Effects of nicotine on bone during orthodontic tooth movement in male rats: Histological and immunohistochemical study

OBJECTIVES: To investigate the effects of nicotine on orthodontic tooth movement and accompanying histological and immunohistochemical changes in rats. METHODS: An experimental study conducted at King Abdulaziz University, Jeddah, Saudi Arabia between 2013 and 2014. Thirty-two rats randomly divided into 4 groups. Three were experimental, received daily nicotine injections: group A: 0.37 mg/kg, group B: 0.57 mg/kg, and group C: 0.93 mg/kg. The control group (group D) received a daily injection of 0.5 mL saline. All rats were subjected to 30 g of orthodontic force on the maxillary left first molars and incisors using a nickel-titanium closed-coil spring. The distance between the 2 teeth was assessed before and after 14 days of force application. Histological, immunohistochemical, and histomorphometric assessments were performed on sections from groups C and D. RESULTS: Groups C (p<0.001) and D (p<0.001) showed the significantly greatest and least amounts of tooth movement . The results were statistically dose-dependent. Unbalanced resorption-apposition bone remodeling patterns and increased osteoclast cell distribution were observed in the nicotine group with significantly smaller percentages of bone surface areas mesially and distally (p<0.05). Immunohistochemical stains showed low alkaline phosphatase activity and intense tartrate-resistant acid phosphatase activity in the nicotine group. CONCLUSIONS: Nicotine accelerated orthodontic tooth movement with unbalanced bone resorption and apposition patterns around the moving teeth.