L e a k a g e of a l i g h t - a c t i v a t e d base: Effect of dentin bonding agents K a i C h i u C h a n , D . D . S . , M.S.,* a n d E d w a r d
J. S w i f t , Jr., D . M . D . , M.S.**
The University of Iowa, College of Dentistry, Iowa City, Iowa This s t u d y i n v e s t i g a t e d the s e a l i n g properties of C a v a l i t e l i g h t - a c t i v a t e d b a s e m a t e r i a l in conjunction w i t h various dentin bonding agents. Thirty e x t r a c t e d m o l a r s w e r e s e l e c t e d and cleaned. Slot preparations w i t h s t a n d a r d d i m e n s i o n s w e r e made. The p r e p a r e d c a v i t i e s w e r e filled w i t h C a v a l i t e m a t e r i a l after application of the dentin bonding a g e n t s Gluma, P r i s m a U n i v e r s a l Bond, Scotchbond 2, and Tenure. S a m p l e s w e r e t h e r m o c y c l e d for 180 c y c l e s b e t w e e n 3 ° C and 60 ° C, then i m m e r s e d in 0.05% c r y s t a l violet solution for 2 hours. The s a m p l e s w e r e e m b e d d e d in clear c a s t i n g resin, sectioned, and e x a m i n e d w i t h a light microscope. Results indicated that C a v a l i t e m a t e r i a l used alone, w i t h o u t a dentin bonding agent, a l l o w e d the g r e a t e s t d e g r e e of dye penetration. C a v a l i t e m a t e r i a l w i t h Tenure bonding a g e n t had the l o w e s t d e g r e e of l e a k a g e . C a v a l i t e m a t e r i a l used w i t h Scotchbond 2, Gluma, or P r i s m a U n i v e r s a l Bond bonding a g e n t s a l l o w e d an i n t e r m e d i a t e d e g r e e of dye penetration. According to an a n a l y s i s of variance, h o w e v e r , there w a s no s t a t i s t i c a l difference in the effects o f Tenure, Scotchbond 2, and Gluma bonding agents. (J PROSTHET DENT 1991;65:790-2.)
I n deep cavity preparations, especially when postoperative sensitivity is expected, the placement of a base to protect the dental pulp from further irritation is recommended.; Chemical toxicity from acid contamination or the ingredients of the restorative material is a less significant factor in pulpal injury than bacterial leakage around the restoration margins. 2 The ability of a base to seal the dentin is essential to adequate pulp protection. Historically, base materials have been chemically cured. Recently, however, light-activated bases have been introduced. 3 The properties of these materials, including their sealing capabilities, have not been thoroughly investigated. The setting of the light-activated basing materials should be similar to the setting of the composite resins, which shrink during polymerization and allow leakage at nonenamel margins. 4' 5 Therefore, leakage of the light-activated basing materials and potential methods for reducing leakage should be considered. This study was done to determine whether dentin bonding agents can improve the seal of light-activated bases. MATERIAL
AND METHODS
Thirty noncarious extracted molars were selected and thoroughly cleaned. The entire surface of each tooth was covered with an acid-resistant varnish. Self-curing acrylic resin was then placed on the occlusal surfaces and the root apices of each tooth. With a 2DT diamond bur (Teledyne
*Professor, Department of Operative Dentistry. **Assistant Professor, Department of Operative Dentistry. 10/1/27551
790
Fig. 1. Cavities "restored" with Cavalite material after treatment with dentin bonding agents. Left, Tenure bonding agent, degree I dye penetration; right, Gluma bonding agent, degree 3 dye penetration.
Densco, Denver, Colo.) used at high speed with water coolant, slots of approximately 1.5 mm in depth and 3 mm in width were cut on the buccal and lingual surfaces of each tooth. The slots were cut so that the enamel was completely removed and dentin was exposed in the slot. Cavities with a width of 1.5 mm, depth of 2 mm, and a length of 2.5 mm were prepared in the dentin on the buccal and lingual slots of each tooth with a No. 55 carbide bur (Midwest Dental Products, Des Plaines, Ill.) used at high speed with water coolant. A vertical groove was cut on the buccal surface next to the slot and marks were placed on the apices of the teeth to identify the type of dentin bonding agent used.
J U N E 1991
V O L U M E 65
NUMBER 6
LEAKAGE OF A LIGHT-ACTIVATED BASE
Table I. ANOVA (general linear model procedure) of dye penetration of samples with and without treatment of dentin bonding agents Source
DF
Model Error Corrected total
5 54 59
SS
MS
F value
PR > F
53.1500 10.6300 11.48 50.0000 0.9259 103.1500
0.0001
DF, Degrees of freedum; SS, sum of squares; MS, mean squares; PR, probability.
Table II. Duncan's multiple range test for degree of dye penetration of samples with and without treatment of dentin bonding agents Group
N
Mean
Control P GR S GN T
10 10 10 10 10 10
4.0 2.5 1.9 1.8 1.8 1.0
Grouping*
A B BC BC BC C
P, Prisma Universal Bond; GR, Gluma with unfilled resin; S, Scotchbond 2; GN, Gluma without unfilled resin; T, Tenure. *Means with same letter are not significantly different.
Ten cavities were restored with Cavalite (Kerr, Romulus, Mich.) light-cured base material without dentin bonding treatment, serving as the control group. Four dentin bonding agents, Gluma (Miles Dental, South Bend, Ind.); Scotchbond 2 (3M Dental Products Division, St. Paul, Minn.); Tenure (Den-Mat Corporation, Santa Maria, Calif.); and Prisma Universal Bond (L. D. Caulk Company, Milford, Del.), were used according to manufacturers' directions to treat the cavities before they were restored with Cavalite material. Twenty cavities were treated with the Gluma bonding system. Ten of these cavities were restored without use of the Gluma sealer (unfilled resin) to examine the effect of the sealer. The Cavalite restorations were polymerized for 40 seconds with a Visilux light-curing unit (3M Dental Products Division) with a voltage of 117-60 Hz and current of 1.1 amps. The teeth were then stored in 100% humidity at room temperature for 24 hours. Excess was removed from samples with a football-shaped finishing bur (Teledyne Densco) in a high-speed handpiece. Samples were cleaned with air-water spray and cycled in a thermocycling machine between 3 ° C and 60 ° C in water for 180 cycles with a dwell time of 30 seconds. The samples were then immersed in 0.05 % crystal violet solution for 2 hours at room temperature. The specimens were removed from the staining solution and dried with paper towels and gauze. They were embedded in clear liquid casting resin (Chemco Resin Crafts, Fields Landing, Calif.), which was allowed to set for
THE JOURNAL OF PROSTHETIC DENTISTRY
F i g . 2. Prisma Universal Bond bonding agent (left) and Scotchbond 2 bonding agent (right) both allowed degree 2 dye penetration.
1 week. At that time, the specimens were sectioned through the restorations with a diamond disk on a sectioning machine (Gillings Hamco, Hamco Machine, Inc., Rochester, N.Y.). The sections were examined under a reflected light microscope (Tessovas, Carl Zeiss, Inc., Thornwood, N.Y.) and the degree of dye penetration of all of the samples was recorded. The degree of dye penetration was determined on the basis of the criteria described by Khera and Chan 6 as follows. 0-No leakage (no dye penetration) 1-Less than and up to one half the depth of the preparation penetrated by the dye 2-More than one half of the depth of the cavity penetrated by the dye but not to the junction of the axial and occlusal or cervical walls 3-Dye penetration to the junction of the axial and occlusal or cervical wall but not including the axial wall 4-Dye penetration including the axial wall The corrected data were subjected to one-way analysis of variance (ANOVA) and Duncan's multiple range test. RESULTS
The least dye penetration occurred in cavity preparations treated with the Tenure dentin bonding system before restoration with Cavalite material. However, according to the ANOVA in Table I and Duncan's multiple range test in Table II, this degree of dye penetration did not differ significantly from that in the Scotchbond 2 and Gluma bonding agent groups. It was significantly less than that in the Prisma Universal Bond bonding agent group. No statistically significant difference in mean dye penetration was found among the Scotchbond 2, Prisma Universal Bond, and Gluma bonding agents groups. There was no difference for the Gluma bonding system used with or without the unfilled resin component (Figs. 1 and 2).
791
CHAN AND SWIFT
All dentin bonding systems significantly reduced the dye penetration in untreated cavities restored with Cavalite material alone. DISCUSSION Microleakage of amalgam and composite resin restorations has been examined extensively. Microleakage of conventional amalgam restorations at the margins will diminish with aging, and the application of cavity varnish reduces marginal microleakage. 7 The microleakage of composite resin restorations can be controlled by using the acid etch technique. However, microleakage is a problem at nonenamel surfaces where enamel etching cannot be used. This microleakage can result in marginal staining, sensitivity, and recurrent caries, s Microleakage is a particular problem with margins in cementum or dentin, where polymerization shrinkage of the composite resin pulls it away from the margins, causing contraction gaps. 9 The setting of resin-based, light-activated bases probably involves a similar polymerization contraction. Therefore, the prior application of dentin bonding agents should be considered to reduce the effects of shrinkage and to maintain a better seal. In our study, Cavalite light-activated basing material allowed severe leakage. Leakage was significantly reduced by using any type of dentin bonding agent. The least amount of leakage occurred with Tenure bonding agent, a system that uses an aluminum oxalate/ nitric acid dentin conditioner, 1° although it did not differ significantly from Scotchbond 2 or Gluma bonding agents. The dentin bonding agents probably counteract the polymerization contraction forces of the resin polymer, thus reducing the size of the contraction gap at the edges of the basing material.
2. This polymerization shrinkage can cause contraction gaps at the margins of the base, reducing its sealing effectiveness. 3. Use of dentin bonding agents before placement of a light-activated base reduces leakage around the base. 4. The most effective dentin bonding system for reduction of dye penetration in this study was the Tenure material, although it did not differ significantly from the Scotchbond 2 and Gluma materials. REFERENCES 1. Grajower R, Hirshfeld Z, Zalkind M. Compatibility of a composite resin with pulp insulating materials. A scanning electron microscope study. J PROSTHETDENT 1974;12:70-7. 2. Cox CF, Keall CL, Keall HJ, Ostro E, Bergenholtz G. Biocompatibility of surface-sealed dental materials against exposed pulps. J PROSTHET DENT 1987;57:1-8. 3. Draheim RN. Cavity bases, liners and varnishes: a clinical perspective. Am J Dent 1988;1:63-6. 4. Pintado MR, Douglas WH. The comparison of microleakage between two different dentin bonding resin systems. Quintessence Int 1988; 19:905-7. 5. Wenner KW, Fairhurst CW, Morris CF, Hawkins IK, Ringle RD. Microleakagc of root restorations. J Am Dent Assoc 1989;117:825-8. 6. Khera SC, Chan KC. Microleakage and enamel finish. J PROSTHET DENT 1978;39:414-9. 7. Gottlieb EW, Retief DH, Bradley EL. Microleakage of conventional and high-copper amalgam restorations. J PROSTHETDENT 1985;53:355-61. 8. Triadan H. When is microleakage a real clinical problem? Oper Dent 1987;12:153-7. 9. Br~innstrSm M. Infection beneath composite resin restorations: can it be avoided? Oper Dent 1987;12:158-63. 10. Gwinnett AJ. Aluminum oxalate for dentin bonding. An SEM study. Am J Dent 1988;1:5-8. Reprint requests to: DR. KAI CHIU CHAN COLLEGE OF DENTISTRY UNIVERSITYOF IOWA IOWACITY, IA 52242
CONCLUSIONS 1. Like composite resin restorative materials, light-activated base materials shrink during polymerization.
B o u n d v o l u m e s a v a i l a b l e to s u b s c r i b e r s
Bound volumes of THE JOURNALOF PROSTHETICDENTISTRYare available to subscribers (only) for the 1990 issues from the publisher at a cost of $44.00 ($56.00 international) for Vol. 63 (January-June) and Vol. 64 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 61 and 62 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351. S u b s c r i p t i o n s m u s t be in f o r c e to qualify. B o u n d v o l u m e s are not a v a i l a b l e in p l a c e of a r e g u l a r JOURNAL s u b s c r i p t i o n .
792
JUNE 1 9 9 1
VOLUME 65
NUMBER 6
J. S w i f t , Jr., D . M . D . , M.S.**
The University of Iowa, College of Dentistry, Iowa City, Iowa This s t u d y i n v e s t i g a t e d the s e a l i n g properties of C a v a l i t e l i g h t - a c t i v a t e d b a s e m a t e r i a l in conjunction w i t h various dentin bonding agents. Thirty e x t r a c t e d m o l a r s w e r e s e l e c t e d and cleaned. Slot preparations w i t h s t a n d a r d d i m e n s i o n s w e r e made. The p r e p a r e d c a v i t i e s w e r e filled w i t h C a v a l i t e m a t e r i a l after application of the dentin bonding a g e n t s Gluma, P r i s m a U n i v e r s a l Bond, Scotchbond 2, and Tenure. S a m p l e s w e r e t h e r m o c y c l e d for 180 c y c l e s b e t w e e n 3 ° C and 60 ° C, then i m m e r s e d in 0.05% c r y s t a l violet solution for 2 hours. The s a m p l e s w e r e e m b e d d e d in clear c a s t i n g resin, sectioned, and e x a m i n e d w i t h a light microscope. Results indicated that C a v a l i t e m a t e r i a l used alone, w i t h o u t a dentin bonding agent, a l l o w e d the g r e a t e s t d e g r e e of dye penetration. C a v a l i t e m a t e r i a l w i t h Tenure bonding a g e n t had the l o w e s t d e g r e e of l e a k a g e . C a v a l i t e m a t e r i a l used w i t h Scotchbond 2, Gluma, or P r i s m a U n i v e r s a l Bond bonding a g e n t s a l l o w e d an i n t e r m e d i a t e d e g r e e of dye penetration. According to an a n a l y s i s of variance, h o w e v e r , there w a s no s t a t i s t i c a l difference in the effects o f Tenure, Scotchbond 2, and Gluma bonding agents. (J PROSTHET DENT 1991;65:790-2.)
I n deep cavity preparations, especially when postoperative sensitivity is expected, the placement of a base to protect the dental pulp from further irritation is recommended.; Chemical toxicity from acid contamination or the ingredients of the restorative material is a less significant factor in pulpal injury than bacterial leakage around the restoration margins. 2 The ability of a base to seal the dentin is essential to adequate pulp protection. Historically, base materials have been chemically cured. Recently, however, light-activated bases have been introduced. 3 The properties of these materials, including their sealing capabilities, have not been thoroughly investigated. The setting of the light-activated basing materials should be similar to the setting of the composite resins, which shrink during polymerization and allow leakage at nonenamel margins. 4' 5 Therefore, leakage of the light-activated basing materials and potential methods for reducing leakage should be considered. This study was done to determine whether dentin bonding agents can improve the seal of light-activated bases. MATERIAL
AND METHODS
Thirty noncarious extracted molars were selected and thoroughly cleaned. The entire surface of each tooth was covered with an acid-resistant varnish. Self-curing acrylic resin was then placed on the occlusal surfaces and the root apices of each tooth. With a 2DT diamond bur (Teledyne
*Professor, Department of Operative Dentistry. **Assistant Professor, Department of Operative Dentistry. 10/1/27551
790
Fig. 1. Cavities "restored" with Cavalite material after treatment with dentin bonding agents. Left, Tenure bonding agent, degree I dye penetration; right, Gluma bonding agent, degree 3 dye penetration.
Densco, Denver, Colo.) used at high speed with water coolant, slots of approximately 1.5 mm in depth and 3 mm in width were cut on the buccal and lingual surfaces of each tooth. The slots were cut so that the enamel was completely removed and dentin was exposed in the slot. Cavities with a width of 1.5 mm, depth of 2 mm, and a length of 2.5 mm were prepared in the dentin on the buccal and lingual slots of each tooth with a No. 55 carbide bur (Midwest Dental Products, Des Plaines, Ill.) used at high speed with water coolant. A vertical groove was cut on the buccal surface next to the slot and marks were placed on the apices of the teeth to identify the type of dentin bonding agent used.
J U N E 1991
V O L U M E 65
NUMBER 6
LEAKAGE OF A LIGHT-ACTIVATED BASE
Table I. ANOVA (general linear model procedure) of dye penetration of samples with and without treatment of dentin bonding agents Source
DF
Model Error Corrected total
5 54 59
SS
MS
F value
PR > F
53.1500 10.6300 11.48 50.0000 0.9259 103.1500
0.0001
DF, Degrees of freedum; SS, sum of squares; MS, mean squares; PR, probability.
Table II. Duncan's multiple range test for degree of dye penetration of samples with and without treatment of dentin bonding agents Group
N
Mean
Control P GR S GN T
10 10 10 10 10 10
4.0 2.5 1.9 1.8 1.8 1.0
Grouping*
A B BC BC BC C
P, Prisma Universal Bond; GR, Gluma with unfilled resin; S, Scotchbond 2; GN, Gluma without unfilled resin; T, Tenure. *Means with same letter are not significantly different.
Ten cavities were restored with Cavalite (Kerr, Romulus, Mich.) light-cured base material without dentin bonding treatment, serving as the control group. Four dentin bonding agents, Gluma (Miles Dental, South Bend, Ind.); Scotchbond 2 (3M Dental Products Division, St. Paul, Minn.); Tenure (Den-Mat Corporation, Santa Maria, Calif.); and Prisma Universal Bond (L. D. Caulk Company, Milford, Del.), were used according to manufacturers' directions to treat the cavities before they were restored with Cavalite material. Twenty cavities were treated with the Gluma bonding system. Ten of these cavities were restored without use of the Gluma sealer (unfilled resin) to examine the effect of the sealer. The Cavalite restorations were polymerized for 40 seconds with a Visilux light-curing unit (3M Dental Products Division) with a voltage of 117-60 Hz and current of 1.1 amps. The teeth were then stored in 100% humidity at room temperature for 24 hours. Excess was removed from samples with a football-shaped finishing bur (Teledyne Densco) in a high-speed handpiece. Samples were cleaned with air-water spray and cycled in a thermocycling machine between 3 ° C and 60 ° C in water for 180 cycles with a dwell time of 30 seconds. The samples were then immersed in 0.05 % crystal violet solution for 2 hours at room temperature. The specimens were removed from the staining solution and dried with paper towels and gauze. They were embedded in clear liquid casting resin (Chemco Resin Crafts, Fields Landing, Calif.), which was allowed to set for
THE JOURNAL OF PROSTHETIC DENTISTRY
F i g . 2. Prisma Universal Bond bonding agent (left) and Scotchbond 2 bonding agent (right) both allowed degree 2 dye penetration.
1 week. At that time, the specimens were sectioned through the restorations with a diamond disk on a sectioning machine (Gillings Hamco, Hamco Machine, Inc., Rochester, N.Y.). The sections were examined under a reflected light microscope (Tessovas, Carl Zeiss, Inc., Thornwood, N.Y.) and the degree of dye penetration of all of the samples was recorded. The degree of dye penetration was determined on the basis of the criteria described by Khera and Chan 6 as follows. 0-No leakage (no dye penetration) 1-Less than and up to one half the depth of the preparation penetrated by the dye 2-More than one half of the depth of the cavity penetrated by the dye but not to the junction of the axial and occlusal or cervical walls 3-Dye penetration to the junction of the axial and occlusal or cervical wall but not including the axial wall 4-Dye penetration including the axial wall The corrected data were subjected to one-way analysis of variance (ANOVA) and Duncan's multiple range test. RESULTS
The least dye penetration occurred in cavity preparations treated with the Tenure dentin bonding system before restoration with Cavalite material. However, according to the ANOVA in Table I and Duncan's multiple range test in Table II, this degree of dye penetration did not differ significantly from that in the Scotchbond 2 and Gluma bonding agent groups. It was significantly less than that in the Prisma Universal Bond bonding agent group. No statistically significant difference in mean dye penetration was found among the Scotchbond 2, Prisma Universal Bond, and Gluma bonding agents groups. There was no difference for the Gluma bonding system used with or without the unfilled resin component (Figs. 1 and 2).
791
CHAN AND SWIFT
All dentin bonding systems significantly reduced the dye penetration in untreated cavities restored with Cavalite material alone. DISCUSSION Microleakage of amalgam and composite resin restorations has been examined extensively. Microleakage of conventional amalgam restorations at the margins will diminish with aging, and the application of cavity varnish reduces marginal microleakage. 7 The microleakage of composite resin restorations can be controlled by using the acid etch technique. However, microleakage is a problem at nonenamel surfaces where enamel etching cannot be used. This microleakage can result in marginal staining, sensitivity, and recurrent caries, s Microleakage is a particular problem with margins in cementum or dentin, where polymerization shrinkage of the composite resin pulls it away from the margins, causing contraction gaps. 9 The setting of resin-based, light-activated bases probably involves a similar polymerization contraction. Therefore, the prior application of dentin bonding agents should be considered to reduce the effects of shrinkage and to maintain a better seal. In our study, Cavalite light-activated basing material allowed severe leakage. Leakage was significantly reduced by using any type of dentin bonding agent. The least amount of leakage occurred with Tenure bonding agent, a system that uses an aluminum oxalate/ nitric acid dentin conditioner, 1° although it did not differ significantly from Scotchbond 2 or Gluma bonding agents. The dentin bonding agents probably counteract the polymerization contraction forces of the resin polymer, thus reducing the size of the contraction gap at the edges of the basing material.
2. This polymerization shrinkage can cause contraction gaps at the margins of the base, reducing its sealing effectiveness. 3. Use of dentin bonding agents before placement of a light-activated base reduces leakage around the base. 4. The most effective dentin bonding system for reduction of dye penetration in this study was the Tenure material, although it did not differ significantly from the Scotchbond 2 and Gluma materials. REFERENCES 1. Grajower R, Hirshfeld Z, Zalkind M. Compatibility of a composite resin with pulp insulating materials. A scanning electron microscope study. J PROSTHETDENT 1974;12:70-7. 2. Cox CF, Keall CL, Keall HJ, Ostro E, Bergenholtz G. Biocompatibility of surface-sealed dental materials against exposed pulps. J PROSTHET DENT 1987;57:1-8. 3. Draheim RN. Cavity bases, liners and varnishes: a clinical perspective. Am J Dent 1988;1:63-6. 4. Pintado MR, Douglas WH. The comparison of microleakage between two different dentin bonding resin systems. Quintessence Int 1988; 19:905-7. 5. Wenner KW, Fairhurst CW, Morris CF, Hawkins IK, Ringle RD. Microleakagc of root restorations. J Am Dent Assoc 1989;117:825-8. 6. Khera SC, Chan KC. Microleakage and enamel finish. J PROSTHET DENT 1978;39:414-9. 7. Gottlieb EW, Retief DH, Bradley EL. Microleakage of conventional and high-copper amalgam restorations. J PROSTHETDENT 1985;53:355-61. 8. Triadan H. When is microleakage a real clinical problem? Oper Dent 1987;12:153-7. 9. Br~innstrSm M. Infection beneath composite resin restorations: can it be avoided? Oper Dent 1987;12:158-63. 10. Gwinnett AJ. Aluminum oxalate for dentin bonding. An SEM study. Am J Dent 1988;1:5-8. Reprint requests to: DR. KAI CHIU CHAN COLLEGE OF DENTISTRY UNIVERSITYOF IOWA IOWACITY, IA 52242
CONCLUSIONS 1. Like composite resin restorative materials, light-activated base materials shrink during polymerization.
B o u n d v o l u m e s a v a i l a b l e to s u b s c r i b e r s
Bound volumes of THE JOURNALOF PROSTHETICDENTISTRYare available to subscribers (only) for the 1990 issues from the publisher at a cost of $44.00 ($56.00 international) for Vol. 63 (January-June) and Vol. 64 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 61 and 62 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351. S u b s c r i p t i o n s m u s t be in f o r c e to qualify. B o u n d v o l u m e s are not a v a i l a b l e in p l a c e of a r e g u l a r JOURNAL s u b s c r i p t i o n .
792
JUNE 1 9 9 1
VOLUME 65
NUMBER 6
