Fabrication of a Surgical Guide for Lateral Sinus Augmentation

Implant placement in the posterior maxilla may require sinus augmentation when inadequate available height of bone is present. Sinus augmentation can be accomplished using either a lateral window approach or a crestal approach. The lateral window approach has been utilized for decades, being first introduced by Dr. Hilt Tatum in the 1970s. This is the desired approach when minimal crestal bone height is present to allow simultaneous implant placement or placement of multiple adjacent implants and a crestal approach will not allow adequate elevation of the sinus to be achieved. The crestal approach is used when sufficient height of crestal bone allows immediate implant placement and less height increase needs to be achieved. 

The lateral sinus approach has surgical challenges. During surgery the practitioner is unable to clearly determine where the sinus floor is in relation to the osseous crest. Measurements can be made on a panoramic radiograph to attain an estimate, but because of distortion in the radiograph such an estimate cannot be determined with complete accuracy. Cone-beam computed tomography (CBCT) allows accurate measurements and an understanding of the anatomy in three dimensions (3D),¹ but the practitioner is still required to visually transfer the information on the CBCT scan to the patient during surgery. 

CBCT scans are becoming frequently used to assist in planning implant treatment, both for determination of volume of bone available and identification of anatomical structures that will influence implant placement.² This improves planning, especially when inadequate bone is present in the posterior maxilla due to proximity of the inferior aspect of the maxillary sinus to the crestal bone. If implants are to be placed into this area, sinus augmentation is often required to provide sufficient bone volume to support dental implants and allow prosthetic loading with predictable long-term results. Use of surgical guides for implant placement as well as sinus augmentation has been reported and aids the practitioner in providing precision treatment.³

This article will discuss a method for fabrication of a surgical guide to transfer the CBCT information intraorally to allow creation of a precisely placed lateral sinus window.

A CBCT scan of the patient is performed (Figure 1) and a stereolithography (STL) bone-level model is ordered. These models are available from several laboratories, including NDX^® nSequence (nsequence.com) or 3D Systems (3dsystems.com). Selection of a two-tone STL model, wherein the teeth are an opaque resin and the bone is a transparent resin, aids in planning such that tooth roots in relation to the maxillary sinus are contrasting materials (Figure 2).

Upon the STL model being returned to the clinician, it is visually examined for the purpose of studying the anatomy of the maxillary sinus; any septa should be noted as well as other anatomical features that will influence where the lateral window will be placed to access the sinus. A fine tip Sharpe marker is used to outline on the buccal of the model the floor of the sinus and its anterior curvature as well as the distal wall. The marker is also used to outline the roots of the teeth present in the area when a partially edentulous arch is being treated (Figure 3). Next, the marker is used to draw the ideal lateral window on the model based on the floor of the sinus, any septa or teeth present. The marker is used to outline where the ideal soft-tissue incision would be placed so that the incisions are not made over the window that will be created. 

In some clinical situations the presence of septa may require creation of two separate lateral windows—one mesial and the other distal to the septa. Orientation of the septa may complicate the surgical procedure, necessitating modification of the surgical technique to avoid the septa and allow elevation of the sinus both mesial and distal to the structure.⁴ Because of the high prevalence of septa, a CBCT scan during planning may be helpful in minimizing complications during sinus augmentation procedures.⁵

A vacuform is then made over the STL model using 2-mm-thick Biocryl resin sheet (Great Lakes Orthodontics, greatlakesortho.com). Though clear plastic can be used for this purpose, use of a colored vacuform material enables better visualization (Figure 4). Following vacuforming on the model, the guide is removed from the model and trimmed to cover the area. In partially edentulous cases, coverage of the teeth in the area aids in stabilization of the guide intraorally during surgical use. When the arch is edentulous or no teeth are present in that half of the arch, it is recommended that the guide cover the entire maxilla with palatal coverage to provide stability when placed. 

A lab handpiece with a lab cutter bur (#HM79HX, Meisinger USA, meisinger.de) is used to create a lateral window on the STL model (Figure 5 and Figure 6). The vacuform guide is placed back on the STL model. The lab cutter bur is pierced through the vacuform guide at the center of the window that was created on the model and used to lateral-cut the window in the guide to match the window that had been created in the model (Figure 7 and Figure 8). The guide is removed from the model and trimmed with surgical scissors to extend 2 mm superior to the window to limit unnecessary tissue elevation during surgery (Figure 9 and Figure 10). If a clear vacuform resin sheet was used to fabricate the guide, the edges of the guide are colored with the Sharpe marker to aid in visualization when placed intraorally. 

An added benefit of this method of guided lateral window sinus augmentation is that the thickness of the lateral aspect where the window will be created can be measured to determine the depth needed to transverse the bone. A Castroviejo caliper (Salvin Dental Specialties, salvin.com) is used around the window to measure the bone thickness on the model (Figure 11). This will aid in decreasing sinus membrane tearing during surgery, as the practitioner will know the exact depth needed to free the lateral window, removing guesswork from the procedure. 

The guide is then disinfected by soaking in sodium hypochlorite for 1 minute followed by thorough rinsing in distilled water; this is done three times. The guide cannot be autoclaved because the heat will warp the guide, making it unusable. 

Local anesthetic is administered to the surgical area. A crestal incision is made with a #15 scalpel blade as planned based on the window on the STL model, with the incision positioned at least 5 mm from the inferior border of the planned lateral window. If the lateral window will be positioned close to the crest due to minimal osseous crest height, the incision is placed on the palatal aspect of the crest to ensure that the suture line does not fall over the window and is supported by solid bone. Vertical releasing incisions are created mesial and distal (at least 5 mm) to the lateral aspects of the window that will be created, and a full-thickness flap is elevated. 

The lateral window surgical guide is inserted intraorally (Figure 12). The window is scored at the window cut in the surgical guide with a #8 round carbide or diamond in a surgical handpiece creating an outline on the buccal bone where the window has been planned (Figure 13). The surgical guide is removed intraorally, and completion of the window can then be accomplished using carbides or diamonds in the surgical handpiece (Figure 14). As an alternative, a piezo surgical unit can be used to complete the osseous window instead of rotary instruments (Figure 15). 

Regardless of the method used, the outline that was created with the surgical guide is deepened until the osseous window is mobilized without tearing the underlying membrane. Integrity of the membrane can be tested once the osseous window has been fully cut, by having the patient inhale while the practitioner pinches the nose. An intact membrane will show movement of the osseous window moving with each breath, whereas a membrane that has torn will not move with inhalation. 

The practitioner has an option to position the osseous window superiorly by elevating it as the membrane is elevated, to become the new roof for the augmented sinus. Alternatively, the osseous window can be removed from the membrane and replaced to its original position buccally after graft placement. The sinus membrane is elevated (Figure 16), cross-linked collagen is placed superior to the graft, appropriate osseous graft material is placed, and collagen covered with platelet-rich fibrin (PRF) seals the lateral window (Figure 17), followed by tension-free repositioning of the flap and placement of sutures (Figure 18).

Use of a surgical guide when performing a lateral sinus augmentation allows accurate placement of a lateral window based on the patient’s anatomy, transferring the information from the CBCT directly to the oral cavity. This eliminates guesswork normally found when visually transferring the CBCT information and freehand positioning the lateral window. Establishment of osseous architecture reference points for the actual surgery is achieved with the guide. Frequently, once the flap is created and elevated the practitioner loses references between visually looking at the CBCT scan and the mouth with regard to the osseous architecture to reference. 

The surgical guide helps planning such that the surgery stays oriented with the anatomy based on the 3D planning. A potential complication when a guide is not used is misjudging the floor of the sinus and creating the lateral window too inferiorly. When this occurs, elevation of the window becomes difficult or impossible necessitating modification of the window more superiorly; this increases the possibility of membrane tearing and makes elevation more complex. Additionally, if the window is created with the inferior aspect too superior in relation to the sinus floor, elevation becomes a challenge and the practitioner may not be able to adequately complete the elevation on the floor or medial wall because access is more limited. Ideally, the window should have its inferior border 3 mm superior to the sinus floor and have a window height of at least 10 mm. Mesially and distally, the window should extend 15 mm for a single implant placement. When multiple adjacent implants are to be placed in the area requiring a sinus augmentation, the window should extend 5 mm mesial to the most anterior implant and 5 mm distal to the most posterior implant as long as adjacent teeth allow the window to be extended. 

The STL model increases the likelihood of a successful graft both in volume and position as window placement is ideally determined before surgery and not during surgery. When the osseous window is not ideally placed, potentially the resulting augmentation may not be adequate to support the planned implants following maturation of the osseous graft. Additionally, a determination of the volume of graft needed based on how much augmentation is required can be accomplished prior to the surgical visit. Before creation of the lateral window in the STL model, water can be poured into the sinus from the superior aspect of the model to the level that will encompass the implants planned. This volume of water can then be poured into a graduated cylinder and the cc of the water would indicate how many cc of osseous graft will be needed. This helps eliminate either having too little graft or wasting graft material at the time of surgery, as typically some guesswork is involved in determining how much graft volume will be sufficient during traditional planning.

Surgical complications, such as accidental contact with adjacent teeth during window creation, can be avoided. Septa can be identified radiographically and windows can be planed to avoid these osseous structures, resulting in less postoperative discomfort due to a more conservative surgery. The surgical guide approach facilitates ideal soft-tissue incisions based on the CBCT-guided window placement. Surgical time is reduced because the practitioner knows how thick the buccal wall is. Thus, inadvertent tearing of the sinus membrane is decreased. If a piezo unit is to be used and the buccal wall is thick, initial cutting can be performed with a rotary instrument (carbide or diamond) in a surgical handpiece and then completed with the piezo, decreasing the amount of surgical time during treatment. 

CBCT-created surgical guides for lateral sinus augmentation simplify the process of sinus augmentation and decrease the potential for complications during window development. An added benefit of the use of an STL model is that this allows practitioners to practice the surgery on that particular patient and become familiar with the anatomy they will encounter surgically. This builds the skills of the practitioner based on that particular patient’s anatomy, decreasing surgical time required to perform the lateral sinus augmentation procedure. 

Robert Stanley, DDS, PhD, MS
Co-Founder and Senior Instructor
Stanley Institute for Comprehensive Dentistry
Cary, North Carolina
Private Practice
Cary, North Carolina
Diplomate
International Congress of Oral Implantologists

Gregori Kurtzman, DDS
Private Practice
Silver Spring, Maryland
Master
Academy of General Dentistry
Diplomate
International Congress of Oral Implantologists