Compare the Difference in Occlusal Force Distribution and Denture Retention Using 2 Different Denture Base Materials in Implant Retained Overdenture

24 Patients will be randomly and equally divided into two treatment groups:

1. Group 1: Each patient in this group will receive conventional maxillary and mandibular complete dentures made of heat-cured acrylic resin PMMA. In the mandible, two implants were inserted in the symphyseal area and retained by equator attachments.
2. Group 2: Patients in this group received the same type of treatment as the patients in group 1, but the mandibular overdentures were made of the flexible acrylic resin "breflex" The present study will be performed to compare the difference in retention, occlusal force distribution, occlusion and disocclusion time, and bite force for implant retained mandibular over denture using PMMA and flexible dentures base materials

• Conventional acrylic resin denture (Procedure): Mandibular complete dentures made of heat-cured acrylic resin (PMMA). In the mandible, two implants were inserted in the symphyseal area and retained by Equator attachments.
• Flexible resin denture (Procedure): Mandibular overdentures were made of the flexible acrylic resin breflex, In the mandible, two implants were inserted in the symphyseal area and retained by Equator attachments

Primary outcomes

• Occlusal force distribution [Follow up visits were scheduled at denture insertion, 6, and 12 months]: Occlusal force distribution will be measured by T-Scan, The latest version (T-Scan III) provides a dynamic visual evaluation of a patient's occlusion from initial tooth contact to maximum intercuspation. The system records relative force values and allows objective quantitative evaluation of occlusal balance by recording numerical values for occlusion and disocclusion times

Secondary outcomes

• Retention of lower denture [Follow up visits were scheduled at denture insertion, 6, and 12 months]: Retention of lower denture will be measured using digital force gauge, Retention will be measured using digital force gauge A digital force meter was used to measure denture resistance to vertical displacement (i.e., retention) by applying a pulling force on a metal hook located in the geometric center of each mandibular conventional denture that was identified on the lower cast at the intersection of three lines bisecting the angles of the triangle, formed by both retromolar pads and the midline. Measurement of mandibular denture retention: The patient was instructed to place his head on chin rest and occlusal plane was set parallel to the floor. Tongue freedom was checked then and three minutes seating time was allowed before taking the measurements. A vertical pulling force was applied using the metallic probe of the digital force-meter that was attached to the hook present at the geometric center of mandibular denture. Average value of six readings was recorded.
• occlusion time [Follow up visits were scheduled at denture insertion, 6, and 12 months]: occlusion and disocclusion time will be measured by T-Scan, The latest version (T-Scan III) provides a dynamic visual evaluation of a patient's occlusion from initial tooth contact to maximum intercuspation. The system records relative force values and allows objective quantitative evaluation of occlusal balance by recording numerical values for occlusion times
• Biting force [Follow up visits were scheduled at denture insertion, 6, and 12 months]: Biting force will be measured by bite force meter
• Disocclusion time [Follow up visits were scheduled at denture insertion, 6, and 12 months]: will be measured by T-Scan, The latest version (T-Scan III) provides a dynamic visual evaluation of a patient's occlusion from initial tooth contact to maximum intercuspation. The system records relative force values and allows objective quantitative evaluation of occlusal balance by recording numerical values for disocclusion times

Sex: All, ages: 60 Years to 70 Years, accepts healthy volunteers

Inclusion Criteria:

1. All patients age must range from 60-70 years old.
2. All patients' ridges should be covered with firm mucosa free from any signs of inflammation or ulceration and exhibit adequate height and width of the residual alveolar ridge.
3. Patients should be free from any metabolic or bone disorder that contraindicate implant installation.
4. All patients must have sufficient inter arch space

Exclusion Criteria:

1. Patients with oral or systemic diseases.
2. Patients with xerostomia or excessive salivation.
3. Patients with parafunctional habits (bruxism or clenching).
4. Heavy smoker or alcoholic patients.
5. Patients with history of temporo-mandibular dysfunction.
6. Patients with brain disorders or psychiatric disorders