According to this article from the Journal of Oral Implantology, implant drills should be replaced about every 50 uses. As the article discusses, the proper use of irrigation to control temperature is an important part of keeping your drills (and bone for that matter) in good condition.

It might be tricky to keep track of how many times each drill is used. A more practical method can be to replace your drills on a yearly basis.

Of course, if you have a very busy implant practice and are placing 300 implants per year, you should consider replacing the drills more often than 1x per year.

https://meridian.allenpress.com/joi/article/41/2/e19/3292/Effects-of-Implant-Drill-Wear-Irrigation-and-Drill