Expansion CALCULATOR
“Let’s do four weeks of expansion”
I don’t know about you, but this drives me absolutely crazy. How can all of our patients—of different shapes, sizes, genders, and ethnicities—need 4 weeks of expansion? I’m exaggerating of course, but I think you get my point.
The Expansion Calculator is a tool to mathematically determine the ideal amount of expansion that can safely be performed to coordinate the arches based on each patient’s unique anatomy. It allows us to avoid using cookie cutter expansion prescriptions for all our patients.
We need 3 initial measurements in order to plan for and achieve this harmony
It should also be mentioned that a narrow maxillary dental arch does not necessarily need an expander to resolve the issue. It all depends on the etiology—are the teeth tipped in or is it a skeletal problem. In other words, is the palatal width is adequate or inadequate.
A proper diagnosis is critical to determine if expansion should be carried out through the use of an appliance (Rapid Palatal Expander) or via archwire expansion. The key is to look at the inclination of the Mx posterior segments. One trick is to look at the models from the posterior.
In the end, you should be able to achieve:
Coordinated maxillary and mandibular dentitions
Coordinated maxillary and mandibular alveolar bases
An appropriate curve of Wilson
The Expansion Calculator can also be used in conjunction with the Space Calculators for borderline extraction cases when you want to determine the maximum amount of space you can create from expansion to try and avoid extractions.
If a crossbite is present
consider this flowchart proposed by Ngan and Fields (1995) to determine how to best resolve the issue