Arch Length Discrepancy
Also written as: ALD — Arch Length Discrepancy
The difference between the available arch length and the space required to accommodate all teeth in proper alignment, quantifying the degree of crowding or spacing.
Full Definition
Arch length discrepancy (ALD) is a fundamental measurement in orthodontic diagnosis, calculated by subtracting the total mesiodistal widths of all teeth in one arch from the measured available arch length. A negative value indicates crowding, while a positive value indicates spacing. Accurate ALD calculation is essential for treatment planning decisions, including whether extractions are required. Editors should note that 'arch length discrepancy' and 'space discrepancy' are often used interchangeably in the literature, though the former is the preferred term. The ALD is different from the Bolton discrepancy, which compares inter-arch tooth proportionality rather than within-arch space.
Usage
Usage note: Distinguish clearly from Bolton discrepancy. Report ALD as a positive or negative millimetre value and specify the arch (maxillary or mandibular).
In Context
- "A mandibular arch length discrepancy of −8 mm indicated severe crowding, necessitating premolar extractions." — Diagnostic records summary
- "The author conflated arch length discrepancy with Bolton discrepancy; the editor added a clarifying footnote." — Peer-review feedback