Teeth - Sherlock Drabble

It really shouldn't surprise John that Sherlock holds brushing one's teeth in contempt.
'But it's basic hygiene."  John is looking at Sherlock with an even mix of disgust and bewilderment. 'Are you saying you've never brushed your teeth?'
Sherlock rewards him with a withering glance, before returning to the specimen under his microscope.
'Of course I've brushed my teeth, John. I worry about your mental state some times; if I never brushed my teeth, I'm certain I wouldn't have any.'
John narrows his eyes and folds his arm over his chest.
'Alright, how often do you brush your teeth, then?'
'When I dictate it necessary.'
'And how often is that?'
Sherlock sighs, but doesn't look away from his work.
'I don't understand why you're so concerned, John. It's like eating - a massive waste of time.'
'Eating is necessary for survival, Sherlock.'
'I know my limits. Besides, you just conceded indirectly that teeth brushing is not necessary for survival by pointing out that eating was.'
John is silent, but Sherlock can feel him looking at him under those frustratingly knotted and raised eyebrows.
'How often, Sherlock?'
'I don't know! Every two weeks, or thereabouts. Whenever Mycroft threatens to tell Mother. Not when there's a case on. Now, would you please go do something useful instead of standing there and using your ridiculously admonishing eyes to bore into the back of my head? Thankyou."