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?
Mucoperiosteal Flap Reflection
Initial lateral window osteotomy
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.
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
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.