Post-traumatic increases in incisor mobility in farm pigs, Sus scrofa

Objectives: Traumatic intrusion of primary teeth occurs frequently in young children and poses a risk to developing secondary teeth.  Although inflammation may stabilize the injured tooth in vivo, damage to the periodontal ligament (PDL) may promote primary tooth mobility.  The objective of this study was to model the effect of intrusive trauma on PDL support in the farm pig, Sus scrofa.  Post-traumatic mobility of porcine central mandibular incisors was hypothesized to be greater than in non-traumatized controls. 

Methods: Mandibular segments containing central incisors were embedded in acrylic with the long axis of the root perpendicular to the applied load.  Treatment samples were intruded 5mm using a class 2 lever with a minimum force of 1280N.  Intruded (n=10) and non-intruded control (n=10) specimens were tested in compression using a Material Testing System (MTS) and the elastic modulus was compared between groups.  Incisor displacement was measured on X-ray images taken before and after trauma (if applicable), and following compressive tests. 

Results: In 8 paired specimens, the average ratio of Young’s Modulus (E_control/E_intrusion) indicated a minimum 2-fold higher stiffness of non-traumatized specimens.  Intruded specimens showed a tendency for an extended slack period that was not observed in controls.  The intrusion group modulus was significantly lower than the control group (4452 vs. 7704 Mpa; p=0.05).  After MTS testing, the root length embedded in bone increased in traumatized and non-traumatized teeth by 2.9mm and 0.81mm, respectively (p=0.03). 

Conclusions: Damage to the PDL led to a delay in load bearing and diminished overall periodontal support of the tooth.  Traumatic injury in porcine incisors produced a significant degree of axial mobility and constitutes an important model for further study of childhood incisor intrusions. Supported by University of Washington Dr. Douglass L. Morell Dentistry Research Fund.