An Update on the Utilization of 2D and Cone Beam Computed Tomography Imaging in Orthodontics

Audrey Yoon, DDS, MS; Linda Phi, DDS, MSD; and Joorok Park, DMD, MSD

ABSTRACT

Background: Modern technology has quickly evolved the imaging tools used in orthodontics and dental sleep medicine. From 2D radiography to 3D imaging, radiology plays an important role in diagnosis and comprehensive treatment planning in orthodontics and dental sleep medicine.

Types of studies reviewed: PubMed, Scopus, Cochrane Library and orthodontic textbooks were searched. The history of radiology in orthodontics, the current usage of cone beam computed tomography (CBCT) and the future directions of orthodontics and airway applications with advancing technology were summarized.

Results: CBCT was regarded as a reliable tool for assessment and management of complex orthodontic cases such as impacted teeth, TMJ evaluation, skeletal measurement and surgical diagnostic and treatment planning applications.

Practical implications: CBCT can provide some insight into the diagnosis and treatment of the airway but should be used in conjunction with other clinical data. CBCT airway imaging plays a powerful role in our understanding of craniofacial structure and obstructive sleep apnea (OSA) and our decision-making process.

Keywords: Oral and maxillofacial radiology, orthodontics, cone beam computed tomography, sleep apnea

__________

AUTHORS

Audrey Yoon, DDS, MS, is an adjunct assistant professor in orthodontics at the University of Pacific, Arthur A. Dugoni School of Dentistry, an adjunct assistant professor at Stanford University Sleep Medicine Center and a co-director of the Pediatric Dental Sleep Mini-Residency Program at Tufts University. She is also a diplomate of the American Board of Dental Sleep Medicine and a diplomate of the American Board of Orthodontics. Dr. Yoon’s areas of research include craniofacial growth modification, the surgery-first approach of maxillomandibular advancement surgery technique and the genomic study to identify genetic anatomical factors relating to OSA. Conflict of Interest Disclosure: None reported.

Linda Phi, DDS, MSD, is a board-certified orthodontist practicing in Southern California. She is an adjunct professor in the orthodontics department at the University of the Pacific, Arthur A. Dugoni School of Dentistry and an adjunct professor in the orthodontics department at the University of California, Los Angeles, School of Dentistry. She received her DDS and MS in oral biology at UCLA and received her orthodontics certificate and MSD at UOP. Conflict of Interest Disclosure: None reported.

Joorok Park, DMD, MSD, is an associate professor and the clinic director of the orthodontics department at the University of the Pacific, Arthur A. Dugoni School of Dentistry. He is a diplomat of the American Board of Orthodontics. He received his MSD and certificate of orthodontics at UOP and earned his DMD at the University of Pennsylvania, School of Dental Medicine. He has done numerous clinical research work at the Craniofacial Research Instrumentation Laboratory. Conflict of Interest Disclosure: None reported.

__________

Modern technology has quickly evolved the imaging tools used in orthodontics. From 2D radiography to 3D imaging, radiology plays a pivotal role in progressing the field. Our understanding of growth and development would not have been possible without this technology. Additionally, imaging is essential for proper diagnosis and comprehensive treatment planning. In order to fully appreciate the wealth of information available, we explore the history of radiology in orthodontics, elaborate on the current usage of cone beam computed tomography (CBCT) and discuss the future directions of orthodontics with advancing technology.

History

Before the advent of radiographic cephalometry, which is a technique used to measure the head with medical imaging, anthropologists quantitatively analyzed dried skulls with craniometry. [1,2] Using various landmarks on the cranium, they derived measurements and compared them in different human populations. [2] Many lines and angles were proposed to measure anatomical structures and their relationship with one another, but these reference points were often challenged due to their reproducibility. [3] However, since the skull only gave information for a single time point, it was not possible to gather longitudinal data for growth studies. [1]

In 1917, Wilhelm C. Röntgen won the Nobel Prize for his discovery of X-rays. Using X-rays, Birdsall Holly Broadbent Sr. developed the roentgenographic cephalometer, which was used to capture an image of the skull in two head positions: a profile view (lateral cephalometric radiograph) as well as a frontal view (posteroanterior or PA cephalometric radiograph). It illustrated the relationship of the maxilla and mandible with respect to the cranial base as well as to each other. By taking cephalometric radiographs at various time points in the individual’s growth, researchers were able to superimpose stable anatomic structures for the purpose of studying normal growth patterns over time.

2D Radiography: Lateral Cephalometric, Posteroanterior Cephalometric and Panoramic Radiographs

Cephalometrics progressed to become a tool to evaluate craniofacial morphology, becoming an integral part in the clinician’s diagnosis and decision-making. [2] Using various landmarks in lateral cephalometric radiographs, analyses such as the Downs, [4] Steiner, [5,6] Tweed, [7] Wits appraisal, [8–10] McNamara [11] and many others [12–15] have been developed to quantify certain morphologic characteristics such as skeletal classification, prognathism or retrognathism, mandibular plane angle, anteroposterior tooth position and angulation. Less widely utilized, the PA cephalometric radiographs are taken to assess asymmetries, molar buccal-lingual angulations and skeletal width discrepancies between the maxilla and mandible. By the middle of the 20th century, the panoramic radiograph was being developed for the purpose of imaging the entire jaw. [16,17] The panoramic radiograph allowed the clinician to detect the following: [18]

■ Dental development.

■ Ectopic eruptions or dental impactions.

■ Congenitally missing teeth or supernumerary teeth.

■ Premature loss of teeth.

■ Prolonged retention, abnormal resorption or ankylosis of primary teeth.

■ Root resorption.

■ Temporomandibular joint (TMJ) condylar morphology and associated pathology.

■ Jaw fractures.

■ Space required/arch length deficiency for permanent teeth eruption and/or serial extractions.

■ Neoplasms, cysts and other pathologies.

With all of these advantages, orthodontists moved toward using panoramic radiographs and lateral cephalometric radiographs as the primary imaging modalities for diagnosis and treatment planning. One limitation of panoramic radiographs is that the resolution is inferior to that of bitewing and periapical films. [18] There is less sharpness and less detail compared to the intraoral radiographs; bitewings and periapical films are still needed in order to assess caries, dental calculus, periapical lesions and other pathologies. Additionally, because panoramic radiographs show a 2D projection of a 3D object, they have distortion, magnification, ghost images and overlapping structures.

Applications of Cone Beam Computed Tomography in Diagnosis, Treatment Planning and Outcome Assessment

Axial computed tomography (CT) scans were first introduced in North America in 1973 at the Mayo Clinic in Rochester, Minnesota. [2] However, the high cost and large radiation exposure made it unfeasible for dental and orthodontic use. [2,19] In 1998, CBCT was introduced in Europe; [20,21] a few years later, it was introduced in the United States for dental use. [20] This technology was groundbreaking in dentistry because the 3D information that was lost with panoramic and lateral cephalometric radiographs was now available. The benefits of using CBCT in orthodontics are as follows. [21,22]

Improved Clinical Diagnosis

One of the most notable strengths of CBCT imaging is that the volumetric image provides true and accurate 3D representation of the patient’s head. Before CBCT images, orthodontic diagnosis traditionally employed 2D panoramic and lateral cephalometric X-rays. Conventional orthodontic analysis starts by conceptually combining information obtained from various types of 2D records, which consist of photographs, study models and X-rays. CBCT images can now serve as the platform on which other 3D digital images can be merged. For example, a digital study model (obtained from an intraoral scan) and a 3D skin (obtained from a 3D facial scan) can be merged accurately onto the CBCT image (FIGURE 1). The merged images will display the patient’s colored facial soft tissue as well as highly detailed dentition simultaneously.

3D Reorientation

2D images also have inherent problems in the errors in the head orientation. CBCT images are constructed with isotropic voxels. Therefore, after the 3D image is initially captured, it can be reorientated in a software to a desired orientation either manually or automatically by using a set of landmarks to an anatomical frame of reference (FIGURES 2).

Skeletal and Dental Measurements

The craniofacial and dental morphology can be meticulously studied in the coronal, axial and sagittal planes of space; these measurements include length, angles and volume calculations. For example, by going through crosssectional coronal slices, we can measure maxillary palatal width, mandibular width and dental buccolingual inclinations of posterior teeth.

3D Cephalometric

Analysis With CBCT imaging, various 3D cephalometric analyses were developed and are especially useful in making linear or angular measurements in the axial and coronal planes. After 3D reorientation, facial asymmetry (i.e., mandibular asymmetry) or occlusal canting can be accurately measured. Severe skeletal asymmetry and canting would require surgical correction; for instance, mandibular asymmetrical set back via bilateral sagittal split osteotomy (BSSO) can improve mandibular asymmetry with Class III subdivision malocclusion (FIGURES 3).

Dentoalveolar Bone and Tooth Evaluation

CBCT can show dentoalveolar bone height and buccal-lingual/buccal-palatal bone width. It also shows accurate 3D positioning of erupted, unerupted and impacted teeth 23 and possible damage to an adjacent tooth (root resorption). An orthodontist can better visualize the direction of force vector during traction of the impacted tooth (FIGURES 4).

Root Morphology, Pathology and Resorption

Although CBCT does not replace the accuracy of periapical radiographs to evaluate dental pathology (e.g., periodontal ligament widening, periapical abscesses, etc.), it is useful in orthodontics to visualize root angulation, position, morphology and resorption (if any) at the initial evaluation, during treatment progress and at treatment completion.

TMJ Morphology and Pathology

CBCT is able to detect osseous changes in condylar morphology. It is especially useful when evaluating for TMJ pathology such as condylar resorption or sclerosis as well as adaptive condylar changes such as osteophytes (FIGURE 5).

Airway Morphology, Volume and Cross-Sectional Area

After designating the most superior and inferior limits, CBCT can calculate the total airway volume and determine the minimal cross-sectional area (MCA) within those boundaries.

Treatment Simulation

3D imaging software can segment and move maxilla, mandible and individual tooth with six degrees of freedom, which allows for treatment simulation of a treatment plan. This kind of treatment simulation is essential in multidisciplinary treatment. For example, before preparing multiple future implant sites, an orthodontist can simulate orthodontic tooth movement, implant placement and crown restoration (FIGURE 6). This kind of simulation can be shared with various restorative dentists and other specialists involved in multidisciplinary care.

Virtual Surgical Planning

Virtual surgical planning (VSP) uses CBCT information and 3D digital models to optimize efficiency and accuracy in orthognathic surgery cases requiring both oral surgery and orthodontics. 24 With VSP, various types of virtual surgeries can be tried, which helps the surgeon to choose the best possible surgical plan (FIGURE 7). After a virtual surgery simulation, 3D-printed custom surgical plates can be used that usually improve surgical accuracy.

For clinicians who prefer assessing traditional panoramic and lateral cephalometric radiographs, both of these images can be extrapolated from a single CBCT. Essentially, with 3D spatial information versus 2D radiographs, more landmarks are available that translate to more measurements and more information. The exponential increase in landmarks with CBCT allows for more accurate superimpositions compared to the few used in 2D superimpositions. 2 Lastly, when the CBCT was first introduced for dental use, the high-radiation dosage was the utmost concern from an ethical standpoint. Now with advanced technology that uses pulsed exposure time and lower settings, some CBCT machines have less radiation compared to panoramic and lateral cephalometric radiographs. 2,25

Conclusion

3D imaging in orthodontics can provide important diagnostic information through 3D analysis such as measurements in the transverse dimension, which was quite challenging with the conventional 2D imaging. 3D imaging also allows for more accurate visualization of skeletal, dental, root and TMJ morphologies as compared to that of 2D imaging. Furthermore, performing 3D dental and jaw surgery simulations can assist clinicians with treatment planning.

Assessment of the Airway and Supporting Structures Using CBCT

Sleep-disordered breathing (SDB) is often associated with obstruction resulting in increased airway resistance. The advantages of 3D imaging over conventional planar (2D) radiography for airway assessment have been gaining popular attention. CBCT technology can be applied for anatomic assessment of the airway and adjacent structures 26 and regional anatomic variables that may contribute to SDB. Integration of 3D imaging into standard clinical practice will enable practitioners to readily evaluate and screen patients for phenotypes associated with SDB.

CBCT alone cannot be used for diagnosis of sleep apnea because CBCT is a static snapshot of the anatomical craniofacial structures; it does not provide dynamic information such as collapsibility of airway, neuromuscular tone or actual function of airway. However, CBCT has an adjunctive role to assess the airway parameters and identifies potential sites that may contribute to a change in airway dimensions 27 (FIGURE 8). The purpose of this portion of the article is to describe the recommended use of CBCT technology for airway evaluations and treatment.

Evaluation of Upper Airway Using CBCT

Because CBCT airway scans include the jaws, teeth, cranial base, spine and facial soft tissues from the tip of the nose to the beginning of the trachea, there is an opportunity to evaluate the functional and developmental relationships between these structures. Because airway obstructions or encroachments increase airway resistance that may contribute to SDB, visualization and calculation of the airway dimensions are important. Common physical encroachments of the airway include turbinates, adenoids, long soft palate, large tongue and pharyngeal and lingual tonsils. Less common airway encroachments include polyps and tumors.

Airway Volume and Minimal Cross-Sectional Area

Accuracy and reliability of airway volume measurements using CBCT have been controversial. 28 Published data have established normal values for airway dimension. The human airway increases in length, cross-sectional area and volume during craniofacial growth but worsens through adulthood. Correlation studies of small airways and obstructive sleep apnea (OSA) symptoms have demonstrated a relationship between OSA and airway minimal cross-sectional area (MCA). 29,30 The probability of airway obstruction is low in adults when MCA is greater than 110 mm 2 , medium between 52 mm 2 and 110 mm 2 and high when less than 52 mm 2 (TABLE 1). The site of the smallest crosssectional area during orofacial growth is bimodal with one site near the palatal plane and the other tangent to C4 vertebra. Patients with MCA above 150 mm 2 show no correlation with risk of having OSA. Most severe OSA in adult patients with MCA is in the retrolingual region. 31

Airway Segmentation

Significant improvements in commercial software products have facilitated segmentation and measurements of the upper airway. Automatic segmentation allows the airway to be displayed and measured along a curved path to assess the risk of OSA in MCA (FIGURES 9).

Nasal Cavity The evaluation of the nasal airway begins at the nares and extends posteriorly to the posterior nasal choanae. Nasal fossa, large turbinates, deviated septum, small nares, nasal mucosal hypertrophy and masses may effectively increase air flow resistance (FIGURES 10).

Inferior turbinate or deviated septum are very common causes for nasal obstruction and mouth breathing, which can be easily detected by CBCT imaging.

Nasopharynx Adenoids

Adenoids form in the posterosuperior region of the nasopharynx and, upon enlargement, they extend toward the posterior nasal conchae and soft palate. Adenoid hypertrophy is a common etiology of nasopharyngeal obstruction. The distance in the midsagittal plane from the posterior outline of the soft palate to the closest point on the adenoid tissue from CBCT images can be used to classify the relative size of the adenoids into four groups: Grade 1 is less than 25% obstruction, Grade 2 is 25% to 50% obstruction, Grade 3 is 50% to 75% obstruction and Grade 4 is more than 75% obstruction (FIGURE 11). CBCT has proven its accuracy for evaluating adenoid size compared with the reference standard nasoendoscopy procedure. As a screening tool, CBCT is reliable and accurate in identifying adenoid hypertrophy with 88% sensitivity and 93% specificity. 32

Oropharynx Palatine Tonsils

The palatine tonsils, commonly

referred to simply as tonsils, are located at the oropharyngeal region. They are

at the isthmus of the fauces, bordered anteriorly by the palatoglossal arch and

posteriorly by the palatopharyngeal arch. Tonsillar hypertrophy often leads to upper airway obstruction with sleep-disordered breathing.

CBCT can adequately visualize tonsillar enlargement. The narrowest distance between the tonsils in the midcoronal plane is used to classify their relative sizes into four classifications (FIGURE 12).

Hyoid Bone

Links between hyoid position and airway resistance have been demonstrated. 33 Increased distance of the hyoid bone to mandibular plane often results in OSA, with increased distances greater than 15 mm considered abnormal. 34,35

Using CBCT for OSA Treatment Plan in Dentistry Skeletal Transverse Discrepancy Analysis for Palatal Expansion Treatment: Rapid Palatal Expansion (RPE), Mini- Screw Assisted Rapid Palatal Expansion (MARPE) and Distraction Osteogenesis Maxillary Expansion (DOME)

An underdeveloped nasomaxillary complex has been recognized as a common anatomic feature of OSA. Constriction of the maxilla with narrow nasal floor and low tongue posture is associated with an increase in nasal airflow resistance and retroglossal airway narrowing; palatal expansion improves OSA and enhances nasal breathing in patients with narrow nasal floor and high palatal arch.

It is important to assess the craniofacial structure in the transverse dimension as early as possible to accurately screen the need for transverse palatal expansion. This will maximize efficiency and effectiveness of palatal expansion treatment for OSA. Three-dimensional volumetric data visualization software can create specific transversal radiographic sectional views to assess areas of clinical interest and is therefore very useful in the diagnosis of the craniofacial transverse dimension. Many studies have confirmed that CBCT 3D imaging accurately represents intermaxillary transverse discrepancies (FIGURE 13). 36,37

Several studies have proposed new 3D transverse analyses with CBCT images using skeletal and dental linear and angular measurements. 37–39

Maxillomandibular Advancement Surgery

Maxillomandibular advancement (MMA) surgery is a well-established treatment for OSA. 40 The conceptual basis of MMA in OSA therapy is to increase the anteroposterior and lateral dimensions at various levels of upper airway thereby reducing upper airway collapsibility and superior and anterior displacement of the hyoid bone. MMA is considered the most successful surgical modality for OSA. 41 MMA increases total airway volume, minimal cross-sectional area, AP and lateral dimension, airway index, airway length, posterior airway space morphology, apnea-hypopnea index (AHI) and Epworth Sleepiness Scale. 42

In the past decade, many research centers and commercial companies have migrated toward a computerized systemized surgical protocol that enables preparation of skeletal surgery treatment planning and accurate simulation of jaw surgical movements using an integrated 3D model and CBCT volumetric data approach.

3D virtual surgical planning and simulation make it much easier determining locations of surgical cuts, planning precise movements of the bony segments relative to each other and designing and determination of size and length of fixation screws/plates.

The methods for computer-aided systems using CBCT revolutionized the treatment planning of skeletal surgery. They allow a comprehensive, systemic, standardized and individualized approach. The workflow for 3D virtual treatment planning procedures is highlighted in FIGURE 14, starting from the images acquired from scanners to the actual surgery performed in the operating room.

Conclusions

CBCT imaging paves the way for a more detailed and accurate 3D representation of the area of concern for airway applications. CBCT can provide some insight into the diagnosis and treatment but should be used in conjunction with other clinical data. Airway measurements and their significance in the development of OSA should be interpreted carefully. CBCT airway imaging plays a powerful role in our understanding of craniofacial structure and OSA and our decision-making process. n

__________

REFERENCES

1. Enlow DH , Hans MG. Essentials of Facial Growth. London: Saunders; 1996.

2. Hans MG, Palomo JM, Valiathan M. History of imaging in orthodontics from Broadbent to cone-beam computed tomography. Am J Orthod Dentofacial Orthop 2015 Dec;148(6):914–21. doi: 10.1016/j.ajodo.2015.09.007.

3. Finlay LM. Craniometry and cephalometry: A history prior to the advent of radiography. Angle Orthod 1980 Oct;50(4):312–21.

4. Downs WB. Variations in facial relationships: Their significance in treatment and prognosis. Am J Orthod 1948 Oct;34(10):812–40. doi: 10.1016/0002-9416(48)90015-3.

5. Steiner CC. Cephalometrics for you and me. Am J Orthod 1953;39(10):729–755. doi.org/10.1016/0002- 9416(53)90082-7.

6. Steiner CC. The use of cephalometrics as an aid to planning and assessing orthodontic treatment. Am J Orthod 1960;46(10):721–735. doi.org/10.1016/0002- 9416(60)90145-7

7. Tweed CH. The Frankfort-mandibular plane angle in orthodontic diagnosis, classification, treatment planning, and prognosis. Am J Orthod Oral Surg 1946 Apr;32:175–230. doi: 10.1016/0096-6347(46)90001-4.

8. Jacobson A. The “Wits” appraisal of jaw disharmony. Am J Orthod 1975 Feb;67(2):125–38. doi: 10.1016/0002- 9416(75)90065-2.

9. Jacobson A. Application of the “Wits” appraisal. Am J Orthod 1976 Aug;70(2):179–89. doi: 10.1016/s0002- 9416(76)90318-3.

10. Jacobson A. Update on the “Wits” appraisal. Angle Orthod 1988 Jul;58(3):205–19.

11. McNamara JA. A method of cephalometric evaluation. Am J Orthod 1984 Dec;86(6):449–69. doi: 10.1016/s0002- 9416(84)90352-x.

12. Jarabak, JR. Technique and Treatment With the Light-Wire Appliance. 2nd ed. St. Louis: CV Mosby; 1972: 128–66

13. Sassouni V. A Classification of Skeletal Facial Types. Am J Orthod 1969 Feb;55(2):109–23. doi: 10.1016/0002- 9416(69)90122-5.

14. Sassouni V. The Class II syndrome: Differential diagnosis and treatment. Angle Orthod 1970 Oct;40(4):334–41.

15. Ricketts RM. Cephalometric Analysis and Synthesis. Angle Orthod 1961;31(3):141–156.

16. Hallikainen D. History of panoramic radiography. Acta Radiol 1996 May;37(3 Pt 2):441–5. doi: 10.1177/02841851960373P207.

17. Paatero YV. Pantomography in theory and use. Acta Radiol 1954 Apr;41(4):321–35. doi: 10.3109/00016925409175858.

18. Graber TM. Panoramic radiography in orthodontic diagnosis. Am J Orthod 1967 Nov;53(11):799–821. doi: 10.1016/0002-9416(67)90088-7.

19. Proffit WR, Fields HW, Sarver DM. Contemporary Orthodontics. 5th ed. St. Louis: Elsevier/Mosby; 2013.

20. Kapila SD, Nervina JM. CBCT in orthodontics: Assessment of treatment outcomes and indications for its use. Dentomaxillofac Radiol 2015;44(1):20140282. doi: 10.1259/dmfr.20140282. PMCID: PMC4277443.

21. Kapila S, Conley RS, Harrell WE. The current status of cone beam computed tomography imaging in orthodontics. Dentomaxillofac Radiol 2011 Jan;40(1):24–34. doi: 10.1259/dmfr/12615645. PMCID: PMC3611465.

22. Kapila S. Cone Beam Computed Tomography in Orthodontics: Indications, Insights, and Innovations. Hoboken, N.J.: Wiley-Blackwell; 2014.

23. Alberto PL. Surgical exposure of impacted teeth. Oral Maxillofac Surg Clin North Am 2020 Nov;32(4):561–570. doi: 10.1016/j.coms.2020.07.008. Epub 2020 Sep 7.

24. Alkhayer A, Piffkó J, Lippold C, Segatto E. Accuracy of virtual planning in orthognathic surgery: A systematic review. Head Face Med 2020 Dec 4;16(1):34. doi: 10.1186/ s13005-020-00250-2. PMCID: PMC7716456.

25. Ludlow JB, Walker C. Assessment of phantom dosimetry and image quality of i-CAT FLX cone-beam computed tomography. Am J Orthod Dentofacial Orthop 2013 Dec;144(6):802–17. doi: 10.1016/j.ajodo.2013.07.013. PMCID: PMC3914004.

26. Hatcher DC. Cone beam computed tomography: Craniofacial and airway analysis. Dent Clin North Am 2012 Apr;56(2):343–57. doi: 10.1016/j.cden.2012.02.002. Epub 2012 Feb 20.

27. Kushida CA. et al. Practice parameters for the indications for polysomnography and related procedures: An update for 2005. Sleep 2005 Apr;28(4):499–521. doi: 10.1093/ sleep/28.4.499.

28. Alsufyani NA, Flores-Mir C, Major PW. Three-dimensional segmentation of the upper airway using cone beam CT: A systematic review. Dentomaxillofac Radiol 2012 May;41(4):276–84. doi: 10.1259/dmfr/79433138. PMCID: PMC3729002.

29. 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 Oct;129(4):336–42.

30. Ogawa T, Enciso R, Shintaku WH, Clark GT. Evaluation of cross-section airway configuration of obstructive sleep apnea. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007 Jan;103(1):102–8. doi: 10.1016/j.tripleo.2006.06.008. Epub 2006 Sep 1. PMCID: PMC1868407.

31. Barkdull GC, Kohl CA, Patel M, Davidson TM. Computed tomography imaging of patients with obstructive sleep apnea. Laryngoscope 2008 Aug;118(8):1486–92. doi: 10.1097/ MLG.0b013e3181782706.

32. Major MP, Witmans M, El-Hakim H, Major PW, Flores-Mir C. Agreement between cone-beam computed tomography and nasoendoscopy evaluations of adenoid hypertrophy. Am J Orthod Dentofacial Orthop 2014 Oct;146(4):451–9. doi: 10.1016/j.ajodo.2014.06.013.

33. Buchanan A, Cohen R, Looney S, Kalathingal S, de Rossi S. Cone-beam CT analysis of patients with obstructive sleep apnea compared to normal controls. Imaging Sci Dent 2016 Mar;46(1):9–16. doi: 10.5624/isd.2016.46.1.9. Epub 2016 Mar 24. PMCID: PMC4816775.

34. Schendel SA, Broujerdi JA, Jacobson RL. Three-dimensional upper-airway changes with maxillomandibular advancement for obstructive sleep apnea treatment. Am J Orthod Dentofacial Orthop 2014 Sep;146(3):385–93. doi: 10.1016/j. ajodo.2014.01.026.

35. Verin E et al. Comparison between anatomy and resistance of upper airway in normal subjects, snorers and OSAS patients. Respir Physiol 2002 Jan;129(3):335–43. doi: 10.1016/ s0034-5687(01)00324-3.

36. Tai B, Goonewardene MS, Murray K, Koong B, Islam SMS. The reliability of using postero-anterior cephalometry and cone-beam CT to determine transverse dimensions in clinical practice. Aust Orthod J 2014 Nov;30(2):132–142.

37. Lee KM, Hwang HS, Cho JH. Comparison of transverse analysis between posteroanterior cephalogram and cone-beam computed tomography. Angle Orthod 2014 Jul;84(4):715–9. doi: 10.2319/072613-555.1. Epub 2013 Dec 10. PMCID: PMC8650435.

38. Miner RM, al Qabandi S, Rigali PH, Will LA. Cone-beam computed tomography transverse analyses. Part 2: Measures of performance. Am J Orthod Dentofacial Orthop 2015 Aug;148(2):253–63. doi: 10.1016/j.ajodo.2015.03.027.

39. Tamburrino RK, Boucher NS, Vanarsdall RL, Secchi A. The transverse dimension: Diagnosis and relevance to functional occlusion. RWISO Journal 2, 13–22 (2010).

40. Hammond RJ et al. A follow-up study of dental and skeletal changes associated with mandibular advancement splint use in obstructive sleep apnea. Am J Orthod Dentofacial Orthop 2007 Dec;132(6):806–14. doi: 10.1016/j. ajodo.2005.08.047.

41. Pirklbauer K, et al. Maxillomandibular advancement for treatment of obstructive sleep apnea syndrome: A systematic review. J Oral Maxillofac Surg 2011 Jun;69(6):e165–76. doi: 10.1016/j.joms.2011.01.038.

42. Robertson C, Herbison P, Harkness M. Dental and occlusal changes during mandibular advancement splint therapy in sleep disordered patients. Eur J Orthod 2003 Aug;25(4):371–6. doi: 10.1093/ejo/25.4.371.

__________

THE CORRESPONDING AUTHOR, Audrey Yoon, DDS, MS, can be reached at audrey12@stanford.edu.