Thanks to 3D Systems (DDD -5.90%), 3-D printing stocks are taking a beating today. The 3-D printing giant released its preliminary 2013 full-year results and issued 2014 full-year guidance, and the market didn't take kindly to the news. Shares of 3D Systems were down as much as $21 a share during the trading session today, losing about 28% of its market value. The news also brought down Stratasys as much as 13%, ExOne down as much as 15%, and voxeljet down as much as 14%.

Why the wheels fell off
Investors reacted so poorly to the news because the company lowered its full-year 2013 earnings guidance, and its full-year 2014 earnings guidance came in much lower than expectations. Originally, 3D Systems was expecting to earn between $0.93 and $1.03 per share in 2013 on an adjusted basis, but now expects to earn between $0.83 and $0.87 per share.

The company's recent plan to accelerate its R&D investments and increase its sales and marketing expenses, along with generally higher costs related to making acquisitions, are playing into why 3D Systems lowered earnings guidance. The hope is that these increased investments in the short term will deliver superior results over the long term. However, investors should recognize 3D Systems' R&D expenditures as a potentially major risk to the long-term story.

Prior to today's announcement, analysts were expecting 3D Systems to earn $1.27 a share on an adjusted basis in 2014 – far above the $0.73-$0.85 a share the company expects to earn in 2014.

It's not all bad news
Despite all the negativity, there were a few notable bright spots to suggest that 3D Systems' long-term story is still on track. The company expects to double its revenue over the next couple of years, and sustain a 30% organic growth rate, adjusting for recent acquisitions. Considering the 3-D printing industry as a whole is expected to grow by around 20% year, this suggests that 3D Systems will be gaining market share in the years ahead. Over the long term, this increased market share could lead to increased material sales, which could boost long-term profitability, primarily because 3-D printing materials remains 3D Systems' most profitable business segment.

In addition, the company's backlog has nearly doubled to $28 million on a sequential basis, indicating that demand for its products, including the high-end, remains strong. This could be viewed as an encouraging sign that 3D Systems' new products are being well received in the market place.

The million-dollar question
As advocates of long-term investing, we Fools believe that it's important to monitor big price moves to ensure major developments haven't materially changed the long-term-investment thesis. Although it's never fun losing 15% or 20% of your investment in one day, it's extremely important to divorce your emotions from the equation and look long and hard at whether these developments will affect the long-term business underneath, and warrant taking action.

The truth of the matter is that 3D Systems told investors during its third-quarter conference call that it expects its 2013 full-year-earnings guidance will come in lighter of expectations because of its aggressive growth initiatives; today's update is merely a revision to that development, and only affects the bottom line. I'd be a lot more worried if revenue guidance was lowered significantly, because it could indicate the there may be structural issues with 3D Systems' business. In other words, I currently don't think there is enough here to warrant selling your shares today.

Ultimately, 3D Systems' management appears to be sacrificing short-term profitability in exchange for long-term future earnings potential. For investors, it's encouraging to see a management team that's more committed to the long-term story than it is with making short-term trade-offs just to please Wall Street expectations. If you're willing to go along for the wild ride, I think investors will likely be well served by sticking with this line of thinking. As a 3D Systems shareholder, I'm holding on tightly today.