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Thermal removal of composite resin: Effect on rebonding etched metal
Thermal removal etched metal
of composite
resin: Effect on rebonding
Van B. Raywood, D.M.D.,* B. Ed Kanoy, Jr., M.A., D.DS,** Karen J. Bruggers, D.D.S.,*** and Steven B. Andreaus**** University of North Carolina, School of Dentistry, Chapel Hill, N.C. f f a correctly etched-metal, resin-bonded iixed partial denture debonds, one recommendation for reuse is to clean the prosthesis by oven burnout, then to recement it without reetching. The purpose of this study was to determine whether the tensile strength of the bond of composite resin cement to either electrolytically or chemically etched metal was affected by earlier removal of residual resin with a burnout procedure. Pairs of rods made of nickel-chromium-beryllium were electrolytically or chemically etched according to accepted techniques, then bonded end-to-end with an enamel bonding agent and composite resin cement in an alignment apparatus. The rods were stored for 24 hours in 37” C water, then debonded to determine the tensile bond strengths in megapascals. After debonding, the rods were placed in the burnout oven at 510° C for 30 minutes. The rods were then ultrasonically cleaned in ethyl alcohol for 6 minutes. The pairs were rinsed under running water and then rebonded and debonded nine more times under the same conditions. A linear regression analysis revealed that there was no statistically significant di%‘erence @ < 0.05) in the tensile strength of the bonds after repeated thermal cleanings and bondings. Correctly etched metal, resin-bonded fixed partial dentures may be recemented without re-etching after thermal cleaning without a statistically significant loss in the tensile strength of the bonds. (J PBOSTAET DENT 1990;63:289-91,)
A
&d-etched, resin-bonded fixed partial dentures have beenin wide usein dentistry for morethan 10years.1”4 Although many of these prosthesesfunction well, some problemsare inherent in their use.One problem is that one retainer may debond while another remains attached. A method for removal of the prosthesis has been demonstrated, by means of an ultrasonic unit with modified ultrasonic scaler tips.5 This method of removal does not damagethe retainer portion of the prosthesisand allows rebonding after appropriate cleaning and fif needed) reetching. Once a prosthesisis removed with no damageto the retainers, the next step is to determine how the prosthesis should be treated to be rebonded successfully.If the original etch was inadequate, the prosthesismust be reetched before ~emen~tion. The adequacy of the etched-metal surface may be determined by examination of the location
This investigation was supported with funds from NIW grant No. Z-SO7-RRO5333. Presented at the International Association for Dental Research, Montreal, Canada. *Assis~t Professor, Dep~tment of Fixed Pr~~~onti~. **Clinical Associate Professor, Department of Fixed Prosthodontics. ***Graduate Prosthodontics resident. ****Student Research Assistant. 10/l/15844
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
of the debondedcomp~i~ resin cement.A lack of resin on the etched-metal surface indicates that the original etch wasinadequate.4The presenceof compositeresin cement on the etched-metal surfaceindicates that the original etch wasadequate. The remaining compositeresin must be removed from the retainers before the procedure is continued. The prosthesismay then be re-etched. The previously etched retainers must be resurfaced to eliminate the original etch. Failure to remove the correctly etched surface will result in an overetch and a sign~cant loss of bond strength.2 An alternative to resufiacing and re-etching of the metal is to clean the residual resin in a manner that preservesthe original etch. Simonsenet al.* have reported that this may be accomplishedby placement of the prosthesis in an oven at 700’ C for 10 to 15 minutes, followed by ultrasonic cleaning in a soap solution for 5 minutes. Evaluation of the adequacy of the cleanedetched surfaces was basedon visual inspection. This study determinedwhether the tensilebond strength of the compositeresin cement to either electrolytically or chemically etched metal is affected by earlier removal of residual resin with a burnout procedure similar to that described by Simonsen.4
MATERIAL
AND METHODS
Matched pairs of rods 2 cm in length and 6.4 mm in diameter were cast in a nickel”chromium-be~lli~ alloy (LiteCast
B, Williams
Gold
Refining
Co., Inc., Buffalo,
289
HAYWOOD
ET AL.
4035-
.
30-
-y-e_.-.
25-
Q ---___
20-
---0 .
D
15-
I
‘j ( , ( , ( , 1 , , ( 0
1
2
3
4 5 6 Run Number
7
6
9
10
Fig. 1. Graph of linear regression analysis of tensile strength of bonds of properly electrolytically and chemically etched metal. N.Y.). To ensure uniform casting temperatures, castings were made by induction (Ticomat casting machine, Ticonium Company, Division of CMP Industries, Inc., Albany, N.Y.). The castings were bench cooled and, with a lathe, each cast-metal rod was then machined along its sides for removal of casting irregularities.6 The ends were machined flat and perpendicular to the long axis of the rod. A retaining hole was drilled 2mm from one end of the rod, perpendicular to and through the long axis. The rods were then air-fired twice in a porcelain furnace at 980” C to simulate degassing and initial porcelain application. The end opposite the retaining hole was air-abraded with 50 pm aluminum oxide. Pairs of rods were matched and numbered to maintain consistent pairing. The retaining hole, which was used to grasp and align the sample during cementation and testing of the tensile bond, was marked on one side only to allow exact replacement in the bonding apparatus and in the alignment apparatus. The pairs were then electrolytically or chemically etched according to accepted techniques.2* r With an accepted etching apparatus (Oxy-Etch, Oxy Dental Products, Inc., Hillside, N.J.) for 6 minutes at a current density of 200 mA/cmP (64 mA), the first pair was etched electrolytically in an 8 ~01% solution of HsS04 (sulfuric acid),8 (103 ml 96% sulfuric acid, 1000 ml distilled water, and 110 ml methanol). Then the rods were cleaned ultrasonically in 18% HCl (hydrochloric acid) for 10 minutes. The second and third pairs were etched chemically in a solution of HNOsHCl (nitric and hydrochloric acids, Assure-Etch, Williams Gold Refining Co.) for the recommended period of time (60 minutes). Because Assure-Etch material has a shelf-life of only 3 months, a fresh batch was mixed for the etching. To confirm that they were correctly etched, all samples were then rinsed with water and evaluated with scanning electron microscopy against known standards.
A bonding-alignment apparatus and technique were used as previously reported.6 The rods were aligned in the apparatus (according to the markings) in the same manner for each evaluation. With a calibrated syringe, equal amounts of the base and catalyst of the composite resin cement (Comspan Opaque, L.D. Caulk Company, Division of Dentsply International, Inc., Milford, Del.) were dispensed. The enamel bonding agent was first mixed and placed on the etched surfaces of the sample pair, and the composite resin cement was applied. The matched rods were then bonded at a premeasured 25 pm film thickness. The bonded sample remained in the apparatus for 15 minutes and was then stored in 37’ C water for 24 hours before testing. Evaluations of the strength of the bonds were completed with the use of a universal testing machine (Instron, Instron Corp., Canton, Mass.) at a crosshead speed of 1 mm/min. The position and orientation of the grasping holes in each rod and the repeatable bonding position resulting from the bonding alignment apparatus ensured a tensile failure. Tensile bond strengths were determined by dividing the recorded strength at failure (kg) by the calculated surface area of the bond (cm2). A conversion was made to megapascals (MPa). Residual composite resin cement on the debonded samples was removed by means of thermal treatment. The debonded samples were placed in an oven at 510” C (950’ F) for 30 minutes, followed by ultrasonic cleaning in ethyl alcohol for 6 minutes. The pairs were then rinsed under running water and rebonded and debonded under the same conditions nine more times. The means and standard deviations were determined for each of the 10 rebondingl debonding sequences, and an analysis of variance (ANOVA) was used to determine whether there was any significant difference among the three groups. Linear regression analysis was performed for each group to test whether repeated
MARCH
1990
VOLUME
6.9
NUMBER
3
REBONDING
OF ETCHED
METAL
cementations resulted in a decrease in the strength of the bond.
(MPa) Bond
RESULTS
1
The tensile strengths of the bonds and their meansand standard deviations are listed in Table I. A linear regression analysis (Fig. 1) revealed no statistically significant difference in the tensile strength of the bonds resulting from repeated thermal cleaningsand rebondingsfor any of the groups (p < 0.05). ANOVA showedthere wasno statistically significant difference among the strength of the bonds for the three groups (p < 0.05).
2 3 4 5 6 7 8 9 10 x
DISCUSSION The burnout technique chosenfor this study useda lower temperature and took a longer time than that previously reported.4 This was done in an attempt to minimize the potential for metal warpage or for porcelain discoloration. The combination of temperature and time wasdetermined by setting the oven at the desired temperature and then evaluating the sampleover time to ascertainthe period required to achieve the cleanest surface. The results of this study are in contrast with the results of a recent study that found a decreasein the strength of a surfacethat hasbeen rebonded.gIn that study, however, the temperature/time for cleaning was very different, a light-cured compositeresinwasused,and only one rebond waspossible.In addition, it wasnot clear how the castings werere-etched after being cleaned,possiblyresulting in an overetch. Up to this point, the large standard deviation in most studieshas been attributed to the variance in etching and bonding of different pieces of metal at different times. However, becausethis was a bonding of the sameetched surface in the sameorientation, other variables must be considered. The large standard deviation in the tensile strength of the bond in this study, which is consistentwith other studies,may actually indicate a weaknessin the laboratory designfor this and other apparatususedfor tensile debonding. In a future study, a universal joint attachment may be placed into the Y-fork debonding apparatus in an attempt to reduce the variance. This rebonding study may provide a useful prototype testing technique for evaluation of the dependability of any laboratory test mechanismbefore other variables are introduced, aswell asprovide clinical information for the rebonding of an etched-metal, resin-bonded prosthesis. In contrast to another study,7 the mean tensile bond strength of the electrolytically etched metal was slightly higher than the mean tensile bond strength of the chemically etched metal. However, our study concurred with that study in demonstrating that there is no statistically significant difference between the resulting tensile strength of
THE
JOURNAL
I. Tensile strength of bonds of etched samples
Table
OF
PROSTHETIC
DENTISTRY
SD PEE: Properly PEC: Properly
PEE
PEC
PEC
24.74 37.96 29.89 22.17 25.36 35.39 27.3 17.2 40.0 15.9 27.60 7.84
37.29 31.97
17.21 28.38 17.65 15.30 23.72 33.26 11.2 17.7 19.3 27.2 21.09 6.47
15.96 15.17 13.88 21.64 24.9 16.2 14.1 20.0 21.11 7.63
etched electrolytically. etched chemically.
the bondsof the electrolytically or chemically etchedmetal when etched correctly.
CONCLUSIONS With no statistically significant loss .of tensile bond strength, correctly etched-metal, resin-bonded prostheses may berecementedwithout re-etching after thermal cleanings alone. REFERENCES 1. Rochette AL. Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 1973;30:418-23. GJ, Thompson VP. Etched casting: an improved retentive 2. Livaditis mechanism for resin-bonded retainers. J PROSTHET DENT 1982;47:52-8. 3. Thompson VP, Del Castillo E, Livaditis GJ. Resin-bonded retainers. Part I: resin bond to electrolytically etched nonprecious alloys. J PROSTHET DENT 1983;50:771-9. 4. Simonsen R, Thompson VP, Barrack G. Etched cast restorations: clin-
5.
6.
I. 8.
9.
ical and laboratory techniques. Chicago: Quintessence Publishing, 1983:140-2. Jordan RD, KrelI KV, Aquilino SA, et al. Removal of acid-etched fixed partial dentures with modified ultrasonic scaler tips. J Am Dent Assoc 1986;112:505-7. Haywood VB, Lundeen TF, Taylor DF. Tensile bond strengths of Comspan to electrolytically etched metal with and without enamel bonding agent. Dent Mater 1987;3:29-32. Livaditis GJ. A chemical etching system for creating micromechanical retention in resin-bonded retainers. J PROSTHET DENT 1986;56:181-8. Haywood VB, Taylor DF, Lundeen TF, Andreaus SB. Concentration of solutions for electrolytically etching Rexillium HI. Dent Mater 1987:3:150-2. Naifeh D, Wendt SL Jr, Dormois LD, McKnight JP. A laboratory evaluation of rebond strengths of solid retainers of the acid-etched fixed partial denture. J PROSTHET DENT 1988;59:583-7.
Reprintrequests to: DR. VAN B. HAYWOOD SCHOOL OF DENTISTRY CB #7450 UNIVERSITY OF NORTH CAROLINA CHAPEL HILL, NC 27599-7450
291
of composite
resin: Effect on rebonding
Van B. Raywood, D.M.D.,* B. Ed Kanoy, Jr., M.A., D.DS,** Karen J. Bruggers, D.D.S.,*** and Steven B. Andreaus**** University of North Carolina, School of Dentistry, Chapel Hill, N.C. f f a correctly etched-metal, resin-bonded iixed partial denture debonds, one recommendation for reuse is to clean the prosthesis by oven burnout, then to recement it without reetching. The purpose of this study was to determine whether the tensile strength of the bond of composite resin cement to either electrolytically or chemically etched metal was affected by earlier removal of residual resin with a burnout procedure. Pairs of rods made of nickel-chromium-beryllium were electrolytically or chemically etched according to accepted techniques, then bonded end-to-end with an enamel bonding agent and composite resin cement in an alignment apparatus. The rods were stored for 24 hours in 37” C water, then debonded to determine the tensile bond strengths in megapascals. After debonding, the rods were placed in the burnout oven at 510° C for 30 minutes. The rods were then ultrasonically cleaned in ethyl alcohol for 6 minutes. The pairs were rinsed under running water and then rebonded and debonded nine more times under the same conditions. A linear regression analysis revealed that there was no statistically significant di%‘erence @ < 0.05) in the tensile strength of the bonds after repeated thermal cleanings and bondings. Correctly etched metal, resin-bonded fixed partial dentures may be recemented without re-etching after thermal cleaning without a statistically significant loss in the tensile strength of the bonds. (J PBOSTAET DENT 1990;63:289-91,)
A
&d-etched, resin-bonded fixed partial dentures have beenin wide usein dentistry for morethan 10years.1”4 Although many of these prosthesesfunction well, some problemsare inherent in their use.One problem is that one retainer may debond while another remains attached. A method for removal of the prosthesis has been demonstrated, by means of an ultrasonic unit with modified ultrasonic scaler tips.5 This method of removal does not damagethe retainer portion of the prosthesisand allows rebonding after appropriate cleaning and fif needed) reetching. Once a prosthesisis removed with no damageto the retainers, the next step is to determine how the prosthesis should be treated to be rebonded successfully.If the original etch was inadequate, the prosthesismust be reetched before ~emen~tion. The adequacy of the etched-metal surface may be determined by examination of the location
This investigation was supported with funds from NIW grant No. Z-SO7-RRO5333. Presented at the International Association for Dental Research, Montreal, Canada. *Assis~t Professor, Dep~tment of Fixed Pr~~~onti~. **Clinical Associate Professor, Department of Fixed Prosthodontics. ***Graduate Prosthodontics resident. ****Student Research Assistant. 10/l/15844
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
of the debondedcomp~i~ resin cement.A lack of resin on the etched-metal surface indicates that the original etch wasinadequate.4The presenceof compositeresin cement on the etched-metal surfaceindicates that the original etch wasadequate. The remaining compositeresin must be removed from the retainers before the procedure is continued. The prosthesismay then be re-etched. The previously etched retainers must be resurfaced to eliminate the original etch. Failure to remove the correctly etched surface will result in an overetch and a sign~cant loss of bond strength.2 An alternative to resufiacing and re-etching of the metal is to clean the residual resin in a manner that preservesthe original etch. Simonsenet al.* have reported that this may be accomplishedby placement of the prosthesis in an oven at 700’ C for 10 to 15 minutes, followed by ultrasonic cleaning in a soap solution for 5 minutes. Evaluation of the adequacy of the cleanedetched surfaces was basedon visual inspection. This study determinedwhether the tensilebond strength of the compositeresin cement to either electrolytically or chemically etched metal is affected by earlier removal of residual resin with a burnout procedure similar to that described by Simonsen.4
MATERIAL
AND METHODS
Matched pairs of rods 2 cm in length and 6.4 mm in diameter were cast in a nickel”chromium-be~lli~ alloy (LiteCast
B, Williams
Gold
Refining
Co., Inc., Buffalo,
289
HAYWOOD
ET AL.
4035-
.
30-
-y-e_.-.
25-
Q ---___
20-
---0 .
D
15-
I
‘j ( , ( , ( , 1 , , ( 0
1
2
3
4 5 6 Run Number
7
6
9
10
Fig. 1. Graph of linear regression analysis of tensile strength of bonds of properly electrolytically and chemically etched metal. N.Y.). To ensure uniform casting temperatures, castings were made by induction (Ticomat casting machine, Ticonium Company, Division of CMP Industries, Inc., Albany, N.Y.). The castings were bench cooled and, with a lathe, each cast-metal rod was then machined along its sides for removal of casting irregularities.6 The ends were machined flat and perpendicular to the long axis of the rod. A retaining hole was drilled 2mm from one end of the rod, perpendicular to and through the long axis. The rods were then air-fired twice in a porcelain furnace at 980” C to simulate degassing and initial porcelain application. The end opposite the retaining hole was air-abraded with 50 pm aluminum oxide. Pairs of rods were matched and numbered to maintain consistent pairing. The retaining hole, which was used to grasp and align the sample during cementation and testing of the tensile bond, was marked on one side only to allow exact replacement in the bonding apparatus and in the alignment apparatus. The pairs were then electrolytically or chemically etched according to accepted techniques.2* r With an accepted etching apparatus (Oxy-Etch, Oxy Dental Products, Inc., Hillside, N.J.) for 6 minutes at a current density of 200 mA/cmP (64 mA), the first pair was etched electrolytically in an 8 ~01% solution of HsS04 (sulfuric acid),8 (103 ml 96% sulfuric acid, 1000 ml distilled water, and 110 ml methanol). Then the rods were cleaned ultrasonically in 18% HCl (hydrochloric acid) for 10 minutes. The second and third pairs were etched chemically in a solution of HNOsHCl (nitric and hydrochloric acids, Assure-Etch, Williams Gold Refining Co.) for the recommended period of time (60 minutes). Because Assure-Etch material has a shelf-life of only 3 months, a fresh batch was mixed for the etching. To confirm that they were correctly etched, all samples were then rinsed with water and evaluated with scanning electron microscopy against known standards.
A bonding-alignment apparatus and technique were used as previously reported.6 The rods were aligned in the apparatus (according to the markings) in the same manner for each evaluation. With a calibrated syringe, equal amounts of the base and catalyst of the composite resin cement (Comspan Opaque, L.D. Caulk Company, Division of Dentsply International, Inc., Milford, Del.) were dispensed. The enamel bonding agent was first mixed and placed on the etched surfaces of the sample pair, and the composite resin cement was applied. The matched rods were then bonded at a premeasured 25 pm film thickness. The bonded sample remained in the apparatus for 15 minutes and was then stored in 37’ C water for 24 hours before testing. Evaluations of the strength of the bonds were completed with the use of a universal testing machine (Instron, Instron Corp., Canton, Mass.) at a crosshead speed of 1 mm/min. The position and orientation of the grasping holes in each rod and the repeatable bonding position resulting from the bonding alignment apparatus ensured a tensile failure. Tensile bond strengths were determined by dividing the recorded strength at failure (kg) by the calculated surface area of the bond (cm2). A conversion was made to megapascals (MPa). Residual composite resin cement on the debonded samples was removed by means of thermal treatment. The debonded samples were placed in an oven at 510” C (950’ F) for 30 minutes, followed by ultrasonic cleaning in ethyl alcohol for 6 minutes. The pairs were then rinsed under running water and rebonded and debonded under the same conditions nine more times. The means and standard deviations were determined for each of the 10 rebondingl debonding sequences, and an analysis of variance (ANOVA) was used to determine whether there was any significant difference among the three groups. Linear regression analysis was performed for each group to test whether repeated
MARCH
1990
VOLUME
6.9
NUMBER
3
REBONDING
OF ETCHED
METAL
cementations resulted in a decrease in the strength of the bond.
(MPa) Bond
RESULTS
1
The tensile strengths of the bonds and their meansand standard deviations are listed in Table I. A linear regression analysis (Fig. 1) revealed no statistically significant difference in the tensile strength of the bonds resulting from repeated thermal cleaningsand rebondingsfor any of the groups (p < 0.05). ANOVA showedthere wasno statistically significant difference among the strength of the bonds for the three groups (p < 0.05).
2 3 4 5 6 7 8 9 10 x
DISCUSSION The burnout technique chosenfor this study useda lower temperature and took a longer time than that previously reported.4 This was done in an attempt to minimize the potential for metal warpage or for porcelain discoloration. The combination of temperature and time wasdetermined by setting the oven at the desired temperature and then evaluating the sampleover time to ascertainthe period required to achieve the cleanest surface. The results of this study are in contrast with the results of a recent study that found a decreasein the strength of a surfacethat hasbeen rebonded.gIn that study, however, the temperature/time for cleaning was very different, a light-cured compositeresinwasused,and only one rebond waspossible.In addition, it wasnot clear how the castings werere-etched after being cleaned,possiblyresulting in an overetch. Up to this point, the large standard deviation in most studieshas been attributed to the variance in etching and bonding of different pieces of metal at different times. However, becausethis was a bonding of the sameetched surface in the sameorientation, other variables must be considered. The large standard deviation in the tensile strength of the bond in this study, which is consistentwith other studies,may actually indicate a weaknessin the laboratory designfor this and other apparatususedfor tensile debonding. In a future study, a universal joint attachment may be placed into the Y-fork debonding apparatus in an attempt to reduce the variance. This rebonding study may provide a useful prototype testing technique for evaluation of the dependability of any laboratory test mechanismbefore other variables are introduced, aswell asprovide clinical information for the rebonding of an etched-metal, resin-bonded prosthesis. In contrast to another study,7 the mean tensile bond strength of the electrolytically etched metal was slightly higher than the mean tensile bond strength of the chemically etched metal. However, our study concurred with that study in demonstrating that there is no statistically significant difference between the resulting tensile strength of
THE
JOURNAL
I. Tensile strength of bonds of etched samples
Table
OF
PROSTHETIC
DENTISTRY
SD PEE: Properly PEC: Properly
PEE
PEC
PEC
24.74 37.96 29.89 22.17 25.36 35.39 27.3 17.2 40.0 15.9 27.60 7.84
37.29 31.97
17.21 28.38 17.65 15.30 23.72 33.26 11.2 17.7 19.3 27.2 21.09 6.47
15.96 15.17 13.88 21.64 24.9 16.2 14.1 20.0 21.11 7.63
etched electrolytically. etched chemically.
the bondsof the electrolytically or chemically etchedmetal when etched correctly.
CONCLUSIONS With no statistically significant loss .of tensile bond strength, correctly etched-metal, resin-bonded prostheses may berecementedwithout re-etching after thermal cleanings alone. REFERENCES 1. Rochette AL. Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 1973;30:418-23. GJ, Thompson VP. Etched casting: an improved retentive 2. Livaditis mechanism for resin-bonded retainers. J PROSTHET DENT 1982;47:52-8. 3. Thompson VP, Del Castillo E, Livaditis GJ. Resin-bonded retainers. Part I: resin bond to electrolytically etched nonprecious alloys. J PROSTHET DENT 1983;50:771-9. 4. Simonsen R, Thompson VP, Barrack G. Etched cast restorations: clin-
5.
6.
I. 8.
9.
ical and laboratory techniques. Chicago: Quintessence Publishing, 1983:140-2. Jordan RD, KrelI KV, Aquilino SA, et al. Removal of acid-etched fixed partial dentures with modified ultrasonic scaler tips. J Am Dent Assoc 1986;112:505-7. Haywood VB, Lundeen TF, Taylor DF. Tensile bond strengths of Comspan to electrolytically etched metal with and without enamel bonding agent. Dent Mater 1987;3:29-32. Livaditis GJ. A chemical etching system for creating micromechanical retention in resin-bonded retainers. J PROSTHET DENT 1986;56:181-8. Haywood VB, Taylor DF, Lundeen TF, Andreaus SB. Concentration of solutions for electrolytically etching Rexillium HI. Dent Mater 1987:3:150-2. Naifeh D, Wendt SL Jr, Dormois LD, McKnight JP. A laboratory evaluation of rebond strengths of solid retainers of the acid-etched fixed partial denture. J PROSTHET DENT 1988;59:583-7.
Reprintrequests to: DR. VAN B. HAYWOOD SCHOOL OF DENTISTRY CB #7450 UNIVERSITY OF NORTH CAROLINA CHAPEL HILL, NC 27599-7450
291