Ever since Downs published the first cephalometric analysis in 1947, orthodontists have used the lateral cephalogram for diagnosis and treatment planning. Recently, cone beam computed tomography has been used to capture a three dimensional image of the face and teeth. This paper illustrates the use of parasagittal information available only on a CBCT to plan orthodontic tooth movements in the coronal plane for the mandibular cuspids. Normative data on the angulation of the mandibular molars and cuspids were derived from pretreatment cone beam computed tomographs of 56 male and 52 female subjects as part of a Master’s Thesis project at Case Western Reserve University by Wanvadee Shewinvanikikul (Shewinvanikikul, W 2008). Subsequent changes in mandibular molar and cuspid angulations during orthodontic treatment
were studied by Nikolos Evangilonakis as part of his 2009 Master’s research project (Evangelonakis, N 2009). Mean pretreatment angulation of the mandibular cuspid was 98.0±4.1º degrees and 74.6±4.7º for mandibular molars. Changes in molar inclination during treatment were modest and in most cases not clinically significant. However, both the mean (-4 degrees) and the range (-10 to +15 degrees) of changes in canine inclination were remarkable and clinically significant. Assuming a mandibular canine length of 27 mm, a 1º bilateral increase in the canine inclination results in a 1 mm increase in intercanine width. This creates approximately 1mm of arch length. Since some patients have canines with a pre-treatment inclination of 80 degrees, increasing the inclination to the average of 97 would create approximately 16 mm of arch length. This could potentially impact the clinician’s decision to extract permanent teeth to resolve lower anterior crowding. The use of buccolingual inclination of the mandibular canines in treatment planning is the first example of the way parasagittal information derived from CBCT images might influence orthodontic treatment planning in the 21st century.