The dimensional changes that occurs during the healing of the grafting material in external sinus lift procedure is always present and sometimes may lead to difficulties in placing the dental implants in the second stage. This study aims to evaluate the efficacy of adding a titanium mesh as a new fixed floor of the sinus to minimize these changes. Materials and Methods: this randomized clinical trial included 8 patients who needed bilateral 2-stages sinus lift. On one side sinus lift was carried out using Deproteinized Bovine Bone Matrix (DBBM) mixed with A-PRF+ (Group A) while on the other side a titanium mesh was fixed as a new sinus floor above the same mixture (Group B). CBCT radiographs were taken preoperatively (T0), directly postoperatively (T1), and 9 months after surgery (T2). Linear measurements were recorded in the same points in all three radiographs, graft volume was measured and compared using 3D Slicer software. Results: the mean bone height (BH) at T1 was 13.08 and 13.56 mm while at T2 was 11.56 and 13.56 mm in groups A and B respectively. The mean reduction in BH was 1.68 and 0.00 mm in groups A and B respectively. The graft volume (GV) at T1 was 1.49 and 1.63 cc and at T2 was 1.19 and 1.53 cc, the mean volume shrinkage was 0.29 and 0.1 cc in groups A and B respectively. The differences between the groups in both linear and volumetric changes were statistically significant. Conclusions: within the limitation of this study it may be concluded that adding a titanium mesh as a new floor of the sinus helps limiting the shrinkage of both the linear dimensions and overall graft volume.