Plaque sticks most readily in areas where it cannot easily be dislodge, like the gingival margins of the teeth, the fissures of the teeth and around the edges of dental restorations (Stagnation areas). Removing plaque with a good brushing technique, brushing into the curve of the teeth, small headed medium texture brush angled into the gum line and interdental cleaning where the brush cannot remove plaque as sufficiently – For further preventive measures the fissures (deep groove) can be sealed by the dentist by placing fissure seals.
Fissure sealant is used to fill in narrow grooves in a tooth that cannot be adequately cleaned by brushing. In some cases, the tooth structure has fine grooves or pits which accumulate plaque, not because the person doesn't brush, but because they're too narrow to allow even one bristle into them. These will develop cavities over time, and you don't want that. So the dentist will brush on a coating that seals the grooves and pits, making it possible to brush off all the plaque and keep your teeth healthy.