I have lived in Thailand since 2001, both in BKK and Chiang Mai, and during that time I have been to many dental clinics. By far the best is Kitcha Clinic in Chiang Mai. The clinic itself is comfortable and spotlessly clean, the staff is friendly and English-speaking, and the dentists are extremely patient and competent. All this at very reasonable prices. I recently had a small problem with treatment from one of the dentists I saw at Kitcha. Ajarn Kitcha himself, the founder and owner of the clinic, took the time to meet immediately with me and he resolved the issue very fairly and quickly.