Tracy,
I second Susan – the smell could be a mouth issue or a stomach/digestion issue.
As for dental hygiene, you could give some bully sticks or other natural chews that actually help clean teeth (kibble doesn’t clean dog teeth any more than a cookie cleans human teeth). His mouth may not smell better but it will be cleaner. Or, if you would, you can give raw meaty bones – now those are supposed to really clean teeth, and combined with daily brushing, you should be good on the oral hygiene.
For the tummy, try considering digestive enzymes and/or probiotics. They may help.
