Apico-coronal Position of Tissue-level Implants Bone Stability

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.

1. Early marginal bone loss (EMBL) is calculated.
2. 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.