14 This physiologic attrition is necessary for mesial shifting of mandible so that flush terminal plane
in the mixed dentition is converted to class I occlusion.
relationship of the second primary molars was evaluated and recorded as class 1: the distal surfaces of maxillary and mandibular primary second molars lie in the same vertical plan; class 2: the distal surface of the mandibular primary second molar is posterior to that of maxillary primary second molar; and class 3: the distal surface of the mandibular primary second molar is anterior to that of the maxillary primary second molar .
Kabue et al9 found that the straight terminal plane
of the deciduous second molars was presented in 53% of the Kenyan children, mesial step in 43% and distal step occlusion in one percent; he concluded that more than half of the children were found to have some form of malocclusion.