in the two - part dental implant shown in the specific embodiments a proximal implant portion is formed by a tooth structure stem portion 10 and a distal implant portion is formed by a distal stem portion 20 . as the perspective view of the tooth structure stem portion 10 shown in fig1 illustrates , it has a longitudinal part 12 of a conical basic geometry which narrows towards the distal end 14 of the tooth structure stem portion 10 . the cone angle is 10 °. in the region of that conical longitudinal part 12 the tooth structure stem portion 10 has a total of four v - shaped projections 16 which face with their tips towards the distal end 14 of the tooth structure stem portion 10 . the four v - shaped projections 16 act as triangular prongs and are symmetrical and are arranged at equal spacings from each other around the periphery of the conical longitudinal part 12 of the tooth structure stem portion 10 . that affords eight flank surfaces 18 which face inclinedly towards the distal end 14 of the tooth structure stem portion 10 . fig2 is a perspective view showing the distal stem portion 20 . it has a longitudinal opening which is open towards its proximal end 22 and which has an inside wall 24 which is also of a conical basic geometry . cut into the inside wall 24 are four v - shaped recesses 26 which have flank surfaces 28 facing inclinedly towards the proximal end 22 of the distal stem portion 20 . when the distal stem portion 20 and the proximal tooth structure stem portion 10 are connected together ( see fig3 ), the relative position of the two stem portions is very accurately defined both in the axial direction and also in the rotational direction , by flank surfaces 18 and 28 respectively which bear snugly against each other . the inclined flank surfaces 18 and 28 respectively of the v - shaped projections and recesses respectively thus form mutually facing abutment surfaces which limit the approach of the two mutually facing surfaces 32 and 34 ( see fig1 ) and thus the maximum compression of the seal 30 ( fig7 and 8 ). that is pictorially illustrated in fig1 . in particular fig1 shows how the surfaces 18 and 28 are in contact and thus form a longitudinal abutment , in the final assembled condition of the dental implant . exact centering of the two stem portions is effected in the assembly operation by the respective mutually opposite inclined flank surfaces 18 and 28 respectively of the v - shaped projections and recesses respectively . upon inserting the tooth structure stem portion 10 into the longitudinal opening of the distal stem portion 20 the inclined flank surfaces 18 and 28 of the projections and recesses respectively meet on an inclined plane . thus upon further insertion into the longitudinal opening of the distal stem portion 20 the tooth structure stem portion 10 slides until it reaches its axial final position and in that situation rotates until all mutually opposite flank surfaces 18 and 28 are in uniform contact with each other . as a result the tooth structure stem portion 10 is forced into its desired final position without impediment to its sliding movement and can then be fixed by a screw pin 40 extending in the longitudinal direction of the stem ( see fig7 ). that screw pin 40 is tightened with a force of 30 ncm . the corresponding flank surfaces 18 and 28 which serve simultaneously as a longitudinal abutment and as a rotation - preventing securing means are then advantageously sunk in the interior of the longitudinal opening of the distal stem portion 20 and are not disposed in the region of the implant shoulder , as in other systems . the implant shoulder can thus be held at exactly the same level . in the variants shown in fig1 to 6 no particular measures are shown for making the transition from the proximal tooth structure stem portion to the distal stem portion bacteria - tight in the region of the outside contour of the finished assembled stem . in accordance with the variant shown in fig7 , provided for that purpose is a sealing ring 30 arranged between an outwardly disposed end face 32 of the proximal tooth structure stem portion 10 ′ and an outwardly disposed end face 34 , which is in opposite relationship thereto , of the distal stem portion 20 ′. when the stem is in the final assembled condition , that is to say when the proximal tooth structure stem portion 10 ′ and the distal stem portion 20 ′ have assumed their definitive axial relative position with respect to each other , the sealing ring 30 is compressed in the axial direction . the sealing ring 30 comprises a biocompatible plastic material . fig7 shows the essential component parts of the stem according to the invention for a dental implant , as an exploded view , more specifically , the proximal stem portion 10 ′, the distal stem portion 20 ′, the sealing body 30 for sealing off the transition between the proximal and distal stem portions and the screw pin 40 serving to screw the proximal and distal portions together . the longitudinal section through the stem according to the invention for the dental implant in fig8 has all of the essential component parts in the final assembled condition , with a correspondingly compressed sealing body 30 . fig9 to 11 show respective longitudinal sections of individual component parts . fig1 shows how the flanks 18 and 28 of the projections 16 on the proximal stem portion 10 and the recesses 26 on the distal stem portion 20 respectively co - operate in such a way that centering is effected by way of those flanks and not for example by way of the peripheral surfaces , which are to be found therebetween , of the stem portions 10 and 20 . the view of the transition between the tooth structure stem portion 10 ′ and the distal stem portion 20 ′, which is a partly sectional perspective view on an enlarged scale in fig1 , shows that the outside contour of the fully assembled stem , in the transitional region from the tooth structure stem portion 10 ′ to the distal stem portion 20 ′, does not have any gaps , in respect of which there is a risk of bacteria permanently collecting therein . that can be seen equally from the outside view of the transition between the tooth structure stem portion 10 ′ and the distal stem portion 20 ′ in fig1 . fig1 shows a perspective detail view on an enlarged scale of the proximal tooth structure stem portion 10 ′. the figure shows a seat 36 for the sealing body 30 as well as the v - shaped projections 16 which have already been discussed with reference to fig1 to 6 . fig1 a and 16 b shows how the flanks 18 and 28 act as abutment surfaces in the longitudinal direction and thus provide for defined compression of the sealing body 30 ( see also fig1 ); fig1 and 18 show a preferred sealing body 30 ′ comprising an elastomer such as ffkm , in cross - section . it will be seen that the sealing surfaces 36 of the sealing body 30 ′ are not flat but project in the axial direction of the implant at the outer edge of the sealing body and in that way form ridges 42 and 44 . those ridges are deformed when the proximal and distal implant portions are tightly connected and thus produce a secure sealing effect . fig1 shows the sealing body 30 ′ of fig1 and 18 with a coating 38 of parylene , as is described hereinbefore . it can also be seen from fig1 that the coated edges of the sealing body 30 ′ are rounded in order to prevent the coating from flaking off in the region of those edges . fig2 shows that the outer peripheral surface 50 of the sealing body can be of a concave shape so that it is straightened to be as approximately straight as possible as a consequence of compression of the sealing body after assembly of the stem according to the invention . fig2 shows the rounding of the edges of the sealing body 30 and the stem portions 10 ′ and 20 ′ at the locations marked by arrows . fig2 to 24 show an alternative sealing body 30 ″ with an elastomer body 60 in the form of an o - ring which is fitted into a ring element 62 of inwardly open , u - shaped cross - section . fig2 shows a view in cross - section of the alternative sealing body 30 ″. fig2 is a view on an enlarged scale showing a part of the alternative sealing body 30 ″ in the fitted condition between the proximal stem portion 10 ′ and the distal stem portion 20 ′. fig2 shows that the alternative sealing body 30 ″ can also have a coating 38 for example of parylene . fig2 to 27 show by way of example a further alternative variant of a sealing body 30 ′″ which has a metal spring 48 in its interior . the metal spring 48 is disposed in an elastic plastic material body 46 which is of an annular configuration and which is of a u - shaped , inwardly open cross - section . the plastic material body preferably comprises ptfe and the metal spring 48 comprises stainless steel . as fig2 shows the plastic material body 46 can have a coating 38 , for example of parylene , on its outside . on its outside , the plastic material body 46 is covered with a layer 38 which is a few nanometers thick and which in the illustrated preferred variant contains titanium particles . the thickness of the layer 38 is shown in greatly exaggerated form in the figure in order to make the layer visible . a nano coating of that kind can be provided on all outside surfaces of the sealing body , more specifically , irrespective of the external form of the sealing body . in alternative variants the springs can also comprise another resilient material , for example titanium or a plastic material such as peek . the springs can also be of a different form as long as they exert a spring action in the longitudinal direction of the sealing body , as indicated by the dash - dotted line ( see fig2 ). fig2 shows a sealing body in which an annular plastic material body 28 ′, for example of ptfe , of inwardly open , u - shaped cross - section , is partially filled with elastomer 64 . fig2 shows a seal having a sealing body 30 ″″ comprising an expandable material such as for example expandable metal or a plastic material with a high coefficient of thermal expansion . the sealing body 30 ″″ of fig2 is in the form of a tube portion . the intermediate space between the proximal and the distal implant portions 10 ″″ and 20 ″″ respectively is of a corresponding configuration . fig3 to 38 show a sealing body carrier 70 which serves as a tool for fitting a sealing body 30 on the proximal stem portion 10 . at one end the sealing body carrier 70 has an inwardly open groove 72 , into which a sealing body 30 can be inserted . preferably the sealing body carrier 70 is fitted with the sealing body directly after manufacture of the sealing body 30 by the manufacturer thereof . that facilitates handling by the physician and improves hygiene . an externally fluted gripping region 74 facilitates handling in that respect .