الفهرس 
Introduction………………………………………………………………………………………………Only 14 pages are availabe for public view
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Abstract
Fourteen completely edentulous patients were selected from the Outpatient Clinic, Prosthodontic Department, Faculty of dentistry, Ain Shams University to participate in this study. The patients were selected and examined carefully to reduce the human variables that may affect the results of this study. Cone Beam Computed Tomography (CBCT) was carried out for all patients to assess the bone quality of the mandibular alveolar ridge, to locate the position of the mental foramina, and to evaluate the available bone width and height at the interforaminal region. All the selected patients were treated by conventional maxillary complete dentures and hybrid implant retained mandibular overdentures. Standard clinical and laboratory techniques were followed for the construction of the dentures for all patients. The patients participated in this study were divided randomly into two equal groups. The first group (seven patients): The patients of this group rehabilitated with two un-splinted (with ball abutments) hybrid implants of 3mm diameters and 14mm lengths (on the canine regions) retaining mandibular overdentures opposed by conventional maxillary complete dentures. The second group (seven patients): The patients of this group rehabilitated with two splinted (with square head abutment) hybrid implants of 3mm diameters and 14mm lengths (on the canine regions) retaining mandibular overdentures opposed by conventional maxillary complete dentures. The patients recalled frequently to perform any needed adjustments. The follow-up visits were scheduled at the time of loading, six, and twelve months after loading for the clinical and radiographic evaluation of the implants.Clinically, a successful osseointegration was assessed by observing the signs of inflammation or infection, the mobility assessed using the handles of two hand instruments, and the percussion was performed by tapping the implants with the end of an instrument handle to examine the ringing sound. The radiographic evaluation of the peri-implant and posterior bone level at each follow-up period was performed using Cone Beam Computed Tomography (CBCT). -The results obtained from this study showed that:-• All patients participated in the study were satisfied with their implant retained mandibular overdentures and accommodated to their use easily within few days. • At the end of the 12 months, a total change of 1.08 mm for group I (with un-splinted implants), and 0.55mm for group II (with splinted implants) was detected. Although, this change was statistically significant, this amount of bone loss was within the accepted range that occurs within the first year. • The bone loss around the implants in the first follow-up period from the base line to 6 months was greater than that in the second follow-up period from 6 to 12 months, this difference was statistically significant for group I (with un-splinted implants) for the most aspects around the implants, while, this change was statistically insignificant for group II (with splinted implants) for all aspects around the implants. • The bone loss around the implants for group I (with un-splinted implants) was greater than that for group II (with splinted implants) at all follow-up periods, the difference between the • Posteriorly, It was found that the bone loss for group II (with splinted implants) was greater than that for group I (with un-splinted implants), but this difference in the bone loss at the posterior residual ridge was statistically insignificant.