This study was conducted according to the guidelines of the ethics committee at the Johann Wolfgang Goethe University in Frankfurt/Main and strictly followed the ethical principles of the World Medical Association Declaration of Helsinki [11]. All patients were informed about the surgical procedure of this study and signed an informed consent.
Patient population
The selection of the patients was made according to the data bank of the surgeon. All the patients were referred to a private clinic and to a department of oral surgery at the university. Patients who suffered from a peri-implantitis and were treated with STG were taken into consideration for this investigation. Patients were contacted by phone to ask for a participation in this study. From 62 patients, 28 agreed to participate in the study. The other 34 patients were either not available by phone or did not agree to participate in the study for personal reasons.
Exclusion criteria
Patients with the following diseases were excluded from this study: untreated diabetes mellitus, pregnancy, bisphosphonate medication, current orthodontic treatment, tumors, and infectious diseases (HIV).
A total of 28 patients (21 females, 7 males, at a mean age 59.4 years) with a total of 54 implants were included. All patients were given a detailed description of the treatment procedures and were required to sign an informed consent form.
There was a total of 20 implants (13 in maxilla, 7 in mandible) in the anterior region (from canine to canine) and 34 implants (20 in maxilla, 14 in mandible) in the posterior region (up to the first premolar).
All implants suffered from peri-implantitis and showed attached keratinized buccal mucosa of ≤2 mm. The definition of peri-implantitis is according to established criteria defined when PPD (pocket probing depth) was >5 mm with or without BOP and with an annual bone loss of >0.2 mm [3]. The assessment of peri-implantitis was carried out 1 year after insertion of the superstructure in this study. The level of bone loss is according to the criteria of Albrektsson et al. [12] and the measurement of bleeding on probing according to the results of the study of Naert et al. [13].
To exclude falsification of a positive diagnosis of peri-implantitis in case of the absence of bleeding on probing in addition to excessive pocket probing depth patients’ discomfort and pain were strict incoming criteria for STG.The following implant systems were used for a treatment before beginning of this retrospective study: 3 × Biomet 3i (Biomet 3i Deutschland GmbH, Munich, Germany), 31 × Ankylos (Dentsply IH GmbH, Mannheim, Germany), 1 × Astra Tech (Dentsply IH GmbH, Mannheim, Germany), 15 × Camlog (Camlog Vertriebs GmbH, Wimsheim, Germany), 3 × IMZ (Friadent, Mannheim, Germany), and 1 × Nobel Replace select (Nobel Biocare Holding AG, Zürich, Switzerland).
Three patients have bar overdentures (all in maxilla), three patients telescoping dentures (one in the maxilla and two in the mandible), and 22 patients fixed prosthesis; 8 of them have single crown restorations.
The average time from the placement of the implants to the soft-tissue grafting was 63.2 ± 44.4 months.
Treatment procedures
Non-surgical procedure
A sub-mucosal ultrasonic curettage with ultrasonic system (Cavitron Ultrasonic scaler® with plastic Scalers, Dentsply, Mannheim, Germany) was made by all patients to reduce the inflammation signs as prerequisite before STG. Furthermore, an antibacterial treatment was made with a sub-mucosal irrigation using hydrogen peroxide 3 % and a local antibiotic application of doxycycline (Ligosan®, Heraeus Kulzer, Hanau, Germany).
If BOP was observed after this non-surgical therapy and during the following 6 months, a surgical treatment in terms of a soft-tissue grafting using onlay or inlay-onlay grafts with respect to the skeletal configuration was conducted. In case of persistent bleeding or other significant peri-implant inflammative symptoms, the protocol prevents, from the ethical point of view, further peri-implant bone loss, excessive antibiotic administration, and occurrence of systemic influence of the pathologic process. To increase comparability and measure reliability, all the baseline measurements used in the statistical analysis were strictly performed after initial phase. All surgical procedures were carried out by one surgeon from 1998–2012.
Surgical procedure
The patient (Fig. 1) was anesthetized using (Ultracain® DS-forte, 1: 100,000, Sanofi-Aventis®, Frankfurt, Germany); then, a vestibular mucosal flap was raised with a preservation of a thin soft-tissue layer on the implant surface.
The thickness of the soft-tissue layer that remained on the implant surface was reduced as much as possible without perforating this layer or exposing the implant surface; for this procedure, microsurgical techniques were used in order to achieve immobility of the transplanted keratinized mucosa.
After decontamination of the exposed implant surfaces with 37 % phosphoric acid gel (Orbis Handels-GmbH, Münster, Germany), an onlay graft was inserted (Figs. 2 and 3). In cases with highly esthetic sensitive areas, an inlay-onlay graft was used, which had, in addition to the keratinized Onlay part, a sub-epithelial connective tissue part to about 50 % [14–16]. In contrast to inlay-onlay graft, an onlay graft consists only of keratinized mucosa with a thickness of approximately 1 mm harvested from palate as well.
The grafts were harvested from the palate in the region between the first premolars and second molars. The desire extension and shape of the graft was transferred with the help of a simple, tailored paper template before graft preparation from the palate, so that it fits exactly into the previously prepared peri-implant defect and thus accurately simulated the needed amount of keratinized mucosa. The appropriate connective tissue grafts were harvested by placing the template on the palate. The grafts’ sizes were of 5–7 mm width and 7–20 mm length.
The graft was degreased with a micro scissor, and then reduced with a scalpel to about 1 mm and after that fixed on the peri-implant lesion in a stable position using non-absorbable size 5–0 and 6–0 mono sutures.
In case of crater- shaped peri-implant defects, circular soft-tissue grafts were placed improving soft-tissue quality and quantity after severe peri-implant infections with BOP and massive suppuration. Because of diminished possibility of STG fixation especially in the lower jaw, onlay grafts were buried with help of deep bucco-lingual sutures and healing abutments in the immediate postoperative period until suture removal. (Figs. 4, 5, 6, 7, 8, 9, and 10)
The palatal donor site was covered with a preoperative custom-made (0.5 mm) plastic surgical bandage.
In all patients, a postoperatively systematic antibiotic medication 3000 mg per day (1000 mg Amoxicillin Ratiopharm, Ratiopharm GmbH, Ulm, Germany) was administrated for 7 days.
To reduce postoperative wound swelling and accompanying postoperative pain, a glucocorticoid was infiltrated sub-mucosal at the vestibular region (Dexabene® 4 mg/ml, Merckle Recordati-KGaA, Darmstadt, Germany).
As analgesic treatment, all patients were given ibuprofen (IBU-ratiopharm 400 acute, Ratiopharm GmbH, Ulm, Germany). The surgical bandage and the suturing were removed after 7 to 10 days.
Clinical parameters
The first clinical examination was carried out after initial anti-infective treatment before surgery (baseline), and the second one was made after a period of 9–180 months (Ø 43 months). In each clinical examination, the following parameters were assessed: the soft-tissue biotype, the skeletal biotype was classified, width and mobility of keratinized mucosa (KM), pocket probing depth (PPD), and bleeding on probing (BOP) as well.
The soft-tissue biotype was determined prior to the STG [17]. Differences were made between thick biotype and thin biotype. During this investigation, the transparency of the mucosa specified the suitable category when the periodontal probe was inserted into the sulcus. The probe was inserted vestibularly into the midpoint of the sulcus of an existing adjacent tooth (preferably at the maxillary central incisor), and by translucency, it was characterized as a thin biotype. A thick biotype was characterized if color impermeability through the mucosa was recognized.
Furthermore, the basic skeletal morphology of the alveolar bone was determined based on the classification of Cawood and Howell [18]. This was manually detected at the mandibular symphysis with a dental caliper (Caliper according to Beerendonk®, DCV instruments Seitingen-Oberflacht, Germany).
A classification as a broad apical base was made when the thickness of the jaw at the apical region in oral-vestibular direction was bigger than the thickness of the jaw at the marginal area of a natural tooth. A middle base was classified, when the thickness of the jaw had the same dimension at the two regions mentioned above and when the jaw at the apical region was thinner than it was at the marginal region of a natural tooth, then it was classified as narrow. If the mandibular symphysis was edentulous, the detection of skeletal biotype was performed at the maxillary anterior region. A schematic overview of various exemplary forms of the apical bases in the symphysis region is shown in Fig. 11.
After staining of the soft tissue using the Schiller iodine solution [19], the width of the KM at each implant was measured using a periodontal probe at midpoint of the vestibular surface.
The mobility of the KM was detected using the long side of the periodontal probe by vertical movement with slight pressure. According to the mobility of the mucosa, it was classified as “movable” or as “immovable”. The worst value per implant and transplant was recorded, and in cases of more than one implant per patient, the worst value was recorded.
The PPD measurements were performed using a periodontal probe (PCP10, Hu-Friedy®, Rotterdam, Netherlands) with 25 N/mm force application on the four surfaces (mesial, distal, buccal/vestibular, and palatal/lingual). To ensure the evaluation in cases of unclear PPD values, the superstructures were removed, and PPD was measured. In patients with more than one implant, the worst PPD value was recorded.
The BOP measurements were made on four surfaces (mesial, distal, buccal/vestibular, and lingual/palatal) using the modified sulcus bleeding index by Lange et al. [20].
In addition, the suppuration was detected. The worst value per implant was recorded, and in cases of more than one implant per patient, the worst value was noted.
Follow-up
Nine to one-hundred eighty months after STG, the following clinical parameters were assessed again: width and mobility of keratinized mucosa (KM), pocket probing depth (PPD), bleeding on probing (BOP), and suppuration (pos./neg.). All the patients enrolled in a regular maintenance program during the follow-up period.
Statistical analysis
Collected data were documented anonymously using the Excel program (Microsoft©) and assessed using the statistical program SPSS 16.0 (SPSS Inc., Chicago, Illinois, USA).
For group comparisons and paired comparisons, paired t tests were applied with an error probability limit of 0.05. A linear regression analysis was performed as well.
