Will my mouth be uncomfortable with braces on?

Your mouth will feel mildly uncomfortable while you are adapting to your new fixed appliances.
This mild discomfort is due to :

A. Pressure on your teeth

The appliance moves your teeth by applying very light pressure.
This pressure may cause your teeth to be tender for a period of 3-4 days when it is first applied. Biting on your teeth stimulates the circulation around them and will help to relieve the tenderness. If desired mild analgesics like paracetamol or asprin can be taken as these have been shown to help after appliances have been fit. Any tenderness should pass after 3-4 days.

B. Irritation of your lips and cheeks

A new appliance rubbing against the inside of your lips and cheeks may cause irritation initially. Over a period of 1-2 weeks your lips and cheeks will adapt to the appliance and it is unusual to experience any irritation after this. Soft wax placed over any irritating areas of the brace will help during the initial period. Additional packs of wax can be obtained by contacting the surgery.