Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 33

The points to be considered when choosing the type of attachment to be placed on impacted teeth are different for the impacted tooth than those relating to an erupted tooth that needs to be brought into its position in the dental arch. The wide array of orthodontic brackets, advertised in the catalogues of the various orthodontic manufacturing companies, represents sophisticated designs of attachment, which will enable the orthodontist to perform any direction of movement on a tooth in all three planes of space. Since many, or perhaps most, impacted teeth require a wide variety of movements, it would seem logical to place a sophisticated orthodontic bracket on the affected tooth from the outset.

The particular stage of the initial movement of the impacted tooth, from its ectopic position until it reaches the main archwire, effectively represents the resolution of the impaction. This entire stage, until the bonded attachment arrives at and engages the main archwire, is the most difficult part of the treatment of the displaced tooth and it is not possible to achieve much more than tipping, extrusion and some rotation. In other words, the value of the bracket up to that point is no greater than that of a simple eyelet [14]. Indeed, on several counts, the potential of the eyelet outweighs that of the conventional bracket during the impaction resolution stage.

The base of a conventional bracket is wide and rigid and is manufactured so as to closely conform to the shape of the crown of the tooth in its mid‐buccal location. It is impossible to adapt this preformed base to the shape of another part of the tooth’s surface than that ‘average, one‐size‐and‐shape‐fits‐all’ contour for which it has been designed. It follows that composite bonding on a different location on the tooth is very likely to lead to failure [14]. Orthodontic brackets are highly specialized, each having a slot milled to a very precise blueprint, specific to the particular tooth for which it is intended. The mesio‐distal angulation differs between one tooth and another, the ‘in–out’ bucco‐lingual depth of the slot will vary, the torque angulation will not be the same for all the individual teeth, and the height at which the bracket should be placed on an incisor will not be the same as that on the canine. These are the basic definitions on which the so‐called straight‐wire appliances are built. Accordingly, it is quite obvious that all this highly sophisticated programmed engineering is only meaningful if the bracket is bonded in its appropriate, predetermined mid‐buccal location on the crown of the tooth. We shall see in later chapters that, at the time of the surgical exposure of an impacted tooth, it is very frequently logistically impossible or inadvisable to bond an attachment in the mid‐buccal position on the crown. This site on the crown of the tooth may not be accessible due to its relationship to the root of an adjacent tooth. An excessive amount of soft and hard tissue might need to be surgically removed in order to provide access to achieve the ideal placement, thereby producing unnecessary surgical damage, which always has a price to pay in the form of appearance and long‐term periodontal prognosis of the treated result [14].

The standard orthodontic bracket in any technique is relatively large, possesses a wide, high and sharp profile, and, even when placed in alternative positions on the tooth (by force of circumstance at the time of surgery), may find itself deeply sited within the surgical wound. The shear bulk of the bracket creates irritation as the tooth is later drawn through the soft tissues, particularly the mucosa (Figure 2.3). A ligature wire or elastic thread, which will have been tied to it, must also originate deep in the wound and will be stretched across the replaced flap tissue in the direction of the labial archwire. This will increase the possibility of impingement of the investing tissues and may lead to inflammation and even to permanent periodontal damage.

Fig. 2.3 As the impacted tooth is about to erupt, the high‐profile Siamese edgewise bracket has fenestrated the swollen gingival tissue.

As the displaced tooth moves towards its place in the arch, exuberant gingival tissue bunches up in front of it, leading to a confrontation with a conventional orthodontic bracket. The existence of the exuberant gingival tissue in advance of the tooth can often cause ‘pinching’ between this tissue and the teeth in the arch immediately adjacent to it. This is less likely to occur if a deliberately generous space has been previously provided in the arch for the tooth. Such a precaution may avoid unnecessary periodontal damage.