Fundamental knowledge of the maxillofacial anatomy and physiology are necessary to perform this advanced procedure. Proper training including the understanding of the prosthetic and surgical biomechanical principles is paramount.
The entire trajectory of the drill as well as the implant path is critical to avoid complications. The apex of the 2.9-mm drill must be directly visualized penetrating through the lateral cortex of the zygoma bone.
Appreciation of the zones of the maxilla and the ZAGA classification, which outlines the contour of the lateral maxillary wall and the level of palatal resorption pattern of the maxillary crestal bone, is critical for the understanding of the intrasinus versus extrasinus position of the midportion of the implant.
Treatment of the edentulous maxillae with the zygoma implant requires extensive knowledge of the anatomy and physiology of the maxillofacial region. This article highlights a few of the principles in the prevention and management of potential complications with the zygoma implants.
Zygoma trajectory: The starting and end points for the zygoma implant are definite and consistent regardless of whether it is placed intrasinus or extrasinus. The platform of the zygoma implant is generally in the second bicuspid/first molar region with the apex of the implant protruding through the lateral cortex of the zygoma bone ( Fig. 1 ).
Whether the midportion of the implant is within the maxillary sinus or outside of the maxillary sinus depends on the contour of the lateral maxillary sinus wall ( Fig. 2 ). The contour of the lateral maxillary sinus wall can be straight (blue line), concave (green line), or severely concave (red line) to missing as seen in maxillectomy cases.
As described by Freedman and colleagues in 2013 and 2015, , presence of bone around the zygoma implant platform is most desirable because it is the primary support of occlusal forces under function ( Fig. 3 ).
Zygoma anatomy-guided approach (ZAGA) classification : Aparicio described the contour of the lateral maxillary sinus wall in their article on zygomatic anatomy-guided approach. However, the classification has been misinterpreted in the literature. This classification simply describes whether the lateral maxillary sinus wall is straight, slightly concave, very concave, or missing ( Fig. 4 ); it is not a technique; it is simply a radiographic observation using the frontal view of the 3-dimensional radiographic study of patients. If the illustrations in Fig. 4 were superimposed on top of each other, the implant platform and the implant apices would exactly overlap on each other confirming that there is a single trajectory to the zygoma implant.
Understanding the relationship of the zygoma implant platform and the prosthetic screw access channel position in the provisional or the final prosthesis is important for the entire implant team. The team has to appreciate that the edentulous maxilla resorbs in the superior and the medial direction, yet the arch form contour remains constant.
In a nonresorbed or a minimally resorbed maxillary alveolus, the implant platform represented by the black dotted line and the arch form representing by the red dotted line are coincident and superimpose on top of each other. Therefore, the prosthetic screw access channel will be in the center of the molars and the cingulum of the anterior teeth as seen in ( Fig. 5 ).
However, in moderate to significantly resorbed maxillae, owing to the medial resorption pattern of the edentulous alveolus, the implant platform will be in the resorbed residual crest, the “new” position of the black dotted line, which is now lingual to the red dotted line. Therefore, the screw access channels will not be in the central fossa of the molar teeth or in the cingulum of the anterior teeth. Instead, the screw access channels will be in the pink portion of the hybrid prosthesis as seen in ( Fig. 6 ).
To claim that for patients with moderate to severe resorption pattern of maxillary alveolar bone the zygoma implant platform can be placed with the screw access channel emerging through the central fossa of the posterior teeth is simply not true. Therefore, removing the crestal bone as described in the extrasinus technique is not in the best interest of the patient ( Fig. 7 ).
Clinicians should be aware that a probable postoperative complication with the placement of the zygoma implant outside the maxillary sinus, as in the extrasinus technique, is the dehiscence of the overlying soft issues due to muscle pull ( Fig. 8 ).
However, in cases of ZAGA 4 where the maxillary crest is severely resorbed or absent as in oncologic cases, the dehiscence of the soft tissues is unavoidable. In ZAGA 0, 1, 2, and 3 cases in which the engaging of the crestal bone with the implant platform is possible, it is difficult to objectively explain the occurrence of soft tissue dehiscence if objections are raised by patients or other clinicians in regard to the ongoing maintenance of the intermittent irritation and infections ( Fig. 9 ).
Rescue concept : Two sites are available for placement of two zygoma implants within the same zygoma bone. As described earlier, the trajectory of the zygoma implant is from the residual crest of the maxilla up into the body of the zygoma bone. In cases in which 2 zygoma implants are placed within the same zygoma bone, the apex of the zygoma implant in the posterior (premolar-molar) region is the lower position shown by the blue arrow. The apical position of the second zygoma implant placed in the anterior (lateral incisor-cuspid) position is shown by the green arrow ( Fig. 10 ).
Understanding the trajectory of the 2 zygoma implants within the same zygoma bone allows the surgeon to remove a fractured or a failed zygoma implant; immediately replace it with a new zygoma implant keeping the implant platform in the original position, on the crest of the maxilla ( Fig. 11 ); and correct the trajectory of the osteotomy to allow for the placement of the apex of the new zygoma implant in the superior position.
The panorex demonstrates a fractured zygoma implant in position no 14 ( Fig. 12 ). The treatment for the immediate replacement of the implant is removal of the fractured implant with immediate replacement with a new zygoma implant as described previously.
The plan ( Fig. 13 ) is to cut the fractured implant at the base of the zygoma bone because attempts to trephine the implant would probably result in removal of the lower lateral portion of the zygoma bone in total.