Shares of

Myriad Genetics

(MYGN) - Get Report

were among the best-performing health-related stocks Tuesday, rising 8% after the maker of medical tests posted better-than-expected second-quarter results.

The company reported a loss of $8 million, or 22 cents a share, on sales of $27.3 million for the December quarter. Analysts polled by Thomson First Call expected a bigger loss of 32 cents a share, with sales of $26.7 million. During the year-ago quarter, the company had a loss of $10 million, or 33 cents a share, on sales of $19.6 million. The "second quarter was particularly strong, with record revenues, strong profit margins and a significant reduction in our net loss," the company said. Shares were trading up $1.60 to $22.68.

Sybron Dental Specialties

( SYD) fell 7% after the maker of dental products posted first-quarter results that fell below expectations. The company earned $14.5 million, or 35 cents a share, on sales of $158 million. Excluding stock-based compensation costs, the company earned 39 cents a share for the quarter ended Dec. 31. Analysts expected earnings of 43 cents a share and sales of $163 million.

"Sales were slightly lower than our expectations due to minor shortfalls in a few professional dental product lines," the company said. "In addition, sales growth in the specialty products segment was slightly lower than expected due to the softness we experienced in our dental implant business." During the year-earlier quarter, the company earned $15 million, or 37 cents a share, on sales of $149 million.

Looking ahead, Sybron Dental sees second-quarter earnings of 43 cents to 48 cents a share, or 49 cents to 54 cents a share excluding stock-based compensation costs. The company predicts sales of $175 million to $180 million. Analysts project earnings, excluding stock-based compensation expense, of 52 cents a share, with sales of $179 million. Shares were trading down $2.76 to $39.26.

Shares of

Thoratec

(THOR) - Get Report

rose 8% after the company said it plans to repurchase $20 million in stock under a new share repurchase program. The maker of heart disease products still has $5 million remaining from its previous $25 million buyback plan. Shares were trading up $1.48 to $20.67.

Mentor

( MNT) fell 4% after the maker of breast implants posted weaker-than-expected third-quarter results and withdrew its fiscal 2006 guidance. For the December quarter, the company earned $12.7 million, or 26 cents a share, on sales of $120.5 million. Excluding items, the company earned $16.1 million, or 33 cents a share. Analysts expected earnings of 38 cents a share on sales of $130.6 million. During the year-earlier period, the company earned $16.3 million, or 34 cents a share, on sales of $120.6 million.

"Our third quarter results were impacted by transitory factors and temporal disruptions related to Mentor's ongoing strategic initiatives and the continuing FDA review of our silicone gel PMA," the company said. "While we strongly believe these activities have the potential to create significant value for Mentor's shareholders, there is uncertainty regarding their timing. Because of a lack of visibility in these areas, we believe it is appropriate to withdraw our full-year financial guidance for fiscal year 2006," the company concluded. Mentor had previously projected it would earn $1.60 to $1.65 a share for the year ending March 31. Analysts forecasts call for earnings of $1.56 a share. Mentor shares were down $1.69 to $42.21.

Shares of

Centene

(CNC) - Get Report

rose 2% after the provider of managed care programs posted in-line fourth-quarter earnings on better-than-expected sales. The company earned $13.9 million, or 31 cents a share, up from $12 million, or 27 cents a share, a year earlier. The company's sales rose to $423.2 million from $288.1 million. Analysts expected earnings of 31 cents a share on sales of $419.3 million.

For the first quarter, Centene expects earnings of 17 cents to 21 cents a share, including 4 cents a share in stock-based compensation costs. Analysts predict earnings of 30 cents a share. Centene forecast sales of $444 million to $449 million, slightly shy of Wall Street's target of $449.3 million. Shares were trading up 51 cents to $26.05.

Other health-care volume movers included

Pfizer

(PFE) - Get Report

, up 21 cents to $25.30;

Boston Scientific

(BSX) - Get Report

, up 32 cents to $21.94;

Genta

( GNTA), up 11 cents to $3.28;

Johnson & Johnson

(JNJ) - Get Report

, down 10 cents to $56.75;

Amgen

(AMGN) - Get Report

, down $1.06 to $72.44;

Bristol-Myers Squibb

(BMY) - Get Report

, up 6 cents to $22.43;

Schering-Plough

( SGP), down 9 cents to $18.51;

Elan

(ELN)

, down 20 cents to $14.65;

Merck

(MRK) - Get Report

, down 13 cents to $33.70; and

Gilead Sciences

(GILD) - Get Report

, up 57 cents to $60.59.