A PolygonMesh is a kind of Geometry. You can navigate a polygon mesh using generic objects such as Facet, Segment, Point and Sample or you can navigate using objects that are specific to the PolygonMesh such as PolygonFace, Edge, Vertex and PolygonNode.

VBScript Example

set oObject = Application.ActiveProject.ActiveScene.Root.AddGeometry("Cube","MeshSurface")
set oPolygonMesh = oObject.ActivePrimitive.Geometry

Primitive.Geometry X3DObject.AddPolygonMesh