The impact of subcrestal placement on short locking-taper implants placed in posterior maxilla and mandible: a retrospective evaluation on hard and soft tissues stability after 2 years of loading.

AIM: Objective of this study was to assess the influence of the subcrestal placement level of short implants with a locking-taper connection design on crestal bone levels and soft tissues health.

METHODS: A clinical retrospective case-control study was conducted between May 2013 and September 2013. The sample was composed of patients who had received at least one 5-to-8-mm-long, plateau-design implant with a locking-taper connection system (Bicon LLC, Boston, MA, USA) in posterior areas of maxilla and mandible, in the period between January 2009 and Dicember 2011. A radiographic evaluation of the degree of subcrestal positioning(t0) was conducted to identify two implant groups: Group 1 was composed of implants placed less than 2 mm under the crestal bone; Group 2 was composed of implants placed 2 mm or more under the crest. The primary outcome variables were the crestal bone levels and the peri-implant bone loss between prosthetic loading and last control visit (t1àt2). Clinical parameters including the keratinized gingival (KG) width, modified bleeding index (mBI), modified plaque index (mPI), and probing depth (PD) were assessed at the follow-up visit. T tests were conducted to identify statistically significant differences between implants groups. Linear regression models were developed to test the dependence of the study variables by the degree of subcrestal surgical implant placement. Significance level was set at P<0.05.

RESULTS: One hundred and thirty-seven implants were followed for an average period of 31 months. At the surgery, the implants were placed, on average, 2.04 mm (mesial) and 1.86 mm (distal) subcrestally. Eighty implants were placed less than 2 mm under the crest (average 1.28 mm), while fifty-seven implants were placed more than 2 mm under the crestal bone (average 2.97 mm). At the prosthetic loading (t1), the average crestal bone level was 1.11 mm, 0.79 mm in Shallow group and 1.86 mm in Deep group, with statistically significant differences between implant groups (P<0.05). At the follow-up visit (t2) the mean crestal bone levels were respectively 0.51 mm and 1.35 mm, with statistically significant differences between implant groups (P<0.05). The average peri-implant bone loss between prosthetic loading and control visit (t1àt2) was 0.04 mm in the Group 1 and 0.33 mm in Group 2. The average keratinized mucosa width was 2.16 mm, the average mBI was 0.24 , the average mPI was 0.17 and the average PD was 2.34 mm. Significant difference between groups was observed regarding to keratinized gingival width (Group 1: 1.97 mm; Group 2: 2.41 mm; P<0.05) but not for the other clinical parameters. Linear regression models confirmed the dependence of crestal bone levels by the degree of subcrestal placement (P<0.05).

CONCLUSION: After two years of observation, the implant of this study have shown minimal peri-implant bone resorption. The greater subcrestal implant placement has resulted in a higher level of the peri-implant bone crest, both after the osseointegration period and after the loading period. Both the study implants groups have shown good health of peri-implant soft tissues.