I was working on a paper that dealt with dog bites and wanted to include some mention of the strength of dog bites for particular breeds. I have been at several conferences dealing with dog behavior and have heard a number of veterinarians quote that the bite force of a Rottweiler (and sometimes a pit bull) is approximately 2000 pounds per square inch.
Since dog behavior, not dog physiology, is my expertise, I tended to accept those statements without too much analysis (except of course, to marvel at the strength of the dog's jaw). However, this time, I thought about these numbers more closely and began to doubt what I had heard.
Let's put these numbers into a meaningful context. Imagine a bite force of 2000 pounds. To achieve this, suppose that we had a dog's jaw and wanted to press the upper portion down with this force. It would require our putting pressure equivalent to the weight of a subcompact automobile (like a smaller Toyota or Hyundai) on the top jaw. That simply did not make sense. For one thing, I doubted that the bone structure of the dog's jaw could withstand such pressures.
So where did this number — a bite strength of 2000 pounds for the Rottweiler — come from?
It turns out that there has not been a lot of research in this area, and most of it has been done using indirect and laboratory measures. An example is the experimental work done by a team headed by Jennifer Lynn Ellis of Guelph University in Canada (published in the Journal of Anatomy in 2008).
This team used two methods to measure bite strength. The first tested live dogs, which were anesthetized and had their jaw muscles electrically stimulated. The second was more theoretical and is based computations made using the architecture of the skulls and jaws of deceased dogs.
One thing that comes out very strongly from their measures is that the bite force varies depending upon where in the mouth you measure it. For example, in one German Shepherd, the measure of bite force in the front portion of the jaw was 170 pounds while in the rear of the jaw (where the lever principle works most strongly) it was 568 pounds. This is a long way from 2000 pounds. So, where did that figure come from?
If you look at the way the data is presented, the researchers are not reporting their results in pounds of force, but rather in a force measure called Newtons. An average of the results of the inner bite strength of the 20 dogs in this study does come out to be around 2000 Newtons. Perhaps that is where the number came from.
However, if that is the case, then reports of 2000 pounds of pressure are greatly in error. A Newton actually equals a 0.22 pounds of force, or a bit more than a fifth of a pound. So a 2000-Newton force is actually approximately equal to a 450-pound force. This is a lot of force — the equivalent of putting a pressure equivalent to the weight of two football linemen on the top jaw — but a lot less than 2000 pounds of pressure.
Could it be that the estimate of the bite strength of the dog has been reported so widely and so wrongly is because the people reading the reports have misread the units of measure, assuming pounds for Newtons? That would at least might explain where the frequently reported numbers come from.
Dr. Brady Barr of National Geographic, for a TV special called Dangerous Encounters: Bite Force, measured bite forces of several different creatures using a more direct measure. Basically, he placed a force-measuring device on a bite protection sleeve (or on a pole for larger more dangerous beasts) and provoked the animals to bite it.
Because of the way that these measures are taken, they actually reflect the bite force closer to the front of the jaw, so they might not measure the maximum force possible. The strength of the bite will also depend upon just how provoked and angry the dog was during the measurement.
In any event, for the three dogs measured (an American Pit Bull, a German Shepherd, and a Rottweiler) the average bite strength was 269 pounds of pressure, with the Rottweiler topping the group with 328 pounds of bite pressure. Compare these to the bite strength of lions and white sharks which are both around 600 pounds, or the bone-crushing hyena at around 1000 pounds, or more shocking, the Nile alligator, which comes in at just under 2500 pounds.
In more recent research (published in 2009 in the Journal of Anatomy), Dr. Ellis and her team were able to show that the size of the animal and the shape of its jaw predicted bite strength. The larger the dog and the dog's head, and the wider the jaw, the higher the bite force turned out to be. The dog breed with the largest head and widest mouth is the Mastiff, so it is perhaps not surprising that it has been recently measured as having a bite strength of 552 pounds — just shy of the bite force that the lion has. This force exceeds that of all breeds measured to date.
And what about humans? We come in at a measly 120 pounds of bite pressure. It is a good thing that we rely more upon our brains than our teeth to survive.
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