Evaluation of volume changes following lateral window maxillary sinus floor elevation using Minics software

Introduction

Bone augmentation through maxillary sinus floor elevation is widely used to treat vertical bone deficiency in the maxillary posterior area. Maintaining graft stability during maxillary sinus elevation is key to successful surgery (1-6). Because of changes in the air pressure of the maxillary sinus and absorption of bone graft material, the bone graft site may undergo compensational remodelling in terms of shape and volume. The factors affecting changes in the volume of the elevation region are complex and diverse, and there may also be individual differences. At present, there is no consensus in this regard; however, numerous studies have suggested that volume change of the grafted site is related to the type of bone graft, sinus gasification, and surgical procedure, among other factors (7,8). The stability of the bone graft material is also important for volume maintenance, and we usually use a biofilm to wrap the bone graft material so that it does not fall apart easily. Several studies have shown significant volume changes 6 months postoperatively, with stabilization thereafter (7-11). At present, there is no gold standard for assessing the shape and volume of the elevation region in the grafted site after implantation, and there is no consensus among studies on this subject (12,13). Cone-beam computed tomography (CBCT) is reliable for the evaluation of bone volume; however, it cannot accurately measure the volume. Therefore, it is necessary to identify a method of measuring volume changes in the maxillary sinus.

Several tools for measuring bone volume are available. “Dolphin” software is used primarily to measure the volume of the maxillary sinus airway, with an error rate of between 9% and 42%. However, the application of this software in the measurement of maxillary sinus bone graft volume has not been reported (14). Only one study in recent years has utilized “Minics” software (Minics version 17.0; Materialise, Leuven, Belgium) to measure the volume of maxillary sinus bone grafts (6). Among the various measurement and analytical software applications currently available, Minics offers the most accurate results (15). As a three-dimensional (3D) volume analysis software, Minics can not only help analyze the airway but can also perform linear measurements of the maxillary sinus elevation region volume in 3D. This study used Minics to measure the maxillary sinus elevation region volume after bone grafting and to analyze the 3D changes in the elevation region volume 6 months after lateral window maxillary sinus floor elevation (LSFE). We present the following article in accordance with the MDAR reporting checklist (available at https://atm.amegroups.com/article/view/10.21037/atm-22-3110/rc).

Methods

Ethical consideration

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the institutional ethics committee of Binhaiwan Central Hospital (No. 2021096) and informed consent was acquired from all individual participants.

Research participants and measurement methods

Participants in this study were those who underwent LSFE surgery at the Stomatology Department of Binhaiwan Central Hospital between 2017 and 2020. A total of 40 participants (men, 26; women, 14; average age, 48.05±0.6 years) were included. Of these, 20 received LSFE with simultaneous implantation and 20 received LSFE with delayed implantation 6 months later.

The inclusion criteria were as follows: (I) surgical site free of local inflammation; (II) no oral mucosal disease present; (III) no sinus disease present; (IV) hygienic oral environment (full mouth plaque score <20%); and (V) follow-up CBCT performed 6 months postoperatively.

The exclusion criteria were as follows: (I) presence of systemic diseases (cardiovascular disease, coagulation and white blood cell disorders, or metabolic disorders); (II) history of radiotherapy in the head and neck area within 12 months preoperatively; (III) ongoing steroid treatment; (IV) presence of neurological or mental illnesses that may interfere with good oral hygiene; (V) immunodeficiencies, including human immunodeficiency virus infection; (VI) history of smoking (more than 10 cigarettes/day); (VII) drug or alcohol abuse; or (VIII) insufficient compliance.

Patients were divided into 2 groups according to the experimental design: (I) LSFE with simultaneous implantation and (II) LSFE with delayed implantation. Preoperative clinical and radiological examinations were performed. Radiographic examination of the maxillary sinus of each patient was performed using CBCT before the LSFE surgery (T0), immediately after the surgery (T1), and 6 months after the surgery (T2). CBCT scans and volume measurements using Minics were performed by the same clinician for all patients. This reduced measurement errors and considerably improved reliability (Figure 1). The following materials were used: bio-absorbable collagen membrane (Heal-All^®, Yantai Zhenghai Bio-tech Co., Ltd., China), Tianbo bone powder (Bio-osteon, BEIJING YHJ, Beijing), and an implant system (Straumann, Switzerland; SIC, Switzerland). Minics was used to measure the 3D data and the volume of the maxillary sinus bone graft material at T1 and T2 and analyze the results.

Figure 1 Volume model of maxillary sinus floor bone graft material constructed by Minics. (A) Position map of the three-dimensional reconstruction of the bone graft material at the sinus floor; (B) three-dimensional reconstruction of the bone graft material; (C) sagittal view; (D) longitudinal view.

CBCT was performed using the KaVo 3D eXam 3D imaging system (KavoSybron, Germany), with a tube voltage of 70 kV, tube current of 31 mA, scanning time of 23 s, and reconstruction thickness of 0.2 mm.

Statistical analysis

SPSS version 25.0 was used for statistical analysis. A normality test was carried out for continuous data, such as patient age. If the data were normally distributed, data were expressed as mean ± SD. A paired-samples t-test was used to compare measured values before and after treatment. Two independent-sample t-tests were used to compare the differences in the measured values between both groups. If the variables did not follow a normal distribution, the median (Q1, Q3) was used to describe the variables. The Wilcoxon signed-rank test was used to compare the measured values before and after treatment, and the Mann-Whitney U test was used to compare the difference in the measured values between both groups. Chi-square analysis was used to compare sex-related differences. Differences were considered statistically significant at P<0.05.

Results

Comparison of demographic data between the groups

The sex and average age of the participants in the simultaneous implantation group (14 men, 6 women; average age, 49.70±12.44 years) were not significantly different from those in the delayed implantation group (12 men, 8 women; average age, 65.50 years) (Tables S1,S2, Figure 2).

Figure 2 The differences in the sex- and age-related characteristics between the groups. The difference in the sex- and age-related characteristics of the groups is not statistically significant. (P_Age=0.507, P_Gender=0.512). SG, simultaneous group; DG, delayed group.

Simultaneous implantation group

In the simultaneous implantation group (n=20), the implant length, width, height, and volume at T1 were 18.23±3.74 mm, 16.85±3.07 mm, 11.75±2.33 mm, and 1,258.536±555.50 mm³ (range, 546.98–2,389.62 mm³), respectively. The implant length, width, height, and volume at T2 were 16.85±3.99 mm, 14.04±2.98 mm, 9.87±1.85 mm, and 901.7845±410.48 (range, 306.18–1,631.93 mm³), respectively. The data between T1 and T2 were significantly different (P<0.05).

Delayed implantation group

In the delayed implantation group (n=20), the implant length, width, height, and volume at T1 were 20.64±3.96 mm, 16.37±3.12 mm, 12.32±2.15 mm, and 1521.56±642.27 mm³ (range, 330.468–2,582.33 mm³), respectively. The implant length, width, height, and volume at T2 were 19.41±3.80 mm, 14.16±2.79 mm, 10.80±2.13 mm, and 1,102.99±529.09 mm³ (range, 244.9–1,743.38 mm³), respectively. The data between T1 and T2 were significantly different (P<0.05) (Tables S3,S4, and Figures 3,4).

Figure 3 The differences in the length, width, height, and volume of the implant between T1 and T2. The differences in the length, width, height, and volume of the implant between T1 and T2 are statistically significant. (Simultaneous Group: P_Length=0.001, P_Width<0.0001, P_Height<0.0001, P_Volume<0.0001; Delayed Group: P_Length=0.004, P_Width<0.0001, P_Height<0.0001, P_Volume<0.0001).

Figure 4 The differences in the length, width, height, and volume of the implant between different groups. The differences in the length, width, height, and volume of the implant between different groups are not statistically significant. (P_{Length difference}=0.507, P_{Width difference}=0.86, P_{Height difference}=0.402, P_{Volume difference}=0.745).

The height from the tip of the implant

The change in height from the tip of the implant was 1.42 (0.35, 2.32) mm in the simultaneous implantation group, while in the delayed implantation group, the change in height was 0.30 (0.16, 0.63) mm. The differences in the values measured immediately and 6 months after implantation were statistically significant (P<0.001). The change in height from the tip of the implant was significant between the 2 groups (Table S5 and Figure 5).

Figure 5 The difference in height from the tip of the implant between different time points. The difference in the height from the tip of the implant between different time points is statistically significant. (P=0.001).

Discussion

Minics

Minics, a representative software for manual segmentation, is one of the most commonly used software packages in clinical settings (16,17). Minics can be used for fracture reduction, orthognathic surgery, local plastic surgery, airway lesions, etc. Weissheimer et al. demonstrated several advantages in terms of imaging and highlighted the wide range of applications of the Minics software in biomedical engineering (18). Minics’ 3D reconstruction and visualization module enables the study of thin-slice CT volumetric datasets in 3 orthogonal planes (transverse, sagittal, and coronal planes), and the image visualization function provides axial, coronal, and sagittal views of the raw data with a reconstructed 3D view, including translation, scaling, and rotation. To date, few studies have been conducted on the application of Minics in measuring volume changes in the LSFE region. We used Minics to evaluate volume changes at the elevation site following LSFE.

Volume changes in the elevation region following LSFE

The factors affecting volume changes in the elevation region post-surgery are complex and diverse, and there may also be individual differences. At present, there are no conclusive findings in this regard. Berberi et al. (7) and Kirmeier et al. (8) have indicated that the volume changes of bone graft material after maxillary sinus floor elevation are related to the preoperative sinus floor bone mass, bone volume, surgical method, maxillary sinus gasification, and implants, along with the implant material’s stability, biochemical properties, absorption mode, and other complex factors. In different studies, the observed volume changes of the same bone graft material can vary greatly, further highlighting that the factors affecting bone graft material absorption are complex and there are individual differences.

Different types of bone graft material also cause differences in volume changes after maxillary sinus floor elevation. The volume changes with bone substitute materials are less than those of autogenous bone (9); however, they all undergo some degree of reduction following surgery (8,19,20). For this reason, the same type of bone graft material was used for all patients in this study to minimize errors. This study found that 6 months after LSFE, the dimensions and volume of the bone graft in both the simultaneous and delayed implantation groups were reduced. We also detected the interesting phenomenon of an air cavity filled with blood in the elevation region, which was present owing to either the implant or the bone graft material supporting the maxillary sinus membrane. This part exhibited a good osteogenic effect after 6 months, even without the bone graft material, and appeared as normal alveolar bone on the image. It is possible that the maxillary sinus membrane stem cells (MSMSCs) have the characteristics of mesenchymal stem cells, which can differentiate into osteoblasts and participate in the osteogenesis in the sinus floor space after maxillary sinus floor elevation (21). Therefore, in many cases, the actual elevation volume was greater than the graft volume. The average shrinkage percentage of the artificial bone graft in the simultaneous implantation group 6 months after LSFE was 28.14% (range, 8.47–52.00%) and that in the delayed group was 25.64% (range, 2.46–75.69%). These results were similar to those reported by Kirmeier et al. (8) where the bone graft volume showed a significant reduction after maxillary sinus elevation. The volume shrinkage percentage (18.3%±2.3%) was similar to that observed by Shanbhag et al. (22). Several studies have demonstrated that volume reduction of the bone graft material during the healing period is because of remodelling and contraction of the bone graft material under the sinus floor mucosa. The degree of contraction and remodelling is determined by the bone remodelling characteristics and the degree of vascularization and mineralization of the bone graft material (23,24). With the continuous gasification of the maxillary sinus and absorption of the bone graft, significant changes have been observed in the shape and volume of the bone graft area (7,24). After surgery, the volume of the bone graft is reduced (25-29).

LSFE with simultaneous and delayed implantation

Whether simultaneous implantation can take place during LSFE depends on the volume of the native alveolar bone. The conventional treatment plan requires bone augmentation first when the residual height of the alveolar ridge is less than 4 mm. Once the bone has formed, the implant is placed. The patient must undergo multiple operations, incur high costs, and wait for a long period to complete treatment. However, Peleg et al. (30) and Manso et al. (31) both found that maxillary sinus elevation and simultaneous implantation may help achieve ideal results and retention rates even when the residual bone volume is less than 4 mm. The presence of less than 4 mm of alveolar ridge height is no longer a contraindication for LSFE and simultaneous implantation. It is possible to maintain the orientation and position of an implant during simultaneous implantation; it does not shift or exfoliate because of inadequate stability during implantation. If the initial stability is adequate, the superstructure can be installed directly, and the non-embedded healing can reduce the need for a second operation and for a period of gingival shaping. If the initial stability is insufficient, a short healing abutment can be installed, and embedded healing can be adopted. In this case, the implant was completely embedded in the mucoperiosteal flap. Following the healing of the mucoperiosteal flap, the implant was pressed against the bone surface owing to the shrinkage of the wound, thereby increasing its stability. Once the osseointegration was complete, the abutment was replaced with one of sufficient height. Pignaton et al. also noted that the remaining alveolar ridge height is not the only factor that determines the initial implant stability (32). Simultaneous implantation may improve preservation of the volume of the bone graft material (33). However, in simultaneous implantation, it is advisable for the graft to be placed up to 2 mm above the tip of the implant and for it to surround the implant to prevent absorption of the material and ensure the stability of the bone at the tip of the implant. The absorption at the tip of the implant with simultaneous implantation is greater than with delayed implantation. When the bone powder at the tip is less than 2 mm, the absorption amount is greater. In the current study, no significant differences were observed in the length, width, height, and volume of the implants between LSFE with simultaneous implantation and LSFE with delayed implantation. This indicates that there are no significant differences between the treatment effects of LSFE with simultaneous implantation and LSFE with delayed implantation in clinical treatment. Nevertheless, simultaneous implantation can reduce the patient’s financial burden and the number of operations, as well as shorten the diagnosis and treatment process, allowing patients to regain their mastication abilities swiftly.

There were certain limitations to this study. The sample size may have been inadequate to obtain sufficient postoperative characteristics to establish a change. In future clinical trials, research plans should be designed and implemented more rigorously than our own.

Conclusions

The length, width, height, and volume of the LSFE region were reduced using Minics software. This suggests that the volume of the elevation site should be enlarged as much as possible during the operation to prevent volume shrinkage. There was no difference between the effect of LSFE with simultaneous implantation and LSFE with delayed implantation, although simultaneous implantation is preferred in most cases.

Acknowledgments

Funding: This study was supported by the Scientific Research Project of Southern Medical University Stomatological Hospital (No. PY2020010) and Scientific Research Program of Traditional Chinese Medicine Administrative Bureau of Guangdong Province (No. 20222142). The funding was used for the deduction of some medical fees of the dental implant, preparation of the preliminary study, data processing and analysis, and polishing of the article.

Footnote

Reporting Checklist: The authors have completed the MDAR reporting checklist. Available at https://atm.amegroups.com/article/view/10.21037/atm-22-3110/rc

Data Sharing Statement: Available at https://atm.amegroups.com/article/view/10.21037/atm-22-3110/dss

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://atm.amegroups.com/article/view/10.21037/atm-22-3110/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the institutional ethics committee of Binhaiwan Central Hospital (No. 2021096) and informed consent was obtained from all individual participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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(English Language Editor: C. Betlazar-Maseh)