Patients
Twenty patients were included in this prospective clinical study. Patients were recruited following registration of the study with the German Clinical Trials Register (DRKS-ID: DRKS000018939) and approval by the responsible ethics committee of the State Medical Association of Baden-Württemberg, Germany (Application No.: F2019-057-z). Implants were placed during the period from February 2020 to July 2020. Patients’ data were collected in the practice of PD Dr. Schnutenhaus in Hilzingen (cooperating partner of the Clinic for Dental Prosthetics, Ulm University Hospital). In cases where multiple implants were to be placed in a patient, a test implant was specified to maintain independent values. After planning the position and number of implants, the test implant was determined preoperatively by randomization using the randomization function in Excel (Microsoft Corporation, Redmond, WA, USA).
The following criteria were formulated for inclusion in the study:
Inclusion criteria:
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Submission of written informed consent
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Restoration of at least one missing tooth using an implant
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At least five residual teeth in the affected jaw
Exclusion criteria:
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People under 18 years or people without legal capacity
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Use of a template for implant placement is not possible (restricted mouth opening)
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Necessary additional augmentation requirements
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Heavy smoker (> 10 cigarettes/day)
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Immediate implant placements
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Intake of bisphosphonates
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Pregnant women
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Alcohol and/or drug abuse
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Patients with infectious diseases, such as hepatitis, HIV, or AIDS
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Poorly controlled diabetes mellitus
Planning
After obtaining written informed consent from the patients, cone beam computed tomography (CBCT) was performed (Gendex CB500, Gendex Dental Systems. Des Plaines, USA). The image was acquired with a constant 0.2 voxel resolution. For implant planning, an alginate impression of the concerned jaw was made to fabricate a diagnostic plaster model for each patient followed by a prosthetic wax-up, which was then optically scanned (3Shape Scanner D 700 3Shape A/S, Copenhagen, Denmark). The 3D implant planning was performed with the implant planning software SMOP (Swissmeda AG, Baar, Switzerland). This made it possible to overlay the CBCT data with the standard tessellation language (STL) data sets of the patient models using the corresponding program function of the planning software. The optimal implant position was determined based on the information regarding the availability of bone, planned prosthetic restoration, and condition of the soft tissues. This implant planning was then saved as an interface data record. Using this plan, the optimal implant position was defined. All planning steps and the subsequent implant placement were performed by the same practitioner (SiS). Based on this plan, a drilling template was designed by an external service center (Camlog Dedicam, Wimsheim, Germany). The design data of the drilling templates were then sent to the dental laboratory in the clinic. For the fabrication of the drilling template, it was stipulated that tooth-support had to be carried out. All drilling templates were fabricated by the same dental technician using a 3D printer (Version 3, Formlabs Inc., Somerville, MA, USA). The templates were cleaned and post-cured according to the manufacturer’s instructions. After inserting the respective drill sleeves, the templates were sterilized in the steam sterilizer and made available to the surgeon in a shrink-wrapped condition.
Implantation
All implants were placed by an experienced surgeon (SiS). Surgical procedures were performed with local anesthesia. After elevating the mucoperiosteal flap, the implant bed was prepared according to the manufacturer’s protocol. To reduce other influencing factors, the procedure was completely template-guided, including the insertion of implant.
Registration of the implant position
All implants were provided with fixed dentures. For prosthetic restoration, the clinical situation was recorded three months (± 2 weeks) post-implantation using an individual tray, impression post, and addition silicone impression material (imprint Quick, 3 M Espe, Seefeld, Germany). All impressions were made by one operator (SiS). After disinfection, the impression was transferred to a plaster model by a dental technician. The impression post was then supplemented with a screwed-on analogous implant and the impression was digitized (3Shape Scanner D 700, 3Shape A/S, Copenhagen, Denmark).
Overlay data sets were created using the Geomagic Studio program (Version 9, Geomagic, NC, USA). All data were consecutively analyzed in terms of location and time by an investigator, regardless of their generation. The data records of the digitized implant impressions were exported as interface files in STL format. The latter represented the clinically achieved implant position. The 3D interface dataset of the implant planning exported from the planning program (SMOP) served as the reference data set.
Data sets were reduced to a defined structure, the unchangeable hard tooth substance, in order to exclude errors due to soft tissue changes or deviating implant positions.
For the planned analysis of the distance and angle deviations, the use of auxiliary constructs was necessary, which reflected the exact planned position of the implant and the clinically achieved implant position. It was created with the aid of the Surfacer 10.6 program (Imageware, Ann Arbor, MI, USA) using simple geometric shapes. The auxiliary constructs were adapted to the respective implant lengths and diameters and then loaded into the Geomagic Studio program for assignment. Thus, it could be ensured that the axis end points and the axis deviation of the implant positions could be determined in a standardized manner for further analysis. This methodology has already been extensively used and described by Schnutenhaus et al. [28].
The assigned auxiliary constructs, which reproduced the key data of the 3D information of the planned and clinically achieved implant position, were loaded into the Surfacer 10.6 Imageware program for further analysis.
Analysis of the implant position
The metric analysis included the following measurements (Fig. 1):
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Three-dimensional deviation: the 3D deviation of the midpoints between the planned implant position and clinically achieved implant position, measured at the implant shoulder and apex (corresponding to the Euclidean distance).
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Apicocoronal deviation (height difference): vertical spatial offset measured at the center of the implant shoulder.
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Axis deviation: angular deviation of the implant axes from planned and clinically achieved implant position.
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Two-dimensional (2D) deviation in the mesiodistal and buccolingual directions measured at the implant shoulder and axis.
The measurement method was based on the principle of Tahmaseb et al. [29] to enable better comparability with current and future studies.
Comparison group
The test implant (Conelog ProgressiveLine, Camlog Wimsheim, Germany) had a pronounced conical outer geometry. The present study compared the influence of the external geometry with a more cylindrical implant body (Conelog ScrewLine, Camlog, Wimsheim, Germany) (Fig. 2).
The data of the comparison group was extracted from a previous study [25].
Power calculation
Since there was no available data from studies on the influence of different macro designs of implants on accuracy, the power analysis was performed from our own data on the influence of different drilling templates, to estimate the sample size [28, 30]. The minimum required sample size of 9–15 implants according to the platform, apex, and angle deviation was calculated using a statistical software (G*Power software version 3.1. Erdfelder, Faul & Buchner, 1986) for the Mann-Whitney U test with 80% of study power and a significance level (α) of 0.05.
Statistical analysis
The mean values, standard deviations, 95% confidence intervals, and the minimum and maximum values were provided for the variables. After testing for normal distribution, statistical testing was performed. For values that were normally distributed, a t test was performed for the mean values in independent random samples to compare the planned and achieved implant positions. If the values were not normally distributed, the Mann-Whitney U test was performed.
A p value of < 0.05 was considered statistically significant. Statistical analysis was performed using IBM SPSS® Statistics Version 26.