Washington, July 29 - For years, scientists have debated the exact nature of the worm like structures inside a human tooth. The structures are not worms, but what they are is still in question.

Micro-images in a dissected molar suggest they caused tooth decay.

Studies by University of Maryland (U-M) Dental School researchers' revealed cylindrical objects extending or 'growing' out of the natural pores or tubules of teeth.

Inside a human tooth, more than 50,000 such tubules per square mm act as channels running from the nerve up through the tooth. They are associated with transporting hot or cold sensitivity to the tooth.

The worm like structures were photographed in clear detail by Ru-Ching Hsia, director of the electron microscope core facility at the school.

'Most (dentists) say 'I have no idea'. Others say they are made of bacteria, or minerals, or hyphal branches of yeast cells (C.