Key points
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Posterior maxillary implant placement is challenging due to anatomic limitations such as atrophy and sinus pneumatization, often requiring sinus lift procedures.
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Maxillary sinus floor elevation is a long-established technique, available via lateral window or transcrestal approaches, but complications—especially Schneiderian membrane perforation—remain common.
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Grafting materials vary widely, including autografts, allografts, xenografts, and synthetics, but there is still no consensus on the optimal grafting material or technique.
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Graftless subantral augmentation has growing scientific support, demonstrating approximately 6 mm average vertical bone gain by relying on natural bone healing principles without particulate grafts.
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Success of graftless techniques depends on sinus anatomy, particularly sinus pneumatization patterns, which influence blood clot stability, angiogenesis, and eventual bone formation.
Introduction
Maxillary sinus floor elevation is a well-established technique for increasing bone height in the posterior maxilla to facilitate dental implant placement. ,, Maxillary sinus elevation became part of our preprosthetic surgical armamentarium after being first presented by Tatum in 1977 and first published by Boyne and James in 1980. We presently have 32 years of clinical research and surgical experience with many innovations in techniques and technology and, yet, there is still no consensus with regard to grafting materials or as to which surgical technique leads to the best clinical outcome.
The procedure involves elevating the sinus membrane and inserting bone graft material to augment the deficient alveolar ridge. It can be performed using either the lateral window approach or the less invasive transcrestal technique. It is not necessary or necessary to discuss every bone graft replacement material available to reach a consensus on trends. However, like any surgical intervention, it carries potential complications—most notably, perforation of the Schneiderian membrane. This complication can compromise outcomes, leading to issues such as sinusitis or graft failure. Several methods are available to manage membrane perforations, including the use of fibrin glue, resorbable membranes, and suturing techniques. A variety of bone graft materials are employed in sinus augmentation, including autografts, allografts, xenografts, and synthetic alloplasts. Among these, autogenous bone is considered the gold standard due to its combined osteoconductive, osteoinductive, and osteogenic properties.
With maxillary sinus elevation, we have developed a surgical intervention with extremely predictable outcomes, yet we constantly seek change and improved outcomes. The reasons for change are as follows: improve the success rate, simplify the procedure for the doctor to reduce complications, and simplify the surgical procedure for the patient by reducing morbidity and complications. We can accomplish this by considering minimally invasive protocols when applicable. The lateral window technique was first described by Tatum in 1977, published by Boyne in 1980. The sinus perforation rate with standard rotary instrumentation is 20% to 25% which led to use of Piezoelectric surgery. This article will briefly review the traditional approach yet presents a novel approach—the “Sinus- Stabilizer technique”—designed to enable simultaneous implant placement in atrophic maxillae, even in cases complicated by Schneiderian membrane perforation.
Graftless sinus augmentation
The idea and concept of a graftless subantral augmentation is not new, with the furthest scientific publications leading all the way back to 2007 and as of the time writing the following article approximately 200 scientific articles are published and available on the topic. The consensus among authors and practitioners is that the techniques is viable and has proven to increase the bone volume without the need for particulated graft usage, such as xenograft, allograft, autograft, or synthetic substitutes. According to data gathered from systemic reviews and meta-analysis publication, the average bone volume increase in the maxillary sinus with the graftless sinus technique is 6 mm vertically. Keeping in mind that according to publication on implant load distribution only the first 5 mm of the implant bare occlusal loads as well as publications proving the efficiency of short implant utilization in posterior maxillary sites, the bone increase should be sufficient in order to place a 6 mm implant and have it be completely covered with native bone without restorative, functional, and mechanical compromise.
The basis of graftless subantral augmentation lies in the principle of bone defect healing. Bone formation in defects occurs if the following conditions are met:
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The defect is surrounded by 4 walls from each side
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Angiogenesis is possible inside the bone defect
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The blood clot inside the defect is immobile.
While vertical and horizontal bone augmentation is hindered by the need to create an imitation of bone walls in order for angiogenesis to occur, as described in the PASS principles, the subantral space naturally has the bone walls intact after schneiderian membrane elevation, allowing an adequate blood clot stabilization and immobilization, thus enabling angiogenesis and subsequent mineralization, leading to autogenous bone formation.
Notably, graftless subantral augmentation utilizing the blood clot does have limitations and does not provide consistent bone formation depending on the anatomy of the maxillary sinus. An important factor to consider while approaching subantral augmentation is the pneumatization of the maxillary sinus which creates vertical force that is distributed onto the area of augmentation, thus leading to compaction of the graft/blood clot. The success of graftless bone formation and the increase in bone volume heavily depend on the shape and size of the maxillary sinus, especially in proximity to the alveolar ridge. In cases where the maxillary sinus is vertically pneumatized and the lateral and medial cortical plates are close to one another, forming a thin space, the blood clot will be better stabilized and angiogenesis will occur faster, contrary to horizontally pneumatized and wider sinuses, where the cortical planes are farther from one another, thus spreading the force of the pneumatization on a wider diameter, therefore leading to less vertical bone gain. Classically, this has been the main reason for participated graft usage in subantral augmentation, such as xenograft or allograft, which does not resorb as quickly in comparison autogenous graft under the effect of pneumatization; however, the histologic results obtained via such techniques cannot be considered as pure autogenous bone, but rather a conglomerate of unresorbed particulated graft in combination with newly formed auto-bone.
Sinus stabilizer principle
The loss of bone in the distal region of the maxilla can occur due to various reasons, with the most prominent ones being either due to the alveolar crest atrophy, pneumatization, and subsequent expansion of the maxillary sinus or a combination of the latter. While prominent in clinical practice, maxillary bone augmentation historically has been a more predictable manipulation, especially in comparison to the mandible, with many different approaches being proposed and successfully utilized in order to restore or create bone proposition for subsequent implant placement. The clinical data suggest that use of different grafting materials and techniques for both vertical and horizontal growth has a high success rate, especially in procedures involving subantral augmentation (sinus lift), with complications and failures being statistically low.
The most prominent issue when it comes to restoring bone proposition in the posterior maxilla is the inability to perform immediate augmentation and implant placement in clinical situations where the crestal bone proposition is less than 2 mm due to the potential risk of the dental implant being pushed through the osteotomy site into the maxillary sinus or not been submerged enough for an adequate prosthodontic and mucogingival management following integration. To compensate for this issue, several concepts have been proposed previously, some utilizing osteosynthesis plates to hold the implant in position without it falling into the sinus or tissue level implants in order to stabilize the body of the implant in the cortical layer utilizing the polished neck of the implant. While having an adequate success with the implants being integrated and held in place mechanically, both of these approaches failed to place the implant into an optimal position in relation to the future restoration and soft tissue proposition, with the first approach leading the implant to be placed bone-level rather than subcrestally and the second only being able to be achieved with the utilization of tissue-level implants, severely limiting the clinician.
With the current biological understanding that the periodontic has about the optimal implant position it is evident that in single-unit restorations implants that are placed subcrestally with a platform-switching element and conical connection are superior to bone-level implants long-term, thus leading clinicians to often solve posterior maxillary atrophies with a 2 stage approach, with the first surgery being augmentation and the second being implant placement into the obtained bone conglomerate/osteoid. This has several disadvantages, the first and most prominent being time management, where the patient has to undergo treatment up to 15 months until he receives a screw-retained fixture-crown and restores his ability for adequate food consumption. The second being that the obtained bone conglomerate/osteoid is histologically not 100% autogenous bone, leading to potentially higher risks of implant failure in comparison to implant placement into native bone.
To solve this issue, we proposed a new approach, utilizing conventional implants in combination with a sinus-stabilizer abutment. From a technical standpoint, the sinus-stabilizer abutment ( Fig. 1 ) is a screw-retained prosthetic element, with the same platform connection as the implant, preferably with an index, which is placed into the implant prior to insertion into the bone and enables it to temporarily become a tissue-level implant. The placement of this implant–abutment complex is then performed with the driver being mounted not directly into the implant itself, but rather into the sinus-stabilizer abutment, due to the abutment also having an internal connection on the other side of it.
Sinus stabilizer abutment: ( A ) connected into the implant and ( B ) Separate from the dental implant.
The aim of the sinus-stabilizer concept is to stabilize the implant with the help of the sinus-stabilizer abutment in the cortical layer of the alveolar bone while simultaneously positioning the prosthetic platform of the implant subcrestally in relation to the future autogenous bone formation.
Design specifications
As of writing, the sinus-stabilizer abutment is a custom-made product developed specifically for a single system of dental implants that was used to evaluate the viability of the protocol and has gone through several iterations with variable results depending on the macro design. To further promote the concept and protocol, we provide the following, most crucial and necessary design choices that should be taken when manufacturing the sinus-stabilizer abutment on other implant systems for commercial use.
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The exterior of the sinus-stabilizer abutment must be made out of polished titanium. No surface treatment is required. This is to ensure that the sinus-stabilizer abutment is able to achieve mucointegration while being unable to fully osseointegrate with the surrounding bone, as to allow for easy removal after bone formation around the implant.
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The macro design of the sinus-stabilizer abutment must be made to resemble the neck of a tissue-level abutment, with the top of the platform being wider than the base of the internal connection of the implant. The macro design must also be conical to ensure adequate mechanical stability in the cortical layer during placement.
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The height of the sinus-stabilizer abutment should not exceed 3 to 3.5 mm. This is to ensure that the platform of the implant is placed subcrestally but not too deep. 3.5 mm enables the implant to stay placed 2 mm subcrestally after bone formation, with the remaining 1 to 1.5 mm remaining above the cortical layer and inside the soft tissue layer.
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Preferably, the sinus-stabilizer abutment should have an index and be screw retained, like a conventional abutment; however, another internal connection should be present in the top part of the sinus-stabilizer abutment as to enable the placement of an implant driver and the simultaneous insertion of the implant and abutment.
Surgical protocol
The surgical protocol for the sinus-stabilizer concept follows for the most part the same steps as a conventional lateral approach technique, with slight exceptions. A lateral approach is crucial in this technique as it allows for a better and wider membrane elevation, which enables a larger area for the blood clot formation in combination with the tenting effect of the implant and sinus-stabiliser combination. The tenting principle is crucial to this technique and is achieved by the tip of the implant acting as the furthest point to hold the maxillary sinus membrane on a stable level and allow for bone formation from the native blood clot formed underneath the sinusal membrane. The crestal approach is not recommended for this technique and has not been tested with the sinus-stabiliser abutment. The surgical protocol is performed as follows:
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Flap elevation
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Lateral osteotomy is the desired area of the sinus
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Membrane elevation ( Fig. 2 )
Fig. 2 Maxillary sinus membrane elevation utilizing a sinus curette.
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Implant site osteotomy
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Insertion of the sinus-stabilizer abutment into the implant extra-orally
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Placement of the implant into the osteotomy site together with the sinus-stabilizer abutment ( Fig. 3 )
Fig. 3 Implant placement together with the sinus stabilizer abutment into the maxillary sinus.
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Collagen matrix/PRF placement into the subantral site ( Fig. 4 )
Fig. 4 Collagen matrix insertion into the maxillary sinus following implant placement.
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Flap suturing
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Implant uncovering 6 months after the initial surgery with the removal of the sinus-stabilizer abutment.
As with conventional implant placement, it is recommended to underprepare the osteotomy site for the implant as to avoid the implant falling through into the maxillary sinus. Primary stability of the sinus-abutment complex is achieved with the sinus-stabilizer abutment jamming into the cortical layer of the bone with the conical exterior component and on average the obtained torque is 10 to 20N, which is sufficient to prevent micro-movements of the implant. Due to this procedure taking advantage of the blood clot formation rather than the use of conventional grafting materials, it is recommended to stabilize the blood clot with collagen matrix or PRF, however, not mandatory. Collagen membranes may also be recommended in situations where potential sinusal membrane perforations or microperfotations may occur.
The healing and bone formation ( Fig. 5 ), following biological evidence, is estimated to be sufficient in 6 months ( Fig. 6 ) following the initial surgery in order to proceed with the restorative phase ( Fig. 7 ). Clinical photographs of the surgical protocol are demonstrated in Figs. 8–15 , with subsequent healing presented in the span of 12 months via CBCT documentation ( Figs. 16 and 17 ).
