الفهرس 
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Abstract
Fourteen patients were selected from the out-patient clinic of the Prosthodontic Department, Faculty of Dentistry, Ain Shams University to compare radiographically the effect of degree of palatal coverage on the mandibular residual ridge between two groups of patients:
- group 1: Patients having maxillary implant retained overdenture with complete palatal coverage opposed by mandibular implant retained overdenture.
- group 2: Patients having maxillary implant retained overdenture with partial palatal coverage opposed by mandibular implant retained overdenture.
The selected patients were free from systematic diseases, temporomandibular joint disorders and with no history of para-functional habits. The patients were subjected to thorough examination to detect any abnormalities in ridge, mucosa or temporomandibular joint.
A mandibular radiographic stent that has five radio-opaque markers was constructed for each patient by duplicating their mandibular overdenture using clear acrylic to be used during radiographic follow-up for measuring bone height of the mandibular residual ridge at these five areas.
Four 3mm diameter, 12mm length one-piece implants were inserted in the maxillary arch of each patient in areas of lateral incisors and first premolars to retain maxillary implant overdenture.
O-ring attachments were used to retain the upper denture to the implants for all the patients in the two groups.
Bone height of the mandibular residual ridge at the pre-determined five areas was measured three times for each patient using Panoramic radiograph, the first time is at the time of pick-up, the second time is after six months and the third time is after 12 months.
Data was recorded, collected, tabulated and statistically analyzed and from this study it was observed that mandibular bone height reduction was significantly greater posteriorly than anteriorly in both groups with insignificant difference between the two groups over the study period.