The panoramic radiograph provides information on the number of teeth present, eruption problems, root form and length, quality of alveolar bone and other pathological conditions. Panoramic radiographs are also often taken during treatment to evaluate the parallelism of the roots and the presence of root resorption or blunting of the root apices. While more than 90% of orthodontic patients experience some degree of root resorption, it is helpful in patients with severe root resorption, consisting of more than 4 mm or one-third the length of the root, to take a 2-3 month pause in treatment to minimize the amount of total root resorption from orthodontic treatment.17
Lateral Cephalometric Head Film
Cephalometrics consists of the use of specific reference points to generate measurements of the craniofacial complex. These measurements are used to evaluate facial growth and development, as well as treatment outcomes. Lateral cephalograms (Figure 20) are obtained by positioning the patient’s head so the median sagittal plane of the head is parallel to the plane of the film and perpendicular to the central ray of the radiation tube. The radiograph enables the orthodontist to determine craniofacial and dentofacial relationships as well as soft tissue relationships. When printed on film 8-10% of magnification exists due to the distance between the patient’s head and the anode. These films are now commonly taken with a digital x-ray machine, resulting in a digital image.
Cephalometric analysis consists of identifying specific anatomical points on the radiograph and using them to determine specific linear and angular measurements. These measurements are then compared with norms and used to determine skeletal, dental, and soft tissue relationships. Specific analyses have been devised, consisting of specific points and measurements to complete the evaluation. One of the first analyses to be developed was the Downs analysis,18 based on facial and skeletal proportions of 25 untreated adolescent Caucasians considered to have ideal dental occlusion. Since then many other analyses have been developed. With printed film, the cephalometric analysis is done via a tracing on acetate paper laid over the image. With advances in digital radiography, softwares (i.e., Dolphin Imaging, QuickCeph) have been developed to digitally adjust for magnification, choose points, and instantly have several analyses after just a few clicks. Cephalometrics provides information about the maxillary relationship to the cranial base; the mandible’s relationship to the cranial base; the maxilla’s relationship to the mandible; vertical skeletal relationships; lip protrusion; vertical facial proportions; and the position of the teeth to the underlying jaws.
Cone Beam Computed Tomography
The use of CBCT is indicated in a number of situations including impacted teeth, craniofacial abnormalities, suspected TMJ pathology and skeletal asymmetries.19 It can provide practitioners with a 3-dimensional image of the location and anatomy of the teeth and of the craniofacial anatomy. CBCT’s can be taken in a variety of volumes which can include a group of teeth, a quadrant of an arch, a full arch, part of the head, or the full head. In cases where a CBCT is indicated, an extended view CBCT including the full head may provide less radiation than a limited view CBCT in addition to a panoramic and cephalometric radiograph. The full CBCT can be used to extract the panoramic and lateral cephalometric radiograph, as well as a P-A cephalometric radiograph when needed. Keeping the amount of radiation exposure to patients as low as possible should always be a priority, and specific indications must be present when taking additional radiographs that may increase the exposure to radiation.
The radiographic information, together with study casts and the clinical examination indicate to the practitioner what type of occlusal and skeletal correction is necessary.
Use of Cone Beam Computed Tomography to locate upper right permanent canine and assess potential root resorption of the upper right lateral incisor.