CA1219476A - Orthodontic bracket - Google Patents
Orthodontic bracketInfo
- Publication number
- CA1219476A CA1219476A CA000432918A CA432918A CA1219476A CA 1219476 A CA1219476 A CA 1219476A CA 000432918 A CA000432918 A CA 000432918A CA 432918 A CA432918 A CA 432918A CA 1219476 A CA1219476 A CA 1219476A
- Authority
- CA
- Canada
- Prior art keywords
- bracket
- metal powder
- layer
- making
- thickness
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000002184 metal Substances 0.000 claims abstract description 155
- 229910052751 metal Inorganic materials 0.000 claims abstract description 155
- 239000000843 powder Substances 0.000 claims abstract description 104
- 239000002245 particle Substances 0.000 claims abstract description 61
- 238000005245 sintering Methods 0.000 claims abstract description 9
- 239000011888 foil Substances 0.000 claims description 72
- 238000004519 manufacturing process Methods 0.000 claims description 50
- 239000000463 material Substances 0.000 claims description 29
- 239000012812 sealant material Substances 0.000 claims description 15
- 238000005056 compaction Methods 0.000 claims description 13
- 238000012856 packing Methods 0.000 claims description 13
- 239000004568 cement Substances 0.000 abstract description 33
- 210000003298 dental enamel Anatomy 0.000 abstract description 7
- 239000000565 sealant Substances 0.000 abstract description 6
- 238000005452 bending Methods 0.000 abstract description 3
- 239000002861 polymer material Substances 0.000 abstract description 2
- 239000000956 alloy Substances 0.000 abstract 1
- 229910045601 alloy Inorganic materials 0.000 abstract 1
- 238000012360 testing method Methods 0.000 description 16
- 238000000034 method Methods 0.000 description 6
- 229910001220 stainless steel Inorganic materials 0.000 description 5
- 239000010935 stainless steel Substances 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 238000001816 cooling Methods 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000002923 metal particle Substances 0.000 description 3
- 229910001111 Fine metal Inorganic materials 0.000 description 2
- 230000001788 irregular Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 241000894006 Bacteria Species 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 241000566512 Orthodes Species 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003479 dental cement Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 125000004386 diacrylate group Chemical group 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000003203 everyday effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000012254 powdered material Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
- A61C7/00—Orthodontics, i.e. obtaining or maintaining the desired position of teeth, e.g. by straightening, evening, regulating, separating, or by correcting malocclusions
- A61C7/12—Brackets; Arch wires; Combinations thereof; Accessories therefor
- A61C7/14—Brackets; Fixing brackets to teeth
- A61C7/16—Brackets; Fixing brackets to teeth specially adapted to be cemented to teeth
Landscapes
- Health & Medical Sciences (AREA)
- Oral & Maxillofacial Surgery (AREA)
- Dentistry (AREA)
- Epidemiology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An orthodontic bracket of the type intended for cementing directly to a previously etched surface of the tooth enamel is made by applying to the lingual face thereof that contacts the tooth enamel surface a thin porous layer of sintered metal powder which is arranged to have a porosity such that it has keying characteristics close to that of the etched enamel and thereby facilitates the cementing adhesion of the bracket to the tooth. A particularly suitable metal powder consists of particles of the same alloy as the bracket metal and of size in the range about 10 to about 150 microns (-100 mesh), preferably from about 10 to about 50 microns (-300 mesh) applied in a thickness of about 0.05 to 0.2 mm, by means of a sintering operation that fuses the particles to the lingual face and to one another. The porous layer preferably is pre-filled with a polymer material compatible with the bonding cement, such as the sealant employed with the cement, so as to protect the layer against mechanical damage caused by bending of the bracket by the orthodontist to conform the bracket surface more closely to the tooth surface to which it is to be applied.
An orthodontic bracket of the type intended for cementing directly to a previously etched surface of the tooth enamel is made by applying to the lingual face thereof that contacts the tooth enamel surface a thin porous layer of sintered metal powder which is arranged to have a porosity such that it has keying characteristics close to that of the etched enamel and thereby facilitates the cementing adhesion of the bracket to the tooth. A particularly suitable metal powder consists of particles of the same alloy as the bracket metal and of size in the range about 10 to about 150 microns (-100 mesh), preferably from about 10 to about 50 microns (-300 mesh) applied in a thickness of about 0.05 to 0.2 mm, by means of a sintering operation that fuses the particles to the lingual face and to one another. The porous layer preferably is pre-filled with a polymer material compatible with the bonding cement, such as the sealant employed with the cement, so as to protect the layer against mechanical damage caused by bending of the bracket by the orthodontist to conform the bracket surface more closely to the tooth surface to which it is to be applied.
Description
~9~7~i 1 ORTHODONTIC BRACKET
Field of the Invention The present invention is concerned with improvements in or relating to orthodontic brackets and especially to methods of making such brackets of the type which in use are bonded to etched enamel surfaces of the teeth.
Review of the Prior Art In the early days of orthodontic practice orthodontic brackets were fastened to respective metal bands which were then placed around the teeth, but an increasing number of orthodontists are using systems in which the brackets are bonded by a cement directly to the teeth surfaces. In one such known direct bonding system the bracket lingual face to which the cement is applied is provided by a thin sheet of fine metal mesh supported by a thin metal foil welded to the bracket body. The tooth surface enamel is first etched to a depth of about 0.01 mm, so as to improve the mechanical bonding of the cement thereto, and a thin layer of unfilled cement is applied over the etched area. A relatively thick layer of filled cement is applied to the lingual face of the metal mesh and pressed firmly into the interstices thereof, so as to maximise the mechanical bonding; the bracket is then pressed firmly into place on the tooth until a small amount of excess cement squeezes from the edges.
The filling of the cement, usually with very finely ground silica, is necessary to provide it with adequate anti-abrasion resistance in the highly hostile environment of ,,, '7~
the human mouth, unfilled cement being eroded relatively quickly. The use of a surplu.s of cement is necessary since the tooth surface usually is not particularly smooth and the foil is too stiff to be able to deform enough to follow the tooth contours under the pressure which is applied in affixing the bracket to the -tooth. It is important to ensure that there are no voids or crevices between the bracket and the tooth surfaces in which, oral fluids, Eood particles, bacteria, etc., can lodge, since these could promote -the formation of decay and could in an extreme case result in a cavity or cavities. It is of course fundamental that there be an excellent bond via the cement between each tooth and the bracket of sufficient strength to withstand the relatively high forces that are applied by normal every-day activities, extending over a period of up to about three years, while permitting the cement bond to be broken relatively easily at the conclusion of the procedure.
The lingual face of each bracket that is applied to the etched tooth surface is pre-formed during manufacture to approximately the curvature of the particular tooth to which it is to be applied. ~ith approximately half of the brackets this pre-formed curvature provides a satisfactory match of the cement-joined surfaces, but with the other half the orthodontist must make some manual adjustment oE the curvature (e.g. by use of pliers) to achieve an acceptable match.
The use of the above-described fine metal mesh has proven to be relatively satisfactory, the interwoven wires providing a large number of re-entrant crevices and the like '76 into which the bonding cement can penetrate to provide the desired mechanical keying. Studies of bracket failures show that predominantly (90% thereof) they result from breaking of the bond between the cement and the bracket, and any improvement in this bond that can be obtained is therefore highly desirable. The production of the brackets involves the secure fastening of the mesh to the foil, and of the foil to the bracket, without damaging any of the components, and any improvements in cost, speed of manufacture, sceap rate reduction, etc., that can be obtained is of course desirable.
There is moveover a constant endeavour to reduce the size of the brackets, not only from the point of view of patient comfort because of the reduced bulk and protrusion, but also to give the orthodontist greater flexibility in the positioning of the brackets on the teeth, so that the required tooth movements can be obtained more readily and without the need to move the location of the brackets on the teeth during the procedure.
However, such miniaturization reduces the area available over which the cement is operative for bonding the bracket to the tooth. Any reduction in thickness of the bracket element that is interposed between the bracket body proper and the tooth surface is highly desirable, in order to reduce the overall thickness of the bracket and its protrusion from the tooth.
There is disclosed and claimed in our prior application 25 Serial No. 411,428, filed 15th September 1982, claiming priority under the provisions of the International Convention of our prior U.S. application Serial No. 302,011, filed 15th September 1981, an orthodontic bracket comprising a bracket body having at 9~'~6 the lingual face thereof a thin layee of metal powder for reception of a bonding mateeial for fixing the bracket to a respective tooth.
Definition of the Invention It is therefore an object of the invention to provide a method of making an orthodontic bracket having a ne~ kind of lingual surface for facilitating the bonding of the bracket to a tooth.
In accordance with the present invention there is provided a method of making an orthodontic bracket comprising the step of applying to the lingual face of a bracket body a thin porous layer of metal powder for reception of a bonding material for fixing the bracket to a respective tooth surface.
Preferably the said particles are adhered to the bracket and to one another by sintering.
The material of the metal powder layer may be the same as that of the bracket lingual face to which it is applied, and the said layer may be of thickness about 0.05 to 0.2 mm.
The said layer of metal powder may be carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and preferably the said metal foil is of thickness about 0~15 to 0.45 mm.
The metal powder may be of particle size about 10 to 150 microns and preferably is of particle size about 30 to 50 microns.
The particles may be of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
7~;
The thin layer may be filled with a cement-cornpatible sealant material to protect it ayainst compaction during mechanical handling thereof.
Description of the Drawings Particular preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein:-FIGURES 1 and 2 are respectively back and front perspective views of an orthodontic bracket of the invention, FIGURE 3 is a top plan view of another orthodontic bracket embodying the invention, and FIGURE 4 is a photograph of a microscopic view of a small portion of the lingual surface of the brackets of Figures 1 and 2 to a magnifica~ion of 300 times, in order to show the nature of the surface obtained by the application of the invention.
Description of the Preferred Embodiments The bracket illustrated in Figures 1 and 2 i-s that described and claimed in U.S. Patent Serial No. 4,248,588 issued to G. Herbert Hanson. Briefly, the bracket consists of a body - 4a -10 of stainless steel havlng therein a mesial-distal extending slot 12 that receives an arch wire 14. The labial side of the slot is opened and closed as required, respectively for the insertion and retention of the arch wire, by respective movements of a generally U-shaped spring member 17 that embraces the bracket body and has an end that in the slot-closed posi-tion is urged by its inherent spring action to protrude into the slot 12 for engagement wi-th the arch wire therein. The bracket has many other features that adapt it for its special task, but the exact s-tructure of the bracket is not essential to a comple-te disclosure of the present invention, and further description thereof is believed to be unnecessary. One of the advantages of the Hanson bracket is the possibility of making it of very small dimensions and a current series has an occlusal-gingival height of 2.48 mm (0.098 in.), a mesial-distal width of 2.50 mm (0.1 in.) and a lingual-labial thickness of 1.52 mm (0.060 in.). The bracket body 10 has fastened to the lingual face thereof by accurate laser welding a thin piece 17 of a thin stainless steel metal foil of 0.15 - 0.2 mm (0.006 - 0.008 in.) thickness and about 3 mm by 4 mm (0.12 to 0.16 in.) dimensions wi-th the longer edges extending mesially-distally.
Prior to its attachment to the bracket body this foil piece has applied to the lingual face thereof by a sintering operation one or more layers 18 of stainless steel metal particles in the size range oE about 37 to 44 microns, the layer or layers 18 being of total thickness 0.13 mm (0.005 in.), so that the total thickness of the foil plus metal layer/s is abou-t 0.33 mm (0.013 in.). The .sintering opera-tion is such that -the particles are not only fused to the foil but they are fused -to one another to form a resultant integral porous layer, or sandwich of porous layers, with excellent mechanical keying properties when a layer of the filled cement is applied to the lingual face of the bracket for its attachment to a tooth. With particles in this size range the resulting porous layer is found to have highly irregular pores varying in size up to 100 microns across their major dimension. It is preferred to use the same stainless steel for the foil 16 and the metal powder layer 18 since ready adhesion by the sintering opera-tion is thereby assured, or at least to use the same -type of metal (e.g.
stainless steel) but different metals can of course be used.
A relatively simple test of the adhesion capabili-ty of a particular cement/metal powder layer combination involves supporting a newly extracted tooth in some suitable manner, e.g.
by burying it in a cement in a holder with the labial face exposed, cementing a bracket to the exposed tooth face and, after the cement has set, applying a progressively increasing tensile force to the bracket until it separates from the tooth.
We suggest that a minimum acceptable figure for the applied tensile force is about 6 kg. Tests performed with brackets o-f the invention, employing the cement sold by 3M Corporation under the trade mark "CONCISE", showed that the brackets did not separate from the tooth when a force of about 6.7 kg was applied, failure occurring at the laser weld of the metal foil to the bracket body.
3~7~i The following table shows the bond strength test values obtained from a series o-f such tests, tests 1-6 employiny brackets with a foil-mesh base structure while tests 7-12 employ brackets with a powder-coated foil of the invention. In these tests failure occurred either at the cement-bracket interface or within the cement itself. These tests were carried out with twelve complete second premolar brackets as illustrated by Figures 1 and 2, of which half incorporated a foil-mesh bonding pad and the others, a powder-coated foil bonding pad of identical shape and peripheral dimensions. The surface area of each pad, calculated on the basis of gross dimensions, was 12.6 mm2 .
Two brackets (one of each type) were cemented directly opposite each other on a tooth, and a length of 0.43 mm dead soft wire was threaded through the auxiliary slot of each in turn and twisted to facilitate gripping by the jaws of an Instron tensile testing machine. Wi-th one wire in place, each tooth was mounted in turn in a special holder in -the testing machine, and the force required to separate the bracket and the tooth was determined. A cross-head speed in the range 2.5 to 5.0 ~m per minute was used. These tooth-bracket assemblies were exposed to air during the interval of approximately 3 hours which elapsed between cementing and testing.
7~j BaRe Structure Test No. _ ~ Bond Strength (kg/mm2) FOIL MESH 1 4 9 68 0.345
Field of the Invention The present invention is concerned with improvements in or relating to orthodontic brackets and especially to methods of making such brackets of the type which in use are bonded to etched enamel surfaces of the teeth.
Review of the Prior Art In the early days of orthodontic practice orthodontic brackets were fastened to respective metal bands which were then placed around the teeth, but an increasing number of orthodontists are using systems in which the brackets are bonded by a cement directly to the teeth surfaces. In one such known direct bonding system the bracket lingual face to which the cement is applied is provided by a thin sheet of fine metal mesh supported by a thin metal foil welded to the bracket body. The tooth surface enamel is first etched to a depth of about 0.01 mm, so as to improve the mechanical bonding of the cement thereto, and a thin layer of unfilled cement is applied over the etched area. A relatively thick layer of filled cement is applied to the lingual face of the metal mesh and pressed firmly into the interstices thereof, so as to maximise the mechanical bonding; the bracket is then pressed firmly into place on the tooth until a small amount of excess cement squeezes from the edges.
The filling of the cement, usually with very finely ground silica, is necessary to provide it with adequate anti-abrasion resistance in the highly hostile environment of ,,, '7~
the human mouth, unfilled cement being eroded relatively quickly. The use of a surplu.s of cement is necessary since the tooth surface usually is not particularly smooth and the foil is too stiff to be able to deform enough to follow the tooth contours under the pressure which is applied in affixing the bracket to the -tooth. It is important to ensure that there are no voids or crevices between the bracket and the tooth surfaces in which, oral fluids, Eood particles, bacteria, etc., can lodge, since these could promote -the formation of decay and could in an extreme case result in a cavity or cavities. It is of course fundamental that there be an excellent bond via the cement between each tooth and the bracket of sufficient strength to withstand the relatively high forces that are applied by normal every-day activities, extending over a period of up to about three years, while permitting the cement bond to be broken relatively easily at the conclusion of the procedure.
The lingual face of each bracket that is applied to the etched tooth surface is pre-formed during manufacture to approximately the curvature of the particular tooth to which it is to be applied. ~ith approximately half of the brackets this pre-formed curvature provides a satisfactory match of the cement-joined surfaces, but with the other half the orthodontist must make some manual adjustment oE the curvature (e.g. by use of pliers) to achieve an acceptable match.
The use of the above-described fine metal mesh has proven to be relatively satisfactory, the interwoven wires providing a large number of re-entrant crevices and the like '76 into which the bonding cement can penetrate to provide the desired mechanical keying. Studies of bracket failures show that predominantly (90% thereof) they result from breaking of the bond between the cement and the bracket, and any improvement in this bond that can be obtained is therefore highly desirable. The production of the brackets involves the secure fastening of the mesh to the foil, and of the foil to the bracket, without damaging any of the components, and any improvements in cost, speed of manufacture, sceap rate reduction, etc., that can be obtained is of course desirable.
There is moveover a constant endeavour to reduce the size of the brackets, not only from the point of view of patient comfort because of the reduced bulk and protrusion, but also to give the orthodontist greater flexibility in the positioning of the brackets on the teeth, so that the required tooth movements can be obtained more readily and without the need to move the location of the brackets on the teeth during the procedure.
However, such miniaturization reduces the area available over which the cement is operative for bonding the bracket to the tooth. Any reduction in thickness of the bracket element that is interposed between the bracket body proper and the tooth surface is highly desirable, in order to reduce the overall thickness of the bracket and its protrusion from the tooth.
There is disclosed and claimed in our prior application 25 Serial No. 411,428, filed 15th September 1982, claiming priority under the provisions of the International Convention of our prior U.S. application Serial No. 302,011, filed 15th September 1981, an orthodontic bracket comprising a bracket body having at 9~'~6 the lingual face thereof a thin layee of metal powder for reception of a bonding mateeial for fixing the bracket to a respective tooth.
Definition of the Invention It is therefore an object of the invention to provide a method of making an orthodontic bracket having a ne~ kind of lingual surface for facilitating the bonding of the bracket to a tooth.
In accordance with the present invention there is provided a method of making an orthodontic bracket comprising the step of applying to the lingual face of a bracket body a thin porous layer of metal powder for reception of a bonding material for fixing the bracket to a respective tooth surface.
Preferably the said particles are adhered to the bracket and to one another by sintering.
The material of the metal powder layer may be the same as that of the bracket lingual face to which it is applied, and the said layer may be of thickness about 0.05 to 0.2 mm.
The said layer of metal powder may be carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and preferably the said metal foil is of thickness about 0~15 to 0.45 mm.
The metal powder may be of particle size about 10 to 150 microns and preferably is of particle size about 30 to 50 microns.
The particles may be of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
7~;
The thin layer may be filled with a cement-cornpatible sealant material to protect it ayainst compaction during mechanical handling thereof.
Description of the Drawings Particular preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein:-FIGURES 1 and 2 are respectively back and front perspective views of an orthodontic bracket of the invention, FIGURE 3 is a top plan view of another orthodontic bracket embodying the invention, and FIGURE 4 is a photograph of a microscopic view of a small portion of the lingual surface of the brackets of Figures 1 and 2 to a magnifica~ion of 300 times, in order to show the nature of the surface obtained by the application of the invention.
Description of the Preferred Embodiments The bracket illustrated in Figures 1 and 2 i-s that described and claimed in U.S. Patent Serial No. 4,248,588 issued to G. Herbert Hanson. Briefly, the bracket consists of a body - 4a -10 of stainless steel havlng therein a mesial-distal extending slot 12 that receives an arch wire 14. The labial side of the slot is opened and closed as required, respectively for the insertion and retention of the arch wire, by respective movements of a generally U-shaped spring member 17 that embraces the bracket body and has an end that in the slot-closed posi-tion is urged by its inherent spring action to protrude into the slot 12 for engagement wi-th the arch wire therein. The bracket has many other features that adapt it for its special task, but the exact s-tructure of the bracket is not essential to a comple-te disclosure of the present invention, and further description thereof is believed to be unnecessary. One of the advantages of the Hanson bracket is the possibility of making it of very small dimensions and a current series has an occlusal-gingival height of 2.48 mm (0.098 in.), a mesial-distal width of 2.50 mm (0.1 in.) and a lingual-labial thickness of 1.52 mm (0.060 in.). The bracket body 10 has fastened to the lingual face thereof by accurate laser welding a thin piece 17 of a thin stainless steel metal foil of 0.15 - 0.2 mm (0.006 - 0.008 in.) thickness and about 3 mm by 4 mm (0.12 to 0.16 in.) dimensions wi-th the longer edges extending mesially-distally.
Prior to its attachment to the bracket body this foil piece has applied to the lingual face thereof by a sintering operation one or more layers 18 of stainless steel metal particles in the size range oE about 37 to 44 microns, the layer or layers 18 being of total thickness 0.13 mm (0.005 in.), so that the total thickness of the foil plus metal layer/s is abou-t 0.33 mm (0.013 in.). The .sintering opera-tion is such that -the particles are not only fused to the foil but they are fused -to one another to form a resultant integral porous layer, or sandwich of porous layers, with excellent mechanical keying properties when a layer of the filled cement is applied to the lingual face of the bracket for its attachment to a tooth. With particles in this size range the resulting porous layer is found to have highly irregular pores varying in size up to 100 microns across their major dimension. It is preferred to use the same stainless steel for the foil 16 and the metal powder layer 18 since ready adhesion by the sintering opera-tion is thereby assured, or at least to use the same -type of metal (e.g.
stainless steel) but different metals can of course be used.
A relatively simple test of the adhesion capabili-ty of a particular cement/metal powder layer combination involves supporting a newly extracted tooth in some suitable manner, e.g.
by burying it in a cement in a holder with the labial face exposed, cementing a bracket to the exposed tooth face and, after the cement has set, applying a progressively increasing tensile force to the bracket until it separates from the tooth.
We suggest that a minimum acceptable figure for the applied tensile force is about 6 kg. Tests performed with brackets o-f the invention, employing the cement sold by 3M Corporation under the trade mark "CONCISE", showed that the brackets did not separate from the tooth when a force of about 6.7 kg was applied, failure occurring at the laser weld of the metal foil to the bracket body.
3~7~i The following table shows the bond strength test values obtained from a series o-f such tests, tests 1-6 employiny brackets with a foil-mesh base structure while tests 7-12 employ brackets with a powder-coated foil of the invention. In these tests failure occurred either at the cement-bracket interface or within the cement itself. These tests were carried out with twelve complete second premolar brackets as illustrated by Figures 1 and 2, of which half incorporated a foil-mesh bonding pad and the others, a powder-coated foil bonding pad of identical shape and peripheral dimensions. The surface area of each pad, calculated on the basis of gross dimensions, was 12.6 mm2 .
Two brackets (one of each type) were cemented directly opposite each other on a tooth, and a length of 0.43 mm dead soft wire was threaded through the auxiliary slot of each in turn and twisted to facilitate gripping by the jaws of an Instron tensile testing machine. Wi-th one wire in place, each tooth was mounted in turn in a special holder in -the testing machine, and the force required to separate the bracket and the tooth was determined. A cross-head speed in the range 2.5 to 5.0 ~m per minute was used. These tooth-bracket assemblies were exposed to air during the interval of approximately 3 hours which elapsed between cementing and testing.
7~j BaRe Structure Test No. _ ~ Bond Strength (kg/mm2) FOIL MESH 1 4 9 68 0.345
2 4.81 0.35
3 4.63 0.341
4 4.54 0.335 4.99 0.368 6 ~.99 0.368 Mean 0.352 POWDER-COATED
FOIL
7 7.72 0.569 8 8.94 0.659 9 8.17 0.602 9.53 0.702 11 9.99 0.736 12 9.53 0.702 Mean 0.662 It will be seen that the mean bond strength with the powder coated foils is 0.662 kg/mm whil.e the mean value for foil mesh bases tested under the same conditions is only 0.352 kg/mm2, so that a clear substantial improvement is obtained.
7~
The mean bond s-trenyths of both the foil mesh and the powder-coated foil do not appear to compare favourably with tensile bond strength as high as 1.83 kg/mm2 reported with use of highly filled diacrylate cement and foil mesh. However, different testing methods and a different cement were used, and owing to time constraints the cement used in the test series described above was allowed to set for only 3 hours prior to testing. The manner in which the pull was applied to the brackets generates a rota-tional moment and a concentration of stresses at the nearest laser welds, to initiate a localized bond failure which can -then spread as the dead soft foil is pulled away from the tooth. ~lthough the specimens were subjected to pull tests, the actual stresses created at the various interfaces could have contained both shear and tensile components in varying proportions. The type of stress on any yiven area of an interface would have been dependent upon its orientation relative to the line of action of the test force.
The embodiment of Figure 3 is a well-known bracket of the type which is attached to an arch wire (not shown) by means ~0 of one or more tie wires (also not shown). In this embodiment the metal powder layer 18 is applied directly to the lingual face of the body 10 instead of to a separate foil. When an intermediate foil is used this preferably will be of thickness from about 0.11 mm to 1.25 mm, (0.00~ to 0.010 in~). The thickness of the metal powder layer preferably is from about 0.5 mm to 10.2 mm (0.002 to 0.008 in.), so that the thickness of the resultant sandwich is from about 0.15 mm to 0.45 mm (0.006 -to 7~
0.018 in.). The minimum satisfactory thickness of a prior art foil/metal mesh sandwich is about 0.2 mm (0.008 in.).
It is believed that the excellent bonding obtained with the brackets of the invention is due to the fact -that the sintered metal porous layer or layers corresponds at least approximately in its keying characteristics to the etched enamel tooth surface, so that the cement employed is able to provide a satisfactory bond both to the tooth surface and the bracket surface. To this end the size of the metal powder particles should be within the range 10 to 150 microns, but preferably are within the range 30 to 50 microns. It is preferred that the particles be of size such that the difference between the smaller and the larger particles is not more than about 50 microns, this uniformity in size ensuring that they will not pack too densely, so as to leave a large number of voids into which the cement can penetrate for mechanical keying thereto.
It will be understood by those skilled in the art that when dealing with particles of this size there is no abrupt cut-off in size and although the difference between the statistically smaller and larger particles is 50 microns -there will in fact be present a much wider range of sizes, but of numbers too small to be significant. It will also be appreciated that the range of particle size for a particular metal powder will be chosen predominantly to ensure a sa-tisfactory bond of the cement to the layer 18; adequate bonding of the metal particles to one another will usually be less critical in such choice since the required particle-to-particle connection s-trength is more easily obtained by a sintering operation and, as indicated above, the majority of failures have,previously occurred in the cement/foil interface and not the bracket/foil junction.
The particle size employed is readily determined by the size of mesh through which the powdered material will pass.
ThuG, a 100 mesh sieve will pass particles of size less than 149 microns but retain any larger, while a 300 mesh sieve will pass particles less than 50 micron size; the preferred material is that which will pass through the 300 mesh sieve.
It is also well known to those skilled in the art that the shapes of the particles are affected substantially by the conditions under which they are prepared. The usual method of preparation is to finely divide metal while molten and then to cool it, and the shapes are affected by the cooling procedure;
thus, it is known that gas cooling tends to result in particles of regular spherical shape, while liquid cooling tends to result in particles of irregular shape.
In other embodiments it may be preferred to-apply the metal powder layer 18 in more than one stage. For example, a first sub-layer can be applied directly to the foil or bracket lingual face which sub-layer is of smaller size particles and/or of a wide range to achieve denser packing; the layer 18 is completed by the application of one or more other sub-layers of particle size and distribution preferred to provide the desired mechanical characteristics for adequate keying of the cement thereto.
A very satisfactory procedure for fastening the particles of the metal powder layer to the remainder of the ~'3~76 bracket, and to one another, is by sintering at about three quarters of the melting temperature. As a specific example, when the material of the foil 16 and the layer 18 is an austenitic stainless steel with a melting point of about 1480C
(27~0F) the sintering will be carried out at about 1100C to 1250C (2012F to 2282F) for about one half hour in a vacuum or hydrogen atmosphere.
- lla -3~
As described above, in a typical orthodontic practice the orthodontist first etches the surfaces of the teeth to which brackets are applied and then applies a layer of unfilled or lightly-filled enamel sealant to the etched surfaces. A
suitable sealant is that sold for e~ample by Reliance Orthod Products of Itasca, Illinois as the sealant portion of its "Phase II orthodontic adhesive system", consisting of clear, so-called "A" and "B" liquids that are mixed just prior to application and sponged onto the etched tooth surface. The cement portion proper of this system is a paste-like material, also supplied as "A" and "B" components, consisting of the sealant liquids filled with very finely divided silica. The paste components are mixed and promptly employed in the manner described above.
We have found it preferable for the orthodontic brackets to have the porous layer thereof pre-filled with a polymer material, such as unfilled or lightly-filled sealant material that is compatible with the bonding cement, since this facilitates the handling of the brackets, and particularly the mechanical bending deformation by the orthodontist to match the shape of the cement receiving lingual surface to that of the tooth surface to which it is to be applied. As mentioned above, about one half of the brackets must be manipulated in this manner. It has been found that even if this bending manipulation is of such severity that cracks appear in the polymer these appear to be repaired by usual application of sealant by the orthodontist just prior to the application of the 34~
bracket to the teeth, so that the orthodontist is given much more freedom of operation in this regard. The unfilled sealant material is used since it is of course inherently compatible with the paste material of the system, but any other compatible material can be employed.
The porous layer is found to be inherently somewhat easily crushed by the type of mechanical handling and deformation required to conform the foil to the tooth shape.
Visual inspection of such a crushed portion shows the surface to have a burnished, compacted appearance contrasting clearly with the characteristic porous appearance of the remainder of the surface, and the crushed portion no longer exhibits the required excellent keying characteristics it possessed prior to the handling and deformation. A bracket of the invention with the porous layer pre-filled as described is found to be capable of manipulation and deformation without this loss of keying characteristic, and is preferred by the orthodontist because of the ease of operation that it provides.
~.~
FOIL
7 7.72 0.569 8 8.94 0.659 9 8.17 0.602 9.53 0.702 11 9.99 0.736 12 9.53 0.702 Mean 0.662 It will be seen that the mean bond strength with the powder coated foils is 0.662 kg/mm whil.e the mean value for foil mesh bases tested under the same conditions is only 0.352 kg/mm2, so that a clear substantial improvement is obtained.
7~
The mean bond s-trenyths of both the foil mesh and the powder-coated foil do not appear to compare favourably with tensile bond strength as high as 1.83 kg/mm2 reported with use of highly filled diacrylate cement and foil mesh. However, different testing methods and a different cement were used, and owing to time constraints the cement used in the test series described above was allowed to set for only 3 hours prior to testing. The manner in which the pull was applied to the brackets generates a rota-tional moment and a concentration of stresses at the nearest laser welds, to initiate a localized bond failure which can -then spread as the dead soft foil is pulled away from the tooth. ~lthough the specimens were subjected to pull tests, the actual stresses created at the various interfaces could have contained both shear and tensile components in varying proportions. The type of stress on any yiven area of an interface would have been dependent upon its orientation relative to the line of action of the test force.
The embodiment of Figure 3 is a well-known bracket of the type which is attached to an arch wire (not shown) by means ~0 of one or more tie wires (also not shown). In this embodiment the metal powder layer 18 is applied directly to the lingual face of the body 10 instead of to a separate foil. When an intermediate foil is used this preferably will be of thickness from about 0.11 mm to 1.25 mm, (0.00~ to 0.010 in~). The thickness of the metal powder layer preferably is from about 0.5 mm to 10.2 mm (0.002 to 0.008 in.), so that the thickness of the resultant sandwich is from about 0.15 mm to 0.45 mm (0.006 -to 7~
0.018 in.). The minimum satisfactory thickness of a prior art foil/metal mesh sandwich is about 0.2 mm (0.008 in.).
It is believed that the excellent bonding obtained with the brackets of the invention is due to the fact -that the sintered metal porous layer or layers corresponds at least approximately in its keying characteristics to the etched enamel tooth surface, so that the cement employed is able to provide a satisfactory bond both to the tooth surface and the bracket surface. To this end the size of the metal powder particles should be within the range 10 to 150 microns, but preferably are within the range 30 to 50 microns. It is preferred that the particles be of size such that the difference between the smaller and the larger particles is not more than about 50 microns, this uniformity in size ensuring that they will not pack too densely, so as to leave a large number of voids into which the cement can penetrate for mechanical keying thereto.
It will be understood by those skilled in the art that when dealing with particles of this size there is no abrupt cut-off in size and although the difference between the statistically smaller and larger particles is 50 microns -there will in fact be present a much wider range of sizes, but of numbers too small to be significant. It will also be appreciated that the range of particle size for a particular metal powder will be chosen predominantly to ensure a sa-tisfactory bond of the cement to the layer 18; adequate bonding of the metal particles to one another will usually be less critical in such choice since the required particle-to-particle connection s-trength is more easily obtained by a sintering operation and, as indicated above, the majority of failures have,previously occurred in the cement/foil interface and not the bracket/foil junction.
The particle size employed is readily determined by the size of mesh through which the powdered material will pass.
ThuG, a 100 mesh sieve will pass particles of size less than 149 microns but retain any larger, while a 300 mesh sieve will pass particles less than 50 micron size; the preferred material is that which will pass through the 300 mesh sieve.
It is also well known to those skilled in the art that the shapes of the particles are affected substantially by the conditions under which they are prepared. The usual method of preparation is to finely divide metal while molten and then to cool it, and the shapes are affected by the cooling procedure;
thus, it is known that gas cooling tends to result in particles of regular spherical shape, while liquid cooling tends to result in particles of irregular shape.
In other embodiments it may be preferred to-apply the metal powder layer 18 in more than one stage. For example, a first sub-layer can be applied directly to the foil or bracket lingual face which sub-layer is of smaller size particles and/or of a wide range to achieve denser packing; the layer 18 is completed by the application of one or more other sub-layers of particle size and distribution preferred to provide the desired mechanical characteristics for adequate keying of the cement thereto.
A very satisfactory procedure for fastening the particles of the metal powder layer to the remainder of the ~'3~76 bracket, and to one another, is by sintering at about three quarters of the melting temperature. As a specific example, when the material of the foil 16 and the layer 18 is an austenitic stainless steel with a melting point of about 1480C
(27~0F) the sintering will be carried out at about 1100C to 1250C (2012F to 2282F) for about one half hour in a vacuum or hydrogen atmosphere.
- lla -3~
As described above, in a typical orthodontic practice the orthodontist first etches the surfaces of the teeth to which brackets are applied and then applies a layer of unfilled or lightly-filled enamel sealant to the etched surfaces. A
suitable sealant is that sold for e~ample by Reliance Orthod Products of Itasca, Illinois as the sealant portion of its "Phase II orthodontic adhesive system", consisting of clear, so-called "A" and "B" liquids that are mixed just prior to application and sponged onto the etched tooth surface. The cement portion proper of this system is a paste-like material, also supplied as "A" and "B" components, consisting of the sealant liquids filled with very finely divided silica. The paste components are mixed and promptly employed in the manner described above.
We have found it preferable for the orthodontic brackets to have the porous layer thereof pre-filled with a polymer material, such as unfilled or lightly-filled sealant material that is compatible with the bonding cement, since this facilitates the handling of the brackets, and particularly the mechanical bending deformation by the orthodontist to match the shape of the cement receiving lingual surface to that of the tooth surface to which it is to be applied. As mentioned above, about one half of the brackets must be manipulated in this manner. It has been found that even if this bending manipulation is of such severity that cracks appear in the polymer these appear to be repaired by usual application of sealant by the orthodontist just prior to the application of the 34~
bracket to the teeth, so that the orthodontist is given much more freedom of operation in this regard. The unfilled sealant material is used since it is of course inherently compatible with the paste material of the system, but any other compatible material can be employed.
The porous layer is found to be inherently somewhat easily crushed by the type of mechanical handling and deformation required to conform the foil to the tooth shape.
Visual inspection of such a crushed portion shows the surface to have a burnished, compacted appearance contrasting clearly with the characteristic porous appearance of the remainder of the surface, and the crushed portion no longer exhibits the required excellent keying characteristics it possessed prior to the handling and deformation. A bracket of the invention with the porous layer pre-filled as described is found to be capable of manipulation and deformation without this loss of keying characteristic, and is preferred by the orthodontist because of the ease of operation that it provides.
~.~
Claims (45)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:-
1. A method of making an orthodontic bracket comprising the step of applying to the lingual face of a bracket body a thin layer of metal powder for reception of a bonding material for fixing the bracket to a respective tooth.
2. A method of making an orthodontic bracket as claimed in claim 1, wherein the said particles are adhered to the bracket and to one another by sintering.
3. A method of making an orthodontic bracket as claimed in claim 2, wherein the metal powder is of particle size about 10 to 150 microns.
4. A method of making an orthodontic bracket as claimed in claim 1, wherein the metal powder is of particle size about 10 to 150 microns.
5. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder layer is the same as that of the bracket lingual face to which it is applied.
6. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm.
7. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body.
8. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, and the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm.
9. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the metal powder is of particle size about 30 to 50 microns.
10. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
11. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
12. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, and wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm.
13. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, and wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body.
14. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, and wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm.
15. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, and wherein the metal powder is of particle size about 30 to 50 microns.
16. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
17. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
18. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the said layer of the metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body.
19. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the said metal foil is of thickness about 0.1 to 0.25 mm, and wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm.
20. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the metal powder is of particle size about 30 to 50 microns.
21. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
22. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
23. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and wherein the metal powder is of particle size about 30 to 50 microns.
24. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
25. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
26. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, and wherein the metal powder is of particle size about 30 to 50 microns.
27. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
28. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
29. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the metal powder is of particle size about 30 to 50 microns, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
30. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the metal powder is of particle size about 30 to 50 microns, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
31. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
32. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body.
33. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, and wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm.
34. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the metal powder is of particle size about 30 to 50 microns.
35. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
36. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
37. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, and wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm.
38. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and wherein the metal powder is of particle size about 30 to 50 microns.
39. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
40. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
41. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, and wherein the metal powder is of particle size about 30 to 50 microns.
42. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, and wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof.
43. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
44. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, wherein the metal powder is of particle size about 30 to 50 microns, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
45. A method of making an orthodontic bracket as claimed in any one of claims 1 to 3, wherein the material of the metal powder is the same as that of the bracket lingual face to which it is applied, wherein the said layer of metal powder is of thickness about 0.05 to 0.2 mm, wherein the said layer of metal powder is carried by a separate thin metal foil constituting part of the bracket and fixed to the remainder of the bracket body, wherein the said metal foil is of thickness about 0.1 to 0.25 mm, wherein the total thickness of the metal foil and the layer of the metal powder is about 0.15 to 0.45 mm, wherein the particles are of size within a range of about 50 microns from the smaller to the larger particles to avoid dense packing thereof, and wherein the thin layer is filled with a cement-compatible sealant material to protect it against compaction during mechanical handling thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000432918A CA1219476A (en) | 1983-07-21 | 1983-07-21 | Orthodontic bracket |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000432918A CA1219476A (en) | 1983-07-21 | 1983-07-21 | Orthodontic bracket |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1219476A true CA1219476A (en) | 1987-03-24 |
Family
ID=4125722
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000432918A Expired CA1219476A (en) | 1983-07-21 | 1983-07-21 | Orthodontic bracket |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1219476A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3146934A1 (en) * | 2015-09-24 | 2017-03-29 | Ormco Corporation | Pads for orthodontic brackets, orthodontic brackets, and methods of making orthodontic brackets |
-
1983
- 1983-07-21 CA CA000432918A patent/CA1219476A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3146934A1 (en) * | 2015-09-24 | 2017-03-29 | Ormco Corporation | Pads for orthodontic brackets, orthodontic brackets, and methods of making orthodontic brackets |
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