Once tartar is present, it really needs to be removed somehow to resolve dental disease, but SMS can at least reduce some of the secondary gingival inflammation. A diet change away from processed food towards real food (especially something that is low carb, like a raw diet) can inhibit further tarter formation.
San Ren Tang combined with the SMS can be helpful if there is a Wind invasion component to the disc disease. If the disc disease has resolved and is stable, then you can just focus on SMS for the Cushings. Note that the above-mentioned diet change can rapidly resolve the Cushing's tendencies, especially in tandem with SMS