The present cross-sectional analysis included 232 partially or fully edentulous patients (134 females and 98 males) exhibiting 574 implants (Ankylos®, DENTSPLY Implants Manufacturing GmbH, Mannheim, Germany). All implants were placed in the Department of Oral Surgery and Implantology, Goethe University, Frankfurt, following a standardized treatment protocol. Each patient had received a detailed description of the procedure, and an informed consent form was obtained prior to participation. The procedures in this study were in accordance with the Declaration of Helsinki, as revised in 2013, and the study protocol was approved by the local ethics committee (registration number 78/18).
Patient selection criteria
The following inclusion criteria were applied for patient selection:
Patients with > 18 years of age rehabilitated with at least one Ankylos® implant;
Patients with treated chronic periodontitis and regular maintenance care;
Non-smokers, smokers, and former smokers;
A good level of oral hygiene as evidenced by a plaque index (PI) < 1 at the implant level;
Attendance of a yearly routine implant maintenance appointment.
Patients were excluded for the following conditions: systemic diseases that could influence the outcome of the therapy, such as diabetes (HbA1c < 7), osteoporosis; a history of malignancy, radiotherapy, chemotherapy, immunodeficiency, or antiresorptive therapy; and pregnancy or lactation at the last follow-up.
Two-piece platform-switched implants (Ankylos®, Dentsply Implants Manufacturing GmbH, Mannheim, Germany) were placed in a prosthetically ideal position and, according to the manufacturer’s surgical protocol, considering a subcrestal positioning of the implant shoulder. Implants in the control group displayed an intact vestibular alveolar bone wall without the need for a lateral bone grafting procedure. Implants in the test group exhibited dehiscence-type defects at the vestibular aspect, which were simultaneously filled with a particulated bovine bone mineral (Bio-Oss spongiosa granules sized 0.25–1 mm, Geistlich, Wolhusen, Switzerland) and covered by a native collagen membrane (Bio-Gide, Geistlich, Wolhusen, Switzerland). While control sites were left to heal in a transmucosal position, all test sites were submerged for a healing period of 4 to 6 months. The implants in both test and control groups were mainly restored with fixed cemented (control 273; test 264) crowns (control 188; test 190) and bridges (control 68; test 59). Screw-retained (control 9; test 25), telescopic (control 5; test 4), and removable restorations (control 0; test 22) were less frequent.
Implant and implant-site characteristics
The following study variables were assessed for both test and control implants:
(1) Implant age (i.e., defined as time after implant placement), (2) implant location (i.e., upper or lower jaw, anterior (i.e., canine to canine) or posterior (i.e., premolar and molar region) segments), and (3) implant diameter.
The following clinical parameters were registered at each implant site using a conventional periodontal probe:
(1) Modified plaque index (mPI) (Löe et al.) , (2) bleeding on probing (BOP)—measured as presence/absence, (3) probing depth (PD)—measured from the mucosal margin to the probable pocket, (4) mucosal recession (MR)—measured from the restoration margin to the mucosal margin, and (5) keratinized mucosa (KM) (mm).
Modified PI, BOP, PD, and MR measurements were performed at six sites per implant: mesiobuccal (mb), midbuccal (b), distobuccal (db), mesiooral (mo), midoral (o), and distooral (do). KM measurement was performed at three aspects per implant: mesiobuccal (mb), midbuccal (b), and distobuccal (db).
The presence of peri-implant disease at each implant site was assessed according to established case definitions :
Peri-implant mucositis defined as the presence of BOP and/or suppuration with on gentle probing with or without increased PDs compared to previous examinations, and an absence of bone loss beyond crestal bone level changes resulting from initial bone remodeling.
Peri-implantitis defined as the presence of BOP and/or suppuration on gentle probing, increased PDs compared to previous examination, and the presence of bone loss beyond crestal bone level changes resulting from initial bone remodeling.
When clinical signs suggested the presence of peri-implant tissue inflammation, panoramic radiographs were assessed. To evaluate the bone-level changes at the implant sites, the obtained radiographs were compared with the baseline situation (i.e., radiographs taken following the placement of the final prosthetic reconstruction). After digitalization of the radiographs (Microtek ScanMaker i800 Plus, Hsinchu, Taiwan; LaserSoft Imaging AG, Kiel, Germany), measurements (i.e., bone-level changes between the baseline and follow-up radiographs) were performed employing the Sidexis XG software (Sirona Dental Systems GmbH, Bensheim, Germany). The measurement scale was based on the known implant height. Two reference horizontal lines were used: one marked the most coronal point of the peri-implant bone crest at mesial and distal sites (BC), and another traced the implant’s most apical point (AP). Vertical lines parallel to the reference line crossing the long axis of the implant were traced perpendicularly to the BC and AP at mesial and distal sites.
The statistical analysis was performed using a commercially available software program (SPSSStatistics 26.0: IBM Corp., Ehningen, Germany). Descriptive statistics (means, standard deviations, medians, and 95% confidence intervals) were calculated for mPI, BOP, PD, and MR values. The analysis was performed at the patient and implant levels. The data were tested for normality by means of the Shapiro-Wilk test. Between-group comparisons of clinical outcomes were accomplished using the unpaired t test. Logistic regression analyses based on the implant-level data were used to depict relationships between BOP, PD, or MR values and the following variables: implant location (anterior/posterior), diameter (< 4.5/≥ 4.5 mm), and KM (< 2/≥ 2 mm). The alpha error was set at 0.05.