Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites

Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites

Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites Tamar Brosh, PhD," Raphael Pilo, D M D , b...

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Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites Tamar Brosh, PhD," Raphael Pilo, D M D , b Nitzan Bichacho, D M D , c and Rita Blutstein, D M D d The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel

Statement o f problem. Enhancement of bond strength between new and old composite usually requires increasing the surface roughness to promote mechanical interlocldng and coating of old composite with unfilled resin bonding agents to advance surface wetting and chemical bonding. Purpose. The purpose of this study was to evaluate the effect of combinations of surface treatments and bonding agents on the shear bond strength between new and old composite. Material and methods. Six surface treatments, two bonding agents, and an untreated control comprised 18 different subgroups. Results. The use of unfilled resin, alone or combined with silane, was the most effective procedure to enhance the shear bond strength of the repaired composite specimens, irrespective of the surface pretreatment processes. Silanation and unfilled resin slightly but not significantly improved the repair strength compared with unfilled resin alone. Conclusions. Different combinations of surface treatments and bonding agents affect shear bond strength differently. The highest shear bond strength values were achieved by grinding the surface with green Carborundum stone or sandblasting, whereas the lowest values were obtained with hydrofluoric acid as the surface treatment agent. (J Prosthet Dent 1997;77:122-26.)

Complete removal o f a f?actured, stained, or defective complex composite restoration is often undesirable, especially if the existing restoration is near the pulp, retained by pins, or is large. Repair o f the restoration by adding new composite to the existing one is a well-established clinical modality carried out between similar and dissimilar commercially available composites, v5 Replacement o f the unsatisfactory part is the m o s t conservative treatment for worn restoration surfaces, 6 as is modifying the veneered portion o f a completed resinveneered restoration to improve color matching or outline form. 7 In addition, an interface between old and new composite may exist when a porcelain laminate veneer is bonded to a t o o t h with old composite restoration .8 Submitted in partial fulfillment of DMD thesis (R. Blutstein). ~Guest Lecturer, Section of Oral Rehabilitation. bLecturer, Section of Oral Rehabilitation. qnstructor, Section of Oral Rehabilitation. ~Dental student, Section of Oral Rehabilitation. 122

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A tendency for b o n d strength between new and old c o m p o s i t e to decrease after aging and storage o f the old material in saliva has b e e n r e p o r t e d . 5,9a° I m p r o v ing the b o n d strength between new and old c o m p o s ite usually requires increased surface roughness to prom o t e mechanical interlocking and coating o f old composite with unfilled resin b o n d i n g agents to advance surface w e t t i n g and chemical b o n d i n g ? Mechanical a n d / o r chemical t r e a t m e n t s to r o u g h e n the surface include air abrasion with 50 p m a l u m i n u m oxide particles, s r o u g h e n i n g with silicon carbide p a p e r or diam o n d s t o n e s , ~°,11 a n d e t c h i n g w i t h h y d r o f l u o r i c a c i d Y 2 B o n d i n g agents that have been used in previous studies include unfilled resins 4a°a3 or the c o m bined use o f silane p r i m e r and unfilled resin. 7 The objectives of this study were to (1) investigate the effect of selected combinations o f surface treatments and bonding agents on the shear bond strength o f the bond between old and newly added composite and (2) identify those that are most effective. VOLUME 77 NUMBER2

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hybrid composite

F.

l I. 2.5 'I" --~2""~'~ I"

, _ _ perspex piston

A

iii

B microfilled composite

~

interface

hybrid composite C Fig. 1. Stages of sample preparation. A, Teflon mold and Perspex piston; B, old composite (hybrid) stage; C, new composite (microfilled) adhered to old hybrid composite.

MATERIAL AND METHODS

Specimen preparation A total of 360 samples were prepared of joined old Pertac-hybrid (Espe, Seefeld, Germany) and Silux Plus (3M, St. Paul, Minn.) composites. Various surface treatments of the old composite were performed before the bonding agents and the new material were added. Cylindrical Teflon molds with an inner diameter of 5 mm and a height of 5 mm were fabricated. A close fitting Perspex piston (Polivar PMMA, Rome, Italy), 5 mm in diameter × 2.5 mm in height, was matched to each hole in the Teflon mold to create a cavity with dimensions 5 m m x 2.5 mm (Fig. 1,A). Hybrid composite (Pertac-hybrid, Espc) was packed against the Perspex piston with a dental spatula. Excess material was removed by pressing a clear glass plate with a Mylar strip on the top surface. The resin was cured for 60 seconds at a 90degree angle to the top surface with a light-curing unit (Elipar II, Espe). The specimens 5 mm in diameter x 2.5 mm in height were gently ejected from the mold, placed in a container of distilled water, and stored in a constant temperature oven at 37 ° C for 14 days. Specimens were randomly divided into six groups of 60 specimens each and the flat circular surface of each sample was subjected to different surface treatments as follows: Group 1 (C). Control with no surface treatment Group 2 (D). Grinding with a diamond stone ( 8 5 6 / 018, Diatech Diamant AG, Hecrbrugg, Switzerland) and water cooled at high speed Group 3 (SB). Sandblasting with a microetcher (Danville Engineering Inc., Danville, Calif.) for 10 seconds with 50 ~amAI203 particles Group 4 (JP). Jet prophylaxis (Deldent Ltd., PetahTikva, Israel) for ] 5 seconds at 2.2 atmospheric pressure and 10 mm distance with sodium bicarbonate particles FEBRUARY 1997

T

T

old new composite composite

E _

interface Fig. 2. Schematic presentation of shear strength experimental technique.

Table I. Results of two-way analysis of variance Source of variation

Sum of squares

Surface treatment 400.79 Bonding agent 460.69 Interaction 222.65 Error 2239.19

Mean DF

square

F-ratio

F-prob

5 2 10 342

80.15 230.34 22.26 6.54

12.24 35.18 3.40

0.0001 0.0001 0.0003

Group 5 (GC). Grinding with green Carborundum stone (Dedeco Dental Products, St. Paul, Minn.) and water cooled at low speed to ensure a controlled removal of the surface Group 6 (HF). Coating with a thin layer of 9.5% hydrofluoric acid (Ultradent Products, South Jordan, Utah ) for 60 seconds, then rinsed with water for 2 minutes and dried with compressed air The test surface of each specimen was rinsed with water for 20 seconds and dried with compressed air for l 0 seconds. All specimens were replaced into the mold, which left half the length of its total original cavity (5 x 2.5 ram) empty (Fig. 1, B). Each group was then divided into three subgroups of 20 specimens each and subjected to a different bonding agent: (1) control with no bonding agent; (2) unfilled bis-GMA resin (Enamel Bond, Ultradent Products) applied, thinned with compressed air, and cured with a 20-second exposure to visible light; and (3) silane (Scotch Prime - Ceramic Primer, 3M Dental Products) applied and allowed to dry for 120 seconds. Any residual solvent was evaporated with compressed air, after which bis-GMA resin was added, air thinned, and cured. Fresh microfilled composite (Silux Plus, 3M Dental Products) was packed against the "old" (14-day) specimen in the mold to complete the repair procedure and 123

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16

Surface treatment I

14

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.

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.

.

: . . . . . . . . . . . . . . . . . . . . . . . . .

!

Bondingagent

SB

JP

GC

ttF

g~ ' 1 2 None

! .

8 toe~ a= tO

..

!I

6

4

C

D

SB

JP

GC

HF

[ ] No bonding [ ] Bis-GMA [ ] Silane + Bis-GMA

Fig. 3. Mean shear bond strength and standard deviation of all combinations of surface treatment and bonding agent groups.

Bis-GMA

5,74

7.90

5.64

5.44

7.93

5.66

(2.10)

(2.92)

(2.98)

(1.90)

(2.12)

(2.17)

8.30

7.95

10.60

8.15

9.95

6.02

(2.72)

(2.45)

(3-57)

(2.41)

(2 84)

(2.27)

Silane plus

8.69

9.14

9,06

10.05

10.71

6.43

BIs-GMA

(2.66)

(2.51)

(2.80)

(2.04)

(2,76)

(2.16)

Fig. 4. Bonferroni's multiple comparison test of shear bond strength. Groups connected by horizontal or vertical lines in same plane are statistically homogenous groups (p >0.05). Mean (SD)in megapascals,

A device was constructed from two identical stainless steel plates 2.5 mm thick with a penetrating cylindrical hole 5 mm in diameter. By combining the plates, a testing chamber was created in which the samples fit exactly (Fig. 2). The device was attached to a universal testing machine (model i026, Instron Corp., Canton, Mass.) and subjected to an increasing shear force, with a crosshead speed of 0.5 mm/minute, until failure. The mean shear bond strength (SBS) required to cause sample failure was calculated by dividing the failure force (Ff) by the cross-sectional area of the specimen (A).

of the different groups for surface treatments, bonding agents, and their interaction (p <0.0003) (Table I). Figure 4 presents the results obtained when Bonferroni's multiple comparisons test was applied to test the significance between specific means. MI surface treatment procedures without subsequent application of bonding agents, yielded a statistically homogenous group (p >0.05). Although not significantly different, grinding with either a diamond stone (group 2) or a green Carborundum stone (group 5) yielded the greatest SBS values (7.90 and 7.93 MPa, respectively). When bisGMA or silane plus bis-GMA bonding agents were applied, the SBS improved in all of the surface treatment groups. This improvement was statistically significant (p <0.05) when the following specific subgroups were compared: control (group 1), sandblasting (group 3), jet prophylaxis (group 4), and green Carborundum stone (group 5) to the corresponding subgroup with silane plus bis-GMA, and sandblasting to the corresponding subgroup with bis-GMA. All surface treatment subgroups subsequently coated with either bis-GMA or Silane plus bis-GMA were not statistically different (p >0.05). Group 6 (HF), with either bis-GMA or Silane plus bis-GMA, yielded the lowest SBS values.

Statistical analysis

DISCUSSION

Bond strength data were subjected to a two-way analysis of variance (ANOVA). When the F ratios were significant, the Bonferroni multiple comparisons test was used to compare specific means. Statistical significance was defined at the 95% level of confidence.

Unfilled bis-GMA resin (Enamel Bond), alone or combined with silane, was the most effective procedure for enhancing the SBS of the repaired composite specimens, irrespective of the surface texture created by different surface treatments. Significantly lower SBS values were found for most subgroups where no unfilled resins, or silanes and unfilled resins, were used. This finding is in agreement with other studies~,~,8,13-~ in which it is reported that the poor wettability properties of the highviscosity new composite material necessitates less viscous unfilled resin to penetrate the microcracks in the matrix o f the old composite and thus obtain

cured for 60 seconds (Fig. I, C). The final completed test specimens (5 mm in diameter and length) were gently released from the mold, placed in distilled water, and stored in a 37 ° C constant temperature oven for 14 days. After the immersion period, all specimens were thermocycled for 300 cycles at 5 ° and 55 ° C, with a dwelling time of 30 seconds in constant temperature bath (Techne Inc., Princeton, N. J.). Shear bond strength testing

RESULTS The mean and standard deviation of the shear bond strength required to separate the two specimen halves are illustrated in Figure 3 for various surface treatments and bonding agents. A statistically significant difference (p <0.0001) was found in the average shear bond strength 124

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B R O S H ET A L

micromechanical retention. The significant (p <0.01) interaction found between surface treatments and bonding agents proves our hypothesis that combinations of surface treatments and bonding agents affect the SBS differently. The highest SBS values were associated with grinding with green Carborundum stone or sandblasting, whereas the lowest values were obtained with HF. The three possible mechanisms during composite repair with the use of intermediate unfilled resins are chemical bond formation to the matrix, chemical bonds to the exposed filler particles, and micromechanical retention caused by penetration of the monomer components to microcracks in the matrix. Previous studies 16 ~8 have shown that mechanical interlocking is the most significant factor contributing to repair strength. Accordingly, the use of different cutting instruments and various surface treatments is likely to generate differences in smearing and matrix cracking and thereby influence the repair SBS value. Sandblasting and jet prophylaxis are surface treatments that cause "micro" retentive features (controlled by the tool); a diamond stone or a green Carborundum stone yield "macro" retentive features (controlled by the operator) and microretentive features. Without a bonding agent, greater SBS value is expected from devices yielding macroretentive features, from a diamond stone and a green Carborundum stone, (7.90 and 7.93 MPa, respectively), compared with from jet prophylaxis and sandblasting (5.44 and 5.64 MPa, respectively). With bonding agents, a better surface wetting occurs by infiltration of the resin into microscopic surfaces. Thus, a greater improvement in SBS values is expected from devices causing more microretentive features: an average increase of 4.19 and 3.66 MPa with sandblasting and jet prophylaxis, respectively, compared with green Carborundum and diamond stones (2.4 and 0.64 MPa, respectively). Other studies have also demonstrated the effectiveness of air abrasion in obtaining stronger repairs compared with sanding with 500 grit sandpaper ~8 or etching with hydrofluoric acid and acidulated phosphate fluoride. 8 Silane coupling agents have been shown to improve the bond of composite to etched, sandblasted, or roughened porcelain i9,20and to significantlyincrease the composite to composite bond in the repair procedure that was tested in this study. Silanation and unfilled resin slightly improved the repair strength compared with unfilled resin alone, but the differences were not statistically significant. Soderholm et al. 17 found no significant difference in repair strength between Scotchbond, Scotchprime, and silane-toluene materials and similar fracture patterns. Azarbal et al.~3 found that in increasing the transverse strength of repaired composites, Scotchbond bonding agent was more efficient than a silane coupling agent. Saunders 2~reported that Scotchbond bonding agent FEBRUARY 1997

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was most effective in promoting bonding ofc0mposite additions for P-50 and Herculite materials, al]d that silane treatment did not improve the fatigue resistance of any of these materials. Swift et al. 12 repo~ted that silanation and Bondlite material, a phosph]ate ester enamel bonding material, slightly improved the repair strength of HF-etched and air abraded HF-etdaed composite compared with Bondlite material alone, but the differences were not statistically significant. In contrast, silanation of specimens that had been only ai~ abraded resulted in somewhat lower repair strength. The failure ofsilane coupfing agents to predictably increase ithe bond of new composite to old composite, compared With dentin/enamel bonding agents, may suggest that mechanical interlocking is the most significant factor contributing to repair strength and thus appears to be unnecessary for composite repair. The only exception to the contribution of unfilled resin, alone or in combination with silane bonding agent, to the SBS value of the repair procedure wag p~eetching with HF acid for 60 seconds. However, Pertacihybrid is heavily filled with nonetchable quartz and thus! serves as a poor candidate for etching. Moreover, the resin matrix contains a more hydrophobic monomer than that of most composites. 8 Swift et al. I2 investigated a 15-second etching time with HF acid ofHerculite XRV composite. Herculite XRV composite contains glass filler particles, which makes it an excellent candidate for etching. A subsequent application of Bondlite bonding agent slightly but not significantly improved the repair strength compared with air abrasion and Bondlite bonding agent. In another study by Swift et al.,8 etching composites with a 9.6% HF gel for 30 seconds either increased or decreased repair strength, dependent on the composite material being repaired. Thus, HF acid is not recommended as a routine treatment method for composite repair, especially when the exact composition of the old composite is not known. SUMMARY In summary, the results of this study indicate that the application of unfilled resin or 8ilane primer plus unfilled resin to the old composite surface gives the strongest bonds of new composite to previously cured and aged composite, particularly when the composite is roughened with a green Carborundum stone or sandblasting. We thank Ms. Rita Lazar for editorial assistance.

REFERENCES 1. Gregory WA, Pounder B, Bakus E. Bond strengths of chemically dissimilar repaired composite resins. J Prosthet Dent 1990;64:664-8. 2. Croll TR Repair of defective Class I composite resin restorations. Quintessence Int 1990;21:695-8. 3. Pounder B, Gregory WA, Powers JM. Bond strengths of repaired composite resins. Oper Dent 1987;12:127-31. 4. Puckett AD, Holder R, O'Hara JW. Strength of posterior composite repairs

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using different composite/bonding agent combinations. Oper Dent 1991 ;16:136-40. 5. Chiba K, Hosoda H, Fusayama T. The addition of an adhesive composite resin to the same material: bond strength and clinical techniques. J Prosthet Dent 1989;61:669-75. 6. Bayne SC, Heymann HO, Swift EI Jr. Update on dental composite restorations. J Am Dent Assoc 1994; 125:687-701. 7. Matsumura H, Hisamatsu N, Atsuta M. Effect of unfilled resins and a silane primer on bonding between layers of a light-activated composite resin veneering material. J Prosthet Dent 1995;73:386-91. 8. Swift EJJr, LeValley BD, Boyer DB. Evaluation of new methods for composite repair. Dent Mater 1992;8:362-5. 9. Boyer DB, Chan KC, Reinhardt JW. Build-up and repair of light-cured composites: bond strength. J Dent Res 1984;63:1241-4. 10. Kao EC, Pryor HG, Johnston WM. Strength of composites repaired by laminating with dissimilar composites. J Prosthet Dent 1988;60:328-33. 11. Eli I, Liberman R, Levi N, Haspel Y. Bond strength of joined posterior lighb cured composites: comparison of surface treatments. J Prosthet Dent 1988;60:185-9. 12. Swift EJJr, C]oe BC, Boyer DB. Effect of a silane coupling agent on composite repair strengths. Am J Dent 1994;7:200-2. 13. Azarbal P, Boyer DB, Chan KC. The effect of bonding agents on the interfacial bond strength of repaired composites. Dent Mater 1986;2:I 53-5. 14. Crumpler DC, gayne SC, Sockwell S, Brunson D, Roberson TM. Bonding to resurfaced posterior composites. Dent Mater 1989;5:417-24. 15. Mitasaki-Matsou HM, Karanika-Kouma A, Papadoyianns Y, TheodoridouPahine S. An in vitro study of the tensile strength of composite resins repaired with the same or another composite resin. Quintessence [nt 1991 ;22:475-81.

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16. Sod~rholm KJ. Flexure strength of repaired dental composites. Scand J Dent Res 1986;94:364-9. 17. Sod&holm KJ, Roberts MJ. Variables influencing the repair strength of dental composites. Scand J Dent Res 1991;99:173-80. 18. Turner CW, Meiers JC. Repair of an aged, contaminated indirect composite resin with a direct, visible light-cured composite resin. Oper Dent 1993;I 8:187-94. 19. Stange[ l, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. J Dent Res 1987;66:1460-5. 20. Roulet ]F, Sod&holm KJ, Longmate J. Effects of treatment and storage conditions on ceramic/composite bond strength. J Dent Res I995;74:381-7. 21. Saunders WP. Effect of fatigue upon the interfacial bond strength of repaired composite resins. J Dent 1990;18:158-62. Reprint requests to: DR. TAMARBROSH SECTIONOF ORAL REHABILITATION THE MAURICEAND GABRIELAGOLDSCHLEGER SCHOOLOF DENTALMEDICINE TEL AVlV UNIVERSITY TEL AVIV 69978

ISRAEL Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/97/$5.00 + 0. 10/1/78116

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