1 If X is a topological (or metric) space and M is a metric space, then the set of all bounded continuous functions from X to M forms a metric space if we define the metric as above: d (f, g) = sup x in X d (f (x), g (x)) for any bounded continuous functions f and g.
Invisalign is orthodontic appliance, so since orthodontic treatment is allowed as an FSA expense, Invisalign is covered. Different companies have different rules concerning amounts set aside and the timing of how funds are used for orthodontics.
In brief: Training. Most Orthodontists want to see at least a high school diploma. Trade school training as a Dental Assistant useful but not mandatory. Many (if not most) Orthodontists train their own assistants in their offices. They're looking for bright personality, little or no body art, clean appearance, willingness to learn/to be challenged/to like kids.