Effect of the abutment shape on soft tissue healing. A randomized clinical pilot study involving a digital superposition methodology

Aim: To compare the effect of the shape of the healing abutment, concave or straight, on the dimensions of the soft tissue after healing.
Materials and methods: Patients needing implant therapy in the posterior area were treated with a 1-stage surgery protocol; concave (CONC) or straight (STR) healing abutments were randomly assigned after implant installation. Before surgery, a CBCT and an intra-oral scan were obtained (IOS#0); IOS#1 was taken after soft tissue healing. The CBCT, IOSs and STL of the abutments were merged; this allowed measuring the gained/lost gingival height (ΔH), the gingival width (GWAbut) and the emergence angles (ANG) of each group.
Results: Twenty-seven implants (Ø 4.2 mm, SEVEN (MIS)) with 14 CONC and 13 STR healing abutments were available for analysis. ΔH of both groups did not differ statistically. The marginal gingiva of CONC either stayed within the abutment concavity (CONCin) or reached its straight portion beyond the concavity (CONCup). When GWAbut and ANG were measured without considering this feature, the differences between STR and CONC were not statistically significant. In contrast, once this feature was considered, the difference between the groups became statistically significant. For GWAbut, results were CONCup>STR>CONCin; for ANG it was STR≈CONCup>CONCin.
Conclusion: Abutment shape did not affect the gingival height. Thickness of the gingiva at the concave abutment depended upon the position of the marginal gingiva, within or beyond the concavity. This exploratory pilot study might suggest that concave abutment height should be carefully chosen to ensure that the marginal gingiva reaches the level beyond the concavity.