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 Superimpositions

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Monitoring treatment progress and outcomes is critical to patient care. The purpose of superimpositions is to aid the orthodontist in determining the skeletal and dental changes that occur over time. Three superimpositions are required by the American Board of Orthodontics: Cranial Base, Maxillary, and Mandibular Superimpositions. These superimpositions must be performed using the structural method,1 which is based on the use of stable structures described in Melsen's research of cranial base growth,2 Bjork and Skieler's implant research,1,3as well as Enlow's investigation of remodeling.4 The structural method has been shown to be reliable and valid.5,6,7

Video Demonstrations of Structural Method for Superimposition

Narrated by Peter Buschang, PhD  Released March, 2014

Superimposition Requirements

  1. Computer technology may be used to produce cephalogram tracings and superimpositions but the examinee will be responsible for the accuracy of software renderings of all anatomical landmarks, planes and angles.
  2. The ABO welcomes and encourages hand-traced cephalograms and manual superimpositions.
  3. If hand-traced, use a small diameter (0.5 mm) pencil or pen on transparent media.
  4. Tracings must be rendered in black, blue, or red as specified below for level of treatment A, A1 and B. All landmarks, reference lines, and measurements must be recorded, preferably in the same color.
  5. The name of the doctor, practice or school should not be visible on any record.
  6. All tracings, physical or digital, must be sized for presentation at a 1:1 ratio to the digital cephalogram. You may need to print and verify a 1:1 ratio. You can ensure that the digital lateral cephalogram image and the tracing are saved in a 1:1 ratio to each other by following these steps:
    • Digitize the cephalogram and save it as a JPG.
    • Trace the digitized cephalogram and save the combined ceph-with-tracing image as a JPG.
    • Extract the tracing (i.e. hide the cephalogram) and save the tracing as a JPG.
  7. Computer-generated tracings must be printed on transparent media. 
  8. Computer-generated superimpositions may be printed on transparent media or white photographic paper.
  9. Affix an ABO record identification label to all hard copy records.
  10. Conform to specific requirements discussed under Cephalometric Tracing Requirements.
  11. Register the superimpositions using the true radiographic anatomical outlines in accordance with the video demonstrations above.
  12. When there is an Interim set of records, separate superimpositions of A and B tracings, A and A1 tracings, and A1 and B tracings are required.
  13. Arrange the three superimpositions on a single page as demonstrated in the following exhibit: Example of Superimpositions

Lateral Cephalometric Radiographs and Superimposition of Tracings Policy

With the advent of three dimensional technologies, the inherent inaccuracies of traditional radiographs have come into question. While no person has ever believed that cephalometric data collection was an exact science, orthodontics has continuously placed a high degree of importance on superimpositions as an accurate way of:

  • Determining changes in growth and development and treatment.
  • Ascertaining the amount and direction of tooth movement.

Three dimensional volumetric assessments produce exact measurements.8,9  When this type of data is compared to traditional cephalometric information (analogue and digital technology), indiscriminant errors in the actual location of vital landmarks necessary to establish superimpositions are found.

In spite of this problem, the Board encourages the continued use of "like" cephalograms (i.e. cephalograms produced on the same machine), and expects examinees to produce high quality cephalometric radiographs using the ABO measurements to determine diagnostic approaches for patient care and to reveal the final treatment results. Use of these accurately traced cephalograms will give the examinee very valuable information about tooth movement, amount and direction of growth, or lack thereof.

While the Board recognizes that magnification errors will always be present unless three dimensional volumetric radiographs are utilized, it does not dismiss the examinee's responsibility to:

  • inform the Board the conditions under which the initial, progress, and final cephalometric radiographs were obtained.
  • create radiographic superimpositions demonstrating the highest degree of accuracy possible.

When the examinee indicates that pre and post-treatment lateral cephalograms were not taken on the same machine:

  1. Cephalometric tracings are still required, but superimposition(s) are not required.
  2. The examinee must explain the reason for the absence of superimposition(s).
  3. The examinee must be able to explain the changes that occurred during the treatment of their patient.
  4. The examinee will be sent a board case(s) with pre- and post-treatment cephalograms which require tracings and superimpositions to be presented with their case reports.
  5. Notate this with a checkmark in the appropriate box of the Written Case Report, Results Achieved section.
  6. You are representing that the lateral cephalograms were not exposed on the same machine and disproportionate magnification occurred. In this situation, superimpositions are preferred but are not required.
  7. You are responsible for knowing and explaining the superimposition requirements and the changes that occurred as a result of treatment and growth.

1 Bjork A, Skieller V. Normal and abnormal growth of the mandible: A synthesis of longitudinal cephalometric implant studies over a period of 25 years. Eur J Orthod 1983;5:1-46. 
2 Melsen B. The cranial base: The postnatal development of the cranial base studied histologically on human autopsy material. Acta Odontol Scand Suppl 1974;32(62):1-126. 
3 Bjork A, Skieller V. Growth of the maxilla in three dimensions as revealed radiographically by the implant method. Br J Orthod 1977;4:53-64. 
4 Enlow DH, Harris DB. A study of the postnatal growth of the human mandible. Amer J Orthod 1964;50:25-50.
5 Buschang PH, LaPalme L, Tanquay R, Demirjian A. The technical reliability of superimposition on cranial base and mandibular structures. Eur J Orthod 1986;8:152-156. 
6 Doppel D, Damon W, Joondeph D, Little R. An investigation of maxillary superimposition techniques using metallic implants. Amer J. Orthod Dentofac Orthop 1994;105:161-168. 
7 Nielsen IL. Maxillary superimposition: A comparison of three methods for cephalometric evaluation of growth and treatment change. Amer J. Orthod Dentofac Orthop 1989;95:422-431.
8Adams GL, Miller AJ, Harrell Jr. WE, and Hatcher DC. Comparison between traditional 2-dimensional cephalometry and a 3-dimensional approach on human dry skulls. Am J Orthod Dentofacial Orthop 2004; 126:397-409
9Harrell WE, Jr., Hatcher DC, Bolt RL. In search of anatomic truth: 3-dimensional digital modeling and the future of orthodontics. Am J Orthod Dentofacial Orthop 2002; 122:325-330.