The purpose of a cleaning is to help the patient return their mouth to a place where simple, home oral hygiene can repel a majority of the plaque/calculus accumulation that results from normal, everyday eating and drinking habits.  Brushing, flossing, and use of mouthwash is advised for home hygiene, because their collective use helps to mechanically and chemically remove any bad bacteria that can cause build-up or decay.  In office dental cleanings are spaced on a 6 month cycle to help patients maintain their oral hygiene while also giving the dentist a chance to evaluate the patient's mouth and give advice on better hygiene habits or to plan future treatment of active decay/infections.  Your dentist may change the timing between your recalls dependent on how at risk of decay you are.

Many call this a "deep cleaning".  SRP or scaling and root planing is a process where the hygienist removes bacteria that has colonized below the level of the gingiva/"gums".  Many times SRP is indicated in patients that are prone to or currently have periodontal disease.  This procedure requires separate appointments to debride the teeth, check healing and evaluate whether the patient needs to be referred to the Periodontist; and a recall appointment for maintenance of the healing tissues.  Periodontal disease is a condition that many times does not hurt the patient until the teeth are mobile or are too infected to save so it is very important to keep regular cleaning and recall appointments with your dental office to help maintain your oral hygiene.

For more information, follow the links below

https://www.mouthhealthy.org/en/az-topics/g/gum-disease 

https://www.mouthhealthy.org/en/az-topics/s/scaling-and-root-planing