Objective: To compare stress dissipation with time during rotational movement between conventional orthodontic spring-bracket device and clear laminated aligner with BAR.
Method: A photoelastic model of a dentate adult maxilla was fabricated using different teeth and bone simulants. One orthodontic appliance was a NiTi spring fixed to a bracket on the distal marginal ridge of tooth #8. The second was a compressible polymer BAR fabricated using CAD/CAM technology positioned on the distal marginal ridge of tooth #9. Load cell exerted 200 grams to both appliances. Force dissipation was measured and stresses were observed using polariscope field. Stress data for spring and BAR were analyzed using computer graphic program to quantify stress intensity by fringe number counting.
Results: Spring and BAR demonstrated similar stress patterns to root and crestal bone of tooth numbers 8 and 9 with respect to number and proximity of fringes. To a lesser degree, stress was evident along root and crestal bone of lateral incisors as well. More rapid dissipation of force and lower levels of force were evident with the spring compared to BAR. At 5 minutes BAR=195gr and spring=185gr. Average force exerted by BAR=150gr, spring=110gr. Overall force was higher and more uniform with BAR compared to spring.
Conclusion: Compressible Polymer BAR demonstrated higher and longer duration of forces compared to spring. Clinical implications may include less office visits and shorter treatment time with BAR. The more uniform force may decrease root-bone resorption. Elimination of brackets allows less invasive, more hygienic, and greater esthetic orthodontic treatment.