Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 40

One possible source for the application of suitable forces is the rare earth magnet. These magnets were developed more than 60 years ago, and it has more recently become possible to reduce them in size with the introduction of lanthanide alloys, so that now they may be exploited in the present context. The professional literature has presented successful clinical results of the treatment of impacted teeth in humans [23–26] using magnetic forces. The ‘pull’ of the rare earth magnet is generated along the line of the magnetic plane and in consequence it is possible to prescribe tooth movement in all three planes [27, 28]. However, these magnets corrode significantly in the intra‐oral environment and have to be carefully coated in order to render them safe. A parylene coating has been shown to seal them successfully and, when embedded in acrylic appliances, these magnets can be isolated from the intra‐oral environment and protected from heavy biting forces [28].

There are a number of other significant problems with the use of the rare magnet. The attracting forces that exist between the two magnets are in inverse proportion to the square of the distance between them. This means that when employed in order to move displaced or ectopically positioned teeth, the magnet that is sited on the appliance must be placed close to the magnet that has been bonded to the displaced tooth, otherwise the force between them will be too low. Furthermore, if the magnets are not ideally sited one on top of the other, there will be a dramatic drop in force level [28, 29].

Fig. 2.10 The bonded magnet ‘backpack’.

Courtesy of Professor A. D. Vardimon.

The notion that traction may be applied without the need to trail a wire or a chain through the soft tissues of the palate has a definite appeal to professional authors. They speculate that this will improve the ultimate periodontal condition of the teeth, since ‘eruption simulates a normal eruption process’. However, the following points should be remembered:

 The tooth must in any event initially be surgically exposed.

 The magnet must be bonded to it.

 An open exposure will be indicated for a very superficial and mildly displaced tooth.

 For a deeper and markedly displaced tooth, the flap must be partially or fully replaced and healing must occur.

 The tooth must then travel through the tissues with this relatively large magnetic ‘backpack’ (Figure 2.10).

Each of these caveats will present an obstacle that signifies a departure from the similarity to a tooth that has erupted normally. Even if the idea is ‘attractive’ [30], the use of magnets for impacted teeth is still in its early developmental stages and seems to have been largely lying dormant since the mid‐1990s. The methods that have been described still demonstrate a number of technological disadvantages, the size of the magnets and the inverse square rule of their force of attraction being the most pertinent. At the present time, this method cannot yet be seen as an unequivocal substitute for the more traditional and conventional methods described above [31–34] and has largely been sidelined.