I am not a professional teacher, but I have recently started teaching English to some friends, and I would say that the answer to your question could be "both." Maybe the dictionary should be thought of as analogous to a nicotine patch, something to ease the pain of going cold turkey, and something that the user needs to be weaned off over time, using it less and less. I know that with a couple of my students, there have been times when the lesson simply could not progress without looking up a key English word in a bilingual dictionary. However, thanks to advice I received here, I have been able to work with my students to have this happen less and less often. Now we are able to conduct our lessons almost entirely in English. Despite the risks that come with using bilingual dictionaries, if you are starting work with a student whose English stops at basic greetings, I think there will be occasional instances where the bilingual dictionary will be simply indispensable.
I am not a teacher, just a learner, then I'd not go for a bilingual dictionary, I think it can dull your mind someway.
Well, it's just a point of view, I think that whether a student can't understand a sentence or even a word, he/she should guess, translations are not the best recommendation. Eventually he/she will find out the meaning, maybe listening to music, watching a movie, talking to friends, and suddenlly that word/sentence comes up, then, he/she get it easily.
If you can't wait... ask an English native speaker.