The last restaurant to receive a new supply was Gisborne, yesterdayafternoon, Mr Kenny said.
An investigation was launched on Friday night.
"What they try and do is put the light bulb back together, all the broken pieces of glass and see what's left over.
"What they don't know, that's what they're trying to work out now, is what percentage of glass could be missing and if it was missing, and it's not on the floor, what could have happened."
It was not known when the lightbulb smashed, but it could have happened as long as a week ago since the room had not been checked since last Sunday.
"... We felt there was probably a couple of days worth of potential that the buns could have been in the restaurants [with glass in them]."
McDonald's had not yet received any complaints from its customers.