Comparison of Bone-Level and Tissue-Level Implants: A Pilot Study with a Histologic Analysis and a 4-Year Follow-up.

This study clinically and histologically evaluated the performance of implants with different crestal morphologies: tissue-level implants and bone-level implants. Nine patients received at least two adjacent implants in an edentulous area: one bone-level implant (EO) and one tissue-level implant (TG) (total: 23 implants), placed beside each other using a single-stage delayed loading protocol. The implants were rehabilitated with screw-retained fixed partial dentures. Plaque Index (PI), bleeding on probing (BOP), probing depth (PD), and peri-implant bone level were recorded at various postsurgical follow-ups, including 2 and 6 months as well as 1 and 4 years. At 3 months postsurgery, soft tissue biopsy samples were taken from all implant sites and histologically analyzed. Longitudinal assessment of the results (TG vs EO implants) was performed using a linear mixed model with random intercept and by using Spearman correlation or chi-square after visual inspection of the probability distribution. Student t test was used to compare means, and chi-square test was used for dichotomic variables. P < .05 was considered statistically significant. All implants were functional at 4 years. Peri-implant bone resorption was limited, with means of 1.20 +/- 0.71 mm and 1.24 +/- 0.82 mm for TG and EO implants, respectively. No significant differences in clinical parameters were identified between EO and TG implants. Histologic analysis revealed normal peri-implant soft tissue healing with poor inflammatory infiltrate. Differences in the histologic appearance of soft tissues were more related to patients than implant type. Both implants appeared to be suitable for partial rehabilitation of edentulous arches without differences in the investigated clinical and histologic parameters. However, TG implants showed a greater risk of implant collar exposure.