An unwrapped stick of chewing gum
|Chicle or polyisobutylene|
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Chewing gum is a soft, cohesive substance intended for chewing but not swallowing. Humans have used chewing gum for at least 5,000 years. Modern chewing gum was originally made of chicle, a natural latex. By the 1960s, chicle was replaced by butadiene-based synthetic rubber which is cheaper to manufacture. Most chewing gums are considered polymers.
Chewing gum in various forms has existed since the Neolithic period. 5,000-year-old chewing gum made from bark tar, with tooth imprints, has been found in Kierikki, Yli-Ii, Finland. The tar from which the gums were made is believed to have antiseptic properties and other medicinal advantages. The ancient Aztecs used chuckle as a base for making a gum-like substance and to stick objects together in everyday use.Women in particular used this type of gum as a mouth freshener.
Forms of chewing gums were also used in Ancient Greece. The Greeks chewed mastic gum, made from the resin of the mastic tree. Many other cultures have chewed gum-like substances made from plants, grasses, and resins. The American Indians chewed resin made from the sap of spruce trees. The New England settlers picked up this practice, and in 1848, John B. Curtis developed and sold the first commercial chewing gum called The State of Maine Pure Spruce Gum. Around 1850 a gum made from paraffin wax was developed and soon exceeded the spruce gum in popularity. William Semple filed an early patent on chewing gum, patent number 98,304, on December 28, 1869.
Modern chewing gum was first developed in the 1860s when chicle was brought from Mexico by the former President, General Antionio Lopez de Santa Anna, to New York, where he gave it to Thomas Adams for use as a rubber substitute. Chicle did not succeed as a replacement for rubber, but as a gum, which was cut into strips and marketed as Adams New York Chewing Gum in 1871.  Black Jack (1884) and “Chiclets” (1899), it soon dominated the market. Synthetic gums were first introduced to the U.S. after chicle no longer satisfied the needs of making good chewing gum. The hydrocarbon polymers approved to be in chewing gum are styrene-butadiene rubber, isobutylene, isoprene copolymer, paraffin wax, and petroleum wax.
Effects on health
Sugar-free gum sweetened with xylitol has been shown to reduce cavities and plaque. The sweetener sorbitol has the same benefit, but is only about one-third as effective as xylitol. Not only are artificial sweeteners, sorbitol and Xylitol in chewing gum, but there are also other artificial sweeteners, such as aspartame and acesulfam that don't cause tooth decay either, even though they are very sweet.  Xylitol is specific in its inhibition of Streptococcus mutans, bacteria that are significant contributors to tooth decay. Xylitol inhibits Streptococcus mutans in the presence of other sugars, with the exception of fructose. Xylitol is a safe sweetener that benefits teeth and saliva production because it is not fermented to acid like most sugars.  Daily doses of xylitol below 3.44 grams are ineffective and doses above 10.32 grams show no additional benefit. Fluoride is one active ingredient in chewing gum that strengthens tooth enamel, another is p-chlorbenzyl-4-methylbenzylpiperazine, which prevents travel sickness. Chewing gum not only increases saliva production and strengthens tooth enamel, but it also doesn't stick to dentures, especially the Freedent brand chewing gum, since it is less tacky, as well as whitens teeth. 
Food and sucrose have a demineralizing effect upon enamel that has been reduced by adding calcium lactate to food. Calcium lactate added to toothpaste has reduced calculus formation. One study has shown that calcium lactate enhances enamel remineralization when added to xylitol-containing gum, but another study showed no additional remineralization benefit from calcium lactate or other calcium compounds in chewing-gum.
Other studies indicated that the caries preventive effect of chewing sugar-free gum is related to the chewing process itself rather than being an effect of gum sweeteners or additives, such as polyols and carbamide.
A helpful way to cure halitosis (bad breath) is to chew gum. Chewing gum not only helps to add freshness to breath but can aid in removing food particles and bacteria associated with bad breath from teeth. It does this by stimulating saliva, which essentially washes out the mouth. Chewing sugar-free gum for 20 minutes after a meal helps prevent tooth decay, according to the American Dental Association, because the act of chewing the sugar-free gum produces saliva to wash away bacteria, which protects teeth. Chewing gum after a meal replaces brushing and flossing, if that's not possible, to prevent tooth decay and increase saliva production  Chewing gum can also help with the lack of saliva or xerostomia since it naturally stimulates saliva production. Saliva is made of chemicals, such as organic molecules, inorganic ions and macromolecules. 0.5% of saliva deals with dental health, since tooth enamel is made of calcium phosphate, those inorganic ions in saliva help repair the teeth and keep them in good condition. The pH of saliva is neutral, which having a pH of 7 allows it to remineralize tooth enamel. Falling below a pH of 5.5 causes the saliva to demineralize the teeth. 
A 2010 study looked at the effects of chewing gum after meals following an orthodontic procedure, to see if chewing exercises caused subjects pain or discomfort, or helped maintain a large occlusal contact area. 35 adult volunteers chewed gum for 10 to 15 minutes before or after three meals each day for 4 weeks. 90% of those questioned said that the gum felt "quite hard", and half reported no discomfort.
Use in surgery
Several randomized controlled studies have investigated the use of chewing gum in reducing the duration of post-operative ileus following abdominal and specifically gastrointestinal surgery. These suggest gum chewing, as a form of "sham feeding"[clarification needed], is a useful treatment therapy.
Chewing gum after a colon surgery helps the patient recover sooner. If the patient chews gum for fifteen minutes for at least four times per day, it will speed up their recovery by a day and a half faster. The average patient took .66 fewer days to pass gas and 1.10 fewer days to have a bowel movement. Saliva flow and production is stimulated when gum is chewed. Gum also gets the juices flowing and is considered "sham feeding". Sham feeding is the role of the central nervous system in the regulation of gastric secretion.
Chewing gum is used as a novel approach for the treatment of gastroesophageal reflux disease (GERD). One hypothesis is that chewing gum stimulates the production of more bicarbonate-containing saliva and increases the rate of swallowing. After the saliva is swallowed, it neutralizes acid in the esophagus. In effect, chewing gum exaggerates one of the normal processes that neutralize acid in the esophagus.[unreliable source?] However, chewing gum is sometimes considered to contribute to the development of stomach ulcers. It stimulates the stomach to secrete acid and the pancreas to produce digestive enzymes that aren't required. In some cases, when consuming large quantities of gum containing sorbitol, gas and/or diarrhea may occur.
Concern has arisen about the possible carcinogenicity of the vinyl acetate (acetic acid ethenyl ester) used by some manufacturers in their gum bases. Currently, the ingredient can be hidden in the catch-all term "gum base". The Canadian government at one point classified the ingredient as a "potentially high hazard substance." However, on January 31, 2009, the Government of Canada's final assessment concluded that exposure to vinyl acetate is not considered to be harmful to human health. This decision under the Canadian Environmental Protection Act (CEPA) was based on new information received during the public comment period, as well as more recent information from the risk assessment conducted by the European Union.
One old wives' tale says that swallowed gum will remain in a human's stomach for up to 7 years, as it is not digestible. According to several medical opinions, there seems to be little truth behind the tale. In most cases, swallowed gum will pass through the system as quickly as any other food.
There have been cases where swallowing gum has resulted in complications requiring medical attention. A 1998 paper describes a four-year-old boy being referred with a two-year history of constipation. The boy was found to have "always swallowed his gum after chewing five to seven pieces each day", being given the gum as a reward for good behavior, and the build-up resulted in a solid mass which could not leave the body. A 1½-year-old girl required medical attention when she swallowed her gum and four coins, which got stuck together in her esophagus. A bezoar is formed in the stomach when food or other foreign objects stick to gum and build up, causing intestinal blockage. As long as the mass of gum is small enough to pass out of the stomach, it will likely pass out of the body easily, but it is recommended that gum should not be swallowed or given to young children who cannot understand this point.
Many schools do not allow chewing gum because students often dispose of it inappropriately, the chewing may be distracting in class, and the gum might carry diseases or bacteria from other students.
The Singapore government outlawed chewing gum in 1992 because it was becoming a danger when it was wedged in the sliding doors of underground trains. However, in 2002 the government allowed sugarless gum to be sold in pharmacies if a doctor or dentist prescribed it.
Detrimental effects on the environment
Chewing gum is not water soluble and unlike other confectionery is not fully consumed and there has been much public education and investment aimed at encouraging responsible disposal. Despite this it is commonly found stuck underneath benches, tables, handrails and escalators. Most however finds its way onto to the surface of sidewalks/pavements and open public areas. It is extremely difficult and expensive to remove once "walked in" and dried. Gum bonds strongly to asphalt and rubber shoe soles because they are all made from polymeric hydrocarbons. It also bonds strongly with concrete paving.
Removal is generally achieved by steam jet and scraper but the process is slow and labour intensive. Most external urban areas with high pedestrian traffic show high incidence of casual chewing gum discard and the Singapore ban on chewing gum sale may be felt to have some merit - Singapore's pavements are uniquely free of gum. More than other litter which can be picked up or is quickly degraded by the weather, chewing gum with its glue-like characteristics is regarded as environmentally damaging. In 2000, a study on Oxford Street, one of London’s busiest shopping streets, showed that a quarter of a million black or white blobs of chewing gum were stuck to its pavement.
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