Occurrence of malocclusion and need of orthodontic treatment in early mixed dentition.

This study analyzed the occlusions of 489 children at the onset of the mixed dentition period (mean age 5.1 years, range 4.0-7.8 years). These children participate in an ongoing clinical trial that is investigating the effects of orthodontic intervention in the early mixed dentition. The aim was to report the occlusal findings at the baseline. The frequencies of mesial step, flush terminal plane, and distal step were 19.1%, 47.8%, and 33.1%, respectively. The canine relationship was Class I in 46.1%, Class II in 52.4%, and Class III in 1.5% of the sides examined. An asymmetrical canine relationship was found in 30.1% of the children, significantly more often on the right side than on the left (P <.001). Overjet ranged from -2 to +10 mm with a mean of 2.9 mm. Overbite ranged from -5 to +8 mm with a mean of 2.8 mm. Excessive (> or =4 mm) overjet was found in 26.7% and overbite in 33.8% of the children; in 15.5% of the children, both variables were 4 mm or more. Anterior crowding was detected in the maxillary arch in 11.6% and in the mandibular arch in 38.9% of the children. Girls showed mandibular crowding more often than boys (P <.01). A posterior crossbite was found in 7.5% of the children, unilaterally in 6.4% and bilaterally in 1.1%. Scissors-bite was detected in 1.1% and an anterior crossbite in 2.2% of the children. The mean maximal opening was 40.3 mm. Joint sounds were registered in 5.2% of the children. The prevalence of malocclusion was between 67.7% and 92.7%, depending on the values of unacceptable parameters used for each occlusal characteristic.