YOU may have noticed that the last tooth brush you bought was not quite so good as the previous one of the same brand. You may also have read that the Chinese government has recently been sending soldiers to clear the bandits and communists from Szechuen, that amazingly rich and populous province which borders on mysterious and inaccessible Thibet. It probably never occurred to you that there was any connection between the two incidents of that banditry around the head waters of the Yangtsze would affect the quality of an English tooth brush.