 William Abler observed in 2001 that Albertosaurus tooth serrations resemble a crack in the tooth ending in a round void called an ampulla . Tyrannosaurid teeth were used as holdfasts for pulling meat off a body , so when a tyrannosaur would have pulled back on a piece of meat , the tension could cause a purely crack @-@ like serration to spread through the tooth . However , the presence of the ampulla would have distributed these forces over a larger surface area , and lessened the risk of damage to the tooth under strain . The presence of incisions ending in voids has parallels in human engineering . Guitar makers use incisions ending in voids to , as Abler describes , " impart alternating regions of flexibility and rigidity " to the wood they work with . The use of a drill to create an " ampulla " of sorts and prevent the propagation of cracks through material is also used to protect airplane surfaces . Abler demonstrated that a plexiglass bar with incisions called " kerfs " and drilled holes was more than 25 % stronger than one with only regularly placed incisions . Unlike tyrannosaurs , ancient predators like phytosaurs and Dimetrodon had no adaptations to prevent the crack @-@ like serrations of their teeth from spreading when subjected to the forces of feeding . 
