Chew toys can help wipe away soft tartar and massage the gums. They also prevent boredom and reduce stress.  Give your dog rawhide, nylon, and rubber chew toys. Ask your veterinarian for a recommendation. Giving your dog chew toys and bones is a good supplement to regular brushing. They are not a good replacement for brushing in the long term. Other alternatives to brushing include sprays and gels that you  can apply regularly. They contain ingredients that help to deter the bacterial growth that causes tartar build-up. Consult with your veterinarian about using these and other products. If your dog will not accept you cleaning its teeth, bring it to the vet and have it done for you. Also be sure to discuss your dog's dental health at your regular vet visits.

Summary:
Use chew toys. Try a gel or spray. Get a professional cleaning.