Enamel, the outermost layer of the teeth, is the hardest natural substance found in the human body, harder than even our strongest bones . It is essential for the protection of the underlying structures and it is the loss of this enamel that leads to problems such as pain and sensitivity.
Causes Of Destruction Of Enamel
Poor Oral Hygiene
The first cause and also the most common one, is poor oral hygiene. The bacterial colonies that form in our mouth have both "good" and "bad" micro-organisms. The bad ones start to dominate in the presence of poor oral hygiene practices.
The main effect of these bad microorganisms is producing acid that destroys the enamel. Clinically, this appears to us as tooth decay.
It is also important to note that once decay has taken root on a tooth, it will continue to develop until the dentist prepares a cavity and then fills it.
The initial destruction of enamel is not painful but as the underlying layers of the teeth start getting exposed, symptoms of discomfort start showing up. 
The next most common reason why enamel gets destroyed in the mouth has nothing to do with a disease process at all. It is in fact due to an excessive effort of the individual to protect their teeth from disease processes.
Individuals that brush their teeth with more force than is required or more times than is necessary, tend to wear away the outer layer of enamel through a process called abrasion and then end up suffering the same symptoms caused by tooth decay .
The destruction caused by improper brushing techniques can actually be far worse than tooth decay, since they tend to affect a group of teeth at the same time rather than just one or two teeth.
What is excessive brushing and what is the right amount of force to exert while brushing? Unfortunately, these questions do not have specific answers, however, there are some solid scientific guidelines to follow.
Researchers believe that brushing more than twice a day is not needed since the bacterial populations require at least 12 hours before they begin to cause disease . As for force, dentists now recommend that people use only soft toothbrushes for brushing and use a gentle hand to clean the teeth. Even a gentle sweep of the tooth surface is enough to remove bacterial plaque .
Internet-connected toothbrushes that come with smartphone apps to give real-time feedback about the efficiency of brushing as well as the force being applied by the users are available today. It is unclear at the moment if they result in a lower incidence of tooth abrasion because of their recent introduction, but they seem to a step in the right direction.
Certain conditions can affect the formation of enamel, making it vulnerable to destruction. The most common developmental disturbance is the formation of pits or grooves on the enamel.
These act as plaque-retentive areas and can be difficult to clean. There is a much higher chance of tooth decay in these areas of the teeth, and this decay will then spread . There are also much more serious conditions like "Amelogenesis Imerfecta" where the enamel is not mineralized completely and is thus much softer than it should be . It is not uncommon for people suffering from the more severe variants of this disease to lose all of their enamel covering and require complete extraction at a very young age.
There are also conditions which affect the joint between enamel and the underlying dentin, once again leading to loss of the entire enamel layer from the dentin at an early age.
Certain diseases like GERD, where the acidic contents of the stomach travel back up the esophagus and into the mouth, or bulimia, where a person habitually vomits the contents of their stomach, can wreak havoc on the enamel .
Saliva protects the enamel from changes in acidity while eating or drinking, which helps keep pH at a neutral level. If, however, the acidic content is enough to overwhelm this protective function of the body, a widespread destruction of enamel called erosion is easy to see. 
How To Prevent This Destruction Of Enamel?
The first couple of causes are relatively easy to protect against, while developmental disturbances are often beyond simple prevention. Patients are advised to brush twice a day and visit their dentist every six months to prevent a whole host of diseases.
The use of fluoride in drinking water, milk, toothpaste or fluoridation programs will help strengthen the enamel and make it more secure from acid attacks .
Systemic conditions like GERD need to be treated so that their associated symptoms disappear as well.
Protecting your teeth and protecting your enamel is often the same thing. Unfortunately, the enamel does not have any nerve endings so its destruction does not cause pain. This is why most people realize the importance of this hard, inert, covering after it has been lost.