Minimally Invasive Transcrestal Sinus Floor Elevation Procedure in Severely Atrophic Ridge: A Case Report Open Access

Implant surgeons have endeavored to overcome challenges in the maxillary posterior region using various techniques. Placement of conventional dental implants in the maxillary posterior regions can be compromised due to both severe ridge resorption and sinus pneumatization. Moreover, density in this region is often less than ideal, adding a condition of low-quality bone to an already compromised situation of low-quantity bone.^1–3  To overcome these challenges, different procedures have been suggested, including the hydrostatic method.

Techniques of maxillary sinus floor elevation have been developed to increase the vertical dimension of the bone for simultaneous or subsequent placement of an implant. To increase the apicocoronal height of the subantral region, graft material is introduced between the membrane and the residual alveolar process before or along with implant placement. This was first described by Tatum⁴  and Boyne and James,⁵  and it is frequently referred to as a lateral window sinus lift.⁶  This procedure can be associated with substantial postoperative swelling and discomfort. In 1994, Summers presented a less invasive technique for lifting the maxillary sinus floor with rodlike osteotomes that are used to lift just that portion of the sinus membrane through the osteotomy immediately apical to the implant site. Referred to as the Summers technique, this procedure involves the application of an osteotome to the coronal aspect of the deficient edentulous ridge and is recommended in cases in which the height of the remaining subantral bone is at least 5–6 mm.⁷  This method avoids the need for an opening of the sinus through its lateral wall and is thus considerably less invasive, although it has its limitations and introduces an increased risk of sinus membrane perforation during the course of the procedure.^7–13 

In the pursuit of less invasive sinus elevation, a number of techniques have been developed, with the goal of providing more predictable and more delicate approaches. The hydraulic method was first introduced by Chen and Cha in 2005.¹⁴  Their method incorporated the use of the air and water spray of the traditional high-speed handpiece with a diamond-tipped bur in the subantral bone. Later, a dedicated syringe system was designed as an alternative to the handpiece to be used in a more controlled fashion. One such device is the crestal approach sinus (CAS) kit, which includes a hydraulic elevation device (Osstem Implant Co, Ltd).

Carefully injecting saline through the osteotomy to hydraulically elevate the membrane, also referred to as hydrostatic sinus elevation or hydrodissection, can provide numerous benefits. Although the use of bone graft material to lift the membrane can introduce sharp edges and points against the delicate membrane, the application of fluid avoids this potential danger. While it is often said that introduction of bone graft material into the sinus produces evenly distributed pressure and symmetrical lifting of the membrane, the anatomy of the region complicates this ideal picture. The Schneiderian membrane is moderately elastic and of variable thickness, causing it to react with an uneven response to pressure. Furthermore, the irregular concavities, convexities, and sometimes even sharp peaks (septa) of the bony architecture of the sinus contribute to an inconsistent response to pressure from uneven sources. When employing a hydraulic lift system, greater than 10 mm of elevation can be expected.^15–18  Hydrodissection permits forces to be more evenly dispersed on the membrane, and this may result in a more delicate elevation that can overcome such obstacles as varying membrane thickness and irregular bony architecture.^17,18 

The literature documents how these various techniques have been repeatedly and successfully employed even when the apicocoronal dimension of the residual bone is less than 6 mm and even when the amount of sinus elevation desired approaches or exceeds that expected with a lateral window approach. In the experience of these authors, the CAS kit can be used for poor osseous conditions. With judicious use, success can be maximized while minimizing surgical trauma and the number and duration of procedures.

A 39-year-old man presented for treatment of an edentulous site at the maxillary right first molar (No. 3). The patient lost the tooth 8 years prior because of complications related to endodontic therapy. Following a clinical and radiographic examination, and after finding an unremarkable medical history, the patient expressed a reluctance to accept any treatment that would be considered invasive, such as lateral window sinus augmentation. Cone-beam computerized tomography (CBCT) evaluation revealed no sinus pathology and 1.7 mm of subantral bone height at the No. 3 site. The following treatment plan was proposed: transcrestal sinus lift with simultaneous implant placement (if conditions permitted) to provide a minimally invasive treatment plan with a reduction in surgical visits (Figures 1 and 2). Despite the minimal height of bone present, simultaneous implant placement was presented as the recommended treatment based on the previous experience of the surgeon and was accepted by the patient. The patient was informed of all reasonable risks and provided informed consent.

Using the DDS-Pro digital planning software (Digital Dental Service Ltd), a 4.5- × 11-mm implant (SPI, Thommen Medical) was treatment planned. To ensure sufficient primary stability in the amount of native bone, underpreparation of the osteotomy was planned.

After achieving local anesthesia with two 1.8-mL cartridges of 4% articaine with epinephrine 1:100 000 (Septanest), a crestal incision 2 mm palatally from the midcrestal and sulcular incisions around the distal aspect of tooth No. 4 (upper right second premolar) and mesial aspect of tooth No. 2 (upper right second molar) were made with a No. 15c scalpel blade. A full-thickness flap was elevated toward the facial, exposing the crestal bone (Figure 3). A CAS drill 2.8 mm in diameter with the stopper (included in the kit) set at 2 mm (Figure 4) was used to prepare an osteotomy at the appropriate position within the edentulous site, reaching the Schneiderian membrane with the safety drill tip (Figure 5). A hydraulic elevation device (Figure 6) was then used to introduce 2 mL of sterile 0.9% NaCl solution directly against the Schneiderian membrane, elevating it to create space for the bone graft material and fixture. As per the manufacturer's instructions, the rubber valve was placed slightly into the osteotomy (Figure 7), and with finger pressure, a seal was formed and the syringe piston was pressed to gently inject NaCl solution under the sinus membrane to softly elevate it from the sinus floor and walls. A gradually increasing volume of fluid was introduced with multiple cycles of plunging and aspiration to best prevent damage to the membrane (Figure 8). During aspiration, the operator observed blood mixed with saline solution; a lack of air bubbles indicates that the Schneiderian membrane has not been torn. One gram of particulate bovine xenograft bone (Bonefill Porous, Bionnovation Biomedical) was mixed with sterile NaCl solution and introduced through the osteotomy, followed by an SPI Element 4.5- × 11-mm fixture with a 0.5-mm polished collar (Thommen Medical) to be placed supracrestal, as per the manufacturer's specifications. A primary stability of 30 Ncm (Figure 9) was achieved with insertion at 30 rpm. A healing abutment was connected to the fixture with a hand driver, and 6-0 nylon sutures (Atramat, Mexico) were used to stabilize the soft tissue around the healing abutment. Postoperative CBCT revealed an intact elevation of the sinus membrane of approximately 14-mm high (Figure 10). After 7 days, the patient presented with asymptomatic satisfactory healing, and sutures were removed (Figure 11). The restorative portion of treatment (Figure 12) was commenced after 6 months of healing, and a single-piece screw-retained crown was fabricated and placed (Figure 13). After 24 months from implant placement and sinus lift, and 18 months from implant restoration, clinical and radiographic examination (Figure 14) revealed a satisfactory volume of bone surrounding the fixture and healthy soft tissue around the crown, along with an assessment of proper function of the restoration.

Coincidentally, a CBCT scan was taken 30 months after surgery (24 months after restoration) for reasons unrelated to this site. This image confirmed the presence of adequate bone around the fixture (Figures 15 and 16).

Elevation of the maxillary sinus floor is a commonly performed preprosthetic procedure in implant dentistry.¹³  Various methods of obtaining access to the sinus have been described, such as open (often referred to as the lateral window approach) and closed method (often referred to as the transcrestal approach).¹⁹  The former method is universally recognized as being more invasive than the latter.

When employing a lateral window approach, the membrane is generally lifted directly via instrumentation, whereas when performing a transcrestal approach, it is generally the case that the membrane is lifted indirectly by the introduction of bone graft material. Various materials can be introduced through the osteotomy and used to elevate the membrane, including bone from autogenous, allogeneic, and xenogeneic sources or alloplastic materials.^20–30  It is also possible to insert fixtures without the introduction of graft material.^24,31,32 

The gentle nature of the presented technique as compared with alternative methods constitutes an advantage for safety. As with any surgical technique, it requires proper technique by the operator. It is most prudent to administer the fluid slowly and gradually, applying only 0.2 mL of fluid at first and then cycling through delicate pushing and aspiration of greater amounts of fluid. Excessive addition or removal of fluid, either in speed or volume, can more readily lead to perforation of the membrane. In such a circumstance, implant placement may be abandoned or a shorter fixture may be used if sufficient native bone exists. Alternatively, a lateral window approach may be performed, to include a more elaborate elevation of the membrane along with its repair, which may include simple placement of a large enough adsorbable membrane or more advanced procedures, such as sutures or surgical glue.

According to the literature, the transcrestal approach has limited capability to increase bone volume. A recent systematic review supports the assertion that transcrestal elevation simultaneous to implant placement contributes to greater implant failure in the presence of less than 4 mm of subantral bone height,³³  but it should be recognized that the focus was entirely on implant survival and not on the success of the sinus elevation procedure as a standalone. In the authors' experience, it is possible to successfully and reproducibly elevate sinus membranes via a transcrestal approach, such as in this case. In a study performing sinus elevation using hydraulic fluid elevation in sheep, the technique was said to only be able to provide a capacity to lift the membrane by only 5 mm.³⁴  Because other publications demonstrate much greater lift potential for hydraulic lift techniques, the authors were contacted to provide clarity. In personal communication with these authors, they suggested that their limitation was likely due to lack of a proper seal of the rubber tip. If the minimal height of the initial subantral bone is a concern because of the available stability for simultaneous implant placement, transcrestal sinus elevation may be performed in preparation for a second surgery after osseous healing, during which the implant can be placed. Although this method may not limit the number of surgeries or the overall duration of treatment, the more minimal invasiveness of the transcrestal approach may still be appreciated by both clinician and patient.

Regretfully, there is limited documentation of such success, and further study ought to be forthcoming. A review by Kim et al³⁵  revealed high or very high satisfaction with the CAS kit system based on surveys of 28 dentists who placed a combined 924 implants, with elevation of the sinus floor. A recent investigation in a sheep model comparing different techniques for the transcrestal approach favored the CAS kit followed by fluid introduction to hydrostatically lift the membrane over the more traditional osteotome technique, although it took more time to perform. However, to achieve a significantly decreased potential for introducing perforations, an average 5-minute increase in surgical time (8.5 vs 3.1 minutes) might be justifiable.³⁴ 

The presented technique may constitute a reliable method for sinus lift procedures. The additional possible intraoperative complication that can occur while employing this method is that of the introduction of fluid into the sinus secondary to a tear in the membrane. This occurs less frequently than the introduction of bone graft material into the sinus when perforation occurs during the transcrestal sinus elevation approach. This can be alleviated by raising the patient into a seated position and suctioning excessive leaked fluid from the sinus through the osteotomy, although this may contribute to further tearing of the membrane and should be considered judiciously by a clinician of advanced skill.

The advantages of the presented technique include decreased invasiveness, which can result in reduced postoperative pain and swelling, as well as obviating the use of traditional osteostomes and mallets, which have, on occasion, been reported to introduce complications to the visual, auditory, and balance systems.^36,37  This technique can be employed for single or multiple adjacent sites and so can be employed even when more extensive reconstruction is planned.

The experience of those authors involved in the surgical case presentation validates the high efficiency of the CAS kit system in difficult conditions due to minimal subantral bone height. In conditions with less than 2 mm of bone, the osteotomy should be further undersized than usual to achieve substantial primary stability. To prevent premature failure of the implant and loss of the implant into the sinus cavity, wider healing abutments can be placed, with explicit instructions to the patient to avoid all forces due to chewing and biting for the duration of healing.

Thus far, case documentation of a crestal approach for sinus elevation with less than 3 mm of subantral bone is rare in the literature. This case demonstrates that with the use of judicious planning, suitable instrumentation, and advanced experience and skill, sinus floor elevation can be achieved with minimal invasiveness despite minimal native bone height. However, it must be recognized that this is merely a single case published retroactively after seeing success. More powerful data must be forthcoming, including study of larger patient populations, to substantiate the generalizability of this conclusion to the general population.

The authors would like to recognize Dr Kara Kramer (Atlanta, Ga) for her efforts in reviewing the manuscript and making pertinent corrections and suggestions.

Dr Łukasz Zadrożny is a course director for Osstem AIC, which is administered by Osstem Implant Co, Ltd, the manufacturer of the kit used in this case. This relationship began after the final draft of this article was written and had no impact on any aspects of this surgery or case report.