Based on your description, the recurrent dark brown/black deposits along the gumline could be a form of extrinsic black stain (chromogenic bacterial stain). These stains are often associated with chromogenic bacteria and iron-containing compounds and can recur after professional cleaning. They are not necessarily an indication of poor oral hygiene.
Since you have previously experienced sensitivity after scaling, I would recommend a conservative, minimally abrasive professional cleaning approach rather than aggressive instrumentation. The treatment should first establish whether the deposits are soft plaque/stain, calculus, or an actual change in the tooth surface.
Next Steps
1. Have the teeth examined clinically and, if possible, photograph the deposits before cleaning.
2. If there is little/no calculus and the deposits are predominantly surface stain, professional polishing or low-abrasive stain removal may be sufficient.
3. If air polishing is available, ask your dentist about low-abrasive powders such as glycine or erythritol, particularly given your sensitivity concerns. Evidence suggests these powders are less abrasive than sodium bicarbonate/
calcium carbonate in relevant applications.
4. If there is calculus underneath the stain, some targeted scaling may still be necessary. It does not automatically mean that the entire mouth needs aggressive ultrasonic scaling.
5. After stain removal, your dentist should check for cervical caries, enamel/root-surface defects and gingival inflammation before deciding on the maintenance plan.
Health Tips
You do not need to “scrub” the stains away at home. Excessive brushing or abrasive products can cause tooth wear and potentially worsen sensitivity.
Air polishing is not automatically non-abrasive, however. The powder matters: sodium bicarbonate/
calcium carbonate can be more abrasive, while glycine/erythritol are generally preferable when a low-abrasion approach is desired. The evidence concerning damage to restorations is largely laboratory-based, so the dentist should select the powder and technique according to your actual tooth surfaces/restorations.
How to reduce recurrence
• Brush twice daily with a fluoride toothpaste, using a soft/ultra-soft brush and gentle pressure.
• Clean between the teeth daily with floss/interdental brushes as appropriate.
• Don’t try to remove the black deposits by scraping them yourself.
• Tell your dentist about any iron supplements, chlorhexidine mouthwash or other medications/supplements you use, because these can contribute to extrinsic staining.
• If this is genuinely black stain, understand that recurrence can occur even after complete removal; periodic professional stain removal may therefore be needed.