Where and when to use?

[RandEnglish]

Hi,

When should as I use 'as little as possible' or 'as less as possible'.

For example, should it be The dentist tried to cause as little pain as possible while filling Tim's cavity or The dentist tried to cause as less pain as possible while filling Tim's cavity.

 

[Rover_KE]

Only 'as little as possible' is used.

Rover