Orthodontic Treatment of Impacted Teeth. Adrian Becker

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      It is well known that movement of teeth adjacent to an impacted tooth will often have a positive effect on the eruptive behaviour of that tooth, particularly if the movement involves the opening of space in the dental arch [1]. By the time the space has increased to be of a suitable size and by the time the oral and maxillofacial surgeon is able to make appropriate arrangements for its surgical exposure in a busy schedule, a new periapical radiograph may indicate that the impacted tooth has significantly improved its position. In such a case, the surgery may become superfluous. Indeed, if the spontaneous eruption seems likely to occur imminently, or at least within a reasonable period, there is obvious merit in waiting for this to actually occur.

      If, on the other hand, eruption looks as if it will take many months, then the orthodontist must weigh the benefits of avoiding surgery against the drawbacks involved in leaving orthodontic appliances in place for an extended period of time. As a general rule, orthodontic appliances increase the susceptibility of the teeth to caries, which is evident with the initial appearance of so‐called white spot lesions [2]. In the case of long‐term presence of appliances, there is a significant risk of proliferative inflammation of the gingivae and serious periodontal involvement. Indeed, the longer the appliances are in place, the greater the risk of damage.

      There is, however, a further factor to be taken into account, because removing the appliances before treatment is completed brings with it the risk of having to replace the appliances. This may be necessitated in order to correct a malposition of the newly erupted (and erstwhile impacted) tooth. The flip side is to accept a compromised and inadequate outcome. To solve this dilemma, the clinician may elect to advise surgical exposure followed by orthodontic traction in order to expedite the eruption of the tooth and thus clear the way to complete the treatment within a very much shorter time.

      A similar dilemma may arise when orthodontic treatment has provided space and surgery is undertaken to remove a physical obstacle. In such an event the elimination of the obstacle will have rendered the impaction potentially resolvable, without further treatment. However, the surgical intervention involved in removing the obstacle will offer the opportunity of anaesthetized access to the unerupted tooth. It would be a pity not to exploit that opportunity, since subsequent healing of the wound will deny that access. If that eruption does not then take place, a second surgical intervention in the same area will have been necessary and much time will have been wasted confirming that spontaneous eruption will not occur.

      It is therefore quite clear that the time factor is most important. Orthodontic appliances are in place and there may be an unsightly space in the dental arch. Orthodontically aided eruption will unquestionably speed up the resolution enormously and, this being so, the patient’s best interests are to be served by including exposing and bonding the impacted tooth among the factors to be considered at the planning stage.

      When the existence of an impaction is only a small part of a complex overall malocclusion, the time factor becomes more critical. It would be a reasonable estimate that a given overall orthodontic problem, by itself, may require two years of treatment. In the case of an awkwardly placed impacted tooth, the resolution of the problem may take a further year or more [3–5]. To add the luxury of a wait‐and‐see period is to add yet more time to this already extended three‐year plus period. During all this time, orthodontic appliances are being worn. The result of all this is that, while the orthodontist may well be rewarded by an improved position of the impacted tooth, a deteriorating state of oral health, due to poor oral hygiene, may deprive the achievement of all meaningful content.

      Let us remind ourselves of the definitions set out in Chapter 1, in which it was noted that a ‘permanent tooth with delayed eruption [is an] unerupted tooth whose root is developed in excess of two‐thirds of its expected final length and whose spontaneous eruption may nevertheless be expected within a reasonable time’. A tooth that is not expected to erupt within a reasonable time in these circumstances is termed an impacted tooth. Thus, in the present context and despite the fact that the tooth may be expected to erupt spontaneously ‘in time’, this period may be considered ‘unreasonable’, when taking into account the likelihood of detrimental iatrogenic effects on the remainder of the dentition, engendered by this extra and often considerable waiting period. This then will reclassify the tooth (in clinical therapeutic terms) as an impacted tooth. As such, a proactive surgical exposure should be considered.

      In this chapter we shall therefore discuss the manner in which the orthodontic treatment of impacted teeth needs to be modified to accommodate the special requirements of the orthodontic appliance, the specific components that may be usefully employed and the accompanying treatment strategy that will make its performance run smoothly. It is not the intention here to discuss the details of appliance therapy. These will be set out in later chapters, where we will discuss the different groups of impacted teeth that are seen in practice. However, some general principles are in order at this juncture.

The anchor unit

For most malocclusions, quality treatment is best provided by the use of one or other of the recognized fixed appliance treatment techniques. If the dental arches are correctly related and adequate space is present, then the teeth are initially ‘levelled’ to a labial archwire of standardized archform and a given coefficient of elasticity. Later, heavier round or rectangular steel archwires are substituted to activate root movements that will pave the way to achieving an optimal result. In cases of incorrectly related dental arches, the use of other appliances is recommended, such as headgear, functional appliances or intermaxillary means of traction, prior to or together with the fixed appliances. Here, space may be provided by the extraction of teeth or by lengthening the arches mesio‐distally or expanding them laterally.

      When dealing with a malocclusion that incorporates an impacted tooth, this procedure will need to be modified. Unlike other teeth in the mouth, the impacted tooth may be severely displaced from its normal position in all three planes of space, and much anchorage will be expended in bringing it into alignment. Accordingly, a rigid anchor base must be developed against which to pit the forces required to resolve the impaction.

      At the age at which an impacted maxillary canine is treated, the full permanent dentition (with the exception of third molars) is usually present. Accordingly, a fully multibracketed appliance would normally be placed in position. With the use of light archwires, the entire dentition will be treated through the stages of levelling and the opening of adequate space in the arch for the impacted tooth. A heavy and more rigid archwire is then placed into the brackets on all the teeth of the fully aligned and complete dental arch. The aim of this is to provide a solid anchorage base [5, 6], which will not allow the distortion that may otherwise result from the forces that will eventually be applied to the impacted tooth after its exposure. One should not underestimate the demands made on the anchor unit by forces designed to resolve a grossly displaced canine, particularly if the forces are applied for an extended duration.

      By contrast, at the age at which an impacted upper central incisor needs to be treated, only first permanent molars and three permanent incisor teeth are present in the maxillary arch. Accordingly, in order not to compromise the remainder of the dentition, it will be necessary to employ alternative means of making the appliance system rigid in order to oppose the light forces that will be applied to the impacted tooth. The anchorage value of the appliance may be enhanced by including a soldered transpalatal bar or by bonding brackets to the deciduous molars and canines.

Attachments

      Some form of attachment must be placed on the tooth in order to be able to influence its positive resolution and to bring it into its place in the dental arch. These attachments have changed over the years, reflecting the advances made in the field of dental materials.

       Lasso wires

In the years prior