Abstract
            Background. Horizontal ridge augmentation surgeries are common procedures in periodontics.  Histological changes in soft tissues affect the success of surgery in many ways. Autologous  conditioned serum (ACS) increases interleukin-1 receptor antagonist (IL-1Ra) and causes  inflammation modulation. Therefore, the present study aimed to investigate the effect of ACS  on histological changes and gene expression of soft tissues after horizontal ridge augmentation  surgeries.  
  Methods. This double-blind split-mouth clinical trial was performed on patients needing  implants with horizontal ridge augmentation (n=21). The control and intervention groups were  considered split-mouth in two areas of the patients’ oral soft tissues. A collagen membrane  impregnated with ACS was used on the test side, and only a collagen membrane was used on  the control side. After four months, histological changes in soft tissues, such as the amount of  connective tissue collagen, fibroblast and inflammatory cell counts, and expression of the IL-1β  gene, were evaluated.  
  Results. The fibroblast counts in the ACS group were significantly higher than in the control  group. In addition, ACS caused a significant increase in the amount of collagen in the soft  tissues compared to the control group (P<0.01). However, the number of inflammatory cells  was similar in the two groups (P>0.05). IL-1β gene expression was not significantly different  between the case and control groups.  
  Conclusion. Under the limitations of the present study and based on the results of histological  examinations, ACS increased the number of fibroblasts and the amount of collagen in soft  tissues without affecting inflammatory cells (P=0.562).