Believe it or not, our Perio book says it's totally fine, yet our fixed professors say NEVER.
Here is an excerpt from the text.
"Based on the evidence available today it can be stated that a combination of implant and tooth support for FDPs is acceptable (Belser et al. 2000). While a recent systematic review (Lang et al. 2004) indicated that tooth–implant reconstructions reveal a 5-year survival rate of 94.1%, comparing very well with the 5-year survival rate of implant–implant reconstructions of 95.0% (Pjetursson et al. 2004),the 10-year survival of tooth–implant reconstruc-tions (77.8%) appears to be signifi cantly lower than the 10-year survival of implant–implant reconstruc-tions (86.7%). However, owing to the fact that the former 10-year survival rate was based on only 60 (I-T) FDPs and the latter on only 219 (I–I) FDPs, the reliability of such 10-year survival has to be questioned."
I don't necessarily agree with the last bit..."well, study size is too small, so we will ignore it" because it could just as easily be worse than better.