How many ( weeks/ months) would you keep temporary cement in new permanent bridge on upper molar natural teeth with no dental issues or concerns.

It depends: It depends upon why one is temporarily cementing in the bridge and the dentist's philosophy. I general do not temporarily cement in bridges,i If they look and fit great, and I show them to the patient prior to the cementation. I rarely have any issues, even over decades of use. If there is any question, I cement them in temporarily for a week or so. A month is not a problem.

No time frame: You can keep it as long as there are no dental issues, for the life of the teeth/bridge/crown.

Months: Temporary cement under a permanent bridge is only a problem if the margins are not proper and cement washes out leaving open margins that trap food and make the tooth susceptible to decay. On a good fitting bridge, things can be good for months. Remember, good home care is important!

Indefinitely: First of all, why is a permanent bridge on with temporary cement? Sometimes this is done when the health of one of the nerves is in question. I usually will try to remove this after 6 months and recement with permanent cement. If it doesn't come off very easily, i will usually just leave it in place and monitor. If it loosens, then remove and recement. If it stays secure, monitor only.

Depends: Some bridges require getting used to when teeth have been missing for some time. It is much easier to make adjustments out of the mouth when they are necessary. Each case will dictate need for temporary cement