Determination of required space for canine and premolar eruption in mixed dentition using mesiodistal width of mandibular incisors

Background and Objective: Determination of the relation between periphery of dental arch and teeth size which mostly done before eruption of some permanent teeth, is of important levels of diagnosis in mixed dentition. Determination of this relationship is not possible without prediction and distinct evaluation of unerupted permanent mesiodistal width (Permanent canines and premolars). The aim of this study was to evaluate the required space for eruption of canine and premolars using total width of lower incisor in Iranian people by Tanaka & Johnston method. Methods: In this study mesiodistal width of permanent first and second premolar and canine in each quadrant also of 4 lower incisors were measured in 604 dental casts of under 20 year old people (In Mazandaran) using Koulis with accuracy of 0.02 millimeter and final measurements were illustrated in a table. Needed teeth for measurement were completely erupted, caries free and without fracture or restoration. Findings: The mean of mesiodistal width of lower incisors, total mesiodistal width of upper and lower canine and premolars and a and b indexes for Tanaka and Johnston equation (Y=aX+b), a=0.167, b=19.387 for mandible and a=0.195, b=18.723 for maxilla have been calculated. Meanwhile X is the sum of lower incisor mesiodistal width and Y is the sum of canine and premolar mesiodistal width in one side. Conclusion: In present study, equation of Tanaka and Johnston is recommended. So its dependence on race is obvious