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Should We Use 3D Imaging For "Routine Orthodontic Cases?" William E. Harrell Jr., DMD, Board Certified Orthodontist

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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” might still need extraction, head gear, functional appliances, temporary anchorage devices (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).

Three-dimensional 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.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 cone beam computed tomography (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.3 BH Broadbent 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).3 Landmark identification errors have also been well documented in the literature.4,5 Two-dimensional cephalometric measurements of the three-dimensional head have major limitations, which have also been thoroughly documented.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 TADs between the roots or in the palate, etc. McKee, et.al.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.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.

Records were taken, which included: traditional Facial and Intraoral 2D photos, traditional study models and CBCT (i-CAT, Imaging Sciences, Inter., Hatfield, Pennsylvania). A 2D lateral ceph and 2D panoramic views were created from the 3D DICOM data using i-CAT Vision software (Imaging Sciences).

Case 1
Case 1 is an African-American female, 12 years, six months old with a chief complaint of “I don’t like my crooked teeth, the space between my front teeth and my lips are full.” Clinical exam revealed Class I molars and canines, moderate crowding, slight diastema between Teeth #8 & 9 (upper centrals) and a bimaxillary protrusion. TMJ function normal with Maximum opening of 50 mm with normal lateral excursions of 12mm. Facial & Intraoral photos confirm these findings. All other medical, dental and clinical TMJ exams are within normal limits.

Case 2
African-American female, 10 years, six 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 45mm, right lateral 10mm, left lateral 10mm).

















Next Month:
Part II of Dr. Harrell’s two-part series reveals the three-dimensional diagnostic information.

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.
Author's Bio
Dr. William “Bill” Harrell graduated from the University of Alabama in Birmingham (UAB) School of Dentistry with a DMD degree in 1975, and received his certification in orthodontics from the University of Pennsylvania in 1977. Dr. Harrell became a Diplomate of the American Board of Orthodontists in 1989 and is a member of the College of Diplomates of the American Board of Orthodontists. Dr. Harrell has served as president (1987-1988) and vice president (1986-1987) of the 9th District Dental Society of Alabama and during that time served on the Alabama Dental Association’s Board of Trustees and House of Delegates. Dr. Harrell has served as the president (1990-1991) and vice president (1989- 1990) of the Alabama Association of Orthodontists and served as a director to the Southern Association of Orthodontists from 1995-1997. Dr. Harrell also teaches at the University of Alabama Birmingham (UAB) and the University of Pennsylvania. Dr. Harrell served as the American Association of Orthodontist’s (AAO) Representative to the American Dental Association (ADA) Standards Committee on Dental Informatics (SCDI) from 2002-2009. Dr. Harrell has had an interest in 3D imaging since the early 1980s and has numerous scientific articles, text book chapters and lectures both nationally and internationally on 3D Imaging, TMJ disorders and sleep apnea as it relates to maxillofacial growth.
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