This clinical study will be done to compare between functional relining and digital altered cast of selective pressure impression techniques for constructing mandibular distal extension removable partial dentures using digitally fabricated frameworks by measuring the abutment alveolar bone height changes.

According to the functional impression techniques, all patients will be classified into two equal groups:

Group A: Functional relining of processed RPD base at insertion:

•After try in, a record base will be attached to the minor connectors and metal frameworks using 3D printed master cast.The finished removable partial denture is relined using the functional relining impression technique.

Group B : Digitally obtained altered cast :

Selective pressure impression technique will be made.

Digital altered cast will be done according to J. Wu, Y. Cheng (20) as follow :

All patients will be informed about the follow up and evaluation recalls.

Evaluation of abutment alveolar bone height changes:

Alveolar bone height changes of abutment teeth will be evaluated radiographically at insertion (T0), and after 6 (T6) & 12 months (T12) after RPD insertion.

Inclusion Criteria:

• 1. All patients having completely edentulous maxilla opposing class I Kennedy mandible.

  2. Sufficient restorative space must be available (from the mucosa covering the crest of the residual ridge to proposed occlusal plane). This will be detected by a tentative jaw relation.

  3. Well formed residual ridge covered by healthy firm mucosa. 4. All patients are of angel's class I maxillo-mandibular relationships. 5. Abutment teeth must fulfil certain criteria:

  1. Abutment teeth should be healthy with good periodontal and bone support.

  2. Should not show a pronounced degree of mobility or advanced gingival recession.

  3. Crown Root Ratio of abutment teeth not more than 1:2

     Exclusion Criteria:

• 1. Sever soft tissue undercuts. 2. Systemic diseases that may affect bone changes such as diabetes and osteoporosis.

  3. History of radiotherapy in the head and neck region.