Evaluation of Accuracy of Three-Dimensionally Guided Zygomatic Implant Installation

Purpose: The aim of this study was to evaluate the accuracy of using a static surgical guide protocol for zygomatic implant placement in patients with compromised zygomaticomaxillary bone.

Materials and methods: All the patients had a pre-operative initial consultation interview with the surgeons mainly for collecting demographic data, taking general medical, surgical, and dental history, and listening to the patient's esthetic complaints and postoperative expectations.

• A pre-operative multiplanar CT scan of the face to evaluate residual maxillary bone, zygomatic bone, and sinus condition to detect any sinus pathology. This gives initial data about the orientation of the zygomatic implant (ZI), positioning, angulation, and length using 3D planning software.
• The resulting DICOM files were segmented, forming STL (Standard Triangulation Language) files that were used as a baseline for post-operative superimposition.
• Under general anesthesia, patients underwent either contralateral nasal intubation to the working side or oral intubation.
• A palatal paracrestal incision was carried out in the maxillary soft tissues with vertical posterior releasing incisions.
• The muco-periosteal flap was elevated to expose the alveolar crest, the piriform aperture, the lateral wall of the maxillary sinus if present, the infraorbital nerve emergence, the maxillary tuberosity, and the central and the posterior part of the zygomatic bone.
• The surgical guide was fitted in its position and fixed with cortical screws. Implant osteotomy was performed. Then zygomatic implants were inserted.
• The wound was irrigated with normal saline and debridement of the surgical field before suturing using Vicryl 3/0.

Post-operative assessment:

All patients were regularly followed up on the 7th & 14th days postoperatively to assess the following parameters:

• The oral health-related quality of life in edentulous adults was assessed using the OHIP-14 questionnaire.

Radiographic assessment:

• A post-operative CT scan of each patient with implants was taken after the surgery, with follow-up CT after 6 months and one year
• The DICOM images of the post-operative CT were uploaded in dedicated software.
• Segmentation based on tissue density was carried out to separate implants from the surrounding bone.
• The STL files of the maxillary bone with the planned implant positions obtained from the initial CT scan were uploaded into the software.

Superimposition

• The postoperative CT scan was imported into Mimics software, where the DICOM file was segmented. It was then brought into 3-matic, and the Postoperative segmentation was aligned with the planned skull using a point registration algorithm. Final refinement of the registration was completed through global registration.
• The amount of deviation was calculated by determining the same point at the center of the implant platform in both the post-operative segmentation and the plan. Then the amount of deviation was calculated by measuring the distance in millimeters between points and the vector of displacement. (coronal, apical, and angular deviations).

Radiographical evaluation:

Implant Placement Accuracy

• The implant lengths By superimposition of the postoperative implant length onto the virtually planned implant length
• The 3D implant angle deviation By measuring the deviation between the postoperative coronal entry point of the implant and the virtually planned coronal entry point
• The accuracy of the abutment position in the occlusal plane. By superimposition of the postoperative position of the multiunit abutments, onto the virtually planned abutment positions

Inclusion criteria

• 1. Lack of maxillary posterior bone in which standard implants are impossible to insert.

• Post-surgical maxillary defects with limitations of maxillary bone reconstruction due to lack of soft tissue coverage.

• Failure of previous reconstructive procedures.

Exclusion criteria

• Opportunity of alternative treatment modalities with bone grafting and standard implants.
• Any relevant systemic or local diseases that might affect the bone healing, like uncontrolled diabetic patients or cancer patients who are still on chemotherapy or previously received radiation on the head and neck region.