plastic aligners

Expansion is a strategy that can be used to create space but how much can we expand and how much space do we obtain? When undergoing #orthodontic treatment, most patients and orthodontists would prefer to avoid #extractions. In most cases (~80%) extractions are avoided but some cases it is indicated to reduce crowding, to help improve the bite, reduce the risk of relapse, or to reduce the risk of the gums receding. Rapid palatal expanders (see previous post) are a common appliance used to correct crossbites (top teeth biting inside the lowers) and this tends to be very stable. Expansion also creates space but not as much as you may think.
When assessing the amount of arch perimeter or space gained (to reduce crowding) with #expansion it was found that only about 1mm of space is created for every 3mm of expansion of the back molar teeth (Germane American Journal of Orthodontics and Dentofacial Orthopedics 1991;100:421-7). Research into expansion beyond correcting crossbites shows that although quite large expansion can be achieved, it invariably relapses back to within 2-3mm of the original dimensions. We therefore can only gain ~3mm of stable expansion which only creates about 1mm of space for reducing crowding – not much really! Fortunately this is not the only strategy orthodontists have for creating space as I discuss in the textbook, Evidence-Based Clinical Orthodontics. We can treat more moderate crowding (5-6mm) by involving other techniques such as incisor proclination (up to ~2mm is stable but this creates ~2mm of space), interproximal reduction/thinning can be used if prudent and E-space maintenance (a future Blog) can contribute ~3-4mm of additional room.