Digitally Guided Lateral Sinus Floor Elevation With Simultaneous Implant Placement: 3 Case Reports With Technical Considerations

The implant placement procedure in the posterior maxillary can be challenging, especially in the atrophic alveolar ridge, because of tooth extraction and maxillary sinus pneumatization.^1,2  Therefore, in some situations, sinus floor elevation via a lateral window (LSFE) is frequently performed with or without simultaneous implant placement. Although LSFE is a predictable and well-documented technique, some complications are reported, including perforation of the Schneiderian membrane and bleeding, often influencing the results of the procedures.^1–3  In addition, several anatomical- and patient-related factors, such as the presence of sinus septa, location of the alveolar antral artery, membrane thickness, buccal wall thickness, and preoperative sinus pathology, must be considered during LSFE treatment planning.¹  Thus, to optimize the success rate during LSFE, cone-beam computed tomography (CBCT) has become a valuable planning tool that assists in evaluating sinus morphology, such as septa, residual bone height, and the presence of maxillary arterial branches.

Therefore, to promote an accurate surgical procedure and improve the surgical workflow with simultaneous implant placement, a 3D printed surgical guide was designed to incorporate the lower contour of the maxillary sinus access window and the ideal 3D position of the implant. Thus, this article aims to present and discuss technical considerations related to using this new maxillary sinus surgical guide to improve surgical outcomes.

This retrospective 3-case report was conducted from January to June 2021. Patients who were qualified for the LSFE with simultaneous implant placement were included in the study. The demographic data of each subject are presented in Table 1. The included patients should fulfill the following inclusion criteria: healthy systemic condition without any serious medical or dental problem affecting the quality of the implant surgery; a healed surgical site with at least 3 months postextraction; available CBCT scan, digital impressions, and clinical photographs; and follow-up appointments to document the treatment outcome. Informed consent was obtained from the patient prior to surgery. All surgical procedures were performed at the Graduate Periodontics Clinic, University of Michigan, School of Dentistry, by a single surgeon (R.S.).

CBCT scans (3D Accuitomo 170; J Morita, Kyoto, Japan) were acquired from all patients, and the images were saved in Digital Imaging and Communications in Medicine (DICOM) format. In addition, a digital impression of the arches and occlusal relations was obtained using an intraoral scanner (Trios 3; 3Shape, Copenhagen, Denmark), and the images were exported as stereolithographic (STL) format files. Following a thorough evaluation and a careful diagnosis, treatment planning was performed based on the clinical and para-clinical findings.

A clinician with experience in digital dentistry designed the all-in-one LSFE and implant placement surgical guide. The technique that was used to delineate the guide is described below (Figures 1 through 7):

1. Import the DICOM and STL files of the maxilla into the implant planning software BlueSky Plan (Blue Sky Bio LLC). Then align and superimpose the maxillary digital model to the CBCT scan.

2. After evaluating sinus anatomy (Figure 1), plan an implant with a tube extending through the lateral sinus wall, using the tube as the reference to define the outline of the lateral window (Figure 2). This step allows the operator to evaluate the sinus anatomy and establish the location of the sinus window on the lateral wall.

3. Create a surface of the maxillary jaw and export it as an STL file—export data together with the tube extension.

4. Into Meshmixer software (Meshmixer; Autodesk Inc. San Francisco, Calif), import the STL file of the maxillary bone, the extension tube, and the patient’s maxilla scan. Next, the maxilla mesh should be transformed into a hollow model (Figure 3a and b) to create contact between the meshes. Next, the model and the bone must be aligned, cut at the same level, and combined (Figure 3c and d). This way, 1 STL file is created with the maxillary bone, teeth, and tube extension (Figure 3e and f).

5. On 3Shape Implant Studio software (3Shape A/G, Copenhagen, Denmark), the surgical guide is designed for implant placement and LSFE. In addition, the planned lateral window antrostomy area is designed around the tube that goes through the buccal bone wall of the sinus (Figure 4).

6. The guide is 3D printed (SprintRay Pro 95; SprintRay. Los Angeles, Calif) utilizing the Surgical Guide 3 resin (SprintRay) (Figure 5), and the post-printing process is performed following the manufacturer’s guidelines.

In all cases, patients presented for implant surgery to replace the missing right maxillary first molar (#3) and LSFE under intravenous sedation. Treatment planning was conducted as described in the surgical technique section for the 3D printed guide fabrication. Following the local anesthesia, the crestal incision was made with a 15C blade extending to a vertical incision on the mesial of #4 and an intra-sulcular on #2, allowing access to the lateral window of the sinus. The window’s dimensions were designed using the 3D printed surgical guide and a Thomson stick to outline the design of the antrostomy (Figures 6through8). The window osteotomy was started with an electric handpiece with a diamond bur and a piezoelectric device until the sinus membrane was reached. Next, the membrane was elevated using sinus curette instruments until achieving complete elevation. Following the drill sequence of the implant, the sinus was grafted. An allograft bone substitute (Puros Cortical Bone Allograft; Zimmer Biomet Dental, Palm Beach Gardens, Fla) was used for all cases. Primary stability of the implant was achieved, the cover screw was installed, and the flaps were re-approximated with sutures.

After 2 weeks, participants presented for a postoperative visit for healing evaluation and suture removal. Subsequent recall visits were at 4 weeks and 8 weeks and after 5 months. All 3 patients underwent LSFE and simultaneous implant placement using the all-in-one surgical guide. None of the patients experienced complications such as unmanageable pain, swelling, nausea, epistaxis, or early implant failure. The postoperative images revealed that all the implants were successfully placed in the planned position. The fixtures were inserted within the lateral sinus window’s side borders, soundly covered by the bone.

The occurrence of complications during and after LSFE surgery, such as sinus membrane perforation and significant bleeding, can be minimized by adopting a new advancement in digital dentistry that improves treatment planning and surgery precision by utilizing surgical templates. This 3-case series technique note demonstrated a novel guided approach for simultaneous LSFE and implant placement using a 3D printed surgical guide. This is in support of Mandelaris and Rosenfeld’s concept,⁴  who proposed using digital guides for LSFE, where they used a prototype cutting guide that was developed through the use of computerized tomographic imaging, computer software, and the stereolithographic process to position the lateral wall window to facilitate LSFEField 4 precisely. Furthermore, Mangano et al⁵  applied a computer-aided design/computer-aided manufacturing (CAD/CAM) technique that calculates the size and shape of a bone graft and trims a bone block into the desired shape. In addition, a customized CAD/CAM osteotomy template was designed and manufactured before surgery and used during the operation.

In this study, we introduced the guided simultaneous LSFE and implant placement surgical guide based on the digital intraoral scans and CBCT images, overcoming the limitations of the previous techniques comprising the higher fabrication cost and higher radiation dose to the patient. Furthermore, regarding the discrepancies between the planned and actual surgical guide outcomes, when a 1-piece surgical guide is designed, the anatomical morphology might compromise the ideal adaptation of the guide to the teeth and bone, which congruently attenuates the favorable result. Likewise, in 2 similar studies, the authors reported the fabrication of 2 separate guides, 1 for the LSFE and the other for implant placement.^5,6  Another study by Goodacre et al⁷  also demonstrated the steps to design a surgical guide for the LSFE. The difference between the guide this group introduced was that it outlines the osteotomy borders, including the superior border. In contrast, the surgical guide designed by our team outlines primarily the lower limits only and secondarily aims to interpret the anatomy and vital structures to maximize success. Furthermore, the limitations of the conventional surgical guides comprise the enormous size, which requires more extensive flap elevation and adequate intraoral space. Due to these limitations, prolonged operation time, increased risk of nerve damage, patient discomfort, and postoperative trauma would be expected. On the contrary, the novel surgical guide introduced in this article reduces the template size. It has easier intraoral handling, facilitating flap elevation, lessening intraoral complications, ameliorating the surgical procedure, and mitigating the patient modality field.^8,9 

The anatomic structure of the maxillary sinus is utterly intricate. For example, the sinus septum is present in approximately 31% of patients. It has various shapes and sizes that increase the difficulty of the membrane elevation and the likelihood of Schneiderian membrane perforation.^10,11  The most commonly reported intraoperative complications of LSFE include sinus membrane perforation and hemorrhagic events.^12,13  Bleeding is often caused by accidental injury of associated arteries, such as the infraorbital artery, the more significant palatine artery, and the posterior superior alveolar artery, which surrounds the sinus cavity.^14,15  Hence, achieving the accurate positioning of the lateral wall for LSFE using a surgical guide designed based on 3D images, such as CBCT, is highly recommended. By following the step-by-step digital design of the guide in this article, the occurrence of the mentioned complications can be significantly minimized. More specifically, in the third step of the presented guide-designing rubric, the anterior antral artery’s location and the sinus walls’ outer limits can be located. Next, the guide can be planned to preserve the vital structures in the desired position, thereby reducing iatrogenic complications. In a randomized clinical study, Osman et al¹⁶  reported a lower incidence of membrane perforations in guided LSFE vs the control group.

A combination of various computer programs aims to optimize the guide design and facilitate access to users. However, potential drawbacks to this proposed technique include the learning curve related to new technologies, including the software and devices applied, and the time required to lay out and fabricate the guide. Moreover, another limitation of our study was the nature of the case-series study. However, the demonstrated clinical scenarios substantiate the utilized techniques; further randomized case-control studies would ideally evaluate and compare the success rate of this method vs freehand augmentation. Finally, it needs to be determined if this approach would translate to multiple implant placements and sites that lack posterior teeth.

Within the limitations of this case-series report, a novel surgical guide allowing predictable digitally guided simultaneous LSFE and implant placement were demonstrated. The relevant digital workflow was described and supported by documentation of 3 clinical cases experiencing successful grafting and implant placement procedures. However, further studies must be performed to determine if this technique would be generalizable, as only 1 operator exists. Additionally, more investigation suggested if this method would translate to multiple implant placements and sites lacking posterior teeth.