Lasso wires
In the years prior to the mid‐1960s, a lasso wire (Figure 2.1), twisted tightly around the neck of the canine, was widely employed, and indeed was the type of attachment that we ourselves used in our very earliest cases. It will be readily appreciated that the shape of the crown of a normally shaped healthy tooth is such that its narrowest waist diameter is at the cemento‐enamel junction (CEJ). This is where the lasso wire will inevitably settle. This undesirable consequence will unavoidably result in irritation and recession of the gingival and periodontal tissues and will actively prevent their reattachment in this vital area. There is also evidence that, as a consequence of employing this method, external resorption and ankylosis have been produced in the area of the CEJ [7]. The excellent alternatives that are available today have rendered the lasso wire obsolete.
Fig. 2.1 Lasso wire encircling the neck of an impacted canine (circa 1971).
Fig. 2.2 Threaded pins set into prepared holes, drilled and tapped into the enamel and dentine of the surgically exposed canines (circa 1973).
Threaded pins
Several systems of threaded pins (Figure 2.2) have been available for many years. Their original specific purpose was to provide retention for an amalgam or composite core and to allow the provision of a cast crown in a severely broken‐down tooth. However, these threaded pins have also been used in the past as the attachment for an impacted tooth [8, 9], although they have now been totally superseded by other methods of attachment. Some of the disadvantages of the threaded pins method include the fact that it is dentally invasive, necessitating subsequent restoration. Given the difficulties of access to many impacted teeth and the desirability of limiting surgical exposure as much as possible, it may be difficult to determine the orientation of the long axis of the tooth and the drilled hole may inadvertently enter the pulp. Moreover, unerupted and non‐functional teeth often have large pulp chambers. Even in the most favourable of circumstances, it seems that this unnecessarily aggressive method actually causes damage to a virgin tooth, in light of the fact that there are eminently suitable, non‐invasive methods and efficacious alternatives, as we shall discuss below. Nevertheless, the method was still in use and apparently recommended as late as 2004, which was, anachronistically, well into the present era of composite bonded attachments [8, 9].
Orthodontic bands
Preformed orthodontic bands with welded attachments [10] largely replaced both the lasso wire and the threaded pin in our protocol. Clinical experience with these bands showed them to be considerably more compatible with ensuring the health of the periodontal tissues. As with the lasso wire, the use of a band dictated a very wide surgical clearance of tissue on all sides of the tooth. However, in order to permit the introduction and cementation of the band, it was imperative, at the time of placement, to adequately control haemorrhage around the crown and to avoid contamination from oozing blood inside the cement‐filled band.
Bonded attachments
With the introduction of acid‐etch composite enamel bonding, all the above‐mentioned methods became obsolete. The adoption of the acid‐etch composite bonding technique to the crown of a tooth has many advantages [11–15], most notably in terms of simplicity and reliability of the bond [14]. However, its greatest advantage is that, to be successful, it requires relatively little exposed surface of enamel, a fact that has contributed much to the subsequent periodontal health of the treated result. It is presently without doubt the method of choice from almost every point of view, and is appropriate to replace other methods in virtually all circumstances.
Standard orthodontic brackets
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,
