The posterior maxilla presents several constraints for dental implant placement due to the limited residual bone height and poor bone quality. Insufficient alveolar bone height is attributed to alveolar bone resorption and increased sinus pneumatization following tooth loss [1].

A sinus augmentation is the most frequently executed pre-prosthetic technique to attain an adequate bone volume in the atrophic maxilla [2, 3]. This predictable technique is employed to address the loss of vertical bone height in the posterior maxilla. Moreover, it can be performed using two common techniques: the lateral window approach and the transcrestal approach [4].

In 1986, Tatum performed a sinus lift, which used a transalveolar approach to the sinus; the sinus membrane was dissected by fracturing the sinus floor using special tools called “socket former” [2]. In 1994, Summer introduced a less aggressive approach to sinus floor elevation, which involved the immediate placement of implants and is commonly referred to as Osteotome Sinus Floor Elevation (OSFE) [3, 4]. This technique has been modified by many researchers to make the procedure more comfortable for the patients and easier for the practitioners. Furthermore, it is also used to reduce the risk of membrane perforation and increase intrasinus bone gain [5-8].

Threaded bone expanders are the instruments used to spread out a dental implant osteotomy. They are used as an alternative to osteotomes in cases of expansion of the atrophic alveolar ridge [9, 10]. Several studies confirmed the superiority of threaded bone expanders over the osteotomes in the expansion and splitting of the alveolar ridge [11, 12].

The threaded bone expanders are also used for rehabilitation of the posterior maxilla as an alternative to sinus lift techniques in the atrophic maxilla. The implant bed can be safely prepared near the anterior wall of the maxillary sinus. This technique is called the “sinus bypass technique” [13].

The properties of these expanders impetus the practitioners to employ them in transalveolar sinus lift [14-16]. The specific aims of the study were to evaluate the bone gain, the intra- and post-operative complications rate, the implant success rate and marginal bone loss in transalveolar sinus lift using threaded bone expanders and analyze the correlation between marginal bone loss and insertion torque in transalveolar sinus floor elevation (TSFE) procedures using motorized threaded bone expanders without bone graft materials.

Maxillary sinus augmentation aims to increase the vertical bone height in the posterior maxilla for dental implant placement. Various techniques and materials have been used in this procedure, which can be divided into lateral approaches and transalveolar approaches [17].

Lateral sinus augmentation has become a common and predictable procedure to increase bone height for dental implant placement in the posterior maxilla. However, the procedure is described as sensitive and requires surgical skill, particularly in Schneiderian membrane dissection. Studies have demonstrated that Schneiderian membrane perforation is considered the most frequent complication, with reported incidence rates ranging from 7 to 60% [18, 19].

The transalveolar sinus lift approach is described as less invasive and more conservative than the lateral approach. Osteotome sinus floor elevation (OSFE), which was introduced by Summer in 1994, was the first and standard transalveolar sinus lift technique [20, 21]. This technique uses tapered osteotomes and a hammer for green-stick fracturing of the sinus floor. Several studies have reported that hammering might result in postoperative vertigo and decrease the patients’ comfort [22]. Several alternative methods have been introduced in recent years to alleviate this issue. The addition of bone graft materials can contribute to absorbing the shock caused by hammering and decreasing the Schneiderian membrane perforation rate [23, 24].

Transalveolar sinus lift using sequential special drills, such as the cosci technique and osseodensification technique, is based on gradual perforation of the sinus floor instead of fracturing it [8, 25, 26]. Therefore, osteotomes and hammering are eliminated. Hydraulic pressure techniques have also been introduced as minimally invasive transalveolar sinus lift techniques without osteotomes [27, 28]. However, non-osteotome-based transalveolar techniques are intricate procedures that necessitate a high level of surgical proficiency, primarily because these methods involve direct contact of instruments with the delicate sinus membrane [25-28].

Threaded bone expanders have demonstrated the capacity to effectively and safely move the cortical plate of the sinus floor, similar to Summer's technique and without using the hammer [15].

Controversy persists regarding the essentiality of bone grafting in conjunction with the placement of dental implants during transalveolar sinus lift. Several studies reported the possibility of bone formation in sinus lift procedures with simultaneous dental implant placement without using bone graft material [29-31]. This can be explained by the implant fixture acting as a tenting pole for space maintenance beneath the Schneiderian membrane [32]. Nonetheless, upon contrasting the amount of intrasinus bone gain between the grafted group and the non-grafted group, it was observed that the grafted group exhibited a more significant degree of bone gain compared to the non-grafted group [33].

A systematic review [34] reported a mean intrasinus bone gain of 3.43 ± 0.09 mm, which was inconsistent with our results (IBG was 1.69 mm). This might be explained by the confirmed relationship between bone gain (IPL) and implant protrusion length (the mean of IPL in our study was 2.01 mm). This also explains the difference in intrasinus bone gain between our study and a study conducted by Kadkhodazadeh [15], who used the same surgical protocol.

High insertion torque values are associated with greater primary stability of dental implants and thus improve osteointegration [35, 36]. However, high insertion torque can generate micro cracks that could result in the progression of marginal bone loss [37]. A systematic review [38] and meta-analysis reported no association between insertion torque value and implant marginal bone loss, which is consistent with our results.

This is the first study that evaluated the motorized threaded bone expander without bone grafting materials in transalveolar sinus lift procedures. The previous study evaluated the bone expanders in transalveolar sinus lift procedures using bone graft materials or a manual method. The limitations of the study are 1- no control group and 2- no follow-up period after the functional loading.

According to the results of this study, transalveolar sinus lift using motorized bone expanders showed effective lifting of the sinus floor, and minimum marginal bone loss presented a good solution for pneumatization of the maxillary sinus to achieve a successful rate of implant placement.