1 Pediatric Dentistry Department, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran

2 Dentist, Tehran, Iran


Background: Crowding is one of the most prevalent types of malocclusion as well as a major problem in clinical orthodontics. It is essential to know the cause of crowding in order to achieve a better treatment.
Objectives: A longitudinal analysis of arch dimension changes in late primary and early mixed dentition periods in children was designed and investigated the effect of eruption of precedence on the arch size in the samples under study.
Methods: This longitudinal study was carried out on 32 children aged 5.5 - 6.5 years who had no erupted permanent dentition. Impression was taken and the arch perimeter, depth and width as well as tooth size were measured by a digital calliper and a brass wire on casts. After eruption of the first permanent tooth, the second impression was taken; the above-mentioned parameters were measured on the second casts. Data were analysed by ANOVA test.
Results: Four pattern of eruption of precedence were as follows: maxillary 1st molar, mandibular incisors, Mandibular 1st molars and simultaneous eruption of maxillary and mandibular 1st molars. With eruption of mandibular central incisors, inter canine width and overjet increased by 0.81 and 0.27 mm, respectively. The mandibular arch perimeter increased by 2.25 mm with simultaneous eruption of maxillary and mandibular permanent first molars. The maxillary arch perimeter increased by 1.25 mm and 1.50 mm with eruption of maxillary first molars and simultaneous eruption of maxillary permanent first molars, respectively.
Conclusions: Eruption precedence had a significant effect on changing mandibular inter canine width, maxillary arch perimeter, mandibular arch perimeter and overjet.