Why do some braces require molar bands and others dont? will molar bands make it hard to eat like with spacers?

Molar bands: Tooth movement with braces uses many different types of brackets and bands, etc. When bands need to be placed on the molars it may indicate that stronger anchorage is needed to more involved tooth realignment, or access may be an issue. Whatever the reason it should not make it more difficult to eat as the bands do not involve the chewing surfaces of the teeth.

Ortho Variations: Different orthodontists use different techniques based upon training, personal preferences and specific requirements of each individual case. Although I am not an orthodontist, in the vast majority of full mouth cases that I have seen, the four first molars (one in each quadrant) get ss bands and the rest of the teeth get brackets.