Effects of retraction force and anchorage reinforcement on occlusal force: a model study.

OBJECTIVES The aim of this study was to investigate the effects of retraction force and anchorage reinforcement with orthodontic mini implants on occlusal force. MATERIALS AND METHODS A strain gauge was attached to the palatal surface of the maxillary right first molar on an en masse retraction model. RESULTS Occlusal forces were measured from this model, according to different retraction forces that were generated by elastic chain, under varied compressive forces (simulating masticatory forces). This retraction experiment was then performed again, after using anchorage reinforcement with an orthodontic mini implant. Occlusal force decreased as retraction force increased. The decrease showed a significant difference above 150g of retraction force (P < 0.05) and was more definite under compressive force higher than 150 N (P < 0.001). After anchorage reinforcement with the orthodontic mini implant, however, occlusal force did not significantly decrease with increasing retraction force. Significant differences in occlusal force were noted between the conditions with and without anchorage reinforcement when the applied retraction force was greater than 200g. CONCLUSION Occlusal force tends to decrease during retraction, and this decrease can be prevented by anchorage reinforcement with orthodontic mini implants. LIMITATIONS Further investigation on the actual masticatory process in humans is required for more clear clinical implication.