re: Quellensteuer Lite
Everything dental is claimable, as long as you exclude cosmetic work like polishing teeth (white). But of course the 4% rule still applies, and in some cantons this is 5%. Also, you have to prove your claimed medical costs, either with bills or the overview sent to you after handing in bills by your insurance company.

Note you have to claim these costs back by 31.03.2008 or you will lose the right to a refund (see pdf).

re: Full tax form
What I would like to know myself if you can ask to fill in the full tax form and then claim the additional deductions like Berufskosten (occupational deductions, which is often a fixed standard amount, and single household deduction etc.).

If you are allowed to fill in a full tax form, the medical costs are calculated differently, then it is not 4% of your annual brutto or net income but another income (reinheitsinkomen?), which is reduced by some factors. So fill in the tax form and see if the resulting tax reduces when you enter your bills.