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Bonding porcelain teeth to acrylic resin denture bases
Bonding porcelain teeth to acrylic resin denture bases
George C. Paffenbarger, DDS W . Tim othy Sweeney, B A R. L. Bowen, DDS, W ashington, D.C.
The chem ical bonding of porcelain teeth to denture bases of cold-curing and heat-curing acrylic resins was accomplished by the use of a silane coupling agent, gamma-methacryloxypropyltrimethoxysilane. In tension, the porcelain-resin interface did not rupture— invari ably the teeth did. Untreated teeth showed no measurable bonding to the resin. Because of a lack of adhesion between porcelain teeth and acrylic resins, the design currently used for most porcelain teeth provides for m echanical locking by use of m etal pins or undercut wells and canals (diatoric form ). These designs weaken the teeth and can be eliminated by the use of a solid tooth that has been treated with an appropriate silane. The bonding strengthens the denture since it makes the e f fective cross-sectional area greater and pre vents seepage between the tooth and the plas tic and thus aids oral hygiene and esthetics. 1018
Direct bonding of acrylic denture bases to por celain teeth has proved inadequate in dental use. It is therefore necessary to place metal pins or retention holes and canals in porcelain teeth to hold them in the denture base. These locking mechanisms are costly, weaken the tooth un necessarily, and do not prevent the entrance of fluids along the tooth-resin interface, which is sensitive to temperature changes. These changes cause widening of the crevice at the tooth-resin interface because the coefficients of thermal ex pansion of the currently used denture bases (70 to 100 ppm per degree Centigrade)1 are from 9 to 12 times that of the porcelain tooth (8 ppm per degree Centigrade).2 Therefore, when a den ture at room temperature (20°C.) is inserted into the mouth (37°C.), the acrylic base may expand as much as 0.17 percent linearly, where as the porcelain tooth expands only 0.013 per cent. Furthermore, the lack of adequate or stable bonding between porcelain teeth and acrylic resin establishes surfaces of fracture, especially in the anterior sections of dentures, which are thin in cross section and subjected to high stress. In almost every broken denture, the surface of frac ture appears to be at the tooth-resin interface (Fig. 1). If porcelain teeth could be bonded stably to the denture base, they could be made without pins or diatoric retention and could be stronger.
M ethods and results
Significant improvements in bonding were ac complished by the use of a silane coupling agent between the porcelain teeth and the acrylic base. This means of bond improvement has been known for several years,3 6 and silane coupling agents
are used extensively in glass-reinforced resins. Since porcelain teeth are made by fusing a mix ture of feldspar (orthoclase), flint (silica), and clay (kaolin) that forms a complex silicate struc ture, appropriate silanes should serve as coupling agents between the porcelain tooth and the den ture base. The silane used in the tests was gammamethacryloxypropyltrimethoxysilane.*f The por celain teeth were cleaned, to remove wax and other contaminants, by washing three times in a boiling water solution of a household detergent and then rinsing in clean hot water. A 0.5 percent solution of the silane (Fig. 2A) in distilled water was prepared and acidified with acetic acid to a pH between 3 and 4 while it was continually stirred. Acidification catalyzes hydro lysis at the methoxy groups (Fig. 2 A to B) arid prepares the silane for bonding to the sur face of the porcelain tooth (Fig. 2C). The hy drolysis reaction was allowed to continue for an hour before the cleaned porcelain teeth were placed in the stirred silane solution for 30 minutes. The teeth were then removed and dried for 10 minutes in an oven at 110°C. The silane solutions were freshly prepared; however, the solution may be used until cloudi ness develops. The bonding was demonstrated by tensile tests on specimens made by polymerizing resin on single teeth and by fabricating dentures of clear acrylic resin by use of silane-treated and untreated teeth.
Fig. 1 ■ Fractures of dentures th a t follow porcelain tooth-denture base interface because of lack of bonding between tooth and plastic. T o p : Upper a crylic denture th a t fra ctu red when p atient chewed piece of hard c a ra mel candy. Slig h tly m alpositioned n atural m olar occluded w ith porcelain tooth shown between pieces of broken denture. C en ter: U pper polystyrene denture th a t fra c tured in use. T y p ica l m idline fractu re th a t involves notch fo r frenum , tooth-resin junction, and central anterior region of denture. Bottom : Low er a crylic denture th a t was broken by pressing it in hand. N o tice impression of proxi mal surface of incisor in piece of broken denture on right side o f figure
■ Tensile test method: The bonding was evalu ated by tensile tests patterned after those de scribed in section 3.7 of American Dental Asso ciation specification no. 15 for acrylic resin teeth.7 The tests consisted of applying tensile forces to the acrylic rods until rupture occurred. In no instance did a rod or the bonding region rupture. The tensile specimen pattern was made by attaching, with baseplate wax, the ends of two glass rods to the labial and lingual surfaces, re spectively, of a large central incisor (Fig. 3). When molars were used, the glass rods were waxed to the occlusal and ridge lap surfaces. Dental porcelain (APCO) was fused to the re tention hole and the canals in the diatoric molars to eliminate mechanical retention. The glass rods were aligned by assembling them and the tooth in a brass jig until the luting wax hardened. The specimen pattern was then flasked in plaster of paris (artificial stone) and placed in boiling water. The glass rods, wax, and porcelain teeth wereremoved from the plaster. The teeth
Pa ffe n b a rg e r— Sweeney— Bow en: B O N D IN G P O R C E L A IN T O A C R Y L I C R E S IN
■ 1019
-CHg
II V C-CI^
c=o I o CHs
C-CEfe
C=0 +H2 0
rHs -CH b OH
CHjg Bq
C-0-£i-0-CI%
? CEfe
9Hs H 6-Si-OH
-H e 0
lT
suirface of porcelain f tooth
? the -O-Si-OT
HO-^i-OH O------ surface -O— ii— O— of the | porcelain O tooth
I B Fig. 2 ■ H yp othetical schem atic diagram of chem ical porcelain teeth with silane coupling agent
were cleaned and treated with the silane as pre viously described. After painting the plaster molds with an algi nate separation medium, the silane-treated teeth were fitted into their respective impressions. Any surface that would abut the resin was not touched. A modification of the forecoins method was
B
Fig. 3 ■ Longitudinal section of tensile specimen shows porcelain tooth ( A ) with plastic rods (B ) Tensile forces were applied p a ra l lel w ith long axis of specimen
B
1020 ■ JA D A , V o l. 74, A p ril 1967
reactions occurring in treatm ent of silica-containing surface of
used in which the teeth were treated with the silane before the tensile test specimen pattern was as sembled. After the halves of the flask were sep arated, the molds were cleaned as described pre viously. Control specimens were prepared in the same manner except that the porcelain teeth were not treated with the silane. The flasks were packed with acrylic dough in the usual manner, with two trial closures, and were processed according to the resin manufac turer’s directions. After heating, the flasks were air-cooled for an hour, water-cooled to room temperature, and then carefully deflasked. The distal ends of the acrylic rods that replaced the glass rods were lathed to a diameter of about 6 mm. Then, an inverted cone bur was used to reduce the sec tion of acrylic resin that was in contact with the tooth’s labial or ridge lap surface to a diameter within about ±0.25 mm. of that of the acrylic rod. This method was used since the specimens containing porcelain teeth could not be machined to a uniform diameter throughout as specified in ADA specification no. 15 for acrylic resin teeth.7 The porcelain tooth would break, indicating that it may have been strained by the bonding. ■ Tensile test results: Bonding test results are summarized in the table. Some specimens were immersed in distilled water at 37°ri-20C. Others were cycled seven or eight times through a tem perature range of 10°±3°C. to 65°±3°C.
Table * Bonding test results Brand of porcelain tooth
No. of treated specimens
Tensile strength* (psi)
Standard deviation!
Coefficient ■ variation (% )
Brand of acrylic resin
Temp.
Time
Trubyte New Hue
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
8
7 days in water at 37°C.
1,610
390
24
Polychrome
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
3
7 days In water at 37°C.
1,610
410
25
Myerson
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
5
Taken through 7 temperature cyclesj
1,530
300
20
Polychrome
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
6
Taken through 8 temperature cycles^
1,570
570
36
Trubyte New Hue
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
6
7 days in water at 37°C.§
1,430
100
7
Trubyte New Hue
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
7
7 days in water at 37°C.§
1,200
470
40
Trubyte New Hue
Densene 33
74°C. 100°C.
1.5 hr. .5 hr.
4
7 days in water at 37°C.
2,050
1,150
56
Trubyte New Hue
Acralite Fastcure
cold-curing
5
29 days in water at 37°C.
1,750
320
18
Trubyte New Hue
Densene 33
cold-curing
5
7 days in water at 37°C.
1,840
330
18
Trubyte Bioblend
Acralite 88
cold-curing
5
7 days in water at 37°C.
1,530
410
27
Trubyte Bioblend
Acralite 88
cold-curing
6
32 days in water at 37°C.
2,280
400
17
Totals and averages
Mode of cure
60
* Force required to rupture tooth divided by cross-section area of contact surface. t
* (x-x)2
Comments
1,670
26
440
X 6 5° rb 3°C. to 10° ± 3°C. during the cycling. These specimens were in water for 2 to 3 days. § Data of lines 5 and 6 were not combined, since it was desired to illustrate the variability of results in a ‘test of this nature with averages of 6 or 7 specimens.
Fig. 4 ■ Fractured tensile specimens show labial surfaces of incisors and ends of a crylic rods polym erized a g a in st la bial surfaces. L e ft: T o p specimen shows untreated tooth undisturbed, which indicates lack o f adhesion. Resin rods did not adhere to a n y untreated tooth. In bottom specimen, surface o f the silane-treated tooth has saucer-shaped co n cavity where porcelain stuck to end of rod. R ig h t: In silane-treated teeth, fractures le ft large part of each tooth on end o f each rod P a ffe n b a rg e r— Sweeney— Bow en : B O N D IN G P O R C E L A IN T O A C R Y L I C
R E S IN
*
1021
in distilled water (See “comments” column in the table). All specimens were loaded at a rate of 90±23 kg./minute. The untreated, control teeth showed no meas urable bonding to the resin. All 30 control speci mens were too weak to withstand deflasking. The porcelain surfaces of the untreated teeth re tained their gloss, and the opposing rods of acrylic resin showed smooth, glossy surfaces, indicating that very little, if any, bonding had taken place (Fig 4 left, top). The silane-treated teeth were bonded with the cold-curing and the heat-curing denture base resins; considerable force was required to rup ture the specimens (table) and, in every in stance, the tooth fractured or pieces of the tooth
adhered to the acrylic resin (Fig. 4 left, bottom; right). Lines 5 and 6 in the table give strengths of specimens that were silane-treated before wax ing as previously described. This treatment ap peared to make little, if any, difference when one considers the large standard deviation. Also, as shown in the table, temperature cycling in water or prolonged soaking in water did not seriously affect the bonding. ■ Treated and untreated teeth in complete den tures: To demonstrate, in another way, the seal ing of the porcelain tooth-acrylic resin interface by the silane treatment, seven upper dentures were constructed. The wax model dentures were made in a common Korogel mold with the same
Fig. 5 ■ Dye penetration of porcelain tooth-denture base in terface. M e th y l blue penetrated between teeth and acrylic base (to p left) where teeth were not treated w ith silane. A n g u la r view of left side of specimen a t top left shows dye pene tration on ridge lap surfaces (b o tto m ). In specimen on top right, teeth were treated with silane and little or no penetration occurred. U pper right second bicuspid was fractu red so dye leaked into diatoric space but did not p enetrate on ridge lap surface. D a rk area is shadow cast by porcelain teeth on le ft side o f denture 1022
■ JADA, Vol. 74, April 1967
Sum m ary
Fig. 6 ■ Fractu red teeth caused by bonding of silanetreated teeth to a crylic denture base. Fractures a re d iffi c u lt to see unless ang le of incidence of lighting is a d justed to cause h a lf of broken tooth to appear darker than other h alf
mold of teeth. The bulk of the wax was softened and removed from the plaster-of-paris molds, which were then cleaned as previously described. In three instances, the silane solution was poured over the teeth in the flask and allowed to remain for 10 minutes in one instance and for 30 minutes in two instances. It was then poured off, and the flask was placed in an oven for 10 minutes at 110°C. The flask was then cooled, the plaster was painted with an alginate separator (care was taken to keep it off the teeth), and the flask was packed with clear acrylic resin. In another instance, the teeth were treated before the wax-up and, in three other instances, the teeth were not treated. Except for the preced ing process, the processing of all seven dentures was identical. All dentures were temperaturecycled six times in distilled water from 8°±3°C. to 65°±3°C. All seven dentures were immersed in a satu rated aqueous solution of methyl blue (1 Gm./ 25 ml.) for 15 minutes in a desiccator evacuated with a mechanical pump. The vacuum assisted penetration of the dye into fissures around the teeth. The dentures were then scrubbed with soap and water. The relative amount of acrylic resin-porcelain tooth interface closure affected by the silane treatment is shown in Figure 5. There was little penetration of the dye around the silanetreated teeth. The silane-treated teeth were so well bonded to the denture base that fracture oc curred in some of the molars and premolars (Fig. 6). These teeth, because of the diatoric design, are susceptible to fracture and would be greatly strengthened if they were solid.
Porcelain teeth can be bonded to an acrylic den ture base by an appropriate silane treatment. The bonding strengthens the denture, prevents seepage of material around the necks and ridge lap portions of the teeth, and thus aids in main taining good denture hygiene. The bonding places strain in the porcelain teeth which may cause them to fracture during or after processing. The suggested silane treatment indicates how to redesign porcelain teeth with the probable elimination of the metal pins and the diatoric design as retaining features, resulting in a stronger, more serviceable, and esthetic porcelain tooth. T h is investigation w as supported in part by U S P H S re search gran t D E 0 1 6 5 9 to the A m eric a n D ental A sso cia tion from the N a tio n al Institute of D ental Research and is part of the dental research program conducted a t the N a tio n al Bureau of Standards in cooperation w ith the Council on Dental Research of the A m erica n Dental A ssociation, the A rm y D ental Corps, the D ental Sciences Division of the School of A erospace M ed icin e ( U S A F ) , and the Veteran s A d m in istration. Doctors Paffenb arg er and Bowen and M r. Sw een ey are research associates from the A m erican D ental A ssociation a t the N atio n al Bureau of Standards, W a sh in g to n , D.C. 2 02 34. * Some com m ercial m aterials and equipm ent are iden tified in this paper to specify ad eq u ately the experim en tal procedure. Such identification does not im ply recom m endation or endorsem ent by the N a tio n al Bureau of Standards or th a t the m aterial or equipm ent is the best a v a ila b le for the purpose. t Union Carbide Silane A - 174, Union C arb id e Corp., N ew Y o rk. A t least one sim ilar silane is a v a ila b le : Dow Corning Sila n e Z - 6 0 3 0 , 3 - (trim ethoxysilyl-propyl m eth acrylate, Dow Chem ical Co., M id la n d , M ich . 1. W o e lfe l, J . B.; Paffenb arger, G. C., and Sweeney, W . T . Some physical properties of organic denture base m aterials. J A D A 6 7 :4 8 9 Oct., 1963. 2. Sacchi, Hector, and Paffenb arg er, G. C. Sim ple technic for m aking porcelain jac k e t crowns. JA D A 5 4 :3 6 6 M a rch , 1957. 3. Vand erb ilt, B. M ., and Sim ko, J . P., Jr . Silane coupling agents in glass-reinforced plastics. M odern Plastics 3 8 :1 3 5 Dec., 1960. 4. C lark, H. A ., and Pleuddem ann, E. P. Bonding of silane coupling agents in glass-reinforced plastics. M o d ern Plastics 4 0 :1 3 3 Ju n e , 1963. 5. Sterm an, S., and M arsden, J . G. Sila n e coupling agents as integral blends in resin-filler systems. M odern Plastics 4 0 :1 2 5 Ju ly , 1963. 6. Sterm an, S., and Toogood, J . B. H ow to promote adhesion with silicones an d silanes. A d hesives A g e 8 :3 4 Ju ly , 1965. 7. A m erican D ental Association. Guide to dental m a terials, ed. 3. Chicago, A m erican D ental Association, 1966.
P affenb arger— Sweeney— Bo w en : B O N D IN G P O R C E L A IN
TO A C R Y L IC
R E S IN
■ 1023
George C. Paffenbarger, DDS W . Tim othy Sweeney, B A R. L. Bowen, DDS, W ashington, D.C.
The chem ical bonding of porcelain teeth to denture bases of cold-curing and heat-curing acrylic resins was accomplished by the use of a silane coupling agent, gamma-methacryloxypropyltrimethoxysilane. In tension, the porcelain-resin interface did not rupture— invari ably the teeth did. Untreated teeth showed no measurable bonding to the resin. Because of a lack of adhesion between porcelain teeth and acrylic resins, the design currently used for most porcelain teeth provides for m echanical locking by use of m etal pins or undercut wells and canals (diatoric form ). These designs weaken the teeth and can be eliminated by the use of a solid tooth that has been treated with an appropriate silane. The bonding strengthens the denture since it makes the e f fective cross-sectional area greater and pre vents seepage between the tooth and the plas tic and thus aids oral hygiene and esthetics. 1018
Direct bonding of acrylic denture bases to por celain teeth has proved inadequate in dental use. It is therefore necessary to place metal pins or retention holes and canals in porcelain teeth to hold them in the denture base. These locking mechanisms are costly, weaken the tooth un necessarily, and do not prevent the entrance of fluids along the tooth-resin interface, which is sensitive to temperature changes. These changes cause widening of the crevice at the tooth-resin interface because the coefficients of thermal ex pansion of the currently used denture bases (70 to 100 ppm per degree Centigrade)1 are from 9 to 12 times that of the porcelain tooth (8 ppm per degree Centigrade).2 Therefore, when a den ture at room temperature (20°C.) is inserted into the mouth (37°C.), the acrylic base may expand as much as 0.17 percent linearly, where as the porcelain tooth expands only 0.013 per cent. Furthermore, the lack of adequate or stable bonding between porcelain teeth and acrylic resin establishes surfaces of fracture, especially in the anterior sections of dentures, which are thin in cross section and subjected to high stress. In almost every broken denture, the surface of frac ture appears to be at the tooth-resin interface (Fig. 1). If porcelain teeth could be bonded stably to the denture base, they could be made without pins or diatoric retention and could be stronger.
M ethods and results
Significant improvements in bonding were ac complished by the use of a silane coupling agent between the porcelain teeth and the acrylic base. This means of bond improvement has been known for several years,3 6 and silane coupling agents
are used extensively in glass-reinforced resins. Since porcelain teeth are made by fusing a mix ture of feldspar (orthoclase), flint (silica), and clay (kaolin) that forms a complex silicate struc ture, appropriate silanes should serve as coupling agents between the porcelain tooth and the den ture base. The silane used in the tests was gammamethacryloxypropyltrimethoxysilane.*f The por celain teeth were cleaned, to remove wax and other contaminants, by washing three times in a boiling water solution of a household detergent and then rinsing in clean hot water. A 0.5 percent solution of the silane (Fig. 2A) in distilled water was prepared and acidified with acetic acid to a pH between 3 and 4 while it was continually stirred. Acidification catalyzes hydro lysis at the methoxy groups (Fig. 2 A to B) arid prepares the silane for bonding to the sur face of the porcelain tooth (Fig. 2C). The hy drolysis reaction was allowed to continue for an hour before the cleaned porcelain teeth were placed in the stirred silane solution for 30 minutes. The teeth were then removed and dried for 10 minutes in an oven at 110°C. The silane solutions were freshly prepared; however, the solution may be used until cloudi ness develops. The bonding was demonstrated by tensile tests on specimens made by polymerizing resin on single teeth and by fabricating dentures of clear acrylic resin by use of silane-treated and untreated teeth.
Fig. 1 ■ Fractures of dentures th a t follow porcelain tooth-denture base interface because of lack of bonding between tooth and plastic. T o p : Upper a crylic denture th a t fra ctu red when p atient chewed piece of hard c a ra mel candy. Slig h tly m alpositioned n atural m olar occluded w ith porcelain tooth shown between pieces of broken denture. C en ter: U pper polystyrene denture th a t fra c tured in use. T y p ica l m idline fractu re th a t involves notch fo r frenum , tooth-resin junction, and central anterior region of denture. Bottom : Low er a crylic denture th a t was broken by pressing it in hand. N o tice impression of proxi mal surface of incisor in piece of broken denture on right side o f figure
■ Tensile test method: The bonding was evalu ated by tensile tests patterned after those de scribed in section 3.7 of American Dental Asso ciation specification no. 15 for acrylic resin teeth.7 The tests consisted of applying tensile forces to the acrylic rods until rupture occurred. In no instance did a rod or the bonding region rupture. The tensile specimen pattern was made by attaching, with baseplate wax, the ends of two glass rods to the labial and lingual surfaces, re spectively, of a large central incisor (Fig. 3). When molars were used, the glass rods were waxed to the occlusal and ridge lap surfaces. Dental porcelain (APCO) was fused to the re tention hole and the canals in the diatoric molars to eliminate mechanical retention. The glass rods were aligned by assembling them and the tooth in a brass jig until the luting wax hardened. The specimen pattern was then flasked in plaster of paris (artificial stone) and placed in boiling water. The glass rods, wax, and porcelain teeth wereremoved from the plaster. The teeth
Pa ffe n b a rg e r— Sweeney— Bow en: B O N D IN G P O R C E L A IN T O A C R Y L I C R E S IN
■ 1019
-CHg
II V C-CI^
c=o I o CHs
C-CEfe
C=0 +H2 0
rHs -CH b OH
CHjg Bq
C-0-£i-0-CI%
? CEfe
9Hs H 6-Si-OH
-H e 0
lT
suirface of porcelain f tooth
? the -O-Si-OT
HO-^i-OH O------ surface -O— ii— O— of the | porcelain O tooth
I B Fig. 2 ■ H yp othetical schem atic diagram of chem ical porcelain teeth with silane coupling agent
were cleaned and treated with the silane as pre viously described. After painting the plaster molds with an algi nate separation medium, the silane-treated teeth were fitted into their respective impressions. Any surface that would abut the resin was not touched. A modification of the forecoins method was
B
Fig. 3 ■ Longitudinal section of tensile specimen shows porcelain tooth ( A ) with plastic rods (B ) Tensile forces were applied p a ra l lel w ith long axis of specimen
B
1020 ■ JA D A , V o l. 74, A p ril 1967
reactions occurring in treatm ent of silica-containing surface of
used in which the teeth were treated with the silane before the tensile test specimen pattern was as sembled. After the halves of the flask were sep arated, the molds were cleaned as described pre viously. Control specimens were prepared in the same manner except that the porcelain teeth were not treated with the silane. The flasks were packed with acrylic dough in the usual manner, with two trial closures, and were processed according to the resin manufac turer’s directions. After heating, the flasks were air-cooled for an hour, water-cooled to room temperature, and then carefully deflasked. The distal ends of the acrylic rods that replaced the glass rods were lathed to a diameter of about 6 mm. Then, an inverted cone bur was used to reduce the sec tion of acrylic resin that was in contact with the tooth’s labial or ridge lap surface to a diameter within about ±0.25 mm. of that of the acrylic rod. This method was used since the specimens containing porcelain teeth could not be machined to a uniform diameter throughout as specified in ADA specification no. 15 for acrylic resin teeth.7 The porcelain tooth would break, indicating that it may have been strained by the bonding. ■ Tensile test results: Bonding test results are summarized in the table. Some specimens were immersed in distilled water at 37°ri-20C. Others were cycled seven or eight times through a tem perature range of 10°±3°C. to 65°±3°C.
Table * Bonding test results Brand of porcelain tooth
No. of treated specimens
Tensile strength* (psi)
Standard deviation!
Coefficient ■ variation (% )
Brand of acrylic resin
Temp.
Time
Trubyte New Hue
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
8
7 days in water at 37°C.
1,610
390
24
Polychrome
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
3
7 days In water at 37°C.
1,610
410
25
Myerson
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
5
Taken through 7 temperature cyclesj
1,530
300
20
Polychrome
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
6
Taken through 8 temperature cycles^
1,570
570
36
Trubyte New Hue
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
6
7 days in water at 37°C.§
1,430
100
7
Trubyte New Hue
Hygienic Acrylic
74°C. 100°C.
1.5 hr. .5 hr.
7
7 days in water at 37°C.§
1,200
470
40
Trubyte New Hue
Densene 33
74°C. 100°C.
1.5 hr. .5 hr.
4
7 days in water at 37°C.
2,050
1,150
56
Trubyte New Hue
Acralite Fastcure
cold-curing
5
29 days in water at 37°C.
1,750
320
18
Trubyte New Hue
Densene 33
cold-curing
5
7 days in water at 37°C.
1,840
330
18
Trubyte Bioblend
Acralite 88
cold-curing
5
7 days in water at 37°C.
1,530
410
27
Trubyte Bioblend
Acralite 88
cold-curing
6
32 days in water at 37°C.
2,280
400
17
Totals and averages
Mode of cure
60
* Force required to rupture tooth divided by cross-section area of contact surface. t
* (x-x)2
Comments
1,670
26
440
X 6 5° rb 3°C. to 10° ± 3°C. during the cycling. These specimens were in water for 2 to 3 days. § Data of lines 5 and 6 were not combined, since it was desired to illustrate the variability of results in a ‘test of this nature with averages of 6 or 7 specimens.
Fig. 4 ■ Fractured tensile specimens show labial surfaces of incisors and ends of a crylic rods polym erized a g a in st la bial surfaces. L e ft: T o p specimen shows untreated tooth undisturbed, which indicates lack o f adhesion. Resin rods did not adhere to a n y untreated tooth. In bottom specimen, surface o f the silane-treated tooth has saucer-shaped co n cavity where porcelain stuck to end of rod. R ig h t: In silane-treated teeth, fractures le ft large part of each tooth on end o f each rod P a ffe n b a rg e r— Sweeney— Bow en : B O N D IN G P O R C E L A IN T O A C R Y L I C
R E S IN
*
1021
in distilled water (See “comments” column in the table). All specimens were loaded at a rate of 90±23 kg./minute. The untreated, control teeth showed no meas urable bonding to the resin. All 30 control speci mens were too weak to withstand deflasking. The porcelain surfaces of the untreated teeth re tained their gloss, and the opposing rods of acrylic resin showed smooth, glossy surfaces, indicating that very little, if any, bonding had taken place (Fig 4 left, top). The silane-treated teeth were bonded with the cold-curing and the heat-curing denture base resins; considerable force was required to rup ture the specimens (table) and, in every in stance, the tooth fractured or pieces of the tooth
adhered to the acrylic resin (Fig. 4 left, bottom; right). Lines 5 and 6 in the table give strengths of specimens that were silane-treated before wax ing as previously described. This treatment ap peared to make little, if any, difference when one considers the large standard deviation. Also, as shown in the table, temperature cycling in water or prolonged soaking in water did not seriously affect the bonding. ■ Treated and untreated teeth in complete den tures: To demonstrate, in another way, the seal ing of the porcelain tooth-acrylic resin interface by the silane treatment, seven upper dentures were constructed. The wax model dentures were made in a common Korogel mold with the same
Fig. 5 ■ Dye penetration of porcelain tooth-denture base in terface. M e th y l blue penetrated between teeth and acrylic base (to p left) where teeth were not treated w ith silane. A n g u la r view of left side of specimen a t top left shows dye pene tration on ridge lap surfaces (b o tto m ). In specimen on top right, teeth were treated with silane and little or no penetration occurred. U pper right second bicuspid was fractu red so dye leaked into diatoric space but did not p enetrate on ridge lap surface. D a rk area is shadow cast by porcelain teeth on le ft side o f denture 1022
■ JADA, Vol. 74, April 1967
Sum m ary
Fig. 6 ■ Fractu red teeth caused by bonding of silanetreated teeth to a crylic denture base. Fractures a re d iffi c u lt to see unless ang le of incidence of lighting is a d justed to cause h a lf of broken tooth to appear darker than other h alf
mold of teeth. The bulk of the wax was softened and removed from the plaster-of-paris molds, which were then cleaned as previously described. In three instances, the silane solution was poured over the teeth in the flask and allowed to remain for 10 minutes in one instance and for 30 minutes in two instances. It was then poured off, and the flask was placed in an oven for 10 minutes at 110°C. The flask was then cooled, the plaster was painted with an alginate separator (care was taken to keep it off the teeth), and the flask was packed with clear acrylic resin. In another instance, the teeth were treated before the wax-up and, in three other instances, the teeth were not treated. Except for the preced ing process, the processing of all seven dentures was identical. All dentures were temperaturecycled six times in distilled water from 8°±3°C. to 65°±3°C. All seven dentures were immersed in a satu rated aqueous solution of methyl blue (1 Gm./ 25 ml.) for 15 minutes in a desiccator evacuated with a mechanical pump. The vacuum assisted penetration of the dye into fissures around the teeth. The dentures were then scrubbed with soap and water. The relative amount of acrylic resin-porcelain tooth interface closure affected by the silane treatment is shown in Figure 5. There was little penetration of the dye around the silanetreated teeth. The silane-treated teeth were so well bonded to the denture base that fracture oc curred in some of the molars and premolars (Fig. 6). These teeth, because of the diatoric design, are susceptible to fracture and would be greatly strengthened if they were solid.
Porcelain teeth can be bonded to an acrylic den ture base by an appropriate silane treatment. The bonding strengthens the denture, prevents seepage of material around the necks and ridge lap portions of the teeth, and thus aids in main taining good denture hygiene. The bonding places strain in the porcelain teeth which may cause them to fracture during or after processing. The suggested silane treatment indicates how to redesign porcelain teeth with the probable elimination of the metal pins and the diatoric design as retaining features, resulting in a stronger, more serviceable, and esthetic porcelain tooth. T h is investigation w as supported in part by U S P H S re search gran t D E 0 1 6 5 9 to the A m eric a n D ental A sso cia tion from the N a tio n al Institute of D ental Research and is part of the dental research program conducted a t the N a tio n al Bureau of Standards in cooperation w ith the Council on Dental Research of the A m erica n Dental A ssociation, the A rm y D ental Corps, the D ental Sciences Division of the School of A erospace M ed icin e ( U S A F ) , and the Veteran s A d m in istration. Doctors Paffenb arg er and Bowen and M r. Sw een ey are research associates from the A m erican D ental A ssociation a t the N atio n al Bureau of Standards, W a sh in g to n , D.C. 2 02 34. * Some com m ercial m aterials and equipm ent are iden tified in this paper to specify ad eq u ately the experim en tal procedure. Such identification does not im ply recom m endation or endorsem ent by the N a tio n al Bureau of Standards or th a t the m aterial or equipm ent is the best a v a ila b le for the purpose. t Union Carbide Silane A - 174, Union C arb id e Corp., N ew Y o rk. A t least one sim ilar silane is a v a ila b le : Dow Corning Sila n e Z - 6 0 3 0 , 3 - (trim ethoxysilyl-propyl m eth acrylate, Dow Chem ical Co., M id la n d , M ich . 1. W o e lfe l, J . B.; Paffenb arger, G. C., and Sweeney, W . T . Some physical properties of organic denture base m aterials. J A D A 6 7 :4 8 9 Oct., 1963. 2. Sacchi, Hector, and Paffenb arg er, G. C. Sim ple technic for m aking porcelain jac k e t crowns. JA D A 5 4 :3 6 6 M a rch , 1957. 3. Vand erb ilt, B. M ., and Sim ko, J . P., Jr . Silane coupling agents in glass-reinforced plastics. M odern Plastics 3 8 :1 3 5 Dec., 1960. 4. C lark, H. A ., and Pleuddem ann, E. P. Bonding of silane coupling agents in glass-reinforced plastics. M o d ern Plastics 4 0 :1 3 3 Ju n e , 1963. 5. Sterm an, S., and M arsden, J . G. Sila n e coupling agents as integral blends in resin-filler systems. M odern Plastics 4 0 :1 2 5 Ju ly , 1963. 6. Sterm an, S., and Toogood, J . B. H ow to promote adhesion with silicones an d silanes. A d hesives A g e 8 :3 4 Ju ly , 1965. 7. A m erican D ental Association. Guide to dental m a terials, ed. 3. Chicago, A m erican D ental Association, 1966.
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