Clinical Indications and Outcomes of Sinus Floor Augmentation With Bone Substitutes: An Evidence‐Based Review

Abstract

Tooth loss, resulting from various causes such as periodontal disease or dental caries, can lead to the subsequent resorption of the alveolar bone process [1]. This fundamentally complicates implant-based rehabilitation, especially in the posterior maxilla. Crestal migration of the maxillary sinus floor due to pneumatization, combined with resorption of the alveolar bone, can result in inadequate residual bone height. This situation may require pre-implant interventions like sinus floor elevation (SFE) to ensure enough bone for implant placement [2, 3]. Several strategies have been introduced to increase the bone height in the posterior maxilla [3-5]. SFE has been shown to have relatively high success in augmenting the posterior maxilla with a deficient bone height. Two main techniques have been introduced: (1) The transalveolar (vertical, closed) SFE, and (2) The lateral window approach (open). It should be noted that several modifications of these techniques have also been introduced [6-8]. Given that this regenerative intervention aims to enhance bone height and width to facilitate proper implant placement, dental implants can be placed simultaneously with the sinus augmentation procedure (referred to as the “one-stage” technique). Alternatively, a staged approach may be employed, where bone augmentation occurs during the initial surgical intervention, followed by the placement of dental implants once adequate bone volume has been established (known as the “two-stage” technique) [9, 10]. The classical sinus lift procedure, introduced by Tatum in the 1970s, involves a lateral window approach [11, 12]. This technique involves creating incisions to expose the sinus wall, followed by a trapdoor osteotomy to access the sinus membrane and cavity. Careful dissection and membrane elevation are performed to create space for graft material. If sufficient basal bone is present, implants may be placed simultaneously, protruding through the sinus cavity and protected by the sinus membrane. The remaining space is typically filled with bone replacement grafts, and the window opening is closed with a barrier membrane. However, a two-stage approach is required if the basal bone is inadequate, and implants are placed only after sufficient bone regeneration [9]. In contrast, an alternative, less-invasive technique introduced by Tatum and modified by Summers is the crestal approach [13]. When indicated, this approach involves elevating the sinus floor through the alveolar crest using osteotomes. Summers' modification utilizes concave-tipped tapered osteotomes to fracture the maxillary floor and elevate the sinus membrane. This technique is less invasive, less time-consuming, and allows for better bone density and implant stability due to lateral compression exerted by the osteotomes. After membrane elevation, various bone grafting materials may be used to fill the resulting space. However, the need for graft material post-lifting has been debated, as clot stabilization may promote new bone formation [14]. Despite favorable implant survival rates exceeding 90% reported in systematic reviews, blind procedures carry risks of complications [15]. This article aims to comprehensively explore different bone grafting materials, histologic, and clinical results, and clinical recommendations for using biomaterials during SFE. The concept of graft-free SFE will be discussed, various grafting materials will be compared, and their roles in influencing biological processes will be evaluated. Additionally, histologic and clinical results will be examined to assess their correlation with clinical outcomes. Clinical recommendations for biomaterial selection during SFE will be provided, and this manuscript will offer suggestions for future research. Several limitations regarding bone graft substitutes in maxillary SFE procedures, such as increased costs, need for autogenous bone harvesting, increased surgical time, increased chance of immunogenic response (in non-autogenous grafts), and complications further necessitated the concept of graft-free (also known as coagulum, blood-only or graftless) SFE [16]. The biological foundation of this approach was derived from the concept of new bone formation following the shrinkage and ossification of the blood clot. This was investigated in a study by Palma et al. [17] on four tufted capuchin primates, where they conducted a comparative histological analysis of sinus membrane elevation using the lateral window technique and simultaneous implant placement with and without adjunctive autogenous bone graft. They found that the sinus floor provided approximately 2.2 mm (SD ± 1.1 mm) of cortical bone for primary stability, while the remaining implant projected into the sinus cavity, which subsequently filled with new bone over time. Notably, the histological examination revealed that sites with membrane elevation exhibited the highest new bone formation at the periphery, often extending toward the center of the augmented area. In contrast, grafted sites showed less bone tissue lining the sinus membrane at the uppermost part of the implant. Moreover, the study investigated different patterns of implant integration based on surface modification. For instance, implants with an oxidized surface demonstrated direct bone formation without evidence of trabeculae projection from the surroundings. In contrast, those with a machined surface showed bone growth primarily from the periphery onto the implants. Morphometric measurements indicated a markedly higher degree of bone-implant contact (BIC) for oxidized implants than machined implants. In a split-mouth pilot randomized controlled trial (RCT), Lie et al. [18] compared graftless lateral SFE with a mixture of autogenous and xenogenous bone grafts. The results of the no-graft group revealed significant new bone formation in all human bone specimens. Histological evaluations demonstrated a smooth transition zone between residual and newly formed bone by osteoinductivity. This indicates spontaneous bone regeneration in the absence of grafting materials. The lack of inflammatory reaction in the neighborhood of the augmented site suggests a favorable environment for bone healing without the need for additional grafting materials. This was in accordance with an animal study by Cricchio et al. [19] on six tufted capuchin primates, where a space-making device was utilized to facilitate two-stage lateral SFE. Histological examination revealed consistent bone formation in contact with the Schneiderian membrane and the space-making device, even when displaced. The study highlighted the importance of the space-making device's stability for predictable bone augmentation to ensure a sustained connection between the membrane and the secluded space. Shifting from the histological and biological outcomes toward clinical results of graft-free SFEs, several parallel [20-24] and split-mouth design RCTs can be noted when lateral window SFE is performed. Fouad et al. [24] performed 20 lateral SFE (with 34 simultaneous implants) on sites with 4–6 mm residual bone height using either a xenograft or graftless approach. The 6-month results revealed a significantly lower bone height gain for the graftless approach (8.59 ± 0.74 mm vs. 4.85 ± 0.5 mm). In a 2-year follow-up study, Ranaan et al. [23] performed a graftless approach following the Slit-window graft-free SFE technique where a rigid bovine pericardium membrane (CopiOs Pericardium Membrane, Zimmer Dental) was inserted within two slits to creating a “tented area” that stabilized the Schneiderian membrane in the elevated position. In to the group Zimmer Dental) and a pericardium membrane Pericardium Membrane, Zimmer a significantly lower bone height was mm vs. mm a systematic with by Lie et al. 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