Early marginal bone loss (EMBL) is a non-infective remodeling process of peri-implant crestal bone occurring within the first year after implant insertion. EMBL has a multifactorial etiology, being influenced by various surgical and prosthetic factors, including insufficient crestal width, surgical trauma, biological width formation, microbial colonization of implant-abutment micro-gap, horizontal implant-abutment mismatch ("the platform-switching concept"), the number of abutment connection/disconnections, prosthetic abutment height, design and mechanical stability of implant-abutment connection and adaptive response to occlusal loading.
Biological width formation is the main factor influencing peri-implant marginal bone adaptive processes prior to prosthesis delivery. When an implant gets exposed to the oral cavity, soft tissues establish a cuff-like barrier sealing the trans-epithelial component of the fixture.
Differently from equicrestal and subcrestal implants, which present a microgap between implant and abutment at the marginal bone level, tissue-level implants have no gap at this region.
The present multicenter prospective study aims to evaluate if EMBL occurring around tissue-level dental implants before prosthesis delivery may be reduced by adapting apico-coronal positioning in relation to supracrestal tissue thickness.
All patients are treated according to one-stage implant. Sutures are removed 12-14 days after surgery. No removable prostheses are utilized during the healing period.
Final impressions were taken five months after the implant placement. After functional and aesthetic try-in, a single-unit screw-retained metal ceramic crown is delivered. The fixation screw was torqued to 30Ncm following manufacturer's guidelines. Screw access is then closed using light-cured composite resin.
Radiographic measurements. Digital radiographs, customized for each patient with a bite jig, are taken using a long-cone paralleling technique with a film holder at the time of implant placement (baseline, T0), 3 months after implant placement (T1), and 5 months after implant placement, immediately before impression taking (T2). All radiographs are performed using the same x-ray generator technology, set with the same parameters (60 kV, 7 mA).
Two different types of bone changes are calculated, as suggested elsewhere.
- Early marginal bone loss (EMBL) is calculated.
- Bone Loss Exposing Implant Surface (BLEIS) is calculated as the difference between the EMBL measurement and the 3 mm length of the transmucosal, machined portion of the implant.
Radiographs demonstrating any deformation, darkness and/or other problem are immediately repeated. All measurements are made by a single calibrated examiner, blind to mucosal thickness, using a 30-inch led-backlit color diagnostic display with Kodak Digital Imaging Software. Each measurement is repeated three times at three different time points as proposed by Gomez-Roman and Launer. Intra-examiner and inter-examiner concordances are 96.1% and 90.4%, respectively, for linear measurements within ±0.1mm.
