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.
Becoming a prothodontist requires firt obtaining a D.D.S from an accredited dentistry school. This takes 4 years and most dental schools require at least 90 hours of college course work and they prefer a college degree (4 years). After completing dental school there will be 2-3 years of graduate study in prosthodontics. So it works out to be about 10 years of study.