1. What Can Researchers Learn from Shark Teeth Found on the Tank Floor?
According to a presentation by Kishimoto Teppei at Shimonoseki City Aquarium, previous studies often required sedating sharks and cutting parts of their jaw teeth to check tooth rows weekly. This method stressed the fish and could not count all teeth because numbers varied by jaw location [1].
Instead, the aquarium tried a simpler method: collecting fallen teeth from tank floors and filtration tanks every 10 to 20 days. The subtitle of their presentation was "What We Learned About Sharks from Trash" [1].
All shark species replace their teeth constantly, though shapes and roles differ by type. This is the premise for the data discussed here. Note that this information comes from an aquarium research presentation abstract, not a peer-reviewed paper, so numbers should be read as values for captive individuals [1].
2. How Many Teeth Do a Blacktip Reef Shark and a Horn Shark Lose Per Day?
The study examined two sharks of similar size: a blacktip reef shark (about 70 cm, water temperature 22.8–24.1°C) and a horn shark (about 72 cm). Over 239 days, the blacktip reef shark lost 489 teeth. Over 213 days, the horn shark lost 176 teeth. This works out to 2.05 teeth per day for the blacktip reef shark and 0.82 for the horn shark [1].
Dividing 2.05 by 0.82 gives a ratio of about 2.5. Even with similar body sizes, tooth loss speed differed greatly between species.
The American Paleontological Society notes that living sharks may replace teeth every 7 days according to some research. However, large adult sharks might slow this to once or twice a year [2].
The aquarium’s data shows "teeth per day," while the "7-day" figure refers to replacement intervals. Because the units differ, these numbers cannot be directly compared.
3. How Does Water Temperature Change a Horn Shark's Tooth Replacement Speed?
For the same horn shark species, replacement frequency changed with water temperature. At 13.0°C, it was 0.26 teeth per day. At 26.0°C, it rose to 1.52 teeth per day. The presentation states that higher temperatures result in about 5 times more tooth loss [1].
At 13°C, the pace is roughly one tooth every 4 days. At 26°C, more than one tooth falls out daily.
The Florida Museum of Natural History notes that nurse shark tooth replacement is faster in warmer summer months and that younger individuals replace teeth faster than adults, citing a 1990 paper [3].
Because speed changes with temperature and age, it is difficult to state a single number like "sharks replace teeth in X days" for all cases.
4. Why Does Tooth Replacement Speed Differ Across Parts of the Same Jaw?
The aquarium reported that for the horn shark, near the center of the jaw (midline), 3.89 rows were replaced during the study period. Near the jaw joint, in molar-like teeth, only 1.5 rows were replaced [1].
Dividing 3.89 by 1.5 gives a ratio of about 2.6. Speed also varies by position in the jaw.
Because speed differs by jaw location, counting teeth separately by area reveals where replacement is fastest. Counting all fallen teeth helps estimate total replacement for one individual.
The American Paleontological Society explains that behind each used shark tooth, there are 5 to 6 developing teeth in a row [2].
The number of these "waiting" teeth is also a clue. In one small shark species, fewer waiting rows suggested slower replacement. However, the link to diet or metabolism remains a hypothesis [5].
5. How Many Teeth Might a Shark Lose in a Lifetime? Reading the Estimates
Since blacktip reef sharks lose 2.05 teeth per day, they lose about 748.3 per year. If males live 10 years, that is about 7,483 teeth. If females live 15 years, it is about 11,224 [1].
For horn sharks, assuming a water temperature of 17.8°C and 0.5 teeth per day, they lose about 182.5 per year. Estimating a lifespan of 12 years based on related species gives about 2,190 teeth in a lifetime [1].
These are not direct measurements but "suggestions" based on captive conditions and assumed lifespans. Remembering that speed changes with temperature and age, we cannot assume the same rates apply to sharks in the ocean.
Still, the numbers from this study for two species fall in the range of "several thousand to just over ten thousand," which is a different order of magnitude than the commonly cited "tens of thousands."
6. Why Do Sharks Never Run Out of Teeth? The Cells That Make New Teeth
A study on the small-spotted catshark found that tooth families are embedded in tissue called the dental lamina, where permanent tooth buds remain. New teeth are created at the edge of this structure, known as the successor lamina [4].
The successor lamina contains cells resembling slow-dividing stem cells (marked by sox2). Researchers described this process as "continuous regeneration via a conveyor belt" [4].
This suggests shark teeth are not rebuilt one by one, but that source tissue constantly sends out new teeth. However, this result is from one small shark species; we cannot say if it applies to all sharks based on this data alone.
7. How Can You Calculate a Shark's Lifetime Tooth Loss Yourself?
If you have a calculator, you can verify the text’s numbers. Multiply the blacktip reef shark’s 2.05 teeth by 365 days to get about 748. Try the same calculation for horn sharks at 13°C (0.26) and 26°C (1.52) to see how much yearly totals differ.
Calculating shows that small daily numbers become large over a year. It also reveals how temperature significantly affects annual totals.
If you visit an aquarium, look at shark tanks and display labels for species and water temperatures. Since these article numbers are from aquariums, other studies are needed to know ocean sharks' speeds.
To read more, refer to the Shimonoseki City Aquarium presentation [1] or the American Paleontological Society explanation [2].