Effects of nicotine on gene expression and osseointegration in rats

Background: While many studies have focused on the hazardous effects of smoking, there is little direct evidence regarding the specific detrimental effects of the nicotine on the osseointegration of implants.Objective: To understand the effects of nicotine on gene expression and osseointegration of titanium implants in rats.Material and methods: Forty-four rats were administered with nicotine or saline for a period of 8 weeks. The femurs were then harvested and analyzed using a three-point bending test. Osseointegration level was determined using bone/implant contact ratio at 2 or 4 weeks after implants were placed. Expression levels of bone matrix-related genes were measured by quantitative real-time polymerase chain reaction.Results: The results of the three-point bending showed that there was no significant difference detected in stiffness between control and nicotine groups at 8 weeks post-saline/nicotine delivery (P=0.705). The bone/implant contact ratio in nicotine-delivered group was significantly decreased compared with those in the control group at 4 weeks (P<0.05). Also, expression levels of osteopontin, type II collagen, bone morphogenic protein-2, bone sialoprotein, and core-binding factor α-1 were significantly down-regulated in the nicotine-delivered group compared with the control.Conclusions: Although systemic exposure to nicotine did not affect rat bone development, bone wound healing around the implant after placement was affected. These findings suggest that nicotine might inhibit the bone matrix-related gene expressions required for wound healing and thereby diminish implant osseointegration at late stage.