- Email: [email protected]
Particle-roughened resin-bonded retainers
CASTING
ACCURACY
OF FIXED
PARTIAL
DENTURES
with modification for reducing expansion to obtain a less-oversize casting should produce consistently accurate dental castings.
4,
REFERENCES
5
1.
2.
3.
Bauer, R. W., and Eden, G. T.: NADL survey of casting alloys in commercial dental laboratories. J Dent Res 56(Special issue B):214, 1’)77. Bauer, R. W.: Survey on the use of casting alloys in commercial dental laboratories. Part II: Ceramic alloys. Natl Assoc Dent Lab J 24:8, 1977. Eden. G. T., Franklin, 0. M., Powell, J. M., Ohta, Y., and
Particle-roughened Jeffrey Medical
L. Hudgins, College
D.D.S.,*
of Virginia,
School
of Dentistry,
Ph.D.,**
Richmond,
I
n 1973, Rochette’ introduced a perforated metal framework for resin-bonded fixed partial dentures that has been used with clinical success.2-4Thompson et al.’ modified the technique by selectively corroding nonprecious alloys to obtain a mechanically retentive surface for bonding retainers to etched enamel. The etched-metal innovation resolved several problems inherent in the Rochette design, and it became a popular technique.’ However, the etched-metal procedure possesses two limitations. It is restricted to nonprecious alloys, and the electrochemical etching procedure is technique sensitive. In 1983 Moon and Knap’ developed a roughened metal surface by using salt crystals to create voids in self-curing acrylic resin patterns. They reported that the particleroughened technique could be used for fabrication of resin-bonded metal retainers to avoid the limitations of the etched-metal approach. The purpose of the present study was to extend the research of Moon and Knap’ to accomplish the following goals: 1. Adapt the particle-roughened pattern technique to an indirect model system 2. Make particle-roughened retainers, bond them to extracted human teeth, and measure the force required to separate the retainer from the tooth
Recipient of the Stanley D. Tylman Research Award. Presented at the American Academy of Crown and Bridge tics, Chicago, Ill. *Graduate student, Fixed Prosthodontics. **Associate Professor and Director, Dental Materials. ***Director, Fixed Prosthodontics Graduate Program. THE
JOURNAL
OF PROSTHETIC
Kt3prznl reymts to: DR. JOHN A TESK NATIONAL BUREAU OF STANDARDS DENTAL AND MEDICAL MATERIALS POLYMER SCIENCE .&ND STANDARDS DIVISION WASHINGTOK, DC 20234
resin-bonded Peter C. Moon,
DENTISTRY
Prosthodon-
Dickson, G.: Fit of porcelain-fused-to-metal crown and bridge castings. J Dent Res 58:2360, 1979. Hollenback, G. M.: Science and Technique of the Cast Restoration. St. Louis, 1964, The C. V. Mosby Co. Phillips, R. W.: Skinner’s Science of Dental Materials. Philadelphia, 1973, W. B. Saunders Co.
retainers and Florian
J. Knap, D.D.S., M.S.***
Va.
3. Initiate a clinical study of the particle-roughened resin-bonded fixed partial denture
MATERIAL
AND METHODS
Extracted human teeth without restorations were debrided with scalers and stored in room-temperature distilled water. Thirty-two teeth were divided into four groups of eight: (1) maxillary incisors, (2) canines, (3) premolars, and (4) molars (excluding third molars). Acceptable tooth preparation guidelines were followed to provide maximal bond area with a rigid path of insertion.3,8,9 The incisors and canines had one proximal surface and the lingual surface prepared. The premolars and molars had a proximal and a lingual surface prepared with a rest seat on the appropriate marginal ridge. An impression of each tooth was made in Reprosil (L. D. Caulk Co., Milford, Del.), and a master cast was poured in die stone. The outline of each retainer pattern was traced on the die with a 0.5 mm red pencil. The tracing and pattern fabrication were performed with a x 10 binocular microscope. Duralay lubricant (Reliance Dental Mfg. Co., Worth, Ill.) was applied to each die with a No. 1 sable brush in an even thickness within the line denoting the pattern’s extension. Sieved salt (U. S. standard sieve series, Humboldt Mfg. Co., Chicago, Ill.) from 149 to 250 pm was sprinkled over the lubricated area.’ By careful application and tapping excess from the cast, an even, one-crystal layer that covered the lubricated area was obtained. Model spray (J. F. Jelenko and Co., Armonk, N.Y.) was lightly applied at a distance of 12 to 471
HUDGINS,
Fig. 1. Photomicrograph of Duralay pattern surface after alumina blasting. (Original magnification x20.) 18 inches to secure the crystals. It was imperative not to apply the spray heavily because the definition between crystals would have been lost. A No. 1 sable brush was dipped in a dappen dish of Duralay monomer, and a small ball of Duralay powder was picked up with the tip of the brush. The wet powder was carefully applied between crystals to prevent displacement. The wet Duralay powder was fluid enough to flow between the crystals but was not saturated with monomer, which triggered movement between crystals. The pattern was formed with repeated application of the Duralay and then allowed to cure. After the cure was completed, a plastic sprue was luted to the pattern with sticky wax and the pattern gently removed from the die. The pattern surface that had contacted the die was blasted for a total of 2 to 3 seconds with a micropencil and 60 pm alumina particles (Sterngold Inc., Stamford, Conn.). The pattern was rinsed with tap water to dissolve the salt, dried with compressed air, and examined under the microscope to ascertain removal of the salt crystals from the pattern (Fig. 1). Additional blasting, washing, and drying was performed if necessary but was kept to a minimum because overblasting erodes the roughness left by crystal removal. A loop was waxed to the lingual surface to 472
MOON,
AND
KN41’
Fig. 2. Schematic of Instron apparatus with mounted samples. F = Force; a = Instron grips; b = steel cable through loop on retainer; c = retainer; d = tooth surface; e = tray acrylic resin; f = acrylic resin sheet.
accommodate a ‘/s inch steel cable to test the bond strength with force directed along the long axis of the tooth (Fig. 2). Equal amounts of isopropyl alcohol and water were mixed in a dappen dish and vibrated over the aluminablasted surface with a No. 1 sable brush until it was wet. This step was necessary to overcome Duralay’s high surface tension as investment flowed across the roughened surface. The pattern was immediately vacuum invested with Biovest (Dentsply International, Inc.; York, Pa.). After it had set, the investment was burned out at 1400” F for 1 hour. A palladium-cobalt alloy (Chemodent Inc., Charlottesville, Va.) was melted with a gas-oxygen torch and centrifugally cast (Fig. 3). The retainer casting was divested, and the particle-roughened surface was examined under the microscope for blebs. The retainers were adapted to the stone dies and the fit verified on the extracted teeth. The tooth root was embedded in a cured ‘/s x 2 x 4 inch acrylic resin sheet to test tensile strength. To improve tooth stability, tray resin was shaped over all APRIL
1985
VOLUME
53
NUMBER
4
PARTICLE-ROIJGHENED
RETAINERS
shearing occurred (Fig. 2). The force required and the character of the bond failure were recorded.
RESULTS Incisois Seven maxillary central incisors and one large maxillary lateral incisor composed this group. A consistent occurrence was observed at bond failure; seven of eight samples fractured at the junction of the middle and incisal thirds of the teeth (Fig. 5). The one retainer that separated cleanly did so at the enamel/resin junction (Table I).
Canines Six retainers, Nos. 1, 2, 3, 4, 6, and 8, separated cleanly from the tooth (Table I). These six casting surfaces exhibited virtually intact resin coverage, which indicated that the bond between the resin and the etched enamel surface was the area of failure. Nos. 5 and 7 sheared the crown in the gingival third prior to retainer separation.
Premolars
Fig. 3. Photomicrograph of particle-roughened of cast retainer. (Original magnification X20.)
surface
surfaces of the tooth except where the retainer fit. The acrylic resin sheet provided a flat area for the Instron grips (Model TIC, Instron Corp., Canton, Mass.) to grasp the sample (Fig. 2). The tooth surface to be bonded was pumiced, washed, dried, and etched for 90 seconds. The acid was removed with tap water and the sample thoroughly dried. Comspan opaque liquid resins (L. D. Caulk Co.) were mixed and applied to the retainer and to the etched enamel. Trapping air bubbles on the retainer surface with liquid resin was kept to a minimum because poor application technique can decrease the bond strength. The liquid resin was applied to an edge of the casting and allowed to flow by gravity across the roughened surface. Comspan opaque filled resin pastes were mixed and carefully applied to the retainer, which was seated with firm pressure. At 2 minutes, the excess resin was gently removed with a hand instrument and at 4 minutes the seating pressure released. After curing for 10 minutes, the bonding sample was placed in distilled water and maintained at 32” C for 7 days (Fig. 4). The ‘/s inch cable was fitted through the loop on the retainer and the sample was mounted on the Instron machine. The force was directed along the long axis of the tooth at a crosshead speed of 0.05 inch/min until THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Five samples fractured at or near the cementoenamel junction and three retainers separated cleanly (Table I). Tooth fracture did not necessarily mean the sample had a high bond strength, because within this group the highest (170 lbs) and the lowest (93 lbs) values were instances of tooth breakage. When clean retainer separation was observed, the failure was at the enamel/resin interface.
Molars Sample No. 2 fractured through the roots, while Nos. 3 and 7 sheared the abutment cusp (Table I). The remaining samples were cleanly removed and displayed the same pattern as the preceding groups; a virtually continuous film of resin remained on the retainer and separation was at the etched enamel/resin interface. The Student t test was used to determine significant differences among the groups. Each pair of groups was statistically different at the 95% confidence level except for the canine/premolar comparison (.lO > p > .OS)and the premolar/molar pair (p > .lO).
Clinical
trial
During a 6-month period, a total of 27 particleroughened resin fixed partial dentures were placed for clinical patients at the Virginia Commonwealth University School of Dentistry. Two fixed partial dentures consisted of two pontics and two retainers while the remainder were one pontic and two retainers. The distribution was as follows: 16 anterior fixed partial dentures (15 maxillary and 1 mandibular) and 11 posterior fixed partial dentures (6 maxillary and 5 mandibular). 473
HUDGINS,
‘t100N,
Table I. Force required
for shearing
Fig. 5. Fracture site (a) of incisor group. ,F = Force. b = loop for bond testing.
(in pounds) Sample No.
Group
Incisors Canines Premolars Molars *Tooth
fractured
1
2
3
4
5
6
7
92* 112 143*
89’ 80 170’ 126*
70* 122 134* 200”
63* 108 100’ 62
90’ 119’ 119 168
114* 114 93’ 200
75 108’ 111 182%
100 prior
to retainer/tooth
-_______-___-..-8 Mean 73’ 60 106 145 ____~..
83.3 102.9 122.0 147.9 ~- --.-.-
SD 16.3 21.5 25.6 49.5 -- --
separation
The frameworks were made and cast by the principal investigator while porcelain addition was provided by the University staff: CM (Chemdent Metal Co., Charlottesville, W. Va.) alloy was used for 26 fixed partial dentures while one mandibular posterior fixed partial denture was made with a conventional type III gold alloy. Bonding was accomplished with Comspan bonding agent by dental students using the following protocol: 1. Isolation was achieved with a rubber dam. 2. The abutments were cleaned with flour of pumice, rinsed, and dried. 3. Etching liquid was applied to the abutment areas for 90 seconds, rinsed, and dried. 4. Unfilled resin was applied to the framework and the abutments. 5. Filled resin was applied to the framework. 6. The fixed partial denture was inserted and held firmly in place with finger pressure. 7. After 10 minutes the rubber dam was removed, the occlusion was adjusted, and final clean-up was accomplished.
474
KNAl
b
a
Fig. 4. Schematic of retainer fit to tooth. a = particleroughened surface; b = loop for bond testing.
AND
The 27 particle-roughened resin-bonded metal fixed partial dentures have been in service for 12 to 18 months. To date there has been one bond failure within the group: a maxillary anterior four-unit fixed partial denture was dislodged after 6 months of service. The bond failure occurred at the Comspan/enamel junction. The fixed partial denture was alumina-blasted clean and rebonded. The reason for failure was inadequate surface area covered by the retainers. The fixed partial denture will be remade to cover more area if bond failure recurs. The particle-roughened pattern technique has been adopted for making resin-bonded fixed partial dentures in the undergraduate dental clinics at the Virginia Commonwealth University School of Dentistry.* Since the original 27 fixed partial dentures were inserted, additional particle-roughened resin-bonded fixed partial dentures have been delivered. The total will increase as *The pattern fabrication technique has been simplified that described in this article, but the retainer surface
APRIL
1985
VOLUME
53
recently from is similar.
NUMBER
4
PARTICLE-ROUGHENED
RETAINERS
the technique is disseminated, and records are being maintained for longitudinal studies. DISCUSSION Retentive strengths have been reported in which castings were removed from metal dies in an axial direction. Lorey and Myers,‘” Potts et al.,” and Kishimoto et al.“, ” used similar procedures to test partial and complete veneer crowns. Values ranged from 57.6 pounds for a canine three-quarter crown with grooves to 243 pounds for a premolar complete veneer crown without grooves. Premolar three-quarter and seveneighths crowns of various designs (with or without grooves) ranged from 92 to 135 pounds. The most retentive mesial-occlusal-distal onlay preparation for premolars averaged 80.2 pounds. Experience has shown that these crown designs provide years of service. All three studies provide data that probably compose a valid simulation of retentive values required clinically. If this assumption is correct then our average values of 83.3 to 147.9 pounds indicate that successcan be expected if the particle-roughened resinbonded technique is properly applied. Bond separation that occurs at the enamel/resin interface also supports this hypothesis, since the phenomenon has been observed experimentally and clinically with similarly successful resin-bonded fixed partial dentures.+” In addition, the retention of the roughened resin-bonded retainer surface equals or exceeds the retention of etched enamel/resin systems. . Tooth fracture occurred in 17 of 32 samples, which affects interpretation of the data. If fracture precedes bond separation, the true maximum bond strength has not been recorded for that tooth. The bond test is then a function of tooth morphology and/or test methods rather than of retainer-to-tooth bond strength (Fig. 5). Since teeth become brittle after extraction the averages reported in Table I are conservative compared with bond strengths attainable in vivo. Resin-bonded systems are dependent on the quality of the resin-to-etched enamel bond. Tooth-to-tooth variation of etched enamel bond strength occurs and cannot be anticipated prior to treatment. For example, there was more than a threefold difference in bond strength measured between molar sample Nos. 4 and 6, yet the teeth appear similar. The principles of framework design and mouth preparation for resin-bonded restorations have been described.-l,X,9These principles should be implemented so that (1) bonding should cover the maximum available surface area, and (2) retention and resistance form are maximized. Both factors improve bond strength because circumferential involvement increases the retention and resistance of retainers.” This point is emphasized by the
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Student t test, because the t values imply a significant difference between tooth types. However, the discriminating factors behind this difference are available bond area and the ability to increase resistance form on posterior teeth. The advantages of the particle-roughened resin-bonded technique over the etched-metal resin-bonded procedure are as follows: 1. The time-consuming and technique-sensitive electrochemical etching of the framework is eliminated, which decreases treatment time by one appointment since the framework try-in is obviated. 2. Contaminating the retentive surface by skin or liquid contact is minimized. 3. The retentive surface is more easily evaluated. 4. Commonly used dental alloys may be used for the framework. This should reduce difficulties such as casting, finishing, polishing, adjustments, and porcelain compatibility, which occur with the nonprecious alloys. 5. The technique uses readily available dental materials. The advantages of the etched-metal resin-bonded framework technique over the particle-roughened resinbonded procedure are (1) pattern fabrication and investment procedures are less technique-sensitive, and (2) smoother margins are achieved between the metal retainers and tooth structure. CONCLUSIONS 1. The particle-roughened metal retainer possesses sufficient mechanical bond strength for resin-bonded systems. 2. The weak link in metal-to-etched-enamel resinbonded systems in this study was the resin/etched enamel interface. 3. It is advisable to cover as much surface as feasible when resin-bonded retainers are etched to enamel. Graphic illustrations xe courtesy of Dr. Charles E. Janus, College of Virginia, Virginia Commonwealth Uniwwty.
Xledical
REFERENCES 1.
2.
3. 4.
5.
Rochetw, h. I,.: .4ttachment of a splint to enamel of lower anterior teeth using the acid etch technique and a cast metal framework. J PROSTHEX DENT 30~418, 1973. Howe, D. F., and Denehy, G. E.: Anterior fixed partial dentures utilizing the acid etch technique and a cast metal framework. ,J PROSTHLT DENT 37:28, 1977. Livaditis, G. J.: Cast metal resin-bonded retainers tor posterior teeth. J Am Dent Assoc 101:926, 1980. Eshleman, J. R., Moon, P. C., and Barnes, R. F.: Clinical evaluation of cast metal resin-bonded anterior fixed partial dentures. J PROWHET DENT 51:761. 1984. Thompson, V. P., Del Castillo, E., and Livaditis. G. J.: Resin bond to electrolytically etched nonprecious alloys for resin bonded
475
HUDGINS,
6.
7.
8.
9.
10. 11.
12.
MOON,
AND
KNAI’
prostheses. J Dent Res GO(Special issue A):377 (Abstr No. 265), 1981. Livaditis, G. J.~ and Thompson, V. P.: Etched castings: f\n improved mechanism for resin bonded retainers. ,J PKOS.~.H~ I’ r)EN.r 4~52, 1982. Moon, P. C.. and Knap, F. J.: Acid-etched bridge bond strength utilizing a new retention method. J Dent Res 62(Sprcial issue) (Abstr No. 296) 1983. Eshleman, J. R., Douglas, H. B., and Barnes. R F: The acid-etch bonded porcelain fused to metal bridge. Va Dent J 56:16, 1977. Wood, M., and Thompson, V. P.: Anterior etched cast resinbonded retainers: An overview of design, fabrication. and clinical use. Compendium Cont Ed Dent 4:3, 1983. Lorey, R. E., and Myers, G. E.: The retentive qualities of bridge retainers. ,J Am Dent Assoc 76~568, 1968. Potts, R. G., Shillingburg, H. T., and Duncanson, M. G.. Retention and resistance of preparations for cast restorations. J PROSTHET DENT 43:303, 1980. Kishimoto, kl., Shillingburg, Jr., H. T., and Duncanson, JI-.. hl
joints J. I. Nicholls, University
Ph.D.,*
of Washington,
and R. W. Lemm** School of Dentistry,
Seattle, Wash
T
he literature on dental soldering can be divided into two categories: (1) distortion that results from soldering and (2) strength of solder joints related to the various solders used to form the joint. Both pre- and postsoldering have been used to form solder joints. Postsoldering is needed to form a union between dissimilar alloys, one of which is a porcelain alloy. The literature on postsoldering is not extensive. Taylor and Teamer’ showed that the gap distance between the units to be joined affects the distortion or accuracy of the system as well as the strength. Ryge2 reported that a gap distance of less than 0.005 inch (0.123 mm) leads to greater porosity and an inherent strength decrease in the soldered joint. He also showed that less porosity results when the units are brought to soldering temperature before solder application. Stade et a1.3 demonstrated a consistent strength increase as gap size increased; oven-soldered units showed parent metal fractures at the larger gap sizes. Rasmussen et al4 postsoldered type III gold-palladium aliop. Their
*Professor, Resmrative Dentistry. **Certified
476
Dental
Technician,
Head
Restorative
Technician
research indicated that statistically significant strength changes were not found with gap distance for pre- and postsoldering, and the postsoldered joints were stronger. Staffanou et al5 studied several combinations of metals with both pre- and postsoldering. They stated that there were no major differences between the pre- and postsoldered joints. However, during testing some presolder specimens failed at such low values that data were not recorded. This did not occur with the postsoldered sequence. They concluded that consistently better solder joints could be accomplished with a high percent of success by using the more controllable postsoldering method. The most recent information regarding postsoldering is that reported by Monday and Asgar.6 In their study, specimens of Olympia (gold-palladium alloy, J.F. jelenko, New York, N.Y.) were cast from a mixture of 42% new metal and 58% old metal. Solder joints were formed by both pre- and p&soldering with both torch and oven soldering techniques. The results indicated that postsoldered joints were weaker than presoldered joints for the solders used. The strength reduction was 400% to 500%. The authors attributed the loss to a slow heating and cooling during the postsoldering cycle. The purpose of the present study was to determine the APRIL
1985
VOLUME
53
NUMBER
4
ACCURACY
OF FIXED
PARTIAL
DENTURES
with modification for reducing expansion to obtain a less-oversize casting should produce consistently accurate dental castings.
4,
REFERENCES
5
1.
2.
3.
Bauer, R. W., and Eden, G. T.: NADL survey of casting alloys in commercial dental laboratories. J Dent Res 56(Special issue B):214, 1’)77. Bauer, R. W.: Survey on the use of casting alloys in commercial dental laboratories. Part II: Ceramic alloys. Natl Assoc Dent Lab J 24:8, 1977. Eden. G. T., Franklin, 0. M., Powell, J. M., Ohta, Y., and
Particle-roughened Jeffrey Medical
L. Hudgins, College
D.D.S.,*
of Virginia,
School
of Dentistry,
Ph.D.,**
Richmond,
I
n 1973, Rochette’ introduced a perforated metal framework for resin-bonded fixed partial dentures that has been used with clinical success.2-4Thompson et al.’ modified the technique by selectively corroding nonprecious alloys to obtain a mechanically retentive surface for bonding retainers to etched enamel. The etched-metal innovation resolved several problems inherent in the Rochette design, and it became a popular technique.’ However, the etched-metal procedure possesses two limitations. It is restricted to nonprecious alloys, and the electrochemical etching procedure is technique sensitive. In 1983 Moon and Knap’ developed a roughened metal surface by using salt crystals to create voids in self-curing acrylic resin patterns. They reported that the particleroughened technique could be used for fabrication of resin-bonded metal retainers to avoid the limitations of the etched-metal approach. The purpose of the present study was to extend the research of Moon and Knap’ to accomplish the following goals: 1. Adapt the particle-roughened pattern technique to an indirect model system 2. Make particle-roughened retainers, bond them to extracted human teeth, and measure the force required to separate the retainer from the tooth
Recipient of the Stanley D. Tylman Research Award. Presented at the American Academy of Crown and Bridge tics, Chicago, Ill. *Graduate student, Fixed Prosthodontics. **Associate Professor and Director, Dental Materials. ***Director, Fixed Prosthodontics Graduate Program. THE
JOURNAL
OF PROSTHETIC
Kt3prznl reymts to: DR. JOHN A TESK NATIONAL BUREAU OF STANDARDS DENTAL AND MEDICAL MATERIALS POLYMER SCIENCE .&ND STANDARDS DIVISION WASHINGTOK, DC 20234
resin-bonded Peter C. Moon,
DENTISTRY
Prosthodon-
Dickson, G.: Fit of porcelain-fused-to-metal crown and bridge castings. J Dent Res 58:2360, 1979. Hollenback, G. M.: Science and Technique of the Cast Restoration. St. Louis, 1964, The C. V. Mosby Co. Phillips, R. W.: Skinner’s Science of Dental Materials. Philadelphia, 1973, W. B. Saunders Co.
retainers and Florian
J. Knap, D.D.S., M.S.***
Va.
3. Initiate a clinical study of the particle-roughened resin-bonded fixed partial denture
MATERIAL
AND METHODS
Extracted human teeth without restorations were debrided with scalers and stored in room-temperature distilled water. Thirty-two teeth were divided into four groups of eight: (1) maxillary incisors, (2) canines, (3) premolars, and (4) molars (excluding third molars). Acceptable tooth preparation guidelines were followed to provide maximal bond area with a rigid path of insertion.3,8,9 The incisors and canines had one proximal surface and the lingual surface prepared. The premolars and molars had a proximal and a lingual surface prepared with a rest seat on the appropriate marginal ridge. An impression of each tooth was made in Reprosil (L. D. Caulk Co., Milford, Del.), and a master cast was poured in die stone. The outline of each retainer pattern was traced on the die with a 0.5 mm red pencil. The tracing and pattern fabrication were performed with a x 10 binocular microscope. Duralay lubricant (Reliance Dental Mfg. Co., Worth, Ill.) was applied to each die with a No. 1 sable brush in an even thickness within the line denoting the pattern’s extension. Sieved salt (U. S. standard sieve series, Humboldt Mfg. Co., Chicago, Ill.) from 149 to 250 pm was sprinkled over the lubricated area.’ By careful application and tapping excess from the cast, an even, one-crystal layer that covered the lubricated area was obtained. Model spray (J. F. Jelenko and Co., Armonk, N.Y.) was lightly applied at a distance of 12 to 471
HUDGINS,
Fig. 1. Photomicrograph of Duralay pattern surface after alumina blasting. (Original magnification x20.) 18 inches to secure the crystals. It was imperative not to apply the spray heavily because the definition between crystals would have been lost. A No. 1 sable brush was dipped in a dappen dish of Duralay monomer, and a small ball of Duralay powder was picked up with the tip of the brush. The wet powder was carefully applied between crystals to prevent displacement. The wet Duralay powder was fluid enough to flow between the crystals but was not saturated with monomer, which triggered movement between crystals. The pattern was formed with repeated application of the Duralay and then allowed to cure. After the cure was completed, a plastic sprue was luted to the pattern with sticky wax and the pattern gently removed from the die. The pattern surface that had contacted the die was blasted for a total of 2 to 3 seconds with a micropencil and 60 pm alumina particles (Sterngold Inc., Stamford, Conn.). The pattern was rinsed with tap water to dissolve the salt, dried with compressed air, and examined under the microscope to ascertain removal of the salt crystals from the pattern (Fig. 1). Additional blasting, washing, and drying was performed if necessary but was kept to a minimum because overblasting erodes the roughness left by crystal removal. A loop was waxed to the lingual surface to 472
MOON,
AND
KN41’
Fig. 2. Schematic of Instron apparatus with mounted samples. F = Force; a = Instron grips; b = steel cable through loop on retainer; c = retainer; d = tooth surface; e = tray acrylic resin; f = acrylic resin sheet.
accommodate a ‘/s inch steel cable to test the bond strength with force directed along the long axis of the tooth (Fig. 2). Equal amounts of isopropyl alcohol and water were mixed in a dappen dish and vibrated over the aluminablasted surface with a No. 1 sable brush until it was wet. This step was necessary to overcome Duralay’s high surface tension as investment flowed across the roughened surface. The pattern was immediately vacuum invested with Biovest (Dentsply International, Inc.; York, Pa.). After it had set, the investment was burned out at 1400” F for 1 hour. A palladium-cobalt alloy (Chemodent Inc., Charlottesville, Va.) was melted with a gas-oxygen torch and centrifugally cast (Fig. 3). The retainer casting was divested, and the particle-roughened surface was examined under the microscope for blebs. The retainers were adapted to the stone dies and the fit verified on the extracted teeth. The tooth root was embedded in a cured ‘/s x 2 x 4 inch acrylic resin sheet to test tensile strength. To improve tooth stability, tray resin was shaped over all APRIL
1985
VOLUME
53
NUMBER
4
PARTICLE-ROIJGHENED
RETAINERS
shearing occurred (Fig. 2). The force required and the character of the bond failure were recorded.
RESULTS Incisois Seven maxillary central incisors and one large maxillary lateral incisor composed this group. A consistent occurrence was observed at bond failure; seven of eight samples fractured at the junction of the middle and incisal thirds of the teeth (Fig. 5). The one retainer that separated cleanly did so at the enamel/resin junction (Table I).
Canines Six retainers, Nos. 1, 2, 3, 4, 6, and 8, separated cleanly from the tooth (Table I). These six casting surfaces exhibited virtually intact resin coverage, which indicated that the bond between the resin and the etched enamel surface was the area of failure. Nos. 5 and 7 sheared the crown in the gingival third prior to retainer separation.
Premolars
Fig. 3. Photomicrograph of particle-roughened of cast retainer. (Original magnification X20.)
surface
surfaces of the tooth except where the retainer fit. The acrylic resin sheet provided a flat area for the Instron grips (Model TIC, Instron Corp., Canton, Mass.) to grasp the sample (Fig. 2). The tooth surface to be bonded was pumiced, washed, dried, and etched for 90 seconds. The acid was removed with tap water and the sample thoroughly dried. Comspan opaque liquid resins (L. D. Caulk Co.) were mixed and applied to the retainer and to the etched enamel. Trapping air bubbles on the retainer surface with liquid resin was kept to a minimum because poor application technique can decrease the bond strength. The liquid resin was applied to an edge of the casting and allowed to flow by gravity across the roughened surface. Comspan opaque filled resin pastes were mixed and carefully applied to the retainer, which was seated with firm pressure. At 2 minutes, the excess resin was gently removed with a hand instrument and at 4 minutes the seating pressure released. After curing for 10 minutes, the bonding sample was placed in distilled water and maintained at 32” C for 7 days (Fig. 4). The ‘/s inch cable was fitted through the loop on the retainer and the sample was mounted on the Instron machine. The force was directed along the long axis of the tooth at a crosshead speed of 0.05 inch/min until THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Five samples fractured at or near the cementoenamel junction and three retainers separated cleanly (Table I). Tooth fracture did not necessarily mean the sample had a high bond strength, because within this group the highest (170 lbs) and the lowest (93 lbs) values were instances of tooth breakage. When clean retainer separation was observed, the failure was at the enamel/resin interface.
Molars Sample No. 2 fractured through the roots, while Nos. 3 and 7 sheared the abutment cusp (Table I). The remaining samples were cleanly removed and displayed the same pattern as the preceding groups; a virtually continuous film of resin remained on the retainer and separation was at the etched enamel/resin interface. The Student t test was used to determine significant differences among the groups. Each pair of groups was statistically different at the 95% confidence level except for the canine/premolar comparison (.lO > p > .OS)and the premolar/molar pair (p > .lO).
Clinical
trial
During a 6-month period, a total of 27 particleroughened resin fixed partial dentures were placed for clinical patients at the Virginia Commonwealth University School of Dentistry. Two fixed partial dentures consisted of two pontics and two retainers while the remainder were one pontic and two retainers. The distribution was as follows: 16 anterior fixed partial dentures (15 maxillary and 1 mandibular) and 11 posterior fixed partial dentures (6 maxillary and 5 mandibular). 473
HUDGINS,
‘t100N,
Table I. Force required
for shearing
Fig. 5. Fracture site (a) of incisor group. ,F = Force. b = loop for bond testing.
(in pounds) Sample No.
Group
Incisors Canines Premolars Molars *Tooth
fractured
1
2
3
4
5
6
7
92* 112 143*
89’ 80 170’ 126*
70* 122 134* 200”
63* 108 100’ 62
90’ 119’ 119 168
114* 114 93’ 200
75 108’ 111 182%
100 prior
to retainer/tooth
-_______-___-..-8 Mean 73’ 60 106 145 ____~..
83.3 102.9 122.0 147.9 ~- --.-.-
SD 16.3 21.5 25.6 49.5 -- --
separation
The frameworks were made and cast by the principal investigator while porcelain addition was provided by the University staff: CM (Chemdent Metal Co., Charlottesville, W. Va.) alloy was used for 26 fixed partial dentures while one mandibular posterior fixed partial denture was made with a conventional type III gold alloy. Bonding was accomplished with Comspan bonding agent by dental students using the following protocol: 1. Isolation was achieved with a rubber dam. 2. The abutments were cleaned with flour of pumice, rinsed, and dried. 3. Etching liquid was applied to the abutment areas for 90 seconds, rinsed, and dried. 4. Unfilled resin was applied to the framework and the abutments. 5. Filled resin was applied to the framework. 6. The fixed partial denture was inserted and held firmly in place with finger pressure. 7. After 10 minutes the rubber dam was removed, the occlusion was adjusted, and final clean-up was accomplished.
474
KNAl
b
a
Fig. 4. Schematic of retainer fit to tooth. a = particleroughened surface; b = loop for bond testing.
AND
The 27 particle-roughened resin-bonded metal fixed partial dentures have been in service for 12 to 18 months. To date there has been one bond failure within the group: a maxillary anterior four-unit fixed partial denture was dislodged after 6 months of service. The bond failure occurred at the Comspan/enamel junction. The fixed partial denture was alumina-blasted clean and rebonded. The reason for failure was inadequate surface area covered by the retainers. The fixed partial denture will be remade to cover more area if bond failure recurs. The particle-roughened pattern technique has been adopted for making resin-bonded fixed partial dentures in the undergraduate dental clinics at the Virginia Commonwealth University School of Dentistry.* Since the original 27 fixed partial dentures were inserted, additional particle-roughened resin-bonded fixed partial dentures have been delivered. The total will increase as *The pattern fabrication technique has been simplified that described in this article, but the retainer surface
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1985
VOLUME
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recently from is similar.
NUMBER
4
PARTICLE-ROUGHENED
RETAINERS
the technique is disseminated, and records are being maintained for longitudinal studies. DISCUSSION Retentive strengths have been reported in which castings were removed from metal dies in an axial direction. Lorey and Myers,‘” Potts et al.,” and Kishimoto et al.“, ” used similar procedures to test partial and complete veneer crowns. Values ranged from 57.6 pounds for a canine three-quarter crown with grooves to 243 pounds for a premolar complete veneer crown without grooves. Premolar three-quarter and seveneighths crowns of various designs (with or without grooves) ranged from 92 to 135 pounds. The most retentive mesial-occlusal-distal onlay preparation for premolars averaged 80.2 pounds. Experience has shown that these crown designs provide years of service. All three studies provide data that probably compose a valid simulation of retentive values required clinically. If this assumption is correct then our average values of 83.3 to 147.9 pounds indicate that successcan be expected if the particle-roughened resinbonded technique is properly applied. Bond separation that occurs at the enamel/resin interface also supports this hypothesis, since the phenomenon has been observed experimentally and clinically with similarly successful resin-bonded fixed partial dentures.+” In addition, the retention of the roughened resin-bonded retainer surface equals or exceeds the retention of etched enamel/resin systems. . Tooth fracture occurred in 17 of 32 samples, which affects interpretation of the data. If fracture precedes bond separation, the true maximum bond strength has not been recorded for that tooth. The bond test is then a function of tooth morphology and/or test methods rather than of retainer-to-tooth bond strength (Fig. 5). Since teeth become brittle after extraction the averages reported in Table I are conservative compared with bond strengths attainable in vivo. Resin-bonded systems are dependent on the quality of the resin-to-etched enamel bond. Tooth-to-tooth variation of etched enamel bond strength occurs and cannot be anticipated prior to treatment. For example, there was more than a threefold difference in bond strength measured between molar sample Nos. 4 and 6, yet the teeth appear similar. The principles of framework design and mouth preparation for resin-bonded restorations have been described.-l,X,9These principles should be implemented so that (1) bonding should cover the maximum available surface area, and (2) retention and resistance form are maximized. Both factors improve bond strength because circumferential involvement increases the retention and resistance of retainers.” This point is emphasized by the
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Student t test, because the t values imply a significant difference between tooth types. However, the discriminating factors behind this difference are available bond area and the ability to increase resistance form on posterior teeth. The advantages of the particle-roughened resin-bonded technique over the etched-metal resin-bonded procedure are as follows: 1. The time-consuming and technique-sensitive electrochemical etching of the framework is eliminated, which decreases treatment time by one appointment since the framework try-in is obviated. 2. Contaminating the retentive surface by skin or liquid contact is minimized. 3. The retentive surface is more easily evaluated. 4. Commonly used dental alloys may be used for the framework. This should reduce difficulties such as casting, finishing, polishing, adjustments, and porcelain compatibility, which occur with the nonprecious alloys. 5. The technique uses readily available dental materials. The advantages of the etched-metal resin-bonded framework technique over the particle-roughened resinbonded procedure are (1) pattern fabrication and investment procedures are less technique-sensitive, and (2) smoother margins are achieved between the metal retainers and tooth structure. CONCLUSIONS 1. The particle-roughened metal retainer possesses sufficient mechanical bond strength for resin-bonded systems. 2. The weak link in metal-to-etched-enamel resinbonded systems in this study was the resin/etched enamel interface. 3. It is advisable to cover as much surface as feasible when resin-bonded retainers are etched to enamel. Graphic illustrations xe courtesy of Dr. Charles E. Janus, College of Virginia, Virginia Commonwealth Uniwwty.
Xledical
REFERENCES 1.
2.
3. 4.
5.
Rochetw, h. I,.: .4ttachment of a splint to enamel of lower anterior teeth using the acid etch technique and a cast metal framework. J PROSTHEX DENT 30~418, 1973. Howe, D. F., and Denehy, G. E.: Anterior fixed partial dentures utilizing the acid etch technique and a cast metal framework. ,J PROSTHLT DENT 37:28, 1977. Livaditis, G. J.: Cast metal resin-bonded retainers tor posterior teeth. J Am Dent Assoc 101:926, 1980. Eshleman, J. R., Moon, P. C., and Barnes, R. F.: Clinical evaluation of cast metal resin-bonded anterior fixed partial dentures. J PROWHET DENT 51:761. 1984. Thompson, V. P., Del Castillo, E., and Livaditis. G. J.: Resin bond to electrolytically etched nonprecious alloys for resin bonded
475
HUDGINS,
6.
7.
8.
9.
10. 11.
12.
MOON,
AND
KNAI’
prostheses. J Dent Res GO(Special issue A):377 (Abstr No. 265), 1981. Livaditis, G. J.~ and Thompson, V. P.: Etched castings: f\n improved mechanism for resin bonded retainers. ,J PKOS.~.H~ I’ r)EN.r 4~52, 1982. Moon, P. C.. and Knap, F. J.: Acid-etched bridge bond strength utilizing a new retention method. J Dent Res 62(Sprcial issue) (Abstr No. 296) 1983. Eshleman, J. R., Douglas, H. B., and Barnes. R F: The acid-etch bonded porcelain fused to metal bridge. Va Dent J 56:16, 1977. Wood, M., and Thompson, V. P.: Anterior etched cast resinbonded retainers: An overview of design, fabrication. and clinical use. Compendium Cont Ed Dent 4:3, 1983. Lorey, R. E., and Myers, G. E.: The retentive qualities of bridge retainers. ,J Am Dent Assoc 76~568, 1968. Potts, R. G., Shillingburg, H. T., and Duncanson, M. G.. Retention and resistance of preparations for cast restorations. J PROSTHET DENT 43:303, 1980. Kishimoto, kl., Shillingburg, Jr., H. T., and Duncanson, JI-.. hl
joints J. I. Nicholls, University
Ph.D.,*
of Washington,
and R. W. Lemm** School of Dentistry,
Seattle, Wash
T
he literature on dental soldering can be divided into two categories: (1) distortion that results from soldering and (2) strength of solder joints related to the various solders used to form the joint. Both pre- and postsoldering have been used to form solder joints. Postsoldering is needed to form a union between dissimilar alloys, one of which is a porcelain alloy. The literature on postsoldering is not extensive. Taylor and Teamer’ showed that the gap distance between the units to be joined affects the distortion or accuracy of the system as well as the strength. Ryge2 reported that a gap distance of less than 0.005 inch (0.123 mm) leads to greater porosity and an inherent strength decrease in the soldered joint. He also showed that less porosity results when the units are brought to soldering temperature before solder application. Stade et a1.3 demonstrated a consistent strength increase as gap size increased; oven-soldered units showed parent metal fractures at the larger gap sizes. Rasmussen et al4 postsoldered type III gold-palladium aliop. Their
*Professor, Resmrative Dentistry. **Certified
476
Dental
Technician,
Head
Restorative
Technician
research indicated that statistically significant strength changes were not found with gap distance for pre- and postsoldering, and the postsoldered joints were stronger. Staffanou et al5 studied several combinations of metals with both pre- and postsoldering. They stated that there were no major differences between the pre- and postsoldered joints. However, during testing some presolder specimens failed at such low values that data were not recorded. This did not occur with the postsoldered sequence. They concluded that consistently better solder joints could be accomplished with a high percent of success by using the more controllable postsoldering method. The most recent information regarding postsoldering is that reported by Monday and Asgar.6 In their study, specimens of Olympia (gold-palladium alloy, J.F. jelenko, New York, N.Y.) were cast from a mixture of 42% new metal and 58% old metal. Solder joints were formed by both pre- and p&soldering with both torch and oven soldering techniques. The results indicated that postsoldered joints were weaker than presoldered joints for the solders used. The strength reduction was 400% to 500%. The authors attributed the loss to a slow heating and cooling during the postsoldering cycle. The purpose of the present study was to determine the APRIL
1985
VOLUME
53
NUMBER
4