Brushing twice a day removes plaque — the soft, sticky film of bacteria that forms on teeth constantly. But if plaque isn't fully removed, it hardens into tartar within a matter of days, and tartar is something no amount of brushing or flossing at home can remove.
Tartar tends to build up most along the gumline and between teeth, areas a toothbrush often can't fully reach. Left there, it irritates the gums, leading to the early stage of gum disease called gingivitis — characterized by redness, swelling, and bleeding when you brush.
Professional scaling uses an ultrasonic tool to break up and remove tartar from both above and below the gumline, something that simply isn't possible with a toothbrush, no matter how diligent you are. Polishing afterward smooths the tooth surface, which actually makes it harder for new plaque to stick as quickly.
The six-month interval most dentists recommend isn't arbitrary — it roughly matches how long it typically takes for tartar to build back up to a level worth professionally addressing. Skipping it for years at a stretch is one of the most common, and most avoidable, paths to gum disease.