If a tooth with a gold crown breaks, it is generally because the underlying tooth structure has fractured or decayed. Gold crowns are not immune to becoming loose, especially if you are eating foods and candy that are harmful to crowns and bridges. Gold crowns also cause the least wear on the opposing tooth.
Making the world better, one answer at a time. An artificial boundary is a boundary made by humans, examples include dams, the fence at the border between the U.S and Mexico. A natural boundary is a boundary made by nature, a boundary that happens naturally, examples include rivers, mountains and such.
Convergent boundaries are the place where two tectonic plates converge (i.e. two plates move toward each other). These zones tend to be where compressional stresses are active and this results in thrust or reverse faults being common. Converging plate boundaries are of two types: Subduction boundaries occur where oceanic lithosphere is pushed beneath continental or oceanic lithospheres. Where two plates converge at an oceanic trench a subduction boundary is formed as cold oceanic lithospheres are pushed back down into the mantle.