Factors Affecting Soft and Hard Tissues Around Two-Piece Transmucosal Implants: A 3-Year Prospective Cohort Study

Purpose: This 3-year study aimed to evaluate hard and soft tissue modification around a two-piece implant characterized by a transmucosal hyperbolic neck in healthy consecutive patients with a need for single-tooth replacement. Materials and Methods: Two-piece implants (n = 66) were placed with a flapless technique in 56 patients (27 men; 29 women; mean age 55 ± 9 years): 16 immediately after root extraction (immediate group), 20 after 8 to 12 weeks (early group), and 30 after 10 or more months (delayed group). The transmucosal hyperbolic neck was exposed 1 to 1.5 mm above gingival level. Customized abutments were positioned 3 months later with the implant-abutment connection located approximately 1 to 1.5 mm above soft tissue level. Provisional cemented resin crowns were designed with the finishing line at the hyperbolic neck and then positioned to avoid excessive compression of soft tissue, to guide gingival contours. Twenty days later, a definitive metal-ceramic crown was cemented. In all patients, the gingival biotype (thin or thick) was also evaluated. The primary outcomes were as follows: 36-month implant survival rate, peri-implant marginal bone level (MBL, in mm) changes observed in single-blind on radiographs at 1, 3, 6, 12, 24, and 36 months (T₁, T₃, T₆, T₁₂, T₂₄, and T₃₆), and pink esthetic score (PES) at T₆, T₁₂, and T₃₆ to analyze soft tissue adaptation after loading and crown application. The secondary outcomes were as follows: plaque score and bleeding on probing (BOP). Linear regression models and multilevel mixed logistic regression were used to detect any statistical difference of MBL according to operative parameters. Kruskal-Wallis one-way analysis of variance (ANOVA) on ranks was performed to assess statistical differences of PES at T₆, T₁₂, and T₃₆. Results: The survival rate was 100%. The dropout rate was 1.79%. No infections, mucositis, or peri-implantitis were reported. Implants placed in thick-biotype tissues showed a statistically different lower bone loss at 36 months with respect to the thin biotype (P .05). At 36 months, the early group showed lower bone loss compared with the delayed group (P .05). Multilevel mixed logistic regression revealed that gingival biotype was the parameter that was most related to MBL variations (P = .025). The PES value (mean ± SD) at T₆ was 10.76 ± 1.19 (median: 11; range: 8 to 13; IQR: 10 to 12). The values statistically increased at T₁₂ and T₃₆, where the mean values were 11.76 ± 1.10 (median: 12; range: 9 to 13; IQR: 11 to 12) and 11.83 ± 1.03 (median: 12; range: 9 to 14; IQR: 11 to 13). Conclusion: MBL and soft tissue clinical parameters measured around two-piece hyperbolic-neck implants were stable during the 3-year follow-up and free from complications. The exposure of the hyperbolic neck for 1.0 to 1.5 mm allowed a flapless one-stage surgery, which supported fast adaptation of the soft tissues, evidenced by high PES values and low percentages of BOP. The results from the study imply a new simple approach in the clinical management of gingival and bone tissue. Keywords: flapless procedure, hyperbolic neck, prospective cohort study, single implant, transmucosal placement