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How a Tooth Decays

How a Tooth Decays

Introduction: (Initial Observation)

Many people in the world, especially children, suffer from tooth decay. This can be extremely painful, as most of us have experienced. This pain, and all the other complications that it may lead to, may be avoidable. For this reason tooth decay can be the subject for a good science project. During this project we will try to find information about all other researches that has been done in this area and also do our own experiments. What we learn may help in saving our own teeth and can also be a help to others that may benefit from our research.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about tooth decay. Read books, magazines or ask professionals who might know in order to learn about the factors that may cause tooth decay. Keep track of where you got your information from.
Following are samples of information that you may find.

In order to understand how tooth decay happens, we need to know about the structure or anatomy of the tooth.

Each tooth consists of 2 parts: the crown and the roots. Only the crown is visible in the mouth. The roots are in the bone, under the gums.

The crown of the tooth has an outer shell made of a very hard substance called enamel. The inside of the tooth is made of a less hard substance called dentin. It is this layer which can be sensitive when exposed to the mouth atmosphere. The center of the tooth is hollow and contains the nerve.

What is tooth decay?

Our mouth is full of bacteria. In fact, bacteria are everywhere. The food we eat combines with saliva and bacteria to form a sticky coating on the teeth. This sticky coating is called plaque and it plays an important role in tooth decay. When sugar is available to the bacteria in plaque, they act on it and create acids. These acids erode tooth enamel. After repeated acid attacks the enamel breaks down and a cavity is formed.

Decay occurs most often on the chewing surfaces of the back teeth. This is because these surfaces have deep pits and fissures, where even the toothbrush bristles cannot reach.

Treatment of Tooth Decay

Once decay has started and a cavity has formed, it becomes necessary to treat it to prevent the process from extending further.

When decay is limited to enamel: Treatment at this initial stage is preventive in nature because it will stop the decay process from extending to deeper areas of the tooth. All that is necessary is a simple filling. It is usually painless at this stage. Your dentist will clean out the decayed part of enamel and fill the resulting cavity with either silver amalgam, or preferably, with the newer tooth colored composite material.

When decay has extended to dentin: This may be painful after eating or with cold water. Food is likely to be lodged in the cavity. Treatment at this stage consists of a more extensive filling. It may be necessary to numb the area during treatment. One of the above materials may be used.

When decay has reached the nerve, severe pain is the usual complaint. The invading bacteria cause the nerve of the tooth to become inflamed. Root canal treatment will be necessary at this stage if the tooth has to be saved.

Infection reaches bone: The bacteria destroy the nerve and spread to the bone of the jaw. The bone is thus inflamed and infected. The infection may erode through the side of the bone into the mouth, face or neck to cause a swelling.

This picture shows an advanced case of tooth decay in a child.

Tooth decay experiments:

Human teeth have a strong enamel that protect them from fast decay. It often takes a few years for each tooth to form noticeable cavities. Students often don’t have a long time for their experiments, that is why they often use seashell or chicken bone instead of real tooth. Seashells often provide the fastest results because they do not contain enamels and proteins.

Use acids instead of sugars:

In our mouth, starch convert to sugar and sugars change to acids. Although the acids are very weak, the enzymes produced by bacteria make them more effective. Conversion of starch to sugar, and sugar to acid happens in the mouth due to the presence of enzymes, microbes, moisture and warm temperature. The same conversion does not happen in a cup or plastic container. That is why you may directly use vinegar, lemon juice or other safe acids instead of sugar or in addition to sugar.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to understand the factors that may cause tooth decay. We hope that our studies will help us to understand what is tooth decay? Why it happens and how can we prevent it.

Our specific questions for this study are:

1. How do different types of acid affect tooth decay?
2. How does the exposure time to acids affect the rate of tooth decay?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

When a tooth is exposed to a corrosive substance such as an acid, the amount of erosion may vary based on the type of corrosive material and the time length of such exposure.

If you choose to find out how do different types of acids affect the tooth erosion, the following is how you may define your variables:

Independent variable (also known as manipulated variable ) is the type of acid.

Dependent variable ( also known as responding variable) is the rate of erosion.

Controlled variable is the temperature.

Constants are the amounts of acids, exposure time, methods and procedures.

If you choose to find out how does the exposure time length affect the tooth erosion, the following is how you may define your variables:

Independent variable (also known as manipulated variable ) is the exposure time.

Dependent variable ( also known as responding variable) is the rate of erosion.

Controlled variable is the temperature.

Constants are the type and the amounts of acid, methods, and procedures.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

For this project we offer a few different hypotheses and experiments associated with that.

Hypothesis 1:
Any acid can cause erosion on the teeth, so by avoiding sour foods we can prevent tooth decay. We can also rinse our mouth with anti-acids such as baking soda to prevent tooth decay.

Hypothesis 2:
As the exposure time of teeth with acids increases, the amount of erosion will increase as well. To avoid that we should wash our teeth after eating sour or sweet material.

Additional sample hypotheses:

Hypothesis 3:
Some foods such as candy, chocolate and other sweet foods can cause tooth decay and this has nothing to do with acids.

Hypothesis 4:
Only acids formed in the mouth by the effect of bacteria on the food can cause tooth decay. So we can prevent tooth decay by removing any food that may have remained in our mouth. We can also prevent tooth decay by killing mouth bacteria and finally we can prevent tooth decay by rinsing our mouth with anti-acids.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: How do different types of acids affect tooth erosion?


Get three cups. Put Vinegar in the first, Lemon Juice in the second and water in the third. Weigh the teeth (or bones or seashells) on the gram scale and record in your science log. Place one tooth in each cup. Make daily observations and weigh the samples every week and record them in your science log. At the end of the given time, weigh the samples for the last time and record them in the science log.


  • In this experiment you are not using soda or other sweet liquids because it takes a long time and certain environmental conditions for sweets to become acidic.
  • If you need faster results (2 to 3 weeks) you must use bones or seashells. Tooth has a protective layer and any possible affect require many months.

Experiment 2: How does the exposure period affect the tooth erosion?


Get four cups and fill them 1/2 with vinegar. Label the cups with numbers from 1 to 4. This number represents the number of weeks a tooth sample will remain in that cup. Weigh tooth samples (or seashell samples or bone samples) and place them in the cups.

After 7 days remove the content of cup number one. Let it dry. Weigh it and record its mass in your results table.

After two weeks from the start of your experiment, remove the content of cup number two. Let it dry. Weigh it and record its mass in your results table.

After three weeks from the start of your experiment, remove the content of cup number three. Let it dry. Weigh it and record its mass in your results table.

After four weeks from the start of your experiment, remove the content of cup number four. Let it dry. Weigh it and record its mass in your results table.

Your results table may look like this:

Exposure period (weeks) Initial mass Final mass Rate of erosion

Rate of erosion is calculated by subtracting final mass from initial mass.

Experiment 3: How do different sugars affect tooth erosion?


  1. Get four cups and fill them up to 3/4 with water.
  2. Do not add anything to the cup number 1. Label this cup with “Pure Water/ Control)
  3. Add a spoon full of sugar to the cup number 2. Stir it and label it as “Water Sugar”. 
  4. Add a spoon full of crushed chocolate to the cup number 3. Stir it and label it as “Chocolate Water”.
  5. Add s spoon full of dry crushed bread to the cup number 4. Stir it and label it bread water. 
  6. Weigh four similar and same size samples of teeth (or seashells), record it in your log and place them in cups. One sample per cup.
  7. Make daily observations and once a week weight the samples and record your measurements in your science log. Before each measurement, wash and dry each sample. You may use water and a tooth brush in your washing process.
  8. At the end of the given time (3 to 4 weeks), weigh the samples for the final time and record it in the science log.

Experiment 4: How do bacteria affect tooth erosion?


Introduction: Bacteria feed on the food remained between your teeth and grow. bacteria release digesting enzymes to digest the food; however, digesting enzymes also decompose and digest adjacent teeth. That is what we call tooth decay. Part of starch and sugar remained between the teeth will feed the bacteria and the other part will change to acids that dissolve the calcium minerals of the teeth.

Since teeth decay very slowly, for better and faster results students may try seashells in their experiment instead of real teeth.


Get four cups. Put sugar water in the first, chocolate water in the second, bread water in the third and pure water in the last cup. (To make sugar water mix a spoon full of sugar in a cup of water. To make chocolate water mix a spoon full of chocolate in a cup of water. To make bread water mix a spoon full of dried crushed bread in a cup of water.)

In each cup add one spoon saliva that contains bacteria from your mouth.
Weigh the teeth on the gram scale and record in your science log. Place one tooth in each cup. Keep the cups in a warm place (To simulate body temperature). Make daily observations and record in your science log. At the end of the given time, remove the samples, wash them, let them dry and weigh them separately. Record the final weights in your science log.

Materials and Equipment:

For this experiment you need:

1. 4 few disposable plastic cups
2. Small amounts of bread, sugar and chocolate
3. Different acids such as vinegar and lemon juice
4. Some teeth that you may get from a local dentist or from a butcher. (If you cannot find teeth, do this experiment with bones or seashells)
Some butchers sell sheep’s heads that you may purchase and extract the teeth.

Results of Experiment (Observation):

Make a table similar to this to record your observations:

 Vinegar Lemon Juice Water
 Initial tooth weight
Tooth weight after 1 week
 Tooth weight after 2 weeks
 Tooth weight after 3 weeks
 Tooth weight after 4 weeks
 Tooth weight after 5 weeks


Use a calculator to divide the final weight of each tooth to the weight of that tooth in the first day. The result is the percentage of the remained tooth. Subtract that number from 1 and what remains is the percentage of tooth loss or tooth decay.

You will later compare the percentage of tooth decay in your different samples to see which sample causes more tooth decay.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

Baby Bottle Tooth Decay

Baby bottle tooth decay is a dental condition that can destroy the teeth of an infant or young child. The upper front teeth are the most susceptible to damage, but other teeth also may be affected.

What causes baby bottle tooth decay?
Baby bottle tooth decay is caused by the frequent and long-term exposure of a child’s teeth to liquids containing sugars. Among these liquids are milk, formula, fruit juice, sodas, and other sweetened drinks. The sugars in these liquids pool around the infant’s teeth and gums, feeding the bacteria that cause plaque. Every time your child consumes a sugary liquid, acid attacks his/her teeth. After numerous attacks, tooth decay can occur, resulting in baby bottle tooth decay.

Parents and care givers should be especially concerned with giving an infant a sugary drink at nap or night time. During sleep, the flow of saliva decreases, allowing the sugary liquids to pool around the child’s teeth for an extended period of time.

How to prevent baby bottle tooth decay
Parents sometimes do not realize that baby’s teeth are susceptible to decay as soon as they appear in the infant’s mouth. By the time the decay is noticed, it may be too late to save the child’s teeth. You can prevent this from happening to your child’s teeth by knowing how to protect them.

After each feeding wipe the child’s teeth and gums with a damp washcloth or small soft toothbrush to remove plaque. Begin brushing your child’s teeth as soon as the first tooth erupts. Flossing should being when all primary teeth have erupted, usually by age 2 or 2 1/2.
Never allow your child to fall asleep with a bottle containing a sweetened liquid.
If your child refuses to fall asleep without a bottle, simply fill it with water and nothing else.
If your local water supply does not contain enough decay-fighting fluoride, check with your dentist to see if your child should receive fluoride supplements.
Start dental visits between six and twelve months of age.
How serious is baby bottle tooth decay?
Baby bottle tooth decay can cause painful toothaches which can hinder eating. Severely decayed teeth can become infected and need to be extracted. If your child’s teeth are infected or lost too early due to baby bottle tooth decay, your child may have some of these problems:

Poor eating habits
Speech problems
Crooked teeth
Damaged adult (permanent) teeth
Yellow or brown adult (permanent) teeth
Keep your child happy and smiling by preventing baby bottle tooth decay.

Clean Teeth and Gums

Having a clean mouth is important. In addition to being healthier, it gives you fresh breath and a nicer smile.

When you eat, bits of food, some too small for you to see, remain in your mouth. They feed bacteria that grow in a sticky film on your teeth. This film, called plaque, is the main cause of tooth decay and gum disease.

Why brush?
Brushing your teeth after meals and between-meal snacks not only gets rid of the food particles that you can see, it removes plaque from your teeth. Using a fluoride toothpaste is important because the fluoride can help kill bacteria, as well as make your teeth stronger.

Ask your dentist to recommend the best toothbrush for you. Generally, a brush with soft, end-rounded or polished bristles is less likely to injure gum tissue. The size and shape of the brush should allow you to reach every tooth. children may need smaller brushes than those designed for adults. Remember: worn-out toothbrushes can not properly clean your teeth and may injure your gums. Toothbrushes should be replaced every three or four months.

Why floss?
Flossing removes plaque and food particles from between teeth and under the gumline, areas your toothbrush can not reach. Because tooth decay and periodontal disease often start in these areas, it is important to clean them thoroughly on a daily basis.

Flossing is a skill that needs to be learned. Do not be discouraged if you find it difficult at first. With practice, you will find that flossing takes only a few minutes of your time each day.

What about mouthrinses and mouthwashes?
If used as directed, in addition to brushing and flossing, mouthrinses and mouthwashes can help to prevent tooth decay.

How often should I see my dentist?
If possible, you should visit your dentist every six months for a preventive check and cleaning. Infants should see a dentist at about 12 months of age.


Also check this site: http://text.nlm.nih.gov/nih/cdc/www/40txt.html#Head0


Oral Health, Tooth Decay, and the Need for Water Fluoridation

Tooth decay is increasingly a disease of social deprivation and is reported to be on the increase in young children in the poorer parts of the UK – except where water has been fluoridated. For example, 5-year-old children in NON-FLUORIDATED BOLTON have around four times more tooth decay than 5-year-olds living in FLUORIDATED SOUTH BIRMINGHAM. (An average of 3.36 and 0.92 teeth affected respectively.)

Studies show that topping up the natural fluoride in water to the optimum level of one part of fluoride per million parts of water is SAFE (in the US where over 60% of the population receive fluoridated water, fluoridation has been practised for over 50 years), and the most cost-effective means of preventing tooth decay. Generally, fluoridation reduces decay rates by around half.

Only 10% of the UK (mainly the West Midlands and North East) receives fluoridated water. Areas with very high tooth decay rates which need fluoridation include the North West, Merseyside, Yorkshire, Scotland, Wales, and Northern Ireland and some socially deprived communities in the South (eg Inner London).

Independent opinion polls consistently show that more than 75% of people think fluoride should be added to water if it can reduce tooth decay.

The Water (Fluoridation) Act 1985, and the associated guidance from the Department of Health, make it clear that responsibility for decisions about water fluoridation lies with health authorities (HAs), who are required to consult the appropriate local authorities, community health councils, and any other local bodies considered appropriate. In addition, HAs must publicise their water fluoridation proposals through the local press and invite public comment. HAs must allow a period of at least three months for this consultation process before making a final decision.

Following a request from a health authority, water suppliers are supposed to fluoridate supplies – unless there are insurmountable technical difficulties. However, some water suppliers are claiming that the Act gives them discretion and to date several water companies, including North West Water, Northumbrian Water, Yorkshire Water, Welsh Water, and Southern Water, have adopted a clear policy of refusing to implement new schemes -regardless of technical feasibility. Clearly it is unacceptable that water suppliers are dictating public health policy in this way. Their actions are denying people protection against a painful, yet preventable, disease.

It is increasingly clear that no health authority will be able to persuade its local water supplier to change its stance, and it is likely that little progress will be made unless there is a review of the working and interpretation of the Water (Fluoridation) Act 1985, and in particular the responsibility (and level of discretion) of the water industry.


Researchers say they have developed a safe, effective and painless vaccine that could prevent tooth decay by eliminating bacteria from the mouth.(CNN)

Developed by California-based Planet Biotechnology, and tested at Guy’s Hospital in London, the plant-based vaccine is painted on teeth and produces antibodies that prevent harmful bacteria from sticking to teeth and causing cavities.

The vaccine was produced by genetically modifying tobacco plants to carry antibodies to streptococcus mutans, which causes 95 percent of tooth decay.

Volunteers received the tasteless, colorless vaccine twice a week for three weeks for a total of six applications.

“What we showed is that by applying this antibody you can prevent the bacteria that is targeted against — streptococcus mutans — from sticking to the teeth,” Dr. Julian Ma said.

To conduct the study, researchers first used a mouth rinse to reduce the levels of the bacteria in the volunteers to zero. Then they applied a control, or placebo solution, to some patients and the vaccine to others.

Within two months, the bacteria returned in the mouths of the control group while those who received the vaccine were protected for up to four months.

Ma said this is the first plant-derived vaccine from genetically modified plants to ever go into human clinical trials.

“We have now found a way of using plants to produce this vaccine safely and in large quantities. It would not be possible otherwise,” he said.

Another vaccine, derived from mice, has proved successful in fighting bacteria, but it is so difficult and expensive to produce it has not been developed for consumer use.

Planet Biotechnology is planning to conduct a larger study this summer with about 60 patients.

The company hopes they can roll out a consumer product in 2001 or 2002.