Patent Application
20170172711
Field of the Invention
The present invention relates to a dental member.
Description of the Related Art
In recent years, dental implants are frequently used, which are embedded into the jaw bone to replace missing tooth roots after tooth loss. Orthodontic anchor screws are also frequently used in various cases of malocclusion as anchorage sources for the movement of teeth under orthodontic treatment. The use of orthodontic anchor screws as anchorage sources for orthodontic treatment enables precise and efficient movement of teeth, which has been conventionally difficult, regardless of the degree of patient cooperation. As dental members including such dental implants and orthodontic anchor screws, dental members made of pure titanium or titanium alloy having relatively high strength and good biocompatibility have been conventionally used.
In addition, metallic glass is known as a material having properties such as high strength, low Young's modulus, and high corrosion resistance. As a highly ductile metallic glass alloy that is excellent in plastic workability and is applicable to metal working process such as cold press working, a metallic glass alloy having a composition represented by formula: ZraNibCucAld [wherein a, b, c, and d denote at. %, “a” ranges from 60 to 75 at. %, “b” ranges from 1 to 30 at. %, “c” ranges from 1 to 30 at. %, and “d” ranges from 5 to 20 at. %] has been proposed by the present inventors (for example, see Patent Literature 1).
Patent Literature 1: JP Patent Publication (Kokai) No. 2009-215610 A
Conventional titanium dental members are relatively large or long with respect to the installation positions, and thus are problematic in that they can have a risk of damaging adjacent tooth roots upon implantation. Further, these dental members are also problematic in that they can be broken or fractured in use. Moreover, these dental members can become unstable or fall off during orthodontic treatment, and thus are problematic in that they are unstable unless used for mature bone.
The present invention has been achieved noting these problems. An object of the present invention is to provide a dental member, which has a reduced size, and thus can prevent damages to tooth roots upon implantation, has higher strength and lower elasticity compared with titanium dental members, and is excellent in stability of engraftment to bone after implantation.
In order to achieve the above object, the dental member according to the present invention is characterized by containing an amorphous alloy having a composition represented by formula: ZraNibCucAld [wherein a, b, c, and d denote at. %, “a” ranges from 60 to 75 at. %, “b” ranges from 11 to 30 at. %, “c” ranges from 1 to 16 at. %, and “d” ranges from 5 to 20 at. %].
The dental member according to the present invention contains an amorphous alloy having higher strength and lower elasticity compared with titanium dental members such as titanium alloy or pure titanium dental members, so that it is hard to be broken or fractured in use, and has a low risk of damaging adjacent tooth roots. Furthermore, the dental member according to the present invention accelerates the formation of new bone around the member after implantation unlike titanium dental members, so that the dental member of the present invention is excellent in stability of engraftment to bone after implantation, and has a low risk of becoming unstable or falling off during orthodontic treatment.
The dental member according to the present invention may be any member such as a bridge, an orthodontic bracket, an orthodontic wire, and an orthodontic band, as long as it is a member that can be formed with an amorphous alloy. In particular, the dental member of the present invention preferably comprises an orthodontic anchor screw or a dental implant. In general, a titanium orthodontic anchor screw has a length of 6-8 mm and a diameter (outer diameter) of 1.4 mm or more, and a titanium dental implant has a length of 8-12 mm and a diameter of 3 mm or more. However, the dental member according to the present invention has higher strength and lower elasticity compared with titanium dental members and is excellent in stability of engraftment to bone, so that the dental member of the present invention can be formed shorter and thinner compared with titanium dental members. For example, the dental member of the present invention can be an orthodontic anchor screw wherein the screw part has a core diameter between 0.5 mm and 1.0 mm or a length between 2 mm and 5 mm, a one-piece-type dental implant wherein the screw part has the largest diameter between 0.5 and 2.9 mm and a length between 2 and 13.4 mm, or, a two-piece-type dental implant wherein the screw part has the largest diameter between 0.5 and 2.9 mm and a length between 2 and 5.9 mm. The dental member of the present invention is shorter and thinner than titanium dental members, but can exert strength, elasticity, and an effect of new bone generation equivalent to or better than those of titanium dental members. Moreover, size reduction can prevent damages to tooth roots upon implantation.
The dental member according to the present invention is preferably characterized in that “a” ranges from 67 to 73 at. %, “b” ranges from 11 to 17 at. %, “c” ranges from 5 to 13 at. %, and “d” ranges from 5 to 9 at. %. In this case, the dental member of the present invention has particularly high strength and low elasticity, and is excellent in stability of engraftment to bone after implantation. Furthermore, preferably, “c” ranges from 7 to 13 at. %, or, “d” ranges from 5 to 7 at. %. Furthermore, “a” may range from 69 to 73 at. %, “b” may range from 13 to 17 at. %, “c” may range from 5 to 10 at. %, and “d” may range from 5 to 9 at. %.
The dental member according to the present invention has preferably the surface coated with zirconia ceramics. In this case, the dental member can be produced by heating the above amorphous alloy in an atmosphere in which oxygen is present at temperatures where no crystallization or no embrittlement takes place. In a specific example, the dental member can be produced by heating the amorphous alloy in air at temperatures ranging from 350° C. to 400° C. Since the surface of the amorphous alloy is coated with very strong zirconia ceramics, leading to improved strength. Moreover, zirconia ceramics on the surface can prevent internal nickel from dissolving and affecting the human body.
According to the present invention, size reduction of the dental member can prevent damages to tooth roots upon implantation, and thus the dental member having higher strength and lower elasticity compared with titanium dental members and being excellent in stability of engraftment to bone after implantation can be provided.
The embodiments of the present invention will be described in detail as follows with reference to the drawings.
The dental member of an embodiment of the present invention comprises an amorphous alloy having a composition represented by formula: ZraNibCucAld [wherein a, b, c, and d denote at. %, “a” ranges from 60 to 75 at. %, “b” ranges from 11 to 30 at. %, “c” ranges from 1 to 16 at. %, and “d” ranges from 4 to 20 at. %].
This amorphous alloy can be produced by metal mold casting, for example. Specifically, first, raw materials including zirconium (Zr), nickel (Ni), copper (Cu), and aluminium (Al) are weighed and mixed to result in a desired composition, and then the mixture is melted and mixed in an inert gas atmosphere to generate a mother alloy. Next, the mother alloy is melted again in air, and then casting is performed with a copper template by an arc-melting tilt-casting method or the like, so that the amorphous alloy can be produced. The shaped raw material of the thus produced amorphous alloy is subjected to machining, and then the dental member of an embodiment of the present invention can be produced.
The dental member of an embodiment of the present invention is made of an amorphous alloy with higher strength and lower elasticity compared with titanium dental members such as titanium alloy dental members and pure titanium dental members, so that the dental member is hard to be broken or fractured in use and has a low risk of damaging adjacent tooth roots. Moreover, the dental member of an embodiment of the present invention accelerates the formation of new bone around the member after implantation unlike titanium dental members. Hence, the dental member of the present invention is excellent in stability of engraftment to bone after implantation, and has a low risk of becoming unstable or falling off during orthodontic treatment.
In addition, an amorphous alloy shaped in a desired shape is heated in air at 350° C. to 400° C. to oxidize the surface, and thus a dental member having the surface coated with zirconia ceramics can be produced. In this case, the surface of an amorphous alloy is covered with very strong zirconia ceramics, so that the strength can be increased.
Experiments shown below were conducted to verify the effect of the dental member of an embodiment of the present invention.
As the dental members of embodiments of the present invention, an orthodontic anchor screw made of an amorphous alloy having a composition of Zr70Ni16Cu6Al8 (hereinafter, referred to as “screw 1 of the present invention”), an orthodontic anchor screw made of an amorphous alloy having a composition of Zr68Ni12Cu12Al8 (hereinafter, referred to as “screw 2 of the present invention”), and an orthodontic anchor screw made of an amorphous alloy having a composition of Zr72Ni16Cu6Al6 (hereinafter referred to as “screw 3 of the present invention”) were produced and subjected to an experiment using rats. Screws 1 to 3 of the present invention used in this experiment are shown in
As shown in
Rats used in this experiment were 12-week-old male Wistar rats (body weight: 250 g to 260 g). To reduce the burden on animals due to the experiment, the procedure was performed by intraperitoneal injection of 5 mg/ml pentobarbital under general anesthesia.
Moreover, in an experiment for measuring values, the thus obtained experimental data were statistically processed by performing one-way analysis of variance, and then performing a multiple comparison test by Tukey-Kramer method. In this test, a significant difference was determined with the significance level of 1% (P<0.01) or 5% (P<0.05), a result with a significance level of less than 1% is denoted as “*” and a result with a significance level of less than 5% is denoted as “*” in each drawing.
Medial surfaces of both lower extremities of each of a plurality of rats were shaved, skin and fascia incisions, each having an about 15.0 mm long, were made in parallel to the long axis of rat tibia, and then the medial surfaces of the tibiae were exposed with raspatories. When immediate loading was applied, drilling was performed at two positions per a side (a position in the vicinity of and a position in the central part of the joint at the boundary with the femur) at a low rotational speed using a round bar, so as to form a 1.0-mm fossa for implantation of a screw. When no immediate loading was applied, drilling was performed at one position per side (in the vicinity of the joint at the boundary with the femur), so as to form a 1.0-mm fossa for implantation of a screw.
When immediate loading was applied, a screw was implanted with an anchor driver, vertically with respect to the cortical bone at an implantation part. Skin and fascial incisions were sutured using nonabsorbable sutures (Keisei Medical Industrial Co., Ltd. “SU-1160NS”). The surgical fields were sterilized with iodine cotton balls, and then 10 g or 50 g of immediate loading was applied by screw types to each screw using coil springs (TOMY INTERNATIONAL INC. “SENTALLOY coil springs”) made of an orthodontic nickel titanium alloy.
Loading was applied immediately after implantation of each screw. After implantation of each screw, loading was kept applied for seven and 28 days of evaluation. In addition, screws to be evaluated were screws implanted in the vicinity of the joint at the boundary with the femur, from among screws implanted in tibiae. Screws implanted in the central parts of tibiae were used as anchorage sources when immediate loading was applied. As the screws for anchorage sources, AbsoAnchor processed to have a length of 3.0 mm was used consistently.
Moreover, when no immediate loading was applied, each screw was implanted with an anchor driver vertically with respect to cortical bone at an implantation part, skin and fascial incisions were sutured with nonabsorbable sutures (Keisei Medical Industrial Co., Ltd. “SU-1160NS”), and then the surgical fields were sterilized with iodine cotton balls. After implantation of each screw, it was retained for seven or 28 days of evaluation.
Screw 1 of the present invention, a titanium alloy screw, and a pure titanium screw were measured for implantation torque values and removal torque values immediately after, seven days after implantation, and 28 days after implantation, respectively, of each screw using a torque gauge (Tohnichi). Implantation torque values were measured by screw types of four screws implanted in the joints. Furthermore, removal torque values were measured by screw types of four screws immediately after implantation. Removal torque values were also measured by screw types of four screws and by weights of immediate loading seven and 28 days after implantation. The highest torque value among torque values of each screw type was employed as a measured torque value. The results of measuring implantation torque values and removal torque values immediately after implantation are shown in
As shown in
Furthermore, as shown in
As shown in
As shown in
Next, screw 2 and screw 3 of the present invention were similarly measured for implantation torque values and removal torque values seven days after implantation. In addition, for comparison, a titanium alloy screw and a pure titanium screw were also measured. The results of measuring implantation torque values and removal torque values seven days after implantation are shown in
As shown in
Moreover, as shown in
For measurement of the stability of the screws after implantation, Screw 1 of the present invention, a titanium alloy screw, and a pure titanium screw were measured for the mobility of the screws implanted into tibiae immediately after implantation, seven days after implantation, and 28 days after implantation using a mobility measuring device, Periotest (Gulden Messtechnik). Measurement was performed by applying Periotest vertically with respect to each screw head portion at 3 sites (one site in the longitudinal direction of tibiae, two sites resulting from 120° rotation from the first site), the mean value of these 3 values was designated as a measurement value (Periotest value). In addition, it is defined that no mobility is confirmed when the Periotest value is between 0 and 9, mobility is sensed by palpation when the Periotest value is between 10 and 19, mobility is visually confirmed when the Periotest value is between 20 and 29, and teeth are moved by tongue and lip when the Periotest value is between 30 and 50. In the case of dental implants such as screws, the value of 10 or higher indicates insufficient osseointegration.
The results of measuring Periotest values are separately shown in
Moreover, in all immediate loading groups, it was confirmed for all screws that Periotest values decreased from those immediately after implantation to seven and 28 days after implantation. This may be because new bone was formed around the screws and gradually became stable as time proceeded after implantation. In addition, it was confirmed for all screws that Periotest values seven and 28 days after implantation were lower in the case of 10 g of immediate loading than the other cases.
As shown in
Next, screw 2 and screw 3 of the present invention were also similarly measured for mobility immediately after implantation and seven days after implantation. In addition, for comparison, a titanium alloy screw and a pure titanium screw were also measured. The results of measuring Periotest values are separately shown in
Moreover, as shown in
Moreover, as shown in
Moreover, screw 2 and screw 3 of the present invention in the case of no immediate loading were also measured for mobility 28 days after implantation. The results are shown in
Screw 1 of the present invention, a titanium alloy screw, and a pure titanium screw were histologically observed by screw type and by weights of immediate loading in order to evaluate the stability of the screws after implantation. Specifically, tissues surrounding the screws were observed seven and 28 days after implantation of the screws. In addition, regarding immediate loading, cases of no immediate loading and 50 g of immediate loading were observed. For observation, first, rats into which screws had been implanted were each subjected to perfusion fixation using a 4% paraformaldehyde solution. Both tibiae of lower extremities were excised, and then bone blocks each containing one screw were prepared. The bone blocks were fixed at 4° C. in a 4% paraformaldehyde solution for 48 hours, and then washed for 30 minutes with running water. After washing, the bone blocks were dehydrated and delipidated with an ethanol rise system under ordinary temperature, followed by treatment with an intermediate agent, xylene. After treatment, resin filtration was performed in a resin permeate (Wako, “Osteoresin Embedding Kit”) at 4° C., and then resin embedding was performed at 35° C. Resin blocks were processed with Saw Microtome Leica SP1600 (Leica Microsystems) into 100-μm-thick resin sections, in parallel to the longitudinal direction of each screw. These sections were stained with Villanueva bone stain reagent (Polysciences, “Villanueva Osteochrome Bone Stain”).
Stained sections were observed under an optical microscope, so as to find the ratio of the periphery of each screw to new bone (BIC; Bone-to-Implant Contact). Furthermore, the area ranging from the periphery of each screw to 240 μm (equals to the height of a screw blade) from the periphery was designated as an evaluation site for analysis (ROI; Region of Interest), and then the percentage of the area of new bone formed in ROI (BA; Bone Area) was found. BIC and BA were analyzed using ImageJ (National Institutes of Health).
In addition, BIC and BA are specifically found by the following formulae.
BIC (%)=[new bone mass (μm) in contact with screw surface/Peripheral length of screw portion implanted (μm)]×100
BA (%)=[new bone area (μm2) in ROI/ROI area (μm2)]×100
Moreover, when the periphery of a screw tip portion was included in an analysis range, the range includes the existing cortical bone region more than necessary, and thus the resulting analytical value is inappropriate to represent new bone mass. Hence, the periphery of a screw tip portion was excluded from the analysis range.
Optical microscopic photographs of stained sections seven and 28 days after implantation of each screw are shown in
As shown in
As shown in
As shown in
For evaluation of the stability of screw 2 and screw 3 of the present invention and a pure titanium screw after implantation, tissues surrounding the screws were observed seven days after implantation of screws by screw type (without immediate loading). A staining method employed for observation was the same method as in
As shown in
Amorphous alloys and pure titanium composing screws 1-3 of the present invention and a pure titanium screw, respectively, were tested for dissolution of components. In this test, first, 5.0 ml of a simulated body fluid (pH7.4) was added to a 15 ml of plastic tube, and then a metallic foil having the surface area of 384 mm2 and formed of each metal was immersed in the fluid. These tubes were placed in a thermostatic bath and then maintained at 37° C. for seven days. Subsequently, the amount of each metal ion of Al, V, Ti, Ni, Cu, and Zr dissolved in simulated body fluids was measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometer). In addition, as “control”, the amount of each metal ion was measured even in cases where no metallic foil was added.
Measurement results are shown in
An orthodontic anchor screw (screw 1 of the present invention) made of an amorphous alloy having a composition of Zr70Ni16Cu6Al8 was heated at 350° C. for one hour, so as to produce an orthodontic anchor screw made of surface-treated Zr70Ni16Cu6Al8 amorphous alloy (hereinafter, referred to as “surface-treated screw”), wherein the surface was coated with zirconia ceramics. The thus produced screw was tested for screw mobility using rats. For comparison, screw 1 of the present invention was subjected to the same test. Screw 1 of the present invention and the surface-treated screw used for the test are shown in
The method for testing screw mobility employed herein was the same method as in
A pure titanium foil (grade2; The Nilaco Corporation), a Zr70Ni16Cu6Al8 amorphous alloy foil, and a surface-treated Zr70Ni16Cu6Al8 amorphous alloy foil having the surface coated with zirconia ceramics (prepared by heating a metallic glass foil at 350° C. for one hour) were cut into a size of 6×6 mm. After sterilization, rat bone marrow cells were seeded, 2×104 cells each, and then cultured. To examine the cell adhesion ability of cells after 1 day of culture, actin (green), vinculin (red), and nuclei (blue) were stained by immunofluorescence staining, and then observed under a confocal microscope. Observation results are shown in
As shown in
As revealed by the above experimental results, the dental members of embodiments of the present invention quickly exhibit new bone formation around an area subjected to implantation and are excellent in stability of engraftment to bone after implantation, compared with titanium alloy screws and pure titanium screws. Moreover, the dental members of embodiments of the present invention exhibit high removal torques, so that the dental members do not fall off inadvertently after implantation, and can compensate for decreases in mechanical friction due to the decreased surface areas after size reduction. Accordingly, the dental members of embodiments of the present invention can be reduced in size smaller than conventional titanium alloy dental members and pure titanium dental members. For example, an orthodontic anchor screw or a dental implant in a screw shape wherein the core diameter of the screw part is as thin as 0.9 mm as shown in
As described above, the dental members of embodiments of the present invention can be reduced in size smaller than conventional products, so that the dental members can be designed as orthodontical implants that do not damage tooth roots upon implantation, are completely safe for living bodies, and do not fall off. Furthermore, the design of short dental members as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-032174 | Feb 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/053303 | 2/5/2015 | WO | 00 |
