Insurance question: Dental

Hello,

I am coming to Zurich from America to work as a Language Assistant at a Gymnasium. I was told by the secretary of the school where I will be working that I will likely be eligible to opt out of buying Swiss insurance (if I decide that this is the thing to do) if I can prove that I am covered through another provider, seeing as how I am here for only a year and for training purposes.

I looked at on of the forms I may have to fill out and saw that dental insurance was mentioned. Here is my question: is it necessary to have dental insurance to work in Switzerland? I am enrolling in HTH Worldwide Expat insurance, which, however I am thinking that they may expect me to also have dental insurance in order to count me as insured and to forgo buying swiss insurance.

I have also heard that it is necessary to show proof of insurance in order to register with the police once I get to Zurich and in order to gain my entry permit as a trainee. Anybody know anything about this?