Injury of deciduous anterior teeth is relatively often encountered in daily clinical dentistry. It occurs in the form of fracture or luxation and, needless to say, is caused by impingement by external force. However, the mechanism of the process of fracture has not yet been adequately explained even in existing textbooks. Especially, little has been studied of the resistance of deciduous anterior teeth against fracture by impact. This study was designed to estimate the resistance of deciduous anterior teeth against impact fracture by carrying out our fracture test using epoxyresin duplicate models of human deciduous anterior teeth and a Izodtype fracture tester.
1) In both upper and lower jaw, a higher degree of resistance against fracture by impact was recorded for deciduous cuspids compared to other teeth. This suggested that deciduous cuspids have high resistance against impact fracture in both upper and lower jaw.
2) When the dental axes of upper deciduous anterior teeth were tilted lingually, all these teeth decreased their resistance against impact fracture. This suggested that upper deciduous anterior teeth lose their resistance against impact fracture when their dental axes are tilted lingually.
3) When the mesial margin of deciduous anterior teeth was twisted medially by 45°, the resistance of upper decidudus cuspids, lower deciduous central incisors and lower deciduous lateral incisors was reduced. This suggested that these anterior teeth lose their resistance against impact fracture when the mesial margin of these teeth is twisted medially.
4) In fracture tests using duplicate models of deciduous anterior teeth with dental roots reduced to less than 50% in length, most of the tooth models fell off from the tester frame. This suggested that the shortening of a dental root such as occurring by root resorption may result in luxation of root-shortened teeth.
5) The accelation of impact was reduced in impact fracture test by the shortening of the dental root. This suggested that the shortening of a dental root such as occurring by root resorption can lead to luxation even by weak impact force.
