I know laughing gas is back in vogue for safe labor pain relief. You can read on the Mayo Clinic's website about it. If it is safe for labor pain, it obviously is safe for dental work. It just apparently, for labor pain, is not always reliably effective.

My recommendation for the dentist is simply a really skilled dentist, numbing cream first, anesthesia shots later, and a few of them, spaced out in increments. And raise your hand if you sill feel a thing - the dentist would add anesthesia. It is as much art as science and a whole lot depends on whether the dentist can give almost painless anesthesia shots. I have been lucky with both dentist and endodontist. I make sure to praise their ability to give almost painless anesthesia shots, to give credit where credit is due as this makes a world of difference. My dentist told me last time that she is fortunate to have a "light" hand.