Porous endosseous implant

Claim 1

1 A m or less and that of the layer 2 is 50 to 200 p m(if necessary, inclusive of a range wider than an average of 200 gm). Needless to say, since this is a range of pores concerning the ingrowth of the bone tissue of a living body, the critical range of pores does not form a restrictive boundary between the respective tissues and it is possible for different tissues to disorderly ingrow through the pores, so that the aforesaid range should be considered at least a reference. In some case, the layers 2 and 2 may be substantially the same in the range of pores and in other case they may be designed to be stepwise staggered in the range of pores. The same can be said of the case of using the layers 1 and 1. The pore gaps which completely permit the ingrowth and penetration of the bone tissue therein are up to the order of 1000 pm, so that when it is difficult to form the pores of the size exceeding this range, it is possible to form the pores by drilling the thickness of the implant by an electrobeam method, laser beam method, electrospark method, mechanical drilling method according to the Japanese patent application No. 264994/1985 which the present applicant filed separately, US patent No. 931,660. British patent No.8626646, West German patent application No.P3639030.5, and Italian patent application No. 22306A/86. Viewed from the point of strength of the sintered body, a coarse powder sintered body is large in pores and relatively small in strength, while a fine powder sintered body is small in pores and large in strength. Porosity (porosity rate) of the sintered metal layers 1 and 2 together with the pores has bearing upon the ingrowth and penetration of the tissues and upon the strength of the layers 1 and 2. Higher porosity is more effective for ingrowth of more tissues, while it works reversely on strength. This point must also be considered when porosity is selected. Included under the metal or alloyed metals to be used are simple substance metals such as Ti, Zr and Ta, Ti alloy, Zr alloy, Ta alloy, Fe-Ni-Cr alloy, Co-Cr-Mo alloy and similar other materials harmless to the human body. It is possible to obtain a sintered metal layer having different pores formed therein by the use of the powder materials mentioned above by laminating Pressure powder zolding layers formed respectively of relatively fine powder and relatively coarse powder and sintering the resulting layers into one body in nonoxidizable atmosphere. If necessary, it is possible to obtain dimensional accuracy in the surface of the sintered metal layer by machining in subsequent to the lamination of the sintered metal layers into one integral body or reopen the pores in the surface by chemically etching the surface of the sintered metal layer having its pores crushed by the machining. Relation between factors in adjusting the pores in the layers 1 and 2 and pore diameter is shown below: Pore size reduced Factor Large Forming pressure Small Small Powder size Large High Sintering pressure -4 Low Long Sintering time -+ Short Notwithstanding the fact that the implant is relatively thin in its entire thickness, the implant of the invention defined in Claim 1 is enabled to be a frameless and coreless implant because of improvement of the whole implant in mechanical strength by relatively fine metal powder sintered layers 1 and 1 disposed on either side of the implant and relatively coarse metal powder sintered layer 2 interposed between the layers 1 and 1 and can softly cope with impact stress because a soft fibrous tissue ingrows substantially into the layers 1 and Pore size increased 1 and penetrates therethrough. The implant defined in Claim 2 permits the substantial ingrowth and penetration therein of osteold and bone tissues through the pores in the relatively coarse metal powder sintered layers 2 and 2 on either side thereof and can sufficiently cope with static stress, although the support of the implant in Claim 2 is not so soft as the one defined in Claim 1. Because it is expected that the implant in this embodiment can be further increased in strength as a whole by the high mechanical strength provided by the sintered.metal layers 2 and 2 on either side of the sintered metal layer interposed therebetween, not only the entire thickness of the implant can be further reduced but ' the fibrous tissue can also make ingrowth and penetration through the layer 1 and partially demonstrate its soft support, depending upon the manner in which the pores are formed in the layer 2. Embodiments: Example 1 The embodiment shown in Figs. 1 and 2 is an embodiment corresponding to Claim 1 and shows a plate type endosseous implant to be embedded in an alveolar bone a, and an implant body 1 is connected by sintering, welding or pressure welding integrally to the lower part of a metal post 4 to be crowned with an artificial'tooth (not shown). The implant body 1, as shown in Fig. 2, is formed of three layers. The three layers are laminated into one body in such manner that the layers 1 and 1 forming the right and wrong side surfaces of the implant 1. - 10 body 1, respectively, have about 30% porosity and include relatively fine pores in the range of 30 to Hiúm in diameter and a sintered metal layer 2 having relatively large pores in the range of 50 to 2001xm is interposed between the layers 1 and 1 and the layers 1, 2 and 1 are laminated into one body by sintering. In the embodiment, by the use of the idea disclosed in the previous Japanese patent application No.264994/1985, the implant further provided at random with tubular channels 3... to permit the bonetissue to penetrate the thickness of each layer by an electrobeam method, laser beam method, electrospark method or mechanical drilling method in order that the implant may have through-holes having a diameter in the range of 200 to 1000g m to permit vigorous penetration of bone tissue into and through the sintered metal layers 1 and 1 forming paticularly the right and wrong sides of the implant. The reason for formation of tubular channels 3... is to promote the penetration through the pores 3 which effectively supports the implant relative to static stress by forming pores in the range of 20 to 1000 pm in point of pore diameter, number and distribution over the area of the layers depending upon the case of disease, the pores being hard to form intentionally by the metal powder of the grain size to be later described. The metal powder was used in such manner that fine pure titanium powder (50 to 100lim) was used for the layers 1 and the powder (100 to 2001im) was used for the layer 2. The three layers 1, 2 and 1 each were formed by pressure powder molding and were thereafter laminated into one body under the sintering conditions: 1 x 10 ' Torr. in degree of vacuum, 100'C in temperature, and 1 hour in treatment time, whereby the layers I and 1 having pores 30 to 5OAm large and a layer having pores 50 to 2000 Am large were obtained respectively. The implant body 1 formed of the thus obtained and a titanium alloy post 4 were subjected to argon arc welding by use of a titanium welding rod by placing the post 4 on the body 1 edge to edge via beveling. Example 2 The embodiment shown in Figs. 3 and 4 is the one corresponding to Claim 2 and shows the case wherein the embodiment is applied to a cylindrical type dental endosseous implant adapted to be screwed into the alveolar bone a. The embodiment is of such three layer construction in which the post 4 is welded integrally to the top of the implant body I formed cylindrical with the lower part left open by interposing the inner layer 1 between the layers 2 and 2 in order reverse to that in Example 1. Accordingly, the cylindrical implant is left hollow with no core inside. The layers 1 and 2 are entirely the same in material, production method and welding method as those of the first embodiment. Incidentally, the post 4 is provided not for the purpose of reinforcing the implant body I but for the purpose of protect- ing a bone mucous membrane and cartilage tissue against possible inflammation and secondary infection caused by bacteria invading that portion of the porous implant projecting beyond the alveolar bone a through the multipores of the projecting portion. In place of the plate type and cylinder type implants described above, the invention can find its application in a general submersible endosseous implant. Because the implant of the invention defined in Claim 1 permits mainly the fibrous tissue to make ingrowth and penetration through the sintered metal layer having a range of relatively fine pores therein, the implant is not only enabled to cope softly with impact stress but is also enabled to maintain necessary strength and to have high porosity on either side layer of the implant to permit ingrowth of a large amount of fibrous tissue irrespective of the implant body being coreless and frameless, because the implant body is reinforced in the direction of tis thickness by the sintered metal layer in the middle of the implant body having a range of relatively coarse pores. Accordingly, the implant of the type described finds its optimum application in the dental field, orthopedic field and the like in which impact stress is iRparted to an afteroperation implant. The implant claimed in Claim 2 is mainly intended for ingrowth and penetration of osteold and bone tissues, so that although different from the implant in Claim 1 from the viewpoint of soft support relative to stress, yet resistance by hard tissue to stress is conversely produced, and consequently the implant is not only suitable for an implant based on static stress but further promotes reduction in the thickness of the implant by the increased strength given by the sintered metal layer on either outside of the implant. Since both embodiments have, in addition to the grain size, forming pressure, sintering temperature, and sintering time to do with adjustment of the pores, not only the adjustment of the pores is easy but the employment of pressure powder molding technique and sintering technique as a production method also facilitates mass production. The invention provides excel- lent effects in this respect. I 1 CLAIMS: A frameless and coreless porous endosseous inplant rising a porous sintered metal layer having a range of relatively large pores and porous sintered metal layers and each having a range of relatively small pores and laminated into one body by sintering integrally with the layer on either side thereof, whereby said three layers each permit the ingrowth and penetration of two or more kinds out of fibrous tissue, osteoid tissue and bone tissue in the pores thereof.