ORTHODONTIC ATTACHMENTS

Abstract: Orthodontic brackets or other dental attachments are provided with particulate material on the tooth engaging surface thereof to improve the strength of the bond of bracket to a tooth surface. The particulate material may be in discrete form or in the form of layers of interconnected particles forming a porous structure.

Description: ORTHODONTIC ATTACHMENTS The present invention relates to novel orthodontic and other dental attachments, such as, brackets, bases, bands, periodontal splints and oral-surgical splints. In orthodontic surgical procedures, orthodontic brackets commonly are attached directly to teeth by adhesive bonding. The tooth surface often is acid etched, so that a micro-mechanical interlock is achieved between the resin and the etched surface. Alternatively, as described in our U.S. Patent No. 4,382,792 issued May 10, 1982, the surface of the tooth may be provided with a crystal growth to which the resin is bonded. There is also a mechanical bond between the bracket base abutting the tooth and the resin. This mechanical bond represents the weak point of the assembly and brackets can become detached from the teeth by failure of the mechanical bond at the bracket/resin interface, if the shear strength thereof is exceeded. A variety of base designs have been proposed and utilized in an attempt to overcome this problem. Some examples include a stainless steel base with perforations, a stainless steel mesh base, a foil mesh base comprising a thin piece of stainless steel welded to a mesh backing, a metal base with machined retentive undercuts, plastic brackets and bases constructed of polycarbonate, and ceramic bases and brackets. Although these bracket designs provide reasonably good bonding, there are a number of practical disadvantages associated with the designs. For example, perforated stainless steel bases may produce staining around the perforations at the adhesive level. In welded brackets, weld spots may obliterate the retentive areas in mesh bases, leading to decreased bond strength, and weld spots at the edges of the base may lead to leakage and corrosion. Plastic bases are difficult to bond to with current resin bonding systems while ceramic bases are bulky and may show brittle characteristics. In accordance with the present invention, there is provided a novel structure of dental attachment which overcomes the problems of the prior art structures and has several advantages when compared with the prior art stuctures. The present invention provides a dental attachment, including brackets, bases, bands, periodontal splints and oral surgical splints, which has the tooth engaging surface thereof provided with an adherent particulate coating. The provision of the particulate coating on the tooth engaging surface thereof enables improved bonding between the tooth and the dental attachment to be achieved, without the problems attendant the prior art structures. The particulate coating may be formed on the tooth engaging surface of the attachment in any convenient manner, such as, by fusion or by sintering. The particles making up the coating may be any convenient shape, including a spherical shape or an irregular shape, and may be constructed of metal (including alloys), ceramic, polymer, or a mixture of materials. The material of construction of the particles usually, but not necessarily, is the same as the material of construction of the substrate, in which case the particles usually are bonded to the substrate through their material of construction. An example of a structure according to the invention wherein dissimilar materials are used is a porous coating of ceramic material on a stainless steel or other metal substrate while an example of a structure according to the invention wherein similar materials are used is a porous coating of stainless steel on a stainless steel substrate. The particulate coating adhered to the tooth engaging surface may take the form of discrete particles which are spaced apart from each other on the surface, or may take the form of a layer or multiple layers of particles bonded together to produce a network of interconnected pores. The particulate coating used in this invention provides a porous interface into which a bonding resin in a fluid uncured state may readily flow and penetrate. Upon curing of the resin to solid form, mechanical interlock is achieved between the cured resin and the particulate coating. Under some circumstances chemical bonding in addition to this mechanical bonding may be achieved, for example, by the use of polycarboxylate or glass ionomer cements with stainless steel and other metallic substrates and with ceramic substrates. The thickness of the particulate coating on the tooth engaging surface of the dental attachment in this invention may vary widely depending on the size of the particles, the form of the coating and the number of layers desired in the coating, if in that form. The thickness of the particulate coating generally is up to about 500 microns, preferably about 50 to about 300 microns. For a coating comprising discrete spaced apart particles, irregular particles or spherical particles of about 20 to about 100 microns in diameter with a spacing of about 20 to about 300 microns between them are preferred. For a coating of integrally-joined particles which make up a porous structure having a plurality of interconnected pores extending therethrough, the particles are usually about -100 mesh (less than about 200 microns) and preferably a mixture of particles of varying particle sizes restricted to one of three size ranges, namely -100 +325 mesh (about 50 to about 200 microns), -325 +500 mesh (about 20 to about 50 microns) and -500 mesh (less than about 20 microns). The size of the particles in the porous structure determines the pore size of the pores between the particles. Smaller-sized pores are preferred for low viscosity fluid resin bonding agents whereas larger-sized pores are preferred for more viscous cementitious bonding materials. The selection of particle size is also used to control the porosity of the coating to within the range of about 10 to about 50% by volume. An adequate structural strength is required for the composite of substrate and coating, so that any fracture of the joint of the bracket to the tooth occurs in the resin and not in the coating. To achieve this condition, the structural strength of the coating, the interface between the coating and the substrate and the substrate itself is at least 8 MPa. One embodiment of the invention comprises an orthodontic bracket constructed of stainless steel or other suitable metal or alloy, and which has the tooth engaging surface of the base provided with a porous coating. The bracket base may vary in size from about 3 mm in diameter to an area of about 4 x 8 mm, according to the type of attachment required. If desired, a continuous strip of stainless steel or other alloy of about 5 to 10 mm wide may be coated with particles. Such strip then may be used to construct the base bonding surface of the orthodontic brackets or other attachments, or may be used to form orthodontic bands. When the invention takes the form of orthodontic bands, these may be preformed and then coated on the interior with the particles to provide the bonding surface. As mentioned above, when the tooth-engaging surface and coating are metal, the coating may be formed by sintering or by fusion. When particles of other materials, such as, ceramics or polymers, are applied to metallic substrates or substrates of other materials, such as, ceramic or polymer, then any convenient technique known in the coating art may be used to produce the coated substrate, such as, by sintering or by adhesion. This invention is illustrated by the following Examples: Example 1 Commercial stainless steel orthodontic bracket bases were coated with a slurry of stainless steel beads having diameters in the range of 44 to 180 micrometers and the coated bases were sintered in a vacuum furnace at a temperature of about 14000C. A porous coated base resulted in which the porous coating had a thickness of 0.5 mm and a porosity of about 40% by volume. When the bases were bonded to acid etched surfaces of human teeth using Orthomite 11 bracket bonding resin (Rocky Mountain Dental Products, Denver, Colorado), the bond strength of the resulting joint was found to be 11.9 kg, compared with 7 kg for brackets having a perforated base. Example 2 A series of commercial stainless steel orthodontic bracket bases was modified by powder coating with cobalt-chromium alloy beads of less than 100 mesh in diameter to produce coatings of 0.5 to 0.7 mm thickness. After bonding to bovine teeth, the bond strength was determined in each case. The results are set fdrth in the following Table I and are compared with those from a conventional mesh base bracket bonded under the same conditions: Table I Sample Average Bond Strength Kg/cm Mesh base 66.5 - 100 +325 mesh beads 154.8 -325 mesh beads 125.8 Example 3 A glass ceramic powder with an average particle size of 40 microns was chemically bonded to a commercial stainless steel orthodontic bracket base. The brackets were bonded to acid etched bovine enamel using Solotack orthodontic bonding resin (L.D. Caulk Co, Milford, Delaware). The average tensile bond strength after 24 hours conditioning in water at 370C was found to be 59 Kg/cm2. In summary of this disclosure, the present invention provides novel orthodontic and other dental attachments which achieve superior bonding to teeth as compared with the prior art. Modifications are possible within the scope of this invention as derined in the following Claims.

Claims: CLAIMS 1. A dental attachment having a tooth engaging surface suitable for adhesive bonding of the attachment to teeth, characterized by particulate material on the tooth engaging surface. 2. The dental attachment claimed in claim 1, characterized in that the particulate material is joined together at its points of contact to define a porous coating on the surface having an interconnected network of pores therein. 3. The dental attachment claimed in claim 1 or 2, characterized in that the tooth engaging surface is constructed of metal and the particulate material is constructed of metal. 4. The dental attachment claimed in claim 1 or 2, characterized in that the tooth engaging surface is constructed of metal and the particulate material is constructed of ceramic material. 5. The dental attachment claimed in any one of claims 1 to 4, characterized in that the coating has a thickness of less than 500 microns, a porosity of 10 to 50% by volume and a failure value of at least 8 MPa. 6. The dental attachment claimed in any one of claims 1 to 5, characterized in that the particulate material has a diameter of less than about 200 microns. 7. The dental attachment claimed in any one of claims 1 to 6, in the form of an orthodontic bracket having a metal tooth engaging surface, characterized in that a porous coating on the tooth engaging surface consists of metal spheres having a diameter of less than 200 microns and joined to each other and to the tooth engaging surface at their points of contact therewith, has a thickness of 50 to 300 microns, and a porosity of 10 to 50 volume %, and the interface between the porous coating and the tooth engaging surface has a structural strength of at least 8 MPa. 8. The dental attachment claimed in claim 7, characterized in that the bracket and the coating are constructed of stainless steel.

Inventors: SMITH, DENNIS CLIFFORD, MAIJER, ROLF
Applicants: MAIJER, ROLF, SMITH, DENNIS CLIFFORD
Application year: 1983
Main classification: A61C7
IPC codes: A61C7