Abstracts (04)
Implant Stabilization by Tissue Ingrowth
R.M. Pilliar Faculty of Dentistry, Dental Implant Group, University of Toronto
Proceedings of an International Congress, Brussels, May 1985 (D. van
Steenberghe, ed.), Excerpta Medica, Amsterdam 1986;60-76
The use of porous-surfaced implants capable of fixation through tissue ingrowth represents a possible method for the long-term stabilization of load-bearing implants. This approach has been used clinically with success for stabilizing orthopaedic implants in bone and the use of porous-surfaced implants is presently being investigated in dentistry. Experience in orthopaedics has been more extensive and some necessary, but not necessarily sufficient, conditions for bone ingrowth have been indicated. These include, in addition to the normal requirements for any implant, an initial maximum allowable movement of the implant relative to the host bone and a minimum pore size.
Although bone ingrowth has been observed within pores as small as 30 microns, for practical purposes a pore size greater than about 100 microns is recommended for extensive bone ingrowth and strong interface fixation to occur. The effect of pore size on bone ingrowth is of great practical significance in view of the requirement of initially limited relative movement between the implant and bone. In practice, this can be achieved by restricting the loading or function of the implant for an initial period after placement. To make this period as short as possible, a rapid rate of bone ingrowth is desirable. It should be noted that this requirement is common to other implant designs which achieve long-term implant fixation by bone remodelling (even those which rely on acrylic bone cements).
Metals, polymers and ceramics in the form of powders, fibres and wire mesh have been used for fabricating porous-surfaced implants. Examination of the resulting surface structures has indicated one area of concern with the use of these systems: their much greater surface areas. The consequences of the greater reactivity and possibly higher levels of trace elements released from these implants require further study. Improved fixation will result in a distinctive tissue structure at the interface (much thinner fibrous encapsulating layers, for example) and this will also influence the nature of the long-term tissue reactivity. Biomechanical effects specific to the more rigid implant fixation resulting from bone ingrowth must be considered in the design and use of such implants, since deleterious bone remodelling can develop.
A unique characteristic of porous-surfaced implants with 3-dimensional inter-connected porosity is the possibility of secure attachment of the implants to surrounding bone via a non-mineralized fibrous connective tissue layer. Studies of porous-surfaced implants stabilized in this manner have been reported. Fixing an implant to bone through a viable ligament-like tissue offers possible benefits over the rigidly fixed, bone-ingrowth implants.
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