A "flabby" or "fibrous" ridge is one which becomes displaceable due to fibrous tissue deposition. Most frequently seen in the upper anterior region. It can occur when natural teeth oppose an edentulous ridge (Combination Syndrome) however this theory has been disproven. A flabby ridge causes instability of the denture. There are a number of different methods to overcome this problem, 3 of which will be discussed below.
This involves removal of the fibrous tissue to leave a firm ridge. However removing the shock absorbing flabby ridge may lead to trauma of the underlying bone (with the patient feeling soreness) and an increased bulk of denture material. There is also the risk that the flabby ridge may recur. Removal of the fibrous material may also reduce the height of the ridge decreasing the chances of a stable denture.
The other technique involves constructing a denture over the flabby ridge. The impression may be either mucostatic or mucodisplacive. Where a mucostatic impression technique is selected then good retention will be obtain when the teeth are out of occlusion. When the denture is put under load, instability may occur.
With a mucodisplacive impression technique, the denture will only fit well when the denture is under load, it may be unstable when at rest because the flabby ridge tends to recoil back into its original position displacing the denture.
A preliminary impression is taken using alginate loaded in a stock tray. The impression is then poured and a customised tray is constructed on the model. The customised tray is close fitting and has a hole or "window" over the area corresponding to the flabby ridge. An impression is taken in zinc oxide eugenol or low viscosity silicone (mucodisplacive in a close fitting tray). Once this has set it is left in place and low or medium viscosity silicone (mucostatic) is injected over the flabby ridge and allowed to set and removed as one impression. The impression is removed as one, cast and the denture constructed on the resulting model.
Selective Displacement / Selective Composition Flaming Technique
This techniques aims to displace but not distort the flabby ridge as if in function. A preliminary impression is taken in a mucostatic impression material (eg impression plaster or alginate) and cast in stone. A spaced customised tray for an impression compound impression is then constructed on this model. The tray is loaded with impression compound and an impression taken of the preliminary model of the patient's mouth. This reduces the risk of displacing the flabby ridge. The impression is tried in the mouth and should be quite retentive. The impression is removed and warmed all over except for the flabby ridge area. The impression is retaken in the mouth, the flabby ridge is compressed but not distorted as the other portions of the impression compound (which are warm) sink into the tissues. The impression is removed inspected and re-tried in the mouth to check that it is stable. If any instability occurs then the impression should be reheated and re-taken. A wash impression may be taken in impression paste over the impression compound to obtain maximum detail however is not always necessary.
The treatment of flabby ridges is controversial and no one treatment stands out against the rest, so it is often the method favoured by the clinician that is used.