Aim of the study: In this study the amount of bone height changes around abutments supporting mandibular overdenture was evaluated when retained by two different types of attachments. Material and methods: This study was conducted on patients with only two remaining mandibular canines with an opposing edentulous maxillary arch. It was performed with two different ball attachments, a conventional type (Group A), and a swivel self-parallelizing type (Group B). The bone height changes around the mesial and the distal surfaces of the abutments were measured by the aid of the Digora computerized system. Paired t-test was performed to study the effect of time on the bone height changes within each group and to compare between the mesial and distal bone height changes of each group. On the other hand, independent t-test was used to compare between the two groups regarding the mesial and the distal bone height changes in the two groups. Results: Regarding the effect of time on the marginal bone height for group (A) and group (B), there was a significant increase in the marginal bone height loss at the mesial