For Christmas, I got an electric toothbrush... after using with it for a week, a chip from my second upper molar fell out! There are lots of dentist clinics around town with signs in English, but I found a small dental clinic ( location ■ ) near where I'm staying, about a 15-minute walk north of the Old City, on the right side of Clang Phueak Road.
The clinic looks modern and clean. The dentist is a very nice young woman who explained everything in English and answered all my questions patiently. She was gentle and careful, told me what she was doing every step of the way, and showed me what she did afterwards. My filling cost just 600 baht, plus 100 baht for local anesthetics which I requested, since apparently most Thais would choose to endure the uncomfortable sensitivity. There's a price list at reception so you can get an idea of how much various procedures cost.
I also had some concerns about sensitivity near the gum line, so she checked everything and made some helpful suggestions. Since my last cleaning was about 5 months ago, I wanted to get a cleaning, but she said it's not necessary at this point and sends me off with a free tube of Sensodyne and a soft bristle toothbrush to help with gum sensitivity. It's so refreshing to meet a dentist who is not trying to charge you for whatever they can! She said if I want to get it done later, I can call or even use facebook to make an appointment — you can see photos of the inside of the dental clinic on their facebook page.