The aim of this study was to assess histologically the bone changes around immediately loaded mini screws and whether there is a difference in those changes upon using corticotomy facilitated (CF) orthodontic tooth movement technique, in comparison to standard (S) orthodontic tooth movement technique.Six dogs, aged 6-9 months, were used in this study. Extraction of the maxillary second premolar and mini screw placement were done bilaterally in the maxilla. On the right (CF) side, corticotomy was performed. The first premolars were distalized against the mini screws with NiTi coil springs on both sides. The dogs were sacrificed weekly after orthodontic force application.Histological analysis showed that osseous formation was progressive around the mini screw along the period of the study in both groups, although osseointegration was not found. There was a histological difference in the peri-screw bone between the two groups. In (S) side the bone formation started much earlier than the (CF) side.During the six weeks period of this study the mini screws depended mainly on mechanical interlocking in their retention. The (CF) technique delayed the osseous bone formation around the mini screws in comparison to the (S) technique.