Background The choice between extraction and expansion treatment is an endless debate in orthodontics. Ethnic and secular variations showed that there was a change in  arch perimeter over the last 50 years. Accordingly, the purpose of this study was to investigate the relation between the arch perimeter and the intercanine and intermolar widths in normal occlusion. Also, to design regression equations for the prediction of the arch perimeter based on arch width, in a sample of the Egyptian population. The images of 340 cast pairs for 11 to 13-year-old patients were traced using TracerNet. Intercanine width, intermolar width and arch perimeter were measured, statistical analysis was performed and regression equations for both arches were formulated. Results There was a positive correlation between the lower arch AP, ICW and IMW and between the upper arch AP and ICW. Lower arch perimeter = 0.536 I33 + 71.642, lower arch perimeter = 0.828 l66 + 58.604 and upper arch perimeter = 1.988 U33 + 30.492 were the significant derived equations. Conclusions The formulation of regression equations offers a tool for the prediction of arch perimeter or arch width that can act as a guide in diagnosis and treatment planning.

Aim: The present study was conducted to determine the correlation between the combined mesiodistal width of teeth, arch length and arch perimeter in a sample of the Egyptian population.Material and methods: Four hundred and twenty pairs of dental casts were traced using TracerNet. The combined mesiodistal width of teeth (CMWT), arch length (AL) and arch perimeter (AP) were measured. Statistical analysis was conducted utilizing Pearson correlation and paired t-test.Results: The results showed a significant positive correlation in the lower arch between the AP and the AL, the CMWT and AL; p<0.05. There were no significant correlations in the upper arch. There was significant difference between the ratio of the upper and lower AP to CMWT; p=0.00.Conclusions: There were positive correlations between the arch perimeter and arch length, combined mesiodistal width of teeth and the arch length in the lower arch, with no correlation between the arch perimeter and the combined mesiodistal width of teeth. Therefore, during orthodontic diagnosis and treatment planning a thought should be given to treatment options that do not involve reduction of tooth mass. The measured values of the different variables could act as a database describing the tooth width and arch dimensions of the representative sample.

Background: The purpose of this study was to investigate the suitability of the widths of some commercially available preformed NiTi arch wires to the dental arch widths of a sample of the Egyptian population.Methods: This cross-sectional study included 420 maxillary and mandibular pairs of casts for subjects with an age range of 10-16 years as part of project by the National Research Centre. The casts were traced using TracerNet; intercanine and intermolar widths were measured on the casts. Anterior and posterior arch lengths were measured to facilitates the measurements on the wires. The intercanine and intermolar widths of eight commercially available archwires were measured on a graph paper. Results: Regression analysis was performed to create a regression model for the predicted means of the intercanine and intermolar widths in different age groups. The mean square error (MSE) was calculated for all the available arch wires in relation to the dental arch. Ormco (Broad arch/small) had the lowest MSE; 1.55 for the upper intercanine width and 1.72 for the upper intermolar width. For the lower intercanine width its MSE was 0.30 for the Ormco and 0.31 for Ortho Technology, while for the lower intermolar width it was 0.78 for Ormco. Conclusions: The commercially available archwires were all considerably larger than the mean dental arch size of the majority of the population, except for the Ormco; thus, inviting potential relapse of treatment. It is necessary to produce a wider range of customized archwires that better suit the dental arch sizes of the Egyptian population.