Editing Tooth enamel (section)

== Dental procedures ==

[[File:Amalgam filling.JPG|right|150px|thumb|An X-ray showing enamel and dentin replaced by an amalgam restoration]]

=== Dental restorations ===

Most [[dental restoration]]s involve the removal of enamel. Frequently, the purpose of removal is to gain access to the underlying decay in the [[dentin]] or inflammation in the [[pulp (tooth)|pulp]]. This is typically the case in [[amalgam (dentistry)|amalgam]] restorations and [[endodontic therapy|endodontic treatment]].

Nonetheless, enamel can sometimes be removed before there is any decay present. The most popular example is the [[dental sealant]]. In the past, the process of placing dental sealants involved removing enamel in the deep fissures and grooves of a tooth, followed by replacing it with a restorative material.<ref>Summitt ''et al.'', p. 273</ref> Presently, it is more common to only remove decayed enamel if present. In spite of this, there are still cases where deep fissures and grooves in enamel are removed in order to prevent decay, and a sealant may or may not be placed depending on the situation. Sealants are unique in that they are preventative restorations for protection from future decay, and have been shown to reduce the risk of decay by 55% over 7 years.<ref>Summitt ''et al.'', p. 274</ref>

Aesthetics is another reason for the removal of enamel. Removing enamel is necessary when placing [[Crown (dentistry)|crowns]] and [[Veneer (dentistry)|veneers]] to enhance the appearance of teeth. In both of these instances, when unsupported by underlying dentin, that portion of the enamel is more vulnerable to fracture.<ref>Summitt ''et al.'', p. 7</ref>

=== Acid-etching techniques ===

Invented in 1955, acid-etching employs dental etchants and is used frequently when bonding dental restoration to teeth.<ref>Summitt ''et al.'', p. 191.</ref> This is important for long-term use of some materials, such as [[dental composite|composites]] and [[dental sealant|sealants]].<ref name="ross443" /> By dissolving minerals in enamel, etchants remove the outer 10&nbsp;micrometers on the enamel surface and make a porous layer 5–50 micrometers deep.<ref name="summitt193">Summitt ''et al.'', p. 193</ref> This roughens the enamel microscopically and results in a greater surface area on which to bond.

The effects of acid-etching on enamel can vary. Important variables are the amount of time the etchant is applied, the type of etchant used, and the current condition of the enamel.<ref name="summitt193" />

There are three types of patterns formed by acid-etching.<ref name="summitt193" /> Type 1 is a pattern where predominantly the enamel rods are dissolved; type 2 is a pattern where predominantly the area around the enamel rods are dissolved; and type 3 is a pattern where there is no evidence left of any enamel rods. Besides concluding that type 1 is the most favorable pattern and type 3 the least, the explanation for these different patterns is not known for certain but is most commonly attributed to different crystallite orientation in the enamel.<ref name=":4" />

=== Tooth whitening ===

The discoloration of teeth over time can result from exposure to substances such as [[tobacco]], [[coffee]], and [[tea]].<ref>American Dental Hygienists' Association</ref> The staining occurs in the interprismatic region internally on the enamel, which causes the tooth to appear darker or more yellow overall. In a perfect state, enamel is colorless, but it does reflect underlying tooth structure with its stains since light reflection properties of the tooth are low.

Tooth whitening or [[tooth bleaching]] procedures attempt to lighten a tooth's color in either of two ways: by chemical or mechanical action. Working chemically, a bleaching agent is used to carry out an [[oxidation reaction]] in the enamel and dentin.<ref>Summitt ''et al.'', p. 402</ref> The agents most commonly used to intrinsically change the color of teeth are [[hydrogen peroxide]] and [[carbamide peroxide]]. Oxygen radicals from the peroxide in the whitening agents contact the stains in the interprismatic spaces within the enamel layer. When this occurs, stains will be bleached and the teeth now appear lighter in color. Teeth not only appear whiter but also reflect light in increased amounts, which makes the teeth appear brighter as well. Studies show that whitening does not produce any ultrastructural or microhardness changes in the dental tissues.<ref name=":0" />

Studies show that patients who have whitened their teeth take better care of them.<ref>Fehrenbach, Popowics, p. 175</ref> However, a tooth whitening product with an overall low pH can put enamel at risk for decay or destruction by demineralization. Consequently, care should be taken and risk evaluated when choosing a product which is very acidic.<ref>Summitt ''et al.'', p. 404</ref> Tooth whiteners in toothpastes work through a mechanical action. They have mild abrasives which aid in the removal of stains on enamel. Although this can be an effective method, it does not alter the intrinsic color of teeth. Microabrasion techniques employ both methods. An acid is used first to weaken the outer 22–27 micrometers of enamel in order to weaken it enough for the subsequent abrasive force.<ref>Summitt ''et al.'', p. 420</ref> This allows for removal of superficial stains in the enamel. If the discoloration is deeper or in the dentin, this method of tooth whitening will not be successful.