Pseudo-Developing Maps for Ideal Triangulations I: Essential Edges and   Generalised Hyperbolic Gluing Equations
  Let N be a topologically finite, orientable 3-manifold with ideal triangulation. We show that if there is a solution to the hyperbolic gluing equations, then all edges in the triangulation are essential. This result is extended to a generalisation of the hyperbolic gluing equations, which enables the construction of hyperbolic cone-manifold structures on N with singular locus contained in the 1-skeleton of the triangulation. 
Henry Segerman and Stephan Tillmann
math.GT