A new orthodontic force simulation system with a simulated periodontal ligament to measure the delivered force at the root apex

Objective: To develop a new orthodontic force simulation system with a simulated periodontal ligament (PDL) that enables measurement of the delivered force at the root apex and to clarify the relationship between the applied orthodontic force and the delivered force at the root apex. Design: In vitro study. Setting: Orthodontics department of a university. Methods: A new orthodontic force simulation system that enables measurement of the force at the root apex of the maxillary central incisor was developed. Lingual and intrusion movements were simulated with applied orthodontic force at three levels: 50, 100 and 200 gf. The delivered forces at the root apex were compared between the two movements. Furthermore, the ratio of delivered force at the root apex to the applied orthodontic force (the apex force ratio) was calculated. Results: The magnitudes of delivered forces at the root apex were significantly greater in intrusion movement than in lingual movement (P < 0.01). The apex force ratios were in the range of 47.3%-56.2% for lingual movement and 85.6%-86.2% for intrusion movement. Conclusion: The present study of a newly developed orthodontic force simulation system showed that the characteristics of the delivered force at the root apex differed according to the direction of tooth movement.