If the surgery site is adequately curettaged ("scraped clean") and rinsed, there is minimal risk of remaining bacteria causing a problem for the future implant. Because implants are cylindrical and teeth roots are not, there is often extra space around the implant in the socket of a freshly extracted tooth. This problem is even more exaggerated in the molar teeth because they have multiple roots. The most ideal plan for a molar is to extract the tooth and bone graft the socket and allow healing for several months before placing the implant. In this situation, the socket can heal for several months and the chance of bacterial contamination of the future implant is essentially zero.
Just wondering if there is a valid reason to remove other teeth. With out reviewing x-rays and your particular situation, this is hard to answer. The simplest approach would be to replace 8 & 9 with implants without removing any other teeth. If teeth like 7 have cavities or other damage and cannot be saved, then it makes sense to extract them. Ideally, extractions and bone grafts should be done with having a final "picture" or destination in mind when it comes to the final implant plan.
