Patient selection
Patients aged 18+ who required an implant in the posterior mandible were eligible for this study.
Exclusion criteria were the following:
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general contraindications to implant surgery
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insufficient oral hygiene and periodontitis
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patients with a history of severe periodontitis
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bone augmentation required
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smokers
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substance abuse
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uncontrolled diabetes
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severe cardiovascular problems
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treated or under treatment with intravenous amino-bisphosphonates
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pregnant or lactating.
The study was conducted in accordance with the standards of the Declaration of Helsinki of 1983 and was approved by the ethics committee of the FEKI (Freiburger Ethik-Kommission International, Feki Code: 014/1210). All 40 recruited patients were informed about the design and aim of this study, and written consent was obtained. The randomization to control group (n = 20) and test group (n = 20) was achieved using a sealed envelope system at time of surgery.
Clinical procedure
All patients had to undergo a professional dental hygiene treatment in advance. One hour prior to surgery, patients were given an antibiotic single shot prophylaxis (600 mg clindamycin). PRF was obtained from each patient of test and control groups and treated according to the PRF protocol with an IntraSpin™ table centrifuge and collection kits provided by Botiss (Zossen, Germany).
After anesthesia with Ultracain® DS-forte (articaine + adrenaline 1:100,000), crestal, lingual, and buccal tissue thickness was tested using an endodontic micro-spreader (Spreader ISO 30, Dentsply Maillefer®) with a silicon stop (illustration 1). The instrument part penetrating the soft tissue was measured with an endodontic longimeter. Measured data was rounded off to the nearest half millimeter (mm).
The initial preparation of the split-flap was carried out the same way in test and control groups using microsurgical instruments. After a crestal incision with a microsurgical blade (SM69, Swann Morton LTD®, Sheffield, England), the split-thickness flap was sharply prepared by elevating the area of the single tooth gap to the middle of the adjacent teeth. The periosteum was split to receive a tension-free adaption of the flaps (illustration 2). Fully threaded titanium implants (Nobel Speedy Replace®, Nobel Biocare, Zurich, Switzerland) were inserted at bone level with primary stability. The implants varied in diameter (narrow platform 3.5 mm, regular platform 4.0 mm, wide platform 5.0 mm) and in length (10 mm, 11.5 mm, 13 mm) (illustrations 3, 4, and 5). For the further procedure, patients were now randomized by a dental assistant using a sealed envelope system. In the test group, the tissue was augmented with a PRF membrane using a double-layered technique. In the control group, the implant treatment was realized without mucosa thickening (illustrations 6 and 7). Flaps were sutured with a non-absorbable polyvinylidene fluoride suture (Seralene®, Serag Wiessner, Naila, Germany) (illustration 8).
After the implantation, standardized digital X-rays were taken with parallel technique (baseline) (illustration 9). For each patient, an individual customized digital film holder was fabricated to ensure a reproducible radiographic analysis. Patients were instructed to avoid chewing hard nutrition in the treated area and to use chlorhexidine mouthwash and a soft brush twice a day for the first 2 weeks. Sutures were removed after 7 to 10 days.
Three months later, a second measurement of crestal, buccal, and lingual tissue thickness and intraoral radiographs were carried out as mentioned above. A small mid-crestal incision was made and cover screws were replaced by healing abutments. Due to the minimal invasive reentry procedure, no sutures were needed. Within the following 2 weeks, one-piece, screwed, full ceramic crowns were inserted as definite restorations (IPS Emax®, Ivoclar Vivadent, Schaan, Liechtenstein; composite: Multilink Implant®, Ivoclar Vivadent, Schaan, Liechtenstein) (illustration 10). In a 6-month follow-up from baseline, patients were recalled for maintenance and another digital X-ray was taken.
Radiographic assessments
The evaluation of the peri-implant bone remodeling was carried out by an independent examiner, who was not involved in the surgical process. Bone loss at the mesial and distal side of each implant was measured with an image analysis software (Kodak dental imaging software, version 6.13.0, 2013). A calibration of length measurement was performed in every radiograph to avoid radiographic distortion (reference value - implant length and width).
Statistical analysis
Data of 31 patients (10 patients of test group and 21 patients of control group) were analyzed with STATISTICA (version 9.1, StatSoft, Inc., Tulsa, USA) and BiAS (version 10.11, Epsilon, Frankfurt, Germany). No data points were missing.
The analysis focused on the following aspects:
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Comparison of tissue thickness (crestal, buccal, lingual) at baseline and 3-month data in test and control groups
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Comparison of tissue gain/loss between test and control groups
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Comparison of mesial and distal bone level at baseline, 3-month and 6-month data in test and control groups
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Comparison of bone level alterations between test and control groups.
Data were expressed as means ± standard deviation. Comparisons were made using the Wilcoxon test, the Mann–Whitney U test, and the multiple comparisons test by Schaich-Hamerle (p = 0.05).