An employee puts finishing touches on a denture at a facility in Newport Beach, California, U.S. (Photographer: Troy Harvey/Bloomberg)  

And the S&P's Biggest Winner This Year Is... A Dental Company

(Bloomberg) -- In a year when the Standard & Poor’s 500 Index reached new records on a regular basis, the best-performing stock is a relatively small provider of dental products.

Align Technology Inc., the maker of the clear teeth-straightener Invisalign, is on pace to become the index’s winner this year with a 136 percent increase as of Dec. 28.

With estimated revenue of $1.49 billion in 2017, the San Jose, California-based company’s sales have almost doubled in just three years as popularity of its smile-correcting products grew. It remains tiny within the S&P 500, where average annual sales are $22 billion.

And the S&P's Biggest Winner This Year Is... A Dental Company

The drivers of growth: American teens, and China. Wall Street is betting Align has more room to grow in 2018, especially after the shares declined this month: 11 of the 12 analysts covering the stock recommend buying it, with one advising to hold it. Their average 12-month price target is $273.73, based on data compiled by Bloomberg, which would be a 21 percent increase from current levels.

Good Health

In a testament to how good a year 2017 was for some health-care stocks, four health companies are among the S&P 500’s 20 biggest gains, three of them businesses with less than $3 billion in annual revenue.

Biotechnology company Vertex Pharmaceuticals Inc. is on pace to more than double this year, the third-largest increase on the S&P 500, driven in part by takeover speculation. Health insurer Centene Corp., DNA-sequencing firm Illumina Inc., and robotic surgery company Intuitive Surgical Inc. are also in the top 20.

Contrast that with 2016, when only one health-care stock was among the S&P 500’s 20 biggest winners. But the sector accounted for seven of the 10 biggest declines last year, including Vertex and Illumina, compared with one this year.

And the S&P's Biggest Winner This Year Is... A Dental Company

Sector Losers

On average, health-care stocks’ gains were in line with the S&P 500, with a 21 percent rise in the 62-member S&P 500 health-care index. The rally makes declining stocks stand out all the more: Only nine companies ended the year lower than they started in the S&P 500 health-care index.

The biggest health-care loser is Envision Health Corp., a struggling provider of services like surgery and medical imaging. It slumped 45 percent while being a target of a shareholder activist. Botox maker Allergan Plc follows with a 22 percent decline for the year, dragged down in part by its stake in struggling Israeli drugmaker Teva Pharmaceutical Industries Ltd. and by concerns of upcoming competition.

And the S&P's Biggest Winner This Year Is... A Dental Company

Celgene Corp. found itself near the bottom after a tough second half of the year. The stock lost more than a quarter of its value during a five-day stretch in October, after a highly anticipated drug for Crohn’s disease failed a late-stage trial and the drugmaker cut its 2020 profit target.

And the S&P's Biggest Winner This Year Is... A Dental Company

©2017 Bloomberg L.P.