Tuesday, July 5, 2016

Is Today’s Dogma Tomorrow’s Tooth Worm?

By John Lewis, VMD, FAVD, DIPL. AVDC
Veterinary Practice News.

"A history lesson about the tooth worm and how it reflects on science today.

Figure 1: A severely discolored right maxillary canine tooth in a Borzoi. Teeth with discoloration of the entire crown like this one have a very low chance of the pulp still being alive.

This month's column will take a diversion, with a history lesson followed by a philosophical discussion. The basis for discussion is this: What is considered today to be strong science may be the stuff of tomorrow's folklore. As an example, let's discuss the story of the tooth worm.

Dental problems that arose in people during ancient times were widely believed to be caused by a worm. The so-called tooth worm was blamed for toothaches, cavities and periodontitis.

The legend's origin has been widely debated but seems to trace back to Sumerian or ancient Egyptian cultures, with historical reference as early as 5,000 B.C. Worms were a common symbol of disease in ancient Egypt, perhaps due to parasites that were noted in sick patients. Belief in the tooth worm may have originated from this general impression that worms played a role in various states of disease.

Belief in the tooth worm persisted during the reign of the Roman Empire. Scribonius Largus, a famous medical doctor to the Emperor Claudius, wrote (circa 43 A.D.) about how to relieve toothache pain. Scribonius recommended using smoked henbane seeds as a topical treatment: "Distribute henbane seeds onto coal, allow the smoke to come to the teeth and rinse again with lukewarm water. While spitting out afterwards, there may occur sometimes tiny worms."

During the Renaissance, Paracelsus believed that a worm developed in a bad tooth and died as soon as it came into contact with air. In German writings, the worms were described to have various colors, including gray, blue, white, red, or black.

The notion of the tooth worm spread across Europe and persisted until the 1700's. In 1728, Pierre Fauchard, a Paris dentist, proposed that various internal and external aspects of the tooth, rather than worms, were the cause of cavities and periodontitis. The era of Enlightenment ushered in a wave of philosophical reasoning that trickled down to medicine, theology and science.

How could so many intelligent people through the ages be compelled to think the tooth worm was the culprit? Take a loot at a couple of example cases of mine from the past year.

A 4-year-old male Borzoi presented with a discolored right maxillary canine tooth. The discoloration was an impressive generalized brownish-gray color (Figure 1). I recommended treating the intrinsically discolored tooth, since dogs don't just tell us when they are experiencing a painful pulpitis. A study published in 2001 showed that of 64 discolored teeth explored via pulpotomy, 59, or 92 percent, had gross evidence of partial or complete pulp necrosis. Forty-two percent of discolored teeth evaluated radiographically had no radiographic evidence of endodontic disease, suggesting that radiographic signs lag behind pulp inflammation and necrosis.

Figure 2: A completely necrotic pulp from the root canal system of a discolored tooth in a Borzoi. After seeing this photo, perhaps it's not quite as much of a stretch of the imagination to see why people in 5000 B.C. thought the source of tooth pain was due to a worm. Their suspicions were probably reinforced when they found that removing the "worm" removed the pain.

Treatment options for the Borzoi included either orthograde root canal therapy, which the owner chose, or extraction. To access the long root of the canine tooth, an access site was made in the tooth a few millimeters from the gingival margin. The provides a straight-line access to the apex of the root.

Upon accessing the endodontic system of the Borzoi, I flushed the canal with an endodontic needle and a syringe of saline. Flushing the canal resulted in a satisfying delivery of a large, fleshy, worm-like structure from the access site. This "worm" was a tan-brown color suggestive of complete necrosis (Figure 2).

Other "worms" I've seen from canine teeth had a pink color, suggesting partial necrosis, which looked very convincingly like an earthworm (Figure 3).

Figure 3: A discolored left maxillary canine tooth in a different dog. In this case, the extirpated pulp is partially necrotic as exhibited by a non-bleeding, pink color.

Findings such as these in human patients during ancient times may have reinforced beliefs in the tooth worm, when there was a more rudimentary understanding of the anatomical contents of the tooth. Remove the worm and the pain goes away.

All this begs the question: Which of the currently accepted practices or medical "facts" of today will result in ridicule and head scratching by scientists in years to come? Things that we believe to be correct today may be proven false tomorrow.

For example, when I was in veterinary school, I was taught that ketamine has no pain-relieving qualities. Today it is given as an IV infusion specifically for pain. This and similar stories remind us that medicine is an evolving discipline, and all we can do is seek out the highest level of evidence-based medicine possible when making medical decisions. Until next month, keep on drilling down for the real answers."

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