Clinical, radiological, and gene expression analyses in smokers and non-smokers, Part 2: RCT on the late healing phase of osseointegration

Background: The mechanisms behind the impact of smoking on osseointegration are not fully understood. Purpose: To investigate the initial clinical and molecular course of osseointegration of different implants in smokers and non-smokers in a randomized controlled trial (RCT). Materials and Methods: Smoking (n516) and non-smoking (n516) patients received 3 implant types: machined, oxidized, and laser-modified surfaces. Baseline bone biopsies were retrieved from the implant sites. After 60 and 90 days, the pain score, implant stability quotient (ISQ), and peri-implant crevicular fluid (PICF) gene expression were analyzed. Furthermore, radiological and clinical assessments were made at 90 days. Results: At 90 days, no pain was reported, irrespective of smoking habit. A higher ISQ was found in smokers compared with non-smokers. Marginal bone loss (MBL) was greater in smokers than in non-smokers. The comparison of implant surfaces revealed greater MBL exclusively at the machined implants in smokers. At 90 days in smokers, the PICF around machined implants revealed a higher expression of the proinflammatory cytokine, interleukin-6 (IL-6), and a lower expression of the osteogenic gene, osteocalcin (OC), compared with the PICF around modified implants. Furthermore, OC expression was lower at machined implants in smokers compared with machined implants in non-smokers. After adjustment for age and implant location (maxilla/mandible), multivariate regression revealed the following predictors of MBL: smoking, bleeding on probing at 90 days, hypoxia-inducible factor 1 alpha (HIF-1 alpha) expression at baseline and IL-6 expression in PICF at 90 days. Conclusions: During the early phase of osseointegration, non-smokers and smokers present a similar, high implant survival. In contrast, smokers present a greater MBL, particularly at machined implants. HIF-1 alpha baseline expression in the recipient bone and IL-6 expression in PICF cells are important molecular determinants for MBL after 90 days. It is concluded that smoking has an early effect on osseointegration, which is dependent on the implant surface properties and the local host response.