Gingivitis difficult to control in 1 year old cat

My 1.5 year old Siberian cat, Charlie, was noted to have gingivitis when I took him to the vet a couple months ago.  The vet told me to brush his teeth daily - I'd been doing it a few times a week but had been falling off the wagon lately.  I inquired at the breeder where I got him, and she said she treats her cats with Petzlife gel daily and has had no problems on that regimen.

So I started brushing daily and using the gel twice a day, and that seemed to help.  Poor thing must have been in pain, because he started playing a lot more once the gingivitis improved.  I went back to occasional brushing but daily doses of the gel - fortunately he will lick it off my finger, especially if I add a dab of CET toothpaste which he likes.

I've now got him to the point where his teeth are all perfectly white and his breath is good (which was always the case), but he still has very noticeable red gum lines on the upper back teeth.  I went back to daily brushing - he doesn't like it because he hates having his head restrained, but I'm managing to at least brush the problem areas for a few seconds - lightly, because I figured out it hurts him to have those spots brushed.  And also back to twice daily use of the petzlife.  However, it's been a week and there's been no change.  In fact, he got a little worse on one side.

Other info, my cats are raw fed and they chew on chunks of meat every 1-2 days.  Also this cat loves to chew so I got him those Petstages dental chew toys which he loves and attacks several times a day.

I'm wondering whether I should take him back to the vet.  But, given that the problem is confined to just the upper back teeth and he did improve (slowly) with the petzlife gel, is there something else I should try first?  Or just keep doing what I'm doing and give it more time?

Since you feed him raw, do you give him chicken wings to chew on occasionally.  Those are supposed to be great to clean their teeth on .  This would NOT take the place of what you are currently doing, but would be in addition to it.

Some cats, like people, are just prone to bad teeth and gums.  I'm guessing the reason he loves to chew is because it soothes his gums, kind of like how babies chew on everything they can get their mouths on when they are teething  

My understand from our Vet is that once the tartar and plaque has built up, especially under the gums, it needs to be removed professionally, under anesthesia (to get the stuff under the gums).  THEN, to keep it from forming again, the brushing needs to be done frequently.  I didn't think anything would get rid of it once it formed, except scraping it off.  That's what I have been told. 

Consider having a dental cleaning done. Some cats need a thorough cleaning before home dental care can work. Some cats are just prone to dental problems because of genetics. You just do the best you can with regular tooth brushing and dental cleanings as needed.