Influence of reinforcement on the creep behaviour of polymeric denture base

ABSTRACT

Acrylic resin, the widely used material for denture bases, creeps under protracted load, this endangers the clinical performance of the dentures as well as their supporting tissues. Therefore creep is an important property but it has not been evaluated to date in the standard dental materials testing. This study characterizes the viscoelastic behavior of three types of polymer based denture base material and eight volume fractions of Aramid fibers reinforced acrylic resin. The instant deformation, primary creep, secondary creep, elastic recovery, time dependent deformation, and the permanent set have been shown. The creep rate, creep compliance have been computed for every material tested. The effect of the magnitude of stress on the creep behavior was also tested. The results given were the mean of four specimens tested in each group of material i.e. 56 specimens were tested. The following conclusions are drawn; 1. The High impact material showed; a permanent set twice that of the heat cure acryl while their creep rates were similar. 2. The light cure material showed higher deformations, a lower value for the permanent set and a similar creep rate compared to the heat cured acryl. 3. The reinforced specimens showed a general improvement in the creep behavior, particularly with the higher volume fraction concentrations 14.5, 15.8, 16 percent. An average decrease in the instant deformation to about half, the permanent set to about 20 times and the creep rate by about 3 times compared to the heat cured acrylic resin. 4. Complete recovery was reached with one group of reinforced specimen 14.0 percent. Therefore Aramid fibers reinforcement can be used with the heat cured acrylic dentures to decrease their creep effect and consequently offer a better clinical service. 5. To obtain efficiency with the fibers reinforcement, the fibers should be uniform, continuous, firmly gripped by the matrix, unidirectional and their direction should be parallel to the direction of the induced stresses in the composite. 6. To obtain reproducibility of the composite properties, effort should be done to apply pressure on the dough without disrupting the fibers arrangement, as occurred with the 10 percent volume fraction specimens. 7. The creep test requires simple instruments, and provides important characterization about the mechanical behavior in service