I've read about benzodiazepines being highly addictive and their potential for withdrawal symptoms or negative effects, but are they safe when taken on a short-term/one-time basis, such as for a lengthy dental appointment or minor surgical procedure?

Benzos: don't take more than 1 for any minor procedure - highly addictive, yes

Anti-anxiety Meds: You have a short-term problem. You only require a short-term solution to prevent dependence. In this case 1 pill taken before your appointment should do it. Talk to your Dentist about appropriate dose. Or you could try non-addicting approaches such as breathing exercises, biofeedback, nitrous-oxide in-office sedation, etc.