My dog weighs 39Kg and is fed two packs of Naturediet a day (780g - 2% of bodyweight) - is this enough? (They are slightly overweight so I have reduced the food intake a bit - they were on 3 packs a day (1170g - 3% of bodyweight). However since I have had them on the Naturediet I have noticed their teeth are getting a lot of plaque on them - is there any way of removing this other than brushing their teeth? I heard that Bonio's are good but I need something that won't put any weight on - I would appreciate any ideas.

bonios won't clean teeth.

You can:

give a raw knuckle bone for them to chew on
administer the homoeopathic remedy fragaria 6c to dissolve tartar
You can clean the teeth regularly with toothbrush and canine toothpaste

Feed by hand and eye, not what it says on the packet; all dogs have differing metabolisms, temperaments and energy requirements; if the dog is too fat it is getting too much food and not enough exercise.

Raw bones would do the trick, anything from chicken wings to marrow bones :)  (just make sure the bones arent cooked)

I hear Logic is very good for teeth ...

I agree with giving raw bones,i would start now before their teeth get worse,i have seen dogs with terrible tartar,but after a month on raw meaty bones their teeth are back to new :D

As for the weight issues,i always reccomend more exercise.