Why is it not Je me les brosses (les dents) rather than je me les brosse?

Hi J, It's because the subject of the verb is 'Je'. So in English, it's 'I brush' and in French 'Je (me) brosse. The verb agrees with the subject and not the object (teeth). And brosser is regular, so Je brosse, etc.

Merci bien, I had forgotten the reflex and was into the preceding direct object.. so easy to get lost in the maze.

Hi i too teplied je les couvres instead of je les couvre... 

so if ive understood corectly it would be tu les couvres 

elles les couvrent ?? 

Subject rather object

Hi Noeleen,  you have, I believe, just upped the confusion stakes another level.  It is only the past participle of the verb that agrees with the preceeding direct object and then only when the auxiliary verb is avoir.  The être verbs in the passé composé agree with the subject.  In the present tense verb construction there is no agreement with the object so yes je les couvre, tu les couvres.  I think this is right but you definitely had me going for a minute.

And of course I too had forgoten that.  Witness my original question.  Oh dear!