Study design and participants
This non-randomized controlled clinical study included a total of 25 patients (female/male: 3/22; age mean ± standard deviation: 58.69 ± 15.07), recruited at the Department of Oral Surgery and Implantology, Goethe University, Frankfurt, being in need for at least one implant-supported single-tooth restoration in the esthetic zone (i.e., anterior maxilla including teeth 15–25). The patients were candidates for either an immediate implant placement (i.e., type 1) in the presence of a non-retainable tooth (n = 16 implant sites) or a late implant placement (> 4 months after tooth extraction) (i.e., type 4) in the presence of a single-tooth tooth gap (n = 16 implant sites) [7].
Each patient was given a detailed description of the study procedures and signed an informed consent before participation. The study was conducted in accordance with the Helsinki Declaration, as revised in 2013, and was approved by the local ethics committee (N: 19-233). The present study considered the STROBE statement checklist items for its reporting [11].
Inclusion and exclusion criteria
The inclusion criteria for patient selection were the following:
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Patient age ≥ 18 years.
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Mental and physical ability to comprehend the aim, risks, and benefits of the study, and willingness to reliably attend the follow-up appointments.
The exclusion criteria were:
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Uncontrolled systemic diseases that could affect bone remodeling during implant osseointegration or soft tissue healing (e.g., uncontrolled diabetes mellitus [HbA1c > 7], osteoporosis).
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Current use of medications that could affect bone remodeling during implant osseointegration or soft tissue healing (e.g., steroids, antiresorptive medication, radiotherapy).
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Pregnancy or lactation periods.
Surgery and prosthetic protocol treatment procedures
Prior to surgery, all patients were prescribed amoxicillin 1000 mg to be taken three times daily for 7 days, starting 1 day before the surgical intervention. Moreover, patients were instructed to rinse with a 0.2% chlorhexidine mouthwash for 1 min.
All surgical interventions were performed under local anesthesia (Ultracain D-S 1:200.000, Sanofi-Aventis, Germany) by the same experienced oral surgeon (P.P.). In the case of type 1 implant placement, special care was taken to perform a flapless atraumatic tooth extraction. If a root remnant had to be extracted, the Benex system (Helmuth Zepf Medizintechnik GmbH, Seitingen-Oberflacht, Germany) was used. Next, granulation tissue was removed, and the alveolar socket was irrigated with sterile saline, while the integrity of the buccal bone wall was evaluated. Then, the implant site was prepared following the manufacturer’s indications, and the implant was free hand placed directly facing the palatal bone wall in a subcrestally ideal prosthetic position. In the case of type 4 implant placement, a minimally invasive full thickness flap was raised at the edentulous site, followed by a conventional drilling protocol as recommended by the manufacturer. Afterward, the implant was placed subcrestally in an ideal prosthetic position. Whenever bone augmentation was considered necessary, a bovine-derived bone substitute (Geistlich BioOss; Geistlich-Pharma, Wolhunsen, Schwitzerland) mixed with autogenous bone chips, obtained from the implant site preparation, was used for gap filling, or in combination with a resorbable collagen membrane (Geistlich BioGide; Geistlich-Pharma, Wolhusen, Schwitzerland) in the cases presenting buccal bone dehiscences for lateral augmentation. Surgical sites were closed with monofilament PTFE sutures (Cytoplast 5–0; Daikin America Inc.; New York; USA) and a postoperative panoramic radiograph was taken. Patients were instructed to rinse with a 0.2% chlorhexidine mouthwash two times a day for 1 week.
Finally, a temporary or definitive abutment (“One Abutment-One Time”) was placed, accompanied by a non-occlusive temporary crown [12]. Whenever the “One Abutment-One Time” was used, a Scanbody was inserted to detect the implant position by performing an intraoral Scan (3 Shape TRIOS MOVE, Germany). Next, an individually manufactured/milled abutment and provisional crown were fabricated by CAD/CAM and delivered the same day.
Sutures were removed after seven and up to 14 days later. Definitive prosthetic restorations were installed after 3–6 months. Patients were included in a maintenance program and re-evaluated at 6 and 12 months.
Data acquisition and follow-up/clinical assessment
The following clinical parameters were assessed postoperatively during the controls using a periodontal probe (PCP UNC 15 Hu-Friedy Inc., Chicago, Illinois, USA), at baseline, 6, and 12 months:
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Probing depth (PD), defined as the distance from the gingival margin to the bottom of the probing pocket.
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Bleeding and/or suppuration on probing (BOP/SUP), appearing within 30 s after probing.
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Plaque Index (PI), measured as presence or absence of plaque.
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Keratinized mucosa (KM) width, measured from the restoration margin to the mucogingival junction.
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Mucosal recession (MR) of the peri-implant soft tissue, measured from the restoration margin to the mucosal margin.
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Periotest value (PTV), considered as maximum value of implant stability.
PD, BOP/SUP, and PI were assessed at six sites per implant (mesio-buccal, mid-buccal, disto-buccal, mesio-oral, mid-oral and disto-oral) by two calibrated investigators (K.M. and K.O.).
The calibration of the investigators was performed prior to the beginning of the study, for the standardization of data collection and clinical assessment. For each clinical variable, each investigator performed a first measurement, and then repeated the measurement in the same site after 5 min. Calibration was considered successful when the measured values of the repeated measurement procedures matched > 95%. Documentation of demographic study variables, implant site characteristics/features, and clinical measurements were also recorded using a standardized documentation form.
Digital/volumetric analysis
Before the patients received the surgical intervention, a preoperative intraoral scan (S0) was made using an intraoral scanner (3 Shape TRIOS MOVE, Germany GmbH) to provide the baseline scan for the generation of the region of interest (ROI) and to digitally fabricate the provisional crown, in the case of immediate implant loading. Having a previously defined ROI, scans were performed at the follow-ups at 6 (S1) and 12 months (S2) after the surgery. These scans were subsequently exported as STL (standard tessellation language) files and served as a basis for the dynamic analysis of peri-implant soft tissue changes. For this, the scan files of the different timepoints were superimposed using the mesh processing software system MeshLab (Meshlab, ISTI, Italy, 2016). Then, the models were aligned on the CAD model (computer aided design) using at least 8 reproducible anatomical structures, including teeth or prosthetic crowns, and subsequently converted to STL files. These were imported into GOM software (GOM inspect Suite 2020, Zeiss Company, Braunschweig, Germany) for digital measurement and volumetric analysis. By superimposing and comparing the delimited areas within files, changes in the ROI could be quantified. This ROI was defined as follows: apically 4 mm from the highest point of the marginal gingiva, laterally to the center of the papilla of the implant crown, and coronally to the height of the marginal gingiva (Fig. 1). Furthermore, the selected ROI was divided into two equivalent sections (i.e., marginal and apical sections) to represent the areas with the most volume change. This process was applied for a comparison of the CAD models S0–S1, S0–S2, and S1–S2, to show a time-dependent course of the volumetric peri-implant tissue changes (Fig. 2).
All measurements were performed by the same experienced and calibrated examiner (K.M.). Each analysis was conducted in triplicate. Prior to the analysis, an intra-examiner calibration was performed to determine the reproducibility of the measurements. The calibration was accepted when ten repeated measurements presented an intraclass correlation coefficient ranging from 0.81 to 1.
Statistical analysis
The clinical and the intraoral scan measurements were collected pseudonymously in a standardized sheet (Microsoft Excel Version 16.43, Microsoft Corporation, Redmond, USA). Data were expressed as means and standard deviations, whereas nominal data were presented as absolute and relative frequencies. The normal distribution of the data was assessed by the Shapiro-Wilk test. The Mann-Whitney U test was used for independent variables, the Wilcoxon test was used for dependent variables, and the sign test was used for the ordinal data analysis. The categorical or nominal data was assessed by applying the chi-square test or Fischer's exact test. Moreover, the comparison between dichotomized data of the different timepoints was done with the modified chi-square test according to McNemar. Apart from that, a binary logistic regression analysis was performed to investigate any association between dependent binary and independent variables. In addition, a paired T test was performed for the continuous data of the volumetric analysis. A two-sided test of significance was performed for all test procedures, with significance at a p value < 0.05. A statistical software (IBM SPSS Statistics 24.0, IBM Deutschland GmbH, Ehningen, Germany) was used to analyze the compiled data.