FORT WORTH, Tex. — Steven Mark Chaney, who was freed from prison in October after 28 years, had to fight back tears as he watched forensic dentists argue here, before the Texas Forensic Science Commission, whether bite patterns on the skin of murder, rape and child abuse victims can offer valid clues to the perpetrator’s identity.

In 1987, he was sentenced to life on murder charges after a dental expert testified that it was virtually certain that his teeth had caused marks on an arm of the victim, a drug dealer who was stabbed to death. This same expert has now repudiated his testimony as unfounded. Mr. Chaney is one of more than a dozen people around the country who have been released or exonerated in cases involving bite-mark testimony that was later debunked.

Now, the Texas commission is seeking to develop guidelines on whether bite-mark comparisons should have any role in the courtroom.

Forensic science more broadly is in turmoil as prosecutors, defense lawyers and judges confront evidence that many long-used methods, like handwriting analysis and microscopic hair comparisons, were based more on tradition than science and do not hold up under scrutiny. Even fingerprint and certain kinds of DNA matches are not quite as certain as many once believed, scientists say.