Shares of 3-D Printing companies had a wild ride at the beginning of the week. Stratasys (SSYS -0.79%) and ExOne (XONE) shares were both down by as much 10% Monday, while shareholders of 3D Systems (DDD -4.17%) watched their holdings drop as much as 8%.

In this video, Motley Fool contributor Brian Stoffel explains what caused the drop, and why long-term investors need not worry about recent volatility.