Sir, while travelling on the train recently, two young women came and sat opposite me. Their conversation fell to dental matters. One, it seemed, had a problem which visits to three dentists had failed to resolve; indeed, the problem had only become worse. Could her friend recommend to her a competent dentist? 'Oh,' extorted her friend, 'Don't talk to me about dentists! I think they're all incompetent, but just in different ways!' Deciding discretion was the better part of valour, I buried myself deeper in my crossword.