Luis Vega1 and Patrick J. Louis2
1Department of Oral and Maxillofacial Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA
2Department of Surgery, University of Alabama, Birmingham, Alabama, USA
A zygomatic implant is a long implant (30–62.5 mm) that obtains its main anchorage from the zygoma bone in the presence or absence of maxillary alveolar bone. Zygomatic implants were designed by Per-Ingvar Brånemark to allow for implant-supported prosthesis placement where maxillary bony support for prosthetic rehabilitation is inadequate.
- Severe atrophy of the posterior maxilla with sufficient bone support for dental implants within the anterior maxilla
- Generalized severely atrophic maxilla
- Acquired maxillary bony defects (benign or malignant pathological ablation, infectious debridement, and avulsive trauma)
- Congenital maxillary bony defects (cleft lip and palate)
- Previous failed dental implant and/or bony reconstructions
- Medically compromised patient
- Acute sinusitis
- Adequate maxillary alveolar bone for conventional dental implants
- Severe trismus (relative contraindication)
- Previous history of head and neck radiation treatment (relative contraindication)
The zygoma bone has a mean anterior-posterior length that ranges from 14.1 to 25.4 mm and a mean mediolateral thickness that ranges from 7.6 to 9.5 mm. When the zygoma bone is measured along the potential implant axis, the bone-to-implant contact ranges from 14 to 16.5 mm, and approximately 36% of the implant is in contact with the zygoma bone. Although poor trabecular bone density has been described, the zygoma bone has a strong cortex, which provides the primary stability of the zygomatic implant. The placement of zygomatic implants was originally described using an intrasinus approach. The main disadvantage of this approach is the palatal emergence of the implant platforms. The palatal emergence occurs because during the process of maxillary resorption, the residual maxillary basal bone is in a more posterior position than the alveolar bone, whereas the position of the zygoma bone remains unchanged. The palatal emergence of the zygomatic implant requires the fabrication of a bulkier prosthesis that is difficult to restore and requires greater buccal cantilevers. Several modifications have been described within the literature that allow for more favorable implant placement, and these are described in this chapter.
Numerous companies have designed and market zygomatic implants worldwide. The implant most commonly used in the United States is available in eight different lengths (30, 35, 40, 42.5, 45, 47.5, 50, and 52.5). All implants have a diameter of 5 mm in the coronal third and 4 mm in the apical two-thirds. The difference of diameters within the coronal and apical portions compensates for the potential widening of the maxillary implant bed that occurs during the determination of the proper trajectory of the drill to engage the zygoma bone. Finally, a 45° platform allows the inclined insertion of the zygomatic implant and its restoration.
- This procedure is typically performed with either general anesthesia or intravenous deep sedation. Local anesthesia is given intraorally within the maxillary vestibule and the posterior hard palate to block the superior alveolar, infraorbital, and greater palatine nerves and to control bleeding during dissection. When the procedure is performed under deep sedation, additional extraoral anesthesia is infiltrated around the zygoma prominence.
- A crestal incision is initiated from tuberosity to tuberosity bisecting the keratinized gingiva. Vertical releases are placed posteriorly along the maxillary buttress and anteriorly within the midline region.
Mucoperiosteal flap elevation is used to expose the alveolar crest, the lateral maxilla, the maxillary antral wall, the infraorbital nerve, the zygomaticomaxillary complex, and the lateral surface of the zygomatic bone cephalically to the incisura (the point between the lateral and medial surfaces of the frontal process of the zygomatic bone and the zygomatic arch; see Figures 8.2 and 8.9 in the Case Reports). Exposure of the infraorbital nerve is important as it serves as the anterior limit for implant placement in cases in which two ipsilateral zygomatic implants are placed. Exposure of the infraorbital rim is not necessary. The palatal mucosa is elevated due to the palatal emergence of the zygomatic implants.
- A zygoma retractor is placed at the incisura. The zygoma retractor is used to retract the soft tissues and to assist with implant angulation during implant placement. Care must be taken to properly insert the zygoma retractor at the incisura as it can be easily malpositioned along the infraorbital rim.
- A sinus window is created within the supero-lateral portion of the maxillary sinus. The window should allow for the elevation of the sinus mucosa, providing direct vision to the roof of the sinus and the base of the zygoma bone. No special effort is made to keep the sinus membrane intact. A larger, trapezoid-shaped window is used when two ipsilateral zygomatic implants are indicated (Figure 8.2, Case Report 8.1).
Determination of the implant trajectory is performed with the aid of a properly placed zygoma retractor and direct visualization of the base of the zygoma bone and sinus roof. For better orientation of the implant trajectory, the measuring device or the drill bit can be placed over the lateral maxillary wall prior to initiating the drilling protocol. The zygomatic implant platforms generally emerge within the areas of the second bicuspid or first molar (Figure 8.12, Case Report 8.2) and within the canine region if a second ipsilateral zygomatic implant is placed (Figure 8.4, Case Report 8.1). The implant osteotomies are planned as far posteriorly as possible and with the crestal emergence located as close to the alveolar crest as possible.
- A 105° zygomatic implant hand piece with a round bur is used to enter the residual maxillary bone, penetrating through the atrophic maxillary alveolus and maxillary sinus and marking the area of the sinus r/>