Table 71 Indications for Treatment with Overdentures

1 Replacement of 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 Unrealistic expectations for FBR

6 Expressed desire for removable prosthesis

7 Economic constraints.

Fig 7-1 The model demonstrates the bar and clip attachment system for retention of an overdenture. The bar is round or oval in shape and soldered to two precision fit cylinders made of precious gold alloy. The clips are incorporated in to the fitting surface of the overdenture. Clips can be crimped to increase activation.

Fig 7-2 The model demonstrates the ball and socket attachment system for retention of an overdenture The ball is screwed directly on to a 45° Uni-Abutment™ and secured by bonding with a small drop of Ceka Bond (Ceka NV, Antwerp. Belgium). Alternatively an all-in-one bali abutment is screwed directly into the fixture. The clips (sockets) are incorporated in to the fitting surface of the overdenture, Clips can be crimped to increase activation.

Fig 7-3 The model demonstrates the magnet attachment system for retention of an overdenture. The magnet keeper is screwed directly on to a 45° Uni-Abutment ™ and secured by bonding with a small drop of Ceka bond (Ceka NV, Antwerp, Belgium). The magnets are incorporated in to the fitting surface of the over-denture. Retentive power can not be altered.

reduction in implant success rates is noted in maxillary overdentures, though this is still comparable to data collated from maxillary fixed bridge-work.

The biting forces created by an overdenture12 are comparable, though in a lower range, than those created by fixed bridgework13'14 and compare favourably to those created by a conventional denture.15"17 However some concern arises as to the distribution of these forces to the underlying implants. An overdenture should derive some of its support from the underlying denture bearing area and as such horseshoe dentures are not recommended (as compared to the hybrid prosthesis). Studies have demonstrated that compressive and tensile forces on implants are reduced under an overdenture18 whilst bending moments are higher as the denture causes flexion of the bar,13 However, it is clear that the inclination and orientation of the implants are not critical with respect to complications arising as a result of function.19 Other attachment systems are also well documented, in particular, the ball and socket or retentive anchor attachment (Fig 7-2) which has been compared to overdentures supported by the bar and clip attachments.e-to These have been separ ately reported in short term prospective studies20-21 which have demonstrated high success rates in mandibular rehabilitation. Furthermore one study has shown a positive response at the periimplant and marginal bone level to the loading of these unsplinted fixtures,21 which is comparable to other studies that have measured similar parameters in the bar and clip overdenture.7- 9-11 However some reports5- sand anecdotal evidence would appear to suggest that the ball and socket attachment should be confined to mandibular overdentures, where bi-cortical fixation is available to resist the high tensile forces imparted to the individual implants on withdrawing the denture.

A more recent free standing attachment, better suited to maxillary rehabilitation, is the magnet attachment (Fig 7-3). An overdenture can derive the necessary retention from magnet attachments, but not stability which must be provided through full coverage of the denture bearing area. The use of magnets to retain dentures is well documented22'2,1 as is the subsequent problems of corrosion and loss of magnetism. However the recent publication of a 3-year prospective study on magnet retained overdentures demonstrates that such problems have been overcome by utilising a neodymium-iron-boron magnet, as compared to the historical cobalt samarium magnet.25 Implant success rates with the magnets would seem comparable to both the ball and socket and the bar and clip attachment systems. However, data would suggest that free standing implants need to be at least 11 mm in length if they are to be able to withstand both the compressive and tensile forces of chewing and withdrawal of the denture.25 A distinct advantage of free standing attachment systems is that prophylaxis is facilitated and the patient is better able to maintain good pen-implant health. Indeed, of all the possible restorations studied, the bar and clip retained overdenture has the highest recorded levels for periimplant complications, in particular mucosal hyperplasia.5-1126

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