A within-subject comparison of mandibular long-bar and hybrid implant-supported prostheses: Evaluation of masticatory function

Sixteen edentulous subjects participated in a within-subject crossover clin ical trial to test the hypotheses that a long-bar overdenture attached to 4 implants gives greater patient satisfaction and masticatory efficiency tha n a two-implant hybrid overdenture. All subjects were given a new maxillary conventional denture. Ten received mandibular long-bar overdentures first and six the hybrid overdentures. Two months later, psychometric assessments and functional tests were repeated 3 times at one-week intervals. The mand ibular prosthesis was then changed, and recordings were repeated after anot her 2 months. Mandibular movements and electromyographic activity of jaw mu scles were recorded while subjects chewed standard-sized pieces of 5 foods: bread, cheese, apple, sausage, and carrot. Measurements included masticato ry time, cleaning time (the time between the end of mastication and the las t swallow), and duration and amplitude of masticatory cycles and phases. Mu ltilevel analyses were performed. No significant differences in masticatory time were found between prostheses for any test food. However, cleaning ti me for carrot [estimated mean of difference (Delta) +/- SE: 1.6 sec +/- 0.7 ] and bread (Delta = 1.0 sec +/- 0.4) was slightly but significantly longer for subjects wearing long-bar overdentures. Cycle duration was longer with the long-bar overdenture only for subjects chewing carrot. The opening pha se was shorter and the closing phase longer with the long-bar overdenture f or almost all test foods. Vertical amplitude was significantly less with th e long-bar overdenture for cheese (Delta = -2.6 mm +/- 1.1), apple (Delta = -2.6 mm +/- 1.0), and sausage (Delta = -2.9 mm +/- 1.3). These results sug gest that mastication with the 2 prostheses is equally efficient, although clearance of some foods from the mouth is longer with the long-bar overdent ures. They also indicate that patients adapt their masticatory movements to the characteristics of different prostheses.