“Three-dimensional” reconstruction, or the shell technique, is a specific form of autogenous bone regeneration. Thin cortical bone blocks are initially used to restore the contours of the alveolar ridge, and the resulting gaps are then filled with autogenous bone chips^1,5. The short- and long-term results after augmentation with the aid of the shell technique demonstrated low complication rates and a stable bone volume even ten years after surgery^6-9.

In addition to using the shell technique, there is also the possibility of reducing resorption processes by combining block transplantation with guided bone regeneration^10,11. With full block transplants, the resorption between augmentation and implantation could be reduced to 5.5-7.2%^10-12. Ten years after implantation, the result was stable with only 0.8% further resorption¹². A disadvantage of this method, however, was the high dehiscence rate of 9.5-27.2%, and the fact that the xenogenic bone substitute material was not integrated in the bone, but rather in connective tissue^10,11. For this reason, De Stavola & Tunkel's method modified the procedure so that the augmentation was carried out using the shell technique, which led to a significant reduction in resorption¹³. An additional GBR with xenogenic bone substitute material and collagen membrane was then performed during the implantation. With this method, known as “augmentative relining”, an additional bone gain of 17% could be achieved. Clinically and radiologically, the incorporation of the biomaterial into the regenerated bone was demonstrated. There was no further resorption of the regenerated bone up to the point of prosthetic restoration.

There is a great desire to avoid bone harvesting, both on the part of the patient and the practitioner, so that the majority of dentists working in implantology try to avoid autogenous bone harvesting. Another, more serious, disadvantage of autogenous bone transplantation is the limited amount of intraorally available bone.

Allogeneic bone materials seem to be the closest to autogenous bone transplants in clinical applications¹⁴. Allogeneic full block transplants are, however, subject to similar resorption processes as autogenous full block transplants^{3,10,11,15,16}. The complication rate is also higher with allogeneic full block transplants than with autogenous bone transplants¹⁷. On the other hand, a split-mouth case series showed that the use of cortical allogeneic bone plates produces results that are equivalent to those of autogenous bone plates in terms of regeneration, resorption and complication rates, and thus could solve the problem of insufficient intraoral bone availability and reduce morbidity¹⁸.

In this case report, a patient with a limited amount of intraorally available bone underwent vertical bone augmentation and two-stage implantation with augmentative relining on both sides of the lower jaw. One half of the jaw was treated with autogenous, the other side with allogeneic, bone plates. There was an equivalent healing on both sides without complications and only a low rate of resorption.

Initial situation

A 60-year-old female patient was referred for implantation with bone augmentation. Her general medical history showed no particular features that restricted the surgery. There was a bilateral free-end situation in the lower jaw with missing teeth 46-47 and 35-37 with a vertical bone defect of approx. 5 mm height loss. There was slight elongation of the upper posterior teeth which, after consultation with the prosthetic referring dentist, could be corrected by grinding (Figs. 1,2).

The preoperative DVT revealed vertical bone defects in the third and fourth quadrants (Fig. 3).

Treatment planning

Placing implants in the correct prosthetic position made a vertical augmentation absolutely essential. The amount of bone that had to be harvested could not be gained in just one retromolar bone harvesting area. Therefore, the patient was advised to undergo one bone block harvesting and have the other site rebuilt by allogeneic bone plates.

The sequence of the treatment planning was as follows:

• Bone harvesting from the right retromolar area
• 3D vertical bone augmentation in the fourth quadrant utilizing the shell technique with autologous bone plates & chips
• 3D vertical bone augmentation in the left mandible utilizing the shell technique with allogeneic struts and autologous bone chips
• 4 months of healing
• Insertion of implants in regions 35, 36, 46 and 47, combined with relining GBR using collagen membranes and DBBM particles
• 4 months of healing
• Second-stage surgery with Kazanjian vestibuloplasty, combined with step incision on both sides
• After 6 weeks of prosthetic rehabilitation

Surgical procedure

At the start of the procedure, a bone block was harvested from the right retromolar area with the aid of a Microsaw®. This was then split lengthwise using thin diamond disks. These plates were then thinned to a thickness of about 0.5 mm with a Safescraper®, and autogenous bone chips were collected at the same time. The plates obtained in this way were fixed buccally and lingually in regions 46-47 with four micro-screws. The resulting bony envelope was then filled with the autogenous bone chips with the application of slight pressure.

Augmentation in the fourth quadrant with autologous bone plates and autologous bone chips using the shell technique: retromolar bone removal (Fig. 4), buccal and lingual fixation (Fig. 5), filling of the bone bed (Fig. 6)

Finally, blunt mobilization of the floor and a periosteal incision was made in the buccal region in order to enable the augmented area to be covered.

The augmentation then took place in the third quadrant. To this end, two allogeneic bone plates (maxgraft® cortico, Straumann GmbH, Freiburg, Germany) were first opened and immersed in sterile saline solution for 10 minutes. During this time the flap was prepared in regions 35-37. The allogeneic bone plates were divided according to the anatomical situation and fixed buccally and lingually in the fourth quadrant using 4 micro-screws. The resulting cavity was then filled with autogenous bone chips that were left over from the augmentation in the third quadrant.

Augmentation in the third quadrant with allogeneic bone plates and autologous bone chips using the shell technique: initial situation after opening (Fig. 7), buccal and lingual fixation (Fig. 8), filling of the bone bed (Fig. 9)

The wound was closed analogously to the procedure on the left side.

After a four-month healing period, a panoramic x-ray with measuring balls revealed a clear vertical bone gain after 4 months in both quadrants (Figs. 10,11)

The third and fourth quadrants were reopened before implantation. To this end, the inserted micro-screws were removed on both sides after the crestal incision and flap formation (Figs. 12,13). Straumann® Bone Level Tapered implants (diameter 4.1 mm, length 10 mm in the area of tooth 35, diameter 4.8 mm, length 10 mm in the area of teeth 36 and 46, and diameter 4.8 mm, length 8 mm in the area of tooth 47, SLActive®) (Straumann GmbH, Freiburg, Germany) were then inserted according to the manufacturer's instructions. After the implants had been inserted, sufficient bone was seen to be available in the buccal and lingual areas, approx. 1-2 mm thick (Figs. 14,15). Following buccal incision of the periosteum, a collagen membrane (Jason® membrane, Straumann GmbH, Freiburg, Germany) was attached to the apical periosteum with resorbable sutures. The alveolar ridge section was then covered with bovine bone material (Xenograft®, Straumann GmbH, Freiburg, Germany) with a layer thickness of one particle size (1.0-2.0 mm). The membrane was then secured with resorbable sutures on the lingual side of the flap (Figs. 15,16). The final step was the plastic covering of these augmentative relinings.

Close-ups from the postoperative OPG after implantation of Straumann® Bone Level Implants and GBR from augmentative relining in the third and fourth quadrants (Figs. 18,19).

After a healing period of four months, the implants were exposed. As the area had been augmented twice, there was a lack of keratinized tissue in the region of the implants (Figs. 20,21).Consequently, a vestibuloplasty according to Kazanjian was performed^19,20. To this end, after the initial preparation of a supramuscular mucosal flap, the muscle was sharply separated from the periosteum in an apical direction. The mucosal flap was secured to the periosteum with resorbable sutures. Finally, the implants were exposed by stab incisions. Conical gingival formers (Conical Shape®, Straumann GmbH, Freiburg, Germany) with diameters of 5 mm in region 35 and 6.5 mm in regions 36, 46 and 47 were used as healing abutments (Figs. 22,23). Postoperative situation on the panoramic x-ray (Figs. 24,25).

Prosthetic procedure

After a healing period of 6 weeks, the prosthetic restoration was carried out by the dentist who made the referral. The final check-up showed stable peri-implant bone conditions and sufficient keratinized tissue with clinically free inflammation (Figs. 26,29).

Treatment outcomes

The augmentative relining technique can also be carried out with allogeneic bone plates. No clinical problems were observed in association with this procedure, and there were signs of good integration of the xenogeneic bone substitute into the augmented bone.

Dr. Tunkel's recommendations

In cases of limited vertical bone availability, when the patient requests a fixed-borne restoration on the posterior area of the mandible, the shell technique for bone augmentation is our first choice as this offers high predictability combined with low complication and resorption rates. Usually, the patient chooses whether to opt for allogeneic or autologous bone shells. In the case of bilateral sites that need to be treated, we often choose the combined approach as we can easily harvest enough autologous bone chips without a second bone harvesting site in order to reduce morbidity and provide a better patient experience. In my daily practice, the allografts have proved to perform equally effectively as autografts in terms of complication and resorption rates with less morbidity.