Aim: This study aimed to compare modified ridge splitting (RS) and distraction osteogenesis (DO) for horizontal ridge expansion clinically (bone width, pain, and soft tissue healing) and radiographically (bone width). Material and methods: This randomized clinical trial was conducted on fourteen patients who had a partial edentulous narrow mandibular posterior alveolar ridge (not less than 4-mm width and 12-mm height). All patients were divided randomly into two equal groups: Group I was treated with a modified bone-splitting technique, and group II was treated with DO technique by the fabricated device as AlveoWider®, and without any graft material for both groups. All patients were followed up clinically to evaluate the increase of bone width at preoperative measurement (T0) and 6 months postoperative (T6), and radiographically by cone-beam computed tomography (CBCT) at T0, 3 months postoperative (T3), and T6. Descriptive and bivariate statistics were computed using the SPSS version (SPSS, IBM Inc., Chicago, IL, USA), and p ≤ 0.05 was considered an indicator of statistical significance. Results: All patients were female. Patients’ ages ranged from 18 to 45 years, with a mean age of 32.07 ± 5.87 years. Radiographically, there is no significant statistical difference in comparing between two groups for the creation of a horizontal alveolar bone; however, there was a highly significant statistical difference (p < 0.001) in each group between different interval periods (T0, T3, and T6) with mean start 5.27 ± 0.53, and 5.19 ± 0.72 at T0 reaching to 7.60 ± 0.89 and 7.09 ± 0.96 at T3, and slightly decreases to 7.52 ± 0.79 and 7.02 ± 0.79 in T6 with radiographic evaluation, and it represented clinically in each group with mean 3.57 ± 0.313 and 4.0 ± 0.58 at T0 increase to 6.55 ± 0.395 and 6.52 ± 0.45 at T6 for both groups, respectively. There is a statistically significant difference in soft tissue healing with the average mean of 4.57 ± 0.24 and 3.57 ± 0.509 and pain with an average mean of 1.66 ± 0.22 and 4.74 ± 0.55 with p = 0.001 and p < 0.001 when comparing between both groups, respectively, that is, p = 0.001 is considered to be statistically significant. Conclusion: Both techniques seem to be useful as augmentation techniques for dental implant placement in a narrow alveolar ridge. Techniques are sensitive and need good experience. The modified splitting technique has fewer complications, less pain, and better soft tissue healing when compared with the DO technique. Clinical significance: Both techniques are alternative methods for the treatment of the atrophic alveolar ridge with uneventful healing except for minor complications that do not interfere with dental implant placement.