Subcrestal placement of dental implants with an internal conical connection of 0.5 mm versus 1.5 mm: Outcome of a multicentre randomised controlled trial 1 year after loading

Purpose: To evaluate whether there are some clinical benefits by placing single dental implants either 0.5 or 1.5 mm subcrestally in healed bone crests. Materials and methods: Sixty partially edentulous patients requiring two single implant-supported crowns had both sites randomly allocated either to 0.5 mm or 1.5 mm subcrestal implant placement according to a split-mouth design at six centres. Implants were submerged in aesthetic areas or nonsubmerged in non-aesthetic areas for 3 months. Provisional acrylic crowns were delivered and were replaced after 2 months by definitive metal-ceramic crowns. Patients were followed to 1 year after loading. Outcome measures were: crown and implant failures; complications; aesthetics assessed using the pink esthetic score (PES); peri-implant marginal bone level changes; and patient preference, recorded by blinded assessors. Results: One patient dropped out. One patient lost both implants to infection at impression taking. Three complications affected three patients of the 0.5 mm group and two complications affected two patients of the 1.5 mm subcrestally placed implants. One patient had complications at both implants. There were no statistically significant differences for complications between group (difference of proportion = 0.02; 95% CI -0.06 to 0.09; P (McNemar test) = 1.000). At delivery of definitive crowns, 2 months after loading, the mean aesthetic score was 11.22 ± 1.91 and 11.12 ± 1.59 for the 0.5 and 1.5 mm group, respectively. At 1 year after loading, the mean aesthetic score was 12.09 ± 1.66 and 12.10 ± 1.52 for the 0.5 and 1.5 mm group, respectively. There were no statistically significant differences between the two groups at 2 months (P (paired t test) = 0.626) or at 1 year (P (paired t test) = 0.920). One year after loading, patients of the 0.5 mm lost on average 0.21 ± 0.51 mm and those of the 1.5 mm group 0.11 ± 0.36 mm, the difference being not statistically significant (difference = 0.10; 95% CI -0.01 to 0.20; P (paired t test) = 0.078). Patients did not prefer any depth of the implant placement over the other. There were no differences in outcomes between centres. Conclusions: No statistical or clinical differences were noticed when placing implants 0.5 mm or 1.5 mm subcrestally, therefore clinicians can do as they prefer.