Hi @mendy-bode , thanks for your question!

To begin with, a tooth filling constitutes anything that is meant to replace a part of the tooth, or to add on the existing tooth.

Some common purposes of tooth fillings are as follow:
1. Decay-ed teeth
2. Any cavities in teeth
3. Adding on to existing tooth structure for aesthetics purposes (e.g changing the shape, closing the gaps, masking the colour of the tooth, etc.)

For decay-ed teeth or teeth with cavities:
The preparations usually just include removing all decay and restoring the tooth with the filling material. The duration usually depends on the size and extent of the decay, but it generally ranges from 15-30mins per filling.

For aesthetic purposes:
The preparation generally doesn’t include removing healthy tooth structure, but merely preparing the surface of the tooth by cleaning it. We will then usually add on the filling material to the tooth after and shape it. The duration also varies depending on extent of filling material, but it generally ranges in approximately 20-30 mins per tooth.

Feel free to clarify if you have any more questions!