Trying to compare date part only of datetime between two timestamps

select this_.id as id45_0_, this_.version as version45_0_, this_.firstname as firstname45_0_, this_.lastname as lastname45_0_, this_.email as email45_0_, this_.text_comment as text6_45_0_, this_.country as country45_0_, this_.subscribe as subscribe45_0_, this_.imported as imported45_0_, this_.creation_datetime as creation10_45_0_ from mail_address this_ where to_date(creation_datetime, 'YYYY-MM-DD') between to_date('2012-12-03 19:49:05.643', 'YYYY-MM-DD') and to_date('2012-12-04 19:49:05.643', 'YYYY-MM-DD') order by this_.firstname asc, this_.lastname asc, this_.email asc

I get an error message:

ERROR at line 1:
ORA-01830: date format picture ends before converting entire input string