I am noticing a lot of craze lines on my lower first back molar. i wear a lower bite splint, how come i am still getting crazelines and is this normal?

Possibly: Many causes for craze lines. Bruxism, restorations, altered occlusion, etc. As long as your bite is correct, and the craze lines are superficial, don't fret. However if they become deeper cracks, and if you begin to have a sharp pain when biting, or if you develop thermal sensitivity, then you need to see your dentist or endodontist.

normal: Craze lines or incomplete enamel fractures, as some call them, are universal. But you may have not noticed them before on this tooth. Wearing you occlusal appliance is the best thing you can do to manage the potentially damaging forces we all apply to our teeth through clenching and grinding. If the cracks become stained or more prominent i would have your dentist check them.

Not normal, but..: If continue to get worse, yes, you should worry and probably get a softer bite splint. It could only be the appearance of the enamel with no further consequences. Watch for fractures or pain. If so, run to see your dentist.

craze lines: If you wear a niteguard or bite splint you likely have a bruxing or grinding problem the craze line likely were from before you got the guard....They can and will show up as time goes on.....Have the dentist who made the gaurd evaluate that tooth.