Dental arch perimeter (or length) is considered as one of the most important dental arch parameters for the diagnosis of orthodontic cases.It can be defined as the space available in the dental arch for the alignment of the teeth. Crowding of teeth is considered as a major problem that affects the dental arch; it can be resolved by careful analysis of the space available (arch perimeter) and the space required (teeth width) and an appropriate method for space creation and/or preservation.
Several methods have been adopted by various authors for calculating the dental arch perimeter, depending on using wires, either brass or soft stainless steel, and catenometer . Other researchers divided the dental arch into multiple segments and used the calipers for measurements. An estimation of the dental arch perimeter was performed using either the regression analysis or Ramanujan’s equation for measurement of the ellipse.
Collaborative work was conducted between Iraqi researcher from College of Dentistry, University of Baghdad represented by Assistant Professor Dr. Mohammed Nahidh and other researchers to develop a new method for prediction dental arch perimeter, depending on dental arch lengths and widths using the step-wise regression analysis.
Sixty-seven pairs of study models for patients with normal occlusion were included in this study. Dental arch width at the level of the canines, first premolars, and first molars, in addition to dental arch length and perimeter, were measured using a digital vernier with 0.01mm accuracy. Data were subjected to step-wise regression analysis to determine the major predictors of arch perimeters and develop regression equations for both arches. The predicted arch perimeters were compared with the actual measured values using paired sample t-test.
The results showed that for both arches, the perimeter showed a direct, moderate to strong, highly significant correlation with the length and width measurements. Findings from step-wise regression analysis indicated that there was a strong correlation between arch perimeter and the inter-canine width and arch length, which explained 67.7% of the variation in arch perimeter in the maxillary arch. In the mandibular arch, inter-molar width, inter-canine width, and arch length explained 55.1% of the variation in the dental arch perimeter. The arch perimeter values predicted from the developed equations were not significantly different from the actual values that were measured.
This new method which used the regression equations based on dental arch width and length at the level of the premolars, molars, and canines were developed to predict dental arch perimeters for both the mandibular and maxillary arches.