As a Dental student about to graduate and as the son of a Dentist, the misinformation that exists about oral health, specifically tooth decay in a opiate user, blows me away. I'm not calling anyone ignorant, but there is an obvious lack of public education in this area. Someone above did a good job of nailing the high points of the conditions most likely contributory to greater incidence of decay in a user, but to reiterate the main problem coincident with opiate use is solely xerostomia or dry mouth. Even that varies from person to person with or without opiates, and even then it's a condition that can be easily overcome with proper preventative measures. This mostly includes brushing consistently 2-3x a day as well as flossing. with that said, the main idea is to keep sugar and acid from soaking into your teeth for the least amount of time as possible. Acid demineralizes teeth on the short term, which makes them susceptible to bacterial attack and stain accumulation. If this occurs frequently enough, it can lead to long term demineralization which in turn makes the susceptibility to bacterial attack or decay and stain accumulation that much easier. even swishing with water or running a brush even without toothpaste over your teeth after sugar or acid intake is enough to help intervene in the process of decay as again, the point is to intervene when acid or sugar has come in contact with your teeth. Sugar is the substrate or food for the bad bacteria which cause decay, and these bacteria thrive in acidic environment. So, combine acid and sugar like with soda, and the perfect storm is created... The enamel is softened, and food is provided to bacteria to eat away at the softened enamel.
bone density and bone loss in an adult are NOT related to a loss of tooth structure. Not only are the components of teeth NOT formed by osteoblasts (try ameloblasts for enamel for example), but tooth formation is completed n early childhood, which is why you receive flourish treatments only as a child on a regular basis... Which is to provide fluoride to the enamel matrix while it's still in development or mineralization. Things that cause bone loss do not cause tooth structure loss in adults. And that's that.
Methadone is on par with any other opiate with its potential for harm to the teeth, which is again revolved around xerostomia and nothing else. It does not cause greater saliva acidity.
The saliva not only physically washes the teeth, but it's a ph buffer, acting to neutralize acid. It also contains elements of our innate immune system, immunoglobulin that activates the immune system as well as good bacteria that inhibit the formation of bad bacteria. There are numerous kinds of this bad bacteria, different kinds for different types of cavities, as well as the bacteria that causes the formation of plaque and subsequently tartar, and subsequently periodontal disease which is a different bear in itself. Naturally, some folks don't provide adequate good bacteria or even the proper immune response. These are the folks who battle tooth decay and perio disease despite their efforts otherwise.
It's generally a combination of things that allows the perception that there is a greater incidence of tooth decay in say methadone patients. For one, they dose everyday so there is a guaranteed constant bombardment of xerostomia. Preparations with sugar don't help, but the amount is so little that to blame it on the sugar preps is a little naive. Sugar cravings, smoking, poor diet, poor hygiene, lack of dental visits, and xerostomia.... Those are the culprits involved with opiate use.
To the OP ... What you describe sounds like calculus to me. This is mineralized plaque, and forms most frequently on lower anterior or front teeth, and generally in between them. It can easily accumulate stain. Calculus can only be removed by a dentist, so if you haven't had a cleaning in awhile... Tis is most likely what you are seeing. So, go get your teeth cleaned!
Edit: the same goes for suboxone use. There is no mechanism of the drug or delivery system that causes tooth decay... Refer to above. Sugar found in delivery system is trivial, but if you dose with it regularly, then it's worth your effort to take a brush to your teeth after its dissolved. If its inconvenient to brush (remember even without dentifrice aka toothpaste is fine, as the goal is to disrupt bacterial attachment) at random times after you dose or eat/drink sugar or acid, then do those things only at times when it is convenient to brush right afterward.
And before someone even thinks it, no brushing after acid intake is not harmful to your teeth. I've heard people laughably think that brushing after acid can cause you to physically remove enamel. Not true. Brushing after acid has softened enamel is the most ideal time to brush, as it will aid in more quickly remineralizing enamel and neutralizing ph.