Complex sentence: Previously, no academic qualifications were needed to work as a Dental nurse in the UK & many nurses began their careers with in house/on the job training programmes (under the direct supervision of a senior dental nurse & dentist).
Split into simpler sentences: Previously, no academic qualifications were needed to work as a Dental nurse in the UK. Previously Dental nurses began their careers with in house training programmes (under the direct supervision of a senior dental nurse & dentist).