where an erupted or partially erupted deciduous or permanent tooth cannot be moved. Ankylosis is usually the term given to these teeth, although infra‐occlusion of deciduous or permanent teeth may not necessarily be due to ankylosis. Successfully replanted teeth that have been avulsed as the result of trauma are usually ankylotic. These teeth may often be included in an orthodontic appliance to act as bone anchors, in much the same way as described above regarding the zygomatic plates and screw TADs. Accordingly, they may be used as the base against which orthodontic forces may be applied to other teeth.
Magnets
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.
References
1 1. Olive RJ. Factors influencing the non‐surgical eruption of palatally impacted canines. Aust Orthod J 2005; 21: 95–101.
2 2. Höchli D, Hersberger‐Zurfluh M, Papageorgiou SN, Eliades T. Interventions for orthodontically induced white spot lesions: a systematic review and meta‐analysis. Eur J Orthod. 2017; 39: 122–133.
3 3. Iramaneerat S, Cunningham SJ, Horrocks EN. The effect of two alternative methods of canine exposure upon subsequent duration of orthodontic treatment. Int J Paediatr Dent 1998; 8: 123–129.
4 4. Becker A. Alternative methods of canine exposure and subsequent duration of treatment. Int J Paediatr Dent 1998; 8: 298–299 [letter to the editor].
5 5. Becker A, Chaushu S. Success rate and duration of orthodontic treatment for adult patients with palatally impacted maxillary canines. Am J Orthod Dentofacial Orthop 2003; 124: 509–514.
6 6. Becker A, Chaushu G, Chaushu A. An analysis of failure in the treatment of impacted maxillary canines. Am J Orthod Dentofacial Orthop 2010; 137: 743–754.
7 7. Shapira Y, Kuftinec MM. Treatment of impacted cuspids: the hazard lasso. Angle Orthod 1981; 51: 203–207.
8 8. Kokich VG, Mathews DP. Surgical and orthodontic management of impacted teeth. Dent Clin North Am 1993; 37: 181–214.
9 9. Kokich VG. Surgical and orthodontic management of impacted maxillary canines. Am J Orthod Dentofacial Orthop 2004; 126: 278–283.
10 10. Becker A, Zilberman Y. The palatally impacted canine: a new approach to its treatment. Am J Orthod 1978; 74: 422–429.
11 11. Gensior AM, Strauss RE. The direct bonding technique applied to the management of the maxillary impacted canine. J Am Dent Assoc 1974; 89: 1332–1337.
12 12. Nielsen LI, Prydso U, Winkler T. Direct bonding on impacted teeth. Am J Orthod 1975; 68: 666–670.
13 13. Hunt NP. Direct traction applied to unerupted teeth using the acid‐etch technique. Br J Orthod 1977; 4: 211–212.
14 14. Becker A, Shpack N, Shteyer A. Attachment bonding to impacted teeth at the time of surgical exposure. Eur J Orthod 1996; 18: 457–463.
15 15. Becker A, Chaushu S. Palatally impacted canines: the case for closed surgical exposure and immediate orthodontic traction. Am J Orthod Dentofacial Orthop 2013; 143: 451–459.
16 16. Ziegler TF. A modified technique for ligating impacted canines. Am J Orthod Dentofacial Orthop 1977; 72: 665–670.
17 17. Lu TC, Wang WN, Tarng TH, Chen JW. Force decay of elastomeric chains – a serial study. Part 2. Am J Orthod Dentofacial Orthop 1993; 104: 373–377.
18 18. Storie DJ, Regennitter F, von Fraunhofer JA. Characteristics of a fluoride‐releasing elastomeric chain. Angle Orthod 1994; 64: 199–210.
19 19. Vachiramon A, Urata M, Kyung HM, Yamashita DD, Yen SL. Clinical applications of orthodontic microimplant anchorage in craniofacial patients. Cleft Palate Craniofac J. 2009; 46: 136–146.
20 20. Kuroda S, Sugawara Y, Kuroda S et al. Clinical use of miniscrew implants as orthodontic anchorage: success rates and postoperative discomfort. Am J Orthod Dentofacial Orthop 2007; 131: 9–15.
21 21. Erverdi N, Usumez S, Solak A. New generation open‐bite treatment with zygomatic anchorage. Angle Orthod 2006; 76: 519–526.
22 22.
