. 6. Skinner, E. W., and Jones, P. M.: Dimensional Stability of Self-Curing Denture Base Acrylic Resin, J. A. D. A. 51: 426, 1955. 7. Smith, D. C.: Research in Dental Materials and Its Relation to Clinical Practice, J. A. D. A. 66: 370, 1963. 8. DeVan, M. M. : The Prosthetic Problem-Its Formulation and Suggestions for Its Solution, J. PROS. DENT. 6: 291, 1956. 9. Faber, B. L.: Lower Cast Metal Base Denture, J. PROS. DENT. 7: 51, 1957. 10. Skinner, E. W.: Acrylic Denture Base Materials: Their Physical Properties and Manipulation, J. PROS. DENT. 1: 161, 1951. 11. Woelfel, J. B., Paffenbarger, G. C., and Sweeney, W. T.: Dimensional Changes Occurring in Dentures During Processing, J. A. D. A. 61: 413, 1960. 12. Woelfel, J. B., and Paffenbarger, G. C.: Dimensional Changes Occurring in Artificial Dentures, Internat. D. J. 9: 451, 1959. 13. Woelfel, J. B., and Paffenbarger, G. C.: Method of Evaluating the Clinical Effect of Warping a Denture, J. A. D. A. 59: 250, 1959. 14. Van Dyke, D. C.: Human, Bone Marrow Distribution in Vivo by Iron 52 and the Positron Scintillation Camera, Science 144: 1587, 1964. 15. Silverman, S, I.: Denture Prosthesis and the Functional Anatomy of the Maxillofacial Structures, J. PROS. DENT. 6: 305, 1956. 16. Skinner, J. W., and Cooper, R. N.: Physical Properties of Denture Resins, Part I. Curing Shrinkage and Water Sorption, J. A. D. A. 30: 1845, 1943. 17. Prothero, J. H.: Prosthetic Dentistry, Chicago, 1912, Medical Dental Publishing Company. 18. Lundquist, D. 0.: An Aluminum Alloy as a Denture-Base Material, J. PROS. DENT. 13: 102, 1963. 19. Sizeland-Coe, J. W.: Cast Aluminum Alloy, Brit. Dent. J. 91: 263-268, 1951. 20. Johnson, W.: Apex Smelting-Metallurgist. Private Papers. 21. Campbell, D. D.: The Cast Aluminum Base Denture, J. A. D. A. 23: 1264, 1936, 3451 SOUTH MICHIGAN CHICAGO, ILL. 60616
AVE.
or metal bases for dentures
F. D. Moore,
Ph.B., D.D.S.
Chicago, Ill.
S
cientific research, development, and progress in the last fifty years has moved faster than at any time in the history of mankind. Dentistry and the study of dental materialslm6 have participated in this forward thrust. However, there is a gap’ between the performance of most dental research and its clinical evaluation and utilization. Smith7 states that many problems in dental materials are capable of solution in general practice. More dental clinicians should be encouraged to participate in research. The purpose of this article is to evaluate and consider the weaknesses, strengths, and most favorable conditions for the use of organic and metal bases in preserving the residual ridges and oral tissues for placement of removable dentures. THE PROBLEM
OF REMOVABLE
RESTORATIONS
The problem* is to provide the edentulous patient with a substitute for his dentition when the mucoperiosteum has replaced the periodontal membrane as the attaching medium. The prosthetic problem revolves about the basic fact that dentures must be related to the underlying bone through the mucoperiosteum, and not through the periodontal membrane as the dentition is related.8 Formulations of the denture problem that do not begin with this essential difference are illogical and misleading. THE
ROLE OF THE
CONNECTIVE
TISSUE
Certain characteristics’ of connective tissue must be clearly perceived for comprehension of the denture problem. These are: (1) Connective tissue is the connecting medium between the teeth (both natural and artificial) and the underlying bone. We cannot directly attach to bone, but only through connective tissue of some sort. (2) Connective tissues vary in thickness, rigidity, location, and site of attachment. An understanding of these differences is of extreme importance in perception and formulation of the nature of the problem. (3) C onnective tissue possesses the property of elasticity. The moment the displacing force is removed, sufficient hydrostatic force is available to bring the soft tissue back to rest position, (4) Water comprises over 80 per cent of the connective tissue. The laws of hydrostatics apply
227
228
J. Pros. Dent. March. 1967
Moore
under these circumstances, wherein force is transmitted undiminished as equal pressure acting in all directions. (5) Connective tissue membranes associated with teeth manifest a greater resistance to axial or vertical loads than to transverse or horizontal loads. BONES,
THE
BODY,
AND
DENTURE
SUPPORT
The prosthetic problem7 requires an understanding of bone, Some of the important characteristics of bone are: (1) Bones form the framework of the body providing both attachment and support to the soft tissues. (2) Essentially, bone is of two types, cancellous and compact. (3) The conversion of an original mass of cancellous bone into compact bone is the result of tensile and shear forces. (4) Cancellous bone is adequate to counteract compressive stresses (the type of stress that requires support). (5) Compact bone is required to counteract tensile stress (the type of stress required to resist muscle pull). (6) Compact bone arranged in a tubular form is required where resistance must be provided for compressive, tensile, and shear stresses combined. This combination of stresses must be resisted when the same bone must provide support to the weight of the body above it and attachment to the muscles around it. (7) Bone is essentially passive-it reacts, but does not act of its own accord; is responds to force, but does not initiate force. (8 ) The alveolar process develops with the teeth, but does not necessarily disappear with the teeth. (9) The widespread disappearance of the alveolar process following removal of teeth is due to unwise surgical procedure during extraction, and disuse and/or abuse atrophy. CLINICAL
OBSERVATIONS
AND
RESEARCH
Acrylic resin dentures have not met all of the requirements for conserving the denture-bearing tissues of patients for whom long satisfactory use was expected. Acrylic resin base+ 6, 9 warp during processing, and after being placed in service. SkinnerI” stated, “The results are in definite agreernent with those of Worner that the dimensional accuracy of the modern acrylic resins is not as good as that of vulcanite of past years.” An important criterion in selection of a denture base material is accuracy of fit; or the ability of the base to reproduce the original impression. Woelfel, Paffenbarger, and Sweeney’l reported that no resin denture accomplished this because “once a denture is removed from the gypsum cast on which it has been cured, the denture when replaced on the cast will not fit it.” However, this discrepancy was not considered significant by other researchers.4. ‘l-l3 Their conclusion, that the dimensional changes are not clinically significant, may not be entirely objective. Any prosthetic restoration that exerts undue pressure on the bony support is an orthodontic appliance as well as a prosthesis. Some of these warping dentures do exert undue pressure. Lammie” outlines four instances in which the combined use of hard and soft plastic may give superior results : ( 1) in the complete lower denture, when the patient shows a marked senile atrophy of the residual ridge; (2) in developing maximal retention, when the residual ridges are bilaterally undercut; (3) in mouths where a hard median palatal raphe is associated with poor retentive potentiality; and (4)
Organic
or metal bases for
dentures
229
in obturators for acquired and congential clefts of the palate. To these four should be added: (5) in patients with controlled cancer of the jaws; and (6) in immediate dentures. A radioisotope technique, using a mechanism known as a Positron Camera, has been developed that will permit scientists to map the distribution of bone marrow in living human subjects. I4 In this technique, a short-lived radioisotope of iron is used. After the isotope concentrates in the bone marrow, a sensitive detector translates it into dots on film. According to Van Dyke,14 the method has already disclosed previously undetected variations in bone marrow distribution associated with such ailments as polycythemia vera and Paget’s disease. The warped,+ I1 distorted, or deformed2 denture base can just as surely alter the distribution of the bone structure under a denture, causing resorption, and disappearance of the bone. Dental research could avail itself of this scientific technique and determine if the inaccuracies of acrylic resins * -4s 6, I13 I51 I6 have a destructive effect on the oral mucosa and its supporting bony structures. Regli and Gaskill concluded that the ability of the denture base to resist deformation is an important factor in adequate distribution of stress to supporting tissues. Their studies indicated that: ( 1) D uring mastication, plastic denture bases exhibit greater deformation than metal denture bases, or dentures with metal inserts. (2) Dentures constructed for high ridges exhibit torsional deformation. (3) Dentures constructed for flat ridges exhibit compression (inward toward the median line movement). (4) D uring deglutition, the dentures for high ridges exhibit extension, while those for flat ridges exhibit very little extension. Skinner and Jones6 found that the curing shrinkage of cold-curing acrylic resin was practically negligible; whereas, in the bases constructed with heat-curing resin, shrinkage was approximately a third of one per cent. When dentures were heated during processing, the curing shrinkage was greater in every instance, whether a heat-curing or a cold-curing resin was used.
THE ALUMINUM
INSERT BASE
Prothero17 reported that the first known casting of an aluminum complete denture base in the United States was in 1867 by Bean in Baltimore. Since that time, improved equipment and alloys have been developed.gp 18-21 An ordinary aluminum alloy contains 3.75 per cent magnesium, and the balance is aluminum of 99.95 per cent high purity. The aluminum alloy used in my dentures has from 2 to 4 per cent magnesium and 5 per cent silicone. Aluminum is characterized by its excellent fit and reproduction of the cast’s detail. Aluminum is the lightest of the metallic bases, when allowance is made for the thinner palate. A denture cast in this alloy is as light as acrylic resin. Aluminum is indicated when a metal base is necessary, especially when bad retentive factors exist. Some important physical properties of denture base materials are compared in Table I.
TECHNIQUE FOR CASTING ALUMINUM
BASES
The equipment for casting aluminum bases consists of a heavy-duty centrifugal casting machine, a high temperature electric furnace, and a blow torch and accessories. In addition to the common oxidation difficulties, there is the problem of
230
Moore
Table I Physical properties
of aluminum
Properties Density Hardness
Aluminum
(Brinell)
Ultimate tensile strength (tons per sq. inch) Melting range (C.) Percentage elongation The
aluminum
“Sizeland-Coe,
alloy*
in the chart
alloy1
compared Acrylic
with resin
2.66 60-68
1.18 23-29
9.6
3
those of other / Chrome
580-640 4 contained
cobalt
8.2-8.6 280 49 1270-1305 5
materials Gold
alloy 15
Soft 138 Hard 210 Soft 26 Hard 49 870-985 Soft 4-25 Hard l-6
4.5 per cent magnesium.
J, W.79
molten gas inclusion (particularly of hydrogen) which may be liberated by the magnesium in the alloy. The residual water will remain in the refractory crucible. The heating of the ingots is begun with a brush flame, and the dross and oxide are wiped away as they appear. In the refractory crucible, which has been heated in the electric furnace one and one half hours, the molten metal is cast at 700’ F. (when it is not yet in the highly liquid state). In view of the low specific gravity of the alloy, it is necessary to use a highly initial velocity of the centrifugal casting machine. The aluminum ingots must not be overheated at the instant of casting. ADVANTAGES
OF CAST METAL
BASES
Over a period of twenty years, my experiences with the insert cast aluminum denture base and other metal inserts confirm the findings of FaberSg The advantages of the aluminum or other cast metal bases, as determined by clinical impressions, are : 1. The metal base prevents warpage during processing, while acrylic resin does not. 2. The metal base is stronger than acrylic resin, and is less subject to breakage. 3. The fit of aluminum is more accurate, and tissue detail is reproduced more faithfully than with acrylic resin bases. 4. Less tissue change seems to occur under aluminum or other metal bases than under those of acrylic resin. 5. A metal base is less porous than organic material. 6. Metal is a better thermal conductor than is acrylic resin. 7. Dentures made with metal bases show less lateral deformation in function’ than do others. 8. Patients appear to master the use of dentures made with metal bases morr quickly than they do with others. 9. The problems of patients with poor ridges have been treated more successfully with metal bases than with others. 10. A snugness of fit, attainable with metal base dentures, seems to be absent in acrylic resin denture bases.
Organic
or metal
bases for
dentures
231
Summary Research findings indicate that all denture resins exhibit dimensional changes during processing. Such warpage is likely to be damaging to the tissues that support removable dentures. Therefore, the scientific method requires the use of discrimination when organic (acrylic) resin complete denture bases are used. Aluminum and other metal denture bases can aid in conserving the supporting tissues of the denturebearing area (basal seat) of dentures. References 1. Van Huysen, G., Fly, W., and Leonard, L.: Artificial Dentures and the Oral Mucosa, J. PROS. DENT. 4: 446, 1954. 2. Regli, C. P., and Gaskill, H. L.: Denture Base Deformation During Function, J. PROS. DENT. 4: 548, 1954. 3. Cornell, J. A., Tucker, J. L., and Powers, C. M.: Physical Properties of Denture-Base Materials, J. PROS. DENT. 10: 516, 1960. 4. Woelfel, J. B., Paffenbarger, G. C., and Sweeney, W. T.: Changes in Dentures During Storage in Water and in Service, J. A. D. A. 62: 643, 1961. 5. Lammie, G. A., and Storer, R.: A Preliminary Report on Resilient Denture Plastics, J. PROS. DENT. 8: 411, 1958. 6. Skinner, E. W., and Jones, P. M.: Dimensional Stability of Self-Curing Denture Base Acrylic Resin, J. A. D. A. 51: 426, 1955. 7. Smith, D. C.: Research in Dental Materials and Its Relation to Clinical Practice, J. A. D. A. 66: 370, 1963. 8. DeVan, M. M. : The Prosthetic Problem-Its Formulation and Suggestions for Its Solution, J. PROS. DENT. 6: 291, 1956. 9. Faber, B. L.: Lower Cast Metal Base Denture, J. PROS. DENT. 7: 51, 1957. 10. Skinner, E. W.: Acrylic Denture Base Materials: Their Physical Properties and Manipulation, J. PROS. DENT. 1: 161, 1951. 11. Woelfel, J. B., Paffenbarger, G. C., and Sweeney, W. T.: Dimensional Changes Occurring in Dentures During Processing, J. A. D. A. 61: 413, 1960. 12. Woelfel, J. B., and Paffenbarger, G. C.: Dimensional Changes Occurring in Artificial Dentures, Internat. D. J. 9: 451, 1959. 13. Woelfel, J. B., and Paffenbarger, G. C.: Method of Evaluating the Clinical Effect of Warping a Denture, J. A. D. A. 59: 250, 1959. 14. Van Dyke, D. C.: Human, Bone Marrow Distribution in Vivo by Iron 52 and the Positron Scintillation Camera, Science 144: 1587, 1964. 15. Silverman, S, I.: Denture Prosthesis and the Functional Anatomy of the Maxillofacial Structures, J. PROS. DENT. 6: 305, 1956. 16. Skinner, J. W., and Cooper, R. N.: Physical Properties of Denture Resins, Part I. Curing Shrinkage and Water Sorption, J. A. D. A. 30: 1845, 1943. 17. Prothero, J. H.: Prosthetic Dentistry, Chicago, 1912, Medical Dental Publishing Company. 18. Lundquist, D. 0.: An Aluminum Alloy as a Denture-Base Material, J. PROS. DENT. 13: 102, 1963. 19. Sizeland-Coe, J. W.: Cast Aluminum Alloy, Brit. Dent. J. 91: 263-268, 1951. 20. Johnson, W.: Apex Smelting-Metallurgist. Private Papers. 21. Campbell, D. D.: The Cast Aluminum Base Denture, J. A. D. A. 23: 1264, 1936, 3451 SOUTH MICHIGAN CHICAGO, ILL. 60616
AVE.