A dental technician or dental hygienist can take many routes not all taking the 5 years required to be a dentist. From a BTEC to a degree as long as you are GDC registered.
a Pearson BTEC Level 3 Extended Diploma - for this you will often need four GCSEs (A-C) in English language, maths and a science can be done in year
a foundation degree you will usually need to be employed in a trainee dental technician role to get on this course
There are many routes to become one some longer than others but most if NOT all NO longer than 3 years. You work whilst you learn and as teeth whitening is nowhere near an advanced dental procedure. Although, the first use of each cycle can be carried out by dental hygienists, therapists or clinical dental technicians under the direct access of a dentist (that is, with a dentist on the premises) , the products after can be provided to the patient to complete the cycle of use.
I.e rent a room within a dentist clinic building client base and clients only need to come once with a dentist present for you to do continual treatments.They could also administer fillers this way.
Do you see what I am getting at... *bangs head against wall*
botox,fillers, teeth whitening is hard to regulate A LOT of the time the people who you believe have trained for years have not. My sister is a Doctor who does botox, fillers and NOT all people are as well trained as you think.