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metal solder connectors
PLAQUE
KETENTION
AND
FULL-CEKAMIC
CROWNS
gold restorations (148%), and acrylic resin veneer crowns (152%) have increasing plaque retention. The results indicate that ceramics are easily cleaned and exhibit low plaque retention. Increasing the area of ceramic surfaces on restorations decreases plaque retention. REFERENCES I.
3-.
Riley E,J. Sozio RH, Shktar G, Krech K. Shrink-free ceramic wown versus ceramometal. a comparative study in dogs. .J ~‘RO?I I-HET thr~. 43766, 1983 Ghan CR, Haraszrhy (;. Geis-Geworfer J, Weber H. The marginal lit of Cereslore full-ceramic crown--- a pretiminarj rrpm Quintessence In[ 16399. 1985.
Ceramic/metal
solder connectors
Harry Rosen, D.D.S., M.R.C.D.(C)* McGill University, Faculty of Dentistry, Montreal, Que., Canada
C
linical evidence suggests that types III and IV gold alloy prostheses used in the 1950s and early 1960s lasted longer than present ceraxnometal restorations. The most common cause of reduced longevity is structural failure of the metal framework at the site of the soldered connector. Solder connector fracture occurs most commonly in long-span restorations where there are few abutment teeth, often after years of function. Patients also have a proclivity for habit patterns that exert excessive occlusal stresseson the vulnerable solder connectors. If fracture is left unattended, irreversible damage to abutment teeth can occur and complicate or negate future treatment. Lautenschlager’ stated that soldered connections can be superior in strength to the parent metal. This statement was accurate for type III and type IV yellow gold alloys, but misleading for many of the present precious ceramic/metal alloys. Previous studies have not compared the strengths of various ceramic/metal connectors with the yellow gold alloys. The literature refers to the “possibility” of soldering precious metals, base ceramic metals, and various combinations instead of the “frequency” with which the metals can be successfully joined.‘-’ Two studies actually excluded defective joints that *Professor
and Direr[or
THE JOURNAL
of Graduate
OF PROSTHETIC
Prosthodontics.
DENTISTRY
fractured during the experiment.‘,’ Consequently the mean values were misleading. Previous studies used castings from plastic tensile bar patterns or Delrin (U.S. Public Health Serivce, San Francisco, Calif.) rods machined to spceifications of the American Society of Testing Methods for tensile testing of metallic materials. In some instances the parent metal fractured before the solder connector. Consequently a predictable range for strength could not be recordcd.6 Allowances were not made in these studies for the weaknesses of the parent metal from improper sprue formation of the plastic tensile bar patterns (unpublished observation by K. Asgar et al.), the heat treatment during the soldering, or the ceramic applications, alone or combined. Staffanou et a1.2suggested that atomic diffusion during soldering increased brittleness in the parent metal adjacent to the solder joint. The present study compared preceramic and postceramic joint strengths of commonly used precious ceramic/metals with type III and type IV gold alloys.
MATERIAL
AND METHODS
A two-member jig was constructed for adjacent proximo-occlusal preparations to receive castings. The jig was designed to enable easy adaptation to an Instron tensile testing machine (Instron Corp., Canton, Mass.). 671
ROSEN
Fig. 1. Casting and assembled jig.
Fig. 2. Casting seated within assembled jig.
The preparations were designed so that the surfaces to be joined measured 1 mm thick by 2.5 mm wide. It was then possible to ensure that all fractures occurred at a specific, predictable location (Figs. 1 through 3). The metals tested and listed in Table I were Jelenko type III (Firmilay), type IV (Jel-4), Jelenko “O”, Olympia high heat, and Jelstar paladium silver (Jelenko Co., New Rochelle, N.Y.). Wax patterns were prepared, invested, and cast (Cerami-Gold Investment, Whip-Mix Corp., Louisville, Ky.) by using standardized techniques recommended by the manufacturer. A total of 104 cast specimens were prepared. Group I. Eight type III gold (Firmilay) castings were cast to determine the ultimate tensile strength (UTS) of the parent metal. Eight type III gold castings were
672
sectioned and soldered to determine the UTS of the low-fusing solder connectors. Group II. The same design as in group I was used, but with type IV gold (Jel-4). Group III. Eight Jelenko “0” ceramic/metal castings were cast to determine the UTS of the parent metal. Eight Jelenko “0” ceramic/metal castings were sectioned and preceramic soldered to determine the UTS of the preceramic high-heat solder connectors. Eight Jelenko “0” ceramic/metal castings were cut and postceramic soldered to determine the, UTS of the postceramic low-fusing solder connectors. Group IV. The same design as in group III was used but with Olympia ceramic/metal and the solders recommended by the manufacturer for the preceramic and postceramic soldering.
DECEMBER
1986
VOLUME
56
NUMBER
6
METAL/CERAMIC
SOLDER
CONNECTORS
Fig. 3. Alignment device separated with a design ensuring uniaxial loading for instron tensile testing.
Table I. Specifications
of five metals tested Precious
metal content
Melting
(%I
AU
Pt
Pd
Jelenko “0”
87.5
4.5
Olympia Jelstar Firmilay
51.5
6.0 38.5
74.5
60.0 3.5
28.0 11.0
66.5
3.5
14.5
Pro&m
mtetd allow
(Type 111 hard) Jel-4 (Type IV extra hard)
Group V. The same design as group III was used but with Jelstar ceramic/metal and solders recommended by the manufacturer for the preceramic and postceramic soldering. The cast specimens were machined and notched to measure 1 mm thick by 2.5 mm wide at the point of intended fracture. They were sectioned at the notch with a fine diamond disk and the surfaces were machined to provide a soidering gap of 0.3 mm (Fig. 4). A gap size of 0.3 mm (H inch) was selected to allow for thermal expension of the assembly to be soldered2 It permitted capillary flow of solder without excessive solder shrinkage.2Sharp edges were slightly rounded to permit easier flow of solder. The specimens were indexed with sticky wax and embedded in their respective low-heat and high-heat soldering investment blocks. Each investment block was prepared for uniform heat application, solder placement, and flow (Fig. 5). SOLDERING PROCEDURE The eight type III and eight type IV gold specimens were soldered with the recommended No. 650 fine
THE JOURNAL
OF PROSTHETIC
DENTISTRY
AU 1.0
Recommended solder mr/voat
range (“F)
UTS (&a/in)
Jelenko “O”/ 18-585
2100to 2150
72,500
Olympia/750 Jelstar pre/ post 650/Color blend
2320 to 2380 2250 to 2380 1710 to 1760
115,000 95,000 H77,OOO
650/615
1635 to 1675
Hlll,,OOO
solder. The individual soldering assemblies were heated in the oven to 1500” F, removed, and placed on a soldering block. The connectors were heated with a gas-air torch until the specimens glowed red. The solder was applied to the joint gap to flow and the assembly was bench cooled CFigs. 6 and 7). The united specimen was refitted onto the alignment device, the excess solder was removed, and the specimen was notched to measure 1 mm thick by 2.5 mm wide. Eight specilmens of the high-heat ceramic/metal alloy were soldered with the recommended preceramic solders (Table I). The soldering assemblies were heated in the oven to 1500” F and soldered with a gas-oxygen torch, similar to the method for the type III and type IV gold alloys. The assemblies were bench cooled, machined, and notched to measure 1 mm thick by 2.5 mm wide. After the soldering procedure, the high-heat preceramic solder specimens were fired five times to simulate a degassing cycle, an opaquing, two body firings, a glaze, and facial characterization. The specimens prepared for postceramic soldering were also fired five times to imitate porcelain applica-
673
ROSEN
Fig. 4. Casting cut and notched to provide
0.3 mm soldering
Fig. 6. Superior
Fig. 5. Cut and notched castings in investment with a soldering gap of 0.3 mm.
surface of soldered casting.
block
tion. Eight specimens of each ceramic alloy were post soldered with the recommended postceramic solders. Flux application was performed as recommended by the manufacturer. The soldering assemblies were heated to 1600” F and heat-soaked. The oven door was then opened and the soldering rods were applied to the solder gap, allowing the solder to flow. The soldered assemblies were removed from the oven and bench cooled. The solder specimens were fitted into the alignment devices machined, and notched to measure 1 mm thick by 2.5 mm wide at the soldered connector.
TESTING THE SPECIMENS Each specimen was placed in the custom-made securing device that ensured uniaxial loading (Fig. 1). A 674
gap.
Fig. 7. Inferior
surface of soldered casting.
tensile load was applied with an Instron testing machine with a crosshead speed of %oinch per minute to evaluate the UTS. The load was applied until the specimens fractured. The fractured specimens were examined with a scanning electron microscope, and photomicrographs of selected fractures were studied for possible explanation of strength values (Figs. 8 and 9). The mean solder DECEMBER
1986
VOLUME
56
NUMBER
6
METAL/CERAMIC
SOLDER
CONNECTORS
Fig. 8. Electron micrograph of poor connector. adhesive failure. (Magnification X200.)
Voids, large grain structure
demonstrate
Fig. 9. Electron micrograph of an acceptable connector, with few voids, small grain structure, and evidence of cohesive failure. (Magnification x200.)
joint tensile strengths are presented in Table II. Values for the ultimate stensile strengths, the standard deviation, and the coefficient of variability are also seen in Table II.
RESULTS Table II reveals that the three ceramic/metals did not compare favorably with types III and IV yellow gold. Type III gold demonstrated an increase (11.7%) in solder joint UTS after soldering. Although the type IV yellow gold demonstrated a decrease of 17% in UTS as a THE JOURNAL
OF PROSTHETIC
DENTISTRY
result of the soldering, the final UTSs of the soldered type IV samples were superior to those of the ceramic metals. The performance of yellow golds was also more consistent than that of the ceramic metals. Jelenko “0” ceramic/metal presoldcr specimens recorded the greatest decrease (59%) in ultimate tensile strength and also exhibited the greatest variability. However, this metal demonstrated the least reduction (7%) in UTS from postsoldering. Jelstar, the least expensive of the three ceramic/metals, recorded tensile strengths
superior
to those of the .Jelenko
“0”
or 675
ROSEN
Table II.
Metal
Mean UTS (psi)
Type III parent Type III soldered
71,780 80,010
Type IV parent Type IV soldered
111,760 92,710
Jelenko 0 parent Jelenko 0 preceramic Jelenko 0 postceramic Olympia Olympia Olympia
parent preceramic postceramic
Jelstar parent Jelstar preceramic Jelstar postceramic
% Change
Low UTS (psi)
Coefficient variability (?a
Standard deviation (psi)
86,106 97,790
61,468 61,722
3,230 14,708.5
* 17
116,840 103,124
105,664 83,820
5,636 9‘723.6
58,420 24,026 54,160
-% 59 --7
77,724 58,928 77,734
20,574 2,540 28,448
21,361 11,541 16,773
38 64 28
95,054 56,563 60,325
x40 ‘437
121,920 93,980 88,646
60,960 29,210 30,480
15,824 20,852 24,059
16 36 40
122,662 64,204 92,050
x 48 Y 25
146,304 109,220 124,460
102,870 33,020 50,292
14,661 24,871.6 27,558.4
11.5 38 30
-v 11.5
Olympia specimens. The final mean postsolder values for Jelstar ceramic/metal compared favorably with type IV gold, but displayed greater variability. The mean presolder solder joint tensile strength values for Jelstar ceramic/metal could not compare favorably with soldered type III or type IV alloys.
DISCUSSION The most striking finding in this investigation was the superiority of yellow-gold connectors compared to ceramic/metal connectors. There was also a demonstrable superiority of postsoldered ceramic/metal joints over presoldered ceramic/metal joints. The type III gold connectors were stronger than the parent alloys. The low-fusing solder contained copper in sufficient quantity to allow age hardening.’ Another noteworthy feature was that the most expensive ceramic metal/alloy with the highest gold content produced the lowest tensile strengths whereas the least expensive ceramic/metal alloy of silver-palladium recorded the best results of the ceramic metals. Examination of the electron micrographs (Figs. 8 and 9) revealed many voids and large grain structure in the low-strength samples whereas few voids and small grain structure were discovered in the high-strength samples. The failures in most connectors were both cohesive and adhesive failures. The ceramic/metals demonstrated more adhesive failures with voids. One hypothesis is that the elements incorporated in the alloy to provide an oxide layer of zinc, indium, tin, and iron for chemically bonding the porcelain also reduce wetting of the solid metal by the molten solder, resulting in a weaker joint. The oven postsolder results were better because oxidation is reduced in the oven. 676
High UTS (psi)
of
11 18 5 10.5
For the presoldered samples, the melting differential between the alloy and the solder was important. The parent alloys and solders with the greatest melting differential produced superior results. The melting range of Jelenko “0” metal was 2100’ F to 2150” F and for Jelenko No. 1 solder was 2010” F to 2090” F. The wetting or flow of solder is better in clinical cases where convex surfaces are opposing each other. The convex surfaces form embrasure spaces that encourage increased capillary action not possible when two flat surfaces are opposing each other as in this study.
CONCLtiSIONS 1. Ceramic/metal solder connectors were weaker and more inconsistent than type III and IV gold solder connectors. 2. Parent ceramic/metal connections were slightly weaker than parent gold connections (one-piece castings). 3. Postceramic connectors were superior to preceramic connectors, particularly for high-gold content ceramic/metal alloys. 4. The highest gold content ceramic/metal preceramic connectors were the weakest. 5. Some type III gold connectors were better than parent metal connections (heat treated). 6. Type III gold joints possessed limited ductility, whereas the others, including type IV gold joints, were brittle despite recorded strength. REFERENCES 1. 2.
Lautenschlager EP, Marker BC, Moore BK, Wildes R: Strength mechanisms of dental solder joints. J Dent Res 6:1361, 1974. Statfanou RS, Radke RA, Jendresen MD: Strength properties of DECEMBER
1986
VOLUME
56
NUMBER
6
METAL/CERAMIC
SOLDER
CONNECTORS
soldered ,joints from various ceramic-metal combinations. J PROSTHE I’ DFXT 43:3 1, 1980. 3 Srade EH. Reisbick MH. Preston JD: Preceramic and postceramlc solder joints. J PROWHET DENT 34527, 1975. 4 \Valler< RA: A photomicrographic evaluation of the solder joint berwrrn precious and nonprecious metal. J PRosrtfET DEST 35:680. 1976. 5. Sloan Rhl. Reisbick X111, Preston JD: Post-ceramic soldering of \.irIs,u\ .~lloys. J PRWI mx Dur 48:686, 1982.
6.
Rasmussen EJ, Goodkind RJ, Gerberich hLw. .\n invesrigallon of tensile strength of dental solder joint,. ,J PRO\.I INI Ikut 41:418, 1979.
Hqmnr requ”I., lo: DR. HARRY RCWN 3545 Cow DES KMXS, STE. 107 MOXTRLAI.. QI.E. H3H IV1 c: 49 .,n.,
In vivo adaptation of restorative materials to dentin Jan W. V. van Dijken, University
of Umei,
D.D.S.,*
and Per Hiirstedt,
lhe enamel acid-etch technique is an integral restorative procedure for composites. It improves marginal adaptation and retention and reduces marginal leakage.’ However, bacterial invasion from the oral environment can still occur at the cavity margins.‘,’ In clinical practice the gingival margin is a weak link. Occurrence of prismless enamel or an exceedingly thin layer of enamel makes the use of the acid-etching technique impossible. Increased marginal leakage can occur. Intensive research on adhesion to dentin started 20 years ago.’ Adhesive bonding to dentin requires removal of the smear layer. The use of cavity cleansers and etching agents has been suggested, although these can enhance the pulpal response.‘,” However, other studies show that acid pretreatment per se did not cause pulpal injury.‘, R Etching the dentin with 37% phosphoric acid for 15 to 60 seconds removes the amorphous smear layer and dissolves the dentin.’ Resin tags penetrating the dentinal tubules have been reported.’ ‘)-‘I These tags can possibly serve as mechanical retention for the restoration. However, dentinal tags do not assure a permanent, serviceable adaptation of the restorative material to the cavity walls in vivo. The tags initially penetrate the dentinal tubules but tend to withdraw because of contraction and stresses. Recently developed commercial dentin bonding agents show reduced leakage and increased bond strength to acid-etched dentin in vitro.‘z”5
Supported by I’;~~en~mrtlelsl~~ndenfor odomologisk Profylaxforskning (Swedish Patent Revenue Fund) and Sc,lnia Dental AR. *.\ssislanr Professor. Dep~~rlmem of (:xiology. Faculty of Odonrolo**?esearch cinr.
Associa~r. Depar~mrn~ of Pathology. Faculty of Mrdi-
THE JOURNAL
M.A.**
Umeri, Sweden
OF PROSTHETIC
DENTISTRY
Table I. Investigated restorations and pretreatment methods ------_-.._ _-- .._ _.
60 Seconds WQ
6 4 6 h 4
6 0 h b 6
6 6 4
4
h
4
Untreated FUJI Cervident Clearfil bonding system Silar (Scotch Bond) Concise/Concise Enamel Bond Concise --~_.
_-
20 Seconds W’O.
The purpose of this investigation on in vivo restorations was to study the adaptation of five commercial resin systems, including three dentin bonding systems, a glass ionomer cement to untreated dentin and enamel, and dentin and enamel acid etched for 20 and 60 seconds, and to correlate the adaptation of the resin systems to the cavity walls with the morphology of restorative surfaces opposing the tooth structure. MATERIAL
AND METHODS
Seventy-eight young premolars diagnosed for extraction for orthodontic reasons were used for the study. Class V buccal cavities were prepared in vivo with a smooth fissure carbide bur in a Kavo supertorque air rater (Kattenbach & Voigt, Biberach, W. Germany) with water spray at ultraspeed. The gingival walls were prepared at a distance of at least 2 mm from the cementoenamel junction. The margins were finished with a 45-degree bevel. The cavities that were filled with the glass ionomer cement were finished with OO-degree margins. After a water spray, followed by a short blast of compressed air, 56 of the cavities were etched with 37% 677
KETENTION
AND
FULL-CEKAMIC
CROWNS
gold restorations (148%), and acrylic resin veneer crowns (152%) have increasing plaque retention. The results indicate that ceramics are easily cleaned and exhibit low plaque retention. Increasing the area of ceramic surfaces on restorations decreases plaque retention. REFERENCES I.
3-.
Riley E,J. Sozio RH, Shktar G, Krech K. Shrink-free ceramic wown versus ceramometal. a comparative study in dogs. .J ~‘RO?I I-HET thr~. 43766, 1983 Ghan CR, Haraszrhy (;. Geis-Geworfer J, Weber H. The marginal lit of Cereslore full-ceramic crown--- a pretiminarj rrpm Quintessence In[ 16399. 1985.
Ceramic/metal
solder connectors
Harry Rosen, D.D.S., M.R.C.D.(C)* McGill University, Faculty of Dentistry, Montreal, Que., Canada
C
linical evidence suggests that types III and IV gold alloy prostheses used in the 1950s and early 1960s lasted longer than present ceraxnometal restorations. The most common cause of reduced longevity is structural failure of the metal framework at the site of the soldered connector. Solder connector fracture occurs most commonly in long-span restorations where there are few abutment teeth, often after years of function. Patients also have a proclivity for habit patterns that exert excessive occlusal stresseson the vulnerable solder connectors. If fracture is left unattended, irreversible damage to abutment teeth can occur and complicate or negate future treatment. Lautenschlager’ stated that soldered connections can be superior in strength to the parent metal. This statement was accurate for type III and type IV yellow gold alloys, but misleading for many of the present precious ceramic/metal alloys. Previous studies have not compared the strengths of various ceramic/metal connectors with the yellow gold alloys. The literature refers to the “possibility” of soldering precious metals, base ceramic metals, and various combinations instead of the “frequency” with which the metals can be successfully joined.‘-’ Two studies actually excluded defective joints that *Professor
and Direr[or
THE JOURNAL
of Graduate
OF PROSTHETIC
Prosthodontics.
DENTISTRY
fractured during the experiment.‘,’ Consequently the mean values were misleading. Previous studies used castings from plastic tensile bar patterns or Delrin (U.S. Public Health Serivce, San Francisco, Calif.) rods machined to spceifications of the American Society of Testing Methods for tensile testing of metallic materials. In some instances the parent metal fractured before the solder connector. Consequently a predictable range for strength could not be recordcd.6 Allowances were not made in these studies for the weaknesses of the parent metal from improper sprue formation of the plastic tensile bar patterns (unpublished observation by K. Asgar et al.), the heat treatment during the soldering, or the ceramic applications, alone or combined. Staffanou et a1.2suggested that atomic diffusion during soldering increased brittleness in the parent metal adjacent to the solder joint. The present study compared preceramic and postceramic joint strengths of commonly used precious ceramic/metals with type III and type IV gold alloys.
MATERIAL
AND METHODS
A two-member jig was constructed for adjacent proximo-occlusal preparations to receive castings. The jig was designed to enable easy adaptation to an Instron tensile testing machine (Instron Corp., Canton, Mass.). 671
ROSEN
Fig. 1. Casting and assembled jig.
Fig. 2. Casting seated within assembled jig.
The preparations were designed so that the surfaces to be joined measured 1 mm thick by 2.5 mm wide. It was then possible to ensure that all fractures occurred at a specific, predictable location (Figs. 1 through 3). The metals tested and listed in Table I were Jelenko type III (Firmilay), type IV (Jel-4), Jelenko “O”, Olympia high heat, and Jelstar paladium silver (Jelenko Co., New Rochelle, N.Y.). Wax patterns were prepared, invested, and cast (Cerami-Gold Investment, Whip-Mix Corp., Louisville, Ky.) by using standardized techniques recommended by the manufacturer. A total of 104 cast specimens were prepared. Group I. Eight type III gold (Firmilay) castings were cast to determine the ultimate tensile strength (UTS) of the parent metal. Eight type III gold castings were
672
sectioned and soldered to determine the UTS of the low-fusing solder connectors. Group II. The same design as in group I was used, but with type IV gold (Jel-4). Group III. Eight Jelenko “0” ceramic/metal castings were cast to determine the UTS of the parent metal. Eight Jelenko “0” ceramic/metal castings were sectioned and preceramic soldered to determine the UTS of the preceramic high-heat solder connectors. Eight Jelenko “0” ceramic/metal castings were cut and postceramic soldered to determine the, UTS of the postceramic low-fusing solder connectors. Group IV. The same design as in group III was used but with Olympia ceramic/metal and the solders recommended by the manufacturer for the preceramic and postceramic soldering.
DECEMBER
1986
VOLUME
56
NUMBER
6
METAL/CERAMIC
SOLDER
CONNECTORS
Fig. 3. Alignment device separated with a design ensuring uniaxial loading for instron tensile testing.
Table I. Specifications
of five metals tested Precious
metal content
Melting
(%I
AU
Pt
Pd
Jelenko “0”
87.5
4.5
Olympia Jelstar Firmilay
51.5
6.0 38.5
74.5
60.0 3.5
28.0 11.0
66.5
3.5
14.5
Pro&m
mtetd allow
(Type 111 hard) Jel-4 (Type IV extra hard)
Group V. The same design as group III was used but with Jelstar ceramic/metal and solders recommended by the manufacturer for the preceramic and postceramic soldering. The cast specimens were machined and notched to measure 1 mm thick by 2.5 mm wide at the point of intended fracture. They were sectioned at the notch with a fine diamond disk and the surfaces were machined to provide a soidering gap of 0.3 mm (Fig. 4). A gap size of 0.3 mm (H inch) was selected to allow for thermal expension of the assembly to be soldered2 It permitted capillary flow of solder without excessive solder shrinkage.2Sharp edges were slightly rounded to permit easier flow of solder. The specimens were indexed with sticky wax and embedded in their respective low-heat and high-heat soldering investment blocks. Each investment block was prepared for uniform heat application, solder placement, and flow (Fig. 5). SOLDERING PROCEDURE The eight type III and eight type IV gold specimens were soldered with the recommended No. 650 fine
THE JOURNAL
OF PROSTHETIC
DENTISTRY
AU 1.0
Recommended solder mr/voat
range (“F)
UTS (&a/in)
Jelenko “O”/ 18-585
2100to 2150
72,500
Olympia/750 Jelstar pre/ post 650/Color blend
2320 to 2380 2250 to 2380 1710 to 1760
115,000 95,000 H77,OOO
650/615
1635 to 1675
Hlll,,OOO
solder. The individual soldering assemblies were heated in the oven to 1500” F, removed, and placed on a soldering block. The connectors were heated with a gas-air torch until the specimens glowed red. The solder was applied to the joint gap to flow and the assembly was bench cooled CFigs. 6 and 7). The united specimen was refitted onto the alignment device, the excess solder was removed, and the specimen was notched to measure 1 mm thick by 2.5 mm wide. Eight specilmens of the high-heat ceramic/metal alloy were soldered with the recommended preceramic solders (Table I). The soldering assemblies were heated in the oven to 1500” F and soldered with a gas-oxygen torch, similar to the method for the type III and type IV gold alloys. The assemblies were bench cooled, machined, and notched to measure 1 mm thick by 2.5 mm wide. After the soldering procedure, the high-heat preceramic solder specimens were fired five times to simulate a degassing cycle, an opaquing, two body firings, a glaze, and facial characterization. The specimens prepared for postceramic soldering were also fired five times to imitate porcelain applica-
673
ROSEN
Fig. 4. Casting cut and notched to provide
0.3 mm soldering
Fig. 6. Superior
Fig. 5. Cut and notched castings in investment with a soldering gap of 0.3 mm.
surface of soldered casting.
block
tion. Eight specimens of each ceramic alloy were post soldered with the recommended postceramic solders. Flux application was performed as recommended by the manufacturer. The soldering assemblies were heated to 1600” F and heat-soaked. The oven door was then opened and the soldering rods were applied to the solder gap, allowing the solder to flow. The soldered assemblies were removed from the oven and bench cooled. The solder specimens were fitted into the alignment devices machined, and notched to measure 1 mm thick by 2.5 mm wide at the soldered connector.
TESTING THE SPECIMENS Each specimen was placed in the custom-made securing device that ensured uniaxial loading (Fig. 1). A 674
gap.
Fig. 7. Inferior
surface of soldered casting.
tensile load was applied with an Instron testing machine with a crosshead speed of %oinch per minute to evaluate the UTS. The load was applied until the specimens fractured. The fractured specimens were examined with a scanning electron microscope, and photomicrographs of selected fractures were studied for possible explanation of strength values (Figs. 8 and 9). The mean solder DECEMBER
1986
VOLUME
56
NUMBER
6
METAL/CERAMIC
SOLDER
CONNECTORS
Fig. 8. Electron micrograph of poor connector. adhesive failure. (Magnification X200.)
Voids, large grain structure
demonstrate
Fig. 9. Electron micrograph of an acceptable connector, with few voids, small grain structure, and evidence of cohesive failure. (Magnification x200.)
joint tensile strengths are presented in Table II. Values for the ultimate stensile strengths, the standard deviation, and the coefficient of variability are also seen in Table II.
RESULTS Table II reveals that the three ceramic/metals did not compare favorably with types III and IV yellow gold. Type III gold demonstrated an increase (11.7%) in solder joint UTS after soldering. Although the type IV yellow gold demonstrated a decrease of 17% in UTS as a THE JOURNAL
OF PROSTHETIC
DENTISTRY
result of the soldering, the final UTSs of the soldered type IV samples were superior to those of the ceramic metals. The performance of yellow golds was also more consistent than that of the ceramic metals. Jelenko “0” ceramic/metal presoldcr specimens recorded the greatest decrease (59%) in ultimate tensile strength and also exhibited the greatest variability. However, this metal demonstrated the least reduction (7%) in UTS from postsoldering. Jelstar, the least expensive of the three ceramic/metals, recorded tensile strengths
superior
to those of the .Jelenko
“0”
or 675
ROSEN
Table II.
Metal
Mean UTS (psi)
Type III parent Type III soldered
71,780 80,010
Type IV parent Type IV soldered
111,760 92,710
Jelenko 0 parent Jelenko 0 preceramic Jelenko 0 postceramic Olympia Olympia Olympia
parent preceramic postceramic
Jelstar parent Jelstar preceramic Jelstar postceramic
% Change
Low UTS (psi)
Coefficient variability (?a
Standard deviation (psi)
86,106 97,790
61,468 61,722
3,230 14,708.5
* 17
116,840 103,124
105,664 83,820
5,636 9‘723.6
58,420 24,026 54,160
-% 59 --7
77,724 58,928 77,734
20,574 2,540 28,448
21,361 11,541 16,773
38 64 28
95,054 56,563 60,325
x40 ‘437
121,920 93,980 88,646
60,960 29,210 30,480
15,824 20,852 24,059
16 36 40
122,662 64,204 92,050
x 48 Y 25
146,304 109,220 124,460
102,870 33,020 50,292
14,661 24,871.6 27,558.4
11.5 38 30
-v 11.5
Olympia specimens. The final mean postsolder values for Jelstar ceramic/metal compared favorably with type IV gold, but displayed greater variability. The mean presolder solder joint tensile strength values for Jelstar ceramic/metal could not compare favorably with soldered type III or type IV alloys.
DISCUSSION The most striking finding in this investigation was the superiority of yellow-gold connectors compared to ceramic/metal connectors. There was also a demonstrable superiority of postsoldered ceramic/metal joints over presoldered ceramic/metal joints. The type III gold connectors were stronger than the parent alloys. The low-fusing solder contained copper in sufficient quantity to allow age hardening.’ Another noteworthy feature was that the most expensive ceramic metal/alloy with the highest gold content produced the lowest tensile strengths whereas the least expensive ceramic/metal alloy of silver-palladium recorded the best results of the ceramic metals. Examination of the electron micrographs (Figs. 8 and 9) revealed many voids and large grain structure in the low-strength samples whereas few voids and small grain structure were discovered in the high-strength samples. The failures in most connectors were both cohesive and adhesive failures. The ceramic/metals demonstrated more adhesive failures with voids. One hypothesis is that the elements incorporated in the alloy to provide an oxide layer of zinc, indium, tin, and iron for chemically bonding the porcelain also reduce wetting of the solid metal by the molten solder, resulting in a weaker joint. The oven postsolder results were better because oxidation is reduced in the oven. 676
High UTS (psi)
of
11 18 5 10.5
For the presoldered samples, the melting differential between the alloy and the solder was important. The parent alloys and solders with the greatest melting differential produced superior results. The melting range of Jelenko “0” metal was 2100’ F to 2150” F and for Jelenko No. 1 solder was 2010” F to 2090” F. The wetting or flow of solder is better in clinical cases where convex surfaces are opposing each other. The convex surfaces form embrasure spaces that encourage increased capillary action not possible when two flat surfaces are opposing each other as in this study.
CONCLtiSIONS 1. Ceramic/metal solder connectors were weaker and more inconsistent than type III and IV gold solder connectors. 2. Parent ceramic/metal connections were slightly weaker than parent gold connections (one-piece castings). 3. Postceramic connectors were superior to preceramic connectors, particularly for high-gold content ceramic/metal alloys. 4. The highest gold content ceramic/metal preceramic connectors were the weakest. 5. Some type III gold connectors were better than parent metal connections (heat treated). 6. Type III gold joints possessed limited ductility, whereas the others, including type IV gold joints, were brittle despite recorded strength. REFERENCES 1. 2.
Lautenschlager EP, Marker BC, Moore BK, Wildes R: Strength mechanisms of dental solder joints. J Dent Res 6:1361, 1974. Statfanou RS, Radke RA, Jendresen MD: Strength properties of DECEMBER
1986
VOLUME
56
NUMBER
6
METAL/CERAMIC
SOLDER
CONNECTORS
soldered ,joints from various ceramic-metal combinations. J PROSTHE I’ DFXT 43:3 1, 1980. 3 Srade EH. Reisbick MH. Preston JD: Preceramic and postceramlc solder joints. J PROWHET DENT 34527, 1975. 4 \Valler< RA: A photomicrographic evaluation of the solder joint berwrrn precious and nonprecious metal. J PRosrtfET DEST 35:680. 1976. 5. Sloan Rhl. Reisbick X111, Preston JD: Post-ceramic soldering of \.irIs,u\ .~lloys. J PRWI mx Dur 48:686, 1982.
6.
Rasmussen EJ, Goodkind RJ, Gerberich hLw. .\n invesrigallon of tensile strength of dental solder joint,. ,J PRO\.I INI Ikut 41:418, 1979.
Hqmnr requ”I., lo: DR. HARRY RCWN 3545 Cow DES KMXS, STE. 107 MOXTRLAI.. QI.E. H3H IV1 c: 49 .,n.,
In vivo adaptation of restorative materials to dentin Jan W. V. van Dijken, University
of Umei,
D.D.S.,*
and Per Hiirstedt,
lhe enamel acid-etch technique is an integral restorative procedure for composites. It improves marginal adaptation and retention and reduces marginal leakage.’ However, bacterial invasion from the oral environment can still occur at the cavity margins.‘,’ In clinical practice the gingival margin is a weak link. Occurrence of prismless enamel or an exceedingly thin layer of enamel makes the use of the acid-etching technique impossible. Increased marginal leakage can occur. Intensive research on adhesion to dentin started 20 years ago.’ Adhesive bonding to dentin requires removal of the smear layer. The use of cavity cleansers and etching agents has been suggested, although these can enhance the pulpal response.‘,” However, other studies show that acid pretreatment per se did not cause pulpal injury.‘, R Etching the dentin with 37% phosphoric acid for 15 to 60 seconds removes the amorphous smear layer and dissolves the dentin.’ Resin tags penetrating the dentinal tubules have been reported.’ ‘)-‘I These tags can possibly serve as mechanical retention for the restoration. However, dentinal tags do not assure a permanent, serviceable adaptation of the restorative material to the cavity walls in vivo. The tags initially penetrate the dentinal tubules but tend to withdraw because of contraction and stresses. Recently developed commercial dentin bonding agents show reduced leakage and increased bond strength to acid-etched dentin in vitro.‘z”5
Supported by I’;~~en~mrtlelsl~~ndenfor odomologisk Profylaxforskning (Swedish Patent Revenue Fund) and Sc,lnia Dental AR. *.\ssislanr Professor. Dep~~rlmem of (:xiology. Faculty of Odonrolo**?esearch cinr.
Associa~r. Depar~mrn~ of Pathology. Faculty of Mrdi-
THE JOURNAL
M.A.**
Umeri, Sweden
OF PROSTHETIC
DENTISTRY
Table I. Investigated restorations and pretreatment methods ------_-.._ _-- .._ _.
60 Seconds WQ
6 4 6 h 4
6 0 h b 6
6 6 4
4
h
4
Untreated FUJI Cervident Clearfil bonding system Silar (Scotch Bond) Concise/Concise Enamel Bond Concise --~_.
_-
20 Seconds W’O.
The purpose of this investigation on in vivo restorations was to study the adaptation of five commercial resin systems, including three dentin bonding systems, a glass ionomer cement to untreated dentin and enamel, and dentin and enamel acid etched for 20 and 60 seconds, and to correlate the adaptation of the resin systems to the cavity walls with the morphology of restorative surfaces opposing the tooth structure. MATERIAL
AND METHODS
Seventy-eight young premolars diagnosed for extraction for orthodontic reasons were used for the study. Class V buccal cavities were prepared in vivo with a smooth fissure carbide bur in a Kavo supertorque air rater (Kattenbach & Voigt, Biberach, W. Germany) with water spray at ultraspeed. The gingival walls were prepared at a distance of at least 2 mm from the cementoenamel junction. The margins were finished with a 45-degree bevel. The cavities that were filled with the glass ionomer cement were finished with OO-degree margins. After a water spray, followed by a short blast of compressed air, 56 of the cavities were etched with 37% 677