Orthodontic appliances having improved bonding characteristics

Orthodontic appliances having improved bonding characteristics and methods of making such orthodontic appliances are disclosed. The appliances to which the present invention is applicable have a metal bonding base and tooth contact surface. Primary mechanical interlock retention means or surface is applied to the tooth contact surfaces. The primary retention surface may be 1) a mesh, 2) a layer of metallic or non-metallic particles (such as spheres, rods, shards, etc.), or 3) grooves, including undercuts, formed in the tooth contact surface. The appliances preferably further comprise secondary mechanical bond strength enhancement means or treatment. Suitable secondary enhancement treatments include 1) surface roughening (e.g., ion bombardment or other etching processes), 2) particles on the order of 5-200.mu. flame spray coated on the primary retention surface, and 3) a chemically activatable material, such as SiO.sub.2 deposited on the primary retention surface. Chemical activation may also be used to activate the chemically activatable material, such as silanation of SiO.sub.2.

FIELD OF THE INVENTION 
This invention relates to orthodontic appliances having improved bonding 
characteristics designed for attachment directly to the teeth of a patient 
and methods of making such appliances. 
BACKGROUND OF THE INVENTION 
In the practice of orthodontics, orthodontic appliances such as brackets 
are typically secured directly to teeth using an adhesive bonding system. 
In the course of most orthodontic procedures, forces are applied to the 
orthodontic brackets by orthodontic archwires, which cause maloccluded 
teeth to move in a predetermined fashion. Thus, the bonding of orthodontic 
appliances to teeth is of critical importance for several reasons: 1) to 
ensure proper transfer of the forces directly to the teeth; 2) to ensure 
that no undue forces are exerted on the teeth, particularly during removal 
of the appliances, which may cause removal of enamel; and 3) to ensure 
that the appliances are not unintentionally debonded prior to the 
completion of the treatment. 
With respect to orthodontic brackets having a metal bonding surface, 
various solutions have been suggested in the prior art to provide or 
enhance the bonding characteristics of the appliance. For example, U.S. 
Pat. Nos. 4,165,561 and 4,068,379 disclose the use of a metal mesh welded 
to the bonding base of the appliance in order to provide acceptable 
mechanical bonding characteristics. U.S. Pat. No. 4,927,361 suggests the 
use of particles in order to provide a porous structure on the tooth 
contact surface of the appliance. However, these types of brackets are 
made of materials which are substantially non-chemically reactive, and 
thus are limited with respect to the bond strengths that can be obtained 
since they rely on the mechanical bonding characteristics of the bracket. 
With respect to non-metal brackets, e.g., brackets made of a ceramic 
material, bonding of the brackets generally incorporates the use of a 
chemical treatment so that high bond strengths between bracket and tooth 
are obtained. However, use of chemically reactive bonding adhesives 
generally requires special handling and care in order to obtain desired 
bonding strengths, as set forth in U.S. Pat. No. 4,681,538. Additionally, 
due to the high bond strengths obtained with ceramic-type brackets, and 
the manner in which the bonds are fractured, a much higher risk is 
presented that enamel may be removed from the tooth during bracket 
removal. 
The present invention is intended to overcome the various drawbacks 
discussed above with respect to bonding brackets to teeth and encompasses 
improved orthodontic appliances and methods of making such appliances 
which result in improved bonding characteristics without presenting any 
substantially increased risk of removing enamel from the tooth. 
SUMMARY OF THE INVENTION 
The invention, in its broadest context, contemplates providing an 
orthodontic appliance (such as a bracket) having a metallic bonding base 
and tooth contact surface with the combination of a) primary mechanical 
interlock retention means, including undercut regions, which has the 
capability of providing adequate bond strength when adhered to a tooth 
enamel surface using a dental adhesive, and b) secondary mechanical bond 
strength enhancement means applied to the primary retention means. 
Generally speaking, the minimum shear bond strength that is considered 
adequate for metal brackets, as tested on brackets adhered to yearling 
bovine enamel tooth surfaces, is approximately 6.0 kilograms of the load. 
This figure is dependent upon several variables, including adhesive type, 
particular bracket base material, and enamel surface preparation, among 
other things. 
In a preferred embodiment, the undercut regions of the primary mechanical 
interlock retention means, which facilitate mechanical bonding of the 
appliance to a tooth enamel surface using a dental adhesive, are provided 
by a) bonding particles to the bracket base such as metal or ceramic 
spheres, shards, rods, cubes, or the like, which in combination with the 
base provide the undercut regions; b) a mesh bonded to the tooth contact 
surface, the strands of which provide the undercut regions; or, 
alternatively, c) forming undercut regions, including grooves, in the 
tooth contact surface. The primary mechanical interlock retention means 
can be provided in accordance with the teachings of one or more of the 
following U.S. Pat. Nos.: 5,108,285, 5,071,344, 4,927,361, 4,838,786, 
4,752,221, 4,460,336, 4,165,561 and 4,068,379. 
The secondary mechanical bond strength enhancement means applied to the 
primary retention means serves to provide additional undercut regions to 
enhance mechanical bonding of the appliance to a tooth enamel surface 
using a dental adhesive and/or to increase the surface area of the primary 
retention means to enhance the mechanical bonding of the appliance to a 
tooth enamel surface. Increasing the surface area of the primary retention 
means may be accomplished by surface etching or roughening or by adhering 
particles to the primary retention means. If etching is used, preferably 
it is accomplished by ion beam bombardment. If particles are adhered to 
the primary retention means to increase its surface area, the particles 
can be of any suitable material and may be bonded in any suitable manner, 
such as metallic cubes sintered to the strands of a metallic mesh primary 
retention means. Increasing the undercut regions of the primary retention 
means may be accomplished by sintering metallic spheres to the strands of 
a metallic mesh. The metal spheres, since they themselves provide undercut 
regions, augment the undercut spaces provided by the primary retention 
means (e.g., metal mesh). Additionally, the spheres provide increased 
surface area, further augmenting or enhancing the mechanical bond strength 
when the bracket is adhered to a tooth enamel surface using a dental 
adhesive. 
In addition to increasing the surface area of the primary retention means 
or increasing the undercut of the primary retention means, the secondary 
mechanical bond strength enhancement means may be accomplished by 
depositing a chemically activatable material on the primary retention 
means. The chemically activatable material may be deposited in a 
continuous or intermittent layer on the primary retention means, or it may 
be applied in the form of particles of a chemically activatable material. 
In the case of particles, one preferred deposition method is Diamond Jet 
Coating of ARMACOR M powder of approximately -400 mesh. The use of such 
particles further enhances the bond strength of the appliance by 
increasing the surface area of the primary retention surface. Finally, 
chemical activation of the chemically activatable material may be employed 
to further enhance the bond strength of the appliance by providing 
additional bonding sites. 
From the foregoing, it is apparent that certain of the secondary mechanical 
bond strength enhancement treatments applied to the primary mechanical 
interlock retention surface can augment the strength of the bond between 
the tooth and appliance provided by the primary retention surface in two 
distinct manners. For example, a secondary treatment of metal spheres or 
particles enhances the mechanical bond strength of the primary surface, 
such as a metal mesh, by providing both added surface area and additional 
undercut spaces. Similarly, a secondary treatment of chemically 
activatable particles such as particles which include or contain silicon 
dioxide (SiO.sub.2) can increase the surface area and, when chemically 
activated, as by silanation, can increase the number of surface bond 
sites. 
The present invention further encompasses methods of improving the bonding 
characteristics of an orthodontic appliance, preferably having a metallic 
bonding base and tooth contact surface. The methods generally comprise 
applying the primary mechanical interlock retention means on the tooth 
contact surface of the appliance and thereafter applying secondary 
mechanical bond strength enhancement means to the primary retention means. 
As discussed above with respect to the orthodontic appliances, the primary 
mechanical interlock retention means application step may comprise a) 
adhering particles to the tooth contact surface, b) bonding a mesh to the 
tooth contact surface, or c) forming undercut regions, including grooves, 
in the tooth contact surface. As will be appreciated, each of the above 
primary retention means includes undercut regions which facilitate 
adequate mechanical bonding of the appliance to a tooth enamel surface 
using a dental adhesive. The subsequent secondary mechanical bond strength 
enhancement means application step is preferably selected from a) surface 
etching to increase the surface area of the primary retention surface, b) 
adhering particles to the primary retention surface, and c) depositing a 
chemically activatable material on the primary retention surface. 
Additionally, the method may further comprise chemically activating the 
chemically activatable material deposited on the primary retention 
surface. 
It will be appreciated that in the context of the present invention the 
term "chemically activatable material" is intended to include any one of 
many materials which includes an oxide of one of the following elements: 
silicon, barium, boron, titanium, magnesium, zirconium, potassium, 
calcium, sodium, and thallium. One particularly suitable material is 
silicon dioxide (SiO.sub.2); however, virtually any glass oxide of the 
type typically used in glass manufacturing is suitable for use in the 
context of the present invention. 
These and other features and advantages of the present invention will 
become apparent to persons skilled in the art with reference to the 
detailed description which follows, taken in combination with the drawings 
.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, there is illustrated an orthodontic appliance 
(bracket) 10 made of a substantially non-chemically reactive material. The 
phrase "chemically reactive" is used herein to refer to the capability of 
a material or coating to be activated for adhesion to a dental adhesive 
when chemically treated, or to have significant chemical adhesion to 
adhesives as compared to the chemical adhesion of stainless steel, and as 
a result of this, to form a suitable chemical bond when a dental adhesive 
is used to bond the tooth contact surface of the bracket to a tooth. 
In the particular embodiment illustrated in FIG. 1, orthodontic appliance 
10 is an orthodontic bracket made of metal, preferably stainless steel. 
Orthodontic appliance 10 has a bonding base 11 which has a tooth contact 
surface 12 designed to be bonded to the exterior surface of a tooth using 
a suitable dental adhesive. As shown, the bonding base 11 is integrally 
formed as a part of the orthodontic appliance 10, however it need not be, 
and is made of stainless steel, or other metallic material. It will be 
understood that orthodontic appliance 10 may be made of any suitable 
material, so long as the bonding base 11 and tooth contact surface 12 are 
substantially chemically non-reactive. The bracket bonding base 11 need 
not be the same material as the body portion 13 of the bracket, and may, 
for example, be metallic or non-metallic, such as ceramic. 
In accordance with the principles of the present invention, tooth contact 
surface 12 is provided with a primary mechanical interlock retention means 
or surface, incorporating undercut regions, spaces or voids, and a 
secondary mechanical bond strength enhancement means or treatment. The 
primary retention surface provides adequate mechanical bond strength to 
enable the bracket to be satisfactorily adhered to a tooth enamel surface 
using a dental adhesive. The secondary treatment enhances the mechanical 
bond strength of the bracket. 
Primary Mechanical Interlock Retention Means 
The bracket 10 is provided with primary mechanical interlock retention 
means (hereinafter "primary retention surface") incorporating undercut 
regions or spaces. As shown in FIGS. 2A and 3A, the primary retention 
surface may comprise a mesh or screen 14 of metal or non-metal secured to 
tooth contact surface 12, as is well known in the art, by sintering or 
diffusion bonding Alternatively, other means may be secured to tooth 
contact surface 12 in order to enhance the mechanical bonding 
characteristics of the bracket. FIGS. 2B and 3B shows as one alternative a 
plurality of metallic or ceramic spherical particles or "balls" 16 
diffusion bonded in a substantially monolayer fashion on tooth contact 
surface 12. Preferably, balls of 20.mu. or greater size are suitable to 
provide sufficient undercut regions for adequate mechanical bonding, as 
defined previously. Alternatively, as shown in FIGS. 2C and 3C, a 
plurality of rod-shaped or irregular particles 18 or shards of any 
suitable material are diffusion bonded in a random pattern on tooth 
contact surface 12. Finally, the primary retention surface may comprise a 
plurality of grooves 20, including undercuts 19, formed (preferably by 
machining) in the tooth contact surface 12 of bracket 10. It will be 
appreciated by persons skilled in the art that other primary mechanical 
retention means may be utilized in the practice of the present invention. 
A preferred embodiment of the present invention is illustrated in exploded 
view in FIG. 4, and includes a mesh 14 made of stainless steel and having 
a mesh size of 100.times.100 openings per inch. It is to be understood 
that the mesh size and mesh material may be varied as desired. Screen 14 
is preferably diffusion bonded to tooth contact surface 12 by procedures 
well known in the art, such as those described in U.S. Pat. Nos. 4,165,561 
and 4,068,379, the contents of which are hereby fully incorporated herein 
by reference. 
Secondary Mechanical Bond Strength Enhancement Means 
It has been determined that applying a secondary mechanical bond strength 
enhancement means or treatment (hereinafter "secondary enhancement 
treatment") to at least a portion of the primary retention surface will 
enhance the overall mechanical bond strength characteristics of 
orthodontic bracket 10 when cemented to a tooth enamel surface. In one 
preferred form, the secondary treatment comprises increasing the surface 
area of the primary retention surface by a fine roughening procedure. It 
will be appreciated that the roughing procedures described below are 
equally applicable to the bracket 10 regardless of the specific primary 
retention surface utilized (i.e., mesh, ball base, rods, particles, 
grooves, etc.). 
In a preferred embodiment, the secondary enhancement treatment comprises a 
roughened surface which is formed by subjecting bracket 10 to a high 
energy surface treatment. More particularly, after woven mesh 14 has been 
secured to tooth contact surface 12, bracket 10 is subjected to ion 
bombardment whereby very small amounts of material are removed from the 
mesh 14 and the exposed areas of tooth contact surface 12. This procedure 
increases the roughness of the exposed surfaces and thus the surface area 
thereof is increased. The increased surface area provides more area for 
mechanical adhesion with the dental adhesive used to bond the bracket to 
the tooth and thus results in increased mechanical bond strength. 
In a preferred procedure, depicted schematically in FIG. 5, a plurality of 
brackets 10 are placed face down (the labial portion of the bracket facing 
downwardly) on a suitable support structure 17 such that the contact 
surface 12 and mesh 14 (primary retention surface) are exposed to a high 
energy source 22 located vertically above the brackets 10 a distance "D". 
High energy source 22 is activated and directs a stream of high energy 
ions toward the exposed surfaces of mesh 14 and tooth contact surfaces 12 
of brackets 10. 
By way of specific example, a plurality of brackets 10 may be subjected to 
argon ion bombardment from a broad-beam, gridded, Kaufman-type ion source 
which removes small amounts of material from the exposed surfaces of mesh 
14 and tooth contact surfaces 12. This type of ion bombardment or ion beam 
implantation is a well known procedure to persons skilled in the art which 
may utilize methods and apparatus commercially available from Spire 
Corporation of Bedford, Mass. 
It has been determined that subjecting only a portion of each bracket 10 to 
the roughening process is preferred to roughening the entire exposed tooth 
contact surface 12 and primary retention surface. Thus, selective 
roughening of tooth contact surface 12 and mesh 14 may be accomplished as 
schematically shown in FIG. 5 by directing the ion beam through a 
screen-type mask 24 positioned vertically above the brackets 10 so that 
only a portion of the exposed surfaces of brackets 10 are subjected to the 
ion bombardment. To accomplish this, a thin screen 24, preferably made of 
stainless steel and having a mesh size of 50.times.50 openings per inch, 
is placed above the tooth contact surfaces 12 of the brackets. By 
selecting the appropriate mesh size of screen 24, the ion bombardment 
procedure will selectively etch only portions of the bracket. Ideally, 
screen 24 is selected so that between about 10% and 90% of the surface 
area of tooth contact surface 12 and mesh 14 are exposed to the ion 
bombardment, and preferably between about 20% and 50% of those surfaces 
are exposed. 
In the particular embodiment illustrated, about 35% of the surface area of 
the contact surface 12 and mesh 14 is exposed to ion bombardment. In this 
preferred embodiment, energy source 22 is located a distance D of about 
one meter above the brackets 10 and an argon ion concentration of about 
1.times.10.sup.14 ions/cm.sup.2 is applied for a time period of about five 
minutes at a power of 300 watts. As will be appreciated by persons skilled 
in the art, the ion concentration, type of ion and duration of ion 
bombardment may be selected to obtain the desired surface roughness for 
the exposed tooth contact surface 12 and primary retention surface (mesh 
14). The distance D which ion source 22 is located above brackets 10 is 
selected to ensure the desired ion concentration at the bombardment sites. 
As depicted in FIG. 5, the ions are directed in the form of a beam at the 
exposed surfaces of brackets 10 at an angle .alpha., which is preferably 
no greater than about 60 degrees, as measured with respect to a plane 
perpendicular to tooth contact surfaces 12. 
As previously noted, this surface roughening or texturing procedure 
provides enhanced mechanical bond strength in the form of increased 
surface area of the primary retention surface (mesh 14) to aid in 
mechanical bonding of the bracket 10 to a tooth enamel surface using 
dental adhesive. FIG. 6A shows an enlarged top plan view of a tooth 
contact surface 12 having a mesh 14 secured thereto, both of which have 
been subjected to a selective roughening procedure as described above. 
Tooth contact surface 12 and mesh 14 are thus both provided with regions 
of surface roughness 26. 
It will be appreciated that alternative treatments may be employed to 
provide the desired surface roughening for increasing the surface area of 
the primary retention means. For example, chemical etching, bead blasting 
and shot peening are all believed to be suitable treatments to accomplish 
the desired roughening, and all are equally applicable regardless of the 
primary retention surface selected. 
Referring specifically to FIG. 6B, a portion of an alternative embodiment 
of an orthodontic bracket made in accordance with the present invention is 
shown. In this embodiment, the mechanical bond strength characteristics of 
the metal bracket 10 are improved or enhanced due to the increased surface 
area provided by bonding small particles 21 to tooth contact surface 12 
and mesh 14. Particles ranging in size from about 5.mu. to about 200.mu. 
are preferred. Particles of 400 mesh (less than about 37.mu.) may also be 
preferred. Particles 21 are preferably made of a material that permits the 
particles to be diffusion bonded to contact surface 12 and mesh 14. One 
suitable material for particles 21 is an alloy sold under the trade name 
ARMACOR M (-400 mesh), which is an alloy of iron, chromium, silicon and 
boron, commercially available from Amorphous Technologies International 
Inc. of Laguna Niguel, Calif. Because the bonding of particles 21 to tooth 
contact surface 12 and mesh 14 increases the surface area of the primary 
retention surface (mesh) available for mechanical retention, the overall 
mechanical bond strength characteristics of the brackets 10 are improved. 
There are several suitable procedures available for bonding particles 21 to 
tooth contact surface 12 and mesh 14. It should be appreciated that in the 
alternative embodiments depicted in FIGS. 2B-2D, wherein the primary 
retention surface is something other than a mesh (i.e., balls, rods, and 
grooves, respectively), the application of particles 21 to enhance the 
mechanical bond strength by increasing the surface area is contemplated by 
the present invention. Thus, the ensuing discussion of bonding particles 
21 to a bracket which has a mesh 14 as the primary retention surface is 
intended solely for purposes of example and is not intended in any way to 
limit the scope of the present invention. 
One preferred method of applying particles 21 to brackets 10 is by thermal 
spray coating, which is the generic term for a group of well-known and 
commonly used processes for depositing metallic and non-metallic coatings. 
These processes include, but are not limited to, flame spray, plasma 
spray, and HVOF spray, wherein the coating may be sprayed from rod or wire 
stock, or from powdered material. These types of processes are described 
in Metals Handbook, J. Clare and D. Crawmer, "Metallic Coating 
Processes--Thermal Spray Coatings", pp. 361-374, Vol. 5, 9th Ed., the 
content of which is hereby expressly incorporated herein by reference. In 
the present invention, which preferably employs powder flame spraying, the 
particles are melted and ejected from a spray gun 25 at very high speeds 
against tooth contact surface 12 and mesh 14 in an arrangement shown 
schematically in FIG. 7A. Alternatively, as shown in FIG. 7B, the powder 
flame spray is directed against a mesh panel 27 to provide the desired 
particle coating and subsequently the mesh panel 27 is cut up and adhered 
to individual brackets in any suitable manner. In the former situation, 
the particles 21 adhere to both tooth contact surface 12 and screen 14, as 
shown in FIG. 8, to provide increased surface area, which enhances the 
mechanical retention and bond strength characteristics of the bracket as a 
whole. It should be appreciated that FIG. 8 is only intended to be 
representative of particles 21 adhered to mesh 14 and tooth contact 
surface 12, and that in actual practice the particle density may be much 
greater than that shown. In the situation wherein the mesh panel 27 is 
flame spray coated prior to adherence to individual brackets, the 
particles 21 will only be adhered to the mesh 14, and not to the tooth 
contact surface 12 of the brackets 10 (not shown). 
In the practice of the present invention, one powder flame spray coating 
process which may be successfully employed to deposit powder particles on 
the primary retention surface of a bracket 10 is the Diamond Jet System 
commercially available from the Boyd Machine & Repair Co., Inc. of 
Kimmell, Ind. This system utilizes a Type DJ Diamond Jet Gun, model DJA, a 
model DJC fluid control unit, and a model DJP powder feed unit, all 
available from METCO (Div. of Perkin-Elmer), Westbury, N.Y., to propel the 
desired powder particles. In a specific example, wherein 11".times.24" 
mesh panels are spray coated with ARMACOR M (-400 mesh) powder, utilizing 
the Diamond Jet System, the following parameters may be employed: 
(1) Equipment control settings: 
(a) powder rate: 4.5-5.0 lbs/hr 
(b) propylene fuel: 39-43% 
(c) nitrogen flow: 25 (CFM) 
(d) oxygen ratio: 45% 
(e) air pressure: 50 psi 
(2) Operator parameters: 
(a) total cycle time: 60-70 seconds per panel 
(b) stroke speed: 1.5-2.0 feet per second (along the length of the panel) 
(c) nozzle distance: about 12" from the panel 
(d) number of passes: 4 total (one horizontal, one vertical, two diagonal) 
In an alternative particle application method, a thin coating of a tacky 
adhesive, such as 3M Scotch spray adhesive, is applied over the exposed 
surfaces of contact surface 12 and the primary retention surface (such as 
mesh 14). Loose particles of the desired size are sprinkled over the 
adhesive coating, preferably so that a substantially monolayer of 
particles has covered the contact surface 12 and mesh screen 14. 
Thereafter, brackets 10 with the particles adhered thereto are subjected 
to heating to a temperature of about 1150.degree. C. for about 30 minutes 
to cause the particles to diffusion bond to tooth contact surface 12 and 
mesh screen 14. Although in the particular example described, the 
particles 21 are a metal alloy, such as ARMACOR M (-400 mesh), it will be 
appreciated that particles 21 may be made of any suitable material, 
including ceramic, and may or may not be chemically activatable. 
FIGS. 10A and 10B show, in an enlarged, schematic cross-section, brackets 
10 which have a monolayer of balls 16 as the primary retention surface, 
and particles 21 applied thereto by flame spray coating and adhesive, 
respectively, as the secondary enhancement treatment. As shown in FIG. 
10A, particles 21 are "slumped" or deformed due to the high temperatures 
utilized in flame spray coating. Conversely, as shown in FIG. 10B, the 
particles 21 have substantially retained their original shape (in this 
case cubic). In either case, the application of particles 21 to the 
primary retention surface, particularly when that surface comprises mesh 
14 or balls 16, results in increased surface area and increased undercuts, 
such as undercuts 23, both of which enhance the overall mechanical bond 
strength of the brackets. 
In addition to the above-described secondary enhancement treatments 
(surface etching or roughening and particle application), another 
alternative secondary treatment contemplated by the present invention is 
the application of a chemically activatable material (as defined 
hereinabove) to the primary retention surface of bracket 10 to further 
enhance the overall bonding characteristics thereof. It will be 
appreciated that the procedures described hereinafter are applicable 
directly to brackets having only a primary retention surface, as well as 
to brackets which have been further treated to include a secondary 
enhancement treatment such as surface roughening or particle application. 
In one embodiment shown in FIG. 9, after surface roughening of mesh 14 and 
tooth contact surface 12, as described hereinabove, a thin, continuous, 
uniform layer 32 of a chemically activatable material is deposited over 
the exposed surfaces of tooth contact surface 12 and mesh 14. To 
accomplish this, an arrangement generally similar to that shown in FIG. 5 
is utilized, but without screen 24 in place. A high-energy source 22 of an 
appropriate ion is directed to a plurality of brackets 10 supported by 
support structure 17. 
In a preferred embodiment, a thin film of a silicon oxide (SiO.sub.x) such 
as silicon dioxide (SiO.sub.2), having a thickness on the order of 
approximately 2.mu., is applied to brackets 10 by evaporating high purity 
silicon dioxide, followed by ionization and impingement on mesh 14 and 
contact surface 12 of each bracket 10. 
By way of specific example, silicon dioxide ions are directed to brackets 
10 at 25 Kev and at an ion concentration of about 1.times.10.sup.14 
ions/cm.sup.2 for approximately 2 hours. The resultant coating formed by 
this ion beam implantation process provides a super-adherent, 
substantially pinhole-free coating 32 over the exposed surfaces of tooth 
contact surface 12 and mesh 14, as shown in FIG. 9. Application of the 
silicon dioxide layer 32 by deposition may be performed under vacuum 
conditions on the order of 1.times.10.sup.-7 Torr. It is believed that the 
high energy application of silicon dioxide ions causes the ions to mix 
with the surface atoms of the mesh 14 and contact surface 12 to form an 
extremely high-strength bond therewith. This high energy surface treatment 
provides a thin, uniform coating which does not substantially affect or 
interfere with any secondary enhancement treatment that may have been 
previously applied, whether it is adhered particles 21 or roughened 
regions 26. Thus, the overall bond strength characteristics of brackets 10 
are further enhanced since the silicon dioxide layer is capable of 
chemically bonding with various dental adhesives, and the primary 
retention surfaces and other secondary enhancement treatment, if utilized, 
mechanically bond with the adhesive to form high strength, substantially 
uniform bonds. 
It will be appreciated that the present invention, including methods and 
the orthodontic appliances so made, contemplates application of a 
chemically activatable layer, such as silicon dioxide, directly onto the 
primary retention surface or, as described above, onto a primary retention 
surface to which a secondary enhancement treatment has already been 
applied. 
Subsequent to application of a chemically activatable material, the 
brackets may be subjected to a suitable treatment which chemically 
activates the chemically activatable material. For example, silicon 
dioxide layer 32 may be subsequently activated by treatment with silane to 
further increase its chemical bonding characteristics and to further 
improve the overall bond strength of bracket 10. This silane activation, 
which serves to create chemical bonding sites, is preferably accomplished 
by immersion of the brackets in a silane solution (composition given 
below) heated to about 50.degree..+-.5.degree. C., for about 20 minutes 
(with periodic stirring). Thereafter, the brackets are sequentially washed 
with a 10% (by weight) isopropanol solution and de-ionized water. Finally, 
the brackets are dried in a forced draft oven at 110.degree. C. A suitable 
silane solution has the following composition: 
______________________________________ 
Component (source) 
Approximate Wt. % 
______________________________________ 
gamma-methacryloxy- 
3% 
propyltrimethoxy silane 
(Petrarch Silicones) 
glacial acetic acid 
3% 
de-ionized water 2% 
isopropyl alcohol 
balance 
______________________________________ 
Alternatively, tooth contact surface 12, the primary retention surface, 
and/or the secondary enhancement treatment may be treated directly with 
silane without any silicon dioxide deposition. This direct silane 
treatment activates the exposed surfaces, to the extent they are 
activatable, to provide chemical bonding between the bracket 10 and the 
dental adhesive used to adhere the bracket to a tooth enamel surface. 
The present invention further contemplates the application of particles, 
such as balls, rods, shards, etc., of a chemically activatable material 
directly to the bracket tooth contact surface 12. In this embodiment, the 
particles are believed to serve the dual functions of 1) a primary 
retention surface which has undercut regions to provide mechanical 
bonding, and 2) chemical bonding with the dental adhesive, and thus will 
provide enhanced bond strength to the bracket. It should be appreciated 
that the chemically activatable material applied directly to the bracket 
tooth contact surface may also be subjected to a chemical activation 
treatment, such as silanation in the case of SiO.sub.2, to even further 
enhance the bracket bond strength. 
COMATIVE EXAMPLES 
It has been determined that orthodontic brackets made in accordance with 
the present invention provide significantly improved bond strengths as 
compared with metal brackets of the type known in the prior art. It has 
further been determined that the increased bond strengths are obtained 
without any substantial increase in the risk of removing enamel from the 
teeth as compared to the bond strengths formed when ceramic brackets are 
utilized. Since metal brackets are typically more ductile than ceramic 
brackets, metal brackets may be removed from teeth in a peeling-type 
action, as opposed to the adhesive fracture-type action required to remove 
the more rigid ceramic brackets. 
Table I below sets forth the results of bond strength tests of prior art 
metal orthodontic brackets having a woven mesh applied to the tooth 
contact surface (column 1), compared to orthodontic brackets made in 
accordance with the present invention (column 2). 
TABLE I 
______________________________________ 
Average 
Col. 1 Col. 2 Brackets Col. 3 
Bond Prior Art 
made in accordance with 
% Improvement 
Strength 
Brackets the present invention 
Col. 2 v. Col. 1 
______________________________________ 
Shear 11.9 kg 20.05 kg 68% 
Tensile 
6.7 kg 11.93 kg 78% 
______________________________________ 
The brackets of column 1, which are of a type known in the prior art, are 
made of stainless steel. A 100.times.100 mesh screen, also made of 
stainless steel, was diffusion bonded to the tooth contact surface of each 
of the brackets. A dental adhesive sold by 3M under the trade name CONCISE 
was used to bond the brackets to etched yearling bovine teeth. The 
adhesive was allowed to properly cure and the bond strength was measured 
by removing the brackets from the teeth in both shear and tensile modes 
using an Instron Tensile Testing Machine, set at a cross-head speed of 5 
mm/min. The average bond strength in the shear and tensile modes are set 
forth in column 1. 
Column 2 of Table I sets forth the average bond strength, in both the shear 
and tensile modes, for brackets made in accordance with the present 
invention. More particularly, stainless steel brackets were provided with 
a 100.times.100 stainless steel mesh diffusion bonded to the tooth contact 
surface thereof. The brackets were then subjected to argon ion bombardment 
through a 50.times.50 stainless steel screen for a period of 5 minutes at 
an ion concentration of 1.times.10.sup.14 ions/cm.sup.2. The roughened 
brackets were then subjected to a silicon dioxide ion bombardment so as to 
deposit a silicon dioxide coating of about 2 microns thickness in a 
substantially uniform layer on the exposed surfaces of the tooth contact 
surface and mesh. The coated tooth contact surface and mesh screen of each 
bracket was then subjected to treatment with a silane solution as 
described hereinabove. Thereafter, the orthodontic brackets were secured 
to etched yearling bovine teeth using the 3M CONCISE brand adhesive. After 
curing of the dental adhesive, the brackets were removed using the same 
procedure described above with respect to the brackets of column 1. The 
results of the bond strength test are set forth in column 2 of Table I. 
Column 3 sets forth the percentage improvement, vis-a-vis the prior 
art-type brackets, of the bond strength of the improved brackets produced 
in accordance with the present invention. A 68% improvement in shear bond 
strength was realized and a 78% improvement in tensile bond strength was 
realized. 
While argon ion bombardment was used for roughening the tooth contact 
surface 12 and mesh 14, it is to be understood that various other high 
energy ion treatments or other roughening procedures may be used to 
accomplish this, depending upon the material of the tooth contact surface 
and mesh 14. Likewise, the size and type of mesh 14 need not be limited to 
the screen specifically described. Additionally, although silicon dioxide 
was applied as the chemically activatable material, in layer form, to 
provide chemical adhesion of the bracket to the dental adhesive. Clearly, 
other appropriate chemically activatable materials are contemplated for 
use in the present invention, as described previously. 
In addition to improving the mechanical and/or chemical bonding 
characteristics of a single bracket, the present invention is applicable 
to provide an overall corrective dental system wherein each of the 
brackets/appliances has substantially the same bond strength 
characteristics as the others. For example, in certain orthodontic 
procedures, metal appliances are adhered to the teeth of a patient and are 
connected by a common archwire. In order to ensure bond strength 
uniformity amongst the various orthodontic appliances, the same chemically 
activatable layer should be applied so that all the appliances have 
substantially the same overall bond strength characteristics. This allows 
the clinician to use a single adhesive to bond all the appliances. 
The roughening procedure described above can also be used to control the 
bond strength of individual brackets, to result in a uniform bracket set 
or system. By controlling the size of the screen through which the ion 
bombardment is applied, as well as the other previously mentioned 
parameters, the specific degree of surface area roughening can be 
controlled. Thus, when greater mechanical bond strength is desired, the 
mesh size of the screen may be selected to increase the amount of surface 
area exposed to ion bombardment. Likewise, if less mechanical bond 
strength is desired, less surface area is exposed. Therefore, by 
controlling both the chemically activatable layer applied to the brackets 
and the degree of surface roughening of each bracket, the overall bond 
strength characteristics of the appliances can be modified to provide a 
balanced system wherein appliances of different materials or sizes possess 
substantially uniform bonding characteristics. 
Metal brackets having metal mesh screens bonded to the tooth contact 
surface thereof have been used in the field of orthodontics for some time 
and provide improvements in terms of bonding characteristics over metal 
brackets which include no mesh or which include means other than a mesh on 
the tooth contact surface thereof. One disadvantage of metal brackets with 
metal mesh, however, is that the bonding strength is based solely on the 
interlocking mechanical bonding characteristics of the bracket since no 
chemical bond is formed with the dental adhesive. Bond failure rates for 
metal brackets with only primary mechanical interlock is typically greater 
than 10%, which is generally unacceptable. Bond failures require 
additional time and expense in the overall orthodontic treatment and it is 
desired to substantially reduce or eliminate such bond failures. It is 
believed that higher and more predictable bond strengths are obtained by 
employing the brackets and methods of the present invention and this will 
result in significantly reduced bond failure rates. 
It is to be understood that various other modifications and changes can be 
made to the present invention as described herein without departing from 
the scope thereof as defined by the following claims.