Editing Tooth enamel (section)

== Enamel loss ==

The high mineral content of enamel, which makes this tissue the hardest in the human body, also makes it
demineralize in a process that often occurs as [[dental caries]], otherwise known as cavities.<ref name="ross443" /> Demineralization occurs for several reasons, but the most important cause of tooth decay is the ingestion of [[Fermentation (biochemistry)|fermentable]] [[carbohydrate]]s.{{citation needed|date=December 2012}}
Tooth cavities are caused when acids dissolve tooth enamel:<ref>Brown, p. 688</ref> Enamel is also lost through [[tooth wear]] and [[enamel fracture]]s.<ref>{{Cite journal|date=2015-01-01|title=Estimated prevalence of erosive tooth wear in permanent teeth of children and adolescents: An epidemiological systematic review and meta-regression analysis|journal=Journal of Dentistry|language=en|volume=43|issue=1|pages=42–50|doi=10.1016/j.jdent.2014.10.012|pmid=25446243|issn=0300-5712|last1=Salas|first1=M.M.S.|last2=Nascimento|first2=G.G.|last3=Huysmans|first3=M.C.|last4=Demarco|first4=F.F.}}</ref>

::Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>(''s'') + 8H<sup>+</sup>(''aq'') → 10Ca<sup>2+</sup>(''aq'') + 6HPO<sub>4</sub><sup>2−</sup>(''aq'') + 2H<sub>2</sub>O(''l'')

Sugars and acids from [[candy|candies]], [[soft drink]]s, and [[juice|fruit juices]] play a significant role in tooth decay, and consequently in enamel destruction.<ref>{{cite web |title=Tooth Enamel Defined |url=https://au.gogosmile.com/blogs/news/tooth-enamel-defined |website=GogoSmile |access-date=4 August 2018}}</ref> The mouth contains a great number and variety of [[bacteria]], and when [[sucrose]], the most common of sugars, coats the surface of the mouth, some intraoral bacteria interact with it and form [[lactic acid]], which decreases the pH in the mouth.<ref name="ross453">Ross ''et al.'', p. 453</ref> The critical pH for tooth enamel is generally accepted to be pH 5.5.  When acids are present and the critical pH is reached, the hydroxyapatite crystallites of enamel demineralize, allowing for greater bacterial invasion deeper into the tooth. The most important bacterium involved with tooth decay is ''[[Streptococcus mutans]]'', but the number and type of bacteria varies with the progress of tooth destruction.<ref name="ross453" />

Furthermore, tooth morphology dictates that the most common site for the initiation of dental caries is in the deep grooves, pits, and fissures of enamel.{{citation needed|date=August 2018}} This is expected because these locations are impossible to reach with a toothbrush and allow for bacteria to reside there. When demineralization of enamel occurs, a dentist can use a sharp instrument, such as a [[explorer (dental)|dental explorer]], and "feel a stick" at the location of the decay. As enamel continues to become less mineralized and is unable to prevent the encroachment of bacteria, the underlying dentin becomes affected as well. When dentin, which normally supports enamel, is destroyed by a physiologic condition or by decay, enamel is unable to compensate for its brittleness and breaks away from the tooth easily.

[[File:Topviewtooth.jpg|left|thumb|The effects of [[bruxism]] on an anterior tooth, revealing the dentin and pulp which are normally hidden by enamel]]
The extent to which tooth decay is likely, known as [[caries|cariogenicity]], depends on factors such as how long the sugar remains in the mouth. Contrary to common belief, it is not the amount of sugar ingested but the frequency of sugar ingestion that is the most important factor in the causation of tooth decay.<ref>British Nutrition Foundation</ref> When the pH in the mouth initially decreases from the ingestion of sugars, the enamel is demineralized and left vulnerable for about 30 minutes. Eating a greater quantity of sugar in one sitting does not increase the time of demineralization. Similarly, eating a lesser quantity of sugar in one sitting does not decrease the time of demineralization. Thus, eating a great quantity of sugar at one time in the day is less detrimental than is a very small quantity ingested in many intervals throughout the day. For example, in terms of oral health, it is better to eat a single [[dessert]] at dinner time than to snack on a bag of [[candy]] throughout the day.

In addition to bacterial invasion, enamel is also susceptible to other destructive forces.  [[Bruxism]], also known as clenching of or grinding on teeth, destroys enamel very quickly. The wear rate of enamel, called [[Attrition (dental)|attrition]], is 8&nbsp;micrometers a year from normal factors.{{Citation needed|date=January 2014}} A common misconception is that enamel wears away mostly from chewing, but actually teeth rarely touch during chewing. Furthermore, normal tooth contact is compensated physiologically by the [[periodontal ligament]]s and the arrangement of dental [[occlusion (dentistry)|occlusion]]. The truly destructive forces are the [[parafunctional activity|parafunctional movements]], as found in bruxism, which can cause irreversible damage to the enamel.

Other nonbacterial processes of enamel destruction include [[abrasion (dental)|abrasion]] (involving foreign elements, such as toothbrushes), [[erosion (dental)|erosion]] (involving chemical processes, such as dissolving by soft drinks<ref>{{cite journal | author = Larsen MJ, Nyvad  | year = 1999 | title = Enamel erosion by some soft drinks and orange juices relative to their pH, buffering effect and contents of calcium phosphate | journal = Caries Res. | volume = 33 | issue = 1| pages = 81–87 | doi=10.1159/000016499| pmid = 9831784 | citeseerx = 10.1.1.464.7695 | s2cid = 28664016 }}</ref> or lemon and other juices), and possibly [[abfraction]] (involving compressive and tensile forces).{{citation needed|date=August 2019}}

Though enamel is described as tough, it has a similar [[brittleness]] to [[glass]], making it, unlike other natural crack-resistant [[composite material|laminate structures]] such as [[Exoskeleton|shell]] and [[nacre]], vulnerable to [[fracture]]. In spite of this it can withstand bite forces as high as 1,000 [[Newton (units)|N]] many times a day during chewing.<ref>{{cite journal|pmid=8526296|year=1995|last1=Braun|first1=S|last2=Bantleon|first2=HP|last3=Hnat|first3=WP|last4=Freudenthaler|first4=JW|last5=Marcotte|first5=MR|last6=Johnson|first6=BE|title=A study of bite force, part 1: Relationship to various physical characteristics|volume=65|issue=5|pages=367–72|journal=The Angle Orthodontist|issn=0003-3219}}</ref><ref>{{cite journal |last1=Xu |first1=H. H. |last2=Smith |first2=D. T. |last3=Jahanmir |first3=S. |last4=Romberg |first4=E |last5=Kelly |first5=J. R. |last6=Thompson |first6=V. P. |last7=Rekow |first7=E. D. |year=1998 |title=Indentation damage and mechanical properties of human enamel and dentin |journal=[[Journal of Dental Research]] |volume=77 |issue=3 |pages=472–480 |pmid=9496920 |doi=10.1177/00220345980770030601 |s2cid=21928580 }}</ref> This resistance is due in part to the microstructure of enamel which contains [[enamel tufts]] that stabilize such fractures at the dentinoenamel junction.<ref name="Chai">{{cite journal |last1=Chai |first1=H. |last2=Lee |first2=J. J. |last3=Constantino |first3=P. J. |last4=Lucas |first4=P. W. |last5=Lawn |first5=B. R. |year=2009 |title=Remarkable resilience of teeth |journal=[[Proceedings of the National Academy of Sciences|PNAS]] |volume=106 |issue=18 |pages=7289–7293 |pmid=19365079 |doi=10.1073/pnas.0902466106 |pmc=2678632 |bibcode=2009PNAS..106.7289C |doi-access=free }}</ref> The configuration of the tooth also acts to reduce the [[Stress (physics)|tensile stresses]] that cause fractures during biting.<ref name="Chai" />

[[Gastroesophageal reflux disease]] can also lead to enamel loss, as acid refluxes up the esophagus and into the mouth, occurring most during overnight sleep.

=== Oral hygiene ===
{{Main|Oral hygiene}}

Because enamel is vulnerable to demineralization, prevention of tooth decay is the best way to maintain the health of teeth. Most countries have wide use of [[toothbrush]]es, which can reduce the number of dental biofilm and food particles on enamel. In isolated societies that do not have access to toothbrushes, it is common for those people to use other objects, such as sticks, to clean their teeth. In between two adjacent teeth, [[Dental floss|floss]] is used to wipe the enamel surfaces free of [[Dental plaque|plaque]] and food particles to discourage bacterial growth. Although neither floss nor toothbrushes can penetrate the deep grooves and pits of enamel, good general oral-health habits can usually prevent enough bacterial growth to keep tooth decay from starting. Structural integrity of the enamel is genetic, and so is its predisposition to demineralization or attack from bacteria.<ref name="Cantù eaah4598" />

=== Fluoride remineralization ===
Fluoride catalyzes the diffusion of calcium and phosphate into the tooth surface, which in turn [[Remineralisation of teeth|remineralizes]] the crystalline structures in a dental cavity. The remineralized tooth surfaces contain fluoridated [[hydroxyapatite]] and [[fluorapatite]], which resist acid attack much better than the original tooth did.<ref>{{cite journal |vauthors=Selwitz RH, Ismail AI, Pitts NB |title= Dental caries |journal=Lancet |volume=369 |issue=9555 |pages=51–59 |year=2007 |pmid=17208642 |doi=10.1016/S0140-6736(07)60031-2|s2cid= 204616785 }}</ref> [[Fluoride therapy]] is used to help prevent dental decay.

[[File:FluorideTrays07-05-05.jpg|thumb|Common dentistry trays filled with fluoride foam]]

Fluoride ions, as an antimicrobial, may activate bacterial genes associated with fluoride [[riboswitch]]es.<ref>{{cite journal|title=New Insight on the Response of Bacteria to Fluoride|journal=Caries Research|volume=46|issue=1|pages=78–81|doi=10.1159/000336397|pmid=22327376|pmc=3331882|year=2012|last1=Breaker|first1=R.R.}}</ref>{{Unreliable medical source|date=February 2022}} The combination of fluoride ions and QAS (quaternary ammonium salts) was found to have a stronger antimicrobial effect on many oral bacteria associated with dental decay, including ''[[S. mutans]]''.

==== Fluoride in drinking water ====
Most dental professionals and organizations agree that the inclusion of fluoride in public water has been one of the most effective methods of decreasing the prevalence of tooth decay.<ref>"one of 10 great public health achievements of the 20th century": [https://www.cdc.gov/fluoridation/ Community Water Fluoridation – Oral Health]; [https://www.cdc.gov/about/history/tengpha.htm Ten Great Public Health Achievements in the 20th Century] – CDC</ref> Fluoride can be found in many locations naturally, such as the ocean and other water sources. The recommended dosage of fluoride in [[drinking water]] does not depend on air temperature.<ref name="U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries">{{cite journal |title=U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries |journal=Public Health Reports |volume=130 |issue=4 |pages=318–331 |publisher=U.S. Department of Health and Human Services Federal Panel on Community Water Fluoridation |pmc=4547570 |year=2015 |author1=<!-- U.S. Department of Health Human Services Federal Panel on Community Water Fluoridation --> |pmid=26346489 |doi=10.1177/003335491513000408 }}</ref><ref>{{cite web | title= Fluoride in Drinking Water| publisher= Environmental Protection Agency| website= EPA.gov| url= http://water.epa.gov/drink/contaminants/basicinformation/fluoride.cfm| date= 12 August 2015}}</ref>

Some groups have spoken out against [[Water fluoridation|fluoridated drinking water]], for reasons such as the [[neurotoxicity]] of fluoride or the damage fluoride can do as [[Dental fluorosis|fluorosis]]. Fluorosis is a condition resulting from the overexposure to fluoride, especially between the ages of 6&nbsp;months and 5&nbsp;years, and appears as mottled enamel.<ref name=":4" /> Consequently, the teeth look unsightly, although the incidence of dental decay in those teeth is very small. Where fluoride is found naturally in high concentrations, filters are often used to decrease the amount of fluoride in water. For this reason, codes have been developed by dental professionals to limit the amount of fluoride a person should take.<ref>{{cite journal |title= Caries diagnosis and risk assessment. A review of preventive strategies and management |journal= J Am Dent Assoc |volume=126 |issue=Suppl |pages=1S–24S |year=1995 |pmid=7790681 |doi=10.14219/jada.archive.1995.0371}}</ref> These codes are supported by the American Dental Association and the American Academy of Pediatric Dentistry.

Furthermore, whereas topical fluoride, found in [[toothpaste]] and [[mouthwash]]es, does not cause fluorosis, its effects are now considered more important than those of systemic fluoride, such as when drinking fluorinated water.<ref>{{cite journal | author = Twetman S | date = Sep 2009 | title = Caries prevention with fluoride toothpaste in children: an update | journal = Eur Arch Paediatr Dent. | volume = 10 | issue = 3| pages = 162–167 | doi=10.1007/bf03262678| pmid = 19772846 | s2cid = 22227878 }}</ref> However, systemic fluoride works topically as well with fluoride levels in saliva increase also when drinking fluoridated water. Lately, dental professionals are looking for other ways to present fluoride (such as in varnish) or other mineralizing products such as [[Amorphous calcium phosphate]] to the community in the form of topical procedures, either done by professionals or self-administered. Mineralization of the incipient lesion instead of restoration later is a prime goal of most dental professionals.