That's strange.  I've looked over Ghostship's teeth shader and do not see anything that would cause graininess to show while rendering.  You could have bad render settings.  The only correction you should with the shader is to disconnect the bump node from the Clearcoat Normal channel.  Ghostship does not have Clearcoat nor the Clearcoat roughness active so there is no need to plug that in.  However, if you want pearly white then increase the Clearcoat value.  FYI, teeth are not naturally white.