Analysis of 8.5 mm Long Dental Implants Provided with Splinted or Solitary Implant Restorations: A 15-Year Prospective Study

<b>Background/Objectives:</b> The long-term effects of implant properties, such as implant length, platform switch, and crown splinting, on peri-implant health require more investigation. Therefore, the aim was to assess the long-term peri-implant health and patient satisfaction in a patient cohort, obtained from two prospective randomized controlled trials, who received 8.5 mm long dental implants, with either splinted or solitary suprastructures and with or without a platform switch, over a period of 15 years. <b>Methods:</b> One hundred and twenty-two patients received either one or two 8.5 mm long dental implants (223 dental implants) with and without platform switch, restored with either a solitary (<i>n</i> = 89) or a splinted (<i>n</i> = 134) restoration in the posterior region. Clinical and radiographical parameters and patient satisfaction were prospectively recorded at 1 month, and 1, 5, and 15 years after the placement of the restoration. Patient satisfaction was recorded with a self-administered questionnaire using a 5-point scale and a visual analog scale (0-10). <b>Results:</b> Eighty-one patients with one hundred and fifty-four implants were assessed after a 15-year follow-up. The clinical parameters were low and comparable between the implant types (OsseoTite XP Certain, OsseoTite XP Certain Prevail, NanoTite XP Certain, NanoTite XP Certain Prevail, PalmBeach Gardens, FL, USA) over time. The implants that incorporated a platform switch showed significantly less bone loss than the implants without a platform switch (-0.37 mm, 95% CI -0.69 to -0.05 mm, <i>p</i> = 0.024 and β = -0.47, 95% CI -0.80 to -0.14, <i>p</i> = 0.006). The implants with splinted restorations experienced more bone loss over time compared to the implants with solitary restorations (0.39 mm, 95% CI 0.15-0.63, <i>p</i> = 0.002). Patient satisfaction was high after 15 years. <b>Conclusions:</b> All the tested dental implants with 8.5 mm length provide satisfactory 15-year results with regard to the clinical and radiographical parameters as well as patient satisfaction. The platform-matched implants were associated with more bone loss compared to the platform-switched implants, and the implants with splinted crowns portrayed more bone loss than the solitary implant crowns.