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Accuracy of stone casts produced by perforated trays and nonperforated trays
Accuracy of stone casts produced and nonperforated trays James D. Woodward, D.M.D., Zafrulla Khan, D.D.S.**
M.Ed.,*
Jack C. Morris,
by perforated
D.M.D.,
M.Sc.,**
trays
and
University of Louisville, Schoolof Dentistry, Louisville, Ky
M
itchell and Damele’ stated that the average deficiency recorded from impression distortion was greatest in a perforated tray. It was reduced with a lubricated nonperforated tray (Rim-Lock, L.D. Caulk Co., Milford, Del.) and further minimized by an undercut lubricated tray. They suggested that distortion might be induced by attachment of the impression material to the tray. One factor not taken into consideration was the size of the tray. Fusayama and Nakamoto2 compared the influence of size, number, interval, and total area of tray perforations on the retention of irreversible hydrocolloid impressions. Hartwell et al3 pointed out that there was no significant difference in the accuracy of irreversible hydrocolloid impressions made in perforated and RimLock trays. The tray size was again kept constant. This study was conducted to determine the distortion caused by perforated and Rim-Lock trays and the influence of tray size on the impressions.
MATERIAL Preparation
AND METHODS of the master casts
An Ivorine maxillary dentulous model (Columbia Dentoform Corp., New York, N.Y.) was chosen as the standard (Fig. 1). Laboratory type reversible hydrocolloid was used to duplicate the model in a low-fusing alloy (Melotte’s metal) (Fig. 2). A twist drill was used to prepare nine dimples in the metal master cast to provide clearly reproducible reference points. The dimples were placed in (1) the distobuccal cusp tip of the maxillary left first molar (point A), (2) the incisal edge of the maxillary left central incisor (point B), (3) the buccal cusp tip of the maxillary right second premolar (point C), (4) the buccal surface of the maxillary left second premolar (point D), (5) the maxillary left buccal fold area (point D’) (Figs. 3 to S), (6) the labial surface of the maxillary right lateral incisor (point E), (7) the maxillary right labial fold area (point E’), (8) the buccal surface of the maxillary
*Professor,Departmentof **Associate ***Assistant THE
Professor, Professor,
JOURNAL
Prosthodontics. Department of Prosthodontics. Department of Prosthodontics.
OF PROSTHETIC
DENTISTRY
Fig. 1. Ivorine maxillary dentulous model.
right first molar (point F), and (9) the maxillary right buccal fold area (point F’) (Figs. 2 to 4).
Selection
of trays
Two Rim-Lock trays and two perforated trays were selected to make the impressions for this study (Fig. 6). One Rim-Lock and one perforated tray were selected by the investigators and judged to be “tight fitting.” The trays fit the master cast so there was a minimum of 2 mm and a maximum of 4 mm thickness of impression material in the critical areas of measurement. The other Rim-Lock and perforated trays were classified as “lose fitting.” These trays fit the master cast to allow 5 to 8 mm thickness of impression material in the area of measurement.
Selection
of materials
A concerted effort was made to establish consistent parameters with the tray size as the only variable. Jeltrate (L. D. Caulk Co.) irreversible hydrocolloid was used to make the impressions and they were poured with yellow Microstone (Whip-Mix Corp., Louisville, KY.).
Making
the impressions
Twenty impressions were made with each tray on the metal master cast. The same procedure was followed in making each of the casts. The amount of water recommended by the manufacturer was used 347
WOODWARD,
Fig. 2. Melotte’s metal master cast.
MORRIS,
AND
KHAN
Fig. 5. Left lateral view of stone cast showing circled dimples on buccal and incisal surfaces of teeth and buccal vestibule.
Fig. 6. Perforated dentulous tray and Rim-Lock tray. .___--~~ - _-. ~~ Fig. 3. Occlusal view of stone cast showing circled dimples.
Table I. Tight-fitting perforated tight-fitting Rim-Lock trays Point of measurement A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock
vs.
Mean
SD
t
P
-.0042 -.0060 -.0018 -.0052 -.0025 -.0041 .0017 .0027 -.OOOl .0059 -.0033 -.0044
.0018 .0026 .OOlO .0035 .0015 .0030 .OOll .0060 .0026 .0031 .0021 .0028
2.43
<.05
4.07
<.OOl
2.09
<.05
0.70
ns
6.54
<.OOl
1.38
ns
Fig. 4. Right lateral view of stone cast displaying circled dimples on buccal surfaces of teeth and buccal vestibule.
,I/ = 38; n = 20; SD = standard deviation; /j = probability; ns = not significant.
with the contents of the prepackaged alginate. The water was at room temperature, which made the gelation time consistent from one mix to the next. The impression material was hand spatulated for the time specified by the manufacturer. All material was mixed and all impressions were made by one investigator to
standardize the technique. The master cast was sprayed with a silicone lubricant to make the separation of the impression easier. The trays were loaded, seated on the master cast, and allowed to set for 8 minutes to compensate for the difference between mouth temperature and room tem-
348
MARCH
1985
t = distribution
VOLUME
53
symbol;
NUMBER
3
IRREVERSIBLE
HYDROCOLLOID
Table II. Loose-fitting loose-fitting
Rim-Lock
Point of measurement A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock
AND
TRAY
perforated trays
Table IV. Loose-fitting
vs.
Rim-Lock
Mean
SD
t
P
.0033 -.0073 -.0009 -.0046 -.OOll -.0042 .0017 .0055 .0018 -.0007 -.0031 -.0041
.oozo .0028 .0014 .0027 .OOll .0030 .0016 .0054 .0025 .0065 .0016 .0024
5.07
<.OOl
5.32
<.OOl
4.33
<.OOl
2.99
<.Ol
1.58
ns
1.50
IIS
(I/= 38; n = 20; SD = standard deviation; /I = probability; ns = not significam.
Table III. Loose-fitting perforated
SELECTION
1 = distribution
symbol;
vs. tight-fitting
Mean
SD
t
A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
-.0033 -.0042 -.0009 -.OOlS -.OOll -.0025 .0017 .0017 .0018 -.OOOl -.0031 -.0033
.0021 ,001s .0014 .OOlO .OOll .0015 .0016 .OOll .0025 .0026 .0016 .0021
1.55
IlS
2.17
<.05
3.41
<.Ol
0.00
IIS
2.31
<.05
0.25
ns
d/= 38; n = 20; SD = standard deviation /I = probability; ns = not significant.
I = distribution
P
symbol;
perature. The impressions were removed from the master casts by releasing the seal with a blast of air in the palatal region and then a snap removal in the direction most parallel to the long axis of the teeth.
Pouring
the casts
Dental stone was vacuum mixed and vibrated into the impression immediately after it was removed from the master cast. The water/powder ratio recommended by the manufacturer was followed and room temperature water was used. The impression containing the stone was placed in a humidor and allowed to set for a period of 45 minutes before separation.
Measuring
the casts
The casts were measured with a vernier caliper accurate to 0.001 inch. All measurements were made THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Point of measurement
Mean
SD
t
P
A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
-.0073 -.0060 -.0046 -.0052 -.0042 -.0041 .0055 .0027 -.0007 .0059 -.0041 -.0044
.0028 .0026 .0027 .0035 .0030 .0030 .0054 .0060 .0065 .0031 .0024 ,002s
1.48
IlS
0.55
IlS
0.10
IIS
1.57
Il.5
loose tight loose tight loose tight loose tight loose tight loose tight
a/= 38; n = 20; SD = standard deviation; /I = probability; ns = not significant.
4.05 0.29
/ = distribution
<.OOl IT3
symbol;
by the same investigator for consistency. Six measurements were made on each cast: lines A-B, A-C, B-C, D-D’, E-E’, and F-F’.
trays
Point of measurement loose tight loose tight loose tight loose tight loose tight loose tight
vs. tight-fitting
trays
RESULTS Measurements in Table I illustrate that tight-fitting perforated trays produced more accurate casts than did tight-fitting Rim-Lock trays. In four of the six measurements, the difference between the perforated and Rim-Lock trays was statistically significant, while two of the measurements were not significant. Comparison of casts made from loose-fitting perforated trays with those from loose-fitting Rim-Lock trays demonstrated that the perforated tray produced a more accurate cast than the Rim-Lock tray (Table II). Of the six comparisons, five were more accurate with the perforated trays, and one was more accurate with the Rim-Lock tray. One of the five was not statistically significant. Tables III and IV show weak evidence that a cast made from an impression made in a loose-fitting tray is more accurate than one made in a tight-fitting tray. Of the 12 comparisons in the two tables, eight were not statistically significant. Of the four comparisons that were statistically significant, three indicated that a loose-fitting tray produced a more accurate cast, while one indicated that a tight-fitting tray produced a more accurate cast.
CONCLUSION This study demonstrated that irreversible hydrocolloid impressions made in perforated trays are more accurate than in Rim-Lock trays for the production of an accurate cast. The findings for loose-fitting and tight-fitting trays are inconclusive. The statistics for eight of the samples were not significant, while the 349
WOODWARD,
3.
remainder was split between the two categories. Therefore, further studies are indicated. REFERENCES :
hlitcheli, J. V., and Damele, J J.: InHuence of tray design tipon elastic impression materials. J PROSTHET DEIUT 2351, Fuwvam.r. I‘ , ,md Nakamato, LX.: The designs of stock trays and the retention of irreversible hydrocolloid impressions. ,J PK~~.IHE.I
Tensile
I)~:xT
21:116.
strength
of Louisville,
AND
School
of Dentistry,
Louisville,
~Jt~[smrient of Pedodonucs. “*:\sw iate Professor.. Department of Pedodontrs. i**Pr~~lrssor. Drpartmrnt of Biomatrrials Sciencr.
and
Ky.
METHODS
-..----
358
DR. JAMES D. WOODWARII UNIVERSITV OF LOUISVILLE SCHOOL 01: DENTISTRY Loutsvrr.~.~, KY 40292
D.M.D.,**
The three soldering methods used were (1) conventional gas-air flame with a blow pipe (Unitek Corp., Monrovia, Calif.), (2) a hydrogen-oxygen flame generated by a Hydroflame unit (Unitek Corp.), and (3) a
“F’ioiessor.
Heartwell, Jr., C. M., Modjeski, P. J., Mullins, Jr., E. E., and Strader, K. H.: Comparison of impressions made in perforated and nonperforated rimlock trays. J PROSTHET DENT 27~494, 1972.
of soldered joints
e tensile strength of silver solder joints used in the fabrication of orthodontic appliances and space maintainers is critical to their success.Two basic methods of soldering have been reported: the traditional gas-air flame method and an electrical technique with a carbon tip used to apply heat. The latter has been reported by Gardiner and Aamodt’ to produce the weakest joint because of large areas of fracture between the solder and stainless steel interface. However, Laird and von Fraunhofer’ did not find significant differences in the tensile strength of joints produced by electrobrazing (electric soldering) and those produced by gas-air brazing (both air cooled and quenched). This study was undertaken to compare the tensile strength of silver solder joints of stainless steel wire to band. materiai produced by (1) a traditional gas-air blowpipe, (2) an electrochemically generated hydrogenoxygen flame, and (3) electric soldering with a spot welder, Joints soldered by the three techniques, both covered (solder completely enveloping the wire) and partially covered, were studied. MATERIAL
KHAN
1969.
T, J, O’Toole, D.M.D., M.S.D.,* G. M. Furnish, f* A. von Frannhofer, Ph.D., M.Sc.*** !‘niversity
AND
12e@v11 rt~qu<~slc lo:
197tl
_
MORRIS,
spot welder (Model No. 660, Rocky Mountain/Orthodontics, Denver, Colo.), set on the soldering position. Orthodontic stainless steel wires, 0.036 inch (0.91 mm) diameter, were soldered to stainless steel strips, 0.75 X 0.25 X0.005 inch (19.1 X6.4X0.13 mm), by the three soldering techniques either with solder covering the wire completely or with half the wire covered by solder (Fig. 1). Two joint lengths, 2 and 4 mm, were studied. The overall length of wire joined to the stainless steel strip was 50 mm. The wire and strip were in contact prior to soldering. Eleven joints were prepared with each technique in the two joint lengths (2 and 4 mm) with and without solder covering the wire. A total of 132 specimens were subjected to tensile testing. Silver solder, 0.025 inch (0.64 mm) diameter (Unitek Corp.), and liquid flux (Rocky Mountain J-41) were used as the soldering media. In the covered joints, solder enveloped the wire for the entire joint length (2 or 4 mm) in a feather-edged configuration onto the stainless steel strip. With the partially covered joints, the solder was confined to 50% or less of the wire diameter and was continuous with wire and strip for the length of the joint (Fig. 1). The electrically soldered joints were prepared by clamping the wire and strip in position with the carbon tip and the opposing rounded right-angle electrode of the spot welder. Flux was added to the soldering site, and as heat was supplied to the joint, silver solder was fed into the joint. This procedure was used for both covered and partially covered joints. Gas-air flame and Hydroflame joints were prepared with the wire and strip held in an investment jig (Fig. 2) MARCH
1985
VOLUME
53
NUMBER
3
M.Ed.,*
Jack C. Morris,
by perforated
D.M.D.,
M.Sc.,**
trays
and
University of Louisville, Schoolof Dentistry, Louisville, Ky
M
itchell and Damele’ stated that the average deficiency recorded from impression distortion was greatest in a perforated tray. It was reduced with a lubricated nonperforated tray (Rim-Lock, L.D. Caulk Co., Milford, Del.) and further minimized by an undercut lubricated tray. They suggested that distortion might be induced by attachment of the impression material to the tray. One factor not taken into consideration was the size of the tray. Fusayama and Nakamoto2 compared the influence of size, number, interval, and total area of tray perforations on the retention of irreversible hydrocolloid impressions. Hartwell et al3 pointed out that there was no significant difference in the accuracy of irreversible hydrocolloid impressions made in perforated and RimLock trays. The tray size was again kept constant. This study was conducted to determine the distortion caused by perforated and Rim-Lock trays and the influence of tray size on the impressions.
MATERIAL Preparation
AND METHODS of the master casts
An Ivorine maxillary dentulous model (Columbia Dentoform Corp., New York, N.Y.) was chosen as the standard (Fig. 1). Laboratory type reversible hydrocolloid was used to duplicate the model in a low-fusing alloy (Melotte’s metal) (Fig. 2). A twist drill was used to prepare nine dimples in the metal master cast to provide clearly reproducible reference points. The dimples were placed in (1) the distobuccal cusp tip of the maxillary left first molar (point A), (2) the incisal edge of the maxillary left central incisor (point B), (3) the buccal cusp tip of the maxillary right second premolar (point C), (4) the buccal surface of the maxillary left second premolar (point D), (5) the maxillary left buccal fold area (point D’) (Figs. 3 to S), (6) the labial surface of the maxillary right lateral incisor (point E), (7) the maxillary right labial fold area (point E’), (8) the buccal surface of the maxillary
*Professor,Departmentof **Associate ***Assistant THE
Professor, Professor,
JOURNAL
Prosthodontics. Department of Prosthodontics. Department of Prosthodontics.
OF PROSTHETIC
DENTISTRY
Fig. 1. Ivorine maxillary dentulous model.
right first molar (point F), and (9) the maxillary right buccal fold area (point F’) (Figs. 2 to 4).
Selection
of trays
Two Rim-Lock trays and two perforated trays were selected to make the impressions for this study (Fig. 6). One Rim-Lock and one perforated tray were selected by the investigators and judged to be “tight fitting.” The trays fit the master cast so there was a minimum of 2 mm and a maximum of 4 mm thickness of impression material in the critical areas of measurement. The other Rim-Lock and perforated trays were classified as “lose fitting.” These trays fit the master cast to allow 5 to 8 mm thickness of impression material in the area of measurement.
Selection
of materials
A concerted effort was made to establish consistent parameters with the tray size as the only variable. Jeltrate (L. D. Caulk Co.) irreversible hydrocolloid was used to make the impressions and they were poured with yellow Microstone (Whip-Mix Corp., Louisville, KY.).
Making
the impressions
Twenty impressions were made with each tray on the metal master cast. The same procedure was followed in making each of the casts. The amount of water recommended by the manufacturer was used 347
WOODWARD,
Fig. 2. Melotte’s metal master cast.
MORRIS,
AND
KHAN
Fig. 5. Left lateral view of stone cast showing circled dimples on buccal and incisal surfaces of teeth and buccal vestibule.
Fig. 6. Perforated dentulous tray and Rim-Lock tray. .___--~~ - _-. ~~ Fig. 3. Occlusal view of stone cast showing circled dimples.
Table I. Tight-fitting perforated tight-fitting Rim-Lock trays Point of measurement A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock
vs.
Mean
SD
t
P
-.0042 -.0060 -.0018 -.0052 -.0025 -.0041 .0017 .0027 -.OOOl .0059 -.0033 -.0044
.0018 .0026 .OOlO .0035 .0015 .0030 .OOll .0060 .0026 .0031 .0021 .0028
2.43
<.05
4.07
<.OOl
2.09
<.05
0.70
ns
6.54
<.OOl
1.38
ns
Fig. 4. Right lateral view of stone cast displaying circled dimples on buccal surfaces of teeth and buccal vestibule.
,I/ = 38; n = 20; SD = standard deviation; /j = probability; ns = not significant.
with the contents of the prepackaged alginate. The water was at room temperature, which made the gelation time consistent from one mix to the next. The impression material was hand spatulated for the time specified by the manufacturer. All material was mixed and all impressions were made by one investigator to
standardize the technique. The master cast was sprayed with a silicone lubricant to make the separation of the impression easier. The trays were loaded, seated on the master cast, and allowed to set for 8 minutes to compensate for the difference between mouth temperature and room tem-
348
MARCH
1985
t = distribution
VOLUME
53
symbol;
NUMBER
3
IRREVERSIBLE
HYDROCOLLOID
Table II. Loose-fitting loose-fitting
Rim-Lock
Point of measurement A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock perforated Rim-Lock
AND
TRAY
perforated trays
Table IV. Loose-fitting
vs.
Rim-Lock
Mean
SD
t
P
.0033 -.0073 -.0009 -.0046 -.OOll -.0042 .0017 .0055 .0018 -.0007 -.0031 -.0041
.oozo .0028 .0014 .0027 .OOll .0030 .0016 .0054 .0025 .0065 .0016 .0024
5.07
<.OOl
5.32
<.OOl
4.33
<.OOl
2.99
<.Ol
1.58
ns
1.50
IIS
(I/= 38; n = 20; SD = standard deviation; /I = probability; ns = not significam.
Table III. Loose-fitting perforated
SELECTION
1 = distribution
symbol;
vs. tight-fitting
Mean
SD
t
A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
-.0033 -.0042 -.0009 -.OOlS -.OOll -.0025 .0017 .0017 .0018 -.OOOl -.0031 -.0033
.0021 ,001s .0014 .OOlO .OOll .0015 .0016 .OOll .0025 .0026 .0016 .0021
1.55
IlS
2.17
<.05
3.41
<.Ol
0.00
IIS
2.31
<.05
0.25
ns
d/= 38; n = 20; SD = standard deviation /I = probability; ns = not significant.
I = distribution
P
symbol;
perature. The impressions were removed from the master casts by releasing the seal with a blast of air in the palatal region and then a snap removal in the direction most parallel to the long axis of the teeth.
Pouring
the casts
Dental stone was vacuum mixed and vibrated into the impression immediately after it was removed from the master cast. The water/powder ratio recommended by the manufacturer was followed and room temperature water was used. The impression containing the stone was placed in a humidor and allowed to set for a period of 45 minutes before separation.
Measuring
the casts
The casts were measured with a vernier caliper accurate to 0.001 inch. All measurements were made THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Point of measurement
Mean
SD
t
P
A-B A-B A-C A-C B-C B-C D-D’ D-D’ E-E’ E-E’ F-F’ F-F’
-.0073 -.0060 -.0046 -.0052 -.0042 -.0041 .0055 .0027 -.0007 .0059 -.0041 -.0044
.0028 .0026 .0027 .0035 .0030 .0030 .0054 .0060 .0065 .0031 .0024 ,002s
1.48
IlS
0.55
IlS
0.10
IIS
1.57
Il.5
loose tight loose tight loose tight loose tight loose tight loose tight
a/= 38; n = 20; SD = standard deviation; /I = probability; ns = not significant.
4.05 0.29
/ = distribution
<.OOl IT3
symbol;
by the same investigator for consistency. Six measurements were made on each cast: lines A-B, A-C, B-C, D-D’, E-E’, and F-F’.
trays
Point of measurement loose tight loose tight loose tight loose tight loose tight loose tight
vs. tight-fitting
trays
RESULTS Measurements in Table I illustrate that tight-fitting perforated trays produced more accurate casts than did tight-fitting Rim-Lock trays. In four of the six measurements, the difference between the perforated and Rim-Lock trays was statistically significant, while two of the measurements were not significant. Comparison of casts made from loose-fitting perforated trays with those from loose-fitting Rim-Lock trays demonstrated that the perforated tray produced a more accurate cast than the Rim-Lock tray (Table II). Of the six comparisons, five were more accurate with the perforated trays, and one was more accurate with the Rim-Lock tray. One of the five was not statistically significant. Tables III and IV show weak evidence that a cast made from an impression made in a loose-fitting tray is more accurate than one made in a tight-fitting tray. Of the 12 comparisons in the two tables, eight were not statistically significant. Of the four comparisons that were statistically significant, three indicated that a loose-fitting tray produced a more accurate cast, while one indicated that a tight-fitting tray produced a more accurate cast.
CONCLUSION This study demonstrated that irreversible hydrocolloid impressions made in perforated trays are more accurate than in Rim-Lock trays for the production of an accurate cast. The findings for loose-fitting and tight-fitting trays are inconclusive. The statistics for eight of the samples were not significant, while the 349
WOODWARD,
3.
remainder was split between the two categories. Therefore, further studies are indicated. REFERENCES :
hlitcheli, J. V., and Damele, J J.: InHuence of tray design tipon elastic impression materials. J PROSTHET DEIUT 2351, Fuwvam.r. I‘ , ,md Nakamato, LX.: The designs of stock trays and the retention of irreversible hydrocolloid impressions. ,J PK~~.IHE.I
Tensile
I)~:xT
21:116.
strength
of Louisville,
AND
School
of Dentistry,
Louisville,
~Jt~[smrient of Pedodonucs. “*:\sw iate Professor.. Department of Pedodontrs. i**Pr~~lrssor. Drpartmrnt of Biomatrrials Sciencr.
and
Ky.
METHODS
-..----
358
DR. JAMES D. WOODWARII UNIVERSITV OF LOUISVILLE SCHOOL 01: DENTISTRY Loutsvrr.~.~, KY 40292
D.M.D.,**
The three soldering methods used were (1) conventional gas-air flame with a blow pipe (Unitek Corp., Monrovia, Calif.), (2) a hydrogen-oxygen flame generated by a Hydroflame unit (Unitek Corp.), and (3) a
“F’ioiessor.
Heartwell, Jr., C. M., Modjeski, P. J., Mullins, Jr., E. E., and Strader, K. H.: Comparison of impressions made in perforated and nonperforated rimlock trays. J PROSTHET DENT 27~494, 1972.
of soldered joints
e tensile strength of silver solder joints used in the fabrication of orthodontic appliances and space maintainers is critical to their success.Two basic methods of soldering have been reported: the traditional gas-air flame method and an electrical technique with a carbon tip used to apply heat. The latter has been reported by Gardiner and Aamodt’ to produce the weakest joint because of large areas of fracture between the solder and stainless steel interface. However, Laird and von Fraunhofer’ did not find significant differences in the tensile strength of joints produced by electrobrazing (electric soldering) and those produced by gas-air brazing (both air cooled and quenched). This study was undertaken to compare the tensile strength of silver solder joints of stainless steel wire to band. materiai produced by (1) a traditional gas-air blowpipe, (2) an electrochemically generated hydrogenoxygen flame, and (3) electric soldering with a spot welder, Joints soldered by the three techniques, both covered (solder completely enveloping the wire) and partially covered, were studied. MATERIAL
KHAN
1969.
T, J, O’Toole, D.M.D., M.S.D.,* G. M. Furnish, f* A. von Frannhofer, Ph.D., M.Sc.*** !‘niversity
AND
12e@v11 rt~qu<~slc lo:
197tl
_
MORRIS,
spot welder (Model No. 660, Rocky Mountain/Orthodontics, Denver, Colo.), set on the soldering position. Orthodontic stainless steel wires, 0.036 inch (0.91 mm) diameter, were soldered to stainless steel strips, 0.75 X 0.25 X0.005 inch (19.1 X6.4X0.13 mm), by the three soldering techniques either with solder covering the wire completely or with half the wire covered by solder (Fig. 1). Two joint lengths, 2 and 4 mm, were studied. The overall length of wire joined to the stainless steel strip was 50 mm. The wire and strip were in contact prior to soldering. Eleven joints were prepared with each technique in the two joint lengths (2 and 4 mm) with and without solder covering the wire. A total of 132 specimens were subjected to tensile testing. Silver solder, 0.025 inch (0.64 mm) diameter (Unitek Corp.), and liquid flux (Rocky Mountain J-41) were used as the soldering media. In the covered joints, solder enveloped the wire for the entire joint length (2 or 4 mm) in a feather-edged configuration onto the stainless steel strip. With the partially covered joints, the solder was confined to 50% or less of the wire diameter and was continuous with wire and strip for the length of the joint (Fig. 1). The electrically soldered joints were prepared by clamping the wire and strip in position with the carbon tip and the opposing rounded right-angle electrode of the spot welder. Flux was added to the soldering site, and as heat was supplied to the joint, silver solder was fed into the joint. This procedure was used for both covered and partially covered joints. Gas-air flame and Hydroflame joints were prepared with the wire and strip held in an investment jig (Fig. 2) MARCH
1985
VOLUME
53
NUMBER
3