Titanium, the metal used in everything from jet engines to eyeglass frames, has taken on yet another role as the crucial component of two toothbrushes that aim to revolutionize the conservative world of dental hygiene. 從噴射引擎到眼鏡框都用的鈦金屬，又扮演另一個角色。有兩種牙刷以鈦為主要元素，有意在保守的牙齒衛生界掀起革命。One of the brushes dispenses with toothpaste, instead employing a core of titanium dioxide that generates a plaque-removing electrochemical reaction. The other uses fine, flexible titanium bristles that can last for years. Both are getting favorable, if preliminary, reviews from scientists, dentists and consumer testers. 其中一把是免用牙膏的牙刷，利用二氧化鈦的芯心產生電化學反應來清潔牙菌斑。另外一把是以纖細又有彈性的鈦刷毛製成，可用好幾年。儘管還是初步結果，科學家、牙醫師、消費者試用，都給這兩把刷子正面的評價。
The manual toothbrush has remained largely unchanged for generations. The new brushes take some getting used to. 手動牙刷幾世代以來大致未變，新牙刷還有待人們慢慢習慣。
“People think it’s hocus-pocus,” said Erik Powers, of Powers International in Henderson, Nevada, who has recently started importing the $29.95 no-toothpaste Soladey brush to the United States. The brush was invented in Japan. “If you put this on the shelf next to a 99-cent toothbrush, which would you buy?” 內華達州罕得森「包爾斯國際公司」的艾瑞克‧包爾斯說：「有人認為這是唬人的玩意兒。上架後和99美分一把的牙刷擺在一起，你會買哪個？」包爾斯最近開始進口一把29.95美元、免牙膏的Soladey牙刷到美國。這個牙刷是日本人發明的。
For Nick Ravotti, a store manager in Manhattan, there is no question. “I’m a believer,” said Mr. Ravotti, who was given a brush by a reporter who received samples from the company. 對紐約曼哈坦一家商店經理尼克‧拉佛提，這把牙刷沒什麼問題。拉佛提說：「我是它的愛用者。」一位記者收到幾個樣品，給他一把試用。
When he eats his favorite salsa, the aftertaste, “normally kind of stagnant and sour,” is simply gone, Mr. Ravotti said. “It’s the most bizarre feeling,” he added. 拉佛提說，每當吃完偏愛的莎莎醬，嘴裏「總有股酸臭感」，現在這種餘味全沒了。他說：「這種感覺真奇妙。」
Admittedly, it’s awkward, because the brush must be activated by bright light. (Mr. Ravotti shines a desk lamp into his mouth.) 他承認，這款牙刷必須靠強光啟動，讓他覺得怪怪的。（拉佛提拿起桌燈照進嘴裡。）
The brush, available at soladey-usa.com, relies on a property of titanium dioxide. It is photocatalytic, meaning that it causes chemical reactions in the presence of light. 這款可以從soladey-usa.com買到的牙刷，全靠二氧化鈦一項特性，那是一種光催化作用，意謂光的照射會使它產生化學反應。
Light shining on the titanium dioxide rod in the brush’s handle generates negatively charged electrons, which steal positively charged ions from dental plaque, causing oxidation. Brushing creates a slurry of negatively charged saliva, which attracts and decomposes plaque. 牙刷握把內有一根二氧化鈦芯，光線照射會產生負電電子，它會竊取牙垢的正電離子，形成氧化作用。刷牙產生的大量負電唾液，會吸引並分解牙垢。
The concept makes sense, said Donald C. Selmarten, a senior scientist at the National Renewable Energy Laboratory in Golden, Colorado. “They are suggesting you can do oxidative electrochemistry inside your mouth,” he said. “The principle sounds reasonable.” 科羅拉多高登市「國家再生能源實驗室」資深科學家唐納‧賽馬頓說，這個概念言之成理。他說：「他們意指你可以在嘴裡行電化學氧化作用。這原理聽起來很合理。 」
But Dr. Selmarten has questions about the details – whether the wavelength of visible light is high enough to drive the reaction inside a dark mouth, and whether the resulting positive charge will actually remove plaque. The assumption is that “saliva, which is an aqueous solution with biomolecules in it, will be enough electrolyte to actually break down the contaminant,” he said. 不過，賽馬頓博士對細節仍有疑問。他懷疑，可見光的波長是否高到能在黑暗的嘴巴內引起反應，後來產生的正電又是否真的能清除牙齒菌斑。他說，這項假設是「唾液這個內含生命分子，有如水般的溶液，會有足夠的電解質，真的能夠分解汙染牙齒的細菌」。
The company says the titanium dioxide core will never lose effectiveness. But it does sell replacement heads, because the nylon bristles will eventually splay. 公司表示，二氧化鈦芯心永遠不會失效。但尼龍刷的毛刷到最後會開花，公司因此販賣更換的刷頭。
That is the problem that the TiFinity toothbrush, with its long-lasting titanium bristles, aims to solve. 這正是以持久型鈦刷毛製造牙刷，TiFinity牙刷公司鎖定解決的問題。
“The efficacy of a nylon brush, which is the plaque-removal ability, drops 30 percent in the first three months,” said TiFinity’s inventor, Dane Q. Robinson, a dentist in Tempe, Arizona. The TiFinity brush should last several years. TiFinity發明人、亞利桑納州天普牙醫師丹恩‧羅賓森說；「尼龍牙刷的功效，亦即清除牙垢的能力，頭三個月即下降30%。」TiFinity牙刷應能使用數年。
Dr. Robinson, who invented the WaterPik automatic flosser, originally tried it with a filament of titanium alloy. He figured it would be excellent bristle material if it could be drawn fine enough. WaterPik牌電動牙線發明人羅賓森博士，最初嘗試使用鈦合金細絲，他認為如果拉得夠細，它是絕佳的刷毛材質。
Nylon bends but does not fully rebound, so the user must “do a lot of wiggling and jiggling,” Dr. Robinson said, to get the brush into the sulcus – the cuff of flesh that encircles each tooth – and the spaces between teeth. 尼龍可彎曲但無法完全反彈，羅賓森說，使用者因此必須「做很多扭動和抖動的動作」，讓刷毛進入牙齒溝槽，亦即包圍每顆牙齒的齒肉間，及牙齒與牙齒之間。
TiFinity’s bristles, on the other hand, should lose neither shape nor effectiveness. Brushers gently move the tips of the bristles under the gumline and into the teeth’s deepest crevices. 易言之，TiFinity的刷毛不會變形，也不會失去功能。刷牙的人以刷毛的頂端在牙齦線下輕輕移動，進入牙齒最深的縫隙中。
Dr. Robinson said the brush will be available from his company’s Web site, TiFinityToothbrush.com. It is to cost $46.95. 羅賓森說，消費者將可從公司網站TiFinityToothbrush.com購買牙刷，每把定價46.95美元。
Dr. Michael Bruno, a Manhattan dentist, examined the brush and was favorably impressed. Long-term testing is necessary, he said, but it seems the brush can easily remove plaque at the “delicate interface” between hard and soft tissues. 曼哈坦牙醫師麥可‧布魯諾試用過，印象不錯。他說，長期試用有必要，但牙刷在軟硬組織的「複雜介面」裡似乎也能輕鬆清除牙垢。
“The brush represents a potential paradigm shift in the profession,” he said. 他說：「這把牙刷可能代表這一行一項巨大的轉變。」
關鍵字句
作者指出兩把牙刷，可能在牙齒衛生（dental hygiene）的世界掀起革命（revolutionize），文章最後還以潛在的（potential）巨大轉變（paradigm shift）形容。
Paradigm shift的觀念，最早由美國科學思想家庫恩（Thomas Samuel Kuhn, 1922-1996年）於他的代表作《科學革命的結構》（The Structure of Scientific Revolutions，1962年）中提出，儘管此一名詞並非他所創（coin a phrase）。
Paradigm shift最早用以指科學理論中根本假設的改變，學術界的定譯是「典範轉移」，但此詞現在廣泛用於所有領域，譯法不妨視情況變通。庫恩指出，任何科學研究的重大突破，幾乎都是先從打破舊思維開始。
本文中的兩把牙刷，均與鈦金屬（titanium）有關，一把是將一個二氧化鈦（titanium dioxide）的芯心（core，rod）置於牙刷的握把（handle）內，利用電化學反應（electrochemical reaction），以達到清除（remove）牙垢（plaque）的效果。
這種牙刷不需要（dispense with）牙膏，公司保證芯心永不失效（lose effectiveness），換句話說，這個芯心可以永不更換，但是尼龍（nylon）刷毛（bristle）用久了會開花（splay），所以公司另外還販賣可以更換的刷頭（replacement head）。
另一把牙刷則是將鈦製成刷毛，這種刷毛持久耐用（long-lasting），用幾年也不變形（lose shape）。它的刷毛非常纖細（fine），且比尼龍刷毛有彈性（flexible）。
有人可能認為新的牙刷是胡說八道、騙人的手法（hocus-pocus，nonsense）。
專家雖認為價格遠高於一般牙刷的這兩把牙刷，還需經過長期測試（long-term testing），才能確知它的功效（efficacy），但初步結果普獲好評（favorably impressed）。
