History of imaging in orthodontics from Broadbent to cone-beam computed tomography

The history of imaging and orthodontics is a story of technology informing biology. Advances in imaging changed our thinking as our understanding of craniofacial growth and the impact of orthodontic treatment deepened. This article traces the history of imaging in orthodontics from the invention of the cephalometer by B. Holly Broadbent in 1930 to the introduction of low-cost, low-radiation-dose cone-beam computed tomography imaging in 2015.

Highlights

  • Broadbent and Todd developed a roentgenographic craniostat in the 1920s.

  • An improved device, the Broadbent-Bolton cephalometer, was introduced in 1931.

  • Cephalometric analysis resulted in an explosion in research on craniofacial form.

  • Computed tomography 3D images in the 1970s came with high radiation, low resolution.

  • New cone-beam computed tomography machines overcame some of these problems.

The history of imaging and orthodontics is a story of technology informing biology. Advances in archwires, brackets, and bands influenced the mechanics of orthodontics. Advances in imaging changed our thinking. This is because imaging gives the specialty a scientific tool to study longitudinal craniofacial growth and the impact of orthodontic treatment on this dynamic process. Throughout the 20th century, 2-dimensional (2D) radiography was used to answer important clinical questions: How much does the maxilla grow between 10 and 12 years of age? What is the relative change in growth between the maxilla and the mandible? This article will trace the history of imaging in orthodontics from the invention of the cephalometer by B. Holly Broadbent in 1930 to the introduction of low-cost, low-radiation-dose cone-beam imaging in 2015. We will highlight the questions that have been answered by cephalometrics in the previous 85 years and mention a few persons whose work in craniofacial imaging we believe was seminal to our specialty. And we will put forth the proposition that the questions we ask in the next 85 years will determine the fate of our specialty. Without a doubt, the most important unanswered question in orthodontics is “How do we change one stable system (a malocclusion) into another stable system (a normal occlusion)?” This is the critical question because if we give up on stability as a goal of treatment, there is no specialty.

Fortunately, the new 3-dimensional (3D) scanners use less ionizing radiation than traditional cephalograms and panoramic views. Now we get more information with less radiation. But the question still remains: what will we do with this increased information? In the words of Peter Parker, “With great power comes great responsibility.” If we choose to use this information to improve our ability to create stable results, we will ensure that the first specialty in dentistry remains viable in the future.

Facial form and craniometrics: The harbinger of the cephalogram

Ancient civilizations, notably Greek and Egyptian, studied facial form. The first modern efforts in craniofacial studies, using planes and measurements, are often credited to the artists and anthropologists of the 13th to the 15th centuries. Leonardo da Vinci in the 1400s provided the first applicable form of facial characterization using a multiline system that allowed him to reliably reproduce head position and evaluate aspects of facial form. Albrecht Dürer (1528) published a treatise, based on his investigations as an artist, evaluating head form using a coordinate system. Physical anthropologists used direct measurements on skulls at the time to obtain data on facial form. In the 16th century, Spiegel introduced the idea of 4 planes (lineae cephalometricae) as the study of head form began to attract greater interest among anthropologists. Most craniometric studies for the next 200 years would be focused on cranial size and shape. The goal of these investigations was to characterize similarities and differences among human populations in an attempt to link brain size and shape with function. Although this would eventually prove to be a futile effort, the planes and angles that were developed formed the basis of what would become cephalometrics. Krogman in his 1950 presentation highlighted several contributors, including Camper’s plane and facial angle (Pieter Camper), Daubenton’s position on the foramen magnum and the occipital angle, Blumenbach’s plane based on the maxillary anterior dentition, and either the occipital condyles (in younger skulls) or the mastoid process in the older skulls. Andres Retzius introduced the concept of the cephalic index, and John Barclay might have been the first to incorporate the mandible into craniometric studies. Discussions on ideal planes as a reference for craniofacial studies continued into the 19th century with Von Baer’s plane, the Frankfort horizontal plane, and Huxley’s basicranial axis. The latter was the first division of the cranial base into 3 parts: anterior, middle, and posterior. However, craniometrics, by its very nature, was limited to cross-sectional studies on human skeletal remains.

Two important developments in the second half of the 19th century paved the way for radiographic cephalometrics. First, the need for standardizing skull position that resulted in the first craniostat by Pierre Broca, an anthropologist from France, and second, the use of x-rays, for which Wilhelm C. Roentgen won the Nobel Prize in 1917. These discoveries made roentgenographic cephalometrics possible. In a 1922 lecture at the Angle College in Pasadena, California, Spencer Atkinson drew attention to use of a roentgenogram of the cranium to determine the relationship of the maxillary first molar to the key ridge. He also pointed out that it was possible to visualize the relationship of the 2 jaws to the cranial base and the rest of the face. One of Angle’s students attending this lecture was Broadbent. The impact of Atkinson’s observation on Broadbent is evident in his 1937 paper. Significantly, in 1922, August A. J. Pacini and Carrera received an award from the American Roentgen Ray Society for their thesis based on obtaining the first radiographs of the skull. Although an early technique with limitations, it was nevertheless a milestone in craniofacial imaging.

The birth of cephalometrics

After his training under Angle, Broadbent joined renowned surgeon-turned-anatomist T. Wingate Todd in Cleveland, where together they developed the Western Reserve University roentgenographic craniostat, which allowed for acquisition of standardized lateral and anteroposterior planar radiographs of the human skull and mandible ( Fig 1 ). These images captured both internal and external bony anatomy but compressed the 3D information into a 2D image. Refinements to this device would result in the Broadbent-Bolton cephalometer in 1931 ( Fig 2 ). Early in their association, Todd and Broadbent superimposed serial roentgenograms made by commercial laboratories of patients under treatment to try to elucidate the effects of treatment. Although they noted changes in soft tissues, articulation of the dentition, and even the nasopharyngeal areas, they concluded that laboratory roentgenography was not sufficiently standardized to allow scientific inquiry. This conclusion drove the refinement in technique that ultimately led to the Broadbent-Bolton cephalometer.

Fig 1
Craniostat developed by Broadbent and Todd as a precursor to the first cepahlometric head holder.

Fig 2
The first cephalometer on display on the third floor of the School of Dental Medicine in the Bolton Brush Growth Study Center, Cleveland, Ohio, ca 1970.

A key feature of the Broadbent-Bolton cephalometer was that it used 2 x-ray sources, thus allowing both lateral and frontal radiographs to be taken without moving the subject’s head. Broadbent recognized that because this was a projection image and there was a distance between the object (patient’s head) and the film, enlargement of anatomic structures was unavoidable. To be able to accurately estimate this enlargement, the distances from the midsagittal plane to the lateral film cassette (mesiolingual distance) and from the transporionic axis to the frontal film cassette (posteroanterior distance) were recorded in millimeters for each radiograph. When used with the Bolton orientator, these distances allowed accurate measurement of anatomic radiographic structures ( Fig 3 ). Although many now believe that the primary purpose of the cephalogram is to characterize craniofacial morphology and inform orthodontic diagnosis, this was not the intent of the inventors. Broadbent and Todd realized that the real value of radiographic cephalometry was the ability to study changes in normal human skeletal anatomy over time. Longitudinal growth studies thus became the plat du jour. In Cleveland, Todd began the Brush Inquiry to study normal development of the appendicular skeleton from birth to adulthood (thought to be about 18 years of age), and Broadbent headed the Bolton Study that focused on the lateral and frontal cephalometric radiographs as well as dental casts. Detailed handwritten notes regarding nutritional, dental, and medical health status and disease history of each subject supplemented the radiographic data. Started in 1929, the Bolton Study examined normal craniofacial and dentofacial growth and development of 4309 children, twice a year from infancy to 20 years of age. Several younger participants were x-rayed every 3 months because of rapid changes noted in their dentition. Of the subjects in the Broadbent-Bolton Growth Study, 2890 were also enrolled in the Brush Inquiry. All records of the subjects in both studies resulted in the formation of the Bolton Brush Growth Study Center at Case Western Reserve University. For a complete history of these collections, see “In search of truth for the good of man” ( dental.case.edu/boltonbrush/ ). In addition to the longitudinal studies in Cleveland, 8 other longitudinal studies were conducted throughout North America. Selected samples from these studies are now part of the American Association of Orthodontists Foundation Legacy Collection ( www.aaoflegacycollection.org/aaof_home.html ). In 1931, Broadbent published the technique of capturing the cephalograms along with his preliminary findings in the first issue of the Angle Orthodontist . In his initial remarks, he credited several people, “Todd, Keith, Hellman, Krogman, Lewis, Simon, Dewey, Stanton, and others whose names merit but space does not permit mention,” reflecting the immense contributions of others along with a sense of humility and collegiality. In this landmark article, he concluded with the significance of orthodontists’ and anthropologists’ new-found ability to study the living and his preliminary finding that the cranial base offers a more stable base for tracings and is an accurate method of measuring changes caused by growth and treatment interventions.

Fig 3
Bolton-Brush orientator, developed to correct for projection errors by using both lateral and posterior anterior views simultaneously.

On March 15, 1937, Broadbent presented his findings from the Bolton Study at the Eastern Association of Graduates of the Angle School of Orthodontia in Cleveland. In his presentation and publication, he demonstrated and justified the use of the Bolton-nasion plane for orientation of images and the use of R point as the most fixed point to study growth of the face. The vertical dimension of growth, the impact of dental eruption on the vertical dimension, the downward and forward growth of the face, the relatively parallel position of the hard palate during the entire growth process, and the timing of cessation of growth of the occipitosphenoidal suture around the age of 9 were key observations. Based on the cephalometric evidence, he pointed out that “submerging teeth,” clinically described by Noyes a year earlier, were, in fact, teeth left behind as the rest of the dentition and the jaw moved toward maturity. Studying dental development, Broadbent described for the first time the roentgenographic findings of dental development in 4 stages—(1) infancy; (2) the age of 3 and a half years, when all deciduous teeth are present and adequate information can be gathered on the positions of the permanent first molars; (3) the mixed dentition stage, when the mouth contains equal numbers of permanent and deciduous teeth (12 each); and (4) the young adult—to illustrate the growth of the mandible that allows for the eruption of the terminal molars and the changing axial inclination of the molars as growth in the area continues. He also substantiated the order of appearance of the permanent incisors and canines originally described by Kronfeld. The clinician in him noted that the “ugly duckling stage” is a normal stage in growth and development that required the clinician to simply observe and monitor growth and development. It was clear that radiographic cephalometrics had much to offer in the study of growth and development of the craniofacial form.

Allan Brodie, another Angle student from Pasadena, realizing the enormous significance of Broadbent’s early work, at once acquired a Broadbent-Bolton cephalometer (in 1932) for the first graduate orthodontic program in the United States at the University of Illinois at Chicago (established in 1930). Six years after acquiring the cephalometer, Brodie et al published the first findings of treatment and posttreatment effects. Brodie personally studied the Class III sample, William B. Downs examined the Class I sample, and Abraham Goldstein and Ernest Myer studied the Class II sample of patients, all treated in their graduate program. The results of their study answered several previously unknown questions. Brodie concluded that identical treatment of different patients yielded different results, and success in treatment was associated with growth and bodily movement of teeth. He also noted that most of the effects of orthodontic treatment were at the level of the alveolar bone. However, Brodie recognized the limitations in the tracing methods, particularly when the thickness of the ink alone exceeded the dimension of the anatomic structure under review. Brodie finished his PhD degree in anatomy at the University of Illinois, largely using the Bolton collection to study craniofacial growth from infancy to 8 years old. For his thesis, he carefully studied growth in 4 specific regions: brain case, nasal area, upper alveolar region, and mandible. Using angular measurements and superimpositions, Brodie concluded that the morphogenetic pattern of growth was probably established by the third month of life. He reported that the angular relationship of the nasal floor, the occlusal plane, and the inferior border of the mandible stays in relatively the same relationship with the cranial base after the age of 3 months. Importantly, he also attributed the increase in anterior facial height to similar increments of growth in the mandible, and established that the mandibular angle maintains a constant angular relationship with the cranial base and that teeth tend to maintain their angular relationships in the face over time.

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Apr 6, 2017 | Posted by in Orthodontics | Comments Off on History of imaging in orthodontics from Broadbent to cone-beam computed tomography
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