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

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

In Part 1 of William Harrell's article (June 2009) on 3D imaging, we looked at the traditional 2D imaging of two similar cases (Class I Bimaxillary Protrusion'). The doctor was asked to determine their treatment plan based on this two-dimensional information. Part II (Sept 2009) reveals the three-dimensional diagnostic information. The question is then asked --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 (For original 2D info, see Figures 1A–1E in Case 1 from June NewsWire)

The following is the three-dimensional information on Case 1 from the previous issue of PCSO NewsWire. The CBCT data can be reformatted to reveal Axial, Coronal and Sagittal views and also Rendered 3D volumes.

Fig 3A – Cross sections of right incisors from DICOM data.
Fig 3B – Cross sections of left incisors from DICOM data

 

Fig 3C – Three-dimensional rendered view showing conical root structure of upper incisors and short roots. Note the “resorption” on the left lateral incisor root apex towards the distal, prior to any treatment. Also the alveolar boney housing for the lower incisors is very narrow.
Fig 3D – Frontal 3D view of cross section of the long axis of the upper right central incisor.

 

Fig 3E – Sagittal 3D view of cross section of the long axis of the upper right central incisor.

• 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. (REF #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 3 F - I.

 

Fig 3F - Initial lateral profile view of the 3D facial scan. Note the perceived “protrusive lips” in profile view.
Fig 3G – A “simulated” genioplasty in the lateral profile view. For this patient, the “simulated genioplasty now gives a nice profile to her face and her lips do not seem to be protrusive.

 

Fig 3H – Initial 45 degree view
Fig 3I – “Simulated” genioplasty in 45 degree view. These 3D scans can be rotated to any view to evaluate asymmetry and “simulated” treatment plans.

CASE 2 (For original 2D info, see Figures 2A–2E Case 2 from June NewsWire)

The following is the three-dimensional information on Case 2 from the June issue of PCSO NewsWire. The CBCT data can be reformatted to reveal Axial, Coronal and Sagittal views and also Rendered 3D volumes.

 
Fig 4A - Sagittal cross sectional views of right incisors. Note “normal” root anatomy and 1:2 crown to root ratio. Also the cortical & alveolar bone housing the lower incisors seems to be of adequate width labio-lingually.
Fig 4B - Sagittal cross sectional views of left incisors

Fig 4C – Three-dimensional rendered view showing “normal” root anatomy of upper incisors, 1:2 crown-to-root ratio. Also the cortical boundary and the alveolar bone housing the lower incisors seems to be adequate.
Fig 4D – Frontal 3D view of cross section of the long axis of the upper right central incisor.

Fig 4E – Sagittal 3D view of cross section of the long axis of the upper right central incisor with 1:2 crown to root ratio.

• 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 normal (REF #8) 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 4 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 4 G - I. Does this “incidental” information make any difference in the over all treatment plan? What are the possible long term effects of respiratory pattern on craniofacial growth? (REF #9) The relationship between the amount of nasal obstruction which has to be present before it effects facial growth is still not clear. (REF #10) This dichotomy may be related to the imaging modalities used and measured in earlier studies (i.e. 2D lateral cephalometrics) verses what we may 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.

 

Fig 4F - The 3D Airway has been segmented out (in yellow) and shown in the frontal view (3DMD Vultus Software, 3dMD, Atlanta, GA). In the upper left (Sagittal view), the purple line is the level of the most constricted area of the airway. The red arrow shows this level and the corresponding cross section and shape of the airway at the most constricted region.
Fig 4G – The 3D Airway (yellow) has been turned to show Sagittal View.

Fig 4H – The cross section and level at the region of the Adenoids (Red Arrow)
Fig 4I –  This graph is the graphical analysis of this patient's airway. The airway is the smallest in the retropalatal area. Adenoid mass (see the Sagittal and Coronal views) is very large and her midface is short. The Axial view shows an asymmetric airway in relation to the tonsils. This Airway Analysis was developed by Stephen A. Schendel, M.D., D.D.S., Professor of Surgery Emeritus at Stanford University Medical Center and Lucile Packard Children’s Hospital and presently a member of the California Sleep Institute (www.calsleep.com). (Drs. Steve Schendel and David Hatcher (Oral Radiologist, Sacramento, CA) will be publishing this analysis 'in press' in the upcoming Journal of Oral and Maxillofacial Surgery.) Note the 3D analysis of the airway in this case. (REF #11-15)

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” may 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:
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 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