Cephalometry in Orthodontics. Katherine Kula
AAO Clinical Practice Guidelines1 also recommend evaluating the patient’s treatment outcome and determining the efficacy of treatment modalities by comparing posttreatment records with pretreatment records. Posttreatment records may include dental casts; extraoral and intraoral images (either conventional or digital, still or video); and intraoral, panoramic, and/or cephalometric radiographs depending on the type of treatment and other factors. Many orthodontists also take progress cephalograms to determine if treatment is progressing as expected. In addition, board certification with the American Board of Orthodontics requires cephalograms and an understanding of cephalometry to explain the decisions for diagnosis, treatment, and the effects of growth and orthodontic treatment. Therefore, it is paramount that orthodontists understand how to use cephalometrics in their practice.
Basics of Cephalometrics
Cephalometrics is used to assist in (1) classifying the malocclusion (skeletal and/or dental); (2) communicating the severity of the problem; (3) evaluating craniofacial structures for potential and actual treatment using orthodontics, implants, and/or surgery; and (4) evaluating growth and treatment changes of individual patients or groups of patients. In general, a lateral cephalogram shows a two-dimensional (2D) view of the anteroposterior position of teeth, the inclination of the incisors, the position and size of the bony structures holding the teeth, and the cranial base (Fig 1-1a). A cephalogram can also provide a different view of the temporomandibular joint than a panoramic radiograph and a view of the upper respiratory tract.
Fig 1-1 (a and b) Lateral and frontal cephalograms.
In addition, cephalograms aid in the identification and diagnosis of other problems associated with malocclusion such as dental agenesis, supernumerary teeth, ankylosed teeth, malformed teeth, malformed condyles, and clefts, among others. They have also been used to identify pathology and can give some indication of bone height and thickness around some teeth. However, they are not very useful in identifying dental caries, particularly initial caries, and periodontal disease, so bitewing radiographs and periapical radiographs are needed for patients who are caries susceptible or show signs of periodontal disease. While some asymmetry can be diagnosed using a lateral cephalogram, an additional frontal cephalogram (Fig 1-1b) is needed to better identify which hard tissue structures are involved in the asymmetry.
Of course all of these conventional radiographs are 2D images. A 3D CBCT can replace multiple 2D radiographs and can allow the entire craniofacial structure to be viewed from multiple aspects (x, y, z format) with one radiograph (Fig 1-2). Intracranial and midline facial structures can be viewed without overlying confounding structures, and bilateral structures can be viewed independently. While the worldwide transition from 2D to 3D imaging is occurring quickly, it is still important for clinicians to understand what has been used for decades (2D), what additional 3D information is needed, and the limitations and potential of 3D imaging.
Fig 1-2 Software screen showing (a) coronal slice (green line in b and c), (b) sagittal slice (red line in a and c), (c) axial slice (blue line in a and b), and (d) 3D CBCT reconstruction of the same study.
The general purpose of this book is to introduce the orthodontic clinician to the use and interpretation of cephalometrics, both 2D and 3D, and to show the potential benefits of using 3D CBCTs. The purpose of this chapter is to provide the background for the current and future use of cephalometrics.
History of Cephalometrics
Prior to the use of radiographs, growth and development of the craniofacial complex was essentially a study of skull measurements (craniometry) (Fig 1-3) or soft tissue. Craniometry2 dates back to Hippocrates in the 4th century BC and is still used today in physical anthropology, forensics, medicine, and art. It is used to determine the size of cranial bones and teeth, their relationship to each other, potential differences among groups of people, and evolutionary changes in the cranium and face. Some of the current cephalometric landmarks, planes, and angles have their origin in craniometry. For example, the Frankfort plane was established in 1882 during a meeting of the German Anthropological Society as a standardized method of orienting the skull horizontally for measurements.2 The anthropologists agreed to define the Frankfort plane as a plane from the upper borders of the auditory meati (external auditory canals) to the inferior margins of each orbit. Later, this plane was modified for cephalometry to indicate that the right and left porion and left orbitale would be used to define the horizontal plane to minimize problems that asymmetry caused.
Fig 1-3 An original Broadbent craniostat used to standardize skull position and measurement. (Courtesy of Dr Juan Martin Palomo, Case Western Reserve University.)
Craniometry, however, had limitations. Each skull represented a one-time peek or snapshot at the development of one individual—in other words, a cross-sectional data point. There was little hope of a longitudinal study. Frequently, the reason for the death of the individual was unknown, resulting in an unknown effect on the growth and development of the skull. Thus, craniofacial development was interpreted based on the skulls of children who died because of trauma, disease, starvation, abuse, or genetics. Todd,3 the chairman of the Department of Anatomy at Case Western Reserve University School of Medicine, considered the measuring of these children’s skulls as studying defective growth and development; the longitudinal effect of orthodontic treatment on growth and development could not be assessed. Animal studies using dyes were obviously limited in providing interpretation of the effect of various factors on human growth and development. Soft tissue studies, particularly longitudinal, were also limited by the lack of reproducible data. Radiographs, however, provided the opportunity to study and compare multiple patients over decades.
The use and standardization of cephalograms continually evolved from their early beginnings in the late 1800s. Similarly, during that time, orthodontics had its inception as a dental specialty. Edward Hartley Angle classified malocclusion in 1899 and was recognized by the American Dental Association for making orthodontics a dental specialty.4 Angle established the first school of orthodontics (Angle School of Orthodontia in St Louis) in 1900, the first orthodontic society (American Society of Orthodontia) in 1901, and the first dental specialty journal (American Orthodontist) in 1907.
Shortly after the discovery of x-rays by Wilhelm Conrad Roentgen in 1895,5 the use of the first facial and cranial radiographs was reported as early as 1896 by Rowland6 and later by Ketcham and Ellis.7 By 1921, B. H. Broadbent was using lateral cephalograms in his private practice.7 In 1922, Spencer Atkinson reported to the Angle College of Orthodontia that he used lateral facial radiographs to identify the position of the first molar below the maxilla’s key ridge.7 Because the radiographs also showed soft tissue, Atkinson suggested that these lateral radiographs had the potential of relating the mandible and the maxilla to the face and to the cranial base.
Initially, the comparison of cephalometric radiographs to show the effects of growth and treatment was difficult because head position and distance from the cephalometric film were not standardized. In an attempt to standardize head position, in 1921 Percy Brown designed a head holder for taking radiographic images of the face.7 In 1922, A. J. Pacini reported standardizing head position for lateral radiographs