Sinus floor elevation: 2-stage window
Introduction
Depending on several parameters, one must select between a 1-stage or 2-stage sinus floor elevation with a "window approach"; see the decision tree below. In case of a 2-stage approach, the sinus must be grafted with a stronger bone substitute (e.g., DBBM) to resist pneumatization forces during the healing period.
L-PRF membranes alone cannot be used; they will resorb too quickly due to the pneumatization.
An L-PRF bone-block (combining pieces of chopped L-PRF membranes, liquid fibrinogen, and a strong bone substitute) offers, however, several advantages, including faster healing, improved bone quality, and less residual bone substitute.
Protocol: step by step
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make a crestal incision and reflect a mucoperiosteal flap to expose the buccal bone for a clear view,
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prepare a lateral window to the sinus (piezotome/diamond bur),
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carefully elevate the sinus membrane; if possible, push the bony window inside, acting as a new floor of the sinus over the implant apex,
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apply two double-folded L-PRF membranes over the inwardly rotated bony window and the elevated sinus membrane (they can patch any membrane tears),
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apply pieces of an L-PRF bone-block in the open sinus area (after membrane elevation), ensure the space is well packed (especially the palatal and anterior areas),
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apply L-PRF membranes in the window area,
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seal the window area with a double layer of L-PRF membranes,
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suture to obtain primary closure
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implant placement can be planned after 4-6 months.
Video: 2-stage sinus floor elevation (window approach, L-PRF bone-block)
When simultaneous implant placement is feasible, an L-PRF bone-block (a combination of a bone substitute, liquid fibrinogen, and small pieces of one L-PRF membrane) can be utilized. After elevating the Schneiderian membrane, the created space can be filled with parts of the L-PRF bone-block. Subsequently, the sinus window can be filled with an L-PRF membrane. The entrance to the sinus can be sealed with another L-PRF membrane (face portion towards the sinus). Perforations in the alveolar bone (eventually through and through) will enhance, if needed, the blood supply to the graft, optimizing bone formation. The implant can be installed after 4-6 months.
Case
(d = day, w = week, m = month, y = year)
2-stage lateral window sinus floor elevation: L-PRF bone-block
d 0: preparation of the window to the sinus.
d 0: meticulous elevation of the sinus membrane.
d 0: exposed (open) area after sinus membrane elevation.
d 0: the entire created space is filled with an L-PRF bone-block.
d 0: subsequently, the area of the bony window is filled with L-PRF membranes.
d 0: the entrance to the sinus is sealed with a double layer of L-PRF membranes.
d 0: initial situation
m 6: a sagittal CBCT image shows the graft healing and densification.
m 9: intra-oral RX 2 m after implant loading.
Cross-sectional CBCT images per op and after 6 months of graft healing, with a slight resorption and a significant increase in radio-opacity. The white arrow represents 10 mm, and the yellow arrow indicates the healing of the window.
Data:
Clinical trials applying L-PRF bone-block for 2-stage lateral window sinus lift
Abbreviations: study type: RCT = randomized controlled trial; Treatment: T = test group, C = control group, L-PRF cl mix = clot mixed with substitute: a: ratio clot/substitute 1:2, b: ratio 3 clots on 1.5 g substitute, L-PRF m = membrane, m mix = mixed with substitute, c: ratio = 1 membrane on 0.5 g substitute, mp = to protect membrane, ms to seal the window, Cm = collagen membrane; L-PRF = leukocyte- and platelet-rich fibrin, T-PRF = titanium-prepared platelet-rich fibrin, FDBA = freeze-dried bone allograft.
Conclusion
Seven RCTs have investigated the beneficial impact of adding L-PRF membranes, clots, or plugs to a bone substitute for a 2-stage sinus floor elevation via a window approach. In 5 out of these 7 studies, the addition of L-PRF resulted in greater new bone formation with less residual bone substitute, even when the healing time for sites with L-PRF was reduced to 4 months instead of the usual 8 months. Consequently, several authors have suggested that the healing period after sinus grafting before implant insertion can be shortened when a mixture of L-PRF and a bone substitute is used.
Eken and co-workers (2024) compared the use of T-PRF membranes with DBBM in a 2-stage sinus floor elevation. Although implants were not inserted in the "L-PRF only" group to prevent sinus pneumatization (acting as tent pillars), significant bone gain was still achieved, although clearly less than with the DBBM alone. For more details, see Valentini et al. 2025.
Decision tree: 1- or 2-stage sinus floor elevation: window approach
(Miron & Pikos 2018, Valentini et al. 2025)
If the bone quality is sufficient and/or favorable for simultaneous implant placement in a one-stage lateral window sinus lift approach, L-PRF membranes can serve as the "sole" grafting material, providing approximately 5 mm of vertical bone gain (VBG). In case of poor bone quality and/or quantity, jeopardizing primary implant stability, a 2-stage approach might be safer.
Avila and co-workers (2010) identified the bucco-palatal width of the sinus as a potential limitation for the use of L-PRF alone. They reported that a lateral sinus augmentation with an allograft in narrow or medium sinuses (<15 mm in width) gave roughly three times more vital bone after 6 months of healing, compared to wide sinuses (>15 mm). Therefore, it could be proposed that for sinuses wider than 15 mm, the combination with a bone substitute is preferable (for more information, see Valentini et al. 2025).
Important notice
Clinical experience:
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More bone gain might be obtained when using the bony window as the new floor of the sinus.
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Protect the sinus membrane with a double layer of L-PRF membranes before applying the L-PRF bone-block.
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Make sure to place some pieces of L-PRF bone-block to the palatal and anterior sites.
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Membranes seem superior to clots.
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Slightly overfill the sinus to compensate for a 20% graft resorption.
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Fill the sinus window with L-PRF membranes, and cover the entrance to the sinus with a double layer of L-PRF membranes.
Additional Benefits:
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The healing will be faster.
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L-PRF will improve the bone quality with more newly formed bone and less "remaining/residual" bone substitute.
Be aware:
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Check for possible arteries (intra-osseous branch of the superior posterior alveolar artery) running in the lateral sinus wall by analyzing the CBCT images (Tofangchiha et al. 2022).
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The choice for a 1- or 2-stage window technique depends on several criteria (see decision tree).
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The prevention and management of intraoperative complications during maxillary sinus augmentation are nicely explained in the following 2 papers (Valentini & Artzi 2023, Valentini & Stacchi 2025).
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Some papers (Öncü et al. 2017, Pinto et al. 2018, Barbu et al. 2021, de Almeida Malzoni et al. 2021) propose to seal a small sinus membrane perforation with L-PRF membranes only, and to proceed with the 2-stage grafting, the latter with beneficial outcomes, at least when the sealing was successful.
Sealing of a sinus membrane perforation using only L-PRF membranes. The video demonstrates an air-tight closure of the perforation, with the membranes moving in sync with the patient's inhaling and exhaling.
Interesting references
Several videos and/or cases on this webpage are discussed more in detail in the following book: Quirynen M & Pinto N 2022. Leukocyte- and Platelet-Rich Fibrin in Oral Regenerative Procedures. Quintessence Publishing;
ISBN: 978-1-78698-105-9