Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 7 4 2021 02 20 186 194 Mohsen Dalband Department of Oral and Maxillofacial Surgery, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Shahabaldin Azizi Department of Oral and Maxillofacial Surgery, School of Dentistry, Iran University of Medical Sciences, Tehran, Iran. Mahdieh Karimzadeh Department of Pediatric, Bushehr University of Medical Sciences, Bushehr, Iran. Mohammad Asnaashari Laser Application in Medical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Abdullah Farhadinasb Behavioural Sciences Research Center, Taleghani Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Mahdokht Azizi Department of Pathology, Valiasr Hospital, Fars, Iran. Mazaher Ramezani Molecular Pathology Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran. 2021 02 02 2021 02 20 Background: Many studies have been performed on the effect of low level laser on wound healing which has been associated with different and sometimes contradictory results. On the other hand, considering that stress may affect the immune system the fact that it may delay wound healing has also been addressed. Therefore, the present study aimed to investigate the simultaneous effect of low level laser therapy and stress on wound healing at the three levels of histology (histological changes), biomechanics (stress and strain assessment) and macroscopic (wound size). Materials and Methods: In this interventional study, 72 male Wistar rats (8-10 weeks old, weight range: 240 to 330g) were randomly divided into three treatment groups and one control group. (18 per group). In all the rats, a 2.5cm full-thickness skin incision was made on the dorsal spine. Intervention was performed from day 1 to day 21 every other day with Kals-DX61 laser (cap s) with wavelength: 660nm, dose 3J/cm2, 100 sec and power density 30mW/cm2. Then, wound size was measured weekly until the third week (day 21). Then, tension metric tests were performed to evaluate the stress and strain of the restored tissue. At the end of each week, three animals from each group were sacrificed for histopathological evaluation. Results: There was a significant difference between the stress/no laser and laser/no stress groups in all stages of evaluation. Mean and standard deviation of stress and strain were not significantly different in the study groups. Conclusion: Stress can potentially slow the wound healing process, while receiving low level laser therapy speeds up the wound healing process, although in the end there was no significant difference in biomechanical characteristics between the groups. Keywords: Low level laser therapy; Rat; Stress; Wound healing. https://jcr.tums.ac.ir/index.php/jcr/article/view/361 https://jcr.tums.ac.ir/index.php/jcr/article/download/361/308