A case report by Dr. Robert Würdinger
In this case report, the usage of allogenic bone struts (maxgraft® cortico) in the shell technique for complex three-dimensional bone augmentation is demonstrated. The cavity between the struts and the alveolar ridge was filled with a mixture of allogenic cancellous (maxgraft® granules) and autologous bone particles obtained from the surrounding area. After 4 months healing period, it was possible to implant in a stable bone and soft tissue situation.
In the case of missing bone, the augmentation of hard tissue with bone grafting material of allogenic, autologous, xenogenic, or alloplastic origin is a central success factor in implantology. Allografts enjoy great acceptance among patients nowadays. Compared with autologous materials, the use of allografts avoids morbidity at the donor site and reduces the burden on the patient. Complications during harvesting can be prevented, and in addition allogenic materials are available in unlimited quantities.
A 52-year-old male patient was referred to the practice for implant planning in the right mandible in January 2016. The further prosthetic treatment was supposed to be carried out by his regular dentist. After three-dimensional x-ray diagnostics (Figs. 1, 2), a combined horizontal and vertical bone loss was revealed due to a tooth extraction carried out about eight years ago. This was accompanied by a severe lingual undercut that was both radiologically and clinically detectable (Fig. 3). Augmentation was essential to maintain the attachment level of the adjacent teeth for correct positioning of the implants. In addition, undesirable crown-implant ratios may also be avoided by vertical augmentation.
Augmentation with allogenic cortical struts
To achieve a three-dimensional bone augmentation, the shell technique with allogenic cortical struts (maxgraft® cortico, Straumann Biomaterials) (Fig. 5), which were fixed both vestibularly and lingually, was applied. Prior to positioning the lingual cortical strut, a mobilization of the mucosa was achieved by the detachment of the mucosa from the supra-hyoidal muscles (Fig. 4). In conjunction with a vestibular incision of the periosteum, this facilitates soft tissue coverage of the graft. A further benefit is being able to position the suture centrally on the alveolar ridge after the augmentation. After the mucosa mobilization was completed, the cortical struts, which were previously rehydrated for 30 min in saline solution, were inserted (Fig. 5).
After processing, adjustment, and removal of all sharp edges, the strut on the vestibular site was fixed with two micro-osteosynthesis screws in the accurate alveolar ridge contour. Then, thesecond strut was fixed with two screws through the mandible on the lingual site (Fig. 6, Fig. 6a). Once both struts were firmly attached, the gaps were filled with autogenous bone chips from the surrounding area (Fig. 7) and mostly allogenic cancellous bone (maxgraft® granules, Straumann Biomaterials). Finally, the graft was covered with a pericardium membrane (Jason® membrane, Straumann Biomaterials) and fibrin membranes prepared from autologous blood (L-PRF, Intralock) for enhanced soft tissue healing (Fig. 8). Finally, a saliva-proof and tension-free wound closure with a combination of horizontal mattress and single button sutures was performed (Fig. 9).
Final implant placement
After a healing period of five months, the alveolar ridge had been very well developed (Fig. 10, 10a, 10b, 11). The entire healing process presented itself without complications (Figs. 12, 13). After opening the ridge (Fig. 14), the augmented site revealed no resorption at the osteosynthesis screws indicating the superior stability of the cortical struts. The mixture of autologous and allogenic bone chips was even firmly fused vestibularly with the cortical bone plates. The bone volume indicated stable and vital tissue conditions. Moreover, the desired attachment level for the implants was achieved as planned. Pseudo-pocket formation can thus be avoided in the later prosthetic restoration. The same attachment level also contributes to the survival rates of the implants. After removal of the osteosynthesis screws, two Straumann Bone Level Tapered Implants (4.8 length 12, regio 46 and 4.8 length 10, regio 47) were placed slightly subcrestally (Fig. 15), and the cover screws for subgingival healing (Figs. 16, 17) were inserted. The use of Tapered Implants was deliberately chosen in this case because of the lingual undercut and proved to be very advantageous to avoid lingual perforations during implant placement (Fig. 18). After additional four months healing, the implants were exposed by puncture incision and soft tissue displacement (Fig. 19a, 19b). At the follow-up examination, both clinically and radiographically (Fig. 20) stable bone and soft tissue conditions were observed, so that the patient can be supplied with the appropriate crowns by his regular dentist (Fig. 21, 21a, 21b, 21c).