Trip to dentist is definitely in order.  Explain the pains and
location to the dentist. Air space under fillings or an undiagnosed
abscess might cause pain.  Confirm he isn't clenching the mouthpiece
too tightly during the dive.  Some people tend to bite the regulator
when nervous.  16-18 age group might be seeing wisdom teeth erupting
soon.

My son had something similar a few yeas back.  We had been
doing some fairly deep diving in Cozumel for several days
and on a shallow dive, he had one tooth POP.  He said it
felt like he had been hit with a bat in his jaw.  Previously
it had been hurting him but he neglected to let anyone know
for fear that we would keep him on the boat.  A trip to the
dentist showed that he had small micro fractures in his
teeth that the dentist attested to chewing ice cubes.  The
theory was that pressurized air (from the deep dives) had
gotten trapped in the tooth and cracked it further trying to
get out.

It was just a theory!  He quit chewing ice and has had no
problems diving ever since!

Go figure!

Some teeth roots run right up into the sinus cavities and maybe it's
possible that an infection or reverse sinus block may be causing the
tooth pain. I've had tooth aches that were caused by sinus infection
but not while diving.

Cam
http://www.CoastalBC.com/
http://www.SurfingVancouverIsland.com/