there is a protective thing installed already which will not allow dust to move inside . i think you should know that .. that layer sometimes got blocked by dust that's why it needs to be cleaned by this way ..cause of that layer even water finds hard to move inside
toothbrush will damage the protective shield over speakers ( sapphire shield or IP and MIL-STD standard shields over microphone and speakers ) which prevents dust and water flow inside the device
check the mobile servicing manuals
better use moist tissue paper or cotton cloth or cotton with a dust vacuum cleaner
( as directed im Smartphone service and maintance manuals )
