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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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Part I of William Harrell’s article (Orthotown Magazine, November 2009) on 3D imaging looked at the traditional 2D imaging of two similar cases (Class I Bimaxillary Protrusion). Part II reveals the three-dimensional diagnostic information. Does the 3D information change your treatment plan in any way and/or reveal additional information, which could be important to know in the overall management of these cases?


Case 1
The following is the three-dimensional information on Case 1 (read Part I of Dr. Harrell’s series in the November issue of Orthotown Magazine here). The CBCT data can be reformatted to reveal Axial, Coronal and Sagittal views and also Rendered 3D volumes.

Now, do you consider this case “routine“ by the 3D information you see here? Did this information “change your treatment plan?“ What are your treatment plan(s) now after seeing the 3D information?

Notice the “perceived root length“ of the upper incisors in the panoramic view (Figure 1B) and compare this to the cross sectional information of the incisors in Figures 3A – 3E. Note the protrusive upper incisors, conical root anatomy and the 1:1 crown to root ratio of upper centrals (normal is 1:2 crown-to-root ratio).8 Note the protrusive lower anterior teeth and small labio-lingual width of the alveolar bone that houses the lower incisors. The root thickness seems to be close to the same width as the labio-lingual alveolar bone. Does this information change your treatment plan in any way?

The following figures are 3dMD (3dMD, Atlanta, GA) facial scan showing this patient in various perspectives. The initial treatment plan I was considering on clinical exam was extraction of four first bicuspids and four TADS to maximally retract the incisors to reduce the bimaxillary protrusion and retract the “full lips.“ After reviewing the 3D information, especially the cross-sections of the upper and lower incisors, I chose to treat this case non-extraction, align her teeth and close diastema, leave her lips full, at this time. Then when she is older (16-18 years old), if the patient so desires, consider a genioplasty. Note the “lack of full lips“ when the chin is moved forward in the 3D facial scans in Figures 3F-3I.

Case 2
The following is the three-dimensional information on Case 2 (read Part I of Dr. Harrell’s series in the November issue of Orthotown Magazine). The CBCT data can be reformatted to reveal Axial, Coronal and Sagittal views and also Rendered 3D volumes.

Now, do you consider this case “routine“ by the 3D information you see here?

Did this information “change your treatment plan“?

What are your treatment plan(s) now after seeing the 3D information?

Note in this case that her upper incisor crown to root ration is 1:2, which is normal8 and there seems to be enough labio-lingual alveolar thickness in order to “retract“ the lower anterior teeth. So in this instance I would consider four first bicuspids and TADs to retract the anterior teeth and reduce lip fullness.

Upon further evaluation of the DICOM data, this patient’s airway seemed to be small due to enlarged tonsils and adenoids (See Figures 4G - I). Does this “incidental“ information make any difference in the overall treatment plan? What are the possible long term effects of respiratory pattern on craniofacial growth?9 The relationship between the amount of nasal obstruction which has to be present before it effects facial growth is still not clear.10 This dichotomy might be related to the imaging modalities used and measured in earlier studies (i.e. 2D lateral cephalometrics) versus what we might find when looking at the three-dimensional airway and studying the air flow and turbulence patterns created with various airway conditions and its possible effects on growth.

This two-part article shows two similar cases which most orthodontists would consider “routine“ and not necessarily in need for 3D information. After considering the 3D information, the treatment plan on case 1 changed from four bicuspid extraction and maximum retraction to non-extraction and a genioplasty. Case 2 led to referral to ENT for tonsil and adenoidectomy.

You don’t know what you don’t know, you don’t know what you can’t see and what you can’t see, you cannot diagnose! “Routine cases“ might not be as routine as we think. It is better to know than not to know what the anatomic truth really is. 3D imaging might help keep us out of trouble.


References
8. Grossmann Y, Sadan A. The prosthodontic concept of crown-to-root ratio: A review of the literature. J Prosthet Dent 2005; 93:559-62
9. McNamara, JA, Influence of respiratory pattern on craniofacial growth, Angle Orthodontist, Oct 1981 (Vol. 51, Issue 4, Pages 269-300)
10. Vig KWL , Nasal obstruction and facial growth: the strength of evidence for clinical assumptions, AJODO, June 1998 (vol 113, Issue 6, pgs 603-611
11. Ogawa et al. “ Evaluation of cross-section airway configuration of obstructive sleep apnea.“ Oral Surg, Oral Med Oral Path 103;2007:102-8
12. Lowe AA, Gionhaku N, Takeuchi K and Fleetham JA. “ Three-dimensional CT reconstructions of tongue and airway in adult subjects with obstructive sleep apnea.“ Am J Orthod Dentofacial Orthop.“ 1986;90(5) 364-74
13. Avrahami E, Englender, M. “ Relation between CT axial cross-sectional area of the oropharynx and obstructive sleep apnea syndrome in adults. Am J Neuroradiol. 1995;16(1):135-40
14. Consentini T, Le Donne R, Mancini D, Colavita N. “ Magnetic resonance imaging of the upper airway in obstructive sleep apnea. Radiol Med 2004;108:404-16
15. Li HY, Chen NH, Wang CR, Shu YH, Wang PC. “Use of 3-dimensional computed tomography scan to evaluate upper airway patency for patients undergoing sleep-disordered breathing surgery.“ Otolaryngol Head Neck Surg 2003;1294):336-42
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 and the University of Pennsylvania. Dr. Harrell served as the American Association of Orthodontist’s Representative to the American Dental Association Standards Committee on Dental Informatics 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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