Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 13 6 2017 01 11 388 393 EN Amir Hossein Mirhashemi Associate Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Mohammad Sadegh Ahmad Akhoundi Professor, Laser Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Rezvaneh Ghazanfari Assistant Professor Department o f Prosthodontics, School of Dentistry International Campus, Tehran University of Medical Sciences, Tehran, Iran Shahroo Etemad-Moghadam Associate Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Mojgan Alaeddini Associate Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Azam Khorshidian PhD Candidate, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran Ahmad Reza Dehpour Professor, Department of Pharmacology, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran Nafiseh Momeni PhD Candidate, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran 2016 09 17 2016 12 08 Objectives: Nitric oxide (NO) is a signaling molecule that mediates mechanical bone loading. Cyclic guanosine 3', 5' monophosphate (cGMP) is a NO-induced effector molecule. The aim of this study was to assess the effect of NO-cGMP pathway on orthodontic tooth movement (OTM) in rats by use of two phosphodiesterase 5 (PDE5) inhibitors namely sildenafil and tadalafil as chemical tools. Materials and Methods: Forty-five male Wistar rats were divided into three equal groups (n=15) based on the substance they received. The first group received daily injections of tadalafil; the second group received daily injections of sildenafil and the third group received daily injections of normal saline. The orthodontic appliances consisted of nickel-titanium closed-coil spring ligated between the maxillary right incisor and the first molar of the animals for 21 days. The amount of tooth movement was measured in all three groups at the end of this period. Histological analysis was performed to assess root resorption lacunae, osteoclast number and periodontal ligament (PDL) thickness. Results: All appliance-treated molars in the experimental and control groups showed evidence of tooth movement. The mean OTM was calculated to be 0.39±0.16, 0.32±0.16 and 0.26±0.16mm in tadalafil, sildenafil and control groups, respectively and there were no significant differences in OTM among the study groups (P>0.05). In the tadalafil group, significantly greater root resorption on the tension side was seen when compared with controls (P≤0.05). Conclusions: Tadalafil and sildenafil PDE-5 inhibitors affecting the NO-cGMP pathway did not affect OTM in rats.   https://fid.tums.ac.ir/index.php/fid/article/view/1536 https://fid.tums.ac.ir/index.php/fid/article/download/1536/925