- Email: [email protected]
Retention capacity of the bracket bases of new esthetic orthodontic brackets
Retention capacity of the bracket bases of new esthetic orthodontic brackets Keith A. Blalock, DDS, MS, a and John M. Powers, PhD b
Houston, Texas Tensile bond strength and bond failure locations were evaluated in vitro for three types of direct bonding cements (self-cured diacrylate, dual-cured diacrylate, and dual-cured glass ionomer) with four types of brackets (stainless steel, polycarbonate, ceramic, and ceramic-polycarbonate) by using a plastic cylinder as the substrate. A highly filled, self-cured diacrylate cement gave the highest bond strength values with the polycarbonate, stainless steel, and ceramic~-polycarbonate brackets. A dual-cured diacrylate cement gave the highest bond strength with a mechanically retained ceramic bracket. The dual-cured glass ionomer cement gave the highest bond strength values with a silanated ceramic bracket. All bond failures occurred at the bracket/cement interface with the stainless steel bracket, whereas failure locations were at the bracket/cement interface and within the cement with the polycarbonate bracket. Bond failures occurred between bracket and cement, within the cement, and within the bracket with the ceramic brackets. (AM J ORTHOD DENTOFACORTHOP1995;107:596-603.)
P o l y c a r b o n a t e direct bonding orthodontic brackets and their problems including discoloration and creep have been investigated extensively. 1-6 The importance of using a plastic bracket primer when bonding polycarbonate brackets with diacrylate cements has been documented. 2'7 The problems with the early polycarbonate brackets necessitated a more reliable means for direct bonding. The arrival of diacrylate cements and stainless steel bracket bases provided a reliable alternative, s-15 however, a mechanical means of retention was necessary because the diacrylate cements did not chemically bond to metal. Mechanical retention of the metal brackets has been reported to be disrupted by factors including weld spots, mesh defects, and roughness or smoothness of the wires, z2-r5 The new highly filled diacrylate cements were not without problems? 6-2° These led to new methods and materials such as direct bonding glass ionomer cements, 2~-29 fluoride-releasing sealants and composite resin cements, 3°-34 and increased operator ease through the use o f light-cured cements.
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Based on a thesis submitted in partial fulfillment of the requirements for the Master's degree at The University of Texas Health Science Center at Houston, Dental Branch, 1993. ~Practieing orthodontist in San Antonio, Texas. bProfessor and Chairman, Department of Oral Biomaterials, The University of Texas Health Science Center at Houston Dental Branch, Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/48818
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Orthodontists and their patients demand esthetic, as well as functional appliances. This demand has directed research toward new orthodontic brackets with improved esthetics and bonding capabilities. 39-45 Orthodontists now have a vast number of direct bonding options because of the large number of direct bonding systems and orthodontic brackets currently available. The purpose of this investigation was to evaluate the in vitro reduction capacity of the bracket bases and bond failure locations for five commercial direct bonding brackets representing four bracket types: stainless steel, ceramic, polycarbonate, and ceramic-polycarbonate. Three types of cements were tested: two-paste, self-cured composite resin; two-paste, dual-cured composite resin; and a dual-cured glass ionomer with plastic cylinders as the bonding substrate. MATERIALS AND METHODS
The codes, products, method of cement retention, and manufacturers of the brackets tested are listed in Table I. Table II lists the codes, products, systems, chemical types, batch numbers, and manufacturers for the direct bonding cements tested. The nominal area of the bracket bases was measured by digitizing an enlarged photograph of each bracket base with software capable of analyzing the digitized dimensions and recorded in square millimeters. Plastic cylinders with undercuts were used as retaining devices for the bonding cements as previously described? 2 A mounting jig was constructed to allow uniform placement of each bracket on the plastic cylinder.
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Table I. C o d e , p r o d u c t , m e t h o d o f c e m e n t r e t e n t i o n , a n d m a n u f a c t u r e r o f t h e b r a c k e t s t e s t e d Method of cement retention
Code
Product*
A C
Allure- ceramic CeramaFlex- ceramic with fused polycarbonate base Mini-Diamond - stainless steel
Silanated Silanated
GAC, Central Islip, N.Y. TP Orthodontics, La Porte, In.
100 gauge brazed mesh base
Spirit bracket - reinforced plastic bracket Transcend- ceramic
Mechanical
Ormco Corporation, Glendora, Calif. Ormco Corporation
M S T
Mechanical
Manufacturer
Unitek Corporation, Monrovia, Calif.
*All brackets tested were for right maxillary central mcisors with bracket slot dimensions of 0.56 mm x 0.71 ram.
Table II. C o d e , p r o d u c t , system, c h e m i c a l type, b a t c h no., a n d m a n u f a c t u r e r o f c e m e n t s Code I
Product
System
CO
Concise
Self-cured adhesive: paste-paste
PF
Photac-Fil Aplicap
Dual-cured
RE
Reliance Phase II Dual Cure
Dual-cured adhesive: paste-paste
Chemical type
Batch no.
Adhesive: Bis-GMA Paste A-2HJ1 Paste Resin diacrylate B-2HK1 80% glass filler by weight Glass Ionomer Cement: 0003 Maleic/acrylic copolymers and light-curing prepolymers, 65% fluorosilicate glass filler by weight Adhesive: Bis-GMA Paste A-079082 Paste diacrylate resin B-099092 Plastic 75% by weight Bracket Primersmall particle glass 112029 Plastic Bracket Primer: methyl methacrylate
The brackets were tied to the jig with 0.25 mm stainless steel ligature wire. To minimize shear forces during loading, each bracket was placed in the center of the cylinder with the bracket slot perpendicular to the cylinder surface and the bracket base parallel to the cylinder surface. The direct bonding cements were mixed according to manufacturers' instructions and loaded into the cylinders with a syringe (Centrix, Shelton, Ct.). Plastic bracket primer (Reliance Orthodontic Products, Inc., Itasca, Ill.) was applied to the polycarbonate brackets. Cement was applied directly to the bracket base to allow intimate contact with all retentive features of the base. The jig-bracket assembly was then pressed into place on the plastic cylinder. The dual-cured cements were polymerized with a visible light curing unit (Ortholux, Model 712-019, #500963, Unitek/3M, Monrovia, Calif.). The intensity of the light was monitored with a curing radiometer (Model 100, Curing Radiometer, #108261, Demetron Research Corp., Danbury, Ct.).
[
Manufacturer 3M DentalProducts St. Paul, Minn.
Espe-Premier Sales Norristown, Pa.
Reliance Orthodontic Products, Inc. Itasca, I1.
After cementation, each bracket was inspected under magnification for any overlapping cement on the labial surface of the bracket. Any cement detected was removed before loading. Six replications for each bracketcement combination were prepared for a total of 90 samples. After storage of samples for 24 hours in deionized water at 37 ° C, a 40-mm length of 0.56 x 0.71-mm stainless steel wire was ligated to each bracket with two 0.30-ram stainless steel ligature wires. Two additional 0.35-ram stainless steel ligature wires were attached to either end of the wire ligated to each bracket and butted directly up against both sides of the bracket and the free ends ligated together forming a tight loop that fit on the hook on the lower member of the testing machine so that the load would be applied directly over the center of each bracket. The samples were placed in a loading jig shown in Fig. 1 and described previously¢6 The loading jig distributed the load evenly during the application of tensile
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Fig. 1. Photograph of testing apparatus used to test tensile bond strength of bonded brackets.
forces while minimizing shear forces. The bonded samples were loaded by a universal testing machine (Model 8501, Instron Corp., Canton, Mass.) at a crosshead rate of 0.05 cm/min. The force (L) at bond failure was recorded in kilograms, converted to Newtons, and used to calculate tensile bond strength in units of MPa with the following equation: BS = L/(nominal area of bracket base). The bond failure sites were examined optically under magnification and classified as bracket/cement interface, within cement, or within bracket. Selected samples were observed in a scanning electron microscope (JSM-820, JEOL, Peabody, Mass.). Mean values and standard deviations of bond strength were calculated. The data were analyzed statistically by analysis of variance with a factorial design. 47 Means were compared by a Tukey interval calculated at the 95% level of confidence.48 Differences between two means that were larger than the Tukey interval were statistically significant. RESULTS
Mean values and standard deviations of bond strength for each of the brackets tested with cements of CO, PF, and R E are listed in Table III, as well as the bracket base dimensions and nominal areas of the bracket bases. The nominal areas ranged from 10.1 mm 2 for bracket S to 15.9 mm 2 for bracket C.
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Fig. 2 shows the mean values for bond strength for all combinations of brackets and cements tested. The mean bond strength for cement CO ranged from 6.0 MPa with bracket M to 10.3 MPa with bracket S. The mean bond strength for cement PF ranged from 1.4 MPa with bracket S to 7.4 MPa with bracket A. The mean bond strength for cement R E ranged from 3.8 MPa with bracket M to 9.7 MPa with bracket S. Tukey intervals were 0.8 MPa for comparing brackets and 0.5 MPa for comparing cements. The coefficient of variation for the bond strength data was 14%. The locations of the failure interface for cements CO, PF, and R E are shown in Fig. 3. Fig. 4 demonstrates the bond failure site for one of the ceramic/polycarbonate brackets (C) with cement CO as seen with scanning electron microscopy. All the failures occurred at the bracket/cement interface when using the metal bracket (M). Of polycarbonate bracket (S) bond failures 94% occurred at the bracket/cement interface and 6% within the cement when tested with plastic bracket primer. Of ceramic bracket (A and T) bond failures 88% occurred at the bracket/cement interface, 8% within the bracket, and 4% within the cement. Of the bond failures 49% occurred at the bracket/cement interface, 36% within the bracket, and 15% within the cement for the ceramic bracket with the polycarbonate base (C) that was tested. Table III shows the differences in bond strength among the three cements tested with bracket M. These differences were statistically significant. The bond strength for the M-CO combination was significantly higher than that of either M-PF or M-RE. The difference between M-PF and M-RE was not significant. Differences in bond strength among the three ceramic brackets and three cements were statistically significant. Ceramic bracket-cement combination T - R E had the highest bond strength for the ceramic brackets tested as seen in Table III. Comparing the cements with each bracket showed there were no statistically significant differences among the cements with bracket A. With bracket C, cement CO gave a bond strength significantly higher than either cement PF or RE. The difference in bond strength between C-PF and C-RE was not significant. With bracket T, cement R E gave a bond strength significantly higher than either cement PF or CO. The bond strength of T-CO was significantly higher than that of T-PF. Comparing the brackets with each cement revealed no statistically significant differences among
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12
i0
8
4
A
C
M
S
T
Brackets
Fig. 2. Bond strength of five brackets tested with cements CO, PF, and RE.
Table III. Code, base dimensions, nominal area, and bond strength for brackets and cements
Bracket Code A C M S T
Base dimensions (Height x Width ram) 3.3 3.7 3.2 3.2 3.2
x x × × x
3.5 4.3 4.5 3.4 3.4
I 2
Nominal area (mm2) 11.1" 15.9 13.9 10.1 11.4
CO 6.9** 7.1 6.0 10.3 7.4
(0.4) (0.4) (0.3) (0.5) (0.7)
Bond strength (MPa) PF 7.4 4.5 3.7 1.4 5.8
(1.2) (0.8) (0.2) (0.4) (0.8)
RE
7.o (o.9) 4.3 (1.2) 3.8 (o.3) 9.7 (1.6) 9.2 (1.6)
*The nominal area was measured from digitized photographs. Multiplying the bracket base dimensions does not give an accurate measurement of the area due to the different geometric shapes of the brackets. All brackets tested had flat bases representative of typical maxillary central incisor brackets. **Mean of six replications with standard deviations in parentheses. Tukey intervals for comparisons of bond strength for brackets and cements were 0.8 MPa and 0.5 MPa, respectively.
the brackets with cement CO. All bracket-cement combinations with cement PF resulted in statistically significant differences. The bond strength of A-PF was significantly higher than T-PF which was significantly higher than C-PF. All bracket-cement combinations with cement RE resulted in statistically significant differences in bond strength. The bond strength of T-RE was significantly higher than A-RE which was significantly higher than C-RE. Differences in bond strength among the three cements tested with bracket S were statistically significant. The bond strength for the S-CO combination was significantly higher than that of S-RE followed by S-PF, which was substantially lower. Bracket-cement combination S-CO had a significantly higher bond strength than any other bracket-
cement combination tested. The lowest bracketcement combination tested was S-PF. DISCUSSION
This study does not provide clinically relevant information on bonding to enamel but rather fundamental information on bonding between cements and brackets. We agree that the interaction between enamel and cement is important but the focus of this study was the bracket/cement interface. Investigators have used both plastic and enamel substrates in bond studies. The use of a plastic substrate deletes the biologic variability of tooth structure from the experiment and allows study of the bracket/cement interface. Three previous stud-
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i00 90 80 70 4J
60
• Bracket/Cement
50
[] Within Cement
40
[] Within Bracket
$4 114
30 20 I0 0 A&T
C
M
S
Brackets Fig, 3. Bond failure site for five brackets and three cements.
ies employing plastic cylinders as the bonding substrate have shown in vitro tensile bond failures occur predominantly at the bracket/cement interface when metal brackets are used. m2'15 This observation is in agreement with other investigators who have found that in vitro tensile bond failures occur at the bracket/cement interface when metal brackets a r e u s e d . 5'a1'35'4°'49 In this study all of the failures occurred at the metal bracket/cement interface. Buzzitta and associates ~s reported the bond failure sites for plastic and ceramic brackets occurred within the bracket and within the cement. de Pulido and Powers 7 found 83% of the bond failures to occur within the bracket and 16% within the cement for plastic brackets tested with plastic bracket primer. One possible reason for the difference for bond failure sites in this study is the polycarbonate bracket (S). This bracket is reinforced with a metal bar and 20% filled by weight with silica fibers, thus greatly increasing its strength. Another reason for the differences might be improved strength of modern ceramic brackets. The vast majority of ceramic brackets marketed today are more than 99% polycrystalline alumina in composition as were all of the ceramic brackets (A, C, and T) tested in this study. The ceramic bracket with the polycarbonate base (C) was designed by the manufacturer to reduce the possibility of enamel fracture on debonding. This may occur as a result of the propen-
sity of this bracket to separate from its fused polycarbonate base as seen in Fig. 4. Table III shows the differences in bond strength among the three cements tested with bracket M. These differences were statistically significant. The difference among the bond strengths of the three cements with bracket M may be the result of the amount of inorganic filler used. Cement CO is a self-cured, diacrylate cement with 80% glass filler by weight. This type of cement has been shown to provide excellent bond strengths when used with metal brackets, n'~5 Cement PF is a dual-cured, glass ionomer cement with 65% glass filler by weight. Cement RE is a dual-cured, diacrylate cement with 75% glass filler by weight. These results agree with several recent investigations that found glass ionomer cements provide significantly lower bond strengths when compared with diacryl a t e c e m e n t s , zg'36,3v's°-53 The results also agree with recent studies that have reported self-cured diacrylate cements provided significantly higher bond strengths than light-cured diacrylate cements. 33'35 All the bond failures occurred at the bracket/cement interface with bracket M as shown in Fig. 3. This finding agrees with earlier investigations that have found in vitro bond strength failures when metal brackets are used occur predominantly at the bracket/cement interface.5'm~2'15'35'4°'49 Bracket A is a ceramic bracket that relies solely on its silanated base to provide a chemical means of retention. Bracket C has a polycarbonate base
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Fig. 4. Scanning electron micrograph of bond failure site for bracket C with cement CO. fused to the ceramic bracket with the center cut out exposing a recessed area that is silanated with shallow dimples. Bracket C was designed to greatly reduce forces on debonding to reduce the possibility of enamel fracture. The fused polycarbonate base of bracket C typically detached from the ceramic bracket entirely or partially on debonding as shown in Fig. 4. Bracket T has filler particles fused with the glass layer of the base giving it a greatly increased surface area. The apparent roughness of its surface gives it many retentive areas for bonding with cements. Concern about enamel fracture on debonding silanated, chemically bonded ceramic brackets has been expressed by several investigators?9'53 Several authors reported silanation of ceramic brackets does not result in higher bond strengths for these brackets as compared with mechanically retained metal or ceramic brackets. 4°'42-44Other investigators reported silanation of ceramic brackets results in significantly higher bond strengths compared with mechanically retained ceramic or metal b r a c k e t s . 39,41,53
This investigation found silanation of ceramic brackets resulted in significantly higher bond strengths for only one bracket-cement combination (A-PF). No statistically significant differences resulted among the ceramic brackets with cement CO. Bracket T provided the highest bond strength with cement RE that was also the highest bond strength for all the ceramic bracket-cement combi-
nations. Bracket T relies solely on a mechanical means of retention with direct bonding cements. This investigation showed that the mechanically retained ceramic bracket (T) provided higher bond strengths than the silanated, chemically retained ceramic brackets (A and C) as seen in Table lII. The bond strength of bracket S with the three cements was similar to that of bracket M in respect to the ranking of the cements in order of highest bond strength with the brackets. Cement CO was the highest followed by RE then PF; however, the difference between RE and PF was not significant for the metal bracket. This is not surprising since bracket S relies primarily on a mechanical means of retention provided by the treatment of its base with the plastic bracket primer. Lopez 13 reported that adequate bond strengths for direct bonding cements range from 3 to 5 MPa. Fajen and associates5~ concluded that a glass ionomer cement used to direct bond metal brackets appeared to provide adequate bond strengths at 3 MPa. All bracket-cement combinations tested met this threshold except for S-PF. CONCLUSIONS
1. For the metal bracket (M), cement CO had the highest bond strength (6.0 MPa). The lowest bond strengths were observed for PF (3.7 MPa) and RE (3.8 MPa). 2. For the polycarbonate bracket (S), cement CO and RE had the highest bond strengths
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(10.3 and 9.7 MPa, respectively). The lowest bond strength (1.4 MPa) was with PF. 3. For the ceramic bracket (A), bond strengths ranged from 6.9 to 7.4 MPa. For bracket (C), cement CO had the highest bond strength (7.1 MPa). With bracket C, cement PF and RE had bond strengths of 4.5 and 4.3 MPa, respectively. For bracket T, bond strengths ranged from 5.8 MPa with PF to 9.2 MPa with RE. 4. All failures occurred at the bracket/cement interface for bracket M. 5. Failures at the bracket/cement interface were 94% of the bond failures for the polycarbonate bracket S, 88% for the ceramic brackets A and T, and 49% for the ceramic bracket C. We acknowledge the cooperation of the following companies in providing products: ESPE-Premier, GAC, Ormco Corp., Reliance Orthodontic Products, TP Orthodontics, Unitek Corp., and 3M Dental Products. REFERENCES 1. Newman GV. Epoxy adhesives for orthodontic attachments: progress report. AM J ORTHOD 1965;51:901-12. 2. Newman GV. Current status of bonding attachments. J Clin Orthod 1973;7:425-49. 3. Newman GV. Adhesion and orthodontic plastic attachments. AM J ORTHOD 1969;56:573-88. 4. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-8. 5. Keizer S, ten Cate JM, M e n d s J. Direct bonding of orthodontic brackets. AM J ORTHOD 1976;69:318-27. 6. Knoll M, Gwinnett AJ, Wolff MS. Shear strength of brackets bonded to anterior and posterior teeth. AM J ORTHOD 1986;89:476-9. 7. de Pulido LG, Powers JM. Bond strength of orthodontic direct-bonding cement-plastic bracket systems in vitro. AM J ORTHOD 1983;83:124-30. 8. Zachrisson B. A posttreatment evaluation of direct bonding in orthodontics. AM J ORTHOD 1977;71:173-89. 9. Moin K, Dogon IL. An evaluation of shear strength measurements of unfilled and filled resin combinations. AM J ORTHOD 1978;74:531-6. 10. Evans LB, Powers JM. Factors affecting in vitro bond strength of no-mix orthodontic cements. AM J ORTHOD 1985;87:508-12. 11. Gorelick L. Bonding metal brackets with a self-polymerizing sealant-composite: a 12-month assessment. AM J ORTHOD 1977;71:542-3. 12. Dickinson PT, Powers JM. Evaluation of fourteen directbonding orthodontic bases. AM J ORTHOD 1980;78:630-9. 13. Lopez JI. Retentive shear strengths of various bonding attachment bases. AM J ORTHOD 1980;77:669-78. 14. Maijer R, Smith DC. Variables influencing the bond strength of metal orthodontic bracket bases. AM J ORTHOD 1981;79:20-34. 15. Buzzitta VAJ, Hallgren SE, Powers JM. Bond strength of
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16.
17.
18.
19.
20. 21. 22.
23.
24. 25. 26. 27. 28. 29.
30.
31.
32.
33.
34.
35.
36.
37.
orthodontic direct-bonding cement-bracket systems as studied in vitro. AM J ORTHOD 1982;81:87-92. Pus MD, Way DC. Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques. AM J ORTHOD 1980;77:269-83. Zachrisson BU, Arthun J. Enamel surface appearance after various debonding techniques. AM J ORTHOD 1979;75:12137. O'Reilly MM, Featherstone JDB. Demineralization and remineralization around orthodontic appliances: an in vivo study. AM J ORTHOD DENTOFAC ORTHOP 1987;92:3340. Gorelick L, Geiger AM, Gwinnett AJ. Incidence of white spot formation after bonding and banding. AM J ORTHOD 1982;81:93-8. Mizrahi E. Surface distribution of enamel opacities following orthodontic treatment. AM J ORTHOD 1983;84:323-31. Wilson AD, Kent BE. A new translucent cement for dentistry. Br Dent J 1972;132:133-5. Hotz P, McLean JW, Seed I, Wilson AD. The bonding of glass ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. Wilson AD, Crisp S, Lewis BG, McLean JW. Experimental luting agents based on the glass ionomer cement. Br Dent J 1977;142:117-22. Swartz ML, Philips RW, Clark HE. Long-term F release from glass ionomer cements. J Dent Res 1984;63:158-60. White LW. Glass ionomer cement. J Clin Orthod 1986;20: 387-91. Forsten L. Fluoride release from a glass ionomer cement. Scand J Dent Res 1977;85:503-4. Wilson AD. Developments in glass-ionomer cements. Int J Prosthodont 1989;2:438-46. Cook PA. Direct bonding with glass ionomer cement. J Clin Orthod 1990;24:509-11. Cook PA, Youngson CC. A fluoride-containing composite r e s i n - a n in vitro study of a new material for orthodontic bonding. Br J Orthod 1989;16:207-12. Sonis AL, Snell W. An evaluation of a fluoride-releasing, visible light-activated bonding system for orthodontic bracket placement. AM J ORTHOD DENTOFAC ORTHOP 1989;95:306-11. Underwood ML, Rawls HR, Zimmerman BF. Clinical evaluation of a fluoride-exchanging resin as an orthodontic adhesive. AM J ORTHOD DENTOFAC ORTHOP 1989;96:93-9. Fox NA, McCabe JF, Gordon PH. Bond strengths of orthodontic bonding materials: an in-vitro study. Br J Orthod 1991;18:125-30. Bishara SE, Swift EJ, Chan DCN. Evaluation of fluoride release from an orthodontic bonding system. AM J ORTHOD DENTOFAC ORTHOP 1991;100:106-9. Ogaard B, Rezk-Lega F, Ruben J, Arends J. Cariostatic effect and fluoride release from a visible light-curing adhesive for bonding of orthodontic brackets. AM J ORTHOD DENTOFAC ORTHOP 1992;101:303-7. King L, Smith RT, Wendt SL, Behrents RG. Bond strengths of lingual orthodontic brackets bonded with light-cured composite resins cured by transillumination. AM J ORTHOD DENTOFAC ORTHOP 1987;91:312-5. Oen JO, Gjerdet NR, Wisth PJ. Glass ionomer cements used as bonding materials for metal orthodontic brackets. An in vitro study. Eur J Orthod 1991;13:187-91. Rezk-Lega F, Ogaard B. Tensile bond force of glass iono-
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38.
39.
40.
41.
42.
43.
44.
45. 46.
mer cements in direct bonding of orthodontic brackets: an in vitro comparative study. AM J ORTHOD DENTOFAC ORTHOP 1991;100:357-61. Compton AM, Meyers CE, Hondrum SO, Lorton L. Comparison of shear bond strength of a light-cured glass ionomer and a chemically cured glass ionomer for use as an orthodontic bonding agent..AM J ORTHOD DENTOFAC ORTHOP 1992;101:138-44. Viazis AD, Cavanaugh G, Bevis RR. Bond strength of ceramic brackets under shear stress: an in vitro report. AM J ORTHOD DENTOFAC ORTHOP 1990;98:214-21. Gwinnett AJ. A comparison of shear bond strengths of metal and ceramic brackets. AM J ORTHOD DENTOFAC ORTHOP 1988;93:346-8. Odegaard J, Segner D. Shear bond strength of metal brackets compared with a new ceramic bracket..AM J ORTHOD DENTOFAC ORTHOP 1988;94:201-6. Britton JC, McInnes P, Weinberg R, Ledoux WR, Retief DH. Shear bond strength of ceramic orthodontic brackets to enamel. AM J ORTHOD DENTOFAC ORTHOP 1990;98:34853. Ostertag A J, Dhuru VB, Ferguson D J, Mayer RA. Shear, torsional, and tensile bond strengths of ceramic brackets using three adhesive filler concentrations. AM J ORTHOD DENTOFAC ORTHOP 1991;100:251-8. Harris AMP, Joseph VP, Rossouw PE. Shear peel bond strengths of esthetic brackets. AM J ORTHOD DENTOFAC ORTHOP 1992;102:215-9. Eden GT, Craig RG, Peyton FA. Evaluation of a tensile test for direct filling resins. J Dent Res 1970;49:428-34. Dalby J. (Programmer): BMD8V-Analysis of variance.
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47. 48.
49.
50.
51.
52. 53.
Ann Arbor: Statistical Research Laboratory, University of Michigan, 1968:1-8. Guenther WC. Analysis of variance. Englewood Cliff, New Jersey: Prentice Hall, 1964. Joseph VP, Rossouw PE. The shear bond strengths of stainless steel orthodontic brackets bonded to teeth with orthodontic composite resin and various fissure sealants. AM J ORTHOD DENTOFAC ORTHOP 1990;98:66-71. Klockowski R, Davis EL, Joynt RB, Wieczkowski G, McDonald A. Bond strength and durability of glass ionorner cements used as bonding agents in the placement of orthodontic brackets. AM J ORTHOD DENTOFAC ORTHOP 1989; 96:60-4. Fajen VB, Duncanson MG, Nanda RS, Currier GF, Angolkar PV. An in vitro evaluation of bond strength of three glass ionomer cements. AM J ORTHOD DENTOFAC ORTHOP 1990;97:316-22. Evans R, Oliver R. Orthodontic bonding using glass ionomer cement: an in vitro study. Eur J Orthod 1991;13:493500. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22:82-8. Winchester LJ. Bond strengths of five different ceramic brackets: an in vitro study. Eur J Orthod 1991;13:293-305.
Reprint requests to: Dr. John M. Powers The University of Texas Health Science Center at Houston Dental Branch Department of Oral Biomaterials P.O. Box 20068 Houston, TX 77225
AAO MEETING CALENDAR 1996 1997 1998 1999 2000 2001 2002
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Denver, Colo., May 11 to 15, Colorado Convention Center Philadelphia, Pa., May 3 to 7, Philadelphia Convention Center Dallas, Texas, May 16 to 20, Dallas Convention Center San Diego, Calif., May 15 to 19, San Diego Convention Center Chicago, II1., April 29 to May 3, McCormick Place Convention Center Toronto, Ontario, Canada, May 5 to 9, Toronto Convention Center Baltimore, Md., April 20 to 24, Baltimore Convention Center
Houston, Texas Tensile bond strength and bond failure locations were evaluated in vitro for three types of direct bonding cements (self-cured diacrylate, dual-cured diacrylate, and dual-cured glass ionomer) with four types of brackets (stainless steel, polycarbonate, ceramic, and ceramic-polycarbonate) by using a plastic cylinder as the substrate. A highly filled, self-cured diacrylate cement gave the highest bond strength values with the polycarbonate, stainless steel, and ceramic~-polycarbonate brackets. A dual-cured diacrylate cement gave the highest bond strength with a mechanically retained ceramic bracket. The dual-cured glass ionomer cement gave the highest bond strength values with a silanated ceramic bracket. All bond failures occurred at the bracket/cement interface with the stainless steel bracket, whereas failure locations were at the bracket/cement interface and within the cement with the polycarbonate bracket. Bond failures occurred between bracket and cement, within the cement, and within the bracket with the ceramic brackets. (AM J ORTHOD DENTOFACORTHOP1995;107:596-603.)
P o l y c a r b o n a t e direct bonding orthodontic brackets and their problems including discoloration and creep have been investigated extensively. 1-6 The importance of using a plastic bracket primer when bonding polycarbonate brackets with diacrylate cements has been documented. 2'7 The problems with the early polycarbonate brackets necessitated a more reliable means for direct bonding. The arrival of diacrylate cements and stainless steel bracket bases provided a reliable alternative, s-15 however, a mechanical means of retention was necessary because the diacrylate cements did not chemically bond to metal. Mechanical retention of the metal brackets has been reported to be disrupted by factors including weld spots, mesh defects, and roughness or smoothness of the wires, z2-r5 The new highly filled diacrylate cements were not without problems? 6-2° These led to new methods and materials such as direct bonding glass ionomer cements, 2~-29 fluoride-releasing sealants and composite resin cements, 3°-34 and increased operator ease through the use o f light-cured cements.
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Based on a thesis submitted in partial fulfillment of the requirements for the Master's degree at The University of Texas Health Science Center at Houston, Dental Branch, 1993. ~Practieing orthodontist in San Antonio, Texas. bProfessor and Chairman, Department of Oral Biomaterials, The University of Texas Health Science Center at Houston Dental Branch, Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/48818
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Orthodontists and their patients demand esthetic, as well as functional appliances. This demand has directed research toward new orthodontic brackets with improved esthetics and bonding capabilities. 39-45 Orthodontists now have a vast number of direct bonding options because of the large number of direct bonding systems and orthodontic brackets currently available. The purpose of this investigation was to evaluate the in vitro reduction capacity of the bracket bases and bond failure locations for five commercial direct bonding brackets representing four bracket types: stainless steel, ceramic, polycarbonate, and ceramic-polycarbonate. Three types of cements were tested: two-paste, self-cured composite resin; two-paste, dual-cured composite resin; and a dual-cured glass ionomer with plastic cylinders as the bonding substrate. MATERIALS AND METHODS
The codes, products, method of cement retention, and manufacturers of the brackets tested are listed in Table I. Table II lists the codes, products, systems, chemical types, batch numbers, and manufacturers for the direct bonding cements tested. The nominal area of the bracket bases was measured by digitizing an enlarged photograph of each bracket base with software capable of analyzing the digitized dimensions and recorded in square millimeters. Plastic cylinders with undercuts were used as retaining devices for the bonding cements as previously described? 2 A mounting jig was constructed to allow uniform placement of each bracket on the plastic cylinder.
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Table I. C o d e , p r o d u c t , m e t h o d o f c e m e n t r e t e n t i o n , a n d m a n u f a c t u r e r o f t h e b r a c k e t s t e s t e d Method of cement retention
Code
Product*
A C
Allure- ceramic CeramaFlex- ceramic with fused polycarbonate base Mini-Diamond - stainless steel
Silanated Silanated
GAC, Central Islip, N.Y. TP Orthodontics, La Porte, In.
100 gauge brazed mesh base
Spirit bracket - reinforced plastic bracket Transcend- ceramic
Mechanical
Ormco Corporation, Glendora, Calif. Ormco Corporation
M S T
Mechanical
Manufacturer
Unitek Corporation, Monrovia, Calif.
*All brackets tested were for right maxillary central mcisors with bracket slot dimensions of 0.56 mm x 0.71 ram.
Table II. C o d e , p r o d u c t , system, c h e m i c a l type, b a t c h no., a n d m a n u f a c t u r e r o f c e m e n t s Code I
Product
System
CO
Concise
Self-cured adhesive: paste-paste
PF
Photac-Fil Aplicap
Dual-cured
RE
Reliance Phase II Dual Cure
Dual-cured adhesive: paste-paste
Chemical type
Batch no.
Adhesive: Bis-GMA Paste A-2HJ1 Paste Resin diacrylate B-2HK1 80% glass filler by weight Glass Ionomer Cement: 0003 Maleic/acrylic copolymers and light-curing prepolymers, 65% fluorosilicate glass filler by weight Adhesive: Bis-GMA Paste A-079082 Paste diacrylate resin B-099092 Plastic 75% by weight Bracket Primersmall particle glass 112029 Plastic Bracket Primer: methyl methacrylate
The brackets were tied to the jig with 0.25 mm stainless steel ligature wire. To minimize shear forces during loading, each bracket was placed in the center of the cylinder with the bracket slot perpendicular to the cylinder surface and the bracket base parallel to the cylinder surface. The direct bonding cements were mixed according to manufacturers' instructions and loaded into the cylinders with a syringe (Centrix, Shelton, Ct.). Plastic bracket primer (Reliance Orthodontic Products, Inc., Itasca, Ill.) was applied to the polycarbonate brackets. Cement was applied directly to the bracket base to allow intimate contact with all retentive features of the base. The jig-bracket assembly was then pressed into place on the plastic cylinder. The dual-cured cements were polymerized with a visible light curing unit (Ortholux, Model 712-019, #500963, Unitek/3M, Monrovia, Calif.). The intensity of the light was monitored with a curing radiometer (Model 100, Curing Radiometer, #108261, Demetron Research Corp., Danbury, Ct.).
[
Manufacturer 3M DentalProducts St. Paul, Minn.
Espe-Premier Sales Norristown, Pa.
Reliance Orthodontic Products, Inc. Itasca, I1.
After cementation, each bracket was inspected under magnification for any overlapping cement on the labial surface of the bracket. Any cement detected was removed before loading. Six replications for each bracketcement combination were prepared for a total of 90 samples. After storage of samples for 24 hours in deionized water at 37 ° C, a 40-mm length of 0.56 x 0.71-mm stainless steel wire was ligated to each bracket with two 0.30-ram stainless steel ligature wires. Two additional 0.35-ram stainless steel ligature wires were attached to either end of the wire ligated to each bracket and butted directly up against both sides of the bracket and the free ends ligated together forming a tight loop that fit on the hook on the lower member of the testing machine so that the load would be applied directly over the center of each bracket. The samples were placed in a loading jig shown in Fig. 1 and described previously¢6 The loading jig distributed the load evenly during the application of tensile
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Fig. 1. Photograph of testing apparatus used to test tensile bond strength of bonded brackets.
forces while minimizing shear forces. The bonded samples were loaded by a universal testing machine (Model 8501, Instron Corp., Canton, Mass.) at a crosshead rate of 0.05 cm/min. The force (L) at bond failure was recorded in kilograms, converted to Newtons, and used to calculate tensile bond strength in units of MPa with the following equation: BS = L/(nominal area of bracket base). The bond failure sites were examined optically under magnification and classified as bracket/cement interface, within cement, or within bracket. Selected samples were observed in a scanning electron microscope (JSM-820, JEOL, Peabody, Mass.). Mean values and standard deviations of bond strength were calculated. The data were analyzed statistically by analysis of variance with a factorial design. 47 Means were compared by a Tukey interval calculated at the 95% level of confidence.48 Differences between two means that were larger than the Tukey interval were statistically significant. RESULTS
Mean values and standard deviations of bond strength for each of the brackets tested with cements of CO, PF, and R E are listed in Table III, as well as the bracket base dimensions and nominal areas of the bracket bases. The nominal areas ranged from 10.1 mm 2 for bracket S to 15.9 mm 2 for bracket C.
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Fig. 2 shows the mean values for bond strength for all combinations of brackets and cements tested. The mean bond strength for cement CO ranged from 6.0 MPa with bracket M to 10.3 MPa with bracket S. The mean bond strength for cement PF ranged from 1.4 MPa with bracket S to 7.4 MPa with bracket A. The mean bond strength for cement R E ranged from 3.8 MPa with bracket M to 9.7 MPa with bracket S. Tukey intervals were 0.8 MPa for comparing brackets and 0.5 MPa for comparing cements. The coefficient of variation for the bond strength data was 14%. The locations of the failure interface for cements CO, PF, and R E are shown in Fig. 3. Fig. 4 demonstrates the bond failure site for one of the ceramic/polycarbonate brackets (C) with cement CO as seen with scanning electron microscopy. All the failures occurred at the bracket/cement interface when using the metal bracket (M). Of polycarbonate bracket (S) bond failures 94% occurred at the bracket/cement interface and 6% within the cement when tested with plastic bracket primer. Of ceramic bracket (A and T) bond failures 88% occurred at the bracket/cement interface, 8% within the bracket, and 4% within the cement. Of the bond failures 49% occurred at the bracket/cement interface, 36% within the bracket, and 15% within the cement for the ceramic bracket with the polycarbonate base (C) that was tested. Table III shows the differences in bond strength among the three cements tested with bracket M. These differences were statistically significant. The bond strength for the M-CO combination was significantly higher than that of either M-PF or M-RE. The difference between M-PF and M-RE was not significant. Differences in bond strength among the three ceramic brackets and three cements were statistically significant. Ceramic bracket-cement combination T - R E had the highest bond strength for the ceramic brackets tested as seen in Table III. Comparing the cements with each bracket showed there were no statistically significant differences among the cements with bracket A. With bracket C, cement CO gave a bond strength significantly higher than either cement PF or RE. The difference in bond strength between C-PF and C-RE was not significant. With bracket T, cement R E gave a bond strength significantly higher than either cement PF or CO. The bond strength of T-CO was significantly higher than that of T-PF. Comparing the brackets with each cement revealed no statistically significant differences among
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12
i0
8
4
A
C
M
S
T
Brackets
Fig. 2. Bond strength of five brackets tested with cements CO, PF, and RE.
Table III. Code, base dimensions, nominal area, and bond strength for brackets and cements
Bracket Code A C M S T
Base dimensions (Height x Width ram) 3.3 3.7 3.2 3.2 3.2
x x × × x
3.5 4.3 4.5 3.4 3.4
I 2
Nominal area (mm2) 11.1" 15.9 13.9 10.1 11.4
CO 6.9** 7.1 6.0 10.3 7.4
(0.4) (0.4) (0.3) (0.5) (0.7)
Bond strength (MPa) PF 7.4 4.5 3.7 1.4 5.8
(1.2) (0.8) (0.2) (0.4) (0.8)
RE
7.o (o.9) 4.3 (1.2) 3.8 (o.3) 9.7 (1.6) 9.2 (1.6)
*The nominal area was measured from digitized photographs. Multiplying the bracket base dimensions does not give an accurate measurement of the area due to the different geometric shapes of the brackets. All brackets tested had flat bases representative of typical maxillary central incisor brackets. **Mean of six replications with standard deviations in parentheses. Tukey intervals for comparisons of bond strength for brackets and cements were 0.8 MPa and 0.5 MPa, respectively.
the brackets with cement CO. All bracket-cement combinations with cement PF resulted in statistically significant differences. The bond strength of A-PF was significantly higher than T-PF which was significantly higher than C-PF. All bracket-cement combinations with cement RE resulted in statistically significant differences in bond strength. The bond strength of T-RE was significantly higher than A-RE which was significantly higher than C-RE. Differences in bond strength among the three cements tested with bracket S were statistically significant. The bond strength for the S-CO combination was significantly higher than that of S-RE followed by S-PF, which was substantially lower. Bracket-cement combination S-CO had a significantly higher bond strength than any other bracket-
cement combination tested. The lowest bracketcement combination tested was S-PF. DISCUSSION
This study does not provide clinically relevant information on bonding to enamel but rather fundamental information on bonding between cements and brackets. We agree that the interaction between enamel and cement is important but the focus of this study was the bracket/cement interface. Investigators have used both plastic and enamel substrates in bond studies. The use of a plastic substrate deletes the biologic variability of tooth structure from the experiment and allows study of the bracket/cement interface. Three previous stud-
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i00 90 80 70 4J
60
• Bracket/Cement
50
[] Within Cement
40
[] Within Bracket
$4 114
30 20 I0 0 A&T
C
M
S
Brackets Fig, 3. Bond failure site for five brackets and three cements.
ies employing plastic cylinders as the bonding substrate have shown in vitro tensile bond failures occur predominantly at the bracket/cement interface when metal brackets are used. m2'15 This observation is in agreement with other investigators who have found that in vitro tensile bond failures occur at the bracket/cement interface when metal brackets a r e u s e d . 5'a1'35'4°'49 In this study all of the failures occurred at the metal bracket/cement interface. Buzzitta and associates ~s reported the bond failure sites for plastic and ceramic brackets occurred within the bracket and within the cement. de Pulido and Powers 7 found 83% of the bond failures to occur within the bracket and 16% within the cement for plastic brackets tested with plastic bracket primer. One possible reason for the difference for bond failure sites in this study is the polycarbonate bracket (S). This bracket is reinforced with a metal bar and 20% filled by weight with silica fibers, thus greatly increasing its strength. Another reason for the differences might be improved strength of modern ceramic brackets. The vast majority of ceramic brackets marketed today are more than 99% polycrystalline alumina in composition as were all of the ceramic brackets (A, C, and T) tested in this study. The ceramic bracket with the polycarbonate base (C) was designed by the manufacturer to reduce the possibility of enamel fracture on debonding. This may occur as a result of the propen-
sity of this bracket to separate from its fused polycarbonate base as seen in Fig. 4. Table III shows the differences in bond strength among the three cements tested with bracket M. These differences were statistically significant. The difference among the bond strengths of the three cements with bracket M may be the result of the amount of inorganic filler used. Cement CO is a self-cured, diacrylate cement with 80% glass filler by weight. This type of cement has been shown to provide excellent bond strengths when used with metal brackets, n'~5 Cement PF is a dual-cured, glass ionomer cement with 65% glass filler by weight. Cement RE is a dual-cured, diacrylate cement with 75% glass filler by weight. These results agree with several recent investigations that found glass ionomer cements provide significantly lower bond strengths when compared with diacryl a t e c e m e n t s , zg'36,3v's°-53 The results also agree with recent studies that have reported self-cured diacrylate cements provided significantly higher bond strengths than light-cured diacrylate cements. 33'35 All the bond failures occurred at the bracket/cement interface with bracket M as shown in Fig. 3. This finding agrees with earlier investigations that have found in vitro bond strength failures when metal brackets are used occur predominantly at the bracket/cement interface.5'm~2'15'35'4°'49 Bracket A is a ceramic bracket that relies solely on its silanated base to provide a chemical means of retention. Bracket C has a polycarbonate base
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Fig. 4. Scanning electron micrograph of bond failure site for bracket C with cement CO. fused to the ceramic bracket with the center cut out exposing a recessed area that is silanated with shallow dimples. Bracket C was designed to greatly reduce forces on debonding to reduce the possibility of enamel fracture. The fused polycarbonate base of bracket C typically detached from the ceramic bracket entirely or partially on debonding as shown in Fig. 4. Bracket T has filler particles fused with the glass layer of the base giving it a greatly increased surface area. The apparent roughness of its surface gives it many retentive areas for bonding with cements. Concern about enamel fracture on debonding silanated, chemically bonded ceramic brackets has been expressed by several investigators?9'53 Several authors reported silanation of ceramic brackets does not result in higher bond strengths for these brackets as compared with mechanically retained metal or ceramic brackets. 4°'42-44Other investigators reported silanation of ceramic brackets results in significantly higher bond strengths compared with mechanically retained ceramic or metal b r a c k e t s . 39,41,53
This investigation found silanation of ceramic brackets resulted in significantly higher bond strengths for only one bracket-cement combination (A-PF). No statistically significant differences resulted among the ceramic brackets with cement CO. Bracket T provided the highest bond strength with cement RE that was also the highest bond strength for all the ceramic bracket-cement combi-
nations. Bracket T relies solely on a mechanical means of retention with direct bonding cements. This investigation showed that the mechanically retained ceramic bracket (T) provided higher bond strengths than the silanated, chemically retained ceramic brackets (A and C) as seen in Table lII. The bond strength of bracket S with the three cements was similar to that of bracket M in respect to the ranking of the cements in order of highest bond strength with the brackets. Cement CO was the highest followed by RE then PF; however, the difference between RE and PF was not significant for the metal bracket. This is not surprising since bracket S relies primarily on a mechanical means of retention provided by the treatment of its base with the plastic bracket primer. Lopez 13 reported that adequate bond strengths for direct bonding cements range from 3 to 5 MPa. Fajen and associates5~ concluded that a glass ionomer cement used to direct bond metal brackets appeared to provide adequate bond strengths at 3 MPa. All bracket-cement combinations tested met this threshold except for S-PF. CONCLUSIONS
1. For the metal bracket (M), cement CO had the highest bond strength (6.0 MPa). The lowest bond strengths were observed for PF (3.7 MPa) and RE (3.8 MPa). 2. For the polycarbonate bracket (S), cement CO and RE had the highest bond strengths
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(10.3 and 9.7 MPa, respectively). The lowest bond strength (1.4 MPa) was with PF. 3. For the ceramic bracket (A), bond strengths ranged from 6.9 to 7.4 MPa. For bracket (C), cement CO had the highest bond strength (7.1 MPa). With bracket C, cement PF and RE had bond strengths of 4.5 and 4.3 MPa, respectively. For bracket T, bond strengths ranged from 5.8 MPa with PF to 9.2 MPa with RE. 4. All failures occurred at the bracket/cement interface for bracket M. 5. Failures at the bracket/cement interface were 94% of the bond failures for the polycarbonate bracket S, 88% for the ceramic brackets A and T, and 49% for the ceramic bracket C. We acknowledge the cooperation of the following companies in providing products: ESPE-Premier, GAC, Ormco Corp., Reliance Orthodontic Products, TP Orthodontics, Unitek Corp., and 3M Dental Products. REFERENCES 1. Newman GV. Epoxy adhesives for orthodontic attachments: progress report. AM J ORTHOD 1965;51:901-12. 2. Newman GV. Current status of bonding attachments. J Clin Orthod 1973;7:425-49. 3. Newman GV. Adhesion and orthodontic plastic attachments. AM J ORTHOD 1969;56:573-88. 4. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-8. 5. Keizer S, ten Cate JM, M e n d s J. Direct bonding of orthodontic brackets. AM J ORTHOD 1976;69:318-27. 6. Knoll M, Gwinnett AJ, Wolff MS. Shear strength of brackets bonded to anterior and posterior teeth. AM J ORTHOD 1986;89:476-9. 7. de Pulido LG, Powers JM. Bond strength of orthodontic direct-bonding cement-plastic bracket systems in vitro. AM J ORTHOD 1983;83:124-30. 8. Zachrisson B. A posttreatment evaluation of direct bonding in orthodontics. AM J ORTHOD 1977;71:173-89. 9. Moin K, Dogon IL. An evaluation of shear strength measurements of unfilled and filled resin combinations. AM J ORTHOD 1978;74:531-6. 10. Evans LB, Powers JM. Factors affecting in vitro bond strength of no-mix orthodontic cements. AM J ORTHOD 1985;87:508-12. 11. Gorelick L. Bonding metal brackets with a self-polymerizing sealant-composite: a 12-month assessment. AM J ORTHOD 1977;71:542-3. 12. Dickinson PT, Powers JM. Evaluation of fourteen directbonding orthodontic bases. AM J ORTHOD 1980;78:630-9. 13. Lopez JI. Retentive shear strengths of various bonding attachment bases. AM J ORTHOD 1980;77:669-78. 14. Maijer R, Smith DC. Variables influencing the bond strength of metal orthodontic bracket bases. AM J ORTHOD 1981;79:20-34. 15. Buzzitta VAJ, Hallgren SE, Powers JM. Bond strength of
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16.
17.
18.
19.
20. 21. 22.
23.
24. 25. 26. 27. 28. 29.
30.
31.
32.
33.
34.
35.
36.
37.
orthodontic direct-bonding cement-bracket systems as studied in vitro. AM J ORTHOD 1982;81:87-92. Pus MD, Way DC. Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques. AM J ORTHOD 1980;77:269-83. Zachrisson BU, Arthun J. Enamel surface appearance after various debonding techniques. AM J ORTHOD 1979;75:12137. O'Reilly MM, Featherstone JDB. Demineralization and remineralization around orthodontic appliances: an in vivo study. AM J ORTHOD DENTOFAC ORTHOP 1987;92:3340. Gorelick L, Geiger AM, Gwinnett AJ. Incidence of white spot formation after bonding and banding. AM J ORTHOD 1982;81:93-8. Mizrahi E. Surface distribution of enamel opacities following orthodontic treatment. AM J ORTHOD 1983;84:323-31. Wilson AD, Kent BE. A new translucent cement for dentistry. Br Dent J 1972;132:133-5. Hotz P, McLean JW, Seed I, Wilson AD. The bonding of glass ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. Wilson AD, Crisp S, Lewis BG, McLean JW. Experimental luting agents based on the glass ionomer cement. Br Dent J 1977;142:117-22. Swartz ML, Philips RW, Clark HE. Long-term F release from glass ionomer cements. J Dent Res 1984;63:158-60. White LW. Glass ionomer cement. J Clin Orthod 1986;20: 387-91. Forsten L. Fluoride release from a glass ionomer cement. Scand J Dent Res 1977;85:503-4. Wilson AD. Developments in glass-ionomer cements. Int J Prosthodont 1989;2:438-46. Cook PA. Direct bonding with glass ionomer cement. J Clin Orthod 1990;24:509-11. Cook PA, Youngson CC. A fluoride-containing composite r e s i n - a n in vitro study of a new material for orthodontic bonding. Br J Orthod 1989;16:207-12. Sonis AL, Snell W. An evaluation of a fluoride-releasing, visible light-activated bonding system for orthodontic bracket placement. AM J ORTHOD DENTOFAC ORTHOP 1989;95:306-11. Underwood ML, Rawls HR, Zimmerman BF. Clinical evaluation of a fluoride-exchanging resin as an orthodontic adhesive. AM J ORTHOD DENTOFAC ORTHOP 1989;96:93-9. Fox NA, McCabe JF, Gordon PH. Bond strengths of orthodontic bonding materials: an in-vitro study. Br J Orthod 1991;18:125-30. Bishara SE, Swift EJ, Chan DCN. Evaluation of fluoride release from an orthodontic bonding system. AM J ORTHOD DENTOFAC ORTHOP 1991;100:106-9. Ogaard B, Rezk-Lega F, Ruben J, Arends J. Cariostatic effect and fluoride release from a visible light-curing adhesive for bonding of orthodontic brackets. AM J ORTHOD DENTOFAC ORTHOP 1992;101:303-7. King L, Smith RT, Wendt SL, Behrents RG. Bond strengths of lingual orthodontic brackets bonded with light-cured composite resins cured by transillumination. AM J ORTHOD DENTOFAC ORTHOP 1987;91:312-5. Oen JO, Gjerdet NR, Wisth PJ. Glass ionomer cements used as bonding materials for metal orthodontic brackets. An in vitro study. Eur J Orthod 1991;13:187-91. Rezk-Lega F, Ogaard B. Tensile bond force of glass iono-
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38.
39.
40.
41.
42.
43.
44.
45. 46.
mer cements in direct bonding of orthodontic brackets: an in vitro comparative study. AM J ORTHOD DENTOFAC ORTHOP 1991;100:357-61. Compton AM, Meyers CE, Hondrum SO, Lorton L. Comparison of shear bond strength of a light-cured glass ionomer and a chemically cured glass ionomer for use as an orthodontic bonding agent..AM J ORTHOD DENTOFAC ORTHOP 1992;101:138-44. Viazis AD, Cavanaugh G, Bevis RR. Bond strength of ceramic brackets under shear stress: an in vitro report. AM J ORTHOD DENTOFAC ORTHOP 1990;98:214-21. Gwinnett AJ. A comparison of shear bond strengths of metal and ceramic brackets. AM J ORTHOD DENTOFAC ORTHOP 1988;93:346-8. Odegaard J, Segner D. Shear bond strength of metal brackets compared with a new ceramic bracket..AM J ORTHOD DENTOFAC ORTHOP 1988;94:201-6. Britton JC, McInnes P, Weinberg R, Ledoux WR, Retief DH. Shear bond strength of ceramic orthodontic brackets to enamel. AM J ORTHOD DENTOFAC ORTHOP 1990;98:34853. Ostertag A J, Dhuru VB, Ferguson D J, Mayer RA. Shear, torsional, and tensile bond strengths of ceramic brackets using three adhesive filler concentrations. AM J ORTHOD DENTOFAC ORTHOP 1991;100:251-8. Harris AMP, Joseph VP, Rossouw PE. Shear peel bond strengths of esthetic brackets. AM J ORTHOD DENTOFAC ORTHOP 1992;102:215-9. Eden GT, Craig RG, Peyton FA. Evaluation of a tensile test for direct filling resins. J Dent Res 1970;49:428-34. Dalby J. (Programmer): BMD8V-Analysis of variance.
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47. 48.
49.
50.
51.
52. 53.
Ann Arbor: Statistical Research Laboratory, University of Michigan, 1968:1-8. Guenther WC. Analysis of variance. Englewood Cliff, New Jersey: Prentice Hall, 1964. Joseph VP, Rossouw PE. The shear bond strengths of stainless steel orthodontic brackets bonded to teeth with orthodontic composite resin and various fissure sealants. AM J ORTHOD DENTOFAC ORTHOP 1990;98:66-71. Klockowski R, Davis EL, Joynt RB, Wieczkowski G, McDonald A. Bond strength and durability of glass ionorner cements used as bonding agents in the placement of orthodontic brackets. AM J ORTHOD DENTOFAC ORTHOP 1989; 96:60-4. Fajen VB, Duncanson MG, Nanda RS, Currier GF, Angolkar PV. An in vitro evaluation of bond strength of three glass ionomer cements. AM J ORTHOD DENTOFAC ORTHOP 1990;97:316-22. Evans R, Oliver R. Orthodontic bonding using glass ionomer cement: an in vitro study. Eur J Orthod 1991;13:493500. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22:82-8. Winchester LJ. Bond strengths of five different ceramic brackets: an in vitro study. Eur J Orthod 1991;13:293-305.
Reprint requests to: Dr. John M. Powers The University of Texas Health Science Center at Houston Dental Branch Department of Oral Biomaterials P.O. Box 20068 Houston, TX 77225
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