Should We Use 3D Imaging For “Routine Orthodontic Cases”?

William E. Harrell, Jr., DMD
Board Certified Orthodontist
Alexander City, Alabama

Part I

How do you define a “routine orthodontic case”? Is it confined to: Class I molar, mild to moderate crowding, mild to moderate OJ and OB, no significant vertical problems? A “routine case” does not necessarily mean the case is simple, just that the doctor has defined systems or protocols of treatment organized to handle certain types of cases that consistently works for them. “Routine cases” may still need extraction, Head gear, functional appliances, TADS, expansion or up-righting of the buccal segments, correction of cross bites, etc., depending on the doctor's philosophy of treatment, patient cooperation and/or other constraints of the case. Something that is “routine” is defined as “a course of normative, standardized actions or procedures that are followed regularly “(ref www.wikipedia.org on 3-22-2009).

3D imaging, at first, seems to be needed only for “complicated cases” such as: those that may require orthognathic or reconstructive surgery, cleft palate surgery, impacted teeth (especially canines), TADS, implants or in a case that the orthodontist might consider “difficult” or “complicated” and in need of “further information”. Should we only consider the information that directly affects our orthodontic treatment? This could include areas such as: airway, TMJ, labio-lingual bone width or even other incidental findings, such as supernumary teeth, congenital absence, etc. Some of these “findings” may affect our treatment plan others may not. How do we know up front? The problem is “we don’t know what we don’t know.” 

In order to decide if 3D imaging is right for your practice, you must first define “your” goals of imaging. What do you want the imaging modalities to be able to show you or to document before treatment? What are you trying to visualize and/or measure? How accurately do you want this information to be in relation to the “biological truth”? What if incidental findings show up, are you equipped to handle them or refer them? What if the findings are outside “our area of expertise”? Some of these issues are covered in the July 2007 issue of the AJODO (REF #1 & 2). Also see the March 2009 issue of The Seminars in Orthodontics (vol 15 # 1) for a good general overview of the basics of Conebeam CT (CBCT), 3D facial imaging, dosimetry, 3D diagnosis and treatment planning issues, 3D modeling, 3D orthognathic surgery, airway, sleep apnea, medico-legal issues, and so forth.

The limitations of two-dimensional imaging have been well documented since its inception (REF #3). BH Broadbent (REF #3) was very aware of the “projective projection” problems (magnification, head position errors, etc.) that occur when a 3D object (the head) is projected to the resultant 2D flat x-ray film planes (i.e. Frontal and Lateral Cephs). Landmark identification errors have also been well documented in the literature (Baumrind, REF#4 & 5). Two-Dimensional Cephalometric measurements of the three-dimensional head have major limitations, which have also been thoroughly documented (Adams, REF #6). The “traditional” Panoramic X-ray is used extensively, not only in orthodontics, but in all of dentistry. One of the major uses for panoramic projections in orthodontics, is to evaluate root position and mesio-distal root angulations, not only at the beginning of treatment but for evaluating progress and the final evaluation. Panoramic x-rays are also used for the evaluation of the space requirements for the placement of Temporary Anchorage Devices (TADS) between the roots or in the palate, etc. McKee, et al. (REF #7)  have studied the problems of measuring and visualizing the root angulations on standard panoramic projections, and concluded: “For the maxillary teeth, the images projected the anterior roots more mesially and the posterior roots more distally, creating the appearance of exaggerated root divergence between the canine and the first premolar. For the mandibular teeth, the images projected almost all roots more mesially than they really were, with the canine and the first premolar the most severely affected. The largest angular difference for adjacent teeth occurred between the mandibular lateral incisor and the canine, with relative root parallelism projected as root convergence. It was concluded that the clinical assessment of mesiodistal tooth angulation with panoramic radiography should be approached with extreme caution and with an understanding of the inherent image distortions.” Peck, et.al. (REF #8) concluded that “Panoramic images did not accurately represent the mesiodistal root angulations on clinical patients.”

The following two cases could be considered, by most orthodontists, to fit into the category of “Routine”. They are similar in clinical presentation. They both had chief complaints “to straighten their teeth.” The format will be to first present the traditional 2D information and then treatment plan the case from the information presented. The 3D information will be shown later and for you to determine if 3D information changes your treatment plan.

Case 1

Fig 1 A - Facial & Intraoral                 Fig 1 B - Panoramic View
Photos

Fig 1 C - Lateral Cephalometric View    Fig 1 D - Ceph Tracing

Fig 1 E Ceph analysis

Questions (use email address below to submit response):

     - What treatment plan(s) would you consider based on the 2D information?

     - Do you consider this case “routine” by the 2D information you see here?

 (if you list more than one treatment plan, please rank them 1st choice, 2nd , and so on…)

Case 2

African-American female, 10 years 6 months old, with a chief complaint of “crooked teeth”. Clinical exam revealed Class I molars and canines, moderate crowding and bimaxillary protrusion. TMJ function within normal limits (Maximum opening 45 mm, right lateral 10 mm, Left lateral 10mm).

Fig 2 A - Facial & Intraoral Photos    Fig 2 B - Panoramic View

Fig 2 C - Lateral Cephalometric View  Fig 2 D Ceph Tracing

Fig 2 E Ceph analysis

Questions (use email address below to submit response):

    - Do you consider this case “routine” by the 2D information you see here?

    - What treatment plan(s) would you consider based on the 2D information?

(if you list more than one, please rank them 1st choice, 2nd , and so on…)

References: 

1. Cha,J, Mah J, Sinclair P:Incidental findings in the maxillofacial area with 3-D Conebeam imaging, AJODO, vol132, #1, 7-14, Jul 2007. 
2. Jerrold, L: Liability regarding computerized axial tomography scans, AJODO, vol132, #1, 122-124, Jul 2007.
3. Broadbent, BH: A new X-ray technique and its application to orthodontia, Angle Orthod, 1:45-46, 1931.
4. Baumrind S, Frantz R C. The reliability of head film measurements. 1. Landmark identification. Am J of Orthod 1971a;60:111-27.
5. Baumrind S, Frantz R C. The reliability of head film measurements. 2. Conventional angular and linear measures. Am J of Orthod 1971b;60:505-517.
6. Adams, GL, Gansky SA, Miller AJ, Harrell WE, Hatcher DC: Comparison between traditional 3-dimensional cephalometry and a 3-dimensional approach on human dry skulls, AJODO, vol126, #4,397-409, Oct 2004.
7. Mckee IW, Williamson PC, Lam EW, Heo G, Glover KE, Major PW. The accuracy of 4 panoramic units in the projection of mesiodistal tooth angulations. Am J Orthod Dentofacial Orthop. 2002 Feb;121(2):166-75
8. Peck JL, Sameshima GT, Miller A, Worth P, Hatcher DC. Mesiodistal root angulation using panoramic and cone beam CT. Angle Orthod. 2007 Mar;77(2):206-13.

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