Sixty male Wistar rats, age of 5 weeks (80–110 g), were purchased from the Experimental Animal Center of China Medical University. All rats were housed in plastic cages in standard temperature-controlled rooms (23–27 °C) with a 12-h light/dark cycle and were given free access to food as well as water. The rats were fed for a week prior to experimentation then were randomly divided into 6 groups containing 10 rats per group. Groups 1, 2 and 3 received 0, 60 and 120 ppm (ppm, mg per liter) of fluoride ions (F−) in their drinking water for 4 weeks, respectively. Groups 4, 5 and 6 rats received 0, 60 and 120 ppm of F− in their drinking water for 12 weeks, respectively.

Sixty male Wistar rats, age of 5 weeks (80–110 g), were purchased from the Experimental Animal Center of China Medical University. All rats were housed in plastic cages in standard temperature-controlled rooms (23–27 °C) with a 12-h light/dark cycle and were given free access to food as well as water. The rats were fed for a week prior to experimentation then were randomly divided into 6 groups containing 10 rats per group. Groups 1, 2 and 3 received 0, 60 and 120 ppm (ppm, mg per liter) of fluoride ions (F−) in their drinking water for 4 weeks, respectively. Groups 4, 5 and 6 rats received 0, 60 and 120 ppm of F− in their drinking water for 12 weeks, respectively.