Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 11 1 2024 08 18 9 19 Feyza Eraydın Department of Orthodontics, Istanbul Gelişim University, Faculty of Dentistry, Istanbul, Turkey. Alev Cumbul Department of Histology and Embryology, Yeditepe University, Faculty of Medicine, Istanbul, Turkey. Merve Kurnaz Department of Orthodontics, Istanbul Kent University, Faculty of Dentistr, Istanbul, Turkey. Fulya Ozdemir Department of Orthodontics, Istanbul Saglik Teknoloji University, Faculty of Dentistry, Istanbul, Turkey. 2024 01 29 2024 04 23 Introduction: The aim of this study was to investigate the histomorphometric effects of bone marrow-derived mesenchymal stem cells (MSCs) transfected with Adeno Associated Virus (AAV) and containing bone morphogenic protein 7 (Bmp7) or osteoprotegerin (OPG) on bone formation after injection into inter-premaxillary suture in rats with Bmp7 or OPG alone. Materials and Methods: In 4 groups (each group n:9), different chemical solutions, namely AAV-Bmp7, AAV-OPG and AAV-Bmp7-OPG and AAV-EGF (control group) were injected into the interpremaxillary suture of rats. Bone volumes (BV), soft tissue volume (STV) and total bone volumes (TBV) of 10μm serial selection with hemotoxylin and eosin staining were calculated according to the Cavalieri principle. Each point in the region of interest was 1000μm3. Results: The BV for AAV-Bmp7, AAV-OPG, AAV-Bmp7-OPG and AAV-EGF were 46.98±1.50 mm3, 49.40±4.72mm3, 42.58±2.89mm3 and 38.82±0.76mm3, respectively. The STV was 11.53±0.99, 13.31±1.88, 8.00±4.43 and 9.57±1.90mm3 for Bmp7, OPG, AAV-Bmp7-OPG and AAV-EGF, respectively. TBV was 58.34±2.28mm3, 63.83±5.17mm3, 53.74±3.34mm3 and 48.13±1.54mm3 for AAV-Bmp7, AAV-OPG, AAV-Bmp7-OPG and AAV-EGF, respectively. The comparison between BV, STV, TBV for AAV-OPG showed a statistically significant difference (p=0.001) compared to AAV-Bmp7 or AAV-Bmp7-OPG and AAV-EGF. Conclusion: During tooth movement and bone remodeling, the ratio of soft and bone tissues is maintained by OPG. Although Bmp7 is not as effective as OPG in bone remodeling, both can reduce the retention time and the risk of recurrence. Keywords: Histomorphometry; Bmp 7; OPG; Maxillary expansion; Orthodontics; Rats. https://jcr.tums.ac.ir/index.php/jcr/article/view/482 https://jcr.tums.ac.ir/index.php/jcr/article/download/482/401