Is Filing Between Teeth at the Beginning of Invisalign Treatment Typical Practice?

While it may seem odd, most cases need some form of space management.  Sometimes teeth are extracted, but often just some polishing of sides of teeth is enough.  This is true for both Invisalign and regular braces.

Filing between teeth or IPR (Interproximal Reduction is what we dentists call it) is commonly done when the size of the combined front teeth, upper or lower, does not match well with the opposite dental arch. The slight reduction generally is accomplished on a number of teeth (to reduce the amount needed on any one tooth) with small amounts taken from between the teeth where they contact each other.  This serves the purpose of 'matching' the two opposing dental arches so either spacing or crowding does not have to occur.  Another benefit can result as well; that of having a more stable result, since the rounded contact point is flattened by the IPR which causes the teeth to resist going out of alignment.  It is most common to need this on the lower front teeth, since it is more common for  the upper teeth to be smaller when matched with the lower.  With the IPR spread out over many teeth, the reduction of enamel on any one tooth is small and of no consequence regarding risk of decay.  In short, the IPR when needed, allows the orthodontic treatment to be more precise and therefore can give a better, more stable result.

What you are describing is called IPR (interproximal reduction) and it is normal in order to create some space for the teeth to move.  Nothing to be concerned with.