"We saw one game where there was 10 out of the 30 [players] that started the game that didn't have them," Hill said.
A note was sent to teams earlier in the competition to remind them of the rule but that yielded little improvement so another memo was issued last week.
"There's some players in some teams who were just ignoring it and we saw an outcome of that on Saturday night," Hill said.
"It's a safety message, that's the key."
Players are not required to wear mouthguards at Super rugby and international level and it's an open secret that some don't.
Auckland coach Wayne Pivac, who admitted he did not wear a mouthguard in his playing days, said his management sent a clear message to players to remindthem of the law before last Thursday's win over Northland.
"From our point of view, if you haven't got a mouthguard, you won't be selected, end of story," Pivac said.
Wellington coach Chris Boyd was slightly bemused by the situation after the game on Saturday but said he supported players wearing mouthguards, although he wanted the issue to be confronted before kick-off by the officials.
Savea, who captained the New Zealand under-20s this year, said he would have to change his approach.
"I've never worn a mouthguard in my life," Savea said. "I find I can't breathe, but my partner's always in my ear telling me to wear one, so I guess I'll wear one from now on."
If he wants to stay on the field during the rest of the season, he might have to heed the advice of his partner and follow the rules.
