3127 Quantification of dental arch form by fitting a fourth order polynomial curve
K. ARAI, Nippon Dental University, Tokyo, Japan, and L.A. WILL, Harvard University, Boston, MA, USA

Objectives: The purpose of this study was to evaluate advantages of fitting fourth-order polynomial to analyze the dental arch form.  Methods: Pretreatment dental casts of twenty-seven cases (13 males and 14 females, mean=16.5 +/- 5.0 years) were randomly selected. Standardized occlusal photographs were taken and ranked from tapered to squared shape by six examiners and the average of each cast was calculated as the rank of dental arch form. All casts were analyzed with a three-dimensional laser scanning system (Surflacer VMS-100F / UNISN, Inc., Japan). Reference points used were the midpoints of incisal edges, canine cusp tips, and the buccal cusps of premolars, midpoints of buccal cusp tips of molars. The data in x-y coordinates were analyzed with an original software program (Archwire form 2001). A fourth-order polynomial equation (y=ax4+ bx3 +cx2 +dx +e) was fit to the reference points using the least square method.  Results: "a" was statistically significantly larger (t=4.08, p<0.01) in the mandible than in maxilla. Statistically significant positive (rs=0.46 for maxilla, and 0.66 for mandible) and negative (rs=-0.83 for maxilla, and -0.84 for mandible) correlations were found between the rank of dental arch form and "a" and "c", respectively.  Statistically significant negative correlations between "a" and "c" were found in maxilla (r=-0.82) and mandible (r=-0.79).  Conclusion: Individual fluctuations of "a" or "c" change only the size of dental arch. An increased value of "a" with a decreased "c" make the arch more square, and a decreased "a" with an increased "c" make a tapered arch form. These findings may provide essential information for future studies of computer based three-dimensional diagnostic tools in clinical orthodontics.

Seq #286 - Post-natal Craniofacial Growth
9:00 AM-11:00 AM, Saturday, 9 March 2002 San Diego Convention Center Room 17A (Mezzanine Level)

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Back to the IADR/AADR/CADR 80th General Session (March 6-9, 2002)

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