Experimental design
This study was a prospective randomized clinical trial to compare the discrepancy between the planned and actual implant positions in immediate implant placement following a static or dynamic CAIS. This study was conducted following the CONSORT statements. The CONSORT flowchart is shown in Fig. 1. The primary outcomes were the global deviation at the entry and apex points and the angular deviation between the planned and actual implant positions. The secondary outcomes assessed the implant placement deviation in mesial–distal, labial–palatal, and coronal–apical directions. This study was approved by the ethical committee of West China Hospital of Stomatology, Sichuan University (WCHSIRB-D-2021-540) and was registered in the Chinese Clinical Trial Registry database (ChiCTR2200056321). Informed consent from all patients enrolled was acquired following the principles of the Declaration of Helsinki. This study was conducted at the Department of Oral Implantology, West China Hospital of Stomatology.
Patient selection
Between February 2022 and October 2022, 40 patients were recruited for this study who fulfilled the eligibility criteria. The inclusion criteria were as follows:
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An age of at least 18 years.
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The maxillary esthetic single tooth sites (13–23) could not be retained due to trauma, endodontic failure, root fracture, root resorption.
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Intact socket walls.
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The absence of acute infection at the site.
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Sufficient apical bone to allow implant placement with Insertion torque 25–40 Ncm [15].
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The length of the implant has at least 3–5 mm in contact with the alveolar bone.
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Good general health.
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Good oral hygiene status determined by plaque index < 10% [16].
The exclusion criteria were as follows:
Sample calculation
For the determination of sample size, the following calculation was based on the mean deviations at the implant platform between the static group and dynamic group reported in previous studies (0.73 ± 0.10 mm vs. 1.05 ± 0.44 mm) [12, 17]. The significance level (α) was set at 0.05, and the power (1 − β) was set at 0.80. The minimum required sample size resulted in 20 for each treatment group calculated by G*Power software (Version 3.1.9.7).
Randomization
Blocked randomization was conducted using a computer-generated permuted block of four (IBM SPSS Statistics, 20.0; SPSS Inc., Chicago, USA). The allocation was concealed utilizing sealed opaque envelopes by an investigator not involved in the following surgeries and evaluations. Patients were randomly divided into static and dynamic CAIS groups. The blinding of participants and surgeons was not possible during the treatment delivery, while the outcome examiner was blinded to the grouping allocation.
Preoperative virtual implant planning
The whole prosthetic-driven implant treatment was designed through a digital workflow. Preoperative cone beam computed tomography (CBCT) scan (J. Morita Inc., Kyoto, Japan) was performed at standardized settings (90 kV, 5 mA, 0.25 × 0.25 × 0.25 mm voxel size, 10 × 10 cm FOV) for every patient. For the dynamic group, a U-shaped registration device with radiopaque fiducial markers covering the surgical site was attached to the dentition during the scan procedure. The intraoral scan (3Shape, Copenhagen, Denmark) was performed, and the following prosthetic restoration was virtually designed by Exocad DentalCAD software (exocad GmbH, Darmstadt, Germany). The digital imaging and communication in medicine (DICOM) data from the CBCT scan were imported in implant planning software, either NobelClinician software (Nobel-Biocare, Kloten, Switzerland) for static CAIS group or dynamic navigation system (Digital-care, Suzhou Digital-health Care Ltd) for dynamic CAIS group. After segmentation and 3-dimension model construction of the surgical site matched with the prosthetic design stereolithography (STL) file, ideal implant positioning was planned based on the prosthetic-driven design concept and biological principles as follows:
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The mesial–distal dimension: The implant was at the midpoint of the mesial–distal restoration width and kept a safe distance of at least 2 mm from adjacent teeth.
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The labia–palatal dimension: The implant was placed in a palatal position, and a gap of at least 2 mm was preserved between the implant and the labial bone filled with a bone substitute.
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The coronal–apical dimension: The implant platform was at 3 mm apical to the bottom point of the ideal labial emergence. The implant screw hole was oriented towards the cingulum of the designed crown.
For the static CAIS group, the teeth-supported stereolithographic fully guided surgical template was manufactured (Surgical Guide UV, HeyGears Inc.). All preoperative implant planning was performed by one experienced surgeon (ZYS).
Surgical protocol
All surgeries were performed by an experienced implant surgeon (XMY) who was familiar with both static and dynamic CAIS systems. The surgical procedures are presented in Figs. 2 and 3. After minimally invasive tooth extraction, each alveolar socket was thoroughly debrided and rinsed. The osteotomy preparation and tapered-implant insertion were performed according to the standardized fully guided protocol for each group (NobelActive, Nobel Biocare, Goteborg, Sweden; Bone Level Tapered, Straumann, Waldenburg, Switzerland). The osteotomies were prepared based on the manufacturer standard protocol. Once the insertion torque reached 35 Ncm or more, a pre-fabricated provisional crown was screwed to the implant using a temporary abutment. Submerged healing was applied if the primary stability failed to meet the requirement. The buccal gap was filled with the bone substitute material (Bio-oss, Geistlich, Inc., Bern, Switzerland). The postoperative CBCT was scanned with the same settings as the preoperative one.
Static CAIS group
Upon verifying the correctly intraoral position, the anchor pin was inserted to confirm the fit and stability of the surgical template in situ. The osteotomy preparation was based on the drill sequence following the fully guided surgery protocol. For each drill, the corresponding drill stop was related to the depth of the borehole. After the preparation of the borehole, the implant was installed with the complete guidance of the surgical template in situ. During the operation, copious irrigation and an “in-an-out” drilling motion were inevitably required to avoid overheating.
Dynamic CAIS group
Prior to the surgery, calibration was performed by mapping the calibration long and short ball drills to the body of the reference frame to determine the relationship between the geometry of the surgical site and the axis of the drill. The reference frame was retained to the dentition by flowable bis-acryl composite resin (Cool Temp Natural, Coltène). Then registration procedure was performed by locating the short drill tip to the fiducial markers attached to the U-shaped template to provide a link between the preoperative planning coordinate system and a real-time intraoperative coordinate system. An infrared tracking camera was set to detect the movement of the handpiece and the patient. Once completed, the U-shaped template was removed. Preparation of the borehole and the insertion of the implant were conducted under the guidance of the dynamic navigation system (Dcarer, Suzhou, China). A calibration of every drill before motoring was performed by positioning the tip of the drill to the cusp of the adjacent teeth. The surgeon examined the position of drills oriented in accordance with the 3D images on the monitor.
Deviation measurement
The postoperative assessment was performed by one examiner (YZF). The preoperative plan was imported into Mimics software (Materialise NV 2018, Version 21.0). The planned implant position was determined, and a mask of the maxilla was created. A three-dimensional reconstruction calculated from the bone mask was exported as an STL file (colored in yellow). These steps were repeated to create the bone mask and the placed implant from the postoperative CBCT scan (colored in red). Therefore, a link between the two coordinate systems of two CBCT scans was established by matching residual dentition and bone anatomical landmarks throughout surface registration. The space relationship between the planned and placed implants was determined through the maxilla bone in the preoperative and postoperative CBCT data. Then, a mask of the placed implant was created in the postoperative data. The contour of the implant was derived from the mask and registered to the corresponding typical implant engineering STL document for measurement (outlined in red). Afterwards, following the bone data, the planned implant position (colored in yellow) and the placed implant position (colored in red) were exported as a separate STL file, respectively, and imported into 3-matic Medical software (Materialise NV 2018, Version 13.0) for deviation measurement (Fig. 4).
Deviations between corresponding planned and placed implants were measured. The primary outcomes were according to the following parameters (Fig. 5):
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Global entry deviation: The linear 3-dimensional displacement between planned and actual implants, measuring at the center point of the implant platform.
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Global apex deviation: The linear 3-dimensional displacement between planned and actual implants, measuring at the center point of the implant apex.
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Angular deviation: The deviation between the central axis of the planned and actual implants.
The secondary outcomes assessed the implant placement deviation in mesial–distal, labial–palatal, and coronal–apical directions. The measurement results could be analyzed for the vector of deviations.
Statistical analysis
One independent investigator conducted the data analysis using the Statistical software program (IBM SPSS Statistics, 20.0; SPSS Inc., Chicago, USA). The categorical variables were expressed in frequency and percentage and analyzed by Chi-square test to test group differences. The continuous data were presented as means ± standard deviations (SD). After verifying the normality assumption with the Shapiro–Wilk test and assessing the equality of variance with the F test, the Student’s two sample t-tests were used to determine the differences when data met normality and variance homogeneity requirements. When the distribution was not normal, the Mann–Whitney U tests were performed. The significance level α was set at p < 0.05.