Thirty patients, who underwent lSFE with minimally invasive technique from May 2015 to November 2019 at West China Hospital of Stomatology, Sichuan University were included in the study. The study was followed strengthening the reporting of the observational studies in epidemiology (STROBE) guidelines. The clinical trial was performed to fully conform to the World Medical Association Declaration of Helsinki59. Ethics Committee of West China Hospital of Stomatology, Sichuan University approved the research procedures (WCHSIRB-CT-2022-452). All patients were informed of the clinical study procedure and signed the informed consent.
4.1 Inclusion criteria
1. Patients older than 18 years old.
2. Patients who signed informed consent.
3. Patients who underwent lSFE with minimally invasive technique (small lateral window and simultaneous placement of single implant).
4. Patients in good health without contraindications to implant surgery.
4.2 Exclusion criteria
1. Pregnant and lactating patients.
2. Patients with active maxillary acute sinusitis or diseases affecting wound healing and osteogenesis.
3. Patients taking immunosuppressive drugs.
4. Patients with a history of neck or head radiotherapy.
5. Patients with bruxism.
4.3 Features of patients with minimally invasive technique of lSFE
The features of patients were collected including (a) sex, (b) age, (c) smoking status, (d) history of periodontitis, (e) sinus membrane thickness, (f) implant sites, (g) pre-surgery residual bone height (RBH), (h) implant system, (i) implant diameter, (j) implant length, (k) initial stability of implants, (l) type of bone graft materials, (m) quantity of bone graft, (n) presence of collagen membrane, (o) length of the implant protruding into the sinus cavity (LIPSC), (p) presence of membrane perforation and (q) the number of lost implants.
4.4 Surgery and prosthetic phase
All surgical procedures were conducted by the same experienced surgeon (X.C., Figure 6). At the beginning of surgery, local anesthesia (primacaine) was administered to the maxillary posterior area. Following crestal and vertical incisions, the mucoperiosteal flap was fully raised to explore the lateral bone of the maxillary sinus. A small rectangular lateral bone window was opened, and the Schneiderian membrane was carefully detached from the sinus floor using a DASK kit (Dentium, Seoul, South Korea). The height and length of the bone window were measured using a periodontal probe. Simultaneously, the implants were placed. The initial stability of the implants was guaranteed in all cases. After implantation, the space between the Schneiderian membrane and the sinus floor was filled with a mixture of autogenous bone and DBBM (Bio-Oss; Geistlich Pharma, Wolhusen, Switzerland) or β-tricalcium phosphate (β-TCP; RTR, Haibo Han, China). A resorbable collagen membrane (Bio-Gide, Geistlich Pharma, Switzerland) was utilized to cover the bone window and implant sites. Mucosal flaps were sutured with 5-0 non-absorbable polypropylene sutures (Prolene; Johnson & Johnson, USA).
Postoperatively, amoxicillin and metronidazole were prescribed three times daily for 7 days. All patients were asked to use a chlorhexidine mouthwash three times a day for 2 weeks. All sutures were removed within 10 to 14 days after surgery.
Six months after surgery, second-stage surgery was performed to replace the closure caps with healing abutments. The final prostheses of the single-ceramic crowns were fabricated. Patients underwent follow-up assessment every 6 months.
2.5 Radiation analysis
All patients in the study were examined with radiation analysis of CBCT (of slice thickness, 0.25 mm) before implant surgery, immediately after implant surgery (T0), 6 months after implant surgery (before second-stage surgery, T1) and at the last follow-up visit (T2). RBH was measured using CBCT images before implant surgery. The distance between the implant platform and the uppermost level of bone graft was defined as BH. BH was measured at five aspects of each implant at T0, T1 and T2: central (BHC), mesial (BHM), and distal (BHD), buccal (BHB), and palatal (BHP) aspects. BHC measurements were made along the central axis of the implant, and BHM, BHD, BHB and BHP analyses were performed along the axis and tangential to each side of the implant, respectively26,30. Radiographic bone gain was calculated by the subtracting BHCT0 and RBH. To analyze the stability of grafted area in the sinus cavity, BH changes from T0 to T1 (ΔBHT0-T1) and from T0 to T2 (ΔBH T0-T2) were used.
2.5 Statistical analysis
All data analyses were performed using Stata software (StataCorp, College Station, TX, USA). All measurement variables were showed as mean ± standard deviation (SD). Significant differences in BH at T0 and T1 and BH at T1 and T2 were assessed by one-way repeated-measures analysis of variance (ANOVA). Pearson correlation analysis was included in the present study to determine any relationships among ΔCBH T0-T1, ΔMBH T0-T1, ΔDBH T0-T1, ΔBBH T0-T1 and ΔPBH T0-T1. The comparison of mean BH changes based on patient characteristics were analyzed using a paired t-test. Multivariate linear regression analysis was used to determine the possible relationship between RBH and ΔBH1. A linear mixed model was adopted to determine the risk factors for ΔBH1. p-values <0.1 were considered statistically significant.