Pacific Coast Society of Orthodontists Bulletin Summer 2015 - (Page 38)

Special Section Pearls of the Pacific CBCT Cone-Beam Computed Tomography Dr. Joorok Park University of the Pacific, San Francisco, CA Differentiating Posterior Crossbites with CBCT Volumetric Images Cone-beam computed tomography (CBCT) can be used in assessing the transverse dimension; for example, it can be used to detect a posterior crossbite (Figure 1). A skeletal crossbite may be the result of either a relatively narrow maxilla or a wide mandible. Dental crossbite is caused by improper buccolingual inclination of molars. When a skeletal crossbite is diagnosed, the clinician should plan for a skeletal expansion of the maxilla. Using coronal cross-sectional images through the posterior teeth and the basal bones, the maxillomandibular width differential and the buccolingual inclination of maxillary and mandibular molars can be measured. The maxillomandibular width differential:  Measurement at the basal bone (Figure 2A): Ricketts/Grummons frontal analysis: The maxillary and mandibular widths are measured at the jugale (J) and antegonion (Ag), respectively. The mean differential, (Ag-gA) - (J-J'), was found to be 17 mm at age 13 and about 20 mm by age 18.1  Measurement at the alveolar bone (Figure 2B): The widths can also be measured between the palatal surfaces of maxilla, and similarly, between the lingual surfaces of mandible, also at the mid-root level. The mandibular width should be 1 ± 3 mm wider than the maxillary width.2 The buccolingual inclination of maxillary and mandibular molars:  Maxillary molars: Angle between the long axis of the molars and the occlusal plane; the mean inclination was found to be approximately 98 ± 3° (Figure 3).2  Mandibular molars: Angle between the long axis of the molars and the occlusal plane: the mean inclination was found to be approximately 104 ± 3° (Figure 3).2 When a patient presents a large maxillomandibular differential with excessive molar inclinations, the diagnosis is most likely maxillary transverse deficiency, which requires skeletal maxillary expansion.  Figure 1. Intraoral photos of a 13-year-old female patient showed a bilateral posterior crossbite tendency. Cross sections generated via CBCT can clarify the actual cause of the crossbite tendency. 38 PCSO Bulletin  Summer 2015

Table of Contents for the Digital Edition of Pacific Coast Society of Orthodontists Bulletin Summer 2015

Staying Connected in a Large, Diverse Orgainziation
Palm Springs: A PCSO Favorite
Trustee Report
PCSO at a Glance
PCSO Member News
AAOF Report
Special Section on CBCT
CBCT Imaging Protocols Within PCSO Residency Programs
Cone-Beam Computed Tomography in Orthodontics - Benefits of Comprehensive Visualization
Case Report Pre-Treatment
CBCT in Today's Orthodontic Practice
Case Report Post-Treatment
Differentiating Posterior Crossbites with CBCT Volumetric Images
Apps for the Orthodontist
Dr. Ib Leth Nielsen, San Francisco, CA
Dr. Robert J. Bendzak
Dr. Arthur A. Dugoni's 90th Birthday Makes for a Special Alumni Meeting in San Francisco
Preparing for the Unexpected: Your Emotional SOS Plan, Part II
Resident Spotlight
Hygiene: A New Battle for an Old War
Dr. Peter Picard, 1919-2013

Pacific Coast Society of Orthodontists Bulletin Summer 2015