Every fact in the three teeth lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Simplifications and care points: this is general science education, not dental advice. The toothpaste strengths (ppm of fluoride) follow the NHS guidance for the UK; other countries may give slightly different advice, and questions about a child's own teeth go to a parent, a dentist or the school nurse. An eggshell is only a rough model of a tooth: the shell is mostly calcium carbonate, while enamel is mostly calcium hydroxyapatite, so the experiments show the idea of an acid attack, not how fast a real tooth would change. The critical pH of about 5.5 is not a fixed number and varies from person to person. Ages for losing milk teeth vary a lot between children.
All sources
[1] Taking care of children's teeth
NHS (UK National Health Service) · Reliability: High
Type: National health service
Brush teeth twice daily for about 2 minutes with fluoride toothpaste. Ages 3–6: a pea-sized amount of children's toothpaste with 1,000–1,500 ppm fluoride, brushing supervised. Ages 7 and over: toothpaste with 1,350–1,500 ppm fluoride; children should be able to brush their own teeth but it is still a good idea to watch them. Spit out after brushing and don't rinse, or the fluoride won't work as well.
[2] The Tooth Decay Process: How to Reverse It and Avoid a Cavity
National Institute of Dental and Craniofacial Research (NIH, USA) · Reliability: High
Type: National health research agency
Tooth decay is the result of an infection with certain bacteria that use sugars in food to make acids, which eat away at the enamel. Enamel loses and regains minerals all day long; it can repair itself with minerals from saliva and fluoride. Repeated acid attacks make it keep losing minerals; a white spot is a sign of early decay. A cavity is permanent damage that a dentist has to repair with a filling.
[3] The Tooth Decay Process (children's oral health)
National Institute of Dental and Craniofacial Research (NIH, USA) · Reliability: High
Type: National health research agency
Plaque is a sticky, colourless film of bacteria. Each time we eat or drink sugar or starch, bacteria make acid that attacks the enamel. Minerals in saliva (such as calcium and phosphate) and fluoride help enamel repair itself; fluoride can stop or even reverse early decay. Limiting between-meal snacks reduces the number of acid attacks and gives teeth a chance to repair.
Humans have 20 primary and 32 permanent teeth. Primary teeth begin to appear about six months after birth; shedding begins about age 5 or 6 and is finished by age 13. Incisors cut, canines cut and tear, premolars cut and grind, molars crush and grind. Enamel is the hardest tissue in the body; dentin forms the main bulk of each tooth; the pulp contains cells, tiny blood vessels and a nerve; cementum covers the root. A tooth has a crown and one or more roots.
[5] Anatomy and Physiology 2e, 23.3 The Mouth, Pharynx, and Esophagus
OpenStax, Rice University (Oregon State University open edition) · Reliability: High
Type: Peer-reviewed open textbook
20 deciduous (baby) teeth begin to come in at about six months and are replaced between roughly ages 6 and 12 by 32 permanent teeth: 8 incisors for cutting, 4 canines (cuspids) for tearing, 8 premolars for mashing and 12 molars for crushing; the third molars are the wisdom teeth. The crown is above the gum and covered with enamel, the hardest substance in the body; dentin lies under the enamel; the pulp cavity holds nerves and blood vessels; the root sits in the jawbone, covered with cementum and held by the periodontal ligament. Caries form when bacteria feeding on sugars release acids.
[6] Community Water Fluoridation: Frequently Asked Questions
Centers for Disease Control and Prevention (USA) · Reliability: High
Type: National public health agency
Fluoride combines with the outer layers of tooth enamel, making teeth tougher and better able to resist decay, and slows the activity of bacteria that cause cavities. Fluoride toothpaste provides a much higher concentration at important times of day, such as bedtime.
[7] Critical pH and Le Châtelier: how everyday substances and habits can dissolve your teeth away
Centre for Advanced Science Education, University of Waterloo (Canada) · Reliability: Medium-high
Type: University chemistry-education article
Calcium hydroxyapatite, Ca10(PO4)6(OH)2, is a component of enamel; it dissolves as Ca10(PO4)6(OH)2 ⇄ 10 Ca2+ + 6 PO4^3− + 2 OH−. Acid consumes hydroxide and lowers phosphate, so by Le Châtelier's principle the forward (dissolving) reaction is favoured. The critical pH is around 5.5 but is not fixed and varies between individuals. Fluoroapatite is less soluble than hydroxyapatite in acid and lowers the critical pH. Juice, soft drinks and vinegar-rich foods are acid sources.
pH = −log[H3O+], so [H3O+] = 10^−pH (a base-10 logarithmic scale). At 25 °C neutral solutions have pH 7, acidic solutions below 7 and basic solutions above 7. A worked example gives vinegar a pH of about 2.4; lime juice is about 2 on the figure.
[9] Chemistry 2e, 18.6 Occurrence, Preparation, and Properties of Carbonates
OpenStax, Rice University · Reliability: High
Type: Peer-reviewed open textbook
Carbonates react with acids to form salts of the metal, gaseous carbon dioxide and water, for example CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l).
[10] ChemShorts for Kids: eggs, soda and tooth enamel
Chicago Section of the American Chemical Society (ChemShorts series by Paul Brandt) · Reliability: Medium-high
Type: Chemistry society education article
Eggshells are made of calcium carbonate (CaCO3) and serve as a rough model for teeth. Soaking eggs in vinegar or soda makes bubbles of carbon dioxide as the acids react with the calcium carbonate, thinning the shell. Enamel is mostly hydroxyapatite; fluoride from toothpaste displaces hydroxy (OH) groups, making enamel harder and less reactive.
teeth.org.au (Australian dental health education site; the PDF does not name its author) · Reliability: Medium
Type: Classroom activity sheet
Eggs are a model for teeth because eggshells are made almost entirely of calcium carbonate and, like enamel, protect the softer material inside. Eggs soaked overnight in water, fluoride mouthwash or cola are then covered with white vinegar (about 4% acetic acid): the water and cola eggs bubble, while the fluoride-treated egg reacts little or not at all. Bacteria in plaque feed on sugars and make acid that attacks enamel.