structure for example by mechanical or adhesive means the adhesive should be a type which will form a secure bond and should be a biologically acceptable medical adhesive silicone based adhesives obtained from dow corning are of a generally acceptable type for this application due to the properties of ptfe bonding is difficult unless bonding sites are provided on the surface of the lower portion 13 off the root structure 12 a suitable etchant to form these sites is available is tetraetch u2122 from w l gore amp associates inc the lower portion 13 of root structure 12 and the boot member 14 are enclosed in a non porous cushioning sheath member 16 to preclude the lower portion 13 of the root structure 12 from contact with the surrounding bone tissue the bone tissue in turn adheres solidly to the roughened outer surface of the sheath member 16 the non porous sheath member 16 is made of a biocompatible material to which bony tissue has an affinity and will readily attach to expedite this affinity the outer surface of sheath member 16 interfacing with the bony tissue is roughened by conventional methods suitable materials include those which are presently used to form the root structures of dental implant devices such as titanium and titanium alloys chromium alloys tantalum and stainless steels ceramics including aluminum oxide and polymeric materials polyurethanes polysulfones polycarboxylates perfluorinated polymers such as polytetrafiuoroethylene and fluorinated ethylene propylene polyacrylics silicone etc a preferred embodiment as a material of construction is titanium and its alloys this sheath member may be from 0 1 to 2 mm thick preferably at least 0 5 mm thick the non porous cushioning sheath member 16 and the.