Leeway space is the most crucial and naturally occurring space for the alignment of permanent teeth. The difference between the summation of the mesiodistal crown widths of the deciduous canines and deciduous molars (first and second) and that of their permanent successors counterparts, which are the secondary '3's and secondary '4's and '5's
According to Nance, this difference is dimension of 1.7 mm in the mandible and 0.9 mm is also observed in the maxilla as regards each quadrant.
Primary molars have greater and larger dimension mesiodistal crown widths than the permanent premolars that later replace them, especially 'E' (the deciduous second molar).
Leeway space has been preserved to be favourable and is utilized to resolve crowding that may have occurred if there is lack of space.
This space is later used in permanent dentition by allowing the first molars to drift mesially so as to establish a Class I molar relationship(according to Edward Angle) in the late mixed dentition.
In a research programme of Taiwanese children, the leeway space of a child aged 5–6 years was significantly greater and exposed than that of a child aged 7–8 years.
"Primary molars have greater mesiodistal crown widths than the permanent premolars that replace them, especially the primary second molar"Source
The leeway space serves as a natural space provider to resolve crowding that is present in the mixed dentition period as regards majority of individuals.
"Leeway space is clinically crucial in pediatric dentistry because it is utilized to resolve tooth crowding and allow the first molars to drift mesially to establish a Class I molar relationship in the later stages of mixed dentition."Source
According to some reports, Leeway space seems to be affected by many factors including;
1- Ethnicity
2- Size of the crowns of the deciduous cuspids and bicuspids
3- Sex
4- Environmental factors and so on
The average leeway space gotten by researchers was said to be about 0.9mm for maxilla and 1.8 mm mandible in each quadrant respectively, for the United States.
Moreso, Leeway space was reported to be about 2.03 mm averagely in the lower arch in Brazil.
"Leeway is the difference between the combined mesio-distal widths of the primary cuspid and molars and their permanent successors. According to Nance,this difference is 1.7 mm in the mandible and 0.9 mm in the maxilla, in each quadrant. The normal leeway according to Moyers is 2.6 mm in the maxilla and 6.2 mm in the mandible. However, this varies considerably and should be measured in each patient. The greatest difference exists between the mesio-distal width of second primary molar and second bicuspid and is often referred to as ‘E’ space."Source
Permanent teeth were demonstrated and were said to have a secular trend of growing, bringing about a significant reduction in leeway space as the teeth erupt.
Girls according to some research were said to have more dimension of leeway space than boys. However, environmental or genetic factors that reduce tooth crown dimensions may have impact on the generally known and usual dimension of leeway space.
Leeway space is more important and crucial in the mandibular arch than in the maxillary arch due to some certain reasons. Take for instance, the therapeutic choices for the mandibular arch are limited and not easily altered because of the low potential for arch expansion and even the issue of difficult molar distalization.
By contrast, arch problems in the maxillary arch can be resolved effectively through arch expansion, buccal pushing or tipping of the anterior segments or even molar distalization.
Due to any of these therapeutic concepts, the leeway space in the maxilla was observed to be negative in several cases. On the other hand, several studies have investigated leeway space in the mandibular arch which makes effective use of leeway space in the mandible as one of the few means of resolving lower anterior arch crowding and getting a good teeth realignment.
That's all for now as regards the Leeway space which is very important especially in the late mixed dentition stage and happy blogging and reading.
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