About Closed Curves
A closed curve is a curve that joins itself. When you create or edit a closed curve, you can make the curve periodic or nonperiodic by toggling 
Periodic Curve.
Periodic Curve.• Periodic curves
Periodic curves have better continuity at the endpoints than nonperiodic curves, and create smoother surfaces. However, there is no tangency control on the endpoints of periodic curves. Additionally, the value for the curve degree must be an odd number. When a curve of an even-numbered degree is changed to periodic, the degree increases by one.
• Nonperiodic curves
Nonperiodic curves split into two halves during regeneration or when you click 
OK to exit the 
Curve or 
Curve Edit tab. This is so you can use the curve to create sketch-based features in Creo Parametric. One composite curve is created so you can references the curve as a single entity outside of Style.
OK to exit the Curve or Curve Edit tab. This is so you can use the curve to create sketch-based features in Creo Parametric. One composite curve is created so you can references the curve as a single entity outside of Style.