As sushi fans know, just a dab of wasabi goes a long way. But that pungent, green horseradish may be doing more than kicking your tuna roll up a notch. According to research presented yesterday in Honolulu at the International Chemical Congress of Pacific Basin Societies, wasabi may help prevent tooth decay. Hideki Masuda, director of the Material Research and Development Laboratories at Ogawa and Company in Japan, reported that, during test tube studies, certain chemical compounds found in wasabi--namely, isothiocyanates--inhibited the growth of Streptococcus mutans, the bacteria that causes dental caries. These isothiocyanates, Masuda says, interfere with the sugar-dependent adherence of the cells to the teeth. (Such antimicrobial properties may also account for wasabi's popularity as an accompaniment to raw fish.) Of course, whether wasabi-based dental care products will make it to market remains to be seen.