Nature tries to fit the teeth into the space available.  The teeth always end up in their most stable position within the dental arch, whether they are crowded, or have extra space between them.  Stability is the name of the game.  There is always a balance between the various forces that affect any given tooth, as well as the amount and position of bone available that helps determine where that tooth is most stable. If a dentist tries simply to move the teeth into better looking positions, Nature may move them right back where they started.  This is why an orthodontist must play certain tricks to make sure the local forces affecting each tooth will cancel each other out after treatment so that the tooth will stay put once it is moved.  

This is why the dentist must usually treat both upper and lower teeth, even if only the appearance of the top teeth are of concern to the patient.  Unless the position of the lower teeth coincide with the position of the uppers, the biting forces produced by the ill fitting lowers will create instabilities that will move the uppers back into crooked positions over time.  This is also the reason that the orthodontist will order the extraction of some teeth.  The extra room created by the removal of these teeth changes the stability equation in favor of the preferred new tooth positions.

Ideally teeth should be aligned during adolescence but most of the time that is not the case. In such situations ,they can be managed at any age except the teeth and gums should be healthy.

Another method to treat crowded teeth at an older age is by use of new generation filling and crown materials. The method is aptly called as smile designing. Taking into consideration that it is not practically possible for everyone to go through the long ordeal of orthodontic correction during adulthood, the crowded or crooked smile is designed to an acceptable and technically correct smile. In such cases , the first step is taking impressions to build plaster study models and X rays for the purpose of treatment planning . Once the Treatment plan is ready, the protruded teeth usually are reduced facially and ceramic crowns or ceramic veneers, as the case maybe are built to cover these teeth. The teeth which are positioned back (retruded ) are usually root canal treated and than built up with the help of post and core to the required aesthetic and stable position in the mouth. The whole procedure should be over within 2 weeks time. The biggest advantage is that in a matter of 2 weeks or even less , one can modify his or her looks drastically. And the treatment is permanent

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