In April 2019, Allan et al. published a paper in the Journal of Small Animal Practice titled "Prospective randomised blinded clinical trial assessing effectiveness of three dental plaque control methods in dogs". The authors' aim was to compare the efficacy of three common methods of plaque control - a dental diet (Hill's Prescription Diet t/d Canine), a dental chew (Pedigree DentaStix) or once daily tooth brushing using a toothbrush and enzymatic toothpaste.
They recruited 33 dogs (although they only included data from 22 dogs, due to drop outs or exclusion) and randomised them to the three treatment groups (based on the authors' power analysis, this number of participants was appropriate). All dogs received a routine scale and polish procedure prior to beginning the study, and blinded scoring of plaque accumulation was performed at a 6-week follow-up visit. Plaque accumulation (coverage and thickness) was scored by a single investigator, using a modified Logan and Boyce technique.
The results of the study indicated that daily tooth brushing resulted in a significantly lower median mouth score of 1.25, compared to feeding the Hills t/d diet with a median mouth score of 4.65; tooth brushing also resulted in a significantly lower mouth score compared to the median mouth score of 4.10 for the DentaStix chew, fed once a day. The mouth score for the diet and dental chews were not significantly different from one another, and there was greater variability in the mouth scores for these two groups of dogs, compared to the tooth brushing group.
In the discussion, the authors acknowledge a limitation of their study, which was that their inclusion and exclusion criteria for recruitment and enrolment of owners and their dogs likely resulted in a selection bias towards a highly motivated sub-population. It is acknowledged that tooth brushing is a very effective method of controlling plaque, however owner compliance can be poor. Brushing the teeth of some dogs can be a real challenge, and not particularly fun for either the dog or the owner! This is even more so the case with cats. So it's important to remember that tooth brushing is effective, as this study shows, but only if you actually do it.
Does this mean that other methods of plaque control, like dental diets and rawhide chews, are worthless? Not necessarily. There is evidence to suggest that particular chews and diets can be effective, to a certain degree, however the best approach to preventing periodontal disease is probably to combine a number of different methods - with tooth brushing being an essential one.
Don't use human toothpaste or try to make your own toothpaste out of baking soda and coconut oil, as some websites suggest. It will taste terrible and make everything much harder!
Flavoured enzymatic toothpaste (chicken, beef, seafood etc) will make tooth brushing easier, and your dog (or cat) will be less likely to hate having their teeth brushed.
Read full paper by Allan at al. here: https://www.ncbi.nlm.nih.gov/pubmed/30575038