Case selection
This single-center retrospective cohort study was conducted from April to October 2017. A total of 39 patients (20 female, 19 male) between 49 and 83 years underwent treatment in the dental clinic OPUS DC in Ulm (Germany) from 2008 to 2011. Forty-nine lower and/or upper jaws of the 39 patients were included in the study. However, 13 patients refused to participate in the study or were lost to follow-up. Three patients died before the evaluation. This study therefore included a total of 170 dental implants in 32 restored edentulous jaws in 23 patients. The patients were followed up from the start of treatment with a minimum period of 6 years in order to detect long-term implant success rates. Only patients receiving four to six dental blueSKY© implants (bredent GmbH & Co. KG, Senden, Germany) in the upper and/or lower jaw with immediate loading by a resin bridge were included in the study. Exclusion criteria included the absence of immediately fixed loading due to a lack of primary implant stability (< 30 N*cm bone insertion torque) and therefore immediately removable loading with a temporary denture after surgery and secondary fixed prosthodontic restoration. Restorations in partially edentulous jaws were also excluded from the study. Final restoration was performed after a 3 to 6 months healing period. Regularly scheduled PTC sessions happened at least twice a year postoperatively. These sessions included a basic periodontal examination, a yearly radiographic examination with a panoramic x-ray, and a professional teeth cleaning. All participating patients also completed a yearly health questionnaire. Special attention was paid to possible risk factors such as nicotine abuse, osteoporosis, and diabetes mellitus.
Surgical protocol
All patients underwent the same surgical procedure following the “fast&fixed” protocol (bredent GmbH & Co. KG, Senden, Germany). Extraction of teeth and smoothing of bony surfaces was performed, if required, before implanting four to six dental implants. Implants in the premolar region were inserted with distal angulation to avoid sinus floor augmentations. In the premolar region of the lower jaw, implants were inserted with distal angulation to avoid damage to the mental nerve. Only implants with sufficient primary stability can be used for this protocol. Therefore, the stability of the implant was tested by the surgeon during and after insertion. The muco-periosteal flap was closed around the positioned impression copings.
Prosthodontic protocol
After the surgical procedure, a polyether impression (Impregum©, 3 M Deutschland GmbH, Neuss, Germany) was taken, and a plaster model for the dental technician was produced. The clinician chose the definitive abutments, which compensated for the tilted implant axis, and the dental technician then created a full arch resin bridge, which was screwed in directly after manufacturing (time range from 120 min for one to 150 min for both jaws). This temporary full-arch bridge provided sufficient fixed prosthodontic restoration during a healing period of at least 3 months. Postoperative follow-up visits were scheduled closely at day 2, 7, 14, and then at least monthly until definitive restoration.
Examination protocol
Besides the clinical examination, risk factors such as nicotine abuse, osteoporosis, diabetes mellitus, and periodontitis prior to treatment, were determined. Individual patient risk factors were recorded in their records. Detection of caries in the opposite jaw, damage or loosening of the prosthetic restoration, sensitivity probe, percussion probe, and mucosal irritations were also recorded. To avoid damaging of the peri-implant tissue and to record reliable values, a 4-point periodontal chart around every implant was recorded in millimeters with a calibrated probe (Click-Probe©, calibrated to 0, 2–0, 25 N, KerrHawe SA, Bioggio, Switzerland). The bone level around the implants was determined by evaluating postoperative and follow-up panoramic x-rays. Additionally, the angulation of the implants was also measured. Five intraoral photographs of every jaw were taken (frontal, occlusal maxilla and mandibula, lateral left, and lateral right). Plaster models of the upper and lower jaw were created, to record the present situation, e.g., prosthetic failures.
Data extraction and outcome measurements
All data was retrieved from medical records and from the follow-up clinical examination. The data was anonymised in accordance with the World Medical Association Declaration of Helsinki (64th WMA General Assembly, October 2013).The approval of the Ethics Committee of the Landesärztekammer Baden-Württemberg was obtained (AZ F-2017-014-z). The clinical success of the implants was assessed, after a minimum period of 6 years, by comparing the radiographic bone level next to the implant and periodontal examinations of bleeding on probing.
Statistical analysis
Parameters like gender, nicotine abuse, diabetes mellitus, osteoporosis, periodontitis preoperatively, bleeding on probing, angulation of implants, and keratinized gingiva were nominally scaled. All were described as absolute or percentage values. Two parameters were opposed in contingency tables to enable the chi-squared test for correlation. Fisher’s exact test was applied in cases of low-expected frequency. Quantitative parameters such as age, number of remaining teeth before treatment, and probing depths were described as means with standard deviation, minimum and maximum as well as quartiles. The Shapiro Wilk Test was applied to test for the normal distribution. The U test was applied to assess the correlation between two independent samples which were not normally distributed. Two-sided P values < 0.05 were considered statistically significant. No adjustments for multiple testing were performed; the results are more descriptive and explorative. All analysis was conducted using IBM SPSS Statistics 25 (SPSS Inc. an IBM Company, Chicago, IL).