Clinical evaluation of a modified maxillary sinus floor elevation technique with immediate implant placement: a retrospective study

Abstract

Objective

The aim of this study was to evaluate the clinical effectiveness and reliability of an improved maxillary sinus floor elevation technique combined with immediate implant placement in patients with insufficient residual bone height in the posterior maxilla.

Methods

A total of 64 edentulous patients with inadequate posterior maxillary bone height were enrolled. Among these patients, 34 underwent the improved maxillary sinus floor elevation technique with simultaneous implant placement, whereas 30 underwent the conventional bone chisel technique under the same surgical protocol. Radiological and clinical assessments were performed to comprehensively evaluate the effectiveness of the improved technique and to compare its osteogenic outcomes with those of the conventional method.

Results

The mean immediate increase in vertical bone height was significantly greater in the improved technique group (6.016 ± 1.312 mm) than in the bone chisel group (2.797 ± 0.898 mm; P < 0.001). Significant differences were also observed between the two groups in terms of apical bone coverage along the implant axis immediately postoperatively and at the 6–10 month follow-up (P < 0.001). Similarly, peri-implant bone coverage significantly increased in the improved technique group at both time points (P < 0.001). No significant differences were found in the short-term implant success or survival rates between the two groups. Notably, no intraoperative maxillary sinus membrane perforations occurred in the improved technique group, and postoperative complications were limited to mild swelling and pain at the surgical site.

Conclusion

The improved maxillary sinus floor elevation technique yields favourable clinical outcomes in patients with severely resorbed posterior maxillae, particularly when the residual bone height is smaller than 5 mm. This technique constitutes a viable alternative to lateral window sinus augmentation for such cases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-026-07951-1.

Introduction

Owing to ongoing advancements in medical technology and increasing awareness of masticatory function and oral health among patients, an increasing number of edentulous individuals are choosing dental implant rehabilitation. The loss of posterior maxillary teeth may cause maxillary sinus pneumatization and resulting in alveolar ridge atrophy and resorption, ultimately leading to inadequate residual bone height (RBH) in the posterior maxillary region. To address sinus pneumatization combined with the occurrence of alveolar bone deficiency, maxillary sinus floor elevation has become a well-established clinical intervention. Currently, two principal surgical techniques are employed, namely, lateral window (external) maxillary sinus floor elevation and transalveolar (internal) maxillary sinus floor elevation [1, 2]. While effective, the lateral approach is associated with greater surgical invasiveness and higher treatment costs, thereby imposing increased physical and economic burdens on patients [3–5]. In recent years, research efforts have increasingly focused on streamlining treatment protocols to shorten the operative duration, alleviate postoperative complications, and reduce financial strain. Owing to continuous improvements in surgical techniques, medical devices, and biomaterials, internal maxillary sinus floor elevation has demonstrated enhanced clinical effectiveness and procedural predictability [6–8].

To preserve a larger amount of bone at the maxillary sinus floor, ensure adequate space for bone graft materials and implant placement, and minimize postoperative discomfort, we compared the short-term clinical effectiveness and reliability of a modified combined technique involving the use of bone chisel and SCA-KIT instruments for maxillary sinus floor elevation and simultaneous implant insertion in patients with insufficient vertical bone height in the posterior maxillary region with those of the conventional bone chisel method.

Materials and methods

This study of modified sinus floor elevation via the alveolar crest was conducted in strict accordance with the ethical principles outlined in the World Medical Association’s Declaration of Helsinki. It was formally reviewed and approved by the Ethics Committee of Jinan Stomatological Hospital, Shandong Province, China (Approval No. JNSKQYY-2025-014). All participants provided written informed consent after receiving a comprehensive explanation of the research objectives, procedures, and potential risks involved.

This study included a total of 64 patients (64 implants; 33 females and 31 males) who were scheduled to undergo maxillary sinus floor elevation via the alveolar crest approach between January 2023 and July 2025, with a follow-up duration ranging from 1 to 2 years. The mean age of the participants was 50 years, with an age range of 26 to 75 years.

Instruments and materials

Internal lifting tool SCA-KIT (South Korea), external lifting tool DASK-Dentium (South Korea), bone extruder (South Korea), bone substitute material, i.e., Bio-Oss bone powder (produced by Geistlich Pharma AG, Switzerland), periosteal membrane, i.e., HaiAo Oral Repair Membrane (manufactured by Yantai Zhenghai Bio-Technology Co., Ltd.), concentrated growth factor (CGF) (prepared from the patient’s autologous blood by a trained nurse via the use of the DU LING JLC-I device) (Fig. 1), and a collagen sponge (Beiling, produced by Beijing Yierkang Bio-Engineering Co., Ltd.) were employed in this study.

Fig. 1.

Concentrated growth factor

Dental implants

Straumann, OSSTEM and Astra.

The inclusion criteria were as follows: 1) presence of at least one missing maxillary posterior tooth; 2) residual bone height (RBH) in the maxillary posterior region ≥ 2 mm and < 10 mm; 3) completed installation of the final prosthesis; and 4) maintenance of good oral hygiene and periodontal health, defined as no sites with bleeding on probing (BOP) at probing depths (PD) not exceeding 4 mm.

The exclusion criteria were as follows: 1) systemic contraindications such as uncontrolled diabetes, hypertension, coagulation disorders, or other conditions affecting general health; 2) local contraindications such as uncontrolled periodontitis, maxillary sinusitis, maxillary osteomyelitis, or other local inflammatory conditions; and 3) heavy smoking, defined as smoking 10 or more cigarettes per day.

Procedure of modified internal lifting surgery

The patient is asked to rinse the mouth with compound chlorhexidine mouthwash for approximately three minutes prior to the procedure. The skin from the infraorbital region to the submandibular and neck areas is disinfected with an iodophor disinfectant solution and then draped with sterile dressings. At the commencement of the procedure, local anaesthesia is induced via an injection of articaine hydrochloride and epinephrine (Novocol Pharmaceutical of Canada, Inc.). An incision is subsequently made along the alveolar ridge, and full-thickness mucoperiosteal flaps on both the buccal and palatal sides are elevated to fully expose the implant site. Blood samples are collected concurrently using a syringe.

First, a ball drill is employed to determine the initial position. A preliminary probe drill equipped with a stop ring is subsequently used to drill to a depth of approximately 0.5–1 mm below the sinus floor. Next, a SCA drill is utilized to gradually prepare the cavity to a depth of approximately 0.5–1 mm below the sinus floor. If the bone at the sinus floor is relatively dense, the cavity may be prepared within 0.5 mm below the sinus floor. Once the desired width of the implant site is achieved, the sinus floor is gently tapped using a convex bone chisel to create a greenstick fracture and slight protrusion. Thereafter, the largest SCA drill is adopted to separate the protruding sinus floor bone from the surrounding sinus mucosa. A separator is then employed to carefully elevate the sinus mucosa around the cavity. Via the use of a convex bone chisel that matches the shape of the cavity, the sinus membrane is lifted by approximately 1–2 mm. This step is followed by the use of various separators (DASK) to gradually separate the adjacent sinus membranes. Once the membranes are separated, a secondary elevation of the sinus membrane is performed to ensure sufficient height for implant placement. Finally, a depth gauge is used to assess the elevation of the sinus membrane, and the integrity of the sinus membrane is confirmed via the Valsalva manoeuvre.

To prevent rupture or perforation of the maxillary sinus mucosa during the elevation procedure, a stepwise mucosal separation technique is employed for patients with thinner sinus membranes. Specifically, the sheet-like collagen sponge is cut into continuous strips and gradually placed in all directions after initial separation of the sinus floor mucosa, thereby elevating the membrane to the desired height. (Fig. 2) Concentrated growth factor (CGF) membranes are then prepared from autologous blood and placed on the sinus floor to minimize the risk of mucosal perforation. Additionally, bone substitute material (Bio-Oss) is thoroughly mixed with autologous blood and carefully packed into the space beneath the elevated sinus membrane to ensure stable grafting.

Fig. 2.

Elevation of the sinus floor mucosa via the use of a collagen sponge

Upon the completion of the bone grafting procedure, an implant of standard length (≥ 8 mm) is positioned at the recipient site. If adequate primary stability (torque ≥ 25 N·cm) is attained, a healing abutment measuring 4 mm in height is affixed atop the implant. However, if the desired primary stability (torque < 25 N·cm) cannot be achieved or if a localized deficiency in the alveolar ridge necessitates additional bone grafting, the implant should be connected to a healing abutment with an increased diameter and a height of 2 mm. This ensures secure fixation of the implant within the cortical bone. Finally, the mucoperiosteal flap is sutured tightly to complete the procedure.

Surgical procedure for osteotome-mediated sinus floor elevation

The preoperative preparation for the bone chisel internal sinus floor elevation procedure is identical to that of the modified technique. Following local anaesthesia, a gingival incision is made, and a mucoperiosteal flap is elevated. A round bur is used to mark the osteotomy site, and then a series of drills of increasing size are used in sequence to prepare the implant site, thereby stopping approximately 1 mm short of the sinus floor. Subsequently, bone chisels of increasing diameter are employed to induce a controlled greenstick fracture and elevate the Schneiderian membrane to the desired height. The dental implant is then inserted into the prepared site. Postoperative management, determined according to the implant insertion torque, is the same as that for the modified technique.

Postoperative management

All patients underwent cone-beam computed tomography (CBCT) following surgery to confirm the precise position of the implant, the height of the newly formed bone surrounding the implant, the mucosal elevation level, and the extent of flap mobilization. Starting on the day of surgery, all patients received a prophylactic anti-inflammatory regimen consisting of metronidazole and amoxicillin for a duration of 3 to 5 days. Sutures were removed on postoperative day 14. The healing period was 6 to 10 months for all patients. Upon completion of the healing phase, CBCT imaging was performed again to evaluate the status of the peri-implant bone. In cases involving submerged implants, a second-stage surgical procedure was conducted.

Data collection

Postoperative follow-ups were scheduled at 2 weeks, 1 month, 6–10 months, and 1–2 years after surgery. The conditions of the peri-implant bone and soft tissues were systematically evaluated and documented in accordance with the consensus of the World Workshop on Periodontal and Peri-implant Diseases and Conditions, and the patients’ subjective experiences were also noted. The vertical bone height at the implant site was assessed via CBCT imaging. The specific measurement method was as follows: the distance from the alveolar crest to the lowest point of the maxillary sinus floor along the predetermined implant axis was defined as the remaining bone height, and the distance from the alveolar crest to the elevated sinus membrane along the long axis of the implant was defined as the elevated bone height. The increase in the vertical bone height was calculated as the difference between the remaining bone height and the elevated bone height. Bone height measurements were performed twice with the same method, namely, immediately after surgery and at 6–10 months postoperatively. Additionally, the bone height covering the apical end of the implant along its long axis was measured, including the distances from the bone planes at the mesial, distal, buccal, and palatal aspects of the implant to the apical reference plane. The correlation with the extent of sinus floor mucosa dissection is indirectly represented by the angle formed between the long axis of the implant and the straight line connecting the apical point of the implant’s long axis to the edge of the sinus floor mucosa dissection. All measurements were performed three times consecutively by the same attending physician, with concurrent supervision by a second attending physician and a radiologist, and the median value was recorded.

Baseline patient information. Mean ± standard deviation (SD) or n (%)

Variable	Modified technique Bone Chisel technique n(%)
Sex
Male	16	13	45%
Female	18	17	55%
Age (years)	48.15±10.33	50.95±12.20
Smoking
Yes	5	6	17%
No	29	24	83%
Sinus membrane thickness (mm)	0.973±0.910	1.565±1.344
Residual alveolar bone height (mm)	4.771±1.580	7.856±1.367
Increase in bone height (mm)	6.016±1.312	2.797±0.898
Periodontitis
No	32	29	95%
Mild/moderate	2	1	5%
Severe	0	0	0%
Number of perforation cases	0	2	3%
Implant brand and model
Straumann4.8x10	12	20	50%
Straumann  4.8x8	13	4	26%
Straumann 4.1X10	6	4	16%
Osstem 4.5X8.5	1	1	3%
Osstem 4.0X10	1	0	2%
Astra   4.8X9	1	1	3%
Absence of posterior teeth
Premolar teeth	4	3	11%
Molar teeth	30	27	89%

Clinical evaluation

Throughout the surgical procedure and postoperative recovery phase, intraoperative complications, including sinus membrane perforation and haemorrhage, as well as post-operative complications such as facial swelling, maxillary sinusitis, headache, and dizziness were documented.

Implant success and survival rates

In this study, the criteria for evaluating implant success include the following: (1) the absence of clinical mobility of the implanted prostheses; (2) the absence of radiographic evidence of peri-implant bone resorption on CBCT; (3) the absence of persistent pain, numbness, paresthesia, or other subjective symptoms reported by the patient; (4) the absence of pathological conditions such as inflammation, bleeding, swelling, or suppuration in the peri-implant soft tissues; and (5) marginal bone loss (MBL) not exceeding 1.0 mm within the first year following implant loading [9].

Statistical methods

In this study, the data were analysed via inferential statistical methods using SPSS 26.0 (IBM SPSS Statistics) software. With respect to the bone coverage height at the implant root margin (measured immediately after surgery and 6–10 months postoperatively) and the axial bone coverage height at the implant root apex (also measured at the same time points), normality of the data distribution was first assessed using normal probability plots. Homogeneity of variance was subsequently evaluated using the F test. Upon confirmation of parametric assumptions, the independent samples t test was used for intergroup comparisons. All statistical tests were two-sided, the confidence interval is 95%, with statistical significance defined as α = 0.05. Linear regression analysis was conducted to examine the association between the measured angular parameter and bone coverage at the implant root apex, thereby providing an indirect assessment of its correlation with the extent of sinus floor mucosa elevation. To ensure consistency across observers, all participants underwent systematic training and successfully passed the required assessment prior to the experiment (Fig. 3).

Fig. 3.

Cone-beam computed tomography (CBCT) evaluations before and after the modified maxillary sinus floor elevation technique. Image A reveals that the extent of sinus floor mucosa detachment is adequate, but the quantity of implanted bone grafting material is insufficient. Image B shows that the range of mucosal stripping is inadequate, although the volume of grafted bone material is sufficient. Image C shows that both the extent of mucosal elevation and the amount of bone graft material are sufficient. Time points: a, preoperative; b and c, immediate postoperative period; d and e, 6–10 months postoperatively; f and g, 2–3 months after prosthesis placement

Results

A total of 64 patients who received 64 dental implants were enrolled in this clinical study. All patients underwent sinus floor elevation via the alveolar ridge crest approach with simultaneous implant placement. Among them, 34 patients underwent the combined bone chisel and SCA technique and exhibited a greater than 3 mm increase in vertical bone height, and all were grafted with a bone substitute material (Bio-Oss) at the time of implantation. The remaining 30 patients, who exhibited a bone height increase exceeding 5 mm, underwent sinus floor elevation via the use of the bone chisel technique alone and received implants simultaneously without the use of bone grafting materials. For the normality assessment, all the measured data points were observed to be uniformly distributed around the theoretical diagonal line, and the confidence intervals for each group excluded zero. Following paired t tests, Bonferroni correction was applied, and subsequent linear regression analysis revealed no significant correlation.

The imaging examination results indicate that all the surgical procedures were successfully completed without complications. Patients who underwent the modified maxillary sinus floor elevation technique demonstrated satisfactory bone augmentation outcomes (Fig. 4). The mean preoperative residual bone height was 4.771 ± 1.580 mm, with a mean immediate postoperative increase in bone height of 6.016 ± 1.312 mm. In contrast, for patients who underwent the conventional osteotome technique, the mean preoperative residual bone height was 7.856 ± 1.367 mm, and the mean immediate postoperative increase in bone height was 2.797 ± 0.898 mm. These findings indicate that the modified technique enables clinically favourable bone augmentation even in patients with limited preoperative residual bone height.

Fig. 4.

Distance between the apical margin of the implant and the maxillary sinus floor following elevation: A shows measurements obtained immediately postoperatively, and B shows measurements taken 6 to 10 months postoperatively. Bone coverage at the apical margin of the implant: C shows the immediate postoperative status, and D shows the status at 6 to 10 months postoperatively. ****: P < 0.001, indicating a statistically significant difference

The axial bone height covering the apical portion of the implant was assessed immediately after surgery and at 6–10 months after surgery. The mean values were 1.92 ± 0.81 mm and 0.51 ± 0.53 mm immediately after surgery for the modified technique and the bone chisel method, respectively. At 6–10 months post-surgery, the corresponding values were 1.36 ± 0.71 mm for the modified method and 0.24 ± 0.36 mm for the bone chisel method, with statistically significant differences between the two techniques. (Fig. 4C. D, Table 1)

Table 1.

Axial apical bone coverage around the implant (mean ± SD mm)

	Modified technique	Bone chisel technique	T value	F value
Immediately following the surgical procedure	1.92 ± 0.81	0.51 ± 0.53	8.05	3.99
Six to ten months following the surgical procedure	1.36 ± 0.71	0.24 ± 0.36	7.78	9.66

P < 0.001

The bone height covering the apical margin of the implant was subsequently analysed at the same time points. Immediately postoperatively, the measurements for the modified method were as follows: mesial 1.639 ± 0.942 mm, distal 1.689 ± 0.922 mm, buccal 1.625 ± 0.959 mm, and palatal 1.807 ± 0.718 mm. For the bone chisel method, the corresponding values were as follows: mesial − 0.296 ± 1.155 mm, distal − 0.254 ± 1.046 mm, buccal − 0.014 ± 0.949 mm, and palatal 0.003 ± 0.749 mm. At 6–10 months post-surgery, the measurements for the modified method were as follows: mesial 0.997 ± 0.723 mm, distal 0.971 ± 0.665 mm, buccal 0.979 ± 0.801 mm, and palatal 1.062 ± 0.591 mm. For the bone chisel method, the respective values were as follows: mesial − 0.697 ± 1.140 mm, distal − 0.650 ± 1.113 mm, buccal − 0.293 ± 0.723 mm, and palatal − 0.327 ± 0.732 mm. All the intergroup comparisons revealed statistically significant differences. (Fig. 4A and B, Tables 2 and 3)

Table 2.

Vertical dimension of the bone at the apical region of the implant immediately following the surgical procedure (mean ± SD mm)

	Modified technique	Bone chisel technique	T value	F value
mesial	1.639 ± 0.942	-0.296 ± 1.155	7.380	1.052
distal	1.689 ± 0.922	-0.254 ± 1.046	7.897	0.012
buccal	1.625 ± 0.959	-0.014 ± 0.949	6.854	0.253
palatal	1.807 ± 0.718	0.003 ± 0.749	9.828	0.287

P < 0.001

Table 3.

Vertical dimension of the bone at the apical region of the implant 6–10 months following the surgical procedure (mean ± SD mm)

	Modified technique	Bone chisel technique	T value	F value
mesial	0.997 ± 0.723	-0.697 ± 1.140	7.184	5.966
distal	0.971 ± 0.665	-0.650 ± 1.113	7.167	5.293
buccal	0.979 ± 0.801	-0.293 ± 0.723	6.639	0.245
palatal	1.062 ± 0.591	-0.327 ± 0.732	8.390	1.080

P < 0.001

Additionally, the angle formed by the straight line connecting the apical vertex of the implant along its long axis and the mucosal separation point from the maxillary sinus floor relative to the long axis of the implant was measured immediately postoperatively. The mean angular values for the modified technique were as follows: mesial, 84.424 ± 22.677°; distal, 79.159 ± 14.170°; buccal, 94.635 ± 18.402°; and palatal, 91.812 ± 15.198°.

In terms of intraoperative complications, sinus membrane perforation occurred in 2 patients who underwent bone chisel elevation alone. Both perforations were less than 2 mm in diameter. One perforation occurred in a patient with a more inclined maxillary sinus floor, whereas the other occurred in a patient with a relatively flat and wide maxillary sinus floor and a thin sinus membrane. Given the small size of the perforations, no surgical repair was performed; instead, shorter implants were placed, and CGF membranes were applied. Postoperatively, both patients were prescribed a one-week course of metronidazole and amoxicillin, along with ephedrine-based decongestant nasal drops. At the 6-month follow-up CBCT evaluation, no signs of infection were observed, and the implants remained clinically stable without evidence of mucositis. No other intraoperative complications were noted in the remaining patients.

With respect to postoperative complications, among the patients who underwent maxillary sinus floor elevation using the bone chisel technique, three experienced mild cephalic discomfort on the day of surgery, attributed to the higher density of the sinus floor cortical bone. In patients who underwent the modified technique, mild swelling and pain at the surgical site were observed between postoperative days 3 and 5, likely because of the more extensive sinus membrane detachment and the irritative effect of the bone grafting material. Apart from minor gingival swelling and discomfort, no significant facial oedema or bruising was noted in any patient. No cases of postoperative maxillary sinusitis were reported, and essential functions such as speech, mastication, and daily communication remained unaffected.

Both the success rate and survival rate of the implants were relatively high, with no statistically significant difference between the two. All implants were successfully placed, and no major complications were observed throughout the duration of the study. During the implant healing period, no cases of implant loosening, peri-implant radiolucency, significant bone resorption, persistent numbness, or abnormal sensory changes were detected. Furthermore, no complications, such as suppuration, bleeding, or soft tissue swelling, were reported. With respect to the survival rate, one modified implant was lost four months after prosthetic restoration. This resulted in a cumulative implant survival rate of 97.1%.

Discussion

The technique of maxillary sinus floor elevation has undergone continuous refinement in parallel with advances in medical technology, and associated postoperative responses exhibit considerable interindividual variability [10–13]. As a technique-sensitive procedure, maintaining adequate space between the root end of the implant and the surrounding area after MSFE is critically important. Bone substitute materials utilized in MSFE can facilitate new bone formation postoperatively. These materials, placed between the sinus membrane and the implant root end as well as its surrounding region, undergo gradual resorption and remodelling [14]. The risk of implant exposure into the maxillary sinus cavity increases in cases where the Schneiderian membrane is not adequately elevated or when an insufficient quantity of bone substitute material is grafted during the procedure [15].

In a comparative experiment of maxillary sinus floor elevation using PRF and normal saline conducted by Cho Yong-Seok et al., a measurable increase in bone volume was observed; however, the overall bone volume remained insufficient, and the risk of implant root exposure was relatively high [16]. In a study on maxillary sinus floor elevation using only a CAS drill by H. Xue et al., a significant increase in bone volume was achieved, but the amount of bone retained at the sinus floor was relatively limited. When a smaller quantity of bone powder was used, the capacity to maintain the elevated sinus cavity space was compromised, leading to increased bone resorption during the later stages [17]. In a study by Alper Saglanmak et al., who employed a bone compaction drill for maxillary sinus floor elevation, the anticipated increase in bone volume was achieved; however, the height of the bone at the implant apex was uneven, thereby increasing the risk of localized implant root exposure postoperatively [18]. In a study by Jiayu Gao et al., which aimed to predict the risk of implant root tip exposure following maxillary sinus floor elevation using a nomogram, the residual maxillary height was not identified as a limiting factor for simultaneous sinus elevation and implant placement. Rather, the determining factor was the initial stability of the implant [19, 20].

In this clinical scenario, we employ the minimally invasive alveolar crest approach, combining the use of a bone chisel with the SCA-KIT drill (modified technique), to elevate the maxillary sinus floor, a procedure of considerable clinical relevance, particularly for patients with a residual bone height less than 5 mm. This approach not only facilitates the preservation of a greater volume of native sinus floor bone but also minimizes patient discomfort in the cranial region and allows for the use of bone substitute materials to provide a buffering effect, ultimately achieving a favourable bone augmentation outcomes.

During the surgical procedure, for a relatively flat maxillary sinus floor, the osteotome size can be selected on the basis of the alveolar bone classification and the bone density of the maxillary sinus floor after preparing the site approximately 0.5–1 mm above the sinus floor. For type III and IV bone, an osteotome corresponding to the final prepared cavity size can be gently tapped to partially separate the sinus floor bone plate and mucosa from the surrounding structures. For type I and II bone, a small osteotome can be used initially to slightly elevate the maxillary sinus floor, after which the cavity can be expanded using osteotomes of increasing size to create a greenstick fracture and to achieve further elevation. In cases where the maxillary sinus floor is sloped, the smallest SCA preparation drill should be used to reach the lowest point of the slope, and the maxillary sinus floor can then be slightly elevated via the use of the smallest osteotome. The cavity can then be expanded using SCA drills and osteotomes of increasing size to achieve further elevation. Once the desired cavity shape is achieved, the largest applicable SCA drill can be used to prepare the site to the required depth and separate the surrounding mucosa. This approach is comparable to the staged sinus floor elevation technique [21]. Afterward, a separator can be used to carefully detach the surrounding mucosa, and finally, bone graft particles can be added incrementally to expand the elevated area until the desired height is achieved.

In cases involving alveolar bone with low bone density, the use of the chisel technique can effectively increase bone mass density, thereby increasing implant stability [22]. In patients with a thin maxillary sinus membrane, a collagen sponge is employed during the procedure to gently separate the surrounding sinus membrane. A CGF membrane is subsequently placed within the sinus cavity to prevent maxillary sinus perforation; alternatively, a gelatine sponge may be used as a protective cushion to minimize the risk of mucosal perforation during the sinus lift procedure [23–26]. Intraoperatively, the CGF membrane can aggregate Bio-Oss bone powder particles, significantly reducing their dispersion into adjacent areas and thereby enhancing the overall quality of bone regeneration. The HaiAo biological membrane is primarily utilized for patients who present with alveolar ridge deficiencies and who require guided bone regeneration (GBR) surgery.

Postoperative CBCT revealed that the side with a greater quantity of implanted bone powder particles following maxillary sinus floor mucosa elevation demonstrated superior bone formation, reduced bone resorption during the remodelling process around the implant, and increased bone coverage at the implant apex and surrounding areas. In contrast, the side with fewer implanted bone powder particles exhibited relatively inferior bone formation outcomes. These findings clearly highlight the importance of maintaining the created space for an extended period after maxillary sinus floor elevation, which allows sufficient time for effective bone remodelling [10, 27, 28]. The greater the extent of periosteal dissection around the maxillary sinus floor mucosa and the greater the number of bone powder particles implanted, the greater the degree of achieved sinus floor elevation and the greater the potential for increased bone remodelling height. This can be analogized to a pyramid: the larger the base, the greater the achievable height. Conversely, as the implanted bone powder is gradually resorbed, the bone coverage around and at the apex of the implant may be reduced.

Patients with an inclined maxillary sinus floor are at increased risk of sinus membrane perforation when the traditional bone chisel technique is used. One of the two patients who sustained a sinus membrane perforation during internal elevation using this technique in our study had a significantly inclined sinus floor [29, 30]. Claudio Stacchi et al. reported that during maxillary sinus floor elevation procedures in patients with a residual bone height ≤ 5 mm, wide maxillary sinuses are more susceptible to sinus membrane perforation than narrow maxillary sinuses are [31]. The other case of sinus membrane perforation in our study involved a patient with a wide maxillary sinus floor and a thin sinus membrane. However, our findings indicated that an inclined maxillary sinus floor was associated with greater elevation height and increased bone augmentation. This phenomenon may be attributed to the presence of one intact bony wall, which facilitates better dispersion of the bone grafting material, thereby significantly increasing the elevation height and range while reducing the risk of sinus membrane perforation. Consequently, postoperative CBCT scans confirmed that an inclined maxillary sinus floor was more conducive to achieving increased bone height. Furthermore, a concave sinus floor with a smaller angle in either the mesiodistal or buccolingual direction was more favourable for bone augmentation than a flat sinus floor was.

With respect to the extent of maxillary sinus floor mucosa dissection, a correlation analysis was conducted between the angle formed by the straight line connecting the apical point of the long axis of the implant to the edge of the maxillary sinus floor mucosa dissection and the bone coverage at the apical region of the implant. The results of the analysis indicate that this angle does not directly correlate with the extent of mucosal dissection. Specifically, a larger angle does not necessarily imply a greater extent of dissection, as it is also influenced by the anatomical dimensions of the maxillary sinus, including the sinus cavity angle and the protrusion length of the implant. Intraoperatively, the angular measurements on the buccal and palatal aspects were significantly greater than those on the mesial and distal sides. This finding is attributed to the fact that, in most patients, the maxillary sinus angle is notably smaller on the buccal and palatal sides than on the mesial and distal planes. To maximize the area of sinus membrane elevation, the mucosal separator from the external sinus lift kit (DASK) was systematically utilized to achieve circumferential dissection of the sinus floor mucosa during the procedure [32–34].

For sinus floor elevation, the bone chisel technique exhibits considerable interindividual variability, and the postoperative outcomes following elevation remain unpredictable. In patients with reduced cortical bone thickness at the sinus floor, the likelihood of sinus membrane perforation during the procedure may be lower. Conversely, in patients with greater cortical bone volume, the morphology of the sinus floor plays a critical role: notably, in the presence of a flat sinus floor, a relatively intact bony flap can often be elevated en bloc, producing a tenting effect that may promote new bone formation beneath the implant site [22]. However, in patients with a sloping sinus floor, the uneven distribution of cortical bone thickness increases the risk of membrane perforation. Furthermore, the extent of vertical elevation is constrained by anatomical limitations. When the elevation height is within 2 mm, adequate bone coverage around the apical region and periphery of the implant is typically observed. Beyond this threshold, increasing elevation height correlates with progressive reductions in bone coverage at these critical sites [11, 30].

In patients who underwent the modified maxillary sinus floor elevation technique, an increase in bone volume around and at the apical region of the implants was observed immediately after surgery and was sustained at 6–10 month postoperative follow-up. Compared with the conventional bone chisel technique, the modified technique was associated with mild postoperative swelling and pain in the surgical area, potentially attributable to the more extensive dissection of the sinus membrane and oedema induced by the bone substitute material. However, these symptoms did not interfere with the patients’ ability to perform daily activities. The modified procedure is longer in terms of duration and requires greater technical proficiency, as it necessitates precise manipulation to elevate the maxillary sinus floor mucosa and properly place the bone graft material. Although no cases of sinus membrane perforation were observed in the initial cohort, such complications were observed in subsequent clinical studies. Therefore, in patients with severely inadequate residual alveolar bone height, careful assessment of sinus membrane health is essential prior to intervention.

Limitations of the Study: This study adopts a non-randomized group design, primarily due to its focus on clinical treatment protocols. Consequently, potential selection biases may arise from subjective factors—including the surgeon’s clinical judgment and the patient’s informed consent process. The assessment of residual alveolar bone height was limited to evaluating the feasibility of the modified maxillary sinus lift procedure; however, the stratification criteria for intergroup differences in residual bone height were not explicitly defined, thereby compromising the comparability between the two study groups. For covariate adjustment, only the broad eligibility of the surgical procedure for adult patients across all age groups was considered; no formal statistical methods—such as multivariate regression analysis—were employed to control for established baseline characteristics. The sample size of this study is limited, which may constrain the generalizability of the findings to broader clinical populations. Future research with larger, more representative samples is warranted to enhance statistical power and support robust inference. The primary outcome measure in this study was analyzed solely using an independent-samples t-test with a 95% confidence interval generated via SPSS software; however, standardized effect size metrics (e.g., Cohen’s d) were not computed. This omission limits the interpretability and comparability of the observed differences across studies and reduces the robustness of statistical inference. For the assessment of inter-observer reliability, observers underwent standardized training prior to study initiation. Although the initial intraclass correlation coefficient (ICC) was 0.81—indicating good agreement—the absence of periodic ICC reassessment throughout the study period may limit the robustness and temporal validity of the reliability estimates. The follow-up duration of this study was limited; therefore, extended longitudinal observation and analysis are warranted to adequately assess long-term implant survival rates and the stability of osseointegration. This study utilized dental implants from multiple commercial systems; however, additional validation is required to identify and characterize the underlying factors influencing the observed outcomes.

Conclusions

The modified maxillary sinus floor elevation technique may serve as a viable treatment option for patients with insufficient residual alveolar bone height, particularly when the residual alveolar bone height is smaller than 5 mm. However, its application is subject to certain limitations, including thickened maxillary sinus mucosa or adhesions of the sinus membrane resulting from chronic apical periodontitis. Moreover, given the methodological limitations of this study, rigorously designed, long-term prospective observational studies are warranted to systematically assess its sustained clinical efficacy and to further validate the consistency and predictability of its therapeutic outcomes.

Authors’ contributions

F.L., aided the conception or design of the study; helped with the acquisition, analysis, or interpretation of the data; drafted the manuscript; and critically revised the manuscript for important intellectual content. J.C., aided the design of the study; helped with the acquisition, analysis, or interpretation of the data; drafted the manuscript; and critically revised the manuscript for important intellectual content. F.Y. and Y.S. , aided the conception of the study; helped with the acquisition or interpretation of data, and critically revised the manuscript for important intellectual content. T.L. , W.Y., J.S. , X.S. , F.L. , T.Y. and Y. H. helped with the acquisition of data and critically revised the manuscript for important intellectual content. All the authors approved the manuscript and are accountable for accuracy and integrity of the work.

Funding

The research, authorship, and/or publication of this article was supported by grants from the Science and Technology Development Program of Jinan Municipal Health Commission (Item Number: 2023-2-160). Special Fund for High-Level Talents in the Medical and Health Industry of Jinan, Shandong Province, P. R. China (grant number: 202412).

Data availability

All data and materials described in the research article are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Ethical approval was obtained from the ethical committee of the Jinan Stomatological Hospital (Approval number: JNSKQYY-2025-014). The study was conducted in accordance with the Declaration of Helsinki. All participants provided written informed consent to participate in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.