This retrospective research was conducted under the approval of the Institutional Review Board of Seoul National University Bundang Hospital and independent ethics committees approved the protocol (IRB No. B-2009/637-101) with each participant providing written, informed consent. The study was performed according to the Declaration of Helsinki and the requirements of Good Clinical Practice.
All patients included in this study were adults who planned the computed-guided implant surgery according to the digital guide protocol based on CBCT (0.2-mm voxel size, Kodak 9500, Carestream Health, Inc., Trophy, France) at the Section of Dentistry of Seoul National University Bundang Hospital from December 2018 to January 2020. The inclusion criteria were as follows: (1) patients over 19 years of age; (2) CBCT data before and after implant placement; (3) informed consent from voluntary participants; (4) fabrication of the surgical guide according to the digital guide protocol, and (5) being partial edentulism (≤ 4 teeth loss in one arch). The exclusion criteria were as follows: (1) uncontrolled systemic disease or dentofacial-related syndrome; (2) being full edentulism; (3) related to pathologic conditions such periapical or periodontal abscesses, acute sinusitis, and untreated gingivitis or periodontitis.
Computer-guided implant surgery process
To establish an implant placement plan and create a digital implant guide, there was several steps to follow. First, we sent preoperative CBCT data. Second, a conventional gypsum material dental cast made from polyvinyl siloxane was scanned and imported to the Dentium Digital Center (Dentium, Suwon, Korea). Third. each model was scanned using Rainbow Scanner Prime (Dentium, Suwon, Korea) and superimposed with CBCT data based on the teeth. Fourth, a computer-guided implant plan was developed, including a digital wax-up of the edentulous region and accurate 3D location of the implants (Fig. 1). Based on the plan, finally, the tooth and mucosa supportive surgical guide was fabricated by using a stereolithography (SLA) 3D Printer (Dentium, Suwon, Korea). The manufactured guides were assessed for preoperative fitness in the oral cavity and adjusted as needed.
Patient allocation according to surgical methods
According to the implant surgical procedure, implants that underwent placement according to a digital guide protocol based on the fabricated guide (VAROguide, Dentium, Suwon, Korea) were allocated in the experimental group, and those that could not be placed according to the guide protocol were allocated in the drop-out group. Among the experimental groups, the patients were classified the subgroups into flap and flapless approaches as groups 1 and 2, respectively. Surgery was performed by two expert surgeons (one oral and maxillofacial surgeon and one periodontal surgeon each; experience over 20 years in implant surgery, and over 5 years in the guide system).
Drop-out group: implants placed differently from the planned surgical guide
Although the patients were planned implants based on preoperative CBCT images, some implants could not be accurately placed according to the fabricated guide, or were displaced compared with the planned position mainly due to poor bone quality and insufficient bone volume compared with the CBCT (Fig. 2).
Group 1: implants placed from the fabricated guide according to the flapless approach
A flapless technique was indicated if there was an appropriate amount of attached gingiva, sufficient bucco-lingual alveolar bone width, and residual bone to major anatomical structures, such as the maxillary sinus and inferior alveolar canal. After drilling according to the surgical guide through the guide sleeves, the implants were placed in the planned positions (Fig. 3). The diameter of the implant was chosen from preoperative planning, but the length varied slightly depending on the clinical circumstances.
Group 2: implant placement from the fabricated guide according to the flapped approach
The flapped approach was performed in cases where bone dimension was insufficient, bone augmentation was required, or primary stability was insufficient due to poor bone quality. After creating the incision, a full-thickness mucoperiosteal flap was elevated before fitting of the fabricated surgical guide. The implant was placed by fixation of the surgical guide with fingers. Drilling was performed sequentially according to the manufacturer’s guidelines (Dentium, Suwon, Korea), and the implants were placed until the indentation depth from the guide was reached (Fig. 4). However, the diameters and lengths of the drills were eventually changed depending on primary stability, bone quality, bone dimension, and the positions of the main anatomical structures. If necessary, bone augmentation was performed, and the wound was sutured after being covered with a shielding membrane. Depending on the degree of primary stability, submerged or non-submerged type implants were chosen.
Postoperative care
All patients had postoperative CBCT immediately after the surgery, and were prescribed methylol cephalexin lysinate 500 mg bid for 5–7 days, celecoxib 200 mg bid for 5–7 days, and chlorhexidine (12% hexamedine solution 100 mL, BukwangPharm, Seoul, Korea) or benzydamine (15% Tantum gargle, 100 mL, SamaPharm, Seoul, Korea) oral gargling tid for 5–7 days. Two internal connection type implants with sandblasted, large grit, acid-etched surfaces were used: Superline (Dentium Co., Suwon, Korea) and Implantium (Dentium Co., Suwon, Korea).
Measurements of the primary stability and evaluation of accuracy for the implant position
The primary stability was examined at fixture implantation, and implant stability quotients (ISQ) were measured with an Osstell Mentor device (Osstell, Gothenburg, Sweden) [19].
CBCT data were superimposed before and after the surgeries to evaluate the accuracy of implant positioning among the groups. Any changes in three-dimensional displacement and the angle of implant entrance after placement were evaluated by CBCT. To obtain images of standardized size, CBCT scans were performed at natural head positions using an occlusal plane aligner. A natural head position was obtained in an upright seated position and distanced gazing. CBCT data were extracted as a file of Digital Imaging and Communications in Medicine (DICOM). A 3-dimentional analysis program (OnDemand 3D, Cybermed, Seoul, Korea) was used to compare the preoperative planned location of the implant with the postoperative implant position by the automated registration software [20]. The software was superimposed on the basis of voxels’ gray level within the anterior cranial bases of the two CBCT. The anatomical structure of the anterior skull base was selected on the thalamus and ornamental and horizontal surfaces of the first input DICOM file. After automated superposition, the thalamus surface, tubular surface, and horizontal surface were formed in the tomographic direction of the initial input image [21]. To compare the position of the preoperative planned implant with the actual position of the implant after the operation, differences in the distance of the entry point and in the degree of the insertion angle were measured on the superimposed CBCT (Fig. 5).
SPSS statistics 25.0 (SPSS Inc., Chicago, IL, USA) program was used for statistical analysis, and significance was considered at a level of 0.05. The differences between the entrance displacement and the insertion angle of the planned and placed implants were measured to calculate the mean and standard deviation. Independent sample t-test was used to analyze the difference of the measurements among the groups.