New Zealand domestic rugby players caught playing without a mouthguard will be sent from the field, under a new penalty aimed to improve player safety.

The New Zealand Rugby Union Board (NZRU) has approved an amendment to its domestic safety law which will give referees the power to enforce the compulsory mouthguard regulations.

NZRU deputy chief executive Steve Tew said under the present law, the wearing of mouthguards was compulsory for those playing at NPC level and below, but there was no penalty for those who flouted the law.

"Under the amended law, which will come into effect on March 15, any player not wearing a mouthguard will be ordered from the field by the referee and will not be allowed to return until they are wearing one," he said.

"If, after 10 minutes, the player is unable to return to the field wearing a mouthguard, then they can be replaced with a player wearing a mouthguard.

"We appreciate that this places increased pressure on volunteer coaches and referees but we believe the safety benefits gained outweigh those concerns,"

Tew said research showed mouthguards reduced the likelihood of damage to teeth and the jaw.

He said that since mouthguards were made compulsory in New Zealand domestic rugby in 1998, there had been a 40 per cent reduction in rugby-related ACC dental injury entitlement claims.

Mouthguards are not mandatory under International Rugby Board law.

"However, we believe that wearing mouthguards is a simple injury prevention strategy that works and by increasing player compliance we expect to see a further drop in unnecessary dental injuries."