Many dental offices still use film, vs. the digital systems.
The lead foil in the film packets is dead soft. The dentist has to pay to get rid of it. Offer a receipt for the scrap lead for his records.
Best to tell a little white lie and say you need it for fishing sinkers.
Keep an eye out for hospitals or health facilities being demoed or remodeled. The x-ray rooms have lead sheeting in the walls. Contrary to popular belief there is NO radiation absorbed or stored in the lead.
(Additional hint, if the guys tearing the stuff out think there is radiation in the lead, who are you to correct them?) wink wink nudge nudge
Note: the above applies to X-ray rooms only, nuclear medicine shielding MAY be different. I have no personal experience with that.
Freedom is not free