How do you meditate to cure fear of needles, dental work?

Hynotherapy helps. I have used a hypnotherapist with patients who are very fearful and have had good results.
Find a mentor. Regular practice will help. Find a good hynotherapist or biofeedback teacher to help. Also the homeopathic remedy argentum nitricum (preferably in a 200 (pyrethins and piperonyl butoxide) c potency...(your health food store can order it for you) will also help with anxiety in general and needle phobia in particular.
CBT. Seek a cognitive-behavioral therapist who specializes in phobias. One method they use is systematic desensitization which slowly and incrementally brings the person closer and closer to the thing they are afraid of in slow, graduated steps that help make the anxiety more tolerable.