In these clinical scenarios, ZAGA Concept recommends to buccally displace the osteotomy with the aim of sinking the implant neck/body as much as possible into the alveolar and lateral maxillary wall bone while maintaining the sinus lining integrity with no membrane perforation at the crest level. This type of osteotomy, not capable of providing a complete covering of the implant mid-body and neck is known as “Canal Osteotomy''. It is a groove made on the coronal alveolar bone, and sometimes also in the lateral maxillary wall and zygomatic buttress. As a waterway or channel; it has a floor, lateral walls with different heights and no roof. When a “Canal Osteotomy” is performed, the maxillary bone is not covering the buccal zygomatic implant mid-part, nor its neck.

This approach belongs to the ZAGA Concept recommendation, and its rational is based on the fact that the implants with minimal crestal bone surrounding their entry point may present bone resorption under function and within time with a subsequent oral-antrum fistula. Indeed, deficient bone to implant contact (BIC) may be jeopardized by different circumstances i.e. periodontal disease history, inadequate oral hygiene, use of water pressure devices at the gingival junction, inadequate use of the dental probe, etc. Moreover, it has been speculated that the lack of crestal bone support would end up in a transversal mobility of the long coronal part of the zygomatic implant facilitating an oral-sinus communication.

Placing the zygoma implant platform partially or outside of the sinus, and with a lateral maxillary bone support/contact; would allow a better prosthetic positioning together with a more conservative approach regarding the sinus integrity preservation.  In order to prevent soft tissue dehiscence when placing the implant laterally to the maxillary wall, it is recommended to groove the buccal bone to house the implant body with as much lateral submergence as possible into bone, in such a way that it does not protrude against the mucosal position and does not compress the soft tissue vascularity. The depth limit for the canal digging is the sinus membrane integrity at this level. The use of a channel section implant adapted to this osteotomy type i.e. the Straumann ZAGA Flat, would help the surgeon to prevent soft tissue complications.

The present case report is intended to demonstrate how a bony canal having section in the shape of an arc of circumference, would optimally be sealed by an implant showing a circumferential arc section as well. Each step of the procedure will be illustrated with figures showing the insertion of a flat zygomatic implant section that fits into a channel with a minimal buccal impact against the soft tissue.

Initial situation

A 75-year-old female patient presented to our office with the chief complaint of deficient chewing function and poor aesthetics. Regarding her medical condition, she reported not suffering systemic diseases and not taking any medication.

The clinical assessment in the upper jaw showed the presence of hopeless teeth on positions #13, #12, #11, #21, #22 and #23, with advanced chronic periodontitis and atrophic ridges on the posterior areas. On the other hand, in the lower jaw she presented an implant on position #43 supporting a failing partially removable prosthesis.

The radiographic assessment depicted an extreme bilateral bone loss on both premolar and molar regions at the upper and lower jaws. Furthermore, a horizontal bone loss in the anterior area on both upper and lower arches was presented.

The patient expectations were high, and she requested a short-lasting therapy avoiding large bone augmentations with an immediate fixed prosthesis at her upper and lower jaws.

The decision was done in favor of the extractions of all remaining teeth which were considered hopeless and immediately followed by the complete rehabilitation of the upper and lower jaws a with fixed prosthesis anchored on oral implants.

Treatment planning

The treatment decision-making process was based on impressions and casts from the upper and lower jaws using a SAM dental articulator, the radiographic assessment (X-rays & CBCT) and a digital planning software (Figs. 1- 4).

Following a careful evaluation; it was planned to perform in the upper jaw a Hybrid Zygoma approach (4 dental-implants and 2 zygoma-implants), that included a ZAGA surgery with two ZAGA flat implants of 40 mm length on the right side and 42.5 mm length on the left side (advanced), four conventional dental implants,  a periodontal plastic surgery (pediculated connective scarf graft) and an immediate fixed restoration consisted on a screwed retained provisional bridge. Moreover, in the lower jaw five conventional implants with an immediate screw-retained fixed restoration were planned.

According to our standard protocol, the final restorations were delivered six months after surgery.

Surgical procedure

The whole procedure was conducted under full narcosis. The hopeless teeth were extracted and a mucoperiosteal flap was elevated by means of supracrestal and three vertical incisions in the tuberosity regions and the midline. These incisions enabled the flap mobilization beyond the infraorbital margin.

The surgeon’s first act after raising the flap should be to mark with a surgical pencil the reference points for the alveolar and zygomatic bone entrances. Therefore, these coronal and the zygomatic entrance points on the left second premolar/first molar position were pointed according to the virtual planning (Figs. 5 & 6).

As the alveolar thickness was less than 4 mm, a “tunnel” osteotomy was not recommended. The drilling protocol consisted on the use of the lateral cutting bur help to initiate a canal and where the next drill tail will slide. The canal diameter was still reduced at this stage in order to precisely embrace and guide the next bur tail. It is important to take into consideration that just the first part of the lateral drill is used to initially prepare a channel with a diameter congruent to the round bur tail (Fig. 7).

The slight adaptation of the lateral bur allowed the use of a round bur, which was supported by the alveolar channel. In this stage; the direction, depth and the inclination of the future implant trajectory was evaluated. Once the channel showed the desired depth and the floor surface became even, the round bur tail slid up and down gently. The grinding with the round bur becomes more precise by gently touching the bone during the slide down movement and by a “grinding-back” movement the round bur is able to eliminate the channel floor irregularities (Figs. 8 & 9).

Once a zygomatic notch was prepared; the channel was evaluated in order to ensure a homogeneous floor, desired inclination and depth. For the final drill diameter, a Ø2.9mm twist drill was used with profuse irrigation and with up and down movements, using short pressure periods of about 4 seconds, allowing the saline to clean and cool the drill (Figs. 10 & 11).

Following the drilling protocol, the ZAGA channel osteotomy prepared according to the virtual planning was appreciated with a minimal destruction of the alveolar bone maxillary wall and zygomatic bone. A precisely congruent to the implant shape maxillary groove was created while maintaining sinus lining integrity (Figs. 12 & 13).

After it was ensured that the implant site was free of soft tissue remnants, the torque control was set at 50Ncm and 15 rpm, and a flat tapered implant design (Straumann Zygomatic Implant ZAGA®-Flat) was inserted at increased torque using the hand piece with the final aid of the manual implant holder. The self-tapping flutes helped this implant design to smoothly penetrate the external cortical of the zygomatic process. Enhanced primary stability was achieved by the implant tapered design and by a conservative final drill-implant diameter difference of 1 mm (Figs. 14 & 15).

Additional remarkable characteristics of this design include the diameter of the implant transport holder which is the same as the implant itself. This feature helps us to easily manage the implant insertion in situations where the implant is inserted close to another implant or into hard bone. As previously planned, the implant (grade 4 titanium) was placed partially outside the bone envelope. Thanks to its flat section, a possible vascular compression of the soft tissues was diminished (Figs. 16-19).

The same procedure was followed on the contralateral side. Additional four conventional implants were placed on the anterior side. To increase the amount of keratinized tissue buccal to the implant, a palatal incision was made. The double pediculate partial flap aimed to make possible a first intention closure of the soft tissue. Finally, a mattress technique with a non-resorbable suture was performed (Figs. 20 & 21).

In the lower jaw, four conventional implants on positions #32, #34, #42 and #44 were placed following the manufacture’s protocol.

Prosthetic procedure

The prosthetic workflow included the positioning of screw retained abutments (SRAs) and positioning transfers in order to perform an analog impression (Fig. 21).

The delivery of the screw-retained temporary bridge was done in the same day and an X-ray control was taken.

Treatment outcomes

The clinical and radiographic one-year follow-up evaluations showed the outstanding outcomes of combining the use the ZAGA Concept for hard and soft tissue management and an implant design (Straumann Zygomatic implant ZAGA flat) with features adapted to the patient anatomy.  Additionally, we could also appreciate the excellent bone and soft tissues stability around Straumann zygomatic abutments that have been achieved.  This was also thanks to the anatomic, prosthetically driven position of the implants and the use of straight non-angulated abutments (Figs. 22-25).

At one-year follow-up, the high level of patient satisfaction was maintained as she considered that all her expectations were fulfilled (Fig. 26).

Acknowledgements

The author particularly appreciated and acknowledge the contribution of Drs. Peter and Madalina Simon, ZAGA Center Stuttgart, Germany for the discussions during the prosthetic-driven implant planning phase and for taking care of the prosthesis manufacturing and placement.