Shares of micro-cap firm National Dentex ( NADX) were shooting up on unusually high volume Wednesday, two days after the dental laboratories owner reported a slight decline in quarterly sales from the previous year.

The Natick, Mass.-based company, which designs, makes and sells dental prosthetics, said sales for the quarter ended Dec. 31, 2008, fell to $41.26 million, down from $41.38 million for the fourth quarter of 2007. On a non-GAAP basis, net income excluding a goodwill impairment charge was $831,000 or 15 cents per diluted share, compared to $656,000, or 12 cents per diluted share for the same period in 2007. Wall Street had expected EPS of 17 cents, according to analysts polled by Thomson Reuters.

National Dentex shares were up 85.9% to $3.55 at midday Wednesday, on volume of about 80,000, roughly five times the three-month average of 15,718.

Among National Dentex's competitors, Dentsply International ( XRAY) was recently up 0.04% to $24.55 and Henry Schein ( HSIC) was up 0.6% to $38.28.