Most of us would like to have a bright, “white” smile—filled with teeth that would make a Hollywood actor proud. Studies show that up to 52 percent of people are dissatisfied with the color of their teeth.
It is hardly surprising, then, that we tend to think that white teeth are not only attractive but also healthy. However, new studies have revealed that pearly teeth don’t always mean great oral health.
There is even one type of stain that some researchers believe might protect against tooth decay. This is the “black stain” which you sometimes see along teeth at the edges of the gum line（牙龈线）. It can look like a series of dark dots. While the cause of the black stain has been in debate for more than a century, some studies have found that children with the stain are less likely to have tooth decay. It’s thought that some microbes in the stain might be somehow protective.
So what if you still want pearl-white teeth, regardless of what they say about your health? There is a wide range of products you can use. Some kinds of toothpaste promise a whitening effect. Most of them contain substances that rub stains off your teeth. Others add some blueish substances to your yellowish teeth, resulting in a bright white color.
Of course, unless you continue using the product or receiving the whitening treatment, the whiteness will only last for as long as you avoid the foods and drinks that cause the stains in the first place. But now you know that even without that Hollywood white smile, it doesn’t mean you don’t have healthy teeth.
| A．Many of the experiments on tooth color have been conducted in laboratory test tubes, rather than in the mouths of living people. |
| B．In countries such as the United States, tooth whitening is one of the most commonly requested dental treatments. |
| C．The color of our teeth is influenced by a number of factors. |
| D．It is no surprise that the red wine leaves the strongest stains. |
| E． There are also professional whitening treatments, but whitening can cause temporary sensitivity in some people’s teeth or gums. |
| F． Of course, in some cases, discoloration can indicate decay or other diseases, so it is worth getting stains checked out by a dentist. |
相似题推荐
【推荐1】Everyone has their favorite food. Some might love chocolate. Some might love potato chips.
Think about your favorite food. Have you ever wondered why your favorite food tastes so good? The answer is about your tongue (舌头) and your nose.
There are some taste buds (味蕾) on your tongue. They give you the sense of taste. How do the taste buds work? In fact, they have many tiny hairs on them. These tiny hairs send messages to your brain about the tastes of different food. In this way, you know whether it is sweet, sour, biter or salty.
An average person has about 10, 000 taste buds. They keep working all the time when we enjoy our food. The taste buds don’t always stay the same. They are replaced every two weeks or so. However, as a person gets older, some of these taste buds don’t get replaced.
An older person may only have 5, 000 working taste buds. That’s why some food may taste stronger for you than they do for an older person.
Besides your tongue, your nose also helps you learn about the taste of food. Sometimes, strong smells can even confuse (使困惑) your sense of taste. Try holding an onion under your nose while eating an apple. What do you taste?
So the next time you enjoy salty pizza and sweet ice cream, thank your tongue and your nose. Without them, you won’t have any sense of taste at all! Without the sense of taste, life will be boring.
1. Which parts of our body can help us taste the food?| A．Tongue and eyes. | B．Tongue and hairs. |
| C．Nose and eyes. | D．Tongue and nose. |
| A．Only parts of them work when people are eating. |
| B．There are tiny hairs sending messages to our brain about the taste of food. |
| C．The taste buds remain the same for two weeks for all the old people. |
| D．Most old people have stronger taste buds than the young. |
| A．About 5,000. | B．Over 6,000. | C．Over 10,000. | D．About 100,000. |
| A．The taste of apple. | B．The taste of onion. |
| C．The taste of sweet ice cream. | D．The taste of potato chips. |
| A．The Use of Tongue. | B．Our Favorite Food. |
| C．How We Can Taste Food. | D．Different Tastes of Food. |
【推荐2】The vision of a completely blind man has been partially restored using light - sensing proteins first found in algae (藻). He was diagnosed with retinitis pigmentosa 40 years ago. When he was treated with optogenetics (光遗传学), which uses light to control precisely the activity of brain cells, the ability of one of his eyes to detect light was restored.
The first step in the treatment was gene therapy (治疗). The genetic instructions for making the light - sensing proteins were taken from algae and given to cells in the deep surviving layers of the retina at the back of his eye. Now when they were hit with light they would send an electrical signal to the brain. However, they would respond only to amber light, so the patient wore a pair of goggles (protective glasses) with a video camera on the front and a projector on the back, to capture what was happening in the real world and project a version in the right wavelength onto the back of the eye. It took months for high enough levels of the rhodopsins to build up in the eye and for the brain essentially to learn a new language to be able to see again.
The man first knew it was working when he realized he could see the painted stripes of a crossing. He can now grab and count objects on a table, Nature Medicine reports. Dr Jose - Alain Sahel, from the Institute of Vision, in Paris, said: "This patient initially was a bit frustrated because it took a long time between the injection and the time he started to see something. But when he started to report he was able to see the white lines to come across the street you can imagine he was very excited. We were all excited.”
Prof Botond Roska, from the University of Basel, said: “The findings provide proof - of - concept that using optogenetic therapy to partially restore vision is possible.”
1. What's the text mainly about?| A．Special proteins found in algae | B．A man suffering from vision problem |
| C．A study related to light and brain cells | D．A therapy to bring back vision partially |
| A．Instructions | B．Cells |
| C．Proteins | D．Layers |
| A．When he wore a pair of goggles |
| B．When he could seize objects and count them |
| C．When he had the injection |
| D．When he saw the white lines of a crossing |
| A．Optimistic | B．Doubtful |
| C．Unconcerned | D．Negative |
【推荐3】Crossing your legs is an extremely common habit; most people don’t even notice that they’re doing it when they sit down. While you may find it comfortable to sit with one knee crossed over the other, it might be causing health problems that you are not aware of.
A study published in Blood Pressure Monitoring stated that sitting with your legs crossed can increase your blood pressure. The reason this happens is because the blood in your legs has to work against gravity to be pumped back to your heart, crossing one leg over the other increases resistance, making it even harder for the blood to circulate. This causes your body to increase your blood pressure to push the blood back to the heart. You won’t feel any immediate effects, but if you sit for long periods of time it’s important that you take note of how long you have your legs crossed for. You shouldn’t have your legs crossed for more than 15 minutes, and it’s important that you get up and walk around at least once every hour.
Crossing your legs can also lead to neck and back pain. Ideally, it’s best for our bodies to sit with our feet planted flat, hip width apart, on the floor, but it’s not easy to maintain perfect posture all day at the office. When you sit with your legs crossed your hips are in a twisted position, which can cause one of your pelvic bones to rotate. Since your pelvic bone supports your neck and spine, this can cause pressure on your lower and middle back and neck.
You also might notice that when you sit with your legs crossed for long periods of time your feet and legs get tingly or have the feeling of being asleep. This is because when one leg sits on top of the other it causes pressure on the veins and nerves in your legs and feet. It can cause numbness and/or temporary paralysis in the legs, ankles, or feet. While the feeling of discomfort may only last a minute or two, repeatedly crossing your legs until they feel numb can cause permanent nerve damage.
So next time you sit down, try to get yourself in the habit of sitting with both of your feet on the floor. Not only will it help your posture and stability, but it will also save your health in the long run.
1. Crossing legs when sitting may cause the following except______.| A．blood pressure increase | B．neck and back pain |
| C．temporary nerve damage | D．numbness in the legs |
| A．All people are used to sitting with legs crossed without their own notice. |
| B．Researchers are unaware of health problems caused by the common sitting habit. |
| C．It is crucial but impossible to get into the habit of sitting with feet planted flat. |
| D．Crossing legs increases resistance of blood circulation throughout the body. |
| A．Maintain a healthy sitting posture | B．Find a comfortable way to sit |
| C．Move the neck to ease discomfort | D．Do exercises to lower blood pressure |
