Mahtab Nouri - Associate professor, Orthodontic department, School of Dentistry, Shahid Beheshti University of Medical Sciences
Amin Aminian - Assistant professor, Orthodontic department, School of Dentistry, Kerman University of Medical Sciences
Majid Heidarpour - Postgraduate student, Orthodontic department, School of Dentistry, Shahid Beheshti University of Medical Sciences
Alireza Akbarzadeh Bagheban - Assistant professor, Iran Center for Dental research, School of Dentistry, Shahid Beheshti University of Medical Sciences
Reza Massudi - Assistant professor, Laser Institute, Shahid Beheshti University

Aims: Comparison of ۳D laser scanning and ۲D conventional scanning in analysis of arch dimensions. Methods: Twenty setups of upper and lower casts were duplicated in ۲۰ corresponding dental stone models. ۳D laser scanner was constructed in Shahid Beheshti University, and then casts were scanned with this machine. ۲D scanning was performed by conventional scanner. Intercanine and intermolar widths and canine and molar depth were calculated directly on casts by digital caliper and on both scans. The mean differences between these three methods were evaluated by repeated measure analysis of variance and between each pair by paired t-test.Results: The correlation between intercanine and intermolar widths of all three modalities were higher than ۰.۹, but for canine and molar depths the correlation was not so strong and for canine depth was the weakest (R=۰.۴۵).The differences between intercanine and intermolar widths of all three modalities for upper and lower casts were significant, but for canine (and molar) depths, only the difference between ۳D and direct technique for the upper casts was significant (P < ۰.۰۵). The highest recorded differences for intercanine and intermolar widths and molar and canine depths were ۰.۶۷, ۰.۴۲, ۰.۵۹ and ۰.۷۱ mm respectively.Conclusions: Digital models are valid reliable clinical tools for arch dimension evaluations. In addition, the most reliable measurements are intercanine and intermolar widths.