1. enamel
   dentin
2. pulp

Enamel is a tooth's outside, translucent coat. While enamel can become stained, it's the layer below the enamel, the dentin, that dictates the tooth's color.

1. cola
   wine
2. milk

Dark liquids and acidic substances are known to contribute to tooth stains, because the acid weakens tooth enamel, allowing the pigment to seep in.

1. Roman
   Egyptian
2. Mayan

The Egyptians valued white teeth as a sign of wealth and beauty.

1. lemon juice
   water
2. wine vinegar

About 4,000 years ago the Egyptians began to whiten their smiles with a mix of ground pumice and wine vinegar.

1. true
2. false

While whitening chewing gum won't get your teeth as white as other products, studies show that gums containing CPP-ACP, an ingredient derived from milk protein, can help keep your smile bright and white.

1. yellowish
   brownish
2. grayish

Teeth with a yellowish hue respond best to whitening because the yellow tint is usually caused by food stains, plaque build-up and aging.

1. lipstick
   smoking
2. tetracycline (an antibiotic)

Actually, depending on the shade of lipstick you choose, it can help make your teeth appear whiter. Choose shades that are blue-based pinks and reds to play up your pearly whites.

1. true
2. false

Urine was once thought of as a good tooth whitener. It's the ammonia content in it that does the trick.

1. iodine
   chlorine
2. fluoride

Fluoride strengthens teeth and keeps cavity-causing bacteria at bay, but too much of it may cause spots, stains and weakened enamel.

1. carbamide peroxide
   potassium hydroxide
2. hydrogen peroxide

Potassium hydroxide, also known as lye, is a common ingredient in soap, biodisel, batteries, disinfectants and some cosmetics.

1. true
2. false

Crunchy fruits and vegetables are naturally abrasive tooth polishers, and they also help to produce saliva which keeps your smile white.

1. frequent use of teeth whiteners
   using a straw when drinking dark liquids
2. swishing with water after eating and drinking

Yes, there is such a thing as too white. Overuse of over-the-counter tooth whitening products can cause teeth to look blotchy.

1. brushing
   flossing
2. baking soda

Flossing removes particles and plaque build-up between teeth, making your smile appear whiter.

1. plum
   blueberry
2. strawberry

Strawberries contain plaque-busting vitamin C and malic acid, which helps lift surface stains from teeth.

1. people who have gum disease
   people who have dental restorations
2. all of the above

Bleach-based tooth whitening products are best for people with healthy teeth and gums and who have no dental restorations, but natural stain-removing methods are often safe for most mouths.

1. true
2. false

Mouthwashes that contain chlorhexidine, an antiseptic, may stain teeth when they react with tannins found in colas, red wine, coffee and tea.

1. bone
   enamel
2. cementum

While over-the-counter whitening products may cause temporary sensitivity, some natural alternatives are highly abrasive and, if used too often, may damage tooth enamel.

1. a slice of bread
   a small piece of cheese
2. a handful of grapes

It's the calcium and phosphate in dairy that help to remineralize tooth's enamel, helping make teeth whiter. Milk, yogurt and some whitening chewing gums also do the same.

1. salt
   lemon juice
2. green tea

Tea, including green and other non-black varieties, is a teeth stainer, not a teeth whitener.

1. saliva dilutes acidic foods and beverages before they can erode enamel
   saliva helps wash away stain-causing particles
2. all of the above

In addition to washing away stain-causing foods and liquids, saliva also contains calcium and phosphates to help strengthen tooth enamel against acidic foods, making enamel less susceptible to discoloration.