Evaluation of fourteen direct-bonding orthodontic bases

Evaluation 0ffouTteen direct-bonding orthodontic bases Philip T. Dickinson, D.D.S., M.S.,* and John M. Powers, Ph.D.** Ann

Arbor,

Mich.

Design

churuc~teristics

f&teen

rvmmercicll

wew

evaluatrd.

bond

plastic,

and

wing

d@erenws

in bond

,fi-ecpently spot-Ll’eldinR

of bonding.

Tensile

trdhesiws, independent

(urw

direct-bonding

strength

of nominul

strength

ut the base-adhesiw

of bruckets

Key words: Orthodontic

teeth mesh

irrterj&xT

to AawL\

bases,

wus

und

with

meusured umong

.size

of

oj’ the implicated

tyr)

with

bond

tltw

buses.

the buses,

us u ,j~~ctor

(s/

btc~c&~t.~

direc~t-l~o~r~li~i~ but

Bond

base.\

\trctr~rh

utttcchcvi

Stutistic~ull\,

the

matul

und

commerciull~~

us substrutes.

obserrwl

und

size,

buses

MIS

nutnrul were

ureu

mesh

mvttrl

.sign~jwunt brand

jirilnrr.\ Dumuge uflecti,l,q

.\treyqth

wtls

oc,clrrr-et/

most

c~urr.wtl

17~

bond

.~trrn~th.

direct bonding, bond strength

S

ince its introduction more than a decade ago, direct bonding of orthodontic brackets to teeth has been accepted and used by the orthodontist. In a recent survey of nearly 2,000 orthodontists, it was found that 93 percent used some form of bonding in their practice.’ With this popularity, there are now available a number of commercial direct-bonding metal bases, including perforated, mesh, and photo-etched designs. In vitro bond testing of direct-bonding systems characteristically has shown that bond failures occur at the base-adhesive interface for metal bases.’ i Yet few studies have evaluated design parameters of bases. Reynolds and von Fraunhofer’j. ’ have studied mesh size and compared mesh to perforated brackets. The purpose of this investigation was to evaluate design characteristics and bond strengths of fourteen commercial direct-bonding metal bases with commercially attached brackets. The characteristics evaluated included area of bonding, mesh size, and type. Tensile bond strength was determined with two direct-bonding adhesives using plastic cylinders and natural teeth as substrates. These data should aid the orthodontist in the selection of a direct-bonding base.

Based on a thesis submitted in partial fulfillment of the requirements for the Master’s degree in the Horace H. Rackham School of Graduate Studies at The University of Michigan, 1980. Correspondence concerning this article should be directed to John M. Powers, School of Dentistry, University of Michigan, Ann Arbor, Mich. 48109. Reprints may be requested from Dr. Powers. *Practicing orthodontist in Muskegon, Mich. **Professor of Dentistry, Department of Dental Materials, School of Dentistry. University of Michigan.

630

oOO2-Y416/80/120630+

lO$Ol

IO/O 0

1980 The C.V

Mo$by Co.

Volume 78 Number 6

Fig. 1. Plastic base.

Fourteen

cylinder

with

undercut

to hold

adhesive

direct-bonding

and with

mounting

orthodontic

jig used

bases

to place

631

the metal

Materials and methods Fourteen commercial metal bases with attached twin edgewise brackets for direct bonding to central incisors were evaluated for design characteristics and bond strength. Codes, catalog numbers, and manufacturers of the products tested are listed in Table I. Design characteristics of the bases included base dimensions, nominal area, and mesh size. The nominal area of each base was measured by planimetry* of enlarged photographs. The mesh size of the bases (except C, H, and N) was determined from these photographs as wires per linear inch. Plastic cylinders and human enamel were used as substrates for bond testing. The plastic cylinders were prepared with undercut holes to gain retention of the bonding adhesive. A special jig* (Fig. 1) was constructed to allow the bases to be mounted on the plastic blocks perpendicular to the debonding force. Base E was also tested with freshly extracted maxillary central incisors mounted in self-curing resin so that only the labial surface was exposed. The teeth were cleaned for 60 seconds with a fluoride-free pumice paste? and were bonded following manufacturers’ recommendations for etching the tooth and placing the bracket. The bonding adhesive was confined to the area of the base and was not overlapped onto the labial surface of the base. Contouring of the bases was not necessary, because the substrates were flat. Tie wires* were attached, one on each wing of the twin edgewise bracket, so that the debonding force would be applied over the center of the bracket. The bonding adhesives (A$ and B”) were mixed according to manufacturers’ instruc*Model 620015 Polar Planimeter, Keuffel and Esser Company, Morristown, N.J. *Precise, Lee Pharmaceuticals, South El Monte, Calif. *Size 0.12, Unitek Corp., Monrovia, Calif. §Endure, adhesive base H0085, adhesive catalyst 9F040, Ormco Corp., Glendora, l’Solo-Tach. No. 040379, L.D. Caulk Co., Milford, Del.

Calif.

Table

A

1. Code,

product,

Trim

Line

catalog

base

number,

and

manufacturer

of

the bases

tested

665.Base 002.008-Bracket

American

Orthodontics

17 14 Cambridge Ave. Sheboygan. WI\. 530X1

B

Ultra-Trim

Line base

663-Base 002.008.Bracket

Amertcan

C

Laminated

perforated

208.176.Base

‘I‘.P. Laboratories,

280-lO4-Bracket

P.O. Box 73 La Porte, Ind 46350 T.P, Laboratories. lnc

base D

Laminated

mesh

E

Mini-mesh

base

F

Ormesh

G

wide

Foil-mesh

base

central

base

210.357.Base 280-104-Bracket

Micro-Lok

base

Inc.

300~0059-Base 100.3022.Bracket

Ormoco Corporation 1332 S. Lone Hill Ave. Glendora, Cahf. Y 1740

300-003

Ormco

Corporation

Masel

Orthodontics

I -Base

lO&3022-Bracket BB-320-Base EDG-6

H

Orthodonticr

0.022

x 0.028-Bracket

K232-CN-22-Base

and

bracket

302 1 Darneli

Div.

Rd

Phtladelphia. Pa. 19 154 GAC International. Inc. P 0. Box Commack,

374 N.Y.

11725

1

Lok-Mesh

base

D-2205.Base A-0216.Bracket

Rocky Mountain Orthodontics P.O. Box 17085 Denver, Cola X02 17

J

Mini-Dyna

Bond base

019-41

Unitek

I-Base

OOI-377-Bracket K

Dyna

L

Micro-mesh

M N

Bond

Foil-mesh Peripheral

‘724

Corporation South Peck Rd.

Monrovia. Cahf. 91016 Umtek Corporation

base

019.31 I-Base 001.377.Bracket

base

Micro-mesh U-l-Base U IR-022/SBracket

“A”-Company, I 1436 Sorrento

base

Foil-mesh

San Diego, Calif. 92121 “A”-Company. Inc.

perforated

UlR-022/SBracket Perp.-pet-f. U- 1-Base

base

U-I -Base

“A”-Company.

Inc. Valley

Rd.

Inc

U I R-022iSBracket

tions and placed into the plastic cylinder by means of a syringe.* Adhesive from each individual mix was also applied to each base, with special attention to wiping the adhesive into the retention areas. Each base then was pressed into adhesive on a plastic cylinder or tooth (for base E). The bonded substrates were stored for 24 hours in water at 37” C. before testing with a loading jig (Fig. 2) described in detail by Eden, Craig, and Peyton.” The jig allowed the samples to be aligned to minimize shear forces during loading in tension. Samples were debonded by a testing machine? at a crosshead rate of 2 mm. per minute. The force required to debond the base was recorded and was divided by the nominal area of the *C-R Syringe, Cleve-Dent., Cleveland, tModel TT-BM, In&on Corp., Canton,

Ohio. Mass.

Volume 78 Number 6

Fourteen direct-bonding

Fig.

orthodontic

bases

633

2. Apparatus for testing tensile bond force of metal bases.

base to obtain bond strength. The failure interface was identified visually. The diametral tensile strength of the bonding adhesives was determined as described by Earnshaw and Smith. lo Five replications were tested for each condition. Mean values and standard deviations of bond strength and diametral tensile strength were computed. Bond strength data for the plastic and tooth substrates were analyzed statistically by analysis of variance” with a factorial design. Means were ranked by a Scheffe interval’* calculated at a 95 percent level of confidence. Differences between any two means that were larger than the Scheffe interval were statistically significant. Results A photograph of the bases is shown in Fig. 3. All the bases tested were of the foil-mesh variety except bases C, H, and N. Base C was a laminated perforated base, H was photo-etched, and N was a peripheral perforated base. Edgewise brackets had been

Table

11. Code.

adhesives

mesh

B

A and

size.

tested

base

dimensions.

on plastic

blocks

nomlnal for

area.

and

bond

qrengh

Horrd Base Code

Mesh

size

(length

dimen.siorzs x width)

tar

bases

Nominul urea (mm.‘)

(mm.)

srrerrgrh

.4dha/w

:I

f kg. / 1111~1. “j --.Adhe.uw

5

N

*

5.6

X S.7

26.69

0.28

(0.04):-

0.41

(0.04)‘;

D

no

4.1

x 4.‘)

16.89

0.34

(0.06)

0.46

(0.13)

G c

80 *

5.5 4.1

x 6.2 x 4.‘)

28.1’) 16.79

0.30 (0.06) 0.34 (0.08)

O.S4 (0.06) O.SY (0.08)

F I J

100 80 40

5.7 3.7 4.0

x 6.0 x 5.0 x 3.9

21.16 16.68 13.45

0.46 0.50 0.44

(0.04) (0.02) (0.08)

O.SY (0.05) 0.59 (O.OY) 0.61 (0.1 I)

K L M

40 80 x0

4.4 x 5.0 3.7 x 4.3 4. I x 5.0

17.65 15.60 19.58

0.42 0.46 0.55

(0.08) (0. IO) (0.05)

tJ.62 (0.04) 0.68 (0.05) 0.72 (0.07)

H

*

3.3

x 4.x

IS.17

0 53 (0.08)

0 91 (0.07)

A B E

60 60 100

4.0 3.0 3.7

x 5.x x 5.7 x 5.1

20.44 15.28 16.25

0.65 (0. 1 I) 0.87 (0. IO) I 17 (0. II)

O.Y4 (0. IO) I .S? (o.tl7) I .83 (0. IO)

*Not

applicable.

tMean value of five replications with standard deviations in parentheses. The Scheffe interval for comparisons of any two means among bases was 0.33 kg./mm.2 when tested on plastic blocks. The coefficient of variation was 12 percent.

Table 111.Bond strength for base E using adhesivesA and B and plastic and enamel substrates Bond Adhesive

*Mean means

value

I .26 (0.07)*

B

1.69 (0.07)

teeth and plastic

with

standard

cylinders

deviations

was 0.17

(kg. /mm. ‘)

teeth

A

of five replications

of natural

Nuturul

strength

Plustic

cylinder

I .32 (0.1 I) I .83 (0. IO) in parentheses.

Scheffe

interval

for comparison

of

k&/mm.’

spot-welded to the bases by the manufacturer, with the exception of base E, where the bracket had been brazed to the base. The code, mesh size, dimensions, and nominal area of the bases are listed in Table II. The nominal area ranged from 13.45 mm.’ for base J to 28.19 mm.2 for base G. The sizes of the wire mesh used in the manufacturing of the various mesh type bases were 40, 60, 80, and 100 mesh. Mean values and standard deviations of tensile bond strength for each of the bases with adhesives A and B using plastic cylinders also are listed in Table II. The bases are ranked according to increasing bond strength with adhesive B. The tensile bond strength ranged from 0.28 kg./mm.* to 1.32 kg./mm.* with adhesive A and from 0.41 kg./mm.* to 1.83 kg./mm.2 with adhesive B. The bond strength was always greater for adhesive B, but the difference was not always significant statistically. With the plastic cylinders 128 of 140 failures (91.4 percent) occurred at the mesh-adhesive interface, eleven failures were

Volume 18 Number 6

Fourteen direct-bonding

Fig.

3. Photograph

of bases

A through

N. (Magnification,

orthodontic

bases

635

x2.2.)

within the bracket, and one was within the adhesive. The failures within the bracket occurred with adhesive B and involved separation of the bracket or foil from the mesh. These failures were distributed as follows: A, four of five; D, one of five; G, five of five; and J, one of five. The one failure within the adhesive occurred with base E and adhesive A. The mean values and standard deviations for tensile bond strength for natural teeth and plastic cylinders using base E and adhesives A and B are listed in Table III. There was no significant difference between the bond strength for each substrate for either adhesive at the 95 percent level of confidence. The failure location of base E with natural teeth or plastic cylinders was at the base-adhesive interface, with one exception. One adhesive failure occurred with adhesive A on a plastic cylinder. The mean values based on five replications and standard deviations of the diametral tensile strength for the two adhesives were A, 3.73 (0.52) kg./mm.2 and B, 5.00 (0.36) kg./mm.2. Discussion This investigation evaluated the bond strength of fourteen commercial direct-bonding metal bases with commercially attached brackets. Base E was tested with teeth because it had the highest bond values to the plastic substrates with both adhesives A and B. If base E did not debond at the tooth-adhesive interface, it would then be reasonable to assume that bases with weaker adhesive-base bond strengths would not debond at the toothadhesive interface either. Since there was no significant difference in bond strength with either adhesive between the teeth or plastic substrates, there was no further need to use teeth for the remaining bases. Plastic cylinders were chosen as substrates because central incisors are hard to obtain. The plastic cylinders appear to be an acceptable model because in vitro bond failures are observed most frequently at the base-adhesive interface.2-7 In this study

Fig.

4. Scanning

electron

micrograph

of base

M

the most retentive base (E) failed at the base-adhesive interface when tested on enamel in vitro. The weakest link in the adhesive-base bonding systems tested in vitro continues to be the base-adhesive interface. Clinically, more failures may be observed at the enameladhesive interface than are observed in vitro, because ideal bonding to enamel is much more difficult to achieve in vivo. Improvements in bond strength of direct bonding systems in vivo, therefore, are dependent not only upon improved retention to bases but also on improved techniques to achieve more ideal bonding of the adhesive to the enamel. The emphasis in the present study, however, was on evaluation of design characteristics of metal bases. The data shown in Table II indicate a statistically significant difference among some of the bases. Bases B and E both had high values of bond strength as compared to the other bases. Several factors have been implicated as being important in the design of the base as related to retention of the adhesive. One of these factors is the size of the base. The over-all size of the base is determined by the area of the tooth available for bonding; the larger the surface available for bonding, the larger may be the base. This over-all size factor also relates to the nominal area of the base available for retaining the adhesive. Analysis of correlation l1 for adhesives A and B demonstrated that bond strength was independent of the nominal area for the bases tested. This independence is in agreement with the observations of Reynolds and von Fraunhofer.” Another factor that may affect the retentive properties of the base is mesh size. As shown in Table II, the mesh sizes of the bases studied varied from 40 to 100 mesh. Analysis of correlation ii for adhesives A and B indicated that bond strength was independent of mesh size for the bases tested. Reynolds and von Fraunhofer,” however, found with experimental meshes spot-welded to lingual buttons that coarser meshes were more retentive than the finer meshes. The present results indicate that other factors are important in determining the retentiveness of a base with a commercially attached bracket.

Volume 78 Number 6

Fourteen

Fig.

5. Scanning

Fig.

electron

6. Scanning

micrograph

electron

direct-bonding

of one

micrograph

spot-weld

of base

orthodontic

of base

bases

637

M.

E.

A factor mentioned only briefly in the literature is the damage to the bases resulting from the spot-welding of the brackets to the bases.13 As shown in Fig. 3, spot-welding appears to cause damage to the base. In Fig. 4 a scanning electron micrograph of base M shows five large spot-welds that have caused considerable damage to the mesh. Fig. 5 shows one of the five spot-welds of base M enlarged. The mesh is completely obliterated by the spot-welding, causing the wire to fracture and leaving sharp areas exposed. Figs. 6 and 7 show scanning electron micrographs of bases E and F, respectively. Both bases are made by the same manufacturer, using the same size wire mesh. The difference is that base E has the bracket brazed to the base, while base F has the bracket spot-welded to the base. Also, base F has a nominal area 1.7 times that of base E. Even though base E

Fig. 7. Scanning

electron

micrograph

of base

F

has less area than F, base E has 3.1 times greater tensile bond strength than base F. As shown in Fig. 3, bases A and B also exhibit visible evidence of damage caused by spot-welding. The damage done by the spot-welding of A and B seems minimal compared to some of the other spot-welded brackets. This minimal damage may be a factor in the relatively high values for tensile bond strength. It should be noted that base A had an 80 percent failure rate in which the bracket and foil separated during tensile loading. Spotweld damage not only may decrease the nominal area available for retention but also may produce an area of stress concentration which can initiate the fracture of the adhesive at the adhesive-base interface. Inadequate spot-welding may lead to separation of the bracket from the base. Conclusions 1. Testing of fourteen bases for tensile bond strength resulted in the determination of statistically significant differences. Bases E and B had the highest values of tensile bond strength, while bases N and D had the lowest values. 2. Tensile bond strength was found to be independent of nominal area and mesh size for the bases tested. 3. Bond failures with plastic substrates occurred at the base-adhesive interface (91.4 percent) or involved separation of the bracket from the base (7.9 percent). All bond failures with natural teeth occurred at the base-adhesive interface for base E. 4. Tensile bond strength was always greater for adhesive B than adhesive A, but the difference was not always significant statistically. 5. Adhesive B had a higher diametral tensile strength than adhesive A. The authors gratefully acknowledge the cooperation of the following companies in providing commercial products: “A’‘-Company, Inc., American Orthodontics. GAC International, Inc., L. D. Caulk Company, Masel Orthodontics Division, Ormco Corporation, Rocky Mountain Orthodontics, T. P. Laboratories, Inc., and Unitek Corporation.

Volume 78 Number 6

Fourteen direct-bonding

orthodontic

bases

639

REFERENCES 1. Gorelick, L.: Bonding/The state of the art: A national survey, J. Clin. Orthod. 13: 39-53, 1979. 2. Gorelick, L.: Bonding metal brackets with a self-polymerizing sealant-composite. A 12-month assessment, Ahl. J. ORTHOD. 71: 542-553, 1977. 3. Reynolds, I. R., and von Fraunbofer, J. A.: Direct bonding in orthodontics: A comparison of attachments, Br. J. Orthod. 4: 65-69, 1977. 4. Reynolds, I. R., and von Fraunhofer, J. A.: Direct bonding of orthodontic attachments to teeth: The relation of adhesive bond strength to gauze mesh size, Br. J. Orthod. 3: 91-95, 1976. 5. Lee, H. L., Orlowski, J. A., Enabe, E., and Rogers, B. J.: In virro and in viva evaluation of direct-bonding orthodontic bracket systems, J. Clin. Orthod. 8: 227-238, 1974. 6. Keizer, S.. ten Cate, J. M., and Arends, J.: Direct bonding of orthodontic brackets, AM. J. ORTHOD. 69: 318-327, 1976. 7. Faust, J. B., Grego, G. N., Fan, P. L., and Powers, J. M.: Penetration coefficient, tensile strength, and bond strength of thirteen direct bonding orthodontic cements, AM. J. ORTHOD. 73: 512-525, 1978. 8. Dickinson, P. T.: Evaluation of fourteen direct bonding orthodontic bases, Master’s thesis, Ann Arbor, 1980, University of Michigan, School of Dentistry. 9. Eden, G. T., Craig, R. G., and Peyton, F. A.: Evaluation of a tensile test for direct tilling resins, J. Dent. Res. 49: 428-434, 1970. 10. Eamshaw, R., and Smith, D. C.: The tensile and compressive strength of plaster and stone, Aust. Dent. J. 11: 415-422, 1966. 11. University of Michigan, Statistical Research Laboratory: A manual of elementary statistics using MIDAS, Ann Arbor, 1975, Statistical Research Laboratory. 12. Guenther, W. C.: Analysis of variance, Englewood Cliffs, N.J., 1964, Prentice-Hall, Inc. 13. Sheykholeslam, Z., and Brandt, S.: Some factors affecting the bonding of orthodontic attachments to tooth surface, J. Clin. Orthod. 11: 734-743, 1977.