For many reasons. Sometimes people aren't able to maintain the recommended frequency of dental checkups. Oftentimes, when an extended time has gone in between cleanings, a more advanced cleaning may be recommended by your doctor. Harmful bacteria and hard tartar deposits called calculus build up on your teeth above and below the gum line, releasing toxins that cause gum disease, also known as periodontitis. Unfortunately, this buildup occurs in areas that can't be taken care of by brushing, flossing, or even irregular dental cleaning over time. As periodontitis progresses, it can lead to increased inflammation, bleeding, receding gums, and ultimately receding bone tissue. Your doctor can recommend a procedure called scaling and root planning to remove these deposits from your teeth. Scaling and root planning is its specialized procedure that removes excessive calculus and bacterial deposits beneath the gumline, and is usually performed with a hand scalar and an ultrasonic cleaner, which uses high frequency vibration to separate the calculus from the tooth. This procedure is for advanced periodontitis cases, and in many cases is so extensive that it must be done in stages. It may require multiple appointments to complete in order to ensure you are as comfortable as possible during the procedure by removing the deposits and bacteria. This procedure is in many cases able to halt the spread of periodontitis. Your doctor will help you determine the next steps for continued rehabilitation of your gum tissue. However, if these symptoms are not treated appropriately, the progression can advance to a point of tooth and bone loss requiring costly and painful reconstructive dentistry to treat.