What is it?

Maxillary sinus augmentation (or sinus lift) is a very effective surgical procedure used to increase bone in the posterior maxilla and therefore allow placement of dental implants. The complications most frequently encountered during this type of surgery are: laceration of an intraosseous artery (causing bleeding) and perforation of the Schneiderian membrane (the membrane lining the maxillary sinus cavity).  In case of bleeding, the procedure has to be suspended (sometimes aborted) until the bleeding is controlled. In case of perforation of the Schneiderian membrane, a repair must be attempted, increasing considerably the length of the procedure and consequently the post-operative discomfort and incidence of complications. The conventional technique for maxillary sinus augmentation involves the use of a high-speed hand-piece for the removal of the thin cortical plate that constitutes the lateral wall of the maxillary sinus. In the vast majority of the cases this bony wall is <1mm (Neiva et al 2004). With the conventional technique, perforation of the Schneiderian membrane occurs in ~40% of the sinus lift procedures. I recently co-developed a technique (Geminiani et al 2011) that significantly reduces the incidence of this type of complications (Weitz et al in press).

How does it work?

Incision Design

The incision starts from the mesial area of tooth #2 (1.7) and extends  intrasulcular until the mesial portion of tooth #3 (1.6). In the edentulous area I always move the midcrestal incision 3-4mm towards the palate and I keep my blade inclined in a bucco-palatal direction (blade tip buccal, blade holder palatal). This ~45 degree bevel will be very helpful to gain primary closure during flap replacement. I try to avoid vertical releasing incisions whenever possible, as they tend to increase the discomfort in the post-operative phase. However, vertical releasing are always needed to gain access to the lateral wall of the maxillary sinus.

Mucoperiosteal Flap Reflection

A full-thickness (mucoperiosteal) flap is reflected to gain access to the lateral wall of the maxillary sinus. In this area the bone is normally very thin, usually <1mm. There is mainly one anatomical structure that could be damage during access to the lateral wall of the maxillary sinus: the infraorbital nerve. This nerve is normally located pretty far cranially (apically) and is normally out of the surgical area. However, in case of severe ridge resorption, it could be exposed during flap reflection.

Initial lateral window osteotomy

The size of the lateral window osteotomy plays a major role in the occurrence of perforation of the Schneiderian membrane. In fact:

An undersized osteotomy of the lateral window, frequently leads to perforation of the Schneiderian membrane.

I have noticed that marking the extension of the window helps me in achieving a properly sized osteotomy. I start tracing the inferior border at the level of the maxillary sinus floor, or slightly cranially (~1mm). To do this, I use a reference point (such as the edentulous ridge, or the CEJ of an adjacent tooth) and measurements taken on the pre-operative cone beam CT. Then I proceed tracing the location of the mesial and distal borders. I tend to avoid rotary instruments (such as a high-speed hand-piece) to trace the extensions of the lateral window, unless the pre-operative image show a thick lateral wall (>2mm). Instead, I use an air-driven sonic hand-piece coupled with a dedicated diamond-coated vibrating insert.

Preparation of the lateral window using a vibrating instrument

I think the sonic hand-piece is the ideal device for the preparation of the lateral window sinus lift. The diamond-coated insert does not rotate, but vibrates (at 6 kHz). This allows a precise and safe osteotomy, reducing significantly the incidence of perforations (Weitz et al, in press).

First, I complete the osteotomy of the inferior border. I follow the tracing previously done (as you can see in the image). The Schneiderian membrane has grayish halo, making it easier to distinguish from the adjacent tissues. The cavitation effect of the sonic instrument produce temporary hemostasis, improving the visibility of the surgical field. Once the inferior border is completed, I proceed to the preparation of the mesial, superior and distal border.

The osteotomy for the preparation of the access window has been completed. The residual “island” of bone should move while the patient takes a deep breath, or when a gentle pressure is applied on its surface. I use the periodontal probe to apply very gentle pressure to the “island” of bone and make sure it is free to move medio-laterally. If the residual piece of bone does not move, it is still attached to the lateral bony wall in some point. In this case, I continue the osteotomy with the sonic hand-piece until the island of bone is completely separated.

Separation of the Schneiderian membrane from the wall of the sinus

This is a critical step. Perforations of the membrane occur frequently during this phase of the sinus lift procedure. To increase safety and reduce complications I use the air-driven sonic hand-piece coupled with the discoid insert. The insert is activated (vibrating and irrigated by the water spray) and then placed between the lateral bone wall and the Schneiderian membrane. The “island” of residual bone can be removed if it does not allow the correct placement of the discoid insert. I start from the superior border of the osteotomy (as shown in the illustration), proceeding mesially, towards the mesio-superior line angle and along the mesial of the window. I proceed to the next step only once I have released the membrane at least 2mm along the superior and mesial border of the window osteotomy.

Elevation of the Schneiderian membrane

Once the membrane has been freed using the discoid insert (at least 2 mm), it is much easier to proceed with its elevation and reflection. Most of the time I use conventional hand instruments. Dedicated sonic inserts are available. They are particularly useful when a septum is present, or in case of recent extractions (<90 days). The arrows in the illustration are pointing at the bony wall. It is interesting to observe that the lateral wall of the maxillary sinus tends to get thinner in a caudo-cranial (corono-apical) direction.

It is important to reflect the membrane up to the medial wall of the maxillary sinus (as shown in the illustration).

Grafting of the maxillary sinus and membrane

The sinus is grafted with the material of choice. I prefer to use a combination of xenograft and allograft, however several kind of grafting materials have been proven effective. Once the graft has been placed in the subantral cavity, the lateral window osteotomy is covered with a collagen membrane. The illustration clearly shows the criteria that I consider important in the placement of the absorbable membrane. The barrier should extend at least 3mm past the border of the window, it should have rounded corners and can be fixated with tacks (to avoid dislodgment). A safety margin of 1-2mm should be left between the tacks and the margin of the barrier, in order to prevent tears.

Flap replacement and suturing technique

Primary closure is fundamental for the success of this procedure. If primary closure can not be achieved by flap replacement, a periosteal releasing incision is indicated. More details on how to perform a safe and effective periosteal releasing incision can be found in an excellent article recently published (Romanos 2010).

The first suture I place (4-0) is a crossed horizontal mattress. I enter the distal portion of the flap from the buccal and run the suture to the palatal flap. Here, the suture engages the flap twice first from the periosteum towards the epithelial surface (on the mesial aspect), then from the epithelium to the periosteum (on the distal aspect). Then the needle enters the mesial portion of the buccal flap from the periosteum exiting in the buccal vestibule. The suture is closed, the knot should lay on the surface of the buccal flap. I use single interrupted sutures (5-0) for the vertical releasing incision and the beveled mid-crestal incision (4-0 and/or 5-0).

Management of Complications

Perforation of the Schneiderian membrane

Perforations most frequently occur along the mesial or the mesio-superior borders, such as in the case here presented. Once the membrane is perforated, reflecting it using hand or sonic instruments would only make the perforation larger. First, you have to expose some sound membrane, removing more bone in the area surrounding the perforation (at least 2mm in every direction).

At this point it is possible to reflect the membrane with the instrument of your choice (hand or sonic). Once the membrane is reflected, it tends to fold on itself, thus sealing the perforation. If a small perforation remains (<1mm) no further treatment is needed, as long as the grafting material placed used is composed by large particles. In case of large perforations (>1mm) or if the grafting material is a combination of large and small particles a collagen membrane can be used to seal the perforation. A flexible membrane (i.e. Bio-Gide) will stick to the membrane, with no further need for stabilization. A thicker membrane (i.e. Biomend Extend) might have to be kept in place with tacks.

Intraosseous artery

Intraosseous arteries intersect the area designed for the preparation of the access window in 15-20% of the sinuses. When this is the case, there are mainly three options: modify the form of the lateral window osteotomy to avoid severing the artery, mobilize and translocate the artery, or abort the procedure  and consider other treatment options.

Before developing the aforementioned technique, I would have never attempted transposing the artery. The surgical high-speed hand-piece did not allow me to perform this procedure safely. With the sonic hand-piece, instead, I can remove bone surrounding the artery, without damaging the blood vessel. Once enough bone has been removed, the release and reflection of the membrane is easier.

Sinus septum

Septae are found in 30% of the maxillary sinuses. Depending of the size of the septum the options are: proceeding with a conventional lateral window osteotomy, modify the shape of the window osteotomy to avoid the septum, or abort the procedure and consider other treatment options. In my experience I’m almost always able to complete the procedure, most of the time without modifications (50% of the cases), or creating to separate windows (45% of the cases). Only in rare cases (~5%) I seek other treatment options.
Illustration courtesy of Dr Dimitrios Papadimitriou. 

More info about the author: Alessandro Geminiani, DDS, MSc, MS is a specialist in periodontics and dental implants. His practice focuses on sinus lift (sinus augmentation) and is located in Rochester, NY.