Hybrid Fixed Detachable Prosthesis

Experience with maxillary fixed prostheses over the last 15 years has drawn attention to a number of problems which arise as a direct result of the distopalatal atrophy of the maxilla, leading to poor implant orientation and inclination, and loss of lip support.

The subsequent prosthesis is often cantilevered labially to restore soft tissue support, with an attendant compromise of aesthetics and phonetics as air and saliva escape through the gaps between the bridge and the residual alveolus. The need therefore exists for an alternative treatment therapy which would provide patients with the occlusal stability and retention of a fixed prosthesis, whilst restoring lip support and optimising conditions for phonetics and oral hygiene at the same time.

In 1991, Lothigius el al12 published a two part article which presented the technical and clinical aspects of a new hybrid prosthesis with a design that incorporated separate support derived from a milled bar with lateral stabilisation obtained by a removable, close fitting, chrome based prosthesis and retention provided by the incorporation of precision attachments. Such prostheses have been followed up successfully for two years and have a reported implant success rate comparable to maxillary fixed bridge prostheses.3

It was proposed that the design of the hybrid prosthesis would present the following features:

1 To splint the implants with the same rigidity as a fixed prosthesis.

2 Avoid patatal coverage, as compared to an overdenture.

3 Provide adequate lip support.

4 Optimise conditions for phonetics.

5 Facilitate oral hygiene procedures.

6 Provide adequate retention.

7 I ncorporate serviceable precision attachments.

The original articles describe a horseshoe shaped overdenture, reinforced by a cast cobalt-chromium (Co/Cr) framework (Fig 6-1), which closely fits over a parallel sided

Fig 6-1 The hybrid prosthesis comprises a standard horseshoe denture which is reinforced with a cast Cobalt/Chromium framework, that is close fitting to the milled bar and incorporates the Ceka Revax {Ceka NV. Antwerp, Belgium) precision attachments.

Fig 6-2 The milted bar is cast in a Type III dental gold alloy and is parallel sided to enhance lateral stability Support for the over-denture is derived from the elevated areas of the bar. Female keepers are incorporated into the distal extensions which in combination with the patrix, provide the necessary retention milled bar, thus attaining support. Retention is derived from Ceka Revax attachments (Ceka NV, Antwerp, Belgium) which locate into the matrix incorporated at the distal ends of the milled bar (Fig 6-2). Lateral stabilisation is provided by the denture coverage, in particular over the tuberosities, and the labial flange ensures both adequate lip support and the prevention of air and salivary leakage.

In being a removable prosthesis, the requirement for hygiene maintenance is satisfied with direct access to the supporting implant substructure. In retrospect it is clear that the indications for use of a hybrid prosthesis may encompass a wide range of otherwise complex restorative cases, which can be identified by their mutual need to accommodate the following criteria:

1 Replacement ol lost hard tissue support.

2 Replacement of lost soft tissue support.

3 The presence of an unfavourable ridge morphology.

4 The presence of unfavourably oriented and inclined implants.

5 The need to restore occlusal stability to a level approaching that of a fixed bridge prosthesis.

When considering the above, it is clear that a variety of developmental and acquired conditions might benefit from such a reconstruction, such as cleft palate patients and patients who have lost substantial hard tissues through trauma.

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