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How CBCT Can Help Jaw Alignment and Airway Issues by Robert Kaspers, DDS, MS

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CBCT technology has uncovered an interesting issue that the orthodontic community should take into consideration when diagnosing and treatment planning for a patient with a retruded lower jaw. Many times, the patient advances his/her lower jaw to achieve maximum intercuspation (MIP), but due to a smooth neuromusculature action of the mandible, the orthodontist is unaware that the patient is positioning the lower jaw forward. With the details that can be seen on a CBCT scan, orthodontists can now treat patients so that jawbones are in alignment at the end of treatment.

It is possible that a patient with a deficient lower jaw could also possess a constricted airway and naturally hold the lower jaw forward because it improves his/her airway. Over time, holding the lower jaw forward may result in muscle fatigue and soreness. With the benefit of CBCT technology, orthodontists can now see that deprogramming a patient's musculature also has the possible result of enhancing a patient's obstructive sleep apnea. Improper diagnosis and treatment of a skeletal Class II (with a retruded mandible) asymmetry may result in experiencing this interesting and perplexing future problem—trying to solve one health problem (TMD) and consequently, worsening the other (sleep apnea).

The following case study illustrates this common—and without CBCT imaging, often missed—condition.

Case study Eleven-year-old Ilana (Figs. 1 & 2) appeared to possess a mild skeletal Class II malocclusion with the maxilla forward and the mandible retruded (Fig. 3). Her lower incisors were flared forward. An i-CAT 3D scan was taken (in MIP) and showed that both condyles were "centered and down" in the glenoid fossa (Figs. 4 & 5). A centered-and-down condylar position is created when a patient fulcrums around a posterior interference by activating his or her lateral pterygoid muscles to achieve maximum intercuspation.







With the information gained from the scan, I decided to utilize a Herbst appliance to stimulate growth of the mandible to correct the skeletal Class II asymmetry as well as improve her constricted airway (Fig. 6). Preparation for the Herbst appliance consisted of utilizing Class III elastics with a four-looped lower archwire to help distalize the lower teeth and upright the flared lower incisors. A 2mm splint was then placed on the lower dental arch to prevent the tongue or lingual bar from flaring the lower incisors. In this way, I could calibrate the Herbst appliance so I could get a 3-4mm stretch of the musculature to stimulate growth of the mandible. Two-millimeter shims were added to the Herbst every four months to activate the appliance and maintain the stretch to stimulate growth.

Without a CBCT scan, Ilana's neuromusculature could have fooled me into thinking she only had a mild dental Class II malocclusion. I certainly would not have known that she possessed a constricted airway (MCA = 110.6mm2) with a total volume from the posterior nasal spine to the hyoid bone of 7.1cc (Fig. 6). It is important to understand that Ilana's centered-and-down condylar position improved her airway significantly, and therefore, a seated condylar position probably would have produced an MCA under 50mm2, which is considered a high risk for obstructive sleep apnea.

The Herbst appliance was removed after one year. Condyles were fairly close to seated in the glenoid fossa, so no dual bite existed. The airway was no longer constricted because the MCA was now 237.7mm2, and the total volume had increased to 14.4cc (Fig. 7).



Eliminating variables By being able to evaluate condylar position in conjunction with a CBCT scan, orthodontists can treat their patients to a seated condylar position with an improved airway. If the patient is treated to a seated condylar position and cuspid guidance, a shutdown of the neuromusculature during sleep will not cause sleep apnea. The scan from my i-CAT viewed within Tx STUDIO software showed me the minimal cross-sectional area (MCA) within the patient's airway. Evaluation of the patient's condylar position by taking the CBCT scan in MIP eliminates variables and provides an excellent idea of the patient's true airway condition. An orthodontist with i-CAT imaging has the opportunity to accurately diagnose a constricted airway and treatment plan accordingly. If the skeletal Class II asymmetry is misdiagnosed during a patient's growth years, the orthodontist may be confronted in the future with trying to solve one health problem (TMD) and consequently, worsening another (sleep apnea). CBCT technology allows an orthodontist to have the detailed 3D volume of the patient's skeletal and airway anatomy so that a proper diagnosis and treatment outcome can be achieved. As Ilana's orthodontist, I can sleep well at night, knowing that she is doing the same.




Dr. Robert Kaspers has an undergraduate degree from Northwestern University, a DDS from University of Michigan, and a Master of Science in orthodontics from Northwestern University Dental School. He attends multiple continuing education seminars each year to stay current with the latest techniques. He also established the company called ProActive Orthodontics to help educate both dentists and orthodontists about a new finding: the Five Condylar Positions, which he discovered with his cone-beam 3D imaging machine. His private practice, Kaspers Orthodontics, is in Northbrook, Illinois.
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