NEW YORK ( TheStreet) -- Since I last looked at 3-D printing companies three months ago, the industry has made a round-trip.

The two largest such companies, 3D Systems ( DDD) and Stratasys ( SSYS), are now trading close to their December levels.

What's going on? Bears and shorts began attacking the shares in earnest last month, writes 24/7 Wall Street, with claims the machines have yet to reach production lines and consumer markets remain untapped.

There were other problems unique to 3D Systems. It "missed" on its latest quarter, Reuters writes, although sales were up 45%. (Sales were supposed to be up 48%, Forbes said.) Co-founder Charles Hull sold more than half his personal position, according to But a 45% rise is hard to call a miss, and Hull is in his mid-70s.

Stratasys also fell, partly in sympathy and partly because its financial reports lack transparency, wrote -- the current company was formed late last year in a merger with Objet, an Israeli firm.

Here is what's really happening. The 3-D printing, or "additive manufacturing," revolution is brand new. When Mitch Free writes at Forbes that it "doesn't live up to the hype yet," the key word is "yet." Charles Hull got his first patent on the process in 1986. Machines today use only a limited number of materials. They're fairly slow. They're only practical in niches -- Stratasys now has a unit for orthodontic clinics, writes.

That doesn't mean the revolution isn't happening, or that it won't happen. The two leading companies aren't guaranteed their place in the final standings, but they're the best horses to bet on. Being public and large, they can make acquisitions -- such as 3D Systems' recent purchase of GeoMagic, a software company.

And 3-D printing itself may just be part of a larger revolution, which Neil Gershenfeld of MIT called "bringing programmability to the physical world" in a recent Wired profile. Gershenfeld's Center for Bits and Atoms is looking to digitize not just design, but materials and process, building something like Legos, 3-D parts that can be assembled accurately in standard ways.

But is it likely that both 3D Systems and Stratasys are going to miss the boat on all this, or that they're going to be made obsolete by some innovation out of left field? In new fields you're always betting on management, on people like 3D CEO Avi Reichental, profiled here at

You're hoping that they're not so devoted to what they have that they ignore what's coming, as Digital Equipment Corp. CEO Ken Olsen famously dismissed personal computers. (Olsen later said he was dismissing digital homes.)

That's always the risk. But match the risk to the potential reward. Note that 3D Systems, which has the longest financial track record, has been growing at nearly 50% per year for some time with rising operating margins. Note that there are bigger companies that could give you a big payday buying these guys out.

I think the risks are worth taking. There are technical traders at 4Traders insisting the next move in this sector is up. Fundamentally, I agree.

Just remember that technology is always a roller coaster, and at some point you may want to get off.

At the time of publication, the author was long DDD.

This article is commentary by an independent contributor, separate from TheStreet's regular news coverage.