Emax Porcelain Onlay Okay to Adjust Chairside By Dentist?

Whether done in the mouth or chairside, this is fine, this is normal.  Emax is a great material and very strong or durable.

Adjusting emax porcelain is very normal both chair side and in the mouth.  Emax is a very durable and strong porcelain material that also has a very natural appearance.  An ideal bite as mentioned above is the most important factor when seating a permanent porcelain restoration.  Your dentist will often have your "bite" on little blue sheets of paper, equilibrating paper.  The blue paper will leave marks on your teeth allowing the dentist to know exactly where he/she needs to adjust.  I actually incorporate a T-Scan system to adjust my patient's bite.  This is a computerized U-shaped wafer that not only tells me where my patients are hitting high but also where they hit first, second, etc.... This enable me to adjust the bite completely and accurately ensuring a stable bite allowing our porcelain restorations to last long term.

Emax is a very strong material. It is very common that any new dental work needs some slight adjustment when it is fitted.

The most important factor is that the bite comes out very precisely. There would be more risk of a problem if the bite was slightly off.

Your dentist did the right thing.