Evidence favoring a secular reduction in mandibular leeway space.

Area of Science:

• Dental anthropology
• Orthodontics
• Human growth and development

Background:

• Secular trends in tooth size have been observed in recent human generations.
• Understanding changes in mandibular leeway space is crucial for orthodontic treatment planning.

Purpose of the Study:

• To investigate changes in mandibular leeway space between cohorts born in the 1930s and 1990s.
• To determine if tooth size has changed, impacting mandibular leeway space.

Main Methods:

• Comparison of dental casts from two cohorts of healthy, phenotypically normal American white individuals (born 1930s vs. 1990s).
• Analysis of primary and permanent tooth dimensions to calculate mandibular leeway space per quadrant.

Main Results:

• The cumulative size of mandibular primary teeth (canine, first and second molars) was slightly larger in the recent cohort.
• The sum of permanent teeth (canine, first and second premolars) was significantly larger in the recent cohort.
• Mandibular leeway space per quadrant significantly decreased from 2.45 mm in the earlier cohort to 2.03 mm in the recent cohort.

Conclusions:

• Mandibular leeway space has significantly decreased in 21st-century American whites.
• This reduction may pose challenges for orthodontists in managing tooth size-arch length discrepancies.
• Further research into secular trends affecting craniofacial development is warranted.