4 A-levels won't make you "stand out" as far as uni admissions goes. Universities do not award "bonus points" to students taking extra A-levels - because not all schools have the facility to offer that to their students, if unis did so they would be necessarily discriminating against students going to those schools (and the schools unable to offer 4 A-levels to all students are probably underperforming ones in the first place with low progression to HE, exactly the students unis are trying to encourage to go to uni by raising their aspirations).
For dentistry physics is unnecessary, and I imagine probably not hugely relevant/useful. For chemical engineering it is much more relevant, although not always required. Bear in mind chemical engineering at uni is like 75% maths, 20% physics, and 5% chemistry or something along those lines. It's mostly maths and physics with a little bit of chemistry (and the chemistry bits largely overlap with the physics). If you struggle in physics in school you might find engineering (of any variety) challenging (although I appreciate school level physics is taught in a rather unmathematical way unlike at uni).