I'm currently using Vet's Best Dental Gel
http://www.vetsbest.com/pdf/VBDentalGel3165810096.pdf and I'm pleased with the results. My girls eat soft food in the morning and kibble in the evening... I do offer antlers, twiggies, etc. for them to chew on. They don't particularly like getting their teeth brushed, but they tolerate it
I also use Leba III
Lebalab Inc for nights when I don't brush.