About the Chapter 90 category

For discussions on products within “Chapter 90: Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical instruments and apparatus; parts and accessories thereof” of the Trade Tariff:

https://www.trade-tariff.service.gov.uk/trade-tariff/chapters/90

Hi
Why Dental chair mentioned in two chapters
90 and 94 , what’s the difference?!