Teeth are numbered in order to identify them with ease. However there are two common systems of numbering teeth that can confuse unless you know which one you are using. America uses the Universal numbering system and numbers teeth like this:
The FDI Dental Federation notation system is widely used (including South Africa) and numbers the teeth as depicted in the image below, where the first digit refers to the quadrant and the second digit refers to the tooth number in that quadrant. The most central tooth is always numbered 1. E.g. tooth number 36 is the sixth tooth from the centre in quadrant 3.
Learn more about dental anatomy from Wikipedia