Jürgen Koebke, Dirk Jansen, Jutta Knifka

Objectives: Dental implants are widely used nowadays in single-tooth loss or for anchoring a dental prosthesis. For a long standing the implant must be sufficiently osseointegrated. In anatomical specimens are to find increasingly dental implants which are useful to investigate.

Methods: Microradiographic and histological analyses were performed on 17 dental screw-type implants deriving from the mandibulae of five anatomical specimens aged from 69 to 87 years. For three individuals data were available by inquiring the relatives: implantation was 11, 10 and 7 years before death. One of the three cases was a tumor patient. The interforaminal part of the mandibula was resected 7 years before death and replaced by an iliac crest autograft, into which four implants had been inserted some time later. Each of the 17 implants was isolated by cutting the mandible into bone blocks. After embedding, cutting and grinding the sections were x-rayed and stained.

Results: With exception of the tumor patient, in all cases an intimate contact between compact and/or cancellous bone and implants was given. No translucent lines between bone and implant were detectable by microradiography. The threads and interspaces of the implants were in contact with mineralized, new compact bone, or spongy trabeculae reached the implants surface rectangulary. Bone resorption phenomena were observed in the crestal area only.

Conclusion: The results show that functional loading for even more than ten years is the basis for biomechanical integration of dental implants. Continuous bone remodeling seems to guarantee implant stabilisation independent from age.

Histological descriptions of osseointegrated human dental implants deriving from anatomical specimens are rare in literature. There exist some histomorphologic patient reports of one, two or three implants with evidence of osseointegration following several months until 4 years after implantation.[1,2,3] A greater number of implants, in place for 1-16 years, was analysed after their failure.[4,5,6,7,8] The authors were able to specify the causes of implant failure only by inspection of a very small sector of bone surrounding the implants.

Post mortem dental implants of healthy maxillae or mandibulae allow not only the analysis of the bone-to-implant contact (BIC) but also the integration of the implant into the cancellous and spongy bone framework. Successful osseointegration and functional stability of dental implants depend not only on the immediate bone-implant contact. There is an essential need of functional incorporation of the implant into the bending-free trabecular network. This basic principle was shown by Koebke et al.[9] for a new designed femoral short stem implant.

In routine dissection courses five specimens (two males of 69 and 79 years; three females of 74, 78, 87 years) with dental implants (n=17: 7 x Brånemark, 4 x Pitt-Easy Bio-Oss, 4 x TPS, 2 x IMZ) were found. All implants were placed in the interforaminal region of the mandibula, serving for connective suprastructures. For three individuals data were available. Implantation was performed 11, 10 and 7 years before death. One of these three cases was a tumor patient with operation 7 years before he died. The interforaminal part of the mandible was resected and replaced by an iliac crest autograft, into which four implants had been inserted some months later. Tested by finger grip, all implants were mechanically stable. The interforaminal part of the mandibles was isolated and x-rayed in labio-lingual direction (Faxitron Cabinet X-Ray System, Hewlett-Packard, USA). Then the mandibles were cut into bone blocks, each containing one implant. After embedding (Technovit 7200, Kulzer, Norderstedt, Germany) cutting and grinding, the sections (thickness 60-80 micrometers) were stained (Masson Trichrom Goldner). The staining allowed to differentiate old and newly formed osteons. From each in situ-implant 3-4 sagittal sections were obtained. Microradiographs were made from all sections (Agfa Structurix film; Faxitron Cabinet X-Ray System, Hewlett-Packard, USA).

Although only for three of the five individuals data were available, we deduce from the types of implants used that the implantation generally was several years before death. With exception of the tumor patient, in all cases an intimate contact between bone and implant was given. Bone resorption phenomena were observable in the crestal area of all implants (Figures 1A, B; 2A; 3A; 4A, B and C). The apical tip of the implants often is settled on dense and close-packed lamellar bone (Figures 1A, C; 2A; and 3A). The threads and interspaces of the implants were in contact with mineralized, new compact bone, or spongy trabeculae reached the implants surface rectangulary (Figures 1A, C, D and 2B). There are typical signs of remodeling and new bone formation (Figures 2A, B; 3A; and B).

In the tumor patient, for two of the Brånemark implants the osseointegration was satisfactory; the others were partly sheated by a layer of fibrous tissue (Figures 4A, B and C). This layer correponds to the translucent line in the microradiograph (Figure 4B).

The biological fixation of endosseous dental implants is a matter of great interest, mostly due to the increase in the use of many types of implants in clinical practise. Bone ingrowth results from a complex process, in which mechanics and biology play a major role. A wide variety of diverse factors can affect the development of the process, such as the properties or geometry of the implant surface, the mechanical stimulation or the initial cell conditions.[2,4]

In general, adaptation of bone to functional demands can result in loss of bone in situations of reduced loading, or in increase in bone when functional strains are exceeded. These adaptations can occur throughout the skeleton or within one limb, one bone, or even at a specifically defined site within a bone. The mandible as the only bone in the skull that is freely movable relative to the rest of the skull bones, is functionally stressed by bending forces. In holding the lower row of teeth, mastication evokes pressure and tensile stresses acting on the trabecular network of the mandible. The architecture of the spongious bone is functionally adaptated, the trabeculae are arranged like the pattern of main stress trajectories.[6]

For a long-term loading the functional integration of dental implants into the trajectorial pattern of the trabecular elements is essential. That means, the surface structure, i.e. the threads have to be in contact with spongious trabeculae rectangularly. By this an immediate strain flow from the implant to the spongious network is possible in a physiological way.

Even in case of an allograft (iliac crest) osseointegration of implants generally follows the same principles.

1.  Grätz KW, Zimmermann AP, Sailer HF. Histological evidence of osseointegration 4 years after implantation. A case report. Clin Oral Implants Res 1994; 5: 173-6.

2.  Rohrer M, Bulard R, Patterson MK Jr. Maxillary and mandibular titanium implants 1 year after surgery: histologic examination in a cadaver. Int J Oral Maxillofac Implants 1995; 10: 466-73.

3.  Uehara T, Takaoka K, Ito K. Histological evidence of osseointegration in human retrieved fractured hydroxyapatite-coated screw-type implants: a case report. Clin Oral Implants Res 2004; 15: 540-5.

4.  de Lange G, Tadjoedin E. Fate of HA coating of loaded implants in the augmented sinus floor. A human case study of retrieved implants. Int J Periodontics Restorative Dent 2002; 22: 287-96.

5.  Piatelli A, Trisi P. A light and laser scanning microscopy study of bone/hydroxyapatite-coated titanium implants interface: histochemical evidence of unmineralized material in humans. J Biomed Material Res 1994; 28: 529-36.

6.  Piatelli A, Scarano A, Piatelli M. Histologic observations on 230 retrieved dental implants: 8 years’ experience (1989-1996). J Periodont 1998; 69: 178-84.

7.  Sennerby L, Ericson LE, Thomsen P, Lekholm U, Åstrud P. Structure of the bone-titanium interface in retrieved clinical oral implants. Clin Oral Implants Res 1991; 2: 103-11.

8.  Steflik DE, Parr GR, Singh BB, et al. Light microscopic and scanning electron microscopic analyses of dental implants retrieved from humans. J Oral Implantol 1994; 20: 8-24.

9.  Koebke J, Xepulias P, Thomas W. Schenkelhalsprothese Typ Cut – eine funktionell-morphologische Analyse. Biomed Technik (Berl) 2000; 49: 135-40.