"No debería": "don't have to" vs "shouldn't"

[jemenake]

I'm discovering that "deber" is a very colorful verb, when it comes to the various conjugations.

When used in the indicative, it connotes an obligation:
"Debo escribir a mi mamá" - "I have to write to my mother".

When used in the conditional, it connotes a recommendation:
"Debería escribir a mi mamá" - "I should write to my mother".

Now, here's were things get really interesting. It seems that, when combined with "no", it connotes the obligation/recommendation not to do something, as opposed to the absence of an obligation to do it (like it would be in English).

"No debo mentir" - "I must not lie" (not: "I don't have to lie")
"No debería reir" - "I shouldn't laugh" (not: "Laughing is not something which is recommended").

My question for the Spanish pro's out there: is there a way to say "I don't have to..." using deber? For example, if dentists used to think that it was beneficial to brush your teeth for five minutes,

"Te deberías cepiar los dientes por cinco minutos".

However, let's say that, later, the dental community concludes that brushing for that long doesn't help. Is is possible to say, with deber, that this is no longer encouraged (without connoting that it's discouraged)?

[AngelicaDeAlquezar]

Hmmm... If I understand your question, no you can't use "deber" like that. In that case, I'd use "tener" or "necesitar" instead.

- No tienes que cepillarte los dientes durante cinco minutos.
- No necesitas cepillarte los dientes durante cinco minutos.