**3.1. Hardness**

Ceramic brackets are known for their hardness. They are notably harder than enamel [4–7]. Thus, contact between enamel and ceramic brackets has to be avoided by all means. This type of contact can lead to severe enamel damage [8]. Particular care has to be exercised with deep bite and/or class II canine relationship patients. If required, bite opening applications must be performed to prevent enamel damage.
