INTRODUCTION:

DISTAL EXTENSION PARTIAL DENTURES are supported by both :
Relatively rigid teeth and Resilient mucosa .
The underlying mucosal base is covered by the free end denture base of the denture.
In order to preserve these teeth soft tissue and bone the denture must take full advantage of these structures without abusing them.
If fabricated incorrectly the teeth will worsen and the ridge will resorb.

DEFINITION:
Functional impression is defined as a dynamic registration of the dentition & edentulous ridge made under functional load for the purpose of equalization of stresses on the teeth and distal extension segment.

NEED FOR FUNCTIONAL IMPRESSION:

Equalize support from residual ridges and teeth
Distal extension cases require functional impression to record & relate tissue under same loading
Distribute the load over large area as possible.
Accurately delineate peripheries of the denture base.
Failure to make a functional impression will cause lack of proper orientation between the denture base and abutment teeth and cause pathologic leverages invariably hampering the support of the abutment teeth, tissue atrophy , occlusal imbalance , irritation and frustration on the part of the patient.

REQUIREMENT FOR FUNCTIONAL IMPRESSION:

CONCEPT OF SUPPORT FOR DIATAL EXTENSION CASES :

APPLEGATE has given this concept according to him” support comes from only one oral structure i.e. alveolar bone “
Between the prosthesis and the alveolar bone two interadjacent structures are present :
Mucosa covering the residual ridge
Periodontal ligament.

Forces are transmitted by stretching of the periodontal ligament fibers and compression of mucosa.

There are 3 reasons that Applegate has given to maintain tooth support:

1. Cushion hammock ligament : supports effectively
2. Proprioception: equips the periodontal ligament with defense against overload.Mucosa does not have proprioceptive mechanism and is frequently abused
3. Stress is transferred better by stretching rather than compression.

If the denture base looses stability then abutment will tilt & produce areas of compression in the periodontal ligament due to linear vertical transfer of forces.

Leverage forces are harmful to the periodontal ligament.