Dental Care

Dental-care device

Dental Care Abstract
A dental-care device is constructed from a planar base and a wire receiving part positioned on the top surface of the planar base. Slots extending straight horizontally are formed at the center of the wire receiving part, and wire is passed through these slots. The device is preferably manufactured by a metal powder injection molding method, and is composed of metal material which contains Ti as the base component, C in an amount of from about 0.03-0.5 wt % by weight of the metal material, O in an amount of from about 0.08-0.8 wt % by weight of the metal material, and N in an amount of from about 0.03-0.6 wt % by weight of the metal material. A large number of pores may be scattered at least in the vicinity of the surface of the metal material. This device can be easily manufactured, has a good surface wetness characteristic, and has functional portions, such as portions of low friction and portions of superior adhesiveness.

Dental Care Claims
What is claimed is:

1. A dental-care device comprising orthodontal braces comprising a planar base and a wire receiving part positioned on a top surface of the base and having a slot through which a wire is passed, wherein the orthodontal braces comprise a metal material comprising a Ti base component, 0.03-0.5 wt % by weight of the metal material of carbon (C), 0.08-0.8 wt % by weight of the metal material of oxygen (O), and 0.03-0.6 wt % by weight of the metal material of nitrogen (N), and wherein a surface layer at an inner surface of the slot has a higher degree of hardness than an inner part of the wire receiving part.

2. The dental-care device of claim 1, in which a bottom surface of the planar base comprises minute indentations.

3. The dental-care device of claim 1, wherein a surface layer at an inner surface of the slot comprises a larger total amount of C, O and N than at an inner part of the wire receiving part.

4. The dental-care device of claim 3, wherein the total amount of C, O and N in the surface layer comprises a% by weight of the metal material, and the total amount of C, O and N at the inner part comprises b% by weight of the metal material, the surface layer is 2-100 .mu.m thick, and the ratio a:b is equal to or greater than 1.1:1.

5. The dental-care device of claim 1, wherein a surface layer of the wire receiving part is hydrophilic.

6. The dental-care device of claim 1, wherein a surface layer of the wire receiving part comprises scattered pores of an average diameter of 0.5-50 .mu.m.

7. The dental-care device of claim 6, wherein the diameters of the pores are in a range of 0.5-100 .mu.m.

8. The dental-care device of claim 6, wherein the number of pores is 0.05-5.0% by volume of the surface layer.

9. The dental-care device of claim 8, wherein the number of pores gradually decreases from the surface layer toward an inner part of the wire receiving part.

10. The dental-care device of claim 1, wherein a bottom surface layer of the base comprises scattered pores of an average diameter of 0.5-5.0 .mu.m.

11. The dental-care device of claim 10, wherein the diameters of the pores are in a range of 0.5-100 .mu.m.

12. The dental-care device of claim 10, wherein the number of pores is 0.05-5.0% by volume of the bottom surface layer.

13. The dental-care device of claim 12, wherein the number of pores gradually decreases from the bottom surface layer toward an inner part of the base.

14. A dental-care device according to claim 11, comprising a plurality of said planar bases and wire receiving parts, wherein said wire is passed through the slot in each said wire receiving part.

15. The dental-care device of claim 1, wherein said orthodontal braces are manufactured by a metal powder injection molding method.

16. A dental-care device comprising orthodontal braces comprising a planar base and a wire receiving part positioned on a top surface of the base and having a slot through which a wire is passed, wherein the orthodontal braces comprise a metal material comprising a Ti base component, 0.03-0.5 wt % by weight of the metal material of carbon (C), 0.08-0.8 wt % by weight of the metal material of oxygen (O), and 0.03-0.6 wt % by weight of the metal material of nitrogen (N), and wherein a surface layer at an inner surface of the slot comprises a larger total amount of C, O and N than at an inner part of the wire receiving part.

17. The dental-care device of claim 16, in which a bottom surface of the planar base comprises minute indentations.

18. The dental-care device of claim 16, wherein the total amount of C, O and N in the surface layer comprises a% by weight of the metal material, and the total amount of C, O and N at the inner part comprises b% by weight of the metal material, the surface layer is 2-100 mm thick, and the ratio a:b is equal to or greater than 1.1:1.

19. The dental-care device of claim 16, wherein a surface layer of the wire receiving part is hydrophilic.

20. The dental-care device of claim 16, wherein a surface layer of the wire receiving part comprises scattered pores of an average diameter of 0.5-50 mm.

21. The dental-care device of claim 16, wherein a bottom surface layer of the base comprises scattered pores of an average diameter of 0.5-5.0 mm.

22. A dental-care device comprising orthodontal braces comprising a planar base and a wire receiving part positioned on a top surface of the base and having a slot through which a wire is passed, wherein the orthodontal braces comprise a metal material comprising a Ti base component, 0.03-0.5 wt % by weight of the metal material of carbon (C), 0.08-0.8 wt % by weight of the metal material of oxygen (O), and 0.03-0.6 wt % by weight of the metal material of nitrogen (N), and wherein a surface layer of the wire receiving part comprises scattered pores of an average diameter of 0.5-50 mm.

23. The dental-care device of claim 22, in which a bottom surface of the planar base comprises minute indentations.

24. The dental-care device of claim 22, wherein the diameters of the pores are in a range of 0.5-100 mm.

25. The dental-care device of claim 22, wherein the number of pores is 0.05-5.0% by volume of the surface layer.

26. The dental-care device of claim 25, wherein the number of pores gradually decreases from the surface layer toward an inner part of the wire receiving part.

Dental Care Description
BACKGROUND OF THE INVENTION

The present invention provides a dental-care device, such as braces for orthodontal correction, that is easy to manufacture, has good surface wetness, particularly with regard to saliva, and in which functional portions, such as portions of low friction and portions of superior adhesiveness, can be easily obtained.

DESCRIPTION OF RELATED ART

As a dental-care device used within the oral cavity, orthodontal braces and wire(s) for use in orthodontal correction of the teeth alignment (row of teeth) are known.

Braces for orthodontal use (referred to below simply as "orthodontal braces") generally comprise a base that is bond fixed to the teeth, and a wire receiving part formed on the top of the base. The wire receiving part has a slot through which wire is passed through. By tightening the wire, taut bridging of the teeth alignment is achieved.

For these kinds of braces, materials such as: 1) metal materials, i.e., stainless steel; 2) ceramics, i.e., those in the zirconia, alumina, and sapphire groups; and 3) hard plastics, i.e., polycarbonates and poly-dimethacrylates, have conventionally been used. However, the following types of defects can be found in any and all of these materials.

Braces made of stainless steel compare unfavorably in suitability for use in the body. In particular, there are deleterious effects on body tissue, causing allergies to metal, or concerns about carcinogens resulting from the elution of Ni and Cr. The appearance of the braces worn by the user is also inferior due to metal luster. Moreover, there is low wetness on the surface with regard to saliva, with the result that dryness easily occurs during use. Further, the lubricating ability of stainless steel compares unfavorably with body tissues such as the mucous membranes of the lips or skin. Accordingly, inflammation may result, causing pain to the patient.

Braces made of ceramic are of a low intrinsic toughness. Therefore, breakage easily occurs during wearing and use of the braces. In particular, it is necessary to exercise care when removing the braces after completion of orthodontic correction of the teeth to prevent breakage. Furthermore, braces made of ceramic are extremely expensive.

Braces made of hard plastic are of low strength and resistance to friction, so that deformation and breakage easily occur. Further, it is difficult to effectively transmit the stress from the tensed wires to is the teeth. Moreover, in the same way as in the stainless steel manufacture, there is poor wetness on the surface with regard to saliva, therefore the same problems occur. Furthermore, there is a great deal of sliding resistance from the wires against the inner surface of the slot, making it difficult to correctly perform minute load adjustments. Moreover, abrasion easily occurs during use.

In recent years, new materials such as Ti or Ti alloys have been proposed for use in orthodontal braces (JP Laid Open Patent 6-14942). Ti or Ti alloys are superior in that they are of light weight and high strength, anticorrosive and compatible with body tissue. However, manufacture and processing of the braces is not easy because it requires cutting machining, using special tools, or laser machining of the cast. The cast can also be formed by super-plastic formation processing. In particular, in processing the material into its complicated and minute form, a complicated manufacturing process and a high degree of skill are necessary, increasing manufacturing costs.

Moreover, particularly in the case of cast articles, the metal structure is very dense. Therefore, there is low surface wetness with regard to saliva, and, as a result, the same problems occur. There is also a comparatively greater sliding resistance of the wires against the inner surface of the slots, causing difficulty in properly making minute load adjustments.

A further problem is the reaction of oxygen or nitrogen during casting, causing the braces to be brittle. This creates the same problems as in ceramic braces.

SUMMARY OF THE INVENTION

The dental-care device of the present invention is lightweight and has sufficient mechanical strength and hardness in addition to the appropriate ductility and elasticity. The dental-care device also has parts which are superior to conventional braces of stainless steel, ceramic or plastic in adhesiveness, sliding characteristics of the wire and the like, anti-friction, and surface wetness characteristics. Furthermore, the dental-care device is superior in compatibility to body tissue, appearance, and ease of removal.

In particular, in a case having a surface layer, the sliding characteristic of the wire and the like, and anti-friction, is even more improved. In a case having pores in the vicinity of the surface, adhesiveness, surface wetness, and appearance are even more improved.

In a case where the manufacturing is performed by a metal powder injection molding method, even a complicated and minute formation can be easily manufactured with a high degree of accuracy and good reproducibility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an embodiment of the dental care device of the invention, applied to orthodontal braces;

FIG. 2 is a bottom view of the embodiment of FIG. 1;

FIG. 3 is a cross-sectional view taken along line III--III of FIG. 1;

FIG. 4 is a plan view showing another embodiment;

FIG. 5 is a cross sectional view denoting an enlargement of the vicinity of the inner surface of the slot in the orthodontal braces;

FIG. 6 is a cross-sectional figure denoting an enlargement of the vicinity of the surface of the wire receiving part in the orthodontal braces;

FIG. 7 is a graph denoting the results of the line analysis of carbon (C), according to an electronic line microanalyzer, in the cross-sectional part denoting an enlargement of the vicinity of the surface of the wire receiving part in the orthodontal braces;

FIG. 8 is a graph denoting the results of the line analysis of oxygen (O), according to an electronic line microanalyzer, in the cross-sectional part denoting an enlargement of the vicinity of the surface of the wire receiving part in the orthodontal braces;

FIG. 9 is a graph showing the results of the line analysis of nitrogen (N), according to an electronic line microanalyzer, in the cross-sectional part denoting an enlargement of the vicinity of the surface of the wire receiving part in the orthodontal braces;

FIG. 10 is a photograph showing the metal composition;

FIG. 11 is a photograph showing the metal composition; and

FIG. 12 is a photograph showing the metal composition.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The dental-care device of the present invention is explained below in detail based on the preferred embodiments shown in the attached figures.

As shown in the figures, the orthodontal corrective braces 1 are composed of a planar base 2, comprising a braces base and a brace(s) stem, and a wire receiving part (tie-wing) 3 formed on the top surface of the base 2.

Slot 4 is formed extending straight at the center of the wire receiving part 3, through which wire 7 passes. The details of the wire will be described below. As shown in FIG. 3, the cross-section of slot 4 in the preferred embodiment has a rectangular shape; however, the embodiment is not limited to this; for example, it may be a V-shaped or a U-shaped slot.

As shown in FIG. 4, such orthodontal braces 1 are fixed to the tooth 15 by adhering the bottom plane (rear plane) 5 of base 2 to the tooth 15 by an adhesive substance. Minute indentations 6 are formed on the bottom plane 5 of base 2. See FIG. 2. In the preferred embodiment, these indentations 6 are formed as grooves, preferably in a grid formation. However, the indentations are not limited to this formation. For example, grooves formed as straight lines or as a concentric annular shape, or grooves with other types of patterns, may be formed. Alternatively, protrusions or dimples may be formed regularly or irregularly (as in scattering).

Through forming these kind of indentations 6, the surface area adhered by the adhesive is increased, and the adhesive properties (adhesive strength) for bonding of the base 2 onto tooth 15 are therefore increased. Preferably, the indentations 6 are formed so that the adhesive area increases by about 5-250%, and more preferably by about 30-100%, as compared to a case in which no indentations are formed. Further, it is preferable to set the depth of the indentations 6 at about 50-300 .mu.m, and more preferably from about 100-150 .mu.m.

FIG. 4 shows the state in which teeth are equipped with the dental-care device of the present invention, composed of a plurality of orthodontal braces 1 and wire 7. Each orthodontal brace 1 is adhered to the surface plane of each tooth 15 corresponding (in a fixed correspondence) through the adhesive material on the bottom plane of the base 2. Wire 7 passes through slot 4 of each orthodontal brace in a state of tension. It is through this tensile force that the load is provided to the orthodontal braces 1 for orthodontically correcting the alignment of the teeth.

Wire 7 may be composed of, for example, Ti or Ti compounds, stainless steel, or super-plastic compounds, or a combination thereof. The cross-sectional formation of the wire may be, for example, rectangular, polygonal, circular, elliptical, semi-circular, or the like.

Orthodontal braces 1, as constructed above, are composed of metal material which contains Ti as the base component, together with carbon (C) in an amount of from about 0.03-0.5 wt % by weight of the metal material, oxygen (O) in an amount of from about 0.08-0.8 wt % by weight of the metal material, and nitrogen (N) in an amount of from about 0.03-0.6 wt % by weight of the metal material.

Ti is light weight, has a high strength and a high degree of hardness; it is difficult for deformation and breakage to occur, so that it is superior in its durability and its anti-corrosive properties. Moreover, elution of the metal components is extremely small, so that allergic reactions from metal allergies and the like can be controlled, thereby providing superior compatibility with the body. Furthermore, Ti has a small metallic luster, unlike stainless steel, and it does not impair the appearance of the teeth which are being equipped with the braces.

In the metal material composing the orthodontal braces 1, C, O and N exist in a form of, for example, a chemical compound with Ti. Because these elements are well balanced in the metal material, the dental-care device maintains the physical attributes of beneficial strength, hardness, ductility (toughness), and elasticity. Among these elements, the content of N is particularly important. Even if the content amount of nitrogen is minute, a high degree of effects and improvements are seen in the physical characteristics of the metal material.

The C content in the metal material is from about 0.03-0.5 wt % by weight of the metal material, preferably from about 0.04-0.2 wt %, and even more preferably 0.05-0.1 wt %. When the C content is less than 0.03 wt %, the strength of the metal material is decreased if the amount of O and N are also small. If the C content exceeds 0.5 wt %, the ductility of the metal material is decreased.

The O content in the metal material is from about 0.08-0.8 wt % by weight of the metal material, preferably from about 0.1-0.5 wt %, and more preferably from about 0.25-0.3 wt %. If the O content is less than 0.08 wt %, and if the amounts of C and N are small, the strength of the metal material decreases. If the O content exceeds 0.8 wt %, the ductility of the metal material decreases.

The N content in the metal material is preferably from about 0.03-0.6 wt % by weight of the metal material, more preferably from about 0.35-0.14 wt %, and even more preferably from about 0.04-0.05 wt %. If the N content is less than 0.03 wt %, and if the amounts of C and O are small, the strength of the metal material decreases. If the N content exceeds 0.6 wt %, the ductility of the metal material decreases.

It is preferable that the total amount of C, O and N in the metal material is from about 0.14-1.0 wt % by weight of the metal material, more preferably from about 0.18-0.8 wt %, and even more preferably from about 0.30-0.4 wt %. If the total amount is less than 0.14 wt %, the strength of the metal material decreases. If it exceeds 1.0 wt %, the ductility of the metal material decreases.

The metal material may also contain, for example, the elements Fe, Cr, Pd, Co, Zr, Al, V, Mo, and other elements, or mixtures thereof, indispensable or intentionally, within a range not causing inflammation (reactions) from metal allergies and the like. The addition of these elements contributes additional strength to the metal material. It is preferable that these elements exist in alloy with Ti or formed with metallic compounds.

FIG. 5 is an enlarged cross section showing the vicinity of the inner surface 41 of slot 4 in the orthodontal braces 1. As shown in the figure, at the inner surface 41 of slot 4, the surface layer 8 is formed with a high degree of hardness as compared to the inner part 9.

There are many reasons for surface layer 8 having a high degree of hardness. However, the major reason resides in the composition of the surface layer. The total amount of C, O, and N in the surface layer 8 is large as compared to that in the inner part 9, with the average value of the total amount of C, O, and N in the surface layer 8 preferably being larger than that in the inner part 9 by about 4-60%, and more preferably about 5-20%.

As a result of the surface layer 8 having this kind of hardness, the sliding ability of wire 7 against the inner surface 41 of the slot 4 is improved (the sliding resistance is reduced), and movement of the orthodontal braces 1 against wire 7 can be easily performed, resulting in more correct and minute load adjustments.

The border between the surface layer 8 and the part on the side further in from the surface layer 8, inner part 9, does not need to be clearly defined. In the vicinity of the border, the degree of hardness may be continuously altered, or the contained elements, such as C, O, and N, may have a prescribed concentration gradient in the depth direction.

For example, in the latter case, if the total amount of C, O, and N in the surface layer 8 is defined as a% by weight of the total composition, and the total amount of C, O, and N in the part further inside from surface layer 8 (inner part 9) is defined as b% by weight, it is preferable that the thickness of the part in which the ratio a:b is equal to or greater than 1.1:1 is from about 2-100 .mu.m, and more preferably from about 5-50 .mu.m. If the thickness is less than 2 .mu.m, the function of the surface layer 8, namely, the improved effect of the sliding characteristic of wire 7, will not be sufficiently demonstrated, or the durability of the effect will be inferior. If the thickness of this part exceeds 100 .mu.m, the metal material will become brittle, breaking easily during use or at the time of removal.

The thickness of this part can be properly adjusted by controlling the burning conditions (burning temperature, burning time, vacuum of the burning atmosphere, gas composition, etc.) during the burning step in the manufacturing process of the orthodontal braces 1, which will be explained below.

The degree of hardness of surface layer 8 is not especially limited; however, it is preferable if the Vickers hardness is from about 200-400, and even more preferable if it is from about 300-380. With this range of hardness, the above-explained effects are demonstrated.

The surface layer 8 may be formed at least at the inner surface 41 of the slots 4. However, it may also be formed at other parts as well, such as covering the entire orthodontal braces 1.

FIG. 6 is an enlarged cross-sectional view of the vicinity of the surface 31 of the wire receiving part 3 of the orthodontal braces 1. As shown in the figure, minute pores are scattered in the vicinity of the surface 31 of the wire receiving part 3, which contribute to the hydrophilic property (water retention function). The hydrophilic property improves the wetness characteristic of the surface 31 of the wire receiving part 3, so that when the surface 31 becomes wet with saliva, it can be maintained in a state of wetness, thus preventing dryness. Consequently, the lubricating ability to body tissue, in particular the lips and other soft tissues, including mucous membranes, can be maintained, reducing inflammatory reactions and preventing pain to the wearer of the orthodontal braces. The existence of the pores 10 also restrains the luster of the surface 31 of wire receiving part 3, which greatly improves the appearance of the braces worn on the teeth.

The average diameter of the pores is preferably from about 0.5-50 .mu.m, and more preferably from about 5-20 .mu.m. If the average diameter is smaller than 0.5 .mu.m, saliva can not sufficiently penetrate, and lubricating ability is reduced. Furthermore, the appearance is impaired because of the luster.

If the average diameter exceeds 50 .mu.m, the strength and ductility of the metal material are reduced. Further, because the open pores are large, food and the like are retained in these open pores during use, causing the propagation of bacteria and the occurrence of other deleterious effects.

It is preferable if most (in particular, more than 66%) of the pores 10 have a diameter within a range of from about 0.5-100 .mu.m, and even more beneficial if the range is from about 5-50 .mu.m. In this case, the function of the distribution curve is not particularly limited. For example, a Gaussian distribution (normal distribution), a binomial distribution, and the like are allowable. As a result, the wetness characteristic of surface 31 is further improved, as well as appearance.

The pores are preferably present in an amount of from about 0.05-5.0 vol % by volume of the surface 31, and even more preferably from about 0.5-2.0 vol %. If the pores are present in an amount less than 0.05 vol %, the improvement in the effect of the wetness characteristic of the surface 31 is not adequate. If the amount exceeds 5.0 vol %, the strength of the metal material, in particular tensile strength, ductility, and elasticity, is reduced.

The number of pores present may be decreased in the depth direction from the surface 31, or may be gradually decreased from the surface 31 toward the inner part 9. In the latter case, the wetness characteristic of the surface 31 can be improved while maintaining a high level of strength and ductility in the orthodontal braces 1.

The pores 10 are easily formed if the orthodontal braces 1 are manufactured through a later-explained metal powder injection molding method. The conditions relating to the pores 10 can be properly adjusted through controlling the manufacturing conditions, such as types and amount of binder, burning conditions (burning temperature, burning time, vacuum of the burning atmosphere, or the gas composition, etc.), and so on.

In the preferred embodiments, pores 10 are formed in the same way as aforesaid, in the vicinity of the bottom plane of the base 2, and particularly in the vicinity of the surface of the indentations 6. As a result, in addition to the operation of indentations 6, the maintaining characteristic of the adhesive material for fixing the orthodontal braces 1 to the teeth is further improved, and the adhering characteristic (adherence strength) for bonding of the base 2 to the teeth 15 is improved.

Although it is sufficient that the pores 10 are formed at least in the vicinity of the surface 31 of the wire receiving part 3, or in the vicinity of the bottom plane 5 of the base 2, they may be formed in other parts as well, and may even be formed throughout the entire orthodontal braces 1.

The manufacturing process of the above-explained orthodontal braces 1 is not limited to a particular technique. However, it is beneficial for the braces to be manufactured by a metal powder injection molding method (MIM: Metal Injection Molding). Below is an explanation of the metal powder injection molding method.

MIM Method

Step 1: Metal powder from Ti (or a Ti alloy) and a binding agent(s) (organic binder) are prepared and kneaded by a kneader to obtain a kneaded object (compound).

The average grain (particle) diameter of the metal powder is not limited to a particular diameter. However, a diameter of about 5-60 .mu.m is generally preferable, and a diameter of about 10-40 .mu.m is even more preferable.

As a binding agent, one or more of the exemplary substances from the following group may be selected: polyethylene; polypropylene; polyolefins, such as ethylene vinyl acetate copolymers; polymethyl methacrylate; polybutyl methacrylate and other acryl group resins; polystyrene and other styrene group resins; polyvinyl chloride; polyamide; polyester; polyether; thermoplastic resins, including copolymers of the above-listed substances; various types of wax; paraffin; and the like.

The binding agents are preferably added in an amount of from about 4.0-15.0 wt % by weight of the metal material, and more preferably in an amount of from about 4.0-8.0 wt %. If the added amount of the binder is less than 4.0 wt %, there will be scant fluidity during the molding, and injection molding becomes impossible or very difficult, or the composition of the molded compact becomes inhomogeneous. If the amount of the binder exceeds 15.0 wt %, the shrinkage rate increases when the molded object obtained through injection molding is burned, decreasing the accuracy of the dimensions. This may cause the number of pores or the C content to exceed the aforesaid ranges.

Moreover, various additives other than the metal powder and the binding agents may be added as necessary during kneading such as, for example, plasticizing agents, lubricating agents, antioxidants, degreasing promotion agents, and surfactants.

As an example of kneading conditions, the knead temperature may be from about room temperature to 150.degree. C., and the knead time may be from about 60-180 minutes.

Step 2: Utilizing the kneaded object obtained from step 1, or pellets made from the kneaded object, injection molding is performed by the injection molder to form a compact having a shape of the orthodontal braces 1. The dimensions of the molded compact are set taking into account the shrinkage that will occur from the later burning step.

For the molding conditions, it is preferable if the temperature of the materials is from about 130.degree.-170.degree. C., and even more preferably from about 150.degree.-160.degree. C. It is preferable for the injection pressure to be from about 300-600 kgf/cm.sup.2, and even more preferably from about 300-400 kgf/cm.sup.2. It is preferred that the mold temperature be from about 5.degree.-50.degree. C., and even more preferably from about 10.degree.-20.degree. C.

Step 3: (This step may be omitted.) A binder extraction process may then be performed to the compact obtained from step 2. The binder removal is performed through heat processing under a non-oxidation atmosphere, for example, under vacuum or reduced pressure conditions, for example, 1.times.10.sup.-1 to 1.times.10.sup.-6 Torr.

In this case, it is preferable for the heat processing conditions to be at a temperature from about 50.degree.-650.degree. C., for about 8-72 hours, and even more preferably at about 60.degree.-550.degree. C., for about 12-18 hours.

The binder extraction process (degreasing process) may be performed by elution of specific components of the binder(s), utilizing a predetermined solvent of fluid or gas.

Step 4: Next, the compact obtained from either Step 2or Step 3is burned to produce a metallic sinter. The burning may be performed once or multiple times.

It is preferable that the burn conditions are at a temperature of from about 400.degree.-1400.degree. C., for about 10-26 hours, and more preferable that the temperature be from about 500.degree.1350 C., for about 15-18 hours. In this case, the burn atmosphere is a non-oxidation atmosphere, proceeding, for example, in argon gas or other inactive gases, under a vacuum or reduced pressure conditions, for example, from about 1.times.10.sup.-2 to about 1.times.10.sup.-6 Torr, or in other atmospheres with reducing properties.

When the surface layer 8 is formed, gas(es) containing at least one of C, O or N is/are injected into the burning atmosphere in the middle of the burning step. For example, appropriate gases may be selected from air, O.sub.2 gas, CO.sub.2 gas, CO gas, N.sub.2 gas, methane gas, acetylene gas, propane gas and mixtures thereof and the like. By controlling the burning conditions, such as the composition of the injected gas, the gas injection amount (partial pressure of the gases in the burning atmosphere), and the post-injection burning time, the conditions of the surface layer 8 described above are determined.

Step 5: As necessary, surface treatment is performed to the surface of the obtained metal sintered compact. For example, shot blasting, honing, grinding, etching, wet plating, vacuum evaporation, ion plating, spattering, CVD, thermal spraying, and other surface processing may be performed. If the surface layer 8 is formed only with necessary parts (for example, the inner surface 41 of the slots 4), unnecessary parts of the surface layer 8 can be removed by grind processing, etching, and the like.

The orthodontal braces 1 formed from the metal sintered compact are obtained by going through the steps explained above.

The metal powder injection molding method described above can eliminate problems seen in the conventional casting method, such as casting defects or liquid flow. Moreover, even a delicate dental device with a complicated shape can be formed monolithically, achieving easy manufacturing with good repeatability. In particular, conventional methods require performing grind processing or fixing meshed material onto the bottom plane 5 of the base 2. However, in the present invention, minute indentations 6 or slot 4 can be monolithically and simultaneously formed without performing these types of operations. This improves the accuracy of the dimensions and yield rate, in addition to facilitating manufacturing.

Through adjustment of types of binding agents, added amounts, binder extraction conditions, and burning conditions, the desired conditions for the composition of the metal materials composing the braces for orthodontal correction, in particular the composition of the surface layer, the pore diameter, or the number of pores, can be set, which is an advantage.

Moreover, with the metal powder injection molding method, minute indentations can be formed on the surface of the metal material, in particular on the inner surface 41 of slot 4, or on the bottom plane 5 of the base 2, as the sintered surface. See FIGS. 10-12. As a result, the sliding characteristic of the wire 7 or adhesion to the teeth, respectively, is further improved.

These minute indentations also contribute to an improved wetness characteristic of the surface, as previously explained. The characteristics of the minute indentations can be controlled by setting the selection of the Ti powder, molding conditions, or sintering conditions.

Although in the preferred embodiments the orthodontal braces 1 are obtained by monolithically forming the base 2 and the wire receiving part 3 through a metal powder injection molding method, the base 2 and the wire receiving part 3 may be manufactured separately and adhered together. In this case, the base 2 and the wire receiving part 3 may each be respectively manufactured by the metal powder injection molding method or by other methods.