Comparative tensile strengths of brackets bonded to porcelain with orthodontic adhesive and porcelain repair systems Robert Eustaquio, DDS,* LaForrest D. Garner, DDS, MSD,** and B. Keith Moore, PhD*** Indianapolis.
Ind.
The acceptance of simplified technical procedures that minimize clinical effort is exemplified by the popularity of direct bonding. This study (1) measured the comparative tensile bond strengths of brackets bonded directly in vitro to both glazed and deglazed porcelains by the use of five adhesive systems, and (2) recorded failure sites. Systems 1 + , Enamelite 500, IsopastSilanit, and ConciseiScotchprime proved to have strengths that should be acceptable clinically. Ultra-bond produced a bond that was significantly less in strength as compared with the other four systems. There was no significant difference in the bond of glazed and deglazed porcelains. Diamond polishing paste was better at restoring the porcelain surface to original smoothness in comparison with polishing stones. Irreversible damage to the porcelain surface may result from the bonding procedure. (AM J ORTHOD DENTOFAC ORTHOP 1988;94:421-5.)
D
irect bonding of orthodontic brackets to enamel has been widely accepted because of its ease, efficacy. and improved esthetics.‘-2 However. an increasing percentage of today’s orthodontic population consists of adults who may need bonding to existing esthetic restorations such as porcelain laminate veneers or metal-ceramic restorations.“.” What remains to be seen is whether the esthetic advantages and other benefits of direct bonding to enamel are also possible for bonding to porcelain surfaces. Little has been reported on bonding to porcelain surfaces for orthodontic purposes. Most of the studies have used porcelain denture teeth whose chemical composition differs significantly from that of a porcelain fused to metal material and have not included thermal cycling before testing.5-9 Reports from porcelain repair studies have demonstrated the importance of thermocycling in an in vitro test of bond strength to assessthe long-term stability of the bond.“,” The differences in thermal expansion coefficients among porcelain, resin, and metal (1: 6: 1) result in fatigue stresses from temperature fluctuations in the mouth.‘2.‘3 A second question relating to orthodontic bonding to porcelain surfaces is whether the porcelain can be From Indiana UnivrrGty. *Graduate orthodontic student. **Professor/Chairman of Orthodonticr ***Profeswr of Dental Materials.
restored to its initial appearance after the brackets are debonded and the resin removed. The purposes of this study were 1. To measure in vitro the tensile bond strengths of brackets bonded to metal-ceramic restorations by the use of five adhesive systems 2. To examine the effects of debonding on glazed and unglazed porcelain surfaces, and the effectiveness of two polishing systems in restoring the porcelains to their original surface finishes METHODS AND MATERIALS Fifty metal-ceramic crowns were treated with five adhesive systems: (1) System I+ with porcelain bonding primer,* (2) Enamelite 500 enamel coating/porcelain repair,? (3) Ultra-bond restorative kit,S (4) Isopast with Silanit contact-resins and (5) Concise with Scotchprime. 11 One adhesive system was used with each group of 10 specimens. For clinical relevance the base-metal copings were cast and baked with a low fusing porcelain (gingival BF vacuum porcelainll). The specimens were then autoglazed. Before bonding, the crowns were cleaned with a pumice slurry, washed. and air dried. “Ormco Corp.. Glendora. Calif. +Lee Pharmaceuticals. South El Monte. Calif. $Den-Mat Corp.. Santa Maria. Calif. (IVivadent. Tonawanda. N.Y. ll3M Company. St. Paul. Minn. ‘ICeramco. Inc.. East Windsor. N.J.
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and deglazed with a green stone and pumice, and then washed and dried. These specimens were used to simulate a deglazed porcelain surface, which most manufacturers recommend for bonding. Each group of 10 was rebonded with the same adhesive system used previously, following the same protocol for bonding, thermocycling, and storage. Tensile testing was then performed as before. To determine whether bonding to porcelain surfaces results in irreversible damage to the porcelain restoration, epoxy replicas were prepared of two specimens per group at four stages in the procedure. This was done for both glazed and deglazed surfaces before bonding, immediately after tensile testing, after removal of residual resin with pliers or scalers, and after attempting to restore the surface with either porcelain polishing wheels* or diamond polishing paste.? These replicas were examined under stereomicroscope and photographs made. RESULTS
Fig. 1. Specimen mounted in lnstron machine for tensile testing.
The sample sizes, mean bond strengths, standard deviations, and failure sites are given in Table I. It is readily apparent that Ultra-bond was significantly different. Because of this disparity in mean values and the fact that five glazed specimens failed during thermocycling, the Ultra-bond glazed and deglazed specimen data were excluded from statistical analysis. Values for
Each adhesive was used to bond 10 Minimesh brackets* to the metal-ceramic crowns following manufacturer’s directions. After bonding, the specimens were stored in 37” C water for 24 hours, thermocycled through 2500 cycles between 16” and 56” C, and returned to 37” C water until testing at 7 days after the start of thermocycling. Tensile testing to failure was done in an Instron machine* (at a crosshead speed of 0.5 mm/min) (Fig. 1). The load at failure was recorded in kilograms and the tensile strength determined by dividing by the
bracket base ares (0.162 cm2). The debonded specimens were examined in a stereomicroscope at magnification x 10 to determine the type of bond failure. These were designated as follows: P = Separationat the porcelain-adhesiveinterface; adhesive failure B = Bracket-adhesiveinterface failure, cohesivefracture in the resin C = Combination adhesive-cohesivefailure with resin remaining on both components after debonding
the other four adhesive systems were analyzed with a two-way factorial analysis of variance, and a significant difference between adhesive systems (p C 0.001) was found; however, the difference between glazed and deglazed porcelain surfaces was not significant
(p G 0.05). Neuman-Keul’s multiple comparisons indicated that the mean tensile strength of System 1 + was significantly greater (p =Z 0.001) than that of the other three adhesives of which the tensile strengths did not differ significantly. Four of the adhesives had failures predominantly at the bracket-resin interface (Table I). Systems 1 + had 100% failure rate at the bracket with most of the resin still bonded to the porcelain. Enamelite 500 had an 80%
failure rate at the bracket and a 20% combination bracket-resin/porcelain-resin failure rate. Isopast/Silanit had a 75% failure rate at the bracket-resin interface;
the other 25% was a combination of failure sites. Seventy percent of Concise/Scotchprime failures occurred at the bracket. Only Ultra-bond exhibited 100% failure at the porcelain-resin interface (adhesive failure)
(Table I).
After tensile testing, the 50 specimens were cleaned *Ins&on Corp.,
Canton, Mass.
*Shofu Dental Corp., Menlo Park, Calif. tTaub Products & Fusion Co., Jersey City, N.J.
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Comparative
Fig. 2. Porcelain porcelain fracture x 20.)
Table
surface showing cratering, scratching, and after resin removal. (Original magnification
Fig. 3. Porcelain inal magnification
tensile
surface x 20.)
polished
strengths
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of brackets
with polishing
stones.
(Orig-
I. Bond strengths and failure sites Tensile Group
Sample
size
strength
kgicn?
&a
Standard
deviation
kglcm’
Failure
site*
Mm
B
C
P
System I + (Ormco) Glazed Deglazed
10 10
67.1 58.8
6.58 5.77
7.91 9.25
0.776 0.907
10 10
0 0
0 0
Enamelite 500 (Lee) Glazed Deglazed
10 10
55.9 54.6
5.48 5.35
6.34 11.94
0.622 1.17
8 8
2 2
0 0
5f 10
6.05 4.75
0.593 0.466
3.75 4.71
0.368 0.462
0 0
0 0
10 10
10 10
52.8 55.2
5.18 5.41
8.73 8.75
0.856 0.858
8 7
2 3
0 0
10 10
52.0 51.2
5.10 5.02
10.32 5.82
1.01 0.571
7 7
3 3
0 0
Ultra-bond
(Den-Mat)
Glazed Deglazed IsopastiSilanit (Vivadent) Glazed Deglazed Concise/Scotchprime (3M) Glazed Deglazed *P = Separation C = combination t Five specimens
at porcelain-adhesive interface-adhesive failure; B = bracket-adhesive interface adhesive-cohesive failure with resin remaining on both components after debonding. failed during thennocycling.
When examining both glazed and deglazed debonded specimens under the stereomicroscope, cratering, scratching, and porcelain fracture could be found (Fig. 2). One specimen per glazed and deglazed groups was polished with the polishing stones for a total of 10 specimens and compared to another 10 specimens polished with the diamond polishing paste. On the whole the diamond paste showed greater ability to return the porcelain surface to its original state than did the pol-
failure,
cohesive
fracture
in the resin;
ishing stones (Figs. 3 and 4). The less damage done to the surface, the greater was the likelihood for restoration of the surface to a near-original state. The diamond paste was capable of restoring the deglazed porcelain specimens to a glossy state, although deep defects could not be removed. DISCUSSION
The mean tensile strength for the four adhesive systerns (excluding Ultra-bond) was 55.6 kg/cm*. This
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the polishing agent to restore the surface is limited and dependent on the extent of the initial damage. From this point of view, it may be preferable to bond to glazed porcelain. SUMMARY AND CONCLUSIONS
4. Porcelain surface after use of diamond polishing paste. (Original magnification x 20.)
Fig.
compares favorably with the bond strength measured to human enamel of 74.7 kg/cm* in a previous experiment with the same brackets and experimental design.14 This would indicate that the bond strength to porcelain should be adequate for successful clinical application. This study did not measure true adhesive strength of the primer and adhesive to porcelain because four of the products demonstrated failure occurring cohesively in the resin at the bracket-resin interface with all or most of the resin remaining on the porcelain surface. The tensile strength values reflect the cohesive strength of the adhesive. This also implies that the nature of the bracket is undoubtedly important. With different mesh gauges or acid etching, the bases may improve mechanical retention of the adhesive if improved tensile strength is required. Handling the System 1 + with porcelain primer showed the technique-sensitive nature of primer and adhesive. There is limited shelf life for the primer and strict precautions must be taken to guard against contamination. An initial problem observed in the pilot study was associated with the activator bottle cap accidentally being interchanged with the porcelain primer cap. Both are packaged in bottles of identical size with unlabeled caps. The manufacturers are urged to market the components in different sized bottles to prevent mixups and contamination. Since the failure sites were at the bracket, no significant difference in bond strengths between surface treatments could be detected. However, deglazed specimens appeared to be more vulnerable to porcelain fracture, possibly because of the increased mechanical retention and surface area for adhesion or microcracks introduced when grinding off the glaze. The ability of
Five groups of 10 glazed porcelain specimens and five groups of 10 deglazed porcelain specimens were bonded with metal brackets by use of porcelain primers to bond orthodontic adhesives and porcelain repair systems. System 1 + , Concise/Scotchprime, and the porcelain repair resins Ultra-bond, Enamelite 500, and Isopast/Silanit were used for bonding of metal brackets to porcelain surfaces; the tensile strengths measured ranged from 5 to 67 kg/cm*. Ultra-bond’s restorative kit showed very low tensile strengths compared with the other four materials. System 1 + had the highest strength (59 to 67 kg / cm’), followed by Enamelite 500, Isopast / Silanit , and Concise/ Scotchprime. The bond strengths of these four systems were comparable to those reported for human enamel. Generally speaking, debonding and cleanup with scalers and pliers created some surface defects such as craters, pits, and porcelain fracture as the resin was removed. Diamond polishing paste was better at restoring the surface than polishing stones. It should be emphasized that irreversible damage to the porcelain after debonding and resin removal may result from bonding orthodontic brackets to porcelain surfaces. Since the bond strengths to glazed and deglazed porcelains were not significantly different. it may be desirable to bond to glazed porcelain to minimize surface damage. REFERENCES 1. Gorelick L. Bonding/the state of the art. A national survey. J Clin Orthod 1979;13:39-53. 2. Hyde KR. An evaluation of the bond strength and failure site of two orthodontic direct-bonding systems [Master’s thesis]. lndianapolis: Indiana Univesity School of Dentistry, 1979. 3. Tutelain L. Dentists drill for a bigger bite of profit. USA Today 1986 Feb 27. 4. Vanarsdall RL, Musich DR. Adult orthodontics-diagnosis and treatment. In: Graber TM, ed. Orthodontics, current principles and techniques. St. Louis: The CV Mosby Company. 1985:792. B. Direct-bonding to porcelain: an in vitro study. 5. Chassemi-Tary AM J ORTHOD 1979;76:80-3. 6. Johnson RG. A new method for direct bonding orthodontic attachments to porcelain teeth using a silane coupling agent: an in vitro evaluation [Abstract]. AM J ORTHOD 1980;78:233-4. 7. Newman GV Bonding to porcelain. J Clin Orthod 1983;17: 53-s. 8. Newman SM. Dressler KB. Grenadier MR. Direct bonding of orthodontic brackets to esthetic restorative materials using a silane. AM J ORTHOD 1984:86:503-6.
Comparative
9. Wood DP. Jordan RE, Way DC, Galil KA. Bonding to porcelain and gold. AM J ORTHOD 1986;89:194-205. 10. Myerson RL. Effects of silane bonding of acrylic resins to porcelain on porcelain structure. .I Am Dent Assoc 1969;78:113-9. Il. Moffa JP. Jenkins WA. Weaver RG. Silane bonding of porcelain denture teeth to acrylic resin denture bases. J Prosthet Dent 1975:33:620-7. 12. O’Brien WJ, Ryge G. An outline of dental materials and their selection. Philadelphia: WB Saunders, 1978:392. 13. Nowlin TP, Barghi N, Norling BK. Evaluation of the bonding of three porcelain repair systems. J Prosthet Dent 1981:46: 516-8.
tensile strengths of brackets
14. Roberts LD. Gamer LD, Moore BK. An adhesion direct bonding of orthodontic brackets [Abstract]. 1983:62:238.
Reprint requesfs to: Dr. LaForrest Garner School of Dentistry Department of Orthodontics Indiana University 1121 West Michigan St. Indianapolis. IN 46202
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