Earlier studies reported similar significant increase in the OB towards the permanent dentition stage followed by a decrease into the adulthood stage.15-17 It was claimed that OB tends to increase in the mixed dentition phase due to the mesial drift of the first permanent molars into the leeway space and the possible closure of the occlusion.12 In the current study, the inter-canine width was also found to increase from the age of 9 years to 11 years of approximately 0.9mm, then it decreased slightly.
Our findings might be related to distalisation of incisors and canine to leeway space or to facial growth, since mal-alignment has multifactorial aetiology and it has been suggested that the position of the incisors might be correlated with the amount and direction of growth.25 When arch dimensions were evaluated in the current study, there were no significant findings in the three stages of development.
Evaluation of mesiodistal width of unerupted canines and premolars in mix dentition is an integral part of the orthodontic assessment.1 It helps in predicting future crowding or spacing and the availability of leeway space. This, in turn helps in deciding treatment modalities like space regaining, space maintenance, space supervision or some extraction pattern like serial extraction.2-4 Mostly the size of primary buccal segment teeth is larger than their succedaneous teeth and is called leeway space.5,6 If not utilized, this space is most commonly lost in mesial drift of the molars.7
More leeway space is present in the mandibular arch as compared with the maxillary arch because of a significant size difference between primary buccal segment teeth and their permanent successors.
At approximately 11 years of age, the permanent first molars migrate forward to close up the ex- cess leeway space
provided by the difference in size between the primary molars and the suc- cedaneous premolars.
What would our orthodontic colleagues think of the recommendation of the wholesale removal of the leeway space
that nature has provided for the permanent dentition by allowing subsequent mesial drift?
He labeled this beneficial size differential "leeway space." The maximum leeway space that he measured from cases in his practice was 8 mm and the least was 0 mm.
Thanks to Steve Dugoni et al, (13) looking at Art Dugoni's records, we learned that leeway space could be successfully held to offset anterior crowding with excellent long-term results.
Mandibular second premolar of three cusps type is relatively larger mesio-distally than the two cusps type premolar.8 So this rare discrepancy in the prediction of leeway space
can leads to slight crowding in the permanent dentition.
Space loss occurred from tipping of the teeth adjacent to the infra-occluded primary molar with the space loss being greater than that normally lost by the leeway space [Becker et al., 1992a] (Figure 2).
The leeway space is mainly due to the difference in widths of the mandibular second primary molar versus the narrower underlying permanent second premolar.
One important factor is loss of leeway space
due to early loss of primary molars.