Since the Academy of Osseointegration Sinus Consensus Conference held in 1998 the sinus lift has been deemed a highly predictable procedure and effective therapeutic modality.1 For nearly 3000 sinus graft implants with a minimum of three years in function, implant success was 90.0 % over a ten-year period. Set against this knowledge the underlying issue is that, while many studies have evaluated the efficacy of implants in sinus grafts, few have focused specifically on the success of the sinus graft itself. Sinus grafting remains one of the more technically challenging procedures due to, amongst other issues, the delicacy of the Schneiderian membrane and the risk of perforation, post-operative infection and loss of the graft.
Membrane perforation complications
In an article recently published in the Journal of Craniofacial Surgery,2 the risk of complications was described as being “quite low,” and yet one of the more common liability issues in dentistry was the failure of implants in sinus grafts due to the inadvertent partial or complete penetration of implants into the maxillary antrum, along with other sinus lift sequelae. By far the most common complication recorded in the literature is perforation of the Schneiderian membrane, which has been reported to occur in approximately 7 % to 40 % of cases.3-6 However, of greater interest are the underlying complications reported to result from membrane perforation, along with the incidence for such complications.
In a recent study of 200 consecutive sinus lift procedures, 25.7 % experienced a perforation, and of this group, 14.9 % developed further post-operative complications.3
In another study of 359 sinus augmentation procedures, perforation was reported in 41.8 % of cases.5 Of note, 11.3 % of these perforations went on to total graft failure. Conversely, if the membrane remained intact, the graft only failed in 3.4 % of the cases. Of the sinuses developing sinusitis or secondary infection requiring antibiotics, 85 % had a membrane perforation. Accordingly, while membrane perforation may not be seen as a particularly significant complication, it is a potential gateway to more serious sequelae that can result in graft failure. Therefore, membrane perforation should be taken seriously, and clinicians should understand how the risk for perforation might be assessed pre-surgically so that appropriate precautions might be taken. Also, intra-operative risk-minimizing procedures can help limit the size of membrane perforations to <5 mm or, more importantly, avoid complete membrane blow-out.
First and foremost, pre-operative planning must be computed tomography (CT)-based,7 providing not only three-dimensional (3-D) information on sinus morphology but also the presence or absence of additional risk factors. Septae, the thickness of the sinus membrane, the degree of sinus opacity, the thickness of the buccal cortex, residual bone height and the location of the zygomatic buttress all have the potential to increase sinus perforation risk. Using the Lund Mackay Classification sinuses can be scored for health, i.e., maxillary, frontal, ethmoidal and sphenoidal, to give an overall rating to the patient’s diagnosis, as well as a score of 0 or 2 for the ostiomeatal complex, which has a major bearing on sinus ventilation and drainage.8
A 3-D valuation is the only way to arrive at a thorough risk assessment. In addition, 3D imagery can be used to assess the risk for tearing or snagging the branch of the maxillary artery that passes through the canal buccally, which can result in significant bleeding9, impairing visibility and further increasing the risk for membrane perforation.
Limiting the size of perforations
Despite the best planning and preparation, perforations can still occur. A simple but effective method for limiting the size of sinus perforations involves using a so-called isolation protocol when a perforation first presents. Typically, a perforation will occur adjacent to the edge of the bony window, and the most important first task is to begin preparing a secondary window remote to the first so that the perforation is centralized within the expanded secondary window. It is important not to remove bone directly around the perforation, since this will typically result in a growing perforation. Prior to elevating the membrane, the perforation should be partially covered with Geistlich Bio-Gide®. There is some question as to the need for the Schneiderian membrane for de novo bone formation within the extra-sinusoidal space, however it is prudent to avoid complete coverage of the Schneiderian membrane with Geistlich Bio-Gide® so that the endosteal tissue might be in contact with the subsequent Geistlich Bio-Oss® graft and assist with native bone induction.
The membrane should be elevated remotely from and surrounding the perforation, gradually detaching it and ensuring that healthy membrane surrounds the perforation, which, again, is protected by Geistlich Bio‑Gide®.
Thickening of the membrane post-operatively
The elevated Schneiderian membrane will thicken notably post-operatively. In a recent study the mean thickness of the membrane prior to surgery was 0.73 mm and thickened up to 7.0 mm seven days’ post-surgery.10 This increase was significant, and it took many months for the membrane thickness to return to baseline. This thickening was directly correlated with the extent of sinus elevation.
Thickening has a potential two-fold effect: on the positive side, it can aid in the closure of small perforations, but on the negative side, it can force graft material back out the access window, reducing graft volume within the extra-sinusoidal space. It is imperative to cover the access window with a second collagen membrane, and there may be a valid argument for securing the membrane with pins to resist graft extrusion.
Use of antibiotics
A final tip, when patients have a history of sinus infection, is to rehydrate both Geistlich Bio-Gide® and Geistlich Bio-Oss® in a tetracycline solution of 1 g tetracycline in 20 ml of sterile saline. Tetracycline is known to chelate tenaciously to hydroxyapatite, and Geistlich Bio-Oss® can act as a slow release carrier for this broad spectrum antibiotic.11 There is also evidence that tetracycline delays the degradation of Geistlich Bio-Gide®, thereby increasing barrier function duration.12,13