Present paper is  a  report  on  the   mandibular  arch  width  changes

   (MAWC)  during  maximum  and   minimum   mouth   opening  in  the  first

   premolar and second molar region. The  effect of  age, sex , and type  of

   occlusion (Angle Classification) have been investigated.

         Cross-arch distance was recorded in two region on each cast of lower

   dental ridge , which had been made  in maximum  opening  and  closing

   position of  jaw  and poured in alginate impressions of sixty - five   referring

   patients to Dental School of Hamadan, with digitalized Kolis (accuracy  to

   0.01 mm) and MAWC was measured.

         The mean of MAWC in the first premolar region  is 0.1456  0.1095 mm

   and in the molar region is 0.26050.1908mm.

         - MAWC decreases with age increase.

         - MAWC is less in female than male.

         - MAWC in the subjects with class II occlusion is less than  the  subjects

   with class I occlusion.