Teeth that have gone bad can not only hurt you when you eat, but can also keep you up at night and keep you from being well rested affecting your entire life. An infected tooth can not heal properly because the body's immune system (that normally kills bacteria) cannot reach the inside of the tooth. The tooth acts like a harbor of infection and if treated with antibiotic, typically the surrounding area will heal, however the internal surface of the tooth does not. This is because blood flow caries the antibiotic and if a tooth is infected it has either lacking or zero blood flow. On the top image we have a healthy and infected tooth in the diagrams, below and to the right we have areas in red where blood is able to flow carrying with it antibiotics and immune cells. Notice how the healthy tooth has blood flow. On the bottom left we have necrotic (dead)areas in blue lacking any blood flow, thereby having no access to the antibiotics and the immune system. You can see how the infected tooth can act as a fortress protecting any bacteria hiding within it until the antibiotics leave and the coast is clear.
Routine extractions are typically one rooted teeth or extractions Dr. Amos deems to be simple. Prior to extraction the tooth will be checked to make sure it is numb using the same technique his father, Dr. Edward Amos, used. In other more difficult extractions, Dr. Amos may refer to a specialist.
Generally any extraction that is not routine is a surgical extraction. During this procedure the tooth will be separated and removed in multiple pieces. Generally this only occurs for multirooted back teeth so that each root can be more gently removed to protect the adjacent gums and teeth.