KEMP-SCHOLTEANDDAVIDSON

3. Vanherle G, Verschueren M, Lambrechts P, Braem M. Clinical investigation of dental adhesive systems. Part I. In vivo study. J PROSWET 15.

DENT 198655157-63.

4. Kemp-Scholte CM, Davidson CL. Marginal sealing of curing contraction gaps in class Vcomposite resin restorations. JDent Res 1988;67:8415. 5. Hansen

6. 7. 8. 9.

10. 11.

12.

16.

EK, Asmussen E. A comparative study of dentin adhesives. Stand J Dent Res 1985;93:280-7. Munksgaard EC, Irie M, Asmussen E. Dentin-polymer bond promoted by Gluma and various resins. J Dent Res 1985;64:1409-11. Komatsu M, Finger W. Dentin bonding agents: correlation of early bond strength with margin gaps. Dent Mat 1986;2:25’7-62. Davidson CL. Resisting the curing contraction with adhesive composites. J PROSTHET DENT 1986;55:446-7. Feilser AJ, De Gee AJ, Davidson CL. Setting stress in composite resin in relation to configuration of the restoration. J Dent Res 1987;66:16369. Crim GA, Chapman KW. Effect of placement techniques on microleakage of a dentin-bonded composite resin. Quintessenc Int 1986;17:21-4. Davidson CL, De Gee AJ, Feilzer AJ. The competition between the composite-dentin bond strength and the polymerization contraction stress. J Dent Res 1986;63:1396-9. Feilzer AJ, De Gee AJ, Davidson CL. Curing contraction of composite restoratives and glass-ionomer cements. J PROSTHET DENT

1’7.

18. 19.

20.

Reprint requests to: DR. CAREL L. DAVIDSON DEPARTMENT OF DENTAL Louw~sw~c 1,1066 THE NETHERLANDS

13. Davidson CL, De Gee AJ. Relaxation of polymerization contraction stresses by flow in dental composites. J Dent Res 1984;63:146-8. 14. Torstenson B, Briinnstr6m M. Contraction gap under composite resin

W. A. Gregory, The University

of chemically

D.D.S., MS.,* B. Pounder,

of Michigan,

MATERIALS

SCIENCE,

ACTA

1988;59:297-300.

Bond strengths resins

restorations: effect of hygroscopic expansion and thermal stress. Oper Dent 1988;13:24-31. Krabbendam CA, Ten Harkel HC, Duijsters PPE, Davidson CL. Shear bond strength determinations on various kinds of luting cements with tooth structure and cast alloys using a new test device. J Dent 1987;15:77-81. Braem M, Davidson CL, Vanherle G, Vandoren V, Lambrechts P. The relationship between test methodology and elastic behavior of composites. J Dent Res 1987;66:1036-9. Lambrechts P, Braem M, Vanherle G. Evaluation of clinical performance for posterior composite resins and dentin adhesives. Oper Dent 1987;12:53-87. Braem M, Lambrechts P, Vanherle G, Davidson CL. Stiffness increase during the setting of dental composites. J Dent Res 1987;66:1713-6. Munksgaard EC, Itoh K, Jorgensen KD. Dentin-polymer bond in resin fillings tested in vitro by thermoand load-cycling. J Dent Res 1985;64:144-6. Eakle WS. Effect of thermal cycling on fracture strength and microleakage in teeth restored with a bonded composite resin. Dent Mater 1986;2:114-7.

dissimilar

D.D.S.,**

and E. Bakus,

EA, AMSTERDAM

repaired

composite

D.D.S.***

School of Dentistry, Ann Arbor, Mich.

Expanded use of composite resins has necessitated repair of fractured, discolored, and former restorations. Laboratory investigations have demonstrated that new composite resin can be bonded to cured composite resin of the same chemistry. The surface chemistry of three composite resins of dissimilar matrix formulae were examined by infrared spectroscopy and the tensile bond strengths of heterogeneous repairs and the site of repair failures were determined. (J FBOSTEET DENT 1990:64:664-8.)

B

uonocorer introduced acid etching of enamel in 1955 for the adhesion of acrylic resin filling materials and Bowen developed Bis-GMA composite resins in 1962. As a result, dentistry gradually expanded their application to include complex restorations.

Composite resins have been used to restore classes 3,4 and posterior class 1,2, and 5 defects, to reveneer crowns and fixed partial dentures, to lute orthodontic brackets, to splint periodontally compromised teeth, and as a direct veneer. This popularity has necessitated repairing of composite resins because of bond failure, cohesive fracture, color changes, and loss of surface from chemical and mechanical deterioration.

This research was partially supported by the Student Summer Research Fellowship Program, School of Dentistry, The University of Michigan, Ann Arbor, Mich. *Assistant Professor, Department of Restorative Dentistry. **General Practice resident, St. Joseph’s Hospital, Pontiac, Mich. ***Clinical Instructor, Department of Restorative Dentistry. 10/l/20013

The preparation design of fractured resin surfaces for retention of new composite resin to former restorations and successful repairs has received wide attention.3-7 The sur-

664

face preparation of old composite resin has been accomplished by mechanically roughening to remove contaminated material,

cleansing

with 30 % to 50 % phosphoric

DECEMBER1999

VOLUME64

acid

NUMBER6

BOND

STRENGTHS

OF REPAIRED

COMPOSITE

Urethane

RESINS

dimethvlacrvla&

cy3

cy3

Y ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A

Fig.

Table

L

6

c3

d:

0

1. Matrix chemistry for composite resins.

I. Materials used in this study Manufacturer Composite

Prisma-Fil (PF) Heliomolar (H) Bonding material Bondlite (B) Prisma Universal Bond (PUB) Heliobond (Hb) Curing light Translux Phosphoric acid Scocthbond etching gel

Kerr/Sybron Inc. Romulus, Mich. L. D. Caulk Co. Milford, Del. Vivadent (USA) Inc. Tonawanda, N.Y. Kerr/Sybron Inc. L. D. Caulk Co. Vivadent (USA) Inc

number

Polymer

chemistry

OF PROSTHETIC

8 1060 and 8 1048

Bis-GMA

1211855

Bis-GMA/UDM mix

309104

UDM

6 1237 0923853 624702

Bis-GMA Bis-G.MA/UDM mix UDM

Kulzer, Inc. Irvine, Calif. 3M Company Minneapolis, Minn.

to reenergize the surface, and treating with an unfilled bonding agent to secure the repair. The tensile bond strengths were approximately half the diametral strengths but within the lower range of clinical function.7-10 Chemical bonding was studied by Van Kerckhoven et al.‘l with infrared spectroscopy to measure residual unreacted groups in Bis-GMA composite resin after curing. They demonstrated that microfilled and large-particle products were 40% to 57% unsaturated and chemical bonding of new resin to previously polymerized resin BisGMA was possible. Ferracane and Greener12 used Fourier transform infrared (FTIR) spectroscopy to determine the polymerization in unfilled Bis-GMA resins and discovered that the degree of polymerization was the highest for the diluted resins because of greater diffusion of reactive groups during polymerization.

JOURNAL

Batch

resin

Command Ultrafine (CUF)

THE

L

c3

DENTISTRY

Powers et a1.i3used FTIR spectroscopy to investigate the in vitro aging of composite resins including a sealant and demonstrated changes in surface chemistry with aging confirmed by modifications in the composite resin spectra between 0 and 900 hours. Organic polymers such as Bis-DMA, TEDMA, Isobis-GMA, and urethane dimethacrylate (UDM), are also used in the manufacture of dental composite resins.l* UDM and a combination of UDM and Bis-GMA are the primary polymers of composite resin formulations. Both of these resins contain double bonds of carbon at the ends of the oligomer chains that can cross link to form the final polymer matrix. Polymerization can be initiated by either chemical or light-activated means in both systems. The basic difference between the two oligomers is that urethane diacrylate contains isocyanate and Bis-GMA possesses benzene rings (Fig. 1).14

665

GREGORY,

Command Ultrofine

Prisma Universal Bond

Bondlite

“hh

POUNDER,

AND

BAKUS

,isma-Fil

lil’ v

16362

1636.7

1636.2

1637.2

P

1636.4

WAVENUMBER

-

Fig. 2. Multiple internal reflection infrared spectroscopy patterns of resin materials with C = C double-bond peaks at 1638 wave numbers.

Chemical

Table II. Composite resin samples tested Substrate

composite

Repaired bars Command Ultrafine Command Ultrafine Command Ultrafine Heliomolar Heliomolar Heliomolar Prisma-Fil Prisma-Fil Prisma-Fil

Bonding

agent

Bondlite Prisma Bond Heliobond Heliobond Prisma Bond Bondlite Prisma Bond Heliobond Bondlite

Repair

composite

Command Ultrafine Prisma-Fil Heliomolar Heliomolar Prisma-Fil Command Ultrafine Prisma-Fil Heliomolar Command Ultrafine

Pure bars: Command Ultrafine, Prisma-Fil, and Heliomolar composite resins. Three pure and nine repaired bars X 10 samples each = 120 samples.

Fracture of repairs theoretically may occur in a combination of three locations: adhesive failure at the interface, cohesive failure within the substrate, or in the repair material. The study investigated the matrix surface chemistry of different composite resins regarding additions of new resin to old, particularly whether different matrix chemistry of the substrate and repair composite resins adversely affects bond strengths, including the location of failures.

MATERIAL

AND

METHODS

Two test procedures were performed: a chemical analytical test with multiple internal reflection (MIR) infrared spectroscopy and a mechanical test for three-point bending. Table I lists the products, batch numbers, and manufacturers used in this study. Three commerical light-cured hybrid dental composite resins and their bonding systems, with different polymer matrix chemistry, were selected to test. 666

investigation

MIR techniques for analysis of surface chemistry of composite resins have been described in detai1.r’ The selective absorption of radiation in the 5 pm of surface material exhibits absorption bands in the infrared region to determine the presence of carbon-carbon double bonds. MIR spectral analysis was conducted for all three composite resins and their bonding agents. Two samples of each composite resin and bonding agent were prepared by placing the material into a four-sided mold of condensation silicone of 10 X 40 X 1 mm. Glass slabs were inserted at the top and bottom of the mold to produce smooth surfaces and prevent inhibition of surface polymerization with oxygen during curing. Samples were light-cured for 60 seconds bilaterally with a slide projector lamp at a distance of 8 inches. After 24 hours, the samples were tested on an SX-60 Fourier transform infrared spectrometer (Nicolet Instrument Corp., Madison, Wise.) in a reflectance (ATR) mode. Two samples were secured in intimate contact for good resolution on each side of a thallium-bromide-iodide crystal that approximated the sample size. This combination was inserted into the test chamber of the spectrophotometer and analyzed by midrange IR light (5000 to 400 wave numbers). The resultant spectra were analyzed by identification of peaks specific to the chemical groups on the sample surface.

Mechanical

test

Specimens in bar form for three-point bending were made in a stainless steel mold, 15 mm long with a cross-section dimension of 2.40 x 2.15 mm, and placed on a glass slab. Ten homogenous bar samples of each resin, of each resin repaired with identical material, and of each resin repaired with two dissimiliar resins were tested (Ta-

DECEMBER

1990

VOLUME

64

NUMBER

6

BOND

STRENGTHS

OF REPAIRED

COMPOSITE

RESINS

SUBSTRATE

REPAIR

SUBSTRATE

SUSSTRATE

I

(COHESIVE) FRACTURE

I

REPAIR

I Fig.

3. Repair fracture site classification.

ble II). The homogenous bars were produced during a single packing of the mold; the repair bars were initially made by filling half of the mold. The specimens were cured for 60 seconds with a dental composite resin curing lamp (Translux, Kulzer, Inc., Irvine, Calif.) and stored in distilled water for 24 hours at 37” C. The interface surfaces of repaired bars were prepared with 600-grit silicon carbide paper and the facial width and breadth were measured. Surface treatment was followed by cleaning for 60 seconds with 35% phosporic acid etching gel, rinsed with distilled water for 20 seconds, and dried with oil-free compressed air. A thin layer of the appropriate bonding resin was applied, light-cured for 20 seconds, and the half-bar was repositioned in the mold. Repair composite resin was packed in the remaining space, cured for 60 seconds, and placed in three-point bending in a testing machine (Model TT-BM, Instron Corp., Canton, Mass.) at a cross-head speed of 0.5 cm/minute to determine transverse bond strength (TBS) of the repair. The TBS for each sample and the mean and standard deviation of each sample category were calculated in Kg/mm.2 The data were analyzed by analysis of variance using a factorial design.15 Means were ranked by a Tukey interval16 calculated at the 95 % level of confidence. Ranges between two means that were larger than the Tukey interval were significantly different. The fracture surfaces were also examined under x13 magnification and the point of failure recorded.

RESULTS Spectral analysis of the three composite resins and their bonding agents identified known chemical groups. Unpolymerized material at the surface after cure was confirmed in the six samples by a C = C double bond peak at 1638 wave numbers (Fig. 2.). The samples, with the exception of Prisma Universal Bond (PUB) materials, demonstrated peaks at approximately 1608 wave numbers indicative of benzene rings, despite the preconception that Heliobond (HB) and Heliomolar (H) materials did not contain benzene rings.

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

III. Mean bond strengths of composite resin repairs: three-point bending (Kg/mm2)

Table

Repair Substrate composite resin

Command Ultrafine Heliomolar Prisma-Fil

Command Ultrafine

7.62

7.90 9.62

composite

Heliomolar

resin

PrismaFil

7.28 6.85 7.87

Tukey interval for rows and columns = 1.0 Kg/mm2. than Tukey interval are statistically significant.

9.21

5.55 9.06 Differences

greater

The means of the three-point bending test for the three pure bars of composite resin were Command Ultrafine (CUF), 10.33 Kg/mm2; H, 7.91 Kg/mm2; and PrismaFil (PF), 12.71 Kg/mm.2 Table III lists the mean values of the repair bond strengths. None of the repaired bars were stronger than the unrepaired bars of the material, although the H/CUF repair was virtually the same as the H alone. The repair of CUF with PF was significantly stronger than the CUF/CUF or the CUF/H repair. PF repaired with CUF was substantially stronger than the CUF/CUF or H/CUF repairs. H was compatible with CUF and the H/CUF repair was significantly stronger than the H/H or the H/PF repair. The H/H repair was appreciably better than H/PF. As a repair material, H with PF substrate performed significantly greater than with H substrate, but was not superior to the CUF/H combination. PF repaired both CUF substrates with higher bond strengths than the H/PF repair. Fractures were grouped by the failure area (Fig. 3); 74% were at the composite resin/composite resin repair interface. There were no failures within PF repair layers, two in the CUF repair layers, and eight in the H repair layers. Three substrate failures occurred in H and five each in CUF and PF.

DISCUSSION Clinical conditions in restorative dentistry, because of physical properties, color, and/or polishability of a com-

667

GREGORY,

posite resin, may require incremental layering of dissimilar composite resins. A dentist may not be aware of the type of composite resin needing repair and be faced with the question of compatibility of materials. The selection of materials should be based on research to ensure success. Patterns of strengths or weaknesses of matrix chemical repair combinations were not evident in this study. One type of composite resin was not superior for repair nor was one type inferior. TBS of repairs ranged from 62% (PF repaired with H) of a solid substrate sample (PF) to 100% (H repaired with CUF; H solid sample). Neither the highest nor lowest values were generated by homogeneous repairs. Although significant differences were evident in various repair combinations of TBS, there was no incompatibility between repairs. The availability of carbon-carbon double bonds in the originally cured polymer for reaction with repair materials allowed the materials to adhere to each other. Failures were possible adhesively at the interface, or cohesively within the substrate or repair composite resins. The lower TBS of repairs suggested that all failures should be adhesive. However, all failures of the repairs were not at the interface but other failures were close to the interface. The 26% “cohesive” failures were attributed to deficienties from air inclusions or poor adaptation near the substrate interface. Attention to nrenaration. nrotection. and application procedures are critical for successbecause fractures within the substrate or the repair material can be technique related. 1

1

I

.

CONCLUSIONS 1. Carbon double bonds were evident at the cured surface of composite resins with a matrix of Bis-GMA, urethane dimethacrylate, and a mix of Bis-GMA and urethane dimethacrylate. 2. Repairs of composite resin with identical matrix chemistry did not produce bond strengths greater than those of different matrix chemistry.

668

POUNDER,

AND

BARUS

3. Repair failures occurred at or adjacent to the repaired interface. REFERENCES 1. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34:849-53. 2. Bowen RL. Dental filling material comprising vinyl silane treated fused silica and a binder consisting of the reaction product of Bis phenol and glycidyl acrylate. 1962 U.S. Pat. 3,066,112. 3. Caspersen I. Residual acrylic adhesive after removal of plastic orthodontic brackets: a scanning electron microscopic study. Am J Orthod 1977;71:637-50. 4. Pounder B, Gregory WA, Powers JM. Bond strengths of repaired composite resins. Oper Dent 1987;12:127-31. 5. Reteif DD. The mechanical bond. Inter Dent J 1978;28:18-27. 6. Boyer DB, Hormati AA. Rebonding composite resin to enamel at sites of fracture. Oper Dent 1980;5:102-6. 7. Boyer DB, Chan DC, Torney DL. The strength of multilayer and repaired composite resin. J PR~STHET DENT 1978;39:63-7. 8. Causton BE. Repair of abraided composite fillings. Br Dent J 1975; 286-8. 9. Boyer DB, Ghan KC, Reinhardt JW. Build-up and repair of light-cured composites: bond strength. J Dent Res 1984;63:1241-4. 10. Soderholm KJ. Flexure strength of repaired dental composites [Abstract]. J Dent Res 1985;64:178. 11. Van Kerchoven H, Lambrechta P, Can Beylen M, Davidson CL, Vanherle G. Unreacted methacrylate groups on the surfaces of composite resins. J Dent Res 1982:61:791-5. 12. Ferracene JL, Greener. EH. Fourier transform infrared analysis of degree of polymerization in unfilled resins-methods comparison. J Dent Res 1984;63:1093-5. 13. Powers JM, Fan PL, Marcotte M. In vitro accelerated aging of composites and a sealant. J Dent Res 1981;60:1672-7. 14. Van Kerckhoven H, Lambrechts P, Van Bevlen M, Vanherle G. Characterization of composite resin by NMR and TEM. J Dent Res 1987; 60:1957-65. 15. Dalby J. (programmer). BMD8V-Analysis of variance. Ann Arbor, Mich: Statistical Research Laboratory, University of Michigan, 1968. 16. Guenther WC. Analysis of variance. Englewood Cliffs, NJ: PrenticeHall, 1964199. Reprint

requests

to:

DR. WILLIAM A. GREGORY SCHOOL OF DENTISTRY THE UNIVEFSITY OF MICHIGAN ANN ARBOR, MI 48109

DECEMBER

lSS0

VOLUME

64

NUMBER

6