If you want to maintain a sharp memory, you may want to brush up: People who have fewer natural teeth remaining perform more poorly on memory tests, a new study suggests. Looking at 273 people ages 55 and older, the researchers found a modest but significant relationship between a person's number of natural teeth and his or her performance on memory tests. The link held when researchers took subjects' ages into account. In other words, it wasn't simply that both teeth and memory abilities tend to disappear with age. Although the reason for the link isn't entirely clear, the new findings are in line with previous animal and human studies, suggesting that the presence of natural teeth has an impact on cognitive function, and having fewer teeth may be regarded as a risk factor for memory problems in the elderly, according to the researchers, who detailed their findings in the August issue of the European Journal of Oral Sciences. Animal studies have shown that rats whose teeth were pulled out showed memory and learning problems. The rats that had lost more teeth showed higher neuronal loss, and more damage to the hippocampus, a part of the brain involved in memory formation. It is possible that losing natural teeth reduces sensory signals that teeth send to the brain, affecting its functions, including memory, the researchers said. Natural teeth send signals to the brain via a nerve that is responsible for sensation in the face, and for motor functions, such as biting and chewing. Prosthetic teeth, though helpful for eating, lack the nerves and ligament that attach natural teeth to the jaw, potentially resulting in a reduced sensory input to the brain. It's also possible that a common factor could be responsible for the link between teeth and memory. For instance, gum infections that could lead to tooth loss may also cause inflammation, which may, in turn, cause neuronal death and memory loss, the researchers said. In the new study, the researchers accounted for other factors that can affect memory — such as participants' years of education, type of occupation and medical history — but the link between teeth and memory remained significant. Study participants had an average of 22 natural teeth, almost one-third fewer than a complete set of human teeth, which may have caused them to avoid or eat less of certain foods that contain the nutrients necessary for maintaining a strong memory, the researchers said. One limitation of the study is the small number of participants. Nevertheless, a previous study involving more than 4,000 participants — and that controlled for several lifestyle factors, such as smoking and alcohol intake — found similar results. People with few or no teeth were more likely to have some memory loss, compared with participants who still had many of their natural teeth. That study was published in the journal Behavioral and Brain Functions in 2011. 译文 自然牙掉落减少了牙齿发送到大脑的感官信号，影响了大脑的功能，这其中可能包括记忆力。如果你想保持敏锐的记忆力，你可能想要你的牙齿更好: 一项新的研究表明，自然牙齿少的人在记忆测试中的表现更差。 研究人员研究了273名年龄为55岁及以上的人，他们发现一个人自然牙齿数量的多少与其在记忆力测试中的表现有着一定的重要联系。 当研究人员把受试者的年龄考虑进来之时，这种联系就产生了。换句话说，牙齿和记忆能力并非随着年龄的增长而消失那么简单。 研究人员称，尽管联系的原因还不完全清楚，但新的研究成果与以前对动物和人类的研究相吻合，这表明自然牙齿的存在影响认知功能，有很少的牙齿可能会被看作是老年人的记忆问题的一种危险因素。8月份出版的《口腔科学欧洲期刊》详细叙述了他们的研究结果。 动物研究已表明，那些被拔掉牙的老鼠记忆认知显现出问题。失去牙齿多的老鼠表现出神经元受损更高，海马（参与记忆形成的大脑部分）受损更大。 研究人员说，失去自然牙齿很可能会减少牙齿发送到大脑的感官信号，影响了包括记忆力在内的大脑功能。 自然牙齿通过神经向大脑发送的信号影响面部表情，还会影响诸如咬和咀嚼等运动功能。假的牙齿虽然能帮助吃饭,但是没有自然牙齿所具有的与下巴相连的神经和韧带, 因而有可能减少了大脑的感觉输入。 寻常因素也有可能造成牙齿和记忆力之间的联系。研究人员说，比如，可能引起牙齿脱落的牙龈感染也会引起炎症，这可能反过来造成神经元死亡和丧失记忆。 在新研究中，研究人员对有可能影响记忆力的其它因素（如参与者的教育年头、职业类型以及病史）进行了解释，但牙齿和记忆之间的联系仍然明显。 研究人员说，研究的参与者平均有22颗自然牙齿，比一副完整的人类牙齿少了几乎三分之一，这可能使他们避免或少吃某些食物，而那些食物中含有保持良好记忆力所必需的营养。参与者人数不多是这项研究的一个局限性。不过，先前的一项研究有4000多名参与者（而且还控制了几个生活方式因素，比如吸烟和饮酒），也发现了类似的结果。相较于仍有许多天然牙齿的参与者，那些牙齿很少或没有牙齿的人更有可能有一些记忆丧失。该研究发表在2011年的《行为和大脑功能》期刊上。
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