toothbrush

A toothbrush is an oral hygiene instrument used to clean the teeth, gums, and tongue. It consists of a head of tightly clustered bristles, atop of which toothpaste can be applied, mounted on a handle which facilitates the cleaning of hard-to-reach areas of the mouth. They are usually used alongside floss.

They are available with different bristle textures, sizes, and forms. Most dentists recommend using a soft toothbrush since hard-bristled toothbrushes can damage tooth enamel and irritate the gums.

Before the invention of the toothbrush, a variety of oral hygiene measures had been used. This has been verified by excavations during which tree twigs, bird feathers, animal bones and porcupine quills were recovered.

The predecessor of the toothbrush is the chew stick. Chew sticks were twigs with frayed ends used to brush the teeth while the other end was used as a toothpick.

The earliest chew sticks were discovered in Sumer in southern Mesopotamia in 3500 BC, an Egyptian tomb dating from 3000 BC, and mentioned in Chinese records dating from 1600 BC. The Greeks and Romans used toothpicks to clean their teeth, and toothpick-like twigs have been excavated in Qin Dynasty tombs.

An electric toothbrush is a toothbrush that makes rapid automatic bristle motions, either back-and-forth oscillation or rotation-oscillation (where the brush head alternates clockwise and counterclockwise rotation), in order to clean teeth. Motions at sonic speeds or below are made by a motor. In the case of ultrasonic toothbrushes, ultrasonic motions are produced by a piezoelectric crystal. A modern electric toothbrush is usually powered by a rechargeable battery charged through inductive charging when the brush sits in the charging base between uses.

Electric toothbrushes can be classified according to the frequency (speed) of their movements as power, sonic or ultrasonic toothbrushes, depending on whether they make movements that are below, in or above the audible range (20–20,000 Hz or 2400–2,400,000 movements per minute), respectively.

In 2014, a Cochrane review demonstrated that power toothbrushes remove more plaque and reduce gingival inflammation more than manual toothbrushes. 2014年，Cochrane的一项研究表明，电动牙刷比手动牙刷清除更多牙菌斑，减少牙龈炎症。This review showed electric toothbrushes had greater effectiveness over manual ones. For example, plaque build-up and gingival inflammation were reduced by 11% and 6% respectively after one to three months of use. After three months of use, the reduction observed was even greater – 21% reduction in plaque and 11% reduction in gingival inflammation. Although the scale of these differences in a clinical setting remains questionable,[10] other reviews have reached similar conclusions. Another large review of studies also concluded that power toothbrushes were more effective in removing plaque than manual brushes for children. For patients with limited manual dexterity or where difficulty exists in reaching rear teeth, electric toothbrushes may be especially beneficial.

Electric brushes can be classified according to their type of action:

• Side to side vibration, which have a brush head action that moves laterally from side to side.
• Counter oscillation, indicates a brush action in which adjacent tufts of bristles (usually six to 10 in number) rotate in one direction and then the other, independently. Each tuft rotating in the opposite direction to that adjacent to it.
• Rotation oscillation, indicates a brush action in which the brush head rotates in one direction and then the other.
• Circular, indicates a brush action in which the brush head rotates in one direction only.
• Ultrasonic, indicates a brush action where the bristles vibrate at ultrasonic frequencies (> 20 kHz).
• Ionic, indicates a brush that aims to impart an electrical charge to the tooth surface with the intent of disrupting the attachment of dental plaque.

六级/考研单词: oral, sanitation, gum, cluster, atop, mount, texture, dental, irritate, verify, successor, chew, dynasty, rapid, alternate, clockwise, rotate, motor, crystal, classify, accord, respective, manual, differentiate, rear, adjacent, vibrate, disrupt

中世纪许多欧洲王室、贵族和骑士，会用一条金链子系上一根金牙签，挂在脖子上。…… 美国经济学家凡勃伦也在《有闲阶级论》写道，嘴里叼牙签是“炫耀性消费”。前文提到查尔斯·福斯特在美国餐厅推广牙签，使得美国高档餐厅开始免费供应牙签。结果，消费者买单之后都会抓一把牙签走，然后叼着牙签出门，表示自己刚刚在餐厅里吃过饭。这是因为当时能在餐厅吃饭的都是有钱人，叼着牙签就是一种证明。甚至女性也不例外，当时的《波士顿邮报》报道，在一些主要街道观察所得，几乎每三名女性中便有一位叼着牙签。直到上世纪初，美国著名保守派杂志《妇女家庭生活》对女性叼牙签现象提出批评，这种风气才渐渐消失。

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