Cosmetic dentistry is a difficult term to provide a definition for. Any treatment that can be argued to improve the appearance of a tooth can be defined as cosmetic.
Aesthetics and beauty are subjective and not absolute and measurable. Personal opinion and fashion affect the assessment, therefore it is essential that you and your dentist understand what you want to achieve and what can be achieved within the time and resources available.
For example, a tooth coloured filling might be considered as cosmetic dentistry. At the upper end of cosmetic dentistry there are techniques of layering filling materials in twenty different shades in one restoration that can make a filling invisible to detect in the tooth. It can take several hours to provide a single filling. However the majority of “cosmetic” tooth coloured fillings are a few carefully chosen layers that blend the filling into the tooth while controlling the cost and time required.
The key to good cosmetic dentistry is communication and understanding because appearance and beauty are often personal opinions. Basic rules can be applied but the adapting of rules to the individual provides the best results.