Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 76

It was in the late 1980s [18, 19] that the use of computerized tomography (CT) scanning was first proposed as a tool for the identification of the exact position of the palatally impacted canine, particularly when root resorption of the lateral incisor is suspected [20]. At that time, while its excellent potential was recognized for diagnosis of the position of impacted and supernumerary teeth, the large dosage of radiation that routine CT imaging required was difficult to justify for all but the most complex and exceptional cases. The previously common use of plain 2D radiography often failed to disclose the exceptional and difficult nature of the particular case – a matter that would later be abundantly clear on a CT scan.

In the years following the first edition of this book, CT has found and established an important place in planning the treatment of impacted teeth. Accurate 3D localization of the impacted tooth is immediately available. In this way, the exact relationships between the impacted teeth and their adjacent teeth could be seen along the entire lengths of the crowns and roots of each.

Using this modality, it has become possible to improve the overall assessment of cases in which the impaction could best be resolved with orthodontic treatment and to sufficiently separate them from those where the tooth was in an intractable position. Trial and error slowly became a practice of the past [21, 22], since it became possible to present a 3D radiographic image of what the surgical field would look like when an impacted tooth was uncovered by the oral surgeon. This helped to eliminate positional misdiagnosis and the consequent undertaking of treatment for those relatively few cases in which the position and proximity of other teeth made it impossible to arrive at a successful conclusion to the treatment.

Similarly, the axial (horizontal) and cross‐sectional (vertical) ‘slices’ as selected provided information in the bucco‐lingual plane, which had been generally impossible to discern with routine plane radiography. These views contributed materially to the evaluation of the prognosis of the intended treatment. Thus, the bucco‐lingual proximity of teeth and the existence and extent of oblique root resorption all become assessable, and these were and are important factors in determining choice of teeth for extraction or indeed whether to undertake treatment at all.

In a study performed in 1988 [19], the prevalence of resorption of the roots of incisor teeth, as associated with an impacted canine, was investigated by plain 2D radiography and found to affect 12% of the individuals in the sample. When the same investigators repeated their study 12 years later using spiral CT scanning [23], the number of affected individuals increased to 48%! There can be little doubt that this was due to this vastly improved diagnostic tool and to the fact that resorption of the buccal or palatal aspects of the roots of the incisor teeth cannot be seen on regular radiograph. It is only when the buccal or palatal resorption has become sufficiently extensive to cause a change in the shape of the mesio‐distal profile of the root that it may be identified by plain 2D radiography and this type of resorption would go undiagnosed.

CT offers advantages in assessing the proximity of the impacted tooth to an adjacent pathological entity. It also provides valuable assistance in evaluating aberration in the shape and appearance of the crowns and roots of teeth that were suspected of having been damaged or have suffered from abnormal development due to past trauma [24].

Conventional spiral CT machines, as used in routine hospital practice for imaging various parts of the body, expose the body to an X‐ray beam in the form of a progressive spiral, encircling the body over a specific, defined area, with continuous radiation during the whole scanning time. This submits the patient to a high dose of ionizing radiation and has been a subject of concern when considering its use in the dental context. The dosage was evaluated by Dula et al. [25, 26] using what they called a ‘hypothetical mortality risk’. In this assessment, the mortality risk associated with routine dental radiographs ranged between 0.05 and 0.3 × 10⁻⁶ units, depending on the type and number of radiographs performed, while a CT scan of the dental area alone was assessed at 28.2 × 10⁻⁶ for the maxilla and 18.2 × 10⁻⁶ for the mandible.