Bill Guthrie is playing catch-up with his dental care, after putting things off for several years.
His new dentist's first task has been to take stock of the old fillings, to see if any need to be replaced.
Dr. Leonard Tau of the Pa. Center for Dental Excellence in Northeast Philadelphia says that's always a been a challenge.
"X-rays are really used to see decay between the teeth. And people think x-rays can see all decay," says Dr. Leonard Tau.
So he'd always relied on a visual examination with his eyes, and a probe to test for softness.
Now, he's also using the Canary cavity detector.
It uses low-power pulsating laser light to search for decay where x-rays can't.
The light penetrates 5 millimeters beneath the tooth surface.
"We're able to see under fillings, under composite restorations - those are the white fillings - under crowns, under sealants, which we could never do before," says Dr. Tau.
The Canary system measures the amount of light reflected by a tooth.
A low score means the tooth is healthy.
"14," chirps the machine. and the number appears in green on the scanner's screen.
But a high score means there trouble under the surface.
During his exam, Canary gave a reading of 71 on one tooth, and then -
"88 - That's a big number," says Dr. Tau, as he shakes his head.
Dr. Tau says for Bill, Canary caught decay under several fillings which didn't seem bad on the initial exam.
However, when the old fillings were removed, there was decay dangerously close to the nerves.
Instead of new fillings, Bill would likely have needed more drastic treatment in the near future.
"Two of my top teeth woyuld have needed root canals within the next 6 months, maybe." says Bill.
"He saved me two root canals, which i'm very grateful for."
Dr. Tau says the Canary cavity detector also helps find decay in irregular pits and nooks on teeth.
And it can help see if a treatment used to strengthen teeth is working.
Not all dentists have the device, but more are starting to use it.