What is scaling of teeth? Is it 100% effective? What are the side effects of it?

Above the gumline. Scaling is the removal of all foreign matter/ collection on the teeth that is above the gumline, & smoothing/polishing of the teeth.
Scaling. According to ada definition: scaling is the removal of plaque, calculus, and stain from teeth. In reality, it's a term used very loosely. Dentists & dental hygienists may use hand instruments, ultrasonic scalers or a combination of both. If done well and you keep your teeth clean, it's effective. Some patients experience some temporary tooth sensitivity and gum soreness.
Sadly nothing. Medical is 100% effective or guaranteed. The process as previously explained removes the accretions / stains / calcified deposits completely. It is incumbent that the patient immediately henceforth adopt and employ excellent oral hygiene techniques to prevent re deposition of the deposits. They only take 24 hours to calcify. Make sure you are using a mechanical toothbrush and a waterpik as pa.
Sometimes discomfort. Scaling is cleaning the root surfaces of the roots of your teeth below your gums where there is a build up of calculus and bacterial toxins and an infection. The goal is to remove the infection and toxins so the pocket can heal and shrink. This may be the first step in treating the pocket, or the only one, depending on the depth and your immune system. Follow all instructions given.