Changes of bite force and occlusal contacts in the retention phase of orthodontic treatment: A controlled clinical trial

Introduction: We aimed to determine whether appliance type affects changes in maximum voluntary bite force (MVBF) and the number of occlusal contacts (NOC) during retention, controlling for sex, age, and body mass index. Methods: The sample comprised 176 examinees (70 male, 106 female) aged 14 to 20 years: 30 had maxillary and mandibular Essix retainers, 30 had wrap-around retainers, and 30 had a combination of fixed mandibular canine-to-canine retainers bonded on each tooth separately (double twisted, 0.254 mm in diameter, stainless steel ligature wire) and Essix retainer in the maxillary arch; 86 with normal occlusion were not treated. MVBF and the NOC were measured immediately after removal of preadjusted edgewise appliances (Roth prescription), 6 weeks after that, and after the next 4 weeks. Results: Increases in MVBF and the NOC were demonstrated, but subjects with 2 Essix retainers showed lower values than did the others. Changes were related to type of appliance, sex, and age (P < 0.05) but not to body mass index. The increase in NOC occurred faster than the increase of MVBF, more and sooner with the wrap-around retainer and in male subjects than with the Essix and in female subjects. MVBF and NOC nearly reached the values of the control subjects. Conclusions: Settling of the occlusion depends on appliance type: it takes longer in female patients and with Essix in both dental arches than with the other tested applianc